Automobile side module

Abstract

This automotive side module is an automotive side module for reinforcing the side outer of an automobile, which is formed by hot stamping a plurality of integrated steel plates. When viewed from the vertical direction of the reference plane, the minimum circumscribed rectangle area is S (m 2 ), among the components of the automotive side module, the total weight of the components with a weight of 0.200 kg or more is W 0.2 (kg), and the total weight of the components with a minimum Vickers hardness of HV510 or more is W 510 . When taking them as such, W 0.2 / S is 7.7 or less, and W 510 / W 0.2 is more than 0.10.

Description

Technical Field

[0001] The present invention relates to an automotive side module for reinforcing the side outer of an automobile. This application claims priority based on Japanese Patent Application No. 2023-197287 filed in Japan on November 21, 2023, and the contents thereof are incorporated herein by reference.

Background Art

[0002] Recently, from the perspective of preventing global warming, it has become more important to suppress the emissions of greenhouse gases (hereinafter referred to as GHG) such as carbon dioxide (CO 2 2). Under such circumstances, with the emergence of electric vehicles, hybrid vehicles, etc. whose GHG emissions are lower than those of conventional internal combustion engine-powered vehicles, it is expected to reduce the GHG emissions from automobiles during driving. In addition, by adopting materials with excellent weight reduction properties such as aluminum and carbon as materials for constructing automobiles, it is expected to reduce the GHG emissions from automobiles during driving.

[0003] Regarding the automobile body, for example, Patent Document 1 below discloses a vehicle body structure with excellent productivity. In addition, related to the vehicle body structure, Patent Document 2 below discloses a method for manufacturing a body side structure frame of an automobile from a plurality of blanks. Furthermore, Patent Document 3 below discloses an automobile body capable of reducing the total amount of GHG generated during a series of life cycles from the manufacturing, use, and disposal of an automobile.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] Considering the life cycle of automobiles, in order to reduce the total amount of GHG emitted in the global environment, it is insufficient to focus only on the reduction of GHG during vehicle use (driving). In addition, no consideration has been given to reducing LC-GHG (hereinafter referred to as life cycle GHG or LC-GHG) generated during a series of life cycles from the manufacturing, use, and disposal of automotive side modules.

[0006] Therefore, an object of the present invention is to provide an automotive side module capable of reducing LC-GHG per unit area. [Means for Solving the Problems]

[0007] The gist of the present disclosure is as follows.

[0008] (1) A first aspect of the present invention is an automotive side module for reinforcing the side outer of an automobile, which is formed by hot stamping a plurality of integrated steel plates. When the minimum circumscribed rectangle area viewed from the vertical direction of the reference plane is S (m 2 ), and the total weight of the components of the automotive side module that weigh 0.200 kg or more is W 0.2 (kg), and the total weight of the components with a minimum Vickers hardness of HV510 or more is W 510 , when W 0.2 / S is 7.7 or less, and W 510 / W 0.2 is more than 0.10. (2) The automotive side module according to (1) above may include at least one of element technology A1 and element technology A2, and at least one of element technology B1, element technology B2, element technology B3a, element technology B3b, element technology B4, element technology B5a, element technology B5b, and element technology B6. The element technology A1 is The chemical composition is, by mass%, C: 0.15 to 0.50%, Si: 0.0010 to 3.000%, Mn: 0.30 to 3.00%, Al: 0.0002 to 2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0 to 0.15%, Ti: 0 to 0.15%, V: 0 to 0.15%, Mo: 0 to 1.0%, Cr: 0 to 1.0%, Cu: 0 to 1.0%, Ni: 0 to 1.0%, B: 0 to 0.0100%, Ca: 0 to 0.010%, and REM: 0 to 0.30% contains, with the balance being composed of Fe and impurities, has a metallographic structure containing martensite, bainite, and tempered martensite with a total area ratio of 90% or more, In the aggregate structure from the surface to the position 1 / 4 of the plate thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1-10> to {001}<-1-10> and the pole density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 1.8, In the aggregate structure from the position 1 / 4 of the plate thickness from the surface to the position 1 / 2 of the plate thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1-10> to {001}<-1-10> and the pole density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 2.3 It is a hot stamping formed body characterized by the following. The above-described element technology A2 is The chemical composition is, by mass%, C: 0.15 to 0.50%, Si: 0.0010 to 3.000%, Mn: 0.30 to 3.00%, Al: 0.0002 to 2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0 to 0.15%, Ti: 0 to 0.15%, V: 0 to 0.15%, Mo: 0 to 1.0%, Cr: 0 to 1.0%, Cu: 0 to 1.0%, Ni: 0 to 1.0%, B: 0 to 0.0100%, Ca: 0 to 0.010%, and REM: 0 to 0.30% containing, with the balance being composed of Fe and impurities, having a metal structure composed of ferrite and granular bainite with a total area ratio of 10 to 30% and the remaining structure composed of one or more of martensite, bainite, and tempered martensite, In the aggregate structure from the surface to the position 1 / 4 of the plate thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1 - 10> to {001}<-1 - 10> and the pole density of the orientation group consisting of {111}<1 - 10> to {111}<-1 - 12> is less than 1.8, In the aggregate structure from the position 1 / 4 of the plate thickness from the surface to the position 1 / 2 of the plate thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1 - 10> to {001}<-1 - 10> and the pole density of the orientation group consisting of {111}<1 - 10> to {111}<-1 - 12> is less than 2.3 It is a hot stamping formed body characterized by the following. The above-described element technology B1 is A superimposed hot stamping formed body comprising a first Al-Fe alloy-plated steel sheet with a plate thickness T1 and a second Al-Fe alloy-plated steel sheet with a plate thickness T2 that is smaller in area than the first Al-Fe alloy-plated steel sheet and is superimposed and welded on the first Al-Fe alloy-plated steel sheet. A superimposed hot stamping formed body that satisfies the relationships of the following formulas (7) to (9). 25 ≦ K1 ≦ 60 ··· Formula (7) 25 ≦ K2 ≦ 60 ··· Formula (8) 0 ≦ (D1 - D2) × (K1 / K2)2 ≦ 5.0 ··· Formula (9) Here, K1: The average value of the plating thickness of the Al-Fe alloy plating layer on the side in contact with the second Al-Fe alloy-plated steel sheet and the plating thickness of the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy-plated steel sheet in the non-superimposed portion of the first Al-Fe alloy-plated steel sheet. K2: The plating thickness of the Al-Fe alloy plating layer on the side not in contact with the first Al-Fe alloy-plated steel sheet in the superimposed portion of the second Al-Fe alloy-plated steel sheet. D1: In the first Al-Fe alloy-plated steel sheet, the thickness of the diffusion layer located in contact with the steel sheet base material in the Al-Fe alloy plating layer on the side in contact with the second Al-Fe alloy-plated steel sheet and the thickness of the diffusion layer located in contact with the steel sheet base material in the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy-plated steel sheet. The average value of D2: The thickness of the diffusion layer located in contact with the steel sheet base material in the Al-Fe alloy plating layer on the side of the second Al-Fe alloy-plated steel sheet not in contact with the first Al-Fe alloy-plated steel sheet. Note that the units of the plate thickness T1 and the plate thickness T2 are mm, and the units of K1, K2, D1, and D2 are μm. The element technology B2 is A base steel sheet and An aluminum plating layer with an aluminum content of 80 mass% or more provided on at least one surface of the base steel sheet. An aluminum-plated steel sheet for hot stamping, having a surface treatment film provided on the aluminum plating layer The surface treatment film contains a compound A containing carbon and a compound B which is an oxide or fluoride of a metal element M and has a rutile-type structure The carbon concentration of the compound A is 80% by mass or more A hot stamping molded body formed using an aluminum-plated steel sheet for hot stamping, characterized in that the concentration of the metal element M satisfies the following formula (1) and the following formula (2). 1 ≦ C bM ≦ 40 ··· Formula (1) 1.5 ≦ C bM / C tM ≦ 10.0 ··· Formula (2) Here, when the average thickness of the surface treatment film is H C in the above formula (2) tM is the concentration of the metal element M at a position 0.05H from the surface of the surface treatment film, in % by mass C in the above formula (1) and the above formula (2) bM is the concentration of the metal element M at a position 0.95H from the surface of the surface treatment film, in % by mass The element technology B3a is a structural member comprising a first steel sheet having a minimum plate thickness and a second steel sheet having a plate thickness larger than that of the first steel sheet, and formed by a plurality of steel sheets joined to each other, and having an annular shape in plan view a film provided on the first steel sheet and containing 0.001 g / m or more of one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide 2 or more and is a structural member The element technology B3b is a structural member A member body formed by a plurality of steel plates joined to each other, including a first steel plate having the smallest plate thickness and a second steel plate having a plate thickness larger than that of the first steel plate, and having an annular shape in plan view. Provided on the first steel plate, a film containing carbon black of 0.500 g / m or less. 2 And having the following. It is a structural member provided with the above. The element technology B4 is A structural member, Including a first steel plate having the smallest plate thickness and a second steel plate having a plate thickness larger than that of the first steel plate, and having a member body formed by a plurality of steel plates joined to each other and having an annular shape in plan view. The first steel plate and the second steel plate are each a plated steel plate having an aluminum-based plating layer on both surfaces of the base steel plate. The thickness of the aluminum-based plating layer in the first steel plate is smaller than the thickness of the aluminum-based plating layer in the second steel plate. It is a structural member. The element technology B5a is A structural member, Including a first steel plate and a second steel plate having an end portion that forms an overlap portion together with the end portion of the first steel plate by being overlapped and joined to the end portion of the first steel plate, and formed by a plurality of steel plates joined to each other, and having a member body having an annular shape in plan view. Provided on the surfaces of the first steel plate and the second steel plate located outside the overlap portion, a film containing 0.001 g / m or more of one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide. 2 And having the following. It is a structural member provided with the above. The element technology B5b is A structural member, Including a first steel plate and a second steel plate having an end portion that forms an overlap portion together with the end portion of the first steel plate by being overlapped and joined to the end portion of the first steel plate, and formed by a plurality of steel plates joined to each other, and having a member body having an annular shape in plan view. Provided on the surfaces of the first steel plate and the second steel plate, each located outside the overlapping portion, is a film containing 0.500 g / m 2 or less of carbon black, and A structural member comprising The element technology B6 is A structural member, Formed by a plurality of steel plates joined to each other, and comprising a member body having an annular shape in plan view, The plurality of steel plates include a first steel plate, a second steel plate, and a third steel plate, The end of the first steel plate is overlapped and joined to the end of the second steel plate to form an overlapping portion having the maximum plate thickness in the member body together with the end of the second steel plate, At least one of the first steel plate and the second steel plate, and the third steel plate, respectively, Is a plated steel plate having aluminum-based plating layers on both surfaces of the base steel plate, The thickness of the aluminum-based plating layer in at least one of the first steel plate and the second steel plate is smaller than the thickness of the aluminum-based plating layer in the third steel plate. A structural member. (3) The automobile side module according to (2) above may include at least one of element technology A1 and element technology A2, and at least one of element technology B1 and element technology B2. (4) The automobile side module according to (2) above may include at least one of element technology A1 and element technology A2, and element technology B3a, element technology B3b, element technology B4, element technology B5a, element technology B5b, and element technology B6. At least one of them. (5) The automobile side module according to (2) above may include at least one of element technology A1 and element technology A2, and at least one of element technology B1 and element technology B2, and element technology B3a, element technology B3b, element technology B4, element technology B5a, element technology B5b, and element technology B6. At least one of them.

Advantages of the Invention

[0009] According to the present disclosure, an automotive side module capable of reducing LC-GHG per unit area can be provided.

Brief Description of the Drawings

[0010]

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[0011] As described above, considering the life cycle of an automobile, in order to reduce the total amount of GHG emitted in the global environment, it is insufficient to focus only on GHG reduction during vehicle use (driving). In addition, since the automotive side module accounts for about 5 to 10% of the total vehicle weight, the contribution to reduction by reducing GHG related to the automotive side module is significant. Currently, the main focus is on multi-materializing automobiles using materials such as aluminum and carbon to reduce the weight of automobiles. However, the inventors 1. GHG generated in the production of materials for the automotive side module (hereinafter referred to as "material production GHG"), 2. GHG generated in the manufacturing process of the automotive side module (hereinafter referred to as "process GHG"), 3. The contribution of the automotive side module to GHG generated during vehicle driving (hereinafter referred to as "driving GHG"), and 4. GHG generated when the automotive side module is discarded (hereinafter referred to as "discard GHG"), focused on these four types of GHG and studied how to reduce their total amount.

[0012] Note that the side module in this specification is a skeletal structure member provided inside the side outer panel to reinforce the side outer panel. The side module includes an A-pillar (front pillar), an A-pillar (front pillar) lower, a B-pillar (center pillar), a C-pillar (rear pillar), a side sill (rocker), and a roof rail. The door is not included in the side module. In addition, in this specification, CO 2 and other GHGs generated during the life cycle are referred to as LC-GHG, and the amount of CO 2 is defined as the sum of other GHGs converted into equivalent mass. 2 Examples of GHGs other than CO 2 include ozone-depleting substances such as methane, nitrous oxide, and fluorocarbon compounds. The equivalent mass of CO 2 is calculated using the conversion factors described in Table 1, which are set for each category of material, process, use, and recycling. "CO 2 equivalent" is also referred to as "CO 2 equivalent mass". In this specification, "CO 2 equivalent", "CO 2 equivalent mass", and "CO 2 converted amount" are defined to have the same meaning. "CO 2 equivalent mass" is the mass calculated by weighting CO 2 (global warming potential: 1) and gases other than CO 2 , such as methane CH 4 (the greenhouse effect per unit mass is 25 times that of CO 2 : global warming potential 25), nitrous oxide N 2 O (the greenhouse effect per unit mass is 298 times that of CO 2 : global warming potential 298), by their global warming potentials and then converting them into CO 2 equivalent mass.

[0013]

Table 1

[0014] (GHG in Material Manufacturing) As a material, steel has the lowest GHG emissions per unit weight compared to other materials. Figure 1 is a characteristic diagram showing the environmental impact (GHG emissions) during the manufacturing of each material for an automotive side module. The vertical axis shows normal steel sheets, high-strength steel sheets (steel sheets with HV510 or higher), aluminum, and carbon fiber reinforced plastics (CFRP) as materials for the automotive side module. The horizontal axis shows the GHG emissions per equivalent function [kg-CO 2 equivalent / kg-equivalent part]. As shown in Figure 1, steel materials (normal steel sheets, high-strength steel sheets) have significantly lower GHG emissions compared to other materials (aluminum, carbon fiber reinforced plastics). It can be seen that mainly using steel materials as the main material for the automotive side module can greatly contribute to the reduction of LC-GHG.

[0015] (GHG in Process) In the manufacturing of automotive side modules, GHG is mainly generated in welding processes, heating processes, painting processes, etc. Therefore, by conducting appropriate process design while ensuring the performance required for automotive side modules, it is possible to contribute to the reduction of LC-GHG.

[0016] (GHG during Driving) By reducing the weight of the automotive side module, the load on the power source such as the internal combustion engine can be reduced. Therefore, reducing the weight of the automotive side module can contribute to the reduction of LC-GHG.

[0017] (GHG at End-of-Life) Steel has -1.60 kg-CO per kg through scrap recycling 2It can contribute to the reduction of GHG in the eq. Although the reduction effect of emissions per kg of steel is smaller than that of aluminum, when using high-strength steel, the weight required to obtain the necessary strength is small. Therefore, it can be said that using high-strength steel can contribute to the reduction of LC-GHG. That is, GHG at the time of disposal, like GHG in material manufacturing, can have its emissions reduced by mainly using steel materials as the materials constituting the automotive side module, and can contribute to the reduction of LC-GHG.

[0018] As described above, in order to reduce LC-GHG, the total GHG emissions should be reduced from four perspectives. For example, "GHG in material manufacturing and GHG at the time of disposal" and "GHG during driving" are considered to be in a trade-off relationship. Furthermore, generally, in order to manufacture lightweight and high-functional parts, "process GHG" tends to increase, and there is a trade-off relationship between "process GHG" and "GHG during driving". Conventionally, GHG reduction methods in each life cycle have been studied and discussed, but the optimal examples of material selection and process design for reducing LC-GHG have not been disclosed conventionally.

[0019] The inventors of the present invention focused on reducing LC-GHG by considering the GHG in the above four categories including the trade-off relationship, and by controlling the weight of the components per unit area and the weight of the high-strength components with HV510 or more within an appropriate range, it was found that the LC-GHG of the automotive side module can be reduced while satisfying the necessary strength (side impact resistance).

[0020] Hereinafter, the automotive side module according to an embodiment of the present invention based on the above findings will be described with reference to the drawings. However, these descriptions are merely intended to be examples of preferred embodiments of the present invention, and are not intended to limit the present invention to such specific embodiments.

[0021] FIG. 2 shows a perspective view of a vehicle body 1 to which the vehicle side module 100 according to the present embodiment is applied. The vehicle body 1 is composed of a frame having a monocoque structure including impact-absorbing skeleton members. The vehicle side module 100 according to the present embodiment has a single door ring structure. FIG. 3 shows a plan view of the vehicle side module 100. As shown in FIG. 3, the vehicle side module 100 is integrally configured with a main body 110. The vehicle side module 100 has a structure that is a single ring shape in an overall view (so-called single door ring structure).

[0022] The main body 110 includes a B-pillar upper part 111, a B-pillar lower part 112, an A-pillar part 113, a front roof rail part 114, and a front side sill part 115.

[0023] Reinforcements (not shown) may be attached to the main body 110 for reinforcement. Examples of the reinforcement members include a side sill reinforcement, a B-pillar reinforcement, an A-pillar reinforcement, and a front roof rail reinforcement.

[0024] The vehicle side module 100 according to the present embodiment is made into an integrated part by hot stamping a single tailored blank. More specifically, a single tailored blank can be obtained by, for example, joining a plurality of hot stamping steel plates corresponding to each part of the main body 110 and laminating and joining (patchwork joining) the hot stamping steel plates to be formed into their respective reinforcement members. Then, by hot stamping this single tailored blank, a vehicle side module 100 having different characteristics (weight, hardness, strength, plate thickness) for each part can be obtained. Note that additional reinforcement parts and brackets may be attached to the vehicle side module 100 after hot stamping.

[0025] Thus, in the automotive side module 100 according to this embodiment, since it is configured by hot stamping a plurality of integrated steel plates, it is possible to reduce the GHG in material production as compared with the case where press forming is performed for each part, unnecessary parts are appropriately trimmed, and then joined by welding. Further, when hot stamping is performed for each part and then welding is performed, the number and time of the heating process of hot stamping are required. However, in the automotive side module 100 according to this embodiment, the number and time of the heating process can be reduced by performing hot stamping after welding a plurality of steel plates. Therefore, according to the automotive side module 100 according to this embodiment, it is possible to reduce the process GHG while achieving the performance required for the automotive side module.

[0026] Furthermore, in the automotive side module 100 according to this embodiment, by controlling the weight of the components per minimum circumscribed rectangle area and the weight of the high-strength components with HV510 or more within an appropriate range, it is possible to reduce the LC-GHG of the automotive side module.

[0027] Specifically, the minimum circumscribed rectangle area S (m 2 ) when viewed from the vertical direction of the reference plane, among the components of the automotive side module, the total weight W 0.2 (kg) of the components with a weight of 0.200 kg or more, and the total weight W 510 of the components with a minimum Vickers hardness of HV510 or more, 0.2 satisfy W 510 / S ≦ 7.7 and W 0.2 / W > 0.10, thereby making it possible to reduce the LC-GHG of the automotive side module.

[0028] Here, the reference plane is a plane parallel to the flange surface on the lower side of the vehicle of the side sill (rocker) in the automotive side module. Substantially, it is a plane perpendicular to the vehicle width direction in the automotive side module in a state attached to the vehicle body. Also, the minimum circumscribed rectangle area S (m 2 ) is the minimum circumscribed rectangle area when viewed from the vertical direction of the reference plane of the automotive side module. In the example shown in FIG. 3, it is the area of the rectangle indicated by the dashed-dotted line. The reason for setting the weight of the component part with a weight of 0.200 kg or more as W 0.2 (kg) is that for component parts with a weight less than 0.200 kg, the influence degree on GHG is relatively small. For example, small component parts such as bolts and brackets with a weight less than 0.200 kg are not considered.

[0029] W 0.2 The value of tends to increase as the vehicle body or side door module is larger. Therefore, in this application, W 0.2 with a value corresponding to the minimum circumscribed rectangle area S of the automotive side module 0.2 / S (m 2 ) is used as an index. W 0.2 When the value of / S is 7.7 or less, weight reduction corresponding to the size of the side door module can be achieved, so it is possible to reduce GHG during driving. For the purpose of reducing GHG during driving, the smaller the value of W 0.2 / S, the better. Preferably, it is 6.9 or less, and more preferably 6.3 or less. W 0.2 The lower limit value of / S is set based on the required safety performance. W 0.2 / S may be, for example, 5.0 or more for the purpose of ensuring the rigidity of the module and achieving both safety performance.

[0030] W 510 / W 0.2 When the value of is more than 0.10, among the members used in the side door module, the proportion of high-strength members with HV510 or more is high, so it is possible to reduce GHG in material manufacturing. For the purpose of reducing the GHG in material production, W 510 / W 0.2 The higher the value of, the better, preferably exceeding 0.3, more preferably exceeding 0.7.

[0031] The method for measuring the Vickers hardness is as follows. A sample having a cross-section perpendicular to the plate surface is taken from the flat part of each part, and the cross-section is prepared as a measurement surface and subjected to a hardness test. The method for preparing the measurement surface is carried out in accordance with JIS Z 2244:2009. After polishing the measurement surface using silicon carbide paper from #600 to #1500, the measurement surface is finished to a mirror surface using a liquid in which diamond powder with a particle size of 1 μm to 6 μm is dispersed in a diluent such as alcohol or pure water. The hardness test is carried out by the method described in JIS Z 2244:2009. Using a micro-Vickers hardness tester, 30 points are measured at the 3 / 8 position of the plate thickness of the sample with a load of 1000 gf at intervals of more than 3 times the indentation, and the average value thereof is taken as the hardness at the center of the plate thickness.

[0032] In the present application, at least one of the elemental technology A1 and the elemental technology A2, at least one of the elemental technology B1, the elemental technology B2, the elemental technology B3a, the elemental technology B3b, the elemental technology B4, the elemental technology B5a, the elemental technology B5b, and the elemental technology B6, By applying, the weight ratio of the steel material in the automobile body 1 is increased to reduce the above-mentioned GHG in material production, and the GHG during driving is reduced by the weight reduction of the automobile body 1, and as a result, a significant reduction in LC-GHG is achieved compared with the conventional automobile body. The above-mentioned elemental technology can be mainly applied to the B-pillar upper part 111, the B-pillar lower part 112, the A-pillar part 113, the front roof rail part 114, and the front side sill part 115 among the components of the automobile side module 100.

[0033] at least one of the elemental technology A1 and the elemental technology A2, at least one of the elemental technology B1 and the elemental technology B2, It is more preferable to apply at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6, it is more preferable to apply at least one of elemental technology A1 and elemental technology A2, and at least one of elemental technology B1 and elemental technology B2, and at least one of elemental technology B3a, elemental technology B3b, elemental technology B4, elemental technology B5a, elemental technology B5b, and elemental technology B6, it is more preferable to apply.

[0034] In this specification, the term "automobile" means a motor vehicle for public road use. A motor vehicle for public road use is a vehicle that meets the safety standards in the regulations (type approval) of each country and has excellent crash safety performance in the crash safety performance evaluation of NCAP (New Car Assessment Programme), which is an assessment test in each country. Note that the assessment test is more stringent than the regulations of each country, and if the highest evaluation (5-star evaluation) is obtained in the assessment test, it can be said that the vehicle is fully capable of running on public roads.

[0035] In addition, the vehicle body of the motor vehicle for public road use to which the automobile side module according to this embodiment is applied is not limited to the vehicle body of an engine vehicle or an electric vehicle, and may be the vehicle body of a hybrid vehicle, a fuel cell vehicle, a hydrogen engine vehicle, etc., which uses an internal combustion engine and an electric motor as drive sources. In addition, in FIG. 2, a vehicle body having a monocoque structure frame is shown, but the vehicle body 1 is not limited to the vehicle body having a monocoque structure frame, and may be a vehicle body having a ladder frame structure. In addition, examples of vehicle types for automobiles for road use include passenger cars or commercial vehicles such as sedans, hatchbacks, station wagons, one-box vehicles, pickup trucks, etc. Furthermore, automobiles for road use include loading vehicles such as trucks.

[0036] FIG. 4 is a plan view of an automotive side module 200 according to a modified example. The automotive side module 200 has a structure in which two ring shapes are connected in an overall view (so-called double door ring structure). As shown in this FIG. 4, the automotive side module 200 may have a double door ring structure in which its main body includes a B-pillar upper part 211, a B-pillar lower part 212, an A-pillar part 213, a front roof rail part 214, a front side sill part 215, a rear roof rail part 216, a C-pillar upper part 217, and a C-pillar lower part 218.

[0037] Also in such an automotive side module 200 having a double door ring structure, similar to the automotive side module 100, the minimum circumscribed rectangle area S (m 2 ) when viewed from the vertical direction of the reference plane, among the components of the automotive side module, the total weight W of the components with a weight of 0.200 kg or more 0.2 (kg), and the total weight W of the components with a minimum Vickers hardness of HV510 or more 510 are such that W 0.2 / S ≤ 7.7, and W 510 / W 0.2 > 0.10, it becomes possible to reduce the LC-GHG of the automotive side module.

[0038] (Example) Hereinafter, the present invention will be specifically described by exemplifying examples. Note that the conditions of the examples are an example adopted to confirm the feasibility and effects of the present disclosure, and the present disclosure is not limited to the conditions of the examples. The present disclosure can adopt various conditions as long as it does not deviate from the gist and achieves its purpose.

[0039] Table 2 and Table 3 show various characteristic values of the automobile side modules according to the invention examples and the comparative examples. Table 2 shows the weight (kg) and hardness HV for each part of the integrated parts constituting the automobile side module. Table 3 shows the weight (kg) and hardness HV of the divided parts (i.e., the parts attached after hot stamping) constituting the automobile side module. The automobile side modules of Invention Examples 1 to 7 and Comparative Examples 1, 3, and 4 are automobile side modules in which tailor-made blanks are formed by joining hot stamping steel sheets having shapes corresponding to the pre-forming shapes of a plurality of parts (seven parts in the case of Invention Example 1) shown in Table 2, and a plurality of divided parts (five parts in the case of Invention Example 1) shown in Table 3 are joined to the main body obtained by hot stamping forming. The automobile side modules of Comparative Examples 2, 5 to 11 are automobile side modules in which a plurality of divided parts shown in Table 3 are joined. The divided parts are basically steel members, but aluminum extrusion members are adopted for Divided Part No. 8 of Comparative Example 8 and Divided Part No. 10 of Comparative Example 10.

[0040] The weight (kg) of the parts shown in Table 2 is the weight when the automobile side module is cut along the weld trace of the tailor-made blank. The weights in the comparative examples were obtained by disassembling the automobile body of a general-purpose public road vehicle in circulation, measuring and analyzing the data of the shape and weight measurement. The weights in some of the comparative examples and the invention examples were obtained by measuring and analyzing the design and development data by CAD (Computer - Aided Design). The hardness HV was determined as follows. A sample having a cross-section perpendicular to the plate surface was taken from the flat portions of each part, the cross-section was prepared as a measurement surface, and the measurement surface was subjected to a hardness test. The method for preparing the measurement surface was carried out in accordance with JIS Z 2244:2009. After polishing the measurement surface using silicon carbide paper from #600 to #1500, the measurement surface was finished to a mirror surface using a liquid in which diamond powder with a particle size of 1 μm to 6 μm was dispersed in a diluent such as alcohol or pure water. The hardness test was carried out by the method described in JIS Z 2244:2009. Using a micro-Vickers hardness tester, 30 points were measured at a position 3 / 8 of the plate thickness of the sample with a load of 1000 gf at intervals of more than 3 times the indentation, and the average value thereof was taken as the hardness at the center of the plate thickness.

[0041] Table 4 shows, for each of the inventive examples and comparative examples, · The minimum circumscribed rectangle area S (m 2 ), · The total weight W 0.2 (kg) of the components having a weight of 0.200 kg or more, · The total weight W 510 (kg) of the components having a minimum Vickers hardness of HV510 or more, and, · The total GHG emissions LC-GHG (kg, CO 2 -eq) In addition, · W 510 / W 0.2 (-), · W 0.2 / S (kg / m 2 ), and, · LC-GHG / S (kg, CO 2 -eq / m 2 ) The calculated values are shown.

[0042] The total GHG emissions are the sum of the above-mentioned material production GHG, process GHG, in-use GHG, and end-of-life GHG calculated for the CO 2 equivalent mass, and correspond to the emissions of LC-GHG. The total GHG emissions are the values calculated by the method described below.

[0043] The characteristic values of Invention Examples 1-7 were obtained by the inventors measuring and analyzing the automobile body 1 configured by the inventors using the above-described respective elemental technologies. In addition, the characteristic values of Comparative Examples 1-7 were obtained by the inventors measuring and analyzing the automobile bodies of automobiles running on public roads that are generally in circulation. For some of the comparative examples, values described as default values on the website of World Auto Steel (WAS: hereinafter referred to as WAS) were used. WAS is an automotive subcommittee of the World Steel Association (World Steel Association) and is composed of 17 steel manufacturers around the world. Note that the analysis of LC-GHG emissions was "Roland Geyer, Parametric Assessment of Climate Change Impacts of Automotive Material Substitution, Environmental Science & Technology 2008 42 (18), 6973-6979, DOI: 10.1021 / es800314w" performed based on.

[0044] (Calculation of GHG for material production) The default settings of the GHG analysis software were used as the basic conditions. In this default setting, the charging rate of scrap into the blast furnace is 11.9%, and the usage rates of recycled materials using scrap are set to 5% for sheet materials, 85% for bar and wire materials, and 100% for cast iron based on statistical data. Assuming these as the base conditions, values were input and calculated so as to obtain the various material compositions shown in Table 1.

[0045] (Calculation of process GHG) The default settings of the GHG analysis software were used as the basic conditions. The material yields in automobile part production were assumed to be 55% for steel sheets, 52% for aluminum alloy sheets, 75% for bar and wire materials, and 80% for cast iron, aluminum extrusion materials, and aluminum casting materials. Values were input and calculated so as to obtain the various material compositions shown in Table 1.

[0046] (Calculation of GHG during driving) An electric vehicle was selected as the power train type of the target vehicle model. Based on the size and weight of each analyzed vehicle, an equivalent mid-sized electric vehicle was set. The driving pattern of the vehicle was set to the following WLTP (Class 3b) mode. WLTP mode · Average speed ··· 36.57 km / h · Maximum speed ··· 97.4 km / h · Driving time ··· 1477 seconds · Driving distance ··· 15.01 km · Idling ratio ··· 15.4% · Cold start ratio ··· 100% Assuming a driving distance of 110,000 km, the power train was resized considering the vehicle body weight reduction. Also, the power consumption during the driving of the electric vehicle was set to be generated in Japan, and the power consumption values of the contribution of the side module obtained by the inventors' analysis were input for calculation.

[0047] (Calculation of GHG at the time of disposal) Based on the default settings of the GHG analysis software at the time of disposal, assuming a recycling rate of 90.3% for steel materials and 78.6% for aluminum alloy materials, the energy recovery by recycling to other than vehicles was also considered as the CO 2 absorption amount for setting.

[0048] CO 2 The calculation of the equivalent mass was based on the GHG in the manufacturing process of the materials shown in Table 1, the vehicle manufacturing process, the fuel manufacturing and use processes, and the recycling processes of the materials and vehicles, using the coefficient for calculating the equivalent mass of CO 2 and obtaining the equivalent mass of CO 2 using the weight or energy amount. These values are the default setting values of the GHG analysis software and are set based on the statistical data of the GHG emissions of each substance and each process. Through the above procedures, CO from material manufacturing GHG, process GHG, GHG during driving, and GHG at the time of disposal2 The LC-GHG described in Table 4 was calculated by calculating and summing the equivalent masses.

[0049]

Table 2

[0050]

Table 3

[0051]

Table 4

[0052] In Invention Examples 1-7, while increasing the usage ratio of steel materials in the automotive side module and applying the above-described respective element technologies in combination to form an integrated part, as a result, W 0.2 / S was 7.7 or less, and W 510 / W 0.2 could be made more than 0.10. As a result, the LC-GHG of the automotive side module could be reduced.

[0053] On the other hand, in Comparative Examples 1 to 5 and 8, W 510 / W 0.2 was 0.00, and in order to ensure the collision performance, it was necessary to increase W 0.2 / S, and the reduction effects of the GHG during material production and during driving could not be sufficiently obtained.

[0054] Also, in Comparative Examples 2, 5 to 11 that did not adopt the integrated structure, since press forming was performed for each part, unnecessary parts were trimmed and removed and then joined by welding, the reduction effects of the GHG during material production and during driving could not be sufficiently obtained. In particular, in Comparative Examples 7, 9, and 10, although there are two or more sites having a hardness of HV510 or more by hot stamping, since an integrated structure is not adopted, the reduction effect of material manufacturing GHG cannot be sufficiently obtained, and the reduction effect of LC-GHG cannot be sufficiently obtained.

[0055] Figure 5 is a graph plotting, for the examples, the horizontal axis being W 510 / W 0.2 and the vertical axis being W 0.2 / S (kg / m 2 ). Figure 6 is a graph showing, for the examples, the horizontal axis being W 510 / W 0.2 and the vertical axis being LC-GHG / S (kg, CO 2 -eq / m 2 ). From these graphs, according to the examples of the present invention, it can be confirmed that LC-GHG is reduced by about 5 to 30% compared to the conventional structure. Thus, according to the present invention, the minimum circumscribed rectangle area S (m 2 ) when viewed from the vertical direction of the reference plane, the total weight W 0.2 (kg) of the components of the automotive side module having a weight of 0.200 kg or more, and the total weight W 510 of the components having a minimum Vickers hardness of HV510 or more satisfy W 0.2 / S ≦ 7.7 and W 510 / W 0.2 > 0.10, whereby it is possible to reduce the LC-GHG of the automotive side module.

[0056] (Example 2) Table 5 shows the results of side collision tests for the inventive examples and comparative examples. In Table 5, the test results for side collisions are shown by evaluation values A to C. In this evaluation, first, the test results in the side impact test of IIHS are disclosed, and numerical analysis of the impact test in the IIHS impact analysis model is performed on the vehicle body of Comparative Example 2 having a good evaluation of impact safety performance, and the obtained intrusion amount is used as a reference (evaluation B). Note that the vehicle bodies of Comparative Examples 1 and 3-11 are also vehicle bodies that have received certification (type certification) under the regulations of each country. The safety performance evaluation results of some vehicle bodies are described in comparison with Comparative Example 2. For Invention Examples 1-7, numerical analysis of the side impact test with only the front side and the outer R / F module replaced was performed, and the safety performance was evaluated based on the relative intrusion amount of the center pillar into the cabin. Then, those with test results better than those of the vehicle (Comparative Example 2) with a 5-star evaluation in the IIHS crash simulation test were evaluated as Evaluation A. Also, those that were inferior to the safety test results of Comparative Example 2 but did not experience component breakage were evaluated as Evaluation C.

[0057]

Table 5

[0058] As shown in Table 5, in Invention Examples 1-7, for side collisions, results equivalent to or better than the safety test results of vehicles with a good evaluation in the IIHS side impact test (Evaluation A or Evaluation B) were obtained.

[0059] Therefore, according to Invention Examples 1-7, it is possible to reduce LC-GHG while satisfying the safety test results of vehicles with a good evaluation in the IIHS side impact test.

[0060] The outline of the element technologies applied to the automobile side module 100 according to this embodiment is as follows. Note that the reference numerals for components, formulas, examples, etc. in the description of each element technology are assigned for each element technology to simplify the description. Therefore, the same reference numeral may be assigned in the descriptions of different element technologies. Also, the term "invention" in the description of the element technology should be read as "element technology".

[0061] <<Element Technology A1>> Element Technology A1 is The chemical composition is, by mass%, C: 0.15 to 0.50%, Si: 0.0010 to 3.000%, Mn: 0.30 to 3.00%, Al: 0.0002 to 2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0 to 0.15%, Ti: 0 to 0.15%, V: 0 to 0.15%, Mo: 0 to 1.0%, Cr: 0 to 1.0%, Cu: 0 to 1.0%, Ni: 0 to 1.0%, B: 0 to 0.0100%, Ca: 0 to 0.010%, and REM: 0 to 0.30% containing the balance being Fe and impurities, having a metal structure containing martensite, bainite, and tempered martensite in a total area ratio of 90% or more, in the aggregate structure from the surface to the position 1 / 4 of the plate thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1 - 10> to {001}<-1 - 10> and the pole density of the orientation group consisting of {111}<1 - 10> to {111}<-1 - 12> is less than 1.8, in the aggregate structure from the position 1 / 4 of the plate thickness from the surface to the position 1 / 2 of the plate thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1 - 10> to {001}<-1 - 10> and the pole density of the orientation group consisting of {111}<1 - 10> to {111}<-1 - 12> is less than 2.3 This is a hot stamping formed body characterized by the above.

[0062] Element technology A1 is the technology disclosed in International Publication No. WO 2021 / 230150. According to this element technology A1, it is possible to provide a hot stamping formed body having excellent strength and bendability and high load resistance.

[0063] <<Element technology A2>> Element technology A2 is The chemical composition is, in mass%, C: 0.15 to 0.50%, Si: 0.0010 to 3.000%, Mn: 0.30 to 3.00%, Al: 0.0002 to 2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0 to 0.15%, Ti: 0 to 0.15%, V: 0 to 0.15%, Mo: 0 to 1.0%, Cr: 0 to 1.0%, Cu: 0 to 1.0%, Ni: 0 to 1.0%, B: 0 to 0.0100%, Ca: 0 to 0.010%, and REM: 0 to 0.30% containing the balance being Fe and impurities, having a metal structure composed of ferrite and granular bainite in a total area ratio of 10 to 30% and the balance structure composed of one or more of martensite, bainite, and tempered martensite, in the aggregate structure from the surface to the position 1 / 4 of the plate thickness from the surface, the ratio of the pole density of the orientation group composed of {001}<1 - 10> to {001}<-1 - 10> and the pole density of the orientation group composed of {111}<1 - 10> to {111}<-1 - 12> is less than 1.8, in the aggregate structure from the position 1 / 4 of the plate thickness from the surface to the position 1 / 2 of the plate thickness from the surface, the ratio of the pole density of the orientation group composed of {001}<1 - 10> to {001}<-1 - 10> and the pole density of the orientation group composed of {111}<1 - 10> to {111}<-1 - 12> is less than 2.3 This is a hot stamping formed body characterized by the above.

[0064] Element technology A2 is the technology disclosed in International Publication No. WO2021 / 230149. According to this element technology A2, it is possible to provide a hot stamping formed body having excellent strength, bendability, and ductility.

[0065] <<Element technology B1>> The above element technology B1 is a superimposed hot stamp formed body including a first Al-Fe alloy plated steel sheet with a plate thickness T1 and a second Al-Fe alloy plated steel sheet with a plate thickness T2 that is smaller in area than the first Al-Fe alloy plated steel sheet and is superposed and welded on the first Al-Fe alloy plated steel sheet, and satisfies the relationships of the following formulas (7) to (9). 25 ≦ K1 ≦ 60 ··· Formula (7) 25 ≦ K2 ≦ 60 ··· Formula (8) 0 ≦ (D1 - D2) × (K1 / K2) 2 ≦ 5.0 ··· Formula (9) Here,[[]] K1: The average value of the plating thickness of the Al-Fe alloy plating layer on the side in contact with the second Al-Fe alloy plated steel sheet and the plating thickness of the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy plated steel sheet in the non-superimposed portion of the first Al-Fe alloy plated steel sheet K2: The plating thickness of the Al-Fe alloy plating layer on the side not in contact with the first Al-Fe alloy plated steel sheet in the superimposed portion of the second Al-Fe alloy plated steel sheet D1: In the first Al-Fe alloy plated steel sheet, the average value of the thickness of the diffusion layer located in contact with the steel sheet base material in the Al-Fe alloy plating layer on the side in contact with the second Al-Fe alloy plated steel sheet and the thickness of the diffusion layer located in contact with the steel sheet base material in the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy plated steel sheet D2: The thickness of the diffusion layer located in contact with the steel sheet base material in the Al-Fe alloy plating layer on the side not in contact with the first Al-Fe alloy plated steel sheet of the second Al-Fe alloy plated steel sheet. Note that the units of the plate thickness T1 and the plate thickness T2 are mm, and the units of K1, K2, D1, and D2 are μm.

[0066] According to the elemental technology B1, it is possible to provide a laminated blank for hot stamping and a laminated hot stamp formed body that can improve both the slow heating rate of the laminated portion and the difference in heating rate between the laminated portion and the single-layer portion when using an Al-based plated steel sheet as a material.

[0067] The inventors of the present invention have conducted intensive research to solve the above problems, and focused on the lightness L defined in JIS Z 8781-4 on the surface of the Al-based plated steel sheet. * As a result, it was confirmed that the lower the lightness, the higher the heating rate of the hot stamping of the Al-based plated steel sheet. This is presumably because the lower the lightness, the more the surface of the Al-based plated steel sheet is blackened, and thus the property of easily absorbing heat is obtained. In particular, in order to improve the slow heating rate of the laminated portion of the patchwork, it was found that it is important to relatively lower the lightness of the laminated portion with respect to the thickness of the laminated portion (that is, the total thickness of the two steel sheets). Furthermore, in order to improve the difference in heating rate between the laminated portion and the single-layer portion, it was found that it is important to provide a difference in lightness between the laminated portion and the single-layer portion (that is, in the laminated portion with a larger thickness, lower the surface lightness, and in the single-layer portion, conversely, increase the surface lightness).

[0068] In addition, by using an Al-based plated steel sheet, a high lightness can be obtained due to the surface having a silver-white metallic luster. Furthermore, by increasing the thickness of the Al-based plating layer, it was found that blackening of the plating surface caused by the alloying of the plating reaching the surface can be suppressed, and a high lightness can be maintained even during heating of the hot stamping.

[0069] Also, it was found that the lightness can be lowered by using a carbon-based black film on the upper layer of the Al-based plated steel sheet. In particular, since the carbon-based black film is burned and lost by combustion due to the oxidation reaction during heating of the hot stamping, it was found that a decrease in the spot weldability of the laminated hot stamp formed parts due to the remaining carbon-based black film can be suppressed.

[0070] With reference to the accompanying drawings, preferred embodiments of the present element technology will be described in detail. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0071] FIG. 7 is an explanatory diagram schematically showing an example of a superimposed blank for hot stamping and a superimposed hot stamping molded body according to an embodiment of the present element technology.

[0072] The superimposed blank for hot stamping according to the present embodiment is a kind of tailored blank and is also called a patchwork blank. The superimposed blank for hot stamping according to the present embodiment is used as a material for the superimposed hot stamping molded body.

[0073] As schematically shown in FIG. 7, the superimposed blank 4 for hot stamping according to the present embodiment is composed of welding 3 a first Al-based plated steel sheet 1 and a second Al-based plated steel sheet 2 having a smaller area than the first Al-based plated steel sheet 1. At this time, in the superimposed blank 4 for hot stamping, the portion where the second Al-based plated steel sheet 2 is superimposed is called a superimposed portion 4a, and the portion that is not superimposed is called a single sheet portion 4b. In the superimposed blank 4 for hot stamping according to the present embodiment, as schematically shown in FIG. 7, the second Al-based plated steel sheet 2 is preferably disposed inside the outer edge portion of the first Al-based plated steel sheet 1 so that there is no portion protruding from the first Al-based plated steel sheet 1.

[0074] On the surface of the first Al-based plated steel sheet 1, Al-based plating layers are applied to both the surface 1a on the side in contact with the second Al-based plated steel sheet 2 and the surface 1b on the side not in contact with the second Al-based plated steel sheet 2. Similarly, for the second Al-based plated steel sheet 2, Al-based plating layers are applied to both the surface 2a on the side in contact with the first Al-based plated steel sheet 1 and the surface 2b on the side not in contact with the first Al-based plated steel sheet 1. Further, on the surface 2b of the second Al-based plated steel sheet 2 that is not in contact with the first Al-based plated steel sheet 1, a carbon-based black film (not shown) is provided on the upper layer of the Al-based plating layer.

[0075] In the hot stamping superposed blank 4, as a method for manufacturing the superposed hot stamping molded body according to this embodiment, by heating in a heating furnace 5 to a temperature equal to or higher than the Ac3 point, the steel sheet is austenitized, and immediately after being taken out of the furnace, it is press-molded and rapidly cooled by a mold 6, whereby the steel sheet undergoes martensite transformation. As a result, the hot stamping superposed blank 4 becomes the superposed hot stamping molded body 12 excellent in impact resistance characteristics according to this embodiment. At this time, at least a part of the superposed portion 4a has a portion that becomes the bent portion 8 when it becomes the superposed hot stamping molded body 12.

[0076] In FIG. 7, as an example of the superposed hot stamping molded body 12, a molded product using a hat-shaped mold is shown. Here, the names of the parts of the hot stamping molded body 12 are the top portion 7, the bent portion 8 of the top portion, the vertical wall portion 10, the flange portion 11, and the bent portion 9 of the flange portion.

[0077] Note that in FIG. 7, the second Al-based plated steel sheet 2 according to this embodiment is arranged outside the top portion 7 side, but the object of this element technology can also be achieved by arranging the second Al-based plated steel sheet 2 inside the top portion 7.

[0078] (1. Hot stamping superposed blank) Hereinafter, the hot stamping superposed blank 4 according to this embodiment will be described in detail.

[0079] As described above, the overlay blank 4 for hot stamping according to the present embodiment has a first Al-based plated steel sheet 1 and a second Al-based plated steel sheet 2 that is welded to the first Al-based plated steel sheet 1 and has a smaller area than the first Al-based plated steel sheet 1. Al-based plating is applied to both sides of each of the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2. That is, the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 according to the present embodiment are aluminum-plated steel sheets having Al-based plating layers on both surfaces of the base steel sheet.

[0080] <Base steel sheet> In the overlay blank 4 for hot stamping according to the present embodiment, the chemical composition of the base steel sheet in each of the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 is not particularly limited. However, for example, for the purpose of obtaining a tensile strength of 1500 MPa or more (Vickers hardness (i.e., HV1 in JIS Z2244-1:2020) of about 400 or more when the test force is 9.8107 N), the chemical composition is, by mass, C: 0.19 to 0.50%, Si: 0.01 to 1.50%, Mn: 0.4 to 2.0%, Cr: 0.01 to 1.00%, Ti: 0.001 to 0.100%, B: 0.0005 to 0.0100%, P: 0.100% or less, S: 0.100% or less, Al: 0 to 1.000%, N: 0.0100% or less, Nb: 0 to 0.100%, Mo, Ni, Cu, Co, W, Sn, V, Sb: 0 to 0.500% each, Mg, Ca, Zr, REM, O: 0 to 0.0100% or less each, and the balance being Fe and impurities. It is preferable to use a base steel sheet. Also, within the above range of chemical composition, the chemical composition of the base steel sheet of the first Al-based plated steel sheet 1 and the chemical composition of the base steel sheet of the second Al-based plated steel sheet 2 may be the same or different.

[0081] The method for manufacturing an Al-based plated steel sheet using the above chemical composition as the base steel sheet is not particularly limited. For example, those manufactured through a conventional steelmaking process and a steelmaking process and then through hot rolling, pickling, cold rolling, and a Zenjimia-type molten aluminum plating process can be used as the above aluminum-plated steel sheet.

[0082] In this embodiment, the thickness t1 (mm) of the first Al-based plated steel sheet 1 and the thickness t2 (mm) of the second Al-based plated steel sheet 2 are preferably 0.5 mm or more and 3.2 mm or less, respectively, by selection. By setting the thickness to 0.5 mm or more, it becomes possible to maintain the productivity of the processes in hot rolling and cold rolling in a desired state. Further, by setting the thickness to 3.2 mm or less, it becomes possible to prevent a phenomenon in which the cooling rate decreases during die quenching of hot stamping and the hardenability becomes insufficient, resulting in failure to obtain a desired tensile strength.

[0083] Note that the thickness t1 of the first Al-based plated steel sheet 1 and the thickness t2 of the second Al-based plated steel sheet 2 can be measured, for example, using a micrometer conforming to JIS B7502:2016. Further, the above-mentioned thicknesses t1 and t2 are the thicknesses including the thicknesses of the Al-based plating layers provided on both sides in addition to the thickness of the base steel sheet.

[0084] <Al-based plating layer> The adhesion amount of the Al-based plating layer applied to both sides of the first Al-based plated steel sheet 1 is W1a (g / m 2 ) on the surface 1a on the side in contact with the second Al-based plated steel sheet 2, and W1b (g / m 2 ) on the surface 1b on the side not in contact with the second Al-based plated steel sheet 2. Further, the adhesion amount of the Al-based plating layer applied to both sides of the second Al-based plated steel sheet 2 is W2b (g / m 2 ) on the surface 2b on the side not in contact with the first Al-based plated steel sheet 2. Here, in any of the above W1a, W1b, and W2b, the values are each independently in the range of 20 g / m 2 or more and 120 g / m 2 or less per side. That is, W1a, W1b, and W2b each satisfy the following formulas (3), (4), and (5). 20 ≤ W1a ≤ 120 ··· Formula (3) 20 ≤ W1b ≤ 120 ··· Formula (4) 20 ≤ W2b ≤ 120 ··· Formula (5)

[0085] Here, the average deposition amount of the Al-based plating layer on the non-overlapped part (single-layer part 4b) in the hot stamping superposed blank 4 is W1 (g / m 2 ) per side. In the first Al-based plated steel sheet 1, the deposition amount of the Al-based plating layer on one side of the surface in contact with the second Al-based plated steel sheet 2 is W1a (g / m 2 ), and the deposition amount of the Al-based plating layer on one side of the surface not in contact with the second Al-based plated steel sheet 2 is W1b (g / m 2 ). In this case, W1 = 0.5×(W1a + W1b). Also, the average deposition amount of the Al-based plating layer on the overlapping part 4a in the hot stamping superposed blank 4 is W2 (g / m 2 ) per side. In the first Al-based plated steel sheet 1, the deposition amount of the Al-based plating layer on one side of the surface 1b not in contact with the second Al-based plated steel sheet 2 is W1b (g / m 2 ), and the deposition amount of the Al-based plating layer on one side of the surface not in contact with the first Al-based plated steel sheet 1 in the second Al-based plated steel sheet 2 is W2b (g / m 2 ). In this case, W2 = 0.5×(W1b + W2b).

[0086] Note that in the first Al-based plated steel sheet 1, the surface 1a in contact with the second Al-based plated steel sheet 2, the surface 1b not in contact with the second Al-based plated steel sheet 2, and in the second Al-based plated steel sheet 2, the surface 2b not in contact with the first Al-based plated steel sheet 1 are the surfaces that are exposed to the heat source when the manufactured superposed blank is heated by hot stamping, and are important surfaces for controlling the heating rate during heating in hot stamping.

[0087] The characteristics required for the Al-based plating layer according to this embodiment include (a) suppressing the generation of Fe scale during hot stamping heating, and (b) suppressing chipping or pressing defects of the plating due to slippage of the plating (also called powdering) during hot stamping forming.

[0088] Powdering occurs due to compressive stress applied to plating on the inner surface of the bent part generated during forming, shear stress applied to plating due to sliding from the mold during forming, and the like. When the deposition amounts W1 and W2 of the Al-based plating layer on each steel sheet are less than 20 g / m 2 2, there is a problem that the thickness of the plating becomes thin and the suppression of Fe scale is insufficient. Therefore, the deposition amounts W1 and W2 of the Al-based plating layer on each Al-based plated steel sheet are each independently 20 g / m 2 2 or more. The deposition amounts W1 and W2 of the Al-based plating layer on each Al-based plated steel sheet are each independently preferably 30 g / m 2 2 or more, more preferably, in order of preference, 35 g / m 2 2 or more, 40 g / m 2 2 or more, 45 g / m 2 2 or more, or 50 g / m 2 2 or more.

[0089] On the other hand, when the deposition amount of plating per side W1 and W2 on each Al-based plated steel sheet exceeds 120 g / m 2 2, there is a problem that the suppression of powdering becomes insufficient. Therefore, in the present embodiment, the deposition amount of plating per side W1 and W2 on each Al-based plated steel sheet are each independently 120 g / m 2 2 or less. The deposition amount of plating per side W1 and W2 on each Al-based plated steel sheet are each independently preferably 110 g / m 2 2 or less, more preferably, in order of preference, 100 g / m 2 2 or less, 95 g / m 2 2 or less, 90 g / m 2 2 or less. Note that for the deposition amount of the Al-based plating layer on the surface of the second Al-based plated steel sheet 2 in contact with the first Al-based plated steel sheet 1, there is no particular regulation.

[0090] Note that the thickness (μm) of the Al-based plating layer on each Al-based plated steel sheet is the plating deposition amount (g / m 2) can be estimated from this. The thickness (μm) of the Al-based plating layer in each Al-based plated steel sheet can generally be obtained by the following formula (10), although it depends on the chemical composition of the Al-based plating layer.

[0091] (Plating thickness) = (Plating deposition amount) / 3 ··· Formula (10)

[0092] FIG. 8 schematically shows the layer structure on one side of the plated steel sheet B1-13 in which the Al-based plating layer according to this embodiment is provided on the surface of the base steel sheet. When the Al-based plating layer according to this embodiment is manufactured by the molten plating method, an aluminum-iron (Al-Fe) alloy layer (not shown) is formed near the boundary between the base steel sheet B1-15 of the Al-based plating layer B1-14.

[0093] In addition, according to the general molten plating method as a method of treating the Al-based plating on the base steel sheet, an Al-based plated steel sheet with the deposition amount adjusted can be manufactured by immersing the base steel sheet in a molten aluminum plating bath and performing gas wiping with nitrogen, air, etc. As a result, inevitably, an aluminum-iron alloy layer is formed at the interface between the Al-based plating layer B1-14 and the base steel sheet B1-15 in FIG. 8 due to the elution of Fe during molten plating. In this specification, the Al-based plating layer B1-14 in FIG. 8 shall also include the aluminum-iron alloy layer.

[0094] The chemical composition of the molten aluminum plating bath for forming the above-mentioned Al-based plating layer (i.e., excluding Fe, it is substantially the same as the chemical composition of the Al-based plating layer B1-14) is not particularly limited. However, in terms of excellent heat resistance required during hot stamping heating, the Al content of the molten aluminum plating bath is preferably 80% by mass or more. Also, in terms of easy control of the thickness of the aluminum-iron alloy layer, the Si content of the molten aluminum plating bath is preferably 2% by mass or more. By setting the Si content to 2% by mass or more, it becomes possible to prevent the aluminum-iron alloy layer from becoming too thick and reducing the formability. On the other hand, by setting the Si content of the molten aluminum plating bath to 15% by mass or less, it becomes possible to prevent the alloying reaction during hot stamping heating from slowing down and reducing the productivity of hot stamping.

[0095] When the molten aluminum plating bath contains Si in an amount of 2% by mass or more and 15% by mass or less, a eutectic structure of Al and Si is formed in the Al-based plating layer B1-14 formed using such a plating bath based on the phase diagram. In the case of the molten plating method, it may unavoidably contain 1% by mass or more and 5% by mass or less of Fe as an eluted component from the base steel sheet. Other unavoidable impurities include elements such as Cr, Mn, Zn, V, Ti, Sn, Ni, Cu, W, Bi, Mg, Ca, etc. caused by the eluted components of the molten plating equipment and the impurities of the ingot of the molten aluminum plating bath, and these elements may be contained in an amount of less than 1% by mass.

[0096] That is, the chemical composition (average chemical composition) of the Al-based plating layer B1-14 according to this embodiment is, by mass%, Al: 80 to 97%, Si: 2 to 15%, Fe: 1 to 15%, Cr: 0% or more and less than 1%, Mo: 0% or more and less than 1%, Zn: 0% or more and less than 1%, V: 0% or more and less than 1%, Ti: 0% or more and less than 1%, Sn: 0% or more and less than 1%, Ni: 0% or more and less than 1%, Cu: 0% or more and less than 1%, W: 0% or more and less than 1%, Bi: 0% or more and less than 1%, Mg: 0% or more and less than 1%, Ca: 0% or more and less than 1%, and the balance may be impurities in the plating layer. Here, as described above, in the molten aluminum plating bath, Fe may inevitably be contained in an amount of 1 mass% or more and 5 mass% or less. On the other hand, since an aluminum-iron alloy layer is formed in the Al-based plating layer, the proportion of Fe increases. Therefore, the chemical composition of the Al-based plating layer B1-14 may be Fe: 1 to 15%.

[0097] As the metal structure of the above aluminum-iron alloy layer, there are a θ phase (FeAl 3 ), an η phase (Fe 2 Al 5 ), a ζ phase (FeAl 2 ), Fe 3 Al, FeAl, a BCC phase (α2, α) of an Al solid solution system, etc. An aluminum-iron alloy layer is composed of a combination of these plating phases. As the metal structure of the aluminum-iron alloy layer when Si is contained, there are a τ1 phase (Al 2 Fe 3 Si 3 ), a τ2 phase (Al 3 FeSi), a τ3 phase (Al 2 FeSi), a τ4 phase (Al 3 FeSi 2 ), a τ5 phase (Al 8 Fe 2 Si), a τ6 phase (Al 9 Fe 2 Si 2 ), a τ7 phase (Al 3 Fe 2 Si 3 ), a τ8 phase (Al 2 Fe 3 Si 4 ), a τ10 phase (Al 4 Fe 1.7Si), τ11 phase (Al 5 Fe 2 Si), etc. (however, each phase may not have a stoichiometric composition), and the metal structure of the aluminum-iron alloy layer is often mainly composed of the τ5 phase or the θ phase.

[0098] Also, the adhesion amount per side of the above Al-based plating layer is measured using the method of JIS G 3314:2019 JB.3 (sodium hydroxide - hexamethylenetetramine·hydrochloric acid stripping gravimetric method) after sealing and protecting the Al-based plating layer on one side in advance.

[0099] <Brightness> Hereinafter, with reference to FIG. 7, the brightness, which is important in this elemental technology, will be described. Such brightness is the CIE1976 lightness index L * (CIE 1976 lightness), and hereinafter, it will be simply referred to as "brightness" or "brightness L" * ".

[0100] Regarding the brightness L of the surface of the first Al-based plated steel sheet 1 * on the surface 1a in contact with the second Al-based plated steel sheet 2, it is denoted as L * 1a, and on the surface 1b not in contact with the second Al-based plated steel sheet 2, it is denoted as L * 1b. Furthermore, regarding the brightness L of the surface of the second Al-based plated steel sheet 2 * on the surface 2b not in contact with the first Al-based plated steel sheet 1, it is denoted as L * 2b. Then, L * 1 = 0.5×(L * 1a + L * 1b), L * 2 = 0.5×(L * 1b + L * 2b) are defined. In this case, the hot stamp lamination blank 4 satisfies the following formulas (1) and (2). In the second Al-based plated steel sheet 2, the brightness of the surface of the Al-based plating layer on the surface 2a in contact with the first Al-based plated steel sheet 1 is not particularly defined.

[0101] 14.0 ≦ (L * 1 - L * 2) × (W1 / W2) 2 ≦ 32.0 ··· Equation (1) 0.86 ≦ {t1 / (t1 + t2)} × (L * 1 / L * 2) 2 ··· Equation (2)

[0102] Here, L * 1 means the brightness of the surface of the average Al-based plating layer of the non-overlapped part (single sheet part 4b) in the hot stamping superposed blank 4. Also, L * 2 means the brightness of the surface of the average Al-based plating layer of the overlapping part 4a in the hot stamping superposed blank 4.

[0103] [(L * 1 - L * 2) × (W1 / W2) 2 : 14.0 or more and 32.0 or less] The lower the value of the brightness, the higher the heating rate during hot stamping of the aluminum-plated steel sheet. This is presumably because the lower the value of the brightness, the more the surface of the aluminum-plated steel sheet is blackened, resulting in the property of being easy to absorb heat. That is, in this embodiment, the brightness is used as an index for evaluating the heating rate during hot stamping. In particular, in order to improve the difference in the heating rate between the overlapping part and the single sheet part, it is important to provide a difference between the brightness of the overlapping part and the brightness of the single sheet part, and increase (L * 1 - L * 2) (that is, it is important to lower the surface brightness in the thick overlapping part with a large plate thickness and increase the surface brightness in the single sheet part conversely).

[0104] Furthermore, by using an Al-based plated steel sheet, high brightness can be obtained due to the surface with a silver-white metallic luster, and by increasing the thickness of the Al-based plating layer (which can also be considered as the deposition amount of the Al-based plating layer), the blackening of the plating surface caused by the alloying of the plating reaching the surface can be suppressed, and high brightness can be maintained even during the heating of hot stamping. That is, it is important to increase the ratio, (W1 / W2), of the deposition amount W1 of the Al-based plating layer in the single-layer part 4b to the deposition amount W2 of the Al-based plating layer in the overlapping part 4a. Also, by using a carbon-based black film on the upper layer of the Al-based plated steel sheet, the brightness can be lowered. Thus, by appropriately controlling the Al-based plating layer used for the Al-based plated steel sheet and the carbon-based black film, it is possible to adjust the brightness to a desired value.

[0105] From the above, to improve the difference in the heating rate between the overlapping part and the single-layer part, since the brightness and the deposition amount are related to each other, it is important to control the product of (L * 1-L * 2) and (W1 / W2) 2 within a certain range.

[0106] (L * 1-L * 2)×(W1 / W2) 2 If the value of is less than 14.0, the improvement in the heating rate during hot stamping is not sufficient, and furthermore, the difference in the heating rate between the overlapping part and the single-layer part is not sufficiently improved, resulting in a decrease in the spot weldability of the overlapping hot stamping molded body. Therefore, the value of (L * 1-L * 2)×(W1 / W2) 2 should be 14.0 or more. The value of (L * 1-L * 2)×(W1 / W2) 2 is preferably 16.0 or more, and more preferably 18.0 or more.

[0107] Also, (L * 1-L * 2)×(W1 / W2) 2When the value of * 1 - L * 2)×(W1 / W2) 2 exceeds 32.0, in addition to the improvement in the heating rate during hot stamping reaching saturation, the deposition amount W1 of the Al - based plating layer of the large first Al - based plated steel sheet 1 increases in terms of area, and the powdering property of the plating during hot stamping molding deteriorates. Therefore, (L * 1 - L * 2)×(W1 / W2) 2 is set to 32.0 or less. The value of (L

[0108] [{t1 / (t1 + t2)}×(L * 1 / L * 2) 2 : 0.86 or more] The lower the value of the lightness, the higher the heating rate during heating of the aluminum - plated steel sheet during hot stamping. This is presumably because the lower the value of the lightness, the more the surface of the aluminum - plated steel sheet is blackened, resulting in the property of being easy to absorb heat. In particular, to improve the slow heating rate at the overlapping part of the patchwork, it is important to relatively lower the lightness of the overlapping part with respect to the plate thickness of the overlapping part (i.e., the total t1 + t2 of the plate thickness t1 of the first Al - based plated steel sheet 1 and the plate thickness t2 of the second Al - based plated steel sheet 2). In the above formula (2), the exponent of the plate - thickness ratio t1 / (t1 + t2) is 1, while the exponent of the lightness ratio (L * 1 / L * 2) is 2. From this, it can be seen that in this elemental technology, the lightness ratio (L * 1 / L * 2) is in a more important position than the plate - thickness ratio t1 / (t1 + t2).

[0109] Furthermore, to improve the difference in heating rate between the overlapping part and the single - layer part, it is important to lower the surface lightness in the thick overlapping part and increase the surface lightness in the single - layer part.

[0110] That is, with respect to the ratio t1 / (t1 + t2) of the plate thickness t1 of the first Al-based plated steel sheet 1, the plate thickness (t1 + t2) of the overlapping portion obtained from the plate thickness t2 of the second Al-based plated steel sheet 2, and the plate thickness t1 of the single-layer portion, the lightness L * 2 of the overlapping portion and the lightness L * 1 of the single-layer portion, the square of the ratio (L * 1 / L * 2) becoming larger than or equal to 0.86 is important for improving the difference in the heating rate between the overlapping portion and the single-layer portion of the patchwork. {t1 / (t1 + t2)} × (L * 1 / L * 2) 2 If the value of is less than 0.86, a difference in the heating rate of the overlapping portion is generated, and the spot weldability deteriorates. {t1 / (t1 + t2)} × (L * 1 / L * 2) 2 The higher the value of is, the more preferable it is. Therefore, if necessary, the lower limit thereof may be set to 0.90 or more, 0.94 or more, 0.98 or more, or 1.02 or more. However, {t1 / (t1 + t2)} × (L * 1 / L * 2) 2 Although the upper limit of the value of is not particularly defined, when it exceeds 3.00, it becomes economically difficult to form a difference in lightness. Therefore, {t1 / (t1 + t2)} × (L * 1 / L * 2) 2 The upper limit value of the value of is substantially 3.00. {t1 / (t1 + t2)} × (L * 1 / L * 2) 2 The value of is preferably 2.50 or less, more preferably 2.00 or less, and still more preferably 1.50 or less.

[0111] As a method for measuring the lightness, for example, a test piece may be cut out to 50 × 50 mm, and measured with a diameter φ15 mm of the measurement beam using a spectrocolorimeter (SC-T-GV5 manufactured by Suga Test Instruments Co., Ltd., including regular reflection light).

[0112] Note that the above formulas (1) and (2) were formulated by conducting a series of verifications, which involved fabricating a superimposed blank while varying the plate thickness of the Al-based plated steel sheet and the deposition amount of the Al-based plating layer, etc., actually performing hot stamping, and evaluating the obtained superimposed hot stamp formed body. In such verifications, for each of the obtained superimposed hot stamp formed bodies, evaluations were performed from the viewpoints of the heating rate of the superimposed portion and spot weldability, and the relationships satisfied by those showing good evaluation results were experimentally formulated.

[0113] <Carbon-based black film> FIG. 9 schematically shows the layer structure on one side of the Al-based plated steel sheet B1-16 in which the Al-based plating layer B1-14 is provided on the surface of the base material steel sheet B1-15 according to the present embodiment, and the carbon-based black film B1-17 is further provided on the upper layer thereof, or alternatively, the layer structure on one side of the Al-based plated steel sheet B1-16 in which the carbon-based black film B1-17 further containing Zn, Ti, Cu, V is provided on the upper layer.

[0114] In the second Al-based plated steel sheet 2, a carbon-based black film B1-17 is provided on the upper layer of the Al-based plating layer located on the surface 2b on the side not in contact with the first Al-based plated steel sheet 1. In the Al-based plated steel sheet, since the surface has a silver-white metallic luster, the brightness is high. Here, by providing a carbon-based black film on the upper layer of the Al-based plated steel sheet, the brightness can be lowered. In particular, the carbon-based black film B1-17 is burned and lost by burning due to the oxidation reaction during heating during hot stamping, and is discharged as CO 2 etc. As a result, it is possible to suppress a decrease in the spot weldability of the superimposed hot stamp formed product due to the remaining carbon-based black film B1-17.

[0115] In addition, as a means for further increasing the brightness of the Al-based plated steel sheet having a silver-white metallic luster, for example, by heating the Al-based plated steel sheet to about 600°C to oxidize the surface, it can be whitened. Thereby, it is possible to further increase the brightness of the surface of the Al-based plated steel sheet.

[0116] [Film Thickness of Carbon-Based Black Coating B1-17] The film thickness of the carbon-based black coating B1-17 is preferably 0.3 μm or more and 10 μm or less. By setting the film thickness of the carbon-based black coating B1-17 to 0.3 μm or more, it is possible to suppress an increase in lightness and increase the temperature rise rate of the overlapping portion. The film thickness of the carbon-based black coating B1-17 is more preferably 0.3 μm or more, still more preferably 0.4 μm or more, and even more preferably, in order of preference, 0.5 μm or more, 0.6 μm or more, and 0.7 μm or more. On the other hand, by setting the film thickness of the carbon-based black coating B1-17 to 10 μm or less, it is possible to lower the lightness while ensuring economy, and to ensure spot weldability without leaving the coating after heating the hot stamp. The film thickness of the carbon-based black coating B1-17 is more preferably 8 μm or less, and still more preferably, in order of preference, 6 μm or less, 5 μm or less, and 4 μm or less.

[0117] The film thickness of the carbon-based black coating B1-17 can be obtained by observing the cross-section of the plating with an optical microscope (for example, area: 100 μm × 100 μm) (without etching), measuring the thickness of the coating on the upper layer of the aluminum plating layer as shown in Fig. 9 in three fields of view, and taking the average value of the film thickness measured in each of the three fields of view. At this time, the coating is analyzed from the cross-section with an electron probe microanalyzer (EPMA), and when the carbon content is 30% by mass or more, it is determined to be a carbon-based black coating. The fact that it is a black coating is judged from the lightness L value from the surface being 60 or less. * value being 60 or less.

[0118] [Binder] The carbon-based black coating B1-17 can selectively contain a resin as a binder for enhancing the adhesion to the Al-based plating layer. The type of resin is not particularly limited, and examples thereof include polyethylene resin, polyolefin resin, polyacrylic resin, polymethacrylic acid resin, polyepoxy resin, polyurethane resin, polycarbonate resin, and the like.

[0119] [Nitrogen Content of Carbon-Based Black Coating] The carbon-based black coating B1-17 preferably has a nitrogen content of 2% by mass or more and 18% by mass or less. Generally, when a carbon-based coating is applied on an Al plating, the adhesion between the coating and the plating decreases. However, for example, by using a polyurethane resin containing nitrogen as a binder component or by mixing ammonia, the nitrogen content can be increased, thereby further enhancing the adhesion to the Al-based plating layer. As a result, the heating rate at the overlapping portion can be further increased.

[0120] Since the effect of improving the adhesion to such an Al-based plating layer can be manifested by setting the nitrogen content to 2% by mass or more, the nitrogen content of the carbon-based black coating B1-17 is preferably 2% by mass or more. Also, by setting the nitrogen content of the carbon-based black coating B1-17 to 18% by mass or less, the decomposition reaction of the resin can be suppressed and peeling of the coating can be prevented. The nitrogen content can be determined by analyzing the coating from a cross-section with an electron probe microanalyzer (EPMA).

[0121] [Containing at Least One of Zn, Ti, Cu, and V in the Carbon-Based Black Coating] With respect to the carbon-based black coating B1-17 located in the upper layer of the Al-based plating layer applied to the surface of the second steel plate 2, at least one of Zn, Ti, Cu, or V is selectively added in a total amount of 0.2 g / m 2 or more and 3.0 g / m 2It is preferable to contain the following. The deposition amount shown here refers to the amount deposited per unit area as Zn, Ti, Cu, or V. Zn, Ti, Cu, and V are elements that constitute oxides with good infrared absorption in addition to improving the emissivity. Therefore, by providing the carbon-based black film layer 17 containing such elements, it is possible to suppress the difference in the heating rate between the overlapping portion with a slow heating rate and the single-layer portion with a fast heating rate, which is a problem when used as an overlay blank. In particular, compared with the carbon-based black film layer 17 burning out during hot stamping heating, Zn, Ti, Cu, or V remains even during hot stamping heating. Therefore, the carbon-based black film layer 17 containing such elements can contribute more to improving the heating rate at high temperatures. Also, Zn, Ti, Cu, and V may be contained in either the metallic state or the oxide state. This is because they all become oxides during the intermediate process of heating and contribute to improving the emissivity.

[0122] The effect of suppressing the difference in the heating rate as described above can be manifested by setting the total deposition amount of such elements to 0.2 g / m 2 or more. Therefore, the total deposition amount of such elements in the carbon-based black film layer 17 is preferably 0.2 g / m 2 or more. The total deposition amount of such elements in the carbon-based black film layer 17 is more preferably 0.4 g / m 2 or more, and even more preferably 0.6 g / m 2 or more.

[0123] On the other hand, by setting the total deposition amount of such elements in the carbon-based black film layer 17 to 3.0 g / m 2 or less, it is possible to manifest the effect of suppressing the difference in the heating rate as described above without saturation. Also, although Zn, Ti, Cu, or V remains even after hot stamping heating, by setting the total deposition amount of such elements in the carbon-based black film layer 17 to 3.0 g / m 2By doing the following, it becomes possible to maintain the spot weldability of the hot stamp formed product. The total adhesion amount of such elements in the carbon-based black film layer 17 is more preferably 2.8 g / m 2 or less, and even more preferably 2.6 g / m 2 or less.

[0124] As a specific method for the adhesion amount (content) of Zn, Ti, Cu, and V, for example, it can be obtained by performing elemental analysis from the surface using a fluorescent X-ray analyzer (ZSX Primus manufactured by Rigaku Corporation) and quantifying the adhesion amounts of Zn, Ti, Cu, and V.

[0125] The treatment method of the carbon-based black film layer 17 described above is not particularly limited. For example, an aqueous coating liquid in which water-dispersed carbon black (for example, RCF#52 manufactured by Mitsubishi Chemical Corporation), zinc oxide (for example, Nano Tek manufactured by C.I. Kasei Co., Ltd.), titanium oxide (for example, Nano Tek manufactured by C.I. Kasei Co., Ltd.), copper oxide (for example, Nano Tek manufactured by C.I. Kasei Co., Ltd.), or vanadium oxide (manufactured by Hongwu International Group Ltd.) is dispersed in water is prepared. After performing the above-mentioned molten aluminum plating treatment, it can be manufactured by coating with a roll coater and performing a drying and baking treatment. Alternatively, it can be manufactured by using a means of vacuum depositing a metal of Zn, Ti, Cu, or V on an aluminum-plated steel sheet.

[0126] In addition, as another aspect of the present embodiment, on the Al-based plating layer, both the carbon-based black film layer 17 and a film layer 17' having at least one of Zn, Ti, Cu, or V (more specifically, these elements in a metallic state or oxides of these elements) may be provided. In this case, the arrangement order of the carbon-based black film layer 17 and the film layer 17' having at least one of Zn, Ti, Cu, or V is not particularly limited either. The carbon-based black film layer 17 may be located on the upper layer of the film layer 17' having at least one of Zn, Ti, Cu, or V, or the film layer 17' having at least one of Zn, Ti, Cu, or V may be located on the upper layer of the carbon-based black film layer 17.

[0127] In addition, even when the film layer 17' having at least one of Zn, Ti, Cu, or V is located on the lower layer of the carbon-based black film layer 17, with the film thickness of the carbon-based black film layer 17 according to the present embodiment, the fluorescent X-ray can easily penetrate the carbon-based black film layer 17. Therefore, even when the film layer 17' having at least one of Zn, Ti, Cu, or V is located on the lower layer of the carbon-based black film layer 17, it is possible to measure the deposition amounts of Zn, Ti, Cu, and V by the fluorescent X-ray analysis method.

[0128] Also, such a carbon-based black film layer 17 and the film layer 17' containing at least one of Zn, Ti, Cu, or V may be provided on both sides of the base steel plate, but it is more preferable to be provided only on the surface of the base steel plate that is exposed to the heat source during the heating of the hot stamp.

[0129] Further, the first Al-based plated steel sheet 1 may have the above-described carbon-based black film as the upper layer of the Al-based plating layer on the side not in contact with the second Al-based plated steel sheet 2.

[0130] <Welding> In the case of the superimposed blank 4 for hot stamping in which the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 are superimposed and welded, as the types of welding, spot welding, seam welding, brazing, laser welding, plasma welding, arc welding, etc. can be selected. Here, in terms of making the superimposed portion contact well, spot welding that can make contact at a plurality of points up to the inside of the superimposed portion and directly join by applying pressure between the steel sheets is more preferable.

[0131] (2. Superimposed hot stamping formed body) In the method for manufacturing a hot stamping formed body according to the present embodiment, as shown in FIG. 7, when the above-described superimposed blank 4 for hot stamping is heated and formed immediately after such heating, by providing a bent portion where bending is applied to at least a part of the superimposed portion, the superimposed hot stamping formed body 12 of the present embodiment is manufactured.

[0132] The temperature of the above heating is not particularly limited, but generally, it is in the temperature range of 800 ° C (for example, the Ac3 point) or higher and 1000 ° C or lower. At the time of forming immediately after heating, by cooling using a refrigerant such as a mold or water, a superimposed hot stamping formed body 12 excellent in impact resistance characteristics can be obtained. The time for which the superimposed blank 4 for hot stamping stays at the above heating temperature is not particularly limited, but may be, for example, 4 minutes or more and 20 minutes or less.

[0133] For example, by a preliminary test in advance, for the superimposed blank 4 for hot stamping of interest, measure the heating time or heating rate to a temperature of 800 ° C or higher and 1000 ° C or lower, and use the obtained preliminary test results to determine the above holding time. In this way, for example, conditions such as "holding a temperature of 910 to 920 ° C for 250 to 1200 seconds" can be determined.

[0134] Note that the above heating temperature means the maximum temperature reached by the steel plate at the overlapping part. Examples of the heating method include heating by an electric furnace, a gas furnace, a far-infrared furnace, a near-infrared furnace, etc., electric heating, high-frequency heating, induction heating, and the like.

[0135] The laminated hot stamping formed body 12 according to the present embodiment manufactured as described above includes a first Al-Fe-based alloy-plated steel sheet having a thickness of T1 (mm), and at least one second Al-Fe-based alloy-plated steel sheet that is laminated and welded on the first Al-Fe-based alloy-plated steel sheet, has a smaller area than the first Al-Fe-based alloy-plated steel sheet, and has a thickness of T2 (mm).

[0136] Note that as described above, the laminated hot stamping formed body 12 is manufactured by heating the laminated blank 4 for hot stamping in which the first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 are laminated and welded, and then further performing bending processing or the like. For this reason, the first Al-Fe-based alloy-plated steel sheet and the second Al-Fe-based alloy-plated steel sheet constituting the hot stamping formed body 12 are not necessarily flat. For example, as shown in FIG. 7, the first Al-Fe-based alloy-plated steel sheet has a bending portion 8 at the top, and the second Al-Fe-based alloy-plated steel sheet has a bending portion 8 at the top and a bending portion 9 at the flange portion. Although the name "steel sheet" is used, it is not necessarily flat. In the present embodiment, for the purpose of distinguishing between the steel sheet constituting the hot stamping formed body 12 and the steel sheet constituting the laminated blank 4, for convenience, the former is referred to as an alloy-plated steel sheet (for example, an Al-Fe-based alloy-plated steel sheet), and the latter is referred to as a plated steel sheet (without the addition of "alloy") (for example, an Al-based plated steel sheet).

[0137] The first Al-Fe alloy-plated steel sheet in the laminated hot stamp formed body 12 is a plated steel sheet having Al-Fe alloy plating layers with an average plating thickness of K1 (μm) on both sides thereof. Here, K1 is the average value of the plating thickness of the Al-Fe alloy plating layer on the side in contact with the second Al-Fe alloy-plated steel sheet and the plating thickness of the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy-plated steel sheet in the non-overlapped portion of the first Al-Fe alloy-plated steel sheet.

[0138] The second Al-Fe alloy-plated steel sheet in the laminated hot stamp formed body 12 is a plated steel sheet having an Al-Fe alloy plating layer with a plating thickness of K2 (μm) on the surface on the side not in contact with the first Al-Fe alloy-plated steel sheet. Here, K2 is the plating thickness of the Al-Fe alloy plating layer on the side not in contact with the first Al-Fe alloy-plated steel sheet in the overlapped portion of the second Al-Fe alloy-plated steel sheet.

[0139] Note that, in the second Al-Fe alloy-plated steel sheet, the plating thickness of the Al-Fe alloy plating layer on the surface on the side in contact with the first Al-Fe alloy-plated steel sheet is not particularly defined.

[0140] Here, the average plating thicknesses K1 and K2 of the Al-Fe alloy plating layers in each Al-Fe alloy-plated steel sheet of the laminated hot stamp formed body 12 are each independently 25 μm or more. Further, the average plating thicknesses K1 and K2 of the Al-Fe alloy plating layers in each Al-Fe alloy-plated steel sheet are each independently 60 μm or less. That is, K1 and K2 satisfy the following formulas (7) and (8). 25 ≦ K1 ≦ 60 ··· Formula (7) 25 ≦ K2 ≦ 60 ··· Formula (8)

[0141] In addition, the average plating thicknesses K1 and K2 of the Al-Fe alloy plating layer on each Al-Fe alloy plated steel sheet are preferably 30 μm or more, more preferably 35 μm or more, independently of each other.

[0142] The average plating thicknesses K1 and K2 of the Al-Fe alloy plating layer on each Al-Fe alloy plated steel sheet are preferably 58 μm or less, more preferably 56 μm or less, 52 μm or less, or 48 μm or less, independently of each other.

[0143] By ensuring that the plating thicknesses of the Al-Fe alloy plating layers of the first and second Al-Fe alloy plated steel sheets are within the above ranges respectively, it is possible to maintain the spot weldability of the overlay hot stamp formed body 12 in a good state.

[0144] The above plating thickness can be obtained by observing the cross-section of the plating after nital etching with an optical microscope (area: 100 μm × 100 μm), measuring the plating thickness in three fields of view, and taking the average value of the plating thicknesses measured in each of the three fields of view. Regarding the plating thickness of the first Al-Fe alloy plated steel sheet, there are the positions of the single-layer part 4b and the overlapping part 4a in contact with the second Al-Fe alloy plated steel sheet. From the point that the heating rate is fast, the heating time in hot stamping is the longest, and the spot weldability is likely to deteriorate, the plating thickness of the first Al-Fe alloy plated steel sheet is measured from the single-layer part.

[0145] The Al-Fe alloy plating layer is a layer formed as a result of Fe diffusing to the surface of the Al-based plating layer by heating during hot stamping (in other words, an alloy plating layer containing at least Al and Fe). The Al-Fe alloy plating layer is a compound layer of Al and Fe, the θ phase (FeAl 3 ), η phase (Fe 2 Al 5 ), ζ phase (FeAl 2 ), Fe 3It is composed of a combination of phases such as Al, FeAl, and Al solid-solution Fe. When Si is contained during plating, the Al-Fe alloy plating layer 2 Fe 3 Si 3 )、τ2 phase (Al 3 FeSi), τ3 phase (Al 2 FeSi), τ4 phase (Al 3 FeSi 2 ), τ5 phase (Al 8 Fe 2 Si), τ6 phase (Al 9 Fe 2 Si 2 ), τ7 phase (Al 3 Fe 2 Si 3 ), τ8 phase (Al 2 Fe 3 Si 4 ), τ10 phase (Al 4 Fe 1.7 Si), τ11 phase (Al 5 Fe 2 Si) also contains (however, each phase may not have a stoichiometric composition.), and the Al-Fe alloy plating layer mainly consists of τ1 phase (Al 2 Fe 3 Si 3 ), η phase (Fe 2 Al 5 ), FeAl phase, BCC phase of Fe with Al solid solution, or a combination of multiple of these phases.

[0146] In particular, upon heating during hot stamping, Al in the Al-based plating and Fe in the base steel sheet mutually diffuse. Therefore, as the phases formed by the diffusion of Al into the base steel sheet, in order from the base steel sheet side, a BCC phase of Fe with Al in solid solution and a layer containing the FeAl phase are formed. The layer containing these phases is also called the diffusion layer. Here, such a diffusion layer can be specified by observing the cross section after nital etching with an optical microscope, as described below. Also, when the diffusion layer cannot be specified by observation with an optical microscope, the diffusion layer can be specified by analyzing the cross section with an electron probe microanalyzer (EPMA). At this time, in the EPMA analysis results, a layer with Al: 30 mass% or less and Fe: 70 mass% or more may be defined as the diffusion layer 20.

[0147] Specifically, as shown in FIGS. 11 and 12, in the superimposed hot stamp formed body B1-18, the layer B1-19 is an Al-Fe alloy plating layer and contains the diffusion layer B1-20. The thickness of the Al-Fe alloy layer is measured as the thickness of the layer B1-19, and the thickness of the diffusion layer is measured as the thickness of the layer 20. For example, FIG. 12 shows an example observed with an optical microscope from the cross section after nital etching.

[0148] The thickness of the diffusion layer contained in the Al-Fe alloy plating layer in the portion of the first Al-Fe alloy plating steel sheet that is not superimposed on the second Al-Fe alloy plating steel sheet is denoted as D1 (μm), and the thickness of the diffusion layer contained in the Al-Fe alloy plating layer of the second Al-Fe alloy plating steel sheet is denoted as D2 (μm). At this time, the difference between D1 (μm) and D2 (μm) (D1 - D2), and the ratio of the plating thickness K1 of the non-superimposed portion of the first Al-Fe alloy plating steel sheet to the plating K2 of the superimposed portion of the second Al-Fe alloy plating steel sheet (K1 / K2) 2 and the product of (D1 - D2) × (K1 / K2) 2 is 5.0 μm or less.

[0149] Here, D1 is the average value of the thickness of the diffusion layer located in contact with the steel sheet substrate in the Al-Fe alloy plating layer on the side in contact with the second Al-Fe alloy plated steel sheet and the thickness of the diffusion layer located in contact with the steel sheet substrate in the Al-Fe alloy plating layer on the side not in contact with the second Al-Fe alloy plated steel sheet in the first Al-Fe alloy plated steel sheet. D2 is the thickness of the diffusion layer located in contact with the steel sheet substrate in the Al-Fe alloy plating layer on the side not in contact with the first Al-Fe alloy plated steel sheet of the second Al-Fe alloy plated steel sheet.

[0150] In the Al-Fe plating layer, the binary alloy of Al-Fe (FeAl 3 , Fe 2 Al 5 , FeAl 2 ) contains a relatively low melting point phase with Al: more than 30% by mass and Fe: less than 70% by mass, and a relatively high melting point phase with Al: 30% by mass or less and Fe: 70% by mass or more. When the heating time of hot stamping is long or the heating temperature is high, the diffusion layer increases, and conversely, the binary alloy (FeAl 3 , Fe 2 Al 5 , FeAl 2 ) decreases. In spot weldability, the presence of the plating layer with a low melting point promotes sufficient fusion between materials. Therefore, when the diffusion layer is thick, the binary alloy (FeAl 3 , Fe 2 Al 5 , FeAl 2 ) decreases, and it is known that the spot weldability deteriorates.

[0151] (D1 - D2)×(K1 / K2) 2 When the value of is more than 5.0 μm, the above-mentioned diffusion layer of the first Al-Fe alloy plated steel sheet increases, and conversely, the binary alloy of Al-Fe becomes thinner, resulting in a decrease in spot weldability. Therefore, it is important to suppress (D1 - D2)×(K1 / K2) 2 to 5.0 μm or less for the spot weldability of the overlapping part. (D1 - D2)×(K1 / K2) 2The value of is preferably 4.5 μm or less, more preferably 4.0 μm or less.

[0152] On the other hand, (D1 - D2)×(K1 / K2) 2 The lower limit of is 0 μm. However, when the value of (D1 - D2)×(K1 / K2) 2 is less than 0.5 μm, the effect saturates.

[0153] As a specific method for the plating thicknesses K1 and K2 of the Al-Fe alloy plating layer and the thicknesses D1 and D2 of the diffusion layer, nitriding etching treatment is performed on the plating cross section in a field of view of 100 μm × 100 μm, and the cross section is observed with an optical microscope. As shown in FIG. 12, the plating thickness and the thickness of the diffusion layer are measured with an optical microscope. More specifically, the plating cross section is observed at at least three locations by the above method, and the plating thickness and the thickness of the diffusion layer at each observation location are specified. Then, the average value of the obtained thicknesses is calculated, and the obtained average value may be used as the plating thickness and the thickness of the diffusion layer. However, when the diffusion layer cannot be specified by observation with an optical microscope, analysis is performed with an electron probe microanalyzer (EPMA), and the thickness of the layer with Al: 30 mass% or less and Fe: 70 mass% or more is measured at at least three locations, and the average value thereof is used as the thickness of the diffusion layer B1-20.

[0154] In addition, since the diffusion layer as described above is a layer formed by inward diffusion in the Al-based plating layer, the thicknesses D1 and D2 of the diffusion layer are strongly reflected only by the influence of the heating conditions of the hot stamp, and are not affected by the initial plating thickness. Also, even if the plating adhesion amount of the second Al-based plated steel sheet is increased, the thickness D2 of the diffusion layer of the second Al-Fe alloy plated steel sheet with a slow heating rate cannot be made substantially the same as the thickness D1 of the diffusion layer of the first Al-Fe alloy plated steel sheet. When a normal hot stamping process is applied to the overlay blank for hot stamping that satisfies formulas (1) to (5), an overlay hot stamped molded body that satisfies formulas (7) to (9) can be easily obtained.

[0155] In addition, the plating thicknesses K1 and K2 of the Al-Fe alloy plating layer are affected not only by the influence of plating adhesion before hot stamping, but also by the heating conditions (heating temperature, holding time) of hot stamping. Further, the plating thicknesses K1 and K2 of the Al-Fe alloy plating layer are affected not only by these influences, but also by the plate thickness and lightness that affect the heating time at high temperature, so they are not only affected by the initial plating thickness.

[0156] Note that the above relational expressions were formulated by conducting a series of verifications in which a superposed blank was produced while changing the plate thickness of the Al-based plated steel sheet and the adhesion amount of the Al-based plating layer, etc., and actually performing hot stamping, and then evaluating the obtained superposed hot stamping molded body. In such verification, for each of the obtained superposed hot stamping molded bodies, evaluation was performed from the viewpoints of the heating rate of the superposed portion and spot weldability, and the relationships satisfied by those showing good evaluation results were experimentally formulated.

[0157] Also, a layer containing at least any one of Zn, Ti, Cu, or V may be selectively provided on the upper layer of the Al-Fe alloy plating layer provided on the surface of the second Al-Fe alloy plated steel sheet. At this time, the adhesion amount (content) of at least any one of Zn, Ti, Cu, or V is preferably more than 0 g / m 2 super. The adhesion amount (content) of at least any one of Zn, Ti, Cu, or V is more preferably 0.2 g / m 2 above 3.0 g / m 2 below. The layer containing Zn, Ti, Cu, and V can be obtained by providing a layer contained in a metallic state or an oxide state before heating of hot stamping. Although most of them become oxides during the intermediate process of temperature rise, a part of the metallic state may remain.

[0158] The adhesion amount (content) shown here refers to the amount adhering per unit area as Zn, Ti, Cu, or V.

[0159] Fig. 13 schematically shows the structure of an Al-Fe alloy-plated steel sheet when a layer containing at least one of Zn, Ti, Cu, or V is provided on the upper layer of the Al-Fe alloy plating layer applied to the surface of the second Al-Fe alloy-plated steel sheet in the superimposed hot stamp formed body B1-22. Such an Al-Fe alloy-plated steel sheet has, on the surface of the base steel sheet B1-21, an Al-Fe alloy plating layer B1-19 (including a diffusion layer B1-20), and a coating layer B1-23 having at least one of Zn, Ti, Cu, or V. Such a coating layer B1-23 is preferably provided on the Al-Fe alloy plating layer B1-19 on the side of the second Al-Fe alloy-plated steel sheet that does not contact the first Al-Fe alloy-plated steel sheet.

[0160] In addition to improving the emissivity, Zn, Ti, Cu, and V have good infrared absorption in the case of oxides. Therefore, by providing such a layer, it is possible to suppress the difference in the heating rate between the superimposed portion (where the heating rate is slow) and the single-layer portion (where the heating rate is fast), which is a problem when used as a superimposed blank. As a result, excessive heating of the single-layer portion can be suppressed, and the spot weldability of the single-layer portion of the hot stamp formed body can be improved.

[0161] In particular, the oxides of Zn, Ti, Cu, or V remain even during heating during hot stamping. Therefore, such a coating layer B1-23 can contribute further to improving the heating rate at high temperatures. When the coating layer B1-23 is provided on the surface of the Al-Fe alloy plating layer B1-19 applied to the surface of the second Al-Fe alloy-plated steel sheet, the adhesion amount of the coating layer B1-23 is 0.2 g / m 2 By setting it as above, it becomes possible to sufficiently exhibit the effect of suppressing the difference in the heating rate. The adhesion amount of the coating layer B1-23 is more preferably 0.4 g / m 2 or more, and still more preferably 0.6 g / m 2 or more. On the other hand, the adhesion amount of the coating layer B1-23 is 3.0 g / m 2By setting the following conditions, it becomes possible to achieve such an effect without saturation. Also, even after hot stamping heating, the oxides of Zn, Ti, Cu, or V remain, but the adhesion amount is 3.0 g / m 2 By setting the following conditions, it becomes possible to prevent a decrease in the spot weldability of the hot stamped product. The adhesion amount of the coating layer B1-23 is more preferably 2.8 g / m 2 or less, and even more preferably 2.6 g / m 2 or less.

[0162] In addition, when the coating layer B1-23 is not provided on the surface of the Al-Fe alloy plating layer B1-19 applied to the surface of the second Al-Fe alloy plated steel sheet, the adhesion amount (content) of Zn, Ti, Cu, or V is all 0 g / m 2 or less.

[0163] Also, in the first Al-Fe alloy plated steel sheet, a layer containing at least any one of Zn, Ti, Cu, or V may be selectively provided on the Al-Fe alloy plating layer on the surface on the side not in contact with the second Al-Fe alloy plated steel sheet. At this time, the adhesion amount (content) of at least any one of Zn, Ti, Cu, or V is preferably more than 0 g / m 2 or less. The adhesion amount (content) of at least any one of Zn, Ti, Cu, or V is more preferably 0.2 g / m 2 or more and 3.0 g / m 2 or less. In addition, when the layer containing at least any one of Zn, Ti, Cu, or V is not provided, the adhesion amount (content) of Zn, Ti, Cu, or V is all 0 g / m 2 or less.

[0164] The adhesion amount of the layer containing Zn, Ti, Cu, or V can be determined, for example, by performing elemental analysis from the surface using a fluorescent X-ray analyzer (ZSX Primus manufactured by Rigaku Corporation) to quantify Zn, Ti, Cu, and V.

[0165] As described above, in the laminated hot stamp formed body according to the present embodiment, in the second Al-Fe alloy plated steel sheet, on the Al-Fe alloy plating layer on the surface not in contact with the first Al-Fe alloy plated steel sheet, the total of the Zn content, Ti content, Cu content, and V content is 0.2 to 3.0 g / m 2 There is a layer that is, and further, in the first Al-Fe alloy plated steel sheet, on the Al-Fe alloy plating layer on the surface not in contact with the second Al-Fe alloy plated steel sheet, the total of the Zn content, Ti content, Cu content, and V content is 0 to 3.0 g / m 2 There may be a layer that is.

[0166] When the laminated hot stamp formed body 12 of the present embodiment is used as an automotive part, generally, welding, phosphating treatment, electrocoating, etc. are performed and used. Therefore, for example, a zinc phosphate film and a phosphate film by phosphating treatment, and an organic film of 5 μm or more and 50 μm or less by electrocoating on the surface of such a film may be formed on the surface of the hot stamp formed body 12. After electrocoating, painting such as intermediate coating and top coating may be further performed to improve appearance quality and corrosion resistance. (Example)

[0167] Hereinafter, the present elemental technology will be described more specifically using examples.

[0168] (Example 1) The first Al-based plated steel sheet 1 and the second Al-based plated steel sheet 2 shown in Table 6 were produced by the method described below, and spot welded 3 as shown in Fig. 7 to produce a superimposed blank 4 for hot stamping. As the first Al-based plated steel sheet 1, a cold-rolled steel sheet (chemical composition: in mass%, C: 0.23%, Si: 0.30%, Mn: 1.2%, P: 0.010%, S: 0.002%, Cr: 0.25%, Ti: 0.020%, Al: 0.042%, N: 0.0030%, B: 0.0020%, balance: Fe and impurities) that had undergone normal hot rolling and cold rolling processes was used as a test material, and Al plating treatment was performed on both sides in a Sendzimir-type molten aluminum plating treatment line. After plating, the plating adhesion amount was adjusted by the gas wiping method, and then cooled to produce the first Al-based plated steel sheet 1. The plating bath composition at this time was 89 mass% Al - 9 mass% Si - 2 mass% Fe. The second Al-based plated steel sheet 2 was also produced in the same manner as the first Al-based plated steel sheet 1, and a carbon-based black film was applied.

[0169] This blank was hot stamped and heated at 920 °C to investigate the heating rate of the overlapping part. After heating for the time when the overlapping part was held at 910 - 920 °C for 300 seconds, it was immediately cooled with a mold to obtain a superimposed hot stamp molded body 12. Two flanged parts 11 of the non-overlapped part (single sheet part) were cut out, and the spot weldability was investigated with the same type of plate assembly.

[0170] Each level in Table 6 shows the invention examples of the present application (hereinafter, simply referred to as "invention examples") as A3 - A7, A10, A11, A13, A20, A21, A23, and the comparative examples as A1, A2, A8, A9, A12, A15 - A19, A22.

[0171] The plate thicknesses t1 and t2 of the steel sheets were measured using a micrometer conforming to JIS B7502:2016 as described above. Also, the plating adhesion amounts W1a, W1b, and W2b per side were measured using the method of JIS G 3314:2019 JB.3 after sealing the back side of the surface to be measured. Also, the lightness L * 1a, L * 1b, L* For 2b, a test piece measuring 50×50 mm was cut out and measured using a spectrophotometer (SC-T-GV5 manufactured by Suga Test Instruments Co., Ltd., including regular reflection light) with a measurement beam diameter of φ = 15 mm. The film thickness of the carbon-based black film was measured from cross-sectional observation as described above.

[0172] To investigate the heating rate of the overlapping part of the blank, a K-type thermocouple was welded to the center of the overlapping part of the overlapping blank 4 for hot stamping shown in Fig. 7. Then, the heating time was determined and the heating rate was evaluated. The heating time was determined from the time when the temperature reached 910°C and evaluated. The evaluation criteria were as follows: based on Comparative Example A15 in which the second Al-based plated steel sheet has no carbon-based black film, the heating time was shortened as follows. Evaluation G3 (Good3) was judged as good, G2 (Good2) as better, G1 (Good1) as particularly good, and evaluation NG (No Good) as bad. In addition, in the column of "heating rate of the overlapping part" of Comparative Example A15, which is the reference for evaluation, it was described as "-" to indicate that it is the reference.

[0173] <Evaluation Criteria> G1: Shortening of the heating time by 90 seconds or more G2: Shortening of the heating time by 60 seconds or more and less than 90 seconds G3: Shortening of the heating time by 30 seconds or more and less than 60 seconds NG: Shortening of the heating time by less than 30 seconds, or extension of the heating time

[0174] In order to investigate the spot weldability of the overlapped blank for hot stamping after heating, the overlapped blank 4 for hot stamping shown in Fig. 7 was hot stamped at 920 °C to investigate the heating rate of the overlapped part. At this time, after heating for the time when the overlapped part was held at 910 - 920 °C for 300 seconds, the mold was immediately cooled to obtain the overlapped hot stamp formed body 12. Two flanged parts 11 of the non-overlapped part (single sheet part) were cut out, and the spot weldability of the same kind of plate assembly was investigated under the welding conditions shown below. The evaluation criteria were as follows: regarding the range between the welding current value at which the welding nugget during spot welding obtained a diameter of 4√t (t is the plate thickness) and the welding current value at which splash occurred (referred to as the appropriate current range), evaluation G3 (Good3) was judged as good, G2 (Good2) was judged as better, G1 (Good1) was judged as particularly good, and evaluation NG (No Good) was judged as bad.

[0175] <Evaluation Criteria> G1: Appropriate current range of 2.0 kA or more G2: Appropriate current range of 1.5 kA or more and less than 2.0 kA G3: Appropriate current range of 1.0 kA or more and less than 1.5 kA NG: Appropriate current range of less than 1.0 kA

[0176] Welding power source: DC inverter, electrode pressure: 400 kgf Electrode shape: DR, tip diameter 6φ (R40) (material: chromium copper) Initial pressurization time: 60 cycles, welding time 22 cycles, holding time 10 cycles Welding current value: 4 kA - 15 kA, welding at 0.2 kA pitch

[0177] Based on the evaluation results regarding the heating rate of the overlapping portion of the above-mentioned blank and the evaluation results regarding the spot weldability after hot stamping (HS), a comprehensive evaluation was conducted. More specifically, based on the evaluation scores "Gx" (x is an integer from 1 to 3) of each item, the product of the numbers x was used as the evaluation value. Those with the obtained evaluation value of "9" or those with the evaluation result of "NG" for at least any one item were regarded as the comprehensive evaluation "NG". Also, for Comparative Example A15, since it serves as the criterion for the evaluation of the heating rate, the column for the comprehensive evaluation was described as "-" without conducting the above-mentioned consideration of the comprehensive evaluation.

[0178] Table 6 summarizes the evaluation results of the heating rate of the overlapping portion of the blank and the spot weldability after hot stamping (HS).

[0179]

Table 6

[0180] Invention examples A3 to A7, A10, A11, A13, A20, A21, A23 have a plating adhesion amount within the scope of this application, have a carbon-based black film, and since the relationships between the plate thickness, the plating adhesion amount, and the lightness satisfy Formula (1) and Formula (2), the heating rate of the overlapping portion and the spot weldability after hot stamping were good. For Comparative Example A1, although it has a carbon-based black film, since it does not satisfy Formula (1) and Formula (2), both the heating rate of the overlapping portion and the spot weldability after hot stamping were poor. For Comparative Examples A8, A9, A12, since they do not satisfy Formula (1), the spot weldability after hot stamping was poor. Also, for Comparative Examples A2, A22, although they have a carbon-based black film, since they do not satisfy Formula (2), they were rated as NG (No Good) in the comprehensive evaluation. Furthermore, in Comparative Examples A16, A18 where the plating adhesion amount is less than 20 g / m 2 scale was formed, and in Comparative Examples A16, A18 where the plating adhesion amount is less than 120 g / m 2In Comparative Examples A17 and A19, powdering occurred during press forming, which is also considered to have affected the spot weldability and caused it to deteriorate. Note that Comparative Example A15 does not have a carbon-based black film and does not satisfy Formulas (1) and (2), so the spot weldability after hot stamping was poor.

[0181] (Example 2) Under the same manufacturing conditions as in Example 1 shown in Table 7, first Al-plated steel sheets and second Al-plated steel sheets with a thickness of 1.0 mm, 1.6 mm, and 2.0 mm were produced, and a superimposed blank for hot stamping was produced. The first Al-plated steel sheet 1 and the second Al-plated steel sheet 2 were produced by the method described below, and a superimposed blank 4 for hot stamping was produced by spot welding 3 as shown in Fig. 7.

[0182] This blank was hot-stamped and heated at 920°C in the same manner as in Example 1 to investigate the heating rate of the overlapping portion. After heating for the time when the overlapping portion was held at 910 - 920°C for 300 seconds, the mold was immediately cooled to obtain a superimposed hot-stamped molded body 12. Two flange portions 11 of the non-overlapped part (single-layer part) were cut out, and the spot weldability was investigated with the same type of plate assembly. Each level in Table 7 is shown with Invention Examples as B1, B5, B6, and Comparative Examples as B2, B3, B4, B7.

[0183] In the investigation of the heating rate of the overlapping part of the blanks, the heating time was obtained and evaluated in the same manner as in Example 1. The evaluation criteria are as follows: for B1, based on Comparative Example B2 which has the same thickness of the first Al-plated steel sheet and the second Al-plated steel sheet but does not have a carbon-based black film on the second Al-plated steel sheet, the heating time is shortened as follows. Similarly, for B3, based on Comparative Example B4 which has the same thickness of the first Al-plated steel sheet and the second Al-plated steel sheet but does not have a carbon-based black film on the second Al-plated steel sheet, the heating time is shortened as follows. Also, for B5 and B6, based on Comparative Example B7 which has the same thickness of the first Al-plated steel sheet and the second Al-plated steel sheet but does not have a carbon-based black film on the second Al-plated steel sheet, the heating time is shortened as follows. Evaluation G3 (Good3) was determined to be good, G2 (Good2) to be better, G1 (Good1) to be particularly good, and evaluation NG (No Good) to be bad. For each comparative example serving as the evaluation criterion, the description in the column of "heating rate of the overlapping part" was written as "-" to indicate that it is the criterion.

[0184] <Evaluation Criteria> G1: Reduction in heating time by 90 seconds or more G2: Reduction in heating time by 60 seconds or more and less than 90 seconds G3: Reduction in heating time by 30 seconds or more and less than 60 seconds NG: Reduction in heating time by less than 30 seconds, or extension of the heating time

[0185] The spot weldability after heating of the overlapping blank for hot stamping was evaluated using the same investigation method and evaluation criteria as in Example 1.

[0186] Based on the evaluation results regarding the heating rate of the overlapping portion of the above-mentioned blank and the evaluation results regarding the spot weldability after hot stamping (HS), a comprehensive evaluation was conducted. More specifically, based on the evaluation scores "Gx" (x is an integer from 1 to 3) for each item, the product of the numbers x was used as the evaluation value. Those with the obtained evaluation value of "9", or those with the evaluation result of "NG" for at least any one item, were given a comprehensive evaluation of "NG". For each comparative example serving as a criterion for the evaluation of the heating rate, the column for the comprehensive evaluation was described as "-" without conducting the consideration of the comprehensive evaluation as described above.

[0187]

Table 7

[0188] Invention examples B1, B5, and B6 had the plating adhesion amount within the scope of the invention of the present application, had a carbon-based black film, and since the relationship between the plate thickness, plating adhesion amount, and lightness satisfied Formula (1) and Formula (2), the heating rate of the overlapping portion and the spot weldability after hot stamping were good. Also, although comparative example B3 had a carbon-based black film, since it did not satisfy Formula (2), the heating rate of the overlapping portion was poor compared to B4. Note that comparative examples B2, B4, and B7 did not have a carbon-based black film and did not satisfy Formula (1) and Formula (2) either, so the evaluation of the spot weldability after hot stamping was poor.

[0189] (Example 3) Under the same manufacturing conditions as level A3 of Example 1, a first Al-based plated steel sheet and a second Al-based plated steel sheet were produced. Those in which Zn, V, Ti, Cu (vacuum evaporation method) were formed on the second Al-based plated steel sheet, and further a carbon-based black film was formed thereon were produced as invention examples C1 to C4. Also, invention examples C5 to C10 were produced by incorporating an aqueous dispersion sol of Zn oxide, V oxide, Ti oxide, and Cu oxide into the carbon-based black film. Regarding these, a hot stamping overlapping blank 4 was produced by spot welding 3 as shown in FIG. 7. The details of invention examples C1 to C10 are as shown in Table 8.

[0190] This blank was hot-stamped and heated at 920 °C in the same manner as in Example 1 to investigate the heating rate of the overlapping portion (the evaluation criteria were the same as in Example 1, and it was evaluated based on Comparative Example A15 in which the second Al-based plated steel sheet did not have a carbon-based black film). After heating for a time when the overlapping portion was held at 910 - 920 °C for 300 seconds, the mold was immediately cooled to obtain the overlapped hot-stamped molded body 12. Two flange portions 11 of the non-overlapped part (single-layer part) were cut out, and the spot weldability was investigated with the same kind of plate assembly (the evaluation criteria were the same as in Example 1). The obtained results are shown in Table 8.

[0191]

Table 8

[0192] Invention Examples C1 - C10 are preferable films having Zn, V, Ti, and Cu in the carbon-based black film. Therefore, compared with A3, they showed better results in terms of the heating rate of the overlapping portion and the spot weldability after HS.

[0193] (Example 4) Under the same manufacturing conditions as Level A3 in Example 1, the first Al-based plated steel sheet and the second Al-based plated steel sheet were produced. A carbon-based black film was formed on the second Al-based plated steel sheet. Those with a nitrogen content of 1% by the above method were designated as D1, and those with 2%, 5%, 8%, 18%, and 20% were designated as D2, D3, D4, D5, and D6, respectively, and a tape peeling test was carried out (tape: CT405AP - 24 manufactured by Nichiban Co., Ltd.). As a result, film peeling was observed in D1 with a nitrogen content of 1% and D6 with a nitrogen content of 20%, and no peeling was observed in the other D2, D3, D4, and D5.

[0194] (Example 5) Under the same manufacturing conditions as those of levels A3, A7, A10, A12, A13, A15, A16 of Example 1 and levels C5, C6, C9, C10 of Example 3 shown in Table 9, a laminated hot stamp formed body was produced, and each level was designated as E1, E6, E7, E8, E9, E10, E11, and E2, E3, E4, E5. Further, an Al-based electroplated steel sheet having a carbon-based black film containing ZnO, V oxide, TiO2, and Cu oxide used for the second Al-based electroplated steel sheet of E2, E3, E4, E5 was used for both the second Al-based electroplated steel sheet and the first Al-based electroplated steel sheet, and a laminated hot stamp formed body was produced under the same manufacturing conditions as those of Example 3, and each level was designated as E12, E13, E14, E15. In addition, the manufacturing conditions in Example 1 and Example 3 as described above applied to obtain the laminated hot stamp formed bodies of each level E1 to E15 are described in Table 9 in an item named "applied manufacturing conditions". Two pieces of the non-laminated part (single sheet part) were cut out, and the spot weldability was investigated with the same kind of plate assembly. Each level in Table 9 shows inventive examples as E1 to E5, E7, E9, E12 to E15, and comparative examples as E6, E8, E10, E11. The evaluation method and criteria for the spot weldability after hot stamping are the same as those in Example 1.

[0195] The plating thickness K1 of the Al-Fe alloy plating layer of the first Al-Fe alloy electroplated steel sheet, the thickness D1 of the diffusion layer, the plating thickness K2 of the Al-Fe alloy plating layer of the second Al-Fe alloy electroplated steel sheet, and the thickness D2 of the diffusion layer were measured by cross-sectional observation with an optical microscope as described above (in each case, three locations were measured, and the average value was obtained).

[0196]

Table 9

[0197] Invention examples E1 to E5, E7, E9, and E12 to E15 had plating thicknesses K1 and K2 of the Al-Fe alloy plating layer within the scope of the invention of the present application. Since the plating thickness of the Al-Fe alloy plating layer and the thickness of the diffusion layer satisfied formula (9), the spot weldability after hot stamping was good. Comparative examples E6, E8, and E10 did not satisfy formula (9), so the spot weldability after hot stamping was poor. Comparative example E11 had a plating thickness of the Al-Fe alloy plating layer of less than 25 μm and did not satisfy formula (9) either, so the spot weldability after hot stamping was both poor.

[0198] Furthermore, invention examples E2, E3, E4, and E5 had oxides of Zn, V, Ti, and Cu on the Al-Fe alloy plating layer of the second Al-Fe alloy plated steel sheet, so they showed better spot weldability after HS than E1.

[0199] Also, invention examples E12, E13, E14, and E15 had oxides of Zn, V, Ti, and Cu on the Al-Fe alloy plating layer of the first Al-Fe alloy plated steel sheet and on the Al-Fe alloy plating layer of the second Al-Fe alloy plated steel sheet, respectively, so they showed better spot weldability after HS than E1.

[0200] (Example 6) Focusing again on levels A2, A3, A5, and A15 of Example 1 shown in Table 6, and further manufacturing under the same manufacturing conditions except that a carbon-based black film was further provided on the first Al-based plating layer for these levels, a hot stamping overlay blank 4 was produced by spot welding 3 as shown in Fig. 7.

[0201] This blank was hot-stamped and heated at 920°C in the same manner as in Example 1 to investigate the heating rate of the overlapping portion (the evaluation criteria were the same as in Example 1, and it was evaluated based on Comparative Example A15 which has no carbon-based black film on the second Al-based plated steel sheet). After heating for the time when the overlapping portion was held at 910 - 920°C for 300 seconds, the mold was immediately cooled to obtain the overlapped hot-stamped molded body 12. Two flanged portions 11 of the non-overlapped part (single sheet part) were cut out, and the spot weldability was investigated with the same kind of plate assembly (the evaluation criteria were the same as in Example 1).

[0202] Each level in Table 10 was shown as F1 - F4. Level F1 is the one where a carbon-based black film was further provided on the first Al-based plated steel sheet of Level A2. Level F2 is the one where a carbon-based black film was further provided on the first Al-based plated steel sheet of Level A3. Level F3 is the one where a carbon-based black film was further provided on the first Al-based plated steel sheet of Level A5. Also, Level F4 is the one where a carbon-based black film was further provided on the first Al-based plated steel sheet of Level A15.

[0203]

Table 10

[0204] As is clear from Table 10 above, it can be seen that for F1 - F4, compared with the corresponding A2, A3, A5, and A15 respectively, the heating rate of the overlapping portion has further increased, and more excellent evaluation results have been obtained.

[0205] <<Element Technology B2>> The said Element Technology B2 is a base steel plate, an aluminum plating layer with an aluminum content of 80 mass% or more provided on at least one surface of the said base steel plate, a surface treatment film provided on the said aluminum plating layer, and in the aluminum-plated steel sheet for hot stamping having the said surface treatment film is Compound A containing carbon and compound B which is an oxide or fluoride of metal element M and has a rutile-type structure, and wherein the carbon concentration of the compound A is 80% by mass or more, the concentration of the metal element M satisfies the following formula (1) and the following formula (2), and is a hot stamp formed body formed using an aluminum-plated steel sheet for hot stamping. 1 ≦ C bM ≦ 40 ··· Formula (1) 1.5 ≦ C bM / C tM ≦ 10.0 ··· Formula (2) Here, when the average thickness of the surface treatment film is H, C in the above formula (2) tM is, in mass%, the concentration of the metal element M at a position 0.05H from the surface of the surface treatment film, C in the above formula (1) and the above formula (2) bM is, in mass%, the concentration of the metal element M at a position 0.95H from the surface of the surface treatment film.

[0206] Element technology B2 aims to provide a hot stamping steel sheet capable of further improving the productivity of hot stamping members.

[0207] To solve the above problems, the present inventors conducted intensive studies. As a result, when manufacturing a hot stamping member using a hot stamping steel sheet, it was found that if the heating rate when the steel sheet is heated to a desired temperature (for example, above the Ac3 point) can be increased, the heating time can be shortened, which contributes to an improvement in productivity. Specifically, it was found that by providing a surface treatment film containing compound A having a carbon concentration of 80% by mass or more and compound B which is an oxide or fluoride of metal element M and has a rutile-type structure on the plating layer, and controlling the concentration range of the metal element M within a predetermined range, the heating rate can be significantly increased.

[0208] (Aluminum-plated steel sheet for hot stamping) The aluminum-plated steel sheet for hot stamping according to the embodiment of the present elemental technology (hereinafter, also referred to as "aluminum-plated steel sheet for HS") can increase the heating rate when heating such an aluminum-plated steel sheet for HS in manufacturing a hot stamping member. That is, by using the aluminum-plated steel sheet for HS of this embodiment in which the heating rate during heating can be increased, it becomes possible to improve the productivity of the hot stamping member.

[0209] The aluminum-plated steel sheet for hot stamping of this embodiment has a surface treatment film containing a predetermined compound on at least one surface of the plated steel sheet on which the aluminum plating layer is formed in order to realize an improvement in the heating rate when heating the aluminum-plated steel sheet for HS. By providing a surface treatment film containing a predetermined compound on at least one surface of the plated steel sheet provided with the aluminum plating layer in this way, the heating rate when the obtained aluminum-plated steel sheet for HS is heated can be increased. Note that the surface treatment film may be provided on both surfaces of the plated steel sheet provided with the aluminum plating layer, or may be provided only on one surface. Also, the surface treatment film may be provided over the entire surface of the plated steel sheet provided with the aluminum plating layer, or may be provided on a part of the surface. From the viewpoint of further improving the productivity of the hot stamping member, it is preferable that the surface treatment film is provided over the entire surface of the plated steel sheet provided with the aluminum plating layer.

[0210] In the aluminum-plated steel sheet for hot stamping according to this embodiment, the type of the steel sheet (base steel sheet) serving as the base material is not particularly limited. Examples of the base steel sheet include various hot-rolled steel sheets and cold-rolled steel sheets. The plated steel sheet constituting the aluminum-plated steel sheet for hot stamping of this embodiment has a plating layer on at least one surface of such a base steel sheet. Examples of the plated steel sheet include a steel sheet plated with molten aluminum plating or the like. However, the plating layer of this embodiment is not limited to molten aluminum plating as long as it can be applied to hot stamping.

[0211] Conventionally, many steel sheets used as automotive skeletal parts, etc. were hot-rolled steel sheets, cold-rolled steel sheets, or plated steel sheets plated with aluminum, zinc, etc. Since these conventional steel sheets have a low emissivity, the heating rate with respect to radiant heating is low.

[0212] In the aluminum-plated steel sheet for hot stamping of the present embodiment, by applying a predetermined surface treatment film to the entire surface of at least one surface of the plating layer, the heating rate during hot stamping heating can be increased. Specifically, by heating an aluminum-plated steel sheet for HS having a predetermined surface treatment film and then hot stamping the aluminum-plated steel sheet for hot stamping after heating, the productivity of the hot stamping member can be further improved.

[0213] <Surface treatment film> FIG. 14 shows a schematic cross-sectional view of the surface portion of one surface of the aluminum-plated steel sheet for hot stamping according to the present embodiment.

[0214] As shown in FIG. 14, the aluminum-plated steel sheet B2-10 for hot stamping according to the present embodiment includes, for example, a base steel sheet B2-11, an aluminum plating layer (Al plating layer) B2-12 provided on at least one surface of the base steel sheet B2-11, and a surface treatment film 13 provided on the aluminum plating layer B2-12. In the aluminum-plated steel sheet B2-10 for hot stamping according to the present embodiment, the surface on the side where the surface treatment film 13 is applied (that is, the surface of the surface treatment film B2-13) has a high emissivity. Therefore, the heating rate during hot stamping heating is large, and as a result, the productivity of the hot stamping member can be further improved. Note that FIG. 14 is a schematic diagram for explanation, and the dimensions of the surface treatment film 13, the aluminum plating layer B2-12, etc. do not necessarily show a preferred embodiment and are not limited to the dimensions in FIG. 14.

[0215] The surface treatment film B2-13 according to this embodiment contains a carbon-containing compound A and a compound B which is an oxide or fluoride of a metal element M and has a rutile-type structure. The surface treatment film B2-13 according to this embodiment may further contain a binder component as needed. Also, the surface treatment film B2-13 according to this embodiment may contain silica. Further, in this embodiment, by adjusting the contents of the compound A and the compound B in the surface treatment film B2-13, the concentration distribution of the metal element M, the application and drying methods of the surface treatment film B2-13, and the film thickness, etc., it is possible to improve the heating rate (heating efficiency) during hot stamping heating.

[0216] Also, in the surface treatment film B2-13 according to this embodiment, the compound B has a predetermined concentration distribution. Specifically, the concentration of the metal element M constituting the compound B with respect to the film has a concentration distribution (concentration gradient) in which the concentration is higher on the plating layer side than on the surface side of the film in the film thickness direction. The presence of the metal element M with such a predetermined concentration distribution makes it possible to further enhance the heating efficiency by the surface treatment film B2-13. When the hot stamping steel sheet according to this embodiment is heated by hot stamping, radiant heat from the heating atmosphere can be efficiently absorbed. In addition, heat can also be efficiently absorbed by heat conduction due to contact with the heated atmosphere gas. As a result, it becomes possible to rapidly heat the entire surface treatment film. Hereinafter, the constituent elements of the surface treatment film B2-13 will be described in detail.

[0217] [Compound A] The carbon concentration of Compound A contained in the surface treatment film B2-13 is 80% by mass or more. When the carbon concentration of Compound A is less than 80% by mass, when the aluminum-plated steel sheet for HS is heated in the hot stamping process, Compound A is decomposed and oxidized even at a relatively low temperature, so Compound A may disappear from the film. When Compound A disappears from the film, the effect of enhancing the temperature rise characteristics cannot be maintained up to a high temperature. Therefore, the carbon concentration of Compound A is set to 80% by mass or more. Preferably, the carbon concentration of Compound A is 82% by mass or more, preferably 85% by mass or more. The carbon concentration of Compound A may be 100% by mass. Examples of Compound A include carbon black (CB), graphite, soot, and the like.

[0218] The carbon concentration of Compound A can be measured by cross-sectional analysis of the surface treatment film using a transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS), and electron diffraction. Specifically, the spectrum of characteristic X-rays during electron beam irradiation is measured, the detection intensity for each energy is calculated, and the elements constituting the compound to be measured can be identified from the energy value. Then, using a calibration curve prepared in advance from the relationship between a substance with a known element concentration and the detection intensity data therefor, the concentration of each element in the compound is calculated from the detection intensity of each element constituting the compound to be measured. The measurement is carried out at 10 locations within the same compound, and when all elements fall within the range where the maximum value of the concentration of each element is 1.0 to 1.3 times the minimum value, it is regarded as the same compound. That is, when measuring 10 locations in one compound observed by TEM-EDS and all elements constituting the compound are within the range where the maximum value of the concentration is 1.0 to 1.3 times the minimum value, it is regarded as the same compound. The TEM observation sample is prepared by the FIB sampling method using a focused ion beam (FIB) processing observation device (for example, "NB5000" manufactured by Hitachi High-Tech Corporation). The acceleration voltage during processing is set to 40 kV.

[0219] The carbon concentration of Compound A is defined as follows. In the cross-sectional analysis of the surface treatment film, within the range surrounded by the film thickness and a length of 5 μm in the direction perpendicular to the film thickness, when measured at 10 locations within the same compound, the median value between the maximum value and the minimum value of the carbon concentration is defined as the carbon concentration of Compound A. When there are multiple Compound As within the above range, the median value is calculated for each Compound A, and the average value of the obtained median values is defined as the carbon concentration of Compound A. By such a method, the concentration of elements such as carbon constituting Compound A can be analyzed. Note that Compound A mainly composed of carbon and Compound B which is an oxide or fluoride of metal element M can be distinguished by the difference in carbon concentration.

[0220] Also, in the present embodiment, when the average thickness of the surface treatment film is H (μm), the content rate of Compound A having a carbon concentration of 80 mass% or more is preferably 10 to 90% or 20 to 90% at 0.90H from the surface of the surface treatment film (hereinafter, also referred to as "interface-side position P". This interface-side position P can be said to be the position 0.10H from the interface between the surface treatment film and the Al plating layer.), and more preferably 30 to 80%.

[0221] Compound A with a carbon concentration of 80% by mass or more has a great effect of absorbing radiant heat. Also, since such compound A has a high carbon concentration, it is less likely to decompose by heating or disappear from the surface treatment film due to volatilization. Therefore, even when the temperature of the outermost surface of the aluminum-plated steel sheet for HS rises due to the heating of the hot stamp, the absorption of radiant heat can be enhanced up to a high temperature range. To obtain such an effect, it is effective to increase the content of compound A. In the present embodiment, by setting the content of compound A at the interface-side position P to preferably 10% or more or 20% or more, more preferably 30% or more, the rate of temperature rise during hot stamp heating can be further improved. On the other hand, compound A itself in the surface treatment film does not have the effect of enhancing film adhesion. Therefore, among the surface treatment films, it is particularly preferable to suppress the content of compound A at the interface-side position P, which is particularly the Al plating layer side, to a predetermined amount or less. Specifically, by setting the content of compound A at the interface-side position P to preferably 90% or less, more preferably 80% or less, the adhesion between the surface treatment film and the Al plating layer is improved. The mechanism by which the film adhesion is improved by setting the content of compound A at the interface-side position P to preferably 90% or less, more preferably 80% or less, is considered to be that chemical and physical bonds between the highly polar rutile-type compound and the binder resin contained in the surface treatment film and the aluminum plating layer can be ensured, and as a result, the effect of enhancing the film adhesion is exhibited.

[0222] The content of compound A at the interface-side position P is determined by the following method. First, by TEM observation, at the interface-side position P, compound A with a carbon concentration of 80% or more is detected by EDS. The "0.90H position" is, for example, when the average thickness H of the surface treatment film is 5 μm, the position at a depth (thickness) of 4.5 μm from the surface of the surface treatment film (that is, the position at a depth (thickness) of 0.5 μm from the interface between the surface treatment film and the Al plating layer toward the film side). Next, in the TEM image of the sample described below, when observing 10 points at 30 nm intervals in a direction perpendicular to the thickness direction of the surface treatment film layer (the direction parallel to the interface between the aluminum plating layer and the surface treatment film and perpendicular to the thickness direction of the sample), if the presence of the compound A is observed at 3 points, the content rate of the compound A at the interface side position P is defined as 30%. Similarly, when the presence of the compound A is observed at 4 points, the content rate of the compound A is defined as 40%, and the same shall apply hereinafter. Therefore, when the compound A with a carbon concentration of 80% or more is observed at 3 or more and 8 or less points, it means that the content rate of the compound A is 30 to 80%. The TEM observation sample used for calculating the content rate of the compound A is prepared by the FIB sampling method using a focused ion beam (FIB) processing observation device (for example, "NB5000" manufactured by Hitachi High-Tech Corporation). The acceleration voltage during processing shall be 40 kV. The thickness of the sample shall be 100 nm ± 10 nm. Note that, as described above, the content rate of the compound A is the ratio (= the number of points where the compound A is present / 10) of the number of points where the compound A is observed (present) among 10 points in a specific direction (the direction parallel to the surface of the surface treatment film and perpendicular to the thickness direction of the sample) in the TEM image of a sample with a thickness of 100 ± 10 nm. Therefore, the unit of the content rate is dimensionless %, not volume % or area %.

[0223] [Compound B] Compound B is an oxide or fluoride of the metal element M and has a rutile structure. Examples of the metal element M include Ti, V, Mn, Ru, Cs, Ir, Ge, Cu, Ag, Ni, etc. If necessary, any one of the above elements, or only a plurality of arbitrary elements, may be used as the metal element M. Also, examples of such a compound B include TiO 2 , VO 2 , β-MnO 2 , RuO 2 , CsO 2 , IrO 2 , GeO 2 , CuO 2 , AgO 2 , NiF 2Examples include the above. If necessary, any one of the above compounds, or only a plurality of arbitrary compounds, may be used as Compound B.

[0224] Increasing the heating rate during hot stamping can be achieved by incorporating Compound B having a rutile-type compound structure into the film. Although the reason for this is not clear, it is speculated as follows. The rutile-type structure has a distorted hexagonal close packing of anions, with cations arranged in its 6-coordination space (6-coordination gap). When a compound B having such a rutile-type compound structure is incorporated into the film, during hot stamping heating, radiation by electromagnetic waves in the infrared or near-infrared region, which is the main heating factor, becomes the active interionic distance. Therefore, it is speculated that the heating rate during hot stamping can be increased. Note that the crystal structure of Compound B and the type of compound (whether it is an oxide or a fluoride) can be determined by cross-sectional analysis of the surface treatment film using TEM, EDS, and electron beam diffraction. Specifically, the electron beam diffraction pattern during electron beam irradiation is compared with a pre-existing database. If the compound is classified as having a rutile-type structure, it can be determined that the compound has a rutile-type structure. Also, by EDS, the compound can be identified from the ratio of elemental concentrations. Furthermore, when the ratio of oxygen or fluorine is 10 mass% or more, it can be determined that the compound is an oxide or a fluoride.

[0225] Also, in this embodiment, the concentration of the metal element M in Compound B satisfies the following formula (1) and the following formula (2).

[0226] 1 ≦ C bM ≦ 40 ··· Formula (1) 1.5 ≦ C bM / C tM ≦ 10.0 ··· Formula (2) Here, when the average thickness of the surface treatment film is H (μm), C in the above formula (2) tM is the concentration (mass%) of the metal element M at a position 0.05H from the surface of the surface treatment film B2-13, and C in the above formula (1) and the above formula (2) bMis the concentration (mass %) of the metal element M at a position 0.95H from the surface of the surface treatment film B2-13.

[0227] As shown in FIG. 14, when the thickness of the surface treatment film B2-13 is H (μm), the concentration C of the metal element M at 0.95H from the surface of the surface treatment film B2-13 bM is in mass %, and is 1% or more and 40% or less. C bM When it is less than 1%, it becomes difficult to improve the temperature rising characteristics, especially in the high temperature range, during heating by hot stamping. Therefore, C bM is 1% or more. C bM is preferably 5% or more, more preferably 8% or more. By setting the concentration C of the metal element M bM to 8% or more, the temperature rising rate during hot stamping can be further increased. On the other hand, when C bM exceeds 40%, while the temperature rising rate during heating by hot stamping saturates, the adhesion between the surface treatment film B2-13 and the Al plating layer B2-12 decreases. This is because since the compound B is relatively hard, when the concentration C bM increases in the surface treatment film B2-13 near the surface of the Al plating layer B2-12, the followability of the surface treatment film B2-13 to the fine irregularities on the surface of the Al plating layer B2-12 decreases. For this reason, C bM is 40% or less. Thereby, the temperature rising rate during hot stamping can be increased and the film adhesion can also be improved. C bM is preferably 35% or less, more preferably 30% or less, and still more preferably 20% or less. By setting the concentration C of the metal element M bM to 20% or less, the adhesion between the surface treatment film B2-13 and the aluminum plating layer B2-12 can be further enhanced.

[0228] Also, as shown in the above formula (2), C bM / C tM is 1.5 to 10.0. The concentration of the metal element M near the interface between the Al plating layer B2-12 and the surface treatment film B2-13 is high, and C bM / C tMWhen it is 1.5 or more, it is possible to conceal the metallic luster on the surface of the Al plating layer B2-12 and suppress the reflection of radiant heat. C bM / C tM is preferably 2.0 or more, more preferably 3.0 or more. On the other hand, C bM / C tM When it exceeds 10.0, the heat absorption on the surface side of the surface treatment film B2-13 is insufficient, and as a result, the heating rate during hot stamping cannot be increased. Therefore, C bM / C tM is set to 10.0 or less. Thereby, the reflection of radiant heat on the surface of the Al plating layer B2-12 and the heat absorption state on the surface side of the surface treatment film B2-13 can be controlled to an appropriate state, and the heating rate can be increased. C bM / C tM is preferably 8.0 or less, more preferably 6.0 or less.

[0229] The concentration (mass%) of the metal element M at 0.05H from the surface of the surface treatment film B2-13 C tM , and the concentration of the metal element M at 0.95H from the surface of the surface treatment film B2-13 C bM As shown in FIG. 14, when the thickness of the surface treatment film B2-13 is H (μm), it can be measured by fluorescence X-ray analysis and glow discharge optical emission spectrometry (GDS). Hereinafter, C bM and C tM The method of obtaining will be described in detail below.

[0230] First, the average concentration (mass%) of the metal element M is obtained as follows. Using an aluminum-plated steel sheet provided with a surface treatment film containing compound A and compound B (oxide or fluoride of metal element M), the detection intensity (kcps, 10 3 count per second) of the metal element M is obtained by fluorescence X-ray analysis. In addition, according to the fluorescence X-ray conforming to JIS K 0119 (2008), the deposition amount (g / m 2 ) of the metal element M in the surface treatment film and the calibration curve between the detection intensity (kcps) of the metal element M are prepared in advance. Using this calibration curve, the deposition amount P (g / m 2 ) of the metal element M in the surface treatment film is determined from the detection intensity (kcps) of the metal element M obtained by X-ray fluorescence analysis. When determining the detection intensity of the metal element M in the surface treatment film by X-ray fluorescence analysis, the concentration of the metal element M in the base steel material does not affect it, that is, it can be ignored. That is, since the X-ray fluorescence is greatly attenuated by the aluminum plating layer and the metal elements of the surface treatment film, the elements in the base steel material at a position deeper than the aluminum plating layer and the surface treatment film may be regarded as having no influence on the detection intensity of the metal element M in the surface treatment film.

[0231] Next, the metal element M is measured in the depth direction of the surface treatment film B2-13 by GDS, and the position where the intensity of the metal element M becomes less than 1 / 2 on the base steel plate side from the depth (thickness) position showing the maximum value of the intensity is defined as the interface between the surface treatment film and the Al plating layer, and the thickness of the surface treatment film B2-13 is determined. This thickness is measured at 5 locations, and the average value of the obtained thicknesses is taken as the thickness H (μm) of the surface treatment film B2-13. Then, the value "P×100 / H" obtained by multiplying the deposition amount P of the metal element M by 100 and dividing by H is regarded as the average concentration (mass%) of the metal element M in the entire depth direction of the surface treatment film.

[0232] On the other hand, using the fact that the relationship between the average value of the intensity of the metal element M from the surface of the surface treatment film measured by GDS to the interface with the Al plating layer and the above average concentration P×100 / H is a one-to-one proportional relationship, the concentration of the metal element M at an arbitrary position in the depth direction of the surface treatment film can be determined. That is, P×100 / H, which is the average concentration (mass%) of the metal element M over the entire film thickness, and the average value α of the intensity of the metal element M from the surface to the interface with the Al plating layer are respectively determined. On the other hand, when the intensity (kcps) of the metal element M at an arbitrary position X in the depth direction is β, the concentration C XM (mass%) of the metal element M at that position X is obtained by the following formula (3) using the proportional relationship.

[0233] C XM =P / H×100×(β / α) ···(3) Let C be the average concentration (mass %) of the metal element M at 0.05H obtained using this formula (3). tM Let C be the concentration (mass %) of the metal element M at a position 0.95H from the surface. bM Assume so.

[0234] In this embodiment, compound B is preferably rutile-type TiO 2 When compound B is rutile-type TiO 2 , the heating rate during hot stamping can be further increased. The reason for this is not clear, but it is speculated as follows. During the heating process of hot stamping, compared with compounds such as Al 2 O 3 that are usually formed on the surface of the aluminum plating layer, rutile-type TiO 2 can maintain a high emissivity even in the high-temperature range from 300°C to 900°C. Therefore, it is speculated that the heat input by radiation can be increased. Also, when the temperature is further increased to a higher temperature range, there is a possibility that a composite oxide of rutile-type TiO 2 and Al 2 O 3 is formed. The fact that the emissivity of this composite oxide of rutile-type TiO 2 and Al 2 O 3 is also higher than that of other oxides is also speculated to be a factor that can further increase the heating rate during hot stamping.

[0235] Compound B is an oxide or fluoride of the metal element M, but compound B may be composed of two or more compounds. For example, TiO 2 and VO 2 may be included as compound B in the surface treatment film. In addition, when two or more compounds are included as compound B in the surface treatment film, it is sufficient that the compound with the highest content has a desired concentration and distribution that satisfy the above (1) and (2).

[0236] In addition, when a treatment liquid containing compound A and compound B which is an oxide or fluoride of a metal element M and has a rutile-type structure, and a treatment liquid containing organic substances and inorganic substances such as a resin serving as a binder component are separately prepared, and these treatment liquids are separately applied onto an aluminum plating layer to form a laminated film, compound B will not exist with the predetermined concentration distribution as described above. Further, when attempting to form a surface treatment film with a multilayer structure using such a plurality of treatment liquids, since the second-layer film must be formed after the first-layer film is formed, the manufacturing equipment becomes larger in size and the manufacturing cost also increases. Therefore, the surface treatment film B2-13 of the present embodiment needs to have a single-layer structure instead of a multilayer structure.

[0237] The aluminum-plated steel sheet B2-10 for hot stamping according to the present embodiment includes the surface treatment film B2-13 having the above-described characteristics, and thus can improve the temperature rising rate during hot stamping. Therefore, by using the aluminum-plated steel sheet B2-10 for hot stamping according to the present embodiment as a material, the productivity of the hot stamping material can be improved.

[0238] Although the reason why the temperature rising rate of the steel sheet during hot stamping can be improved by providing the surface treatment film B2-13 according to the present embodiment is not clear, it is considered that one of the reasons may be that there are many active bonds with respect to infrared rays having a wavelength of 1 to 10 μm, which is particularly effective for the absorption of radiant heat.

[0239] In addition to the above-described compound A and compound B, the surface treatment film B2-13 according to the present embodiment can contain resins and additives as various binder components. By containing a resin, the adhesion between the surface treatment film B2-13 and the Al plating layer B2-12 can be enhanced. Examples of the additives contained in the surface treatment film B2-13 include a leveling agent, an antifoaming agent, a coloring agent, a viscosity modifier, an ultraviolet absorber, and the like. The coating liquid for forming the surface treatment film B2-13 is preferably obtained by dispersing or dissolving the above-described respective components in water or a solvent.

[0240] In this embodiment, specific methods for applying the surface treatment film B2-13 include methods such as coating and laminating, but are not limited to these methods. The surface treatment film B2-13 may be applied to only one surface of the aluminum-plated steel sheet, or may be applied to both surfaces of the aluminum-plated steel sheet.

[0241] When applying the surface treatment film B2-13 to the entire surface of the aluminum plating layer B2-12 by coating, first, for example, a treatment liquid containing a compound A with a carbon concentration of 80% by weight or more and a compound B that is an oxide or fluoride of a metal element M and has a rutile-type structure is prepared. Then, after applying the treatment liquid to the entire surface of the aluminum plating layer B2-12 with a roll coater, a curtain coater, an inkjet, etc., the volatile components in the treatment liquid are dried, whereby the surface treatment film B2-13 is applied. In particular, coating by inkjet is preferable because the film thickness can be continuously changed.

[0242] Here, conventionally (for example, in JP-A-2011-149084, etc.), when the surface treatment film contains an organic substance such as a carbon pigment, when the plated steel sheet is heated to a high temperature range (for example, 750°C or higher), all of these organic substances disappear, and there has been a problem that the temperature rising characteristics (temperature rising rate) deteriorate. However, the present inventors have found that in the case of the surface treatment film B2-13 according to this embodiment, even if the organic substance disappears, it can be efficiently heated to a high temperature range. Although the mechanism by which it can be heated to a high temperature range even when the organic substance disappears is not clear, it is presumed that the compound B (oxide or fluoride of the metal element M) contained in the film enhances the heat input by radiation at high temperatures.

[0243] [Binder component (resin)] The content of the binder component (resin) that can be contained in the surface treatment film B2-13 according to this embodiment is preferably 40% by volume or more with respect to the total volume of the surface treatment film B2-13. As the binder component, various known resins can be used.

[0244] The resin as the binder component is not particularly limited. For example, polyurethane resin, polyester resin, acrylic resin, epoxy resin, fluororesin, polyamide resin, polyolefin resin, and polymer compounds obtained by hydrolyzing and polycondensing silane coupling agents can be mentioned. As the resin, these resins crosslinked with crosslinking agent components such as butylated melamine resin, methylated melamine resin, butylmethyl mixed melamine resin, urea resin, isocyanate resin, or a mixed system thereof can also be mentioned. Also, electron beam curable resins, ultraviolet curable resins, etc. can be mentioned. Among these, as the resin as the binder component, any one or more of polyester resin, epoxy resin, acrylic resin, and polyurethane resin are preferable. These resins as the binder component may be used alone or in combination of two or more.

[0245] When using, for example, polyurethane resin as the binder component, the polyurethane resin is preferably a polyether-based polyurethane resin. By using a polyether-based polyurethane resin, generation of hydrolysis by acids or alkalis can be prevented as compared with polyester-based polyurethane resins, and formation of a hard and brittle film can be suppressed as compared with polycarbonate-based polyurethane resins, thereby ensuring adhesion during processing and corrosion resistance of the processed part.

[0246] Whether the polyurethane resin is contained or not can be determined based on whether characteristic absorptions at 3330 cm -1 (N-H stretching), 1730 cm -1 (C=O stretching), 1530 cm -1 (C-N), 1250 cm -1 (C-O) are observed in the infrared absorption spectrum obtained by infrared spectroscopy. Also, regarding the content of the polyurethane resin, by preparing a calibration curve showing the relationship between the content and the intensity of the characteristic absorption using a sample with a known content in advance, the content can be specified from the intensity of the obtained characteristic absorption.

[0247] Also, regarding resins other than the above polyurethane resin, by paying attention to the characteristic absorption derived from the functional groups peculiar to each resin, it is possible to determine the presence or absence and the content in the same manner as the above polyurethane resin. As components in the treatment liquid for dispersing or dissolving the resin, water or a solvent can be used.

[0248] [Additive] In the surface treatment film B2-13 according to this embodiment, various additives such as a leveling agent, a water-soluble solvent, a metal stabilizer, and an etching inhibitor can be contained as additives at the time of preparing the treatment liquid before film formation, as long as the effects of this elemental technology are not impaired.

[0249] Examples of the leveling agent include nonionic or cationic surfactants such as polyethylene oxide or polypropylene oxide adducts, and acetylene glycol compounds.

[0250] Examples of the water-soluble solvent include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol, and propylene glycol; cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether; esters such as ethyl acetate and butyl acetate; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0251] Examples of the metal stabilizer include chelate compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid).

[0252] Examples of the etching inhibitor include amine compounds such as ethylenediamine, triethylenetetramine, guanidine, and pyrimidine.

[0253] Note that the content of the above binder component and additive can also be measured in the same manner as in the case of the above compounds A and B.

[0254] [Silica] The surface treatment film B2-13 according to this embodiment may contain silica. When containing silica, the content of silica is preferably 0.01 to 0.3 g / m 2 . By containing 0.01 g / m 2 or more of silica, it is possible to prevent the film from being scratched by contact with other steel plates, equipment, etc. When the silica content exceeds 0.3 g / m 2 , the temperature increase effect cannot be expected while the cost becomes high, so it is not preferable in terms of economy. Further, since silica is a substance with low electrical conductivity, when the silica content exceeds 0.3 g / m 2 , it is not preferable in terms of weldability after hot stamping. In the case of containing silica, the smaller the content of silica in the surface treatment film B2-13, the better. The silica content of the surface treatment film is more preferably 0.10 g / m 2 or less, and even more preferably 0.05 g / m 2 or less.

[0255] [Film thickness of the surface treatment film] The average film thickness H of the surface treatment film B2-13 containing the above components is preferably, for example, 0.5 to 15.0 μm. When the average film thickness of the surface treatment film B2-13 is less than 0.5 μm, the absorption of radiant heat is insufficient, so the temperature increase rate during hot stamping cannot be increased sufficiently. On the other hand, when the average film thickness of the surface treatment film B2-13 exceeds 15.0 μm, the heat capacity of the surface treatment film B2-13 itself becomes large, which becomes a barrier when heat is transferred to the aluminum plating layer B2-12. As a result, the temperature increase rate cannot be improved sufficiently, and the cost increases, so it is not preferable in terms of economy. By setting the average film thickness of the surface treatment film B2-13 in the range of 0.5 to 15.0 μm, the temperature increase rate can be improved. The average film thickness of the surface treatment film B2-13 is more preferably 1.0 to 7.0 μm.

[0256] [Undercoat treatment film] Between the surface treatment film B2-13 and the aluminum plating layer B2-12, as shown in Fig. 15, a substrate treatment film (chemical conversion treatment layer) B2-14 may be provided to improve the adhesion of the surface treatment film B2-13. Note that Fig. 15 is a schematic diagram for explanation, and the dimensions of the surface treatment film 13, the aluminum plating layer B2-12, the substrate treatment film 14, etc. do not necessarily show a preferred embodiment, nor are they limited to the dimensions in Fig. 15.

[0257] The substrate treatment film B2-14 may contain any one or more selected from resins, silane coupling agents, zirconium compounds, silica, phosphoric acid and its salts, fluorides, and vanadium compounds. When these substances are included, further, the film-forming property after application of the chemical conversion treatment agent, the barrier property (compactness) of the film against corrosion factors such as moisture and corrosive ions, and the film adhesion to the plating surface are improved, contributing to enhancing the corrosion resistance of the film. In particular, when the chemical conversion treatment layer contains any one or more of a silane coupling agent and a zirconium compound, a crosslinked structure is formed in the film, and further the bond with the plating surface is strengthened, so that the adhesion and barrier property of the film can be enhanced. Also, when the substrate treatment film B2-14 contains any one or more of silica, phosphoric acid and its salts, fluorides, and vanadium compounds, as an inhibitor, a precipitation film or a passive film is formed on the plating surface or the base steel plate surface, thereby improving the corrosion resistance.

[0258] [Adhesion amount of the substrate treatment film B2-14] The adhesion amount of the substrate treatment film B2-14 per one side of the plating layer is preferably 10 - 1000 mg / m 2 in terms of solid content conversion. If the adhesion amount of the substrate treatment film B2-14 is less than 10 mg / m 2 , sufficient processing adhesion and corrosion resistance cannot be ensured. If the adhesion amount of the substrate treatment film B2-14 exceeds 1000 mg / m 2 , the processing adhesion may decrease. The adhesion amount of the substrate treatment film B2-14 per one side of the plating layer is more preferably 20 - 800 mg / m 2 , and even more preferably 50 - 600 mg / m2 is.

[0259] <aluminum plating layer> The aluminum-plated steel sheet B2-10 for hot stamping according to this embodiment preferably has an aluminum plating layer B2-12 on at least one surface of the base steel sheet B2-11 and on the base steel sheet B2-11. By having the aluminum plating layer B2-12, the corrosion resistance after painting after hot stamping can be further improved. Further, the presence of the aluminum plating layer B2-12 between the base steel sheet B2-11 and the surface treatment film B2-13 can prevent the generation of iron scale due to heating during hot stamping. Iron scale is a manufacturing burden because it contaminates the heating furnace or adheres to the rolls used for conveyance. Therefore, when iron scale is generated, a process such as shot blasting is required to remove the iron scale, which is not economically preferable.

[0260] The type of the aluminum plating layer is not particularly limited. Examples of the composition constituting such an aluminum plating layer include aluminum plating, Al-Si plating, Al-Si-Mg, Al-Si-Ca plating, and the like. For example, the chemical composition (average chemical composition) of the aluminum plating layer may be a plating layer containing, by mass%, Al: 80.0 to 95.0%, Si: 2.0 to 15.0%, Fe: 1 to 15.0%, Cr: 0% or more and less than 1.0%, Mo: 0% or more and less than 1.0%, Zn: 0% or more and less than 1.0%, V: 0% or more and less than 1.0%, Ti: 0% or more and less than 1.0%, Sn: 0% or more and less than 1.0%, Ni: 0% or more and less than 1.0%, Cu: 0% or more and less than 1.0%, W: 0% or more and less than 1.0%, Bi: 0% or more and less than 1.0%, Mg: 0% or more and less than 1.0%, Ca: 0% or more and less than 1.0%, and the balance being impurities.

[0261] If the Al content in the aluminum plating layer is less than 80.0%, the corrosion resistance after hot stamping (corrosion resistance in the hot-stamped molded body) deteriorates. Therefore, the Al content is preferably 85.0% or more. More preferably, the Al content is 88.0% or more. On the other hand, if the Al content in the aluminum plating layer exceeds 95.0%, the plating adhesion may deteriorate. Therefore, the Al content is preferably 95.0% or less. More preferably, the Al content is 92.0% or less.

[0262] If the Si content in the aluminum plating layer is less than 2.0%, the plating adhesion may deteriorate. Therefore, the Si content is preferably 2.0% or more. More preferably, the Si content is 3.0% or more, and even more preferably 4.0% or more. On the other hand, if the Si content in the aluminum plating layer exceeds 15.0%, the plating adhesion may deteriorate. Therefore, the Si content is preferably 15.0% or less. More preferably, the Si content is 13.0% or less.

[0263] The Fe content is preferably 1.0% or more and 15.0% or less.

[0264] The chemical composition of the aluminum plating layer can be measured by the fluorescent X-ray method conforming to JIS G K 0119:2008. That is, using a sample with a known content of the target element, the relationship between the X-ray intensity and the content is determined in advance. Based on the calibration curve created from this, the content of each element, that is, the chemical composition, of the unknown sample can be determined.

[0265] [Adhesion amount of aluminum plating layer] The aluminum plating layer B2-12 is applied to one or both sides of the base steel plate B2-11. The adhesion amount is preferably 5 g / m 2 ~140 g / m 2 per side. When the adhesion amount per side is 5 g / m 2If it is less, in the heating process of hot stamping, iron scale is generated on the surface of the base material steel sheet, and a process of removing the scale is required. On the other hand, when the adhesion amount per side is more than 140 g / m 2 2 exceeds, since it takes time to advance the alloying reaction of Al and Fe in the hot stamping heating process necessary to enhance the corrosion resistance after painting, it is not preferable from the viewpoint of productivity. Therefore, the adhesion amount of the aluminum plating layer B2-12 is preferably 5 g / m~140 g / m 2 per side.

[0266] <Base material steel sheet> Next, the base material steel sheet B2-11 of the aluminum-plated steel sheet B2-10 for hot stamping according to the present embodiment will be described. The base material steel sheet B2-11 is not particularly limited as long as it is a steel sheet that can be suitably used in the hot stamping method. The chemical composition of the base material steel sheet B2-11 applicable to the aluminum-plated steel sheet B2-10 for hot stamping according to the present embodiment is, for example, in mass%, C: 0.03 to 0.60%, Si: 0.01 to 0.60%, Mn: 0.50 to 3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.100% or less, Ti: 0.01 to 0.10%, B: 0.0001 to 0.0100%, N: 0.010% or less, Cr: 0 to 1.00%, Ni: 0 to 2.00%, Cu: 0 to 1.000%, Mo: 0 to 1.00%, V: 0 to 1.00%, Nb: 0 to 1.00%, Sn: 0 to 1.00%, W: 0 to 1.00%, Ca: 0 to 0.010%, REM: 0 to 0.30%, and the balance may be Fe and impurities. In addition, examples of the form of the base steel plate B2-11 include steel plates such as hot-rolled steel plates and cold-rolled steel plates. Hereinafter, the preferable ranges of the respective elements of the base steel plate B2-11 of the aluminum-plated steel plate B2-10 for hot stamping and the reasons therefor will be described in detail. In the following description of the chemical composition of the base steel plate B2-11, the notation of “%” means “mass %” unless otherwise specified.

[0267] [C: 0.03 to 0.60%] C is contained to ensure the desired mechanical strength. When the C content is 0.03% or more, sufficient improvement in mechanical strength can be obtained, and the effect of containing C can be sufficiently obtained. Therefore, the C content is preferably 0.03% or more. More preferably, the C content is 0.20% or more. On the other hand, when the C content is 0.60% or less, while improving the strength of the steel plate, a decrease in elongation and drawing can be suppressed. Therefore, the C content is preferably 0.60% or less. More preferably, the C content is 0.40% or less.

[0268] [Si: 0.01 to 0.60%] Si is one of the strength-improving elements that improve mechanical strength and is contained to ensure the desired mechanical strength, like C. When the Si content is 0.01% or more, the strength-improving effect is sufficiently exhibited, and sufficient improvement in mechanical strength can be obtained. Therefore, the Si content is preferably 0.01% or more. More preferably, the Si content is 0.10% or more. On the other hand, since Si is also an easily oxidizable element, when the Si content is 0.60% or less, a decrease in wettability during molten Al plating due to the influence of Si oxide formed on the surface layer of the steel plate can be suppressed, and the occurrence of non-plating can be suppressed. Therefore, the Si content is preferably 0.60% or less. More preferably, the Si content is 0.40% or less.

[0269] [Mn: 0.50 to 3.00%] Mn is one of the strengthening elements that strengthen steel and is also one of the elements that increase hardenability. Furthermore, Mn is an element effective in preventing hot shortness caused by S, which is one of the impurities. When the Mn content is 0.50% or more, these effects can be sufficiently obtained. Therefore, in order to surely exhibit the above effects, the Mn content is preferably 0.50% or more. The Mn content is more preferably 0.80% or more. On the other hand, since Mn is an austenite-forming element, when the Mn content is 3.00% or less, the amount of retained austenite phase does not become too large, and a decrease in strength is suppressed. Therefore, the Mn content is preferably 3.00% or less. The Mn content is more preferably 1.50% or less.

[0270] [P: 0.050% or less] P is an impurity contained in steel. When the P content is 0.050% or less, it is possible to suppress P contained in the steel sheet from segregating at the grain boundaries of the steel sheet and reducing the toughness of the base material of the hot-stamped formed body, and it is possible to suppress a decrease in the stress corrosion cracking resistance of the steel sheet. Therefore, the P content is preferably 0.050% or less, and it is preferable to make the P content as small as possible. If necessary, the P content may be 0.045% or less or 0.040% or less. The lower limit of the P content is 0%, but the lower limit may be 0.001% or 0.005%.

[0271] [S: 0.020% or less] S is an impurity contained in steel. When the S content is 0.020% or less, it is possible to suppress S contained in the steel sheet from forming sulfides and reducing the toughness of the steel sheet, and it is possible to suppress a decrease in the stress corrosion cracking resistance of the steel sheet. Therefore, the S content is preferably 0.020% or less, and it is preferable to make the S content as small as possible. If necessary, the S content may be 0.015% or less or 0.010% or less. The lower limit of the S content is 0%, but the lower limit may be 0.001% or 0.002%.

[0272] [Al: 0.100% or less] Al is generally used for the purpose of deoxidizing steel. On the other hand, when the Al content is 0.100% or less, the increase in the Ac3 point of the steel sheet is suppressed, so that the heating temperature required to ensure the hardenability of the steel during hot stamping can be reduced, which is desirable for hot stamping production. Therefore, the Al content of the steel sheet is preferably 0.100% or less, more preferably 0.050% or less, and still more preferably 0.030% or less. The lower limit of the Al content is 0%, but the lower limit may be 0.001%, 0.003% or 0.007%.

[0273] [Ti: 0.01~0.10%] Ti is one of the strength strengthening elements. When the Ti content is 0.01% or more, the strength improvement effect and the oxidation resistance improvement effect can be sufficiently obtained. Therefore, in order to surely exhibit the above effects, the Ti content is preferably 0.01% or more. The Ti content is more preferably 0.03% or more. On the other hand, when the Ti content is 0.10% or less, for example, the formation of carbides and nitrides is suppressed, the softening of the steel can be suppressed, and the target mechanical strength can be sufficiently obtained. Therefore, the Ti content is preferably 0.10% or less. The Ti content is more preferably 0.08% or less.

[0274] [B: 0.0001~0.0100%] B has the effect of acting during quenching to improve the strength. When the B content is 0.0001% or less, such a strength improvement effect can be sufficiently obtained. Therefore, the B content is preferably 0.0001% or more. The B content is more preferably 0.0010% or more. On the other hand, when the B content is 0.0100% or less, the formation of inclusions is reduced, the embrittlement of the steel sheet is suppressed, and the decrease in fatigue strength can be suppressed. Therefore, the B content is preferably 0.0100% or less. The B content is more preferably 0.0040% or less.

[0275] [N: 0.010% or less] N is an impurity contained in steel. When the N content is 0.010% or less, the formation of nitrides due to N contained in the steel sheet is suppressed, and a decrease in the toughness of the steel sheet can be suppressed. Furthermore, when B is contained in the steel sheet, the combination of N contained in the steel sheet with B and the resulting decrease in the amount of dissolved B are suppressed, and a decrease in the hardenability improvement effect of B can be suppressed. Therefore, the N content is preferably 0.010% or less, and more preferably as low as possible.

[0276] Moreover, the base steel sheet of the hot stamping steel sheet according to the present embodiment may further contain, as optional elements, one or more elements selected from the group consisting of Cr, Mo, Ni, Cu, V, Nb, Sn, W, Ca, and REM. The lower limit of the content of these elements is 0%.

[0277] [Cr: 0 to 1.00%] Cr is an element that improves the hardenability of the steel sheet. In order to sufficiently obtain such an effect, the Cr content is preferably 0.01% or more. On the other hand, by setting the Cr content to 1.00% or less, while sufficiently obtaining the effect, an increase in cost can be suppressed. Therefore, when contained, the Cr content is preferably 1.00% or less. If necessary, the Cr content may be 0.70% or less or 0.50% or less.

[0278] [Ni: 0 to 2.00%] Ni is an element that enhances the hardenability of steel and enables the strength of the steel sheet member after quenching to be stably ensured. In order to sufficiently exhibit such an effect, the Ni content is preferably 0.10% or more. On the other hand, when the Ni content is 2.00% or less, while sufficiently obtaining the above effects, the economic efficiency is enhanced. Therefore, when contained, the Ni content is preferably 2.00% or less. If necessary, the Ni content may be 1.20% or less, 0.80% or less, or 0.50% or less.

[0279] [Cu: 0 to 1.000%] Cu is an element that enhances the hardenability of steel and enables the stable securing of the strength of the steel plate member after quenching. Also, Cu improves pitting corrosion resistance in a corrosive environment. To fully exhibit such effects, it is preferable that the Cu content be 0.100% or more. On the other hand, when the Cu content is 1.000% or less, economic efficiency is enhanced while obtaining the above effects sufficiently. Therefore, it is preferable that the Cu content when incorporating be 1.000% or less. If necessary, the Cu content may be 0.600% or less, 0.400% or less, or 0.200% or less.

[0280] [Mo: 0 to 1.00%] Mo is an element that enhances the hardenability of steel and enables the stable securing of the strength of the steel plate member after quenching. To fully exhibit such effects, it is preferable that the Mo content be 0.10% or more. On the other hand, when the Mo content is 1.00% or less, economic efficiency is enhanced while obtaining the above effects sufficiently. Therefore, it is preferable that the Mo content when incorporating be 1.00% or less. If necessary, the Mo content may be 0.60% or less, 0.40% or less, or 0.20% or less.

[0281] [V: 0 to 1.00%] V is an element that enhances the hardenability of steel and enables the stable securing of the strength of the steel plate member after quenching. To fully exhibit such effects, it is preferable that the V content be 0.10% or more. On the other hand, when the V content is 1.00% or less, economic efficiency is enhanced while obtaining the above effects sufficiently. Therefore, it is preferable that the V content when incorporating be 1.00% or less. If necessary, the V content may be 0.60% or less, 0.40% or less, or 0.20% or less.

[0282] [Nb: 0 to 1.00%] Nb is an element that enhances the hardenability of steel and enables the stable assurance of the strength of the steel plate member after quenching. In order to fully exhibit such an effect, it is preferable that the Nb content is 0.01% or more. On the other hand, when the Nb content is 1.00% or less, the economy is enhanced while sufficiently obtaining the above effects. Therefore, it is preferable that the Nb content when contained is 1.00% or less. If necessary, the Nb content may be 0.50% or less, 0.20% or less, or 0.10% or less.

[0283] [Sn: 0 to 1.00%] Sn is an element that improves pitting corrosion resistance in a corrosive environment. In order to fully exhibit such an effect, it is preferable that the Sn content is 0.01% or more. On the other hand, when the Sn content is 1.00% or less, the decrease in grain boundary strength is suppressed, and the decrease in toughness can be suppressed. Therefore, it is preferable that the Sn content when contained is 1.00% or less. If necessary, the Sn content may be 0.40% or less, 0.10% or less, or 0.05% or less.

[0284] [W: 0 to 1.00%] W is an element that enhances the hardenability of steel and enables the stable assurance of the strength of the steel plate member after quenching. Also, W improves pitting corrosion resistance in a corrosive environment. In order to fully exhibit such an effect, it is preferable that the W content is 0.01% or more. On the other hand, when the W content is 1.00% or less, the economy is enhanced while sufficiently obtaining the above effects. Therefore, it is preferable that the W content when contained is 1.00% or less. If necessary, the W content may be 0.60% or less, 0.40% or less, or 0.20% or less.

[0285] [Ca: 0 to 0.010%] Ca is an element that has the effect of refining inclusions in steel and improving toughness and ductility after quenching. In order to fully exhibit such an effect, the Ca content is preferably 0.001% or more, and more preferably 0.002% or more. On the other hand, when the Ca content is 0.010% or less, the cost can be suppressed while sufficiently obtaining the effect. Therefore, the Ca content when adding is preferably 0.010% or less, and more preferably 0.004% or less. If necessary, the Ca content may be 0.008% or less, 0.006% or less, or 0.0004% or less.

[0286] [REM:0~0.30%] REM is an element that has the effect of refining inclusions in steel and improving toughness and ductility after quenching, similar to Ca. In order to fully exhibit such an effect, the REM content is preferably 0.001% or more, and more preferably 0.002% or more. On the other hand, when the REM content is 0.30% or less, the cost can be suppressed while sufficiently obtaining the effect. Therefore, the REM content when adding is preferably 0.30% or less, and more preferably 0.20% or less. If necessary, the REM content may be 0.10% or less, 0.05% or less, or 0.02% or less.

[0287] Here, REM refers to a total of 17 elements including Sc, Y, and lanthanoids, and the content of the above REM means the total content of these elements. REM is added to the molten steel using, for example, an Fe-Si-REM alloy, and this alloy contains, for example, Ce, La, Nd, Pr.

[0288] The remainder other than the above components is Fe and impurities. The base steel plate B2-11 may contain impurities that are mixed in during the manufacturing process, etc., as long as they do not inhibit the effects of this element technology, in addition to the above components. Examples of such impurities include Zn (zinc) and Co (cobalt).

[0289] The chemical composition of the base steel plate B2-11 of the above-mentioned aluminum-plated steel plate B2-10 for hot stamping may be measured by a general analysis method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). C and S may be measured using the combustion-infrared absorption method, N may be measured using the inert gas fusion-thermal conductivity method, and O may be measured using the inert gas fusion-non-dispersive infrared absorption method. When the steel plate for hot stamping has a plating layer on its surface, the plating layer on the surface may be removed by mechanical grinding and then the chemical composition may be analyzed.

[0290] Among the surfaces of the plated steel plate composed of the base steel plate B2-11 and the aluminum plating layer B2-12 having the above chemical components, the portion where the surface treatment film B2-13 is applied can be made into a hot stamping member having a high-strength tensile strength by heating and quenching by the hot stamping method. Also, in the hot stamping method, since press working can be performed in a softened state at a high temperature, it can be easily formed.

[0291] (Manufacturing Method of Aluminum-Plated Steel Plate for Hot Stamping) Hereinafter, an example of the manufacturing method of the aluminum-plated steel plate for hot stamping according to the present embodiment will be described. Note that the manufacturing method of the aluminum-plated steel plate for hot stamping according to the present embodiment is not particularly limited as long as it has the above-described configuration. The following manufacturing method is an example for manufacturing the aluminum-plated steel plate for hot stamping according to the present embodiment, and is a preferred example of the manufacturing method of the aluminum-plated steel plate for hot stamping according to the present embodiment.

[0292] <Base Steel Plate> The base steel plate to be subjected to aluminum plating is not particularly limited as long as it is a steel plate that can be suitably used for the hot stamping method. Examples of the form of the base steel plate include steel plates such as hot-rolled steel plates and cold-rolled steel plates.

[0293] <Formation of Aluminum Plating Layer> Methods for forming an aluminum plating layer include, but are not particularly limited to, molten plating, electroplating, physical vapor deposition, chemical vapor deposition, etc. An aluminum plating layer is formed on the surface of the base steel plate by a known method.

[0294] <Method for manufacturing a surface treatment film> The method for manufacturing the surface treatment film is not particularly limited. For example, a method may be mentioned in which each film-forming component is mixed, stirred with a disperser, and the mixed treatment liquid thus dissolved or dispersed is applied onto the plating layer and then dried. The mixed treatment liquid is prepared, for example, by preparing a treatment liquid of compound A and a treatment liquid of compound B respectively, adjusting the pH, and then mixing each treatment liquid with other optional components such as resin. This will be specifically described below.

[0295] Examples of compound A to be contained in the surface treatment film include carbon black, graphite, soot, etc. In the method for manufacturing the surface treatment film, it is preferable to use a treatment liquid in which these powders are dispersed in water or the like.

[0296] Compound A is pulverized by a machine or the like so that the powder diameter (particle size) is between 30 and 300 nm, and then compound A is introduced into a treatment liquid adjusted to pH 9.0 to 13.0 containing sodium hydroxide. Thereafter, by performing a pretreatment of stirring the treatment liquid into which compound A has been introduced at 50°C to 80°C for 1 to 4 days, compound A having a particle size of 30 to 300 nm can be more stably dispersed in the treatment liquid. In addition, when the surface treatment film is formed, compound A can be uniformly present in the film layer, so that the temperature rise characteristics can be enhanced.

[0297] Furthermore, by heating the treatment liquid with a pH of 9.0 to 13.0 into which Compound A has been introduced at a temperature of 50°C to 80°C for 1 to 4 days (i.e., satisfying the aforementioned pretreatment conditions), the carbon concentration of Compound A in the film can also be increased. When the treatment liquid is subjected to this pretreatment, an area with a low carbon concentration outside the particles of Compound A (for example, a portion with a high ratio of oxygen (O), nitrogen (N), sulfur (S), etc.) is dissolved by the treatment liquid containing sodium hydroxide, and an area with a high carbon concentration inside the particles remains. Thereby, the carbon concentration of Compound A in the film can also be increased. On the other hand, when the aforementioned pretreatment conditions are not satisfied (for example, when the stirring time is less than 1 day), the dissolution amount of the area with a low carbon concentration outside the particles of Compound A decreases, and relatively, the carbon concentration of Compound A in the film decreases. Therefore, in order to sufficiently increase the carbon concentration of Compound A in the film, it is necessary to control the conditions of the pretreatment before applying the treatment liquid.

[0298] For Compound B, which is an oxide or fluoride of metal element M and has a rutile-type structure, it is also advisable to use a treatment liquid dispersed in powder, water, or a solvent.

[0299] Compound B is pulverized by a machine or the like so that the powder diameter (particle size) is between 10 and 300 nm, and then introduced into a treatment liquid adjusted to a pH of 3 to 7 containing sodium fluoride, and subjected to a pretreatment of stirring at a temperature of 50°C to 80°C for 4 to 24 hours. Thereby, Compound B with a particle size of 10 to 300 nm can be stably dispersed in the treatment liquid. As a result, since the existence form of Compound B as described later can be realized in the film when the surface treatment film is formed, the temperature increase characteristics can be enhanced.

[0300] By using a mixed treatment liquid obtained by appropriately adding a binder component (resin) to the raw materials and treatment liquid thus screened, the surface treatment film of the present embodiment can be obtained.

[0301] The method for producing the mixed treatment liquid by combining the treatment liquid of compound A and the treatment liquid of compound B is not particularly limited. For example, a method of mixing the treatment liquid containing compound A obtained by the above method and the treatment liquid containing compound B, stirring with a disperser, dissolving or dispersing, and then adding a binder (resin) or silica as necessary can be mentioned. In order to improve the solubility or dispersibility of each film-forming component, a known hydrophilic solvent or the like may be added as necessary. In the treatment liquid, an acid, an alkali, or the like may be added for pH adjustment within a range where its performance is not impaired. Hereinafter, the method for producing the mixed treatment liquid will be specifically described.

[0302] In order to realize the surface treatment film that satisfies the above formulas (1) and (2), first, each of compound A and compound B is dispersed in water or a mixed liquid of water and a solvent such as ethanol, and each treatment liquid is prepared by the above adjustment method. Then, the treatment liquid of the binder component (such as resin) and compound A is mixed, and subsequently, the treatment liquid of compound B is mixed to prepare a mixed treatment liquid. Incidentally, after stirring the treatment liquid of compound B with a pH of 3 to 7 at 30 to 50 ° C for 4 to 25 hours, immediately before mixing with the treatment liquid of compound A, the treatment liquid of compound B is adjusted to a pH of 8 or more using aqueous ammonia or the like. When silica is to be included in the surface treatment film, it is preferable to add silica after mixing the treatment liquid of compound B into the mixed liquid. In order to make the content rate of compound A at the interface side position P of the surface treatment film 30% or more, the concentration (content) of compound A in the mixed treatment liquid is 15% by mass or more in terms of dry weight (mass) ratio. In order to make the content rate of compound A at the interface side position P of the surface treatment film 80% or less, the concentration (content) of compound A in the mixed treatment liquid is 50% by mass or less in terms of dry weight (mass) ratio. In order to satisfy formulas (1) and (2) regarding the concentration of metal element M, the concentration (content) of compound B in the mixed treatment liquid is 3 to 50% by mass in terms of dry weight (mass) ratio. The total of the concentration (content) of compound A and the concentration (content) of compound B in the mixed treatment liquid is 18 to 90% in terms of dry weight (mass) ratio. Next, it is preferable to stir the obtained mixed treatment liquid at 150 rpm or more and 300 rpm immediately before coating, and apply the mixed treatment liquid after stirring within 5 seconds.

[0303] Also, in order to realize a surface treatment film that satisfies the above formulas (1) and (2), the dynamic viscosity of the mixed treatment liquid at a shear rate of 10 -3 / s is set to 3 to 16 mPa·s, and the surface tension is set to 20 to 60 mN / m. When the dynamic viscosity is less than 3 mPa·s, C in formula (2) bM / C tM exceeds 10.0, and there is a possibility that the desired temperature increase rate cannot be obtained. Therefore, the dynamic viscosity of the mixed treatment liquid is 3 mPa·s or more, preferably 6 mPa·s or more. On the other hand, when the dynamic viscosity exceeds 16 mPa·s, C in formula (2) bM / C tM is less than 1.5, and there is a possibility that the desired temperature increase rate cannot be obtained. Therefore, the dynamic viscosity of the mixed treatment liquid is 16 mPa·s or less, preferably 12 mPa·s or less.

[0304] Also, when the surface tension of the mixed treatment liquid is less than 20 mN / m, C bM is less than 1 mass%, and the desired temperature increase rate cannot be obtained. Therefore, the surface tension of the mixed treatment liquid is 20 mN / m or more, preferably 30 mN / m or more. On the other hand, when the surface tension exceeds 60 mN / m, the desired temperature increase rate cannot be obtained in the same way. Therefore, the surface tension of the mixed treatment liquid is 60 mN / m or less, preferably 40 mN / m or less.

[0305] To form the surface treatment film layer, the treatment liquid is applied onto the aluminum plating layer (or chemical conversion treatment layer), and the applied film is heated and dried. The application method of the treatment liquid is not particularly limited, and generally known application methods, such as roll coating, dipping, etc., can be used.

[0306] In order to control Compound B to have a predetermined concentration distribution as shown in Formula (1) and Formula (2), regarding the heating and drying temperature after coating, the reaching temperature shall be 55°C to 120°C. Here, the "reaching temperature" means the temperature of the surface of the base steel plate. When the reaching temperature is less than 55°C, the evaporation rate of moisture is slow and sufficient film-forming properties cannot be obtained, so the film adhesion may be insufficient. Furthermore, when the reaching temperature is too low, since the evaporation rate of the treatment liquid is slow, the metal element M in Compound B is concentrated on the side of the Al plating layer, and C bM / C tM becomes excessively high. As a result, the heat absorption on the surface side of the surface treatment film B2-13 is insufficient, and there is a risk that the temperature rising characteristics during hot stamping deteriorate. On the other hand, when the reaching temperature exceeds 120°C, the binder component may be denatured due to thermal decomposition or the like, and the adhesion and corrosion resistance may decrease. The reaching temperature is more preferably 65 to 100°C.

[0307] Also, when the time for the temperature of the surface of the base steel plate to reach from 25°C to 65°C is t1 (if it does not reach 65°C, the final reaching temperature of the base material), and the time for cooling to decrease from 65°C (or the final reaching temperature of the base material) to 40°C is t2, t1 shall be 1.5 seconds to 14.0 seconds, t2 shall be 0.5 seconds to 8.6 seconds, and t1 / t2 shall be in the range of 0.35 to 10.0. Thereby, it becomes easy to control the concentration distribution C bM / C tM in the surface treatment film of Compound B, and the temperature rising rate is further improved.

[0308] Furthermore, when the time for the temperature of the surface of the base steel plate to reach from 25°C to 55°C is t3, t3 shall be 5.0 seconds to 12.0 seconds. Thereby, the content rate of Compound A at the interface side position P can be made 30 to 80%.

[0309] The method for heating and drying the treatment liquid after coating is not particularly limited, and examples include methods using hot air, induction heating, near-infrared rays, direct fire, etc. alone or in combination. As components in the treatment liquid for dispersing or dissolving the resin, it is possible to use water or a solvent.

[0310] (Method for manufacturing hot stamping member) Various hot stamping members exemplified by skeletal parts for automobiles can be manufactured using a hot stamping aluminum-plated steel sheet having a surface treatment film applied to the entire surface of at least one surface as described above.

[0311] First, for example, by subjecting an aluminum-plated steel sheet with a surface treatment film to various processes such as cutting or punching with a press, a hot stamping aluminum-plated steel sheet according to the present embodiment is obtained. Also, a hot stamping aluminum-plated steel sheet according to the present embodiment can be obtained by applying a surface treatment film to an aluminum-plated steel sheet that has been cut or punched with a press. Further, by partially thinning the film thickness of the surface treatment film, for example, in applications where a plurality of steel sheets are welded before hot stamping, it becomes easier to conduct electricity and the spot weldability can be improved.

[0312] The hot stamping aluminum-plated steel sheet with the surface treatment film applied as described above is hot stamped. As the heating device, for example, there are an electric heating furnace, a gas heating furnace, a normal heating device equipped with a far-infrared furnace or an infrared heater, etc. The surface on which the surface treatment film is applied and the emissivity is increased has a high heat transfer effect due to radiation and thus a fast heating rate. Therefore, it is rapidly heated to a temperature equal to or higher than the Ac3 point at which the metal structure transforms into the austenite phase. Thereby, in the method for manufacturing a hot stamping member according to the present embodiment, by shortening the heating time, the productivity of the hot stamping member can be further improved. In the present embodiment, specific heating conditions are not particularly limited, and the heating device used etc. may be appropriately controlled.

[0313] Next, the heated steel sheet is formed and cooled. The portion heated to a temperature equal to or higher than the Ac3 point at which the metal structure of the steel material transforms into the austenite phase is quenched simultaneously with forming and the strength is increased. Thereby, a hot stamping member with improved strength can be obtained. (Examples)

[0314] Hereinafter, embodiments of the present elemental technology will be described. However, the conditions in the embodiments are merely one example of the conditions adopted to confirm the feasibility and effects of the present elemental technology, and the present invention is not limited to this one example of conditions. The present elemental technology can adopt various conditions as long as it does not deviate from the gist of the present elemental technology and can achieve the purpose of the present elemental technology.

[0315] As the base steel plate, it is preferable to use a steel plate having high mechanical strength (meaning various properties related to mechanical deformation and fracture such as tensile strength, yield point, elongation, drawing, hardness, impact value, fatigue strength, etc.). The chemical components of the base steel plate before plating used for the hot stamping steel plate shown in the following examples are shown in Table 11 below.

[0316]

Table 11

[0317] For the base steel plates (Steel Nos. S1 to S10) having the chemical compositions shown in Table 11, steel plates (base steel plates) with a width of 100 mm × a length of 200 mm and a plate thickness of 2.3 mm were prepared, and an aluminum plating layer and a surface treatment film were applied over the entire surfaces of both sides of the base steel plates by the method described below. Here, the notation "-" in Table 11 means that the corresponding element content is 0% in the significant figures (numerical values up to the least significant digit) defined in this embodiment.

[0318] First, as Compound A, an aqueous treatment solution (solvent: water) containing at least one of carbon black (CB), graphite, and soot pulverized so that the powder diameter (particle size) is between 30 and 300 nm, and as Compound B, an aqueous treatment solution (solvent: water) containing a metal oxide or a metal fluoride pulverized so that the powder diameter (particle size) is between 30 and 300 nm were prepared separately. Then, the respective treatment solutions were mixed, and a treatment solution to which a polyurethane resin was further added was applied onto the aluminum plating layer and dried to form a surface treatment film. The film thickness of the surface treatment film was in the range of 1.0 to 2.5 μm, and the same type of film was applied to both sides.

[0319] Table 12A and Table 12B describe the manufacturing method of the surface treatment film, such as the compound species and additives used. The polyurethane resin was added so that the solid content ratio in the treatment liquid was 10 to 92% by mass in all the manufacturing methods of Table 12A and Table 12B. Also, in all the manufacturing methods of Table 12A and Table 12B, sodium fluoride was used as an additive when adjusting Compound B. Further, when mixing the treatment liquids of Compound A and Compound B, it was adjusted to have the dry weight ratio as shown in Table 12A and Table 12B. Note that the underlines in Table 12A and Table 12B indicate that the conditions deviate from the preferred conditions of the manufacturing method of this elemental technology. Also, the dynamic viscosity (mPa·s) shown in Table 12A and Table 12B is the dynamic viscosity at a shear rate of 10 -3 / s. The "time t1", "time t2", and "time t3" shown in Table 12A and Table 12B indicate the "time for the temperature on the surface of the base steel plate to reach from 25°C to 65°C", the "time until the temperature on the surface of the base steel plate drops from 65°C to 40°C", and the "time for the temperature on the surface of the base steel plate to reach from 25°C to 55°C", respectively.

[0320]

Table 12A

[0321]

Table 12B

[0322] Thereafter, a thermocouple was connected to the surface of the aluminum-plated steel sheet (aluminum-plated steel sheet for HS) with the surface treatment film so that the temperature at each position could be measured. Then, the aluminum-plated steel sheet for HS was heated in an electric heating furnace at a set temperature of 940°C, and when the surface temperature reached 930°C, the aluminum-plated steel sheet for HS was taken out from the heating furnace. Thereafter, the aluminum-plated steel sheet for HS was rapidly cooled with a flat die to obtain a hot stamping member.

[0323] In this example, the base steel plate was subjected to Al-10 mass% Si plating by the molten plating method, and then the above surface treatment film was applied. In the case of the molten plating method, after immersing the base steel plate in the plating bath, the adhesion amount was adjusted to 100 g / m per side by the gas wiping method. 2 Adjusted to.

[0324] The film composition, heating rate (heating characteristics), and film adhesion of the surface treatment film were investigated. Note that the hot stamping member is not necessarily used as a member that receives sliding or the like. Therefore, in this example, the film adhesion is not an essential characteristic that the hot stamping member should have, but a preferable characteristic if it has.

[0325] The evaluation methods for each evaluation item were as follows.

[0326] (1) Heating rate (heating characteristics) (Score) From the temperature change obtained from the thermocouple provided on each aluminum-plated steel plate for HS and the heating time in the electric heating furnace, the heating rate of each aluminum-plated steel plate for HS was calculated and evaluated. Specifically, the heating rate from room temperature to 910 °C was calculated and evaluated based on the following evaluation criteria. A score of "2" or more was considered a pass.

[0327] (Score) 4: Heating rate 5.7 °C / s or more 3: Heating rate 4.3 °C / s or more and less than 5.7 °C / s 2: Heating rate 3.5 °C / s or more and less than 4.3 °C / s 1: Heating rate less than 2.5 °C / s

[0328] (2) Film adhesion After installing the obtained hot stamping molded body on a rubbing tester (manufactured by Imoto Seisakusho, "Rubbing Tester 1509"), absorbent cotton impregnated with ethanol was rubbed 10 times (back and forth) at a stroke distance of 100 mm, a speed of 30 reciprocations per minute, and a load of 0.5 kgf / cm 2 The film state after sliding was evaluated according to the following evaluation criteria.

[0329] (Rating) 3: No trace at all over the entire sliding part. 2: Slight trace on a part of the sliding part. 1: The film on the sliding part disappears.

[0330] <Example 1> In Table 13, B1 to B16 are invention examples, and b1 to b10 are comparative examples. In this example, when adjusting the aqueous treatment liquid, carbon black (CB), graphite, soot powder, and an aqueous dispersion were used as compounds other than the binder component.

[0331] In Comparative Example b1, the carbon concentration of Compound A was as low as 71%. In Comparative Examples b2 to b4, Compound B did not have a rutile-type structure. In Comparative Examples b5, b8, and b10, Equation (1) was not satisfied. In Comparative Examples b5, b6, b7, b8, and b9, Equation (2) was not satisfied. While the rating of the heating rate was 1 in Comparative Examples b1 to b10, the rating of the heating rate was 2 or 3 in Invention Examples B1 to B16.

[0332]

Table 13

[0333] <Example 2> As shown in Table 14, Invention Examples C2 to C11, in which the content of Compound A at the position of 0.90H from the surface of the surface treatment film (i.e., the interface-side position P) was 30 to 90%, were superior in heating rate to C1 in which the content of Compound A at that position was 20%.

[0334]

Table 14

[0335] <Example 3> As shown in Table 15, Invention Examples D6 to D9 in which Compound B was TiO 2 were Invention Example D1 in which Compound B was IrO 2 and Invention Example D1 in which Compound B was GeO2 It was superior in heating rate to Invention Example D5.

[0336]

Table 15

[0337] <<Elemental technology B3a, B3b>> The elemental technology B3a is a structural member comprising a member body formed by a plurality of steel plates joined to each other, including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness larger than that of the first steel plate, and having an annular shape in plan view, and a film provided on the first steel plate and containing 0.001 g / m or more of one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide 2 or more, and is a structural member. The elemental technology B3b is a structural member comprising a member body formed by a plurality of steel plates joined to each other, including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness larger than that of the first steel plate, and having an annular shape in plan view, and a film provided on the first steel plate and containing 0.500 g / m or less of carbon black 2 or less, and is a structural member.

[0338] Elemental technologies B3a and B3b are intended to provide a blank for hot stamping that can improve the performance of a member when forming an annular structural member, particularly a large-sized annular structural member, including a steel plate with a small plate thickness compared to other steel plates.

[0339] The blank for hot stamping according to the embodiment includes a plurality of steel plates. The plurality of steel plates are arranged and joined so as to have an annular shape in a plan view of the blank. The plurality of steel plates include a first steel plate and a second steel plate. The first steel plate has the smallest plate thickness among the plurality of steel plates. The second steel plate has a plate thickness larger than that of the first steel plate. The first steel plate is configured such that the emissivity on at least one of the two surfaces of the first steel plate is larger than the emissivity on the two surfaces of the second steel plate (first configuration).

[0340] The blank according to the first configuration includes a first steel plate having the smallest plate thickness and a second steel plate having a plate thickness larger than that of the first steel plate. The emissivity of at least one surface of the first steel plate is larger than the emissivity of the two surfaces of the second steel plate. Thereby, when the blank is heated during hot stamping, the heating rate of the first steel plate, which is the thin-walled part, can be increased. Therefore, the first steel plate can be heated to the temperature in the austenite region more quickly, and the holding time of the first steel plate at that temperature can be ensured to be long. Thus, the austenite crystal grains in the first steel plate can be coarsened. As a result, since the ferrite transformation region (ferrite nose) in the CCT diagram shifts to the long-time side, after the heating of the blank is completed, the start of the transformation of the first steel plate into ferrite can be delayed, and the forming of the blank can be started while maintaining the microstructure of the first steel plate in the austenite phase. That is, the hardenability of the first steel plate with a small plate thickness can be improved.

[0341] In the blank according to the first configuration, since the hardenability of the first steel plate with a small plate thickness is improved, when forming a structural member from the blank by hot stamping, the first steel plate can also be properly hardened. Therefore, the hardness of the structural member is likely to be uniformized, and a partial strength reduction of the structural member can be suppressed. Further, since non-uniform stress is unlikely to occur in the structural member, even if the formed structural member is annular, torsion is unlikely to occur, and good dimensional accuracy can be ensured in the structural member. Therefore, when forming an annular structural member including the first steel plate having a smaller plate thickness than the second steel plate, particularly a large-sized and annular structural member, from the blank, strength defects and dimensional accuracy defects of the structural member can be reduced, and the impact absorption performance (crashworthiness) of the structural member can be improved.

[0342] In the blank according to the first configuration, the emissivity of the first steel plate with the minimum plate thickness is larger than the emissivity of the second steel plate with a relatively large plate thickness. In this case, the first steel plate heats up faster than the second steel plate, and compared with the case where the first steel plate has the same emissivity as the second steel plate, the high-temperature holding time of the first steel plate, that is, the time from when the first steel plate reaches the temperature in the austenite region until the second steel plate and the entire blank reach the temperature in the austenite region becomes longer. Thereby, after the heating of the blank is completed, non-uniformity of the phase transformation due to the difference in the cooling rate between the steel plates is reduced. Specifically, the start of the phase transformation from austenite to ferrite can be delayed for the first steel plate with the minimum plate thickness, and the difference in the phase transformation start time between the first steel plate with the minimum plate thickness and the other steel plates becomes smaller. As a result, the hardenability can be uniformized between the first steel plate with the minimum plate thickness and the other steel plates.

[0343] In the first configuration, the first steel plate may have a plate thickness of less than 1.4 mm (second configuration).

[0344] When the thickness of the first steel plate is less than 1.4 mm as in the second configuration, the first steel plate is particularly likely to be heat-extracted after the heating of the blank is completed, and the hardenability of the first steel plate is more likely to deteriorate. However, even when the thickness of the first steel plate is less than 1.4 mm, by making the emissivity of at least one surface of the first steel plate higher than that of the relatively thick second steel plate, when the blank is heated during hot stamping, the temperature rise of the first steel plate can be promoted and the high-temperature holding time of the first steel plate can be ensured to be long. Therefore, the hardenability of the first steel plate can be improved.

[0345] In the first or second configuration, the first steel plate may be a plated steel plate. In this case, the first steel plate can have a base steel plate and an aluminum-based plating layer provided on the base steel plate (third configuration).

[0346] When the first steel plate is a plated steel plate having an aluminum-based plating layer as in the third configuration, when the blank is heated during hot stamping, the heating rate of the first steel plate tends to be low. Since the aluminum-based plating layer is close to white, it easily reflects thermal energy and inhibits the temperature rise of the first steel plate. However, even when the first steel plate is a plated steel plate having an aluminum-based plating layer, by making the emissivity of at least one surface of the first steel plate higher than that of the relatively thick second steel plate, when the blank is heated during hot stamping, the temperature rise of the first steel plate can be promoted. Therefore, the high-temperature holding time of the first steel plate can be ensured to be long, and the hardenability of the first steel plate can be improved.

[0347] In any of the first to third configurations, at least one surface of the first steel plate may be coated with a film having an emissivity of 60% or more at a wavelength of 8.0 μm at 25°C (fourth configuration).

[0348] In any one of the first to third configurations, at least one surface of the first steel plate may be coated with a film. This film may contain carbon black, one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, and 0 to 0.30 g / m 2 of silica. When the content of carbon black in the film is X CB (g / m 2 ) and the content of the oxide is X Oxide (g / m 2 ), it is preferable that X CB and X Oxide satisfy the following formula (1) (see International Publication No. 2022 / 215229) (fifth configuration). 118.9 ≦ 24280 / {6700 / (100 + 76×X CB ) + 18000 / (130 + 65×X Oxide )} ≦ 332.0 (1)

[0349] In any one of the first to fifth configurations, the first steel plate may be a plated steel plate having a base steel plate and a plating layer provided on the base steel plate. In this case, when the plate thickness of the first steel plate is t min and the plate thickness of the steel plate having the maximum plate thickness among the plurality of steel plates is t max , it is preferable that 1.0 < t max / t min ≦ 3.2 (sixth configuration).

[0350] When the difference in plate thickness between the first steel plate having the minimum plate thickness t min and another steel plate having the maximum plate thickness t max among the plurality of steel plates included in the blank is large, it becomes difficult to secure a process window in the manufacture of the structural member. For example, when the difference between the minimum plate thickness t min and the maximum plate thickness t max is large, when the blank is heated during hot stamping, the maximum plate thickness t maxWhile waiting for the steel sheet having [it] to reach the temperature in the austenite region, the alloying of the plating layer of the first steel sheet that has been previously heated to the temperature in the austenite region progresses, and the diffusion layer thickens, and there may be a case where the corrosion resistance or weldability of the first steel sheet by the plating layer cannot be ensured. Therefore, in the sixth configuration, the ratio of the maximum plate thickness t min to the minimum plate thickness t max is set to 3.2 or less. Thereby, since the heating rate of the steel sheet having the maximum plate thickness t max and the heating rate of the first steel sheet having the minimum plate thickness t min do not deviate too much, the heating of other steel sheets can be completed before the alloying of the plating layer of the first steel sheet progresses excessively. Therefore, a structural member can be manufactured while maintaining the corrosion resistance or weldability of the first steel sheet, and a process window in the manufacture of the structural member can be ensured.

[0351] In any of the first to sixth configurations, the first steel sheet may be a plated steel sheet having a base steel sheet and a plating layer provided on the base steel sheet. The blank can further include an overlap portion. The overlap portion is formed by overlapping the ends of two adjacent steel sheets among the plurality of steel sheets, which are steel sheets other than the second steel sheet. The overlap portion can have a total plate thickness greater than 2.5 mm and 4.0 mm or less. In this case, it is preferable that the two steel sheets are each configured such that the emissivity on the surface located outside the overlap portion is greater than the emissivity on both surfaces of the second steel sheet (seventh configuration).

[0352] When there is an overlap portion formed by overlapping the ends of two steel plates in the blank, it may not be possible to secure the process window in the manufacture of the structural member. Specifically, when there is a difference in plate thickness among a plurality of steel plates included in the blank and the total plate thickness of the overlap portion exceeds 2.5 mm, when the blank is heated during hot stamping, while waiting for the overlap portion to reach the temperature in the austenite region, the alloying of the plating layer of the first steel plate having the minimum plate thickness progresses, the diffusion layer thickens, and the corrosion resistance or weldability of the first steel plate due to the plating layer may not be ensured. Therefore, in the seventh configuration, in each of the two steel plates forming the overlap portion, the emissivity of the outer surface of the overlap portion is increased. Thereby, since the temperature rise of the overlap portion can be promoted, the heating of the overlap portion can be completed before the alloying of the plating layer of the first steel plate progresses excessively, and the structural member can be manufactured while maintaining the corrosion resistance or weldability of the first steel plate. That is, it becomes easier to secure the process window in the manufacture of the structural member. However, even when the emissivity of the overlap portion is increased, if the total plate thickness of the overlap portion becomes excessive, it becomes difficult to secure the process window. Therefore, the total plate thickness of the overlap portion is preferably 4.0 mm or less.

[0353] The method for manufacturing a structural member according to the embodiment includes a step of preparing a blank according to any one of the first to seventh configurations, a step of heating a plurality of steel plates included in the blank to a temperature equal to or higher than the austenite transformation completion temperature, and a step of using a mold to form the heated blank into an annular structural member in plan view and performing quenching (eighth configuration).

[0354] The structural member according to the embodiment includes a member body and a film. The member body is formed of a plurality of steel plates joined to each other and has an annular shape in plan view. The plurality of steel plates includes a first steel plate having the minimum plate thickness and a second steel plate having a plate thickness larger than the plate thickness of the first steel plate. The film is provided on the first steel plate. The film contains 0.001 g / m of one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide. 2Contained above (ninth configuration).

[0355] The structural member according to the embodiment includes a member main body and a film. The member main body is formed of a plurality of steel plates joined to each other and has an annular shape in plan view. The plurality of steel plates include a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness larger than that of the first steel plate. The film is provided on the first steel plate. The film contains carbon black at 0.500 g / m 2 Contained below (tenth configuration).

[0356] In the ninth or tenth configuration, the structural member may be an automobile door ring component. In this case, the member main body can include a front pillar, a center pillar, and a rocker connecting the front pillar and the center pillar (eleventh configuration).

[0357] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding components in each figure are denoted by the same reference numerals, and the same description will not be repeated.

[0358] <First Embodiment> [Structural Member] FIG. 16 is a view (plan view) seen from above in a state where the structural member B3-10 according to the present embodiment is placed on a horizontal plane. The structural member B3-10 is used, for example, for an automobile body. The structural member B3-10 is typically an automobile door ring component. In the present embodiment, an example in which the structural member B3-10 is a door ring component will be described.

[0359] The structural member B3-10 is a hot stamping member. That is, the structural member B3-10 is formed by hot stamping (hot press working) a blank composed of a plurality of steel plates. The structural member B3-10 includes a member main body B3-11. The member main body B3-11 has an annular shape in a plan view of the structural member B3-10. The member main body B3-11 includes a front pillar B3-111, a center pillar B3-112, and a rocker B3-113. When the structural member B3-10 is assembled to an automobile body, the center pillar B3-112 is disposed behind the front pillar B3-111. The center pillar B3-112 extends substantially in the vertical direction of the vehicle body. The front pillar B3-111 extends toward the center pillar B3-112. When the structural member B3-10 is assembled to an automobile body, the rocker B3-113 is disposed below the front pillar B3-111 and the center pillar B3-112. The rocker B3-113 connects the front pillar B3-111 and the center pillar B3-112.

[0360] In the present embodiment, the member main body B3-11 is formed by a plurality of steel plates B3-21, 22, 23 joined to each other. In the example of FIG. 16, the front pillar B3-111 is mainly composed of the steel plates B3-21, 22. The center pillar B3-112 is mainly composed of the steel plate B3-23. The rocker B3-113 is composed of the steel plates B3-21, 23.

[0361] Figure 17 is a sectional view taken along line II-II of Figure 16. In Figure 17, a cross-section of the structural member B3-10 cut along the thickness direction at the position of the steel plate B3-21 is shown. As shown in Figure 17, the steel plate B3-21 has an open cross-section. The steel plate B3-21 has, for example, a generally hat shape in a cross-sectional view of the structural member B3-10. More specifically, the steel plate B3-21 includes a top plate B3-211, vertical walls B3-212 and B3-213, and flanges B3-214 and B3-215. The vertical wall B3-212 is disposed on the side opposite to the vertical wall B3-213 with respect to the top plate B3-211. In a cross-sectional view of the structural member B3-10, one ends of the vertical walls B3-212 and B3-213 are connected by the top plate B3-211. In a cross-sectional view of the structural member B3-10, flanges B3-214 and B3-215 are respectively connected to the other ends of the vertical walls B3-212 and B3-213. The flanges B3-214 and B3-215 respectively protrude outward from the structural member B3-10 from the vertical walls B3-212 and B3-213.

[0362] In the structural member B3-10, the width W of the steel plate B3-21 may be 30 mm or more and 750 mm or less. The height H of the steel plate B3-21 may be 25 mm or more and 150 mm or less. The width W is the distance from the R stop on the vertical wall B3-212 side of the corner portion between the top plate B3-211 and the vertical wall B3-212 to the R stop on the vertical wall B3-213 side of the corner portion between the top plate B3-211 and the vertical wall B3-213 in the cross-section of the structural member B3-10. The height H is the distance along the thickness direction of the top plate B3-211 from the top plate B3-211 to the flanges B3-214 and B3-215.

[0363] Although illustration is omitted, other steel plates B3-22 and B3-23 also have an open cross-section similar to the steel plate B3-21. The steel plates B3-22 and B3-23 can also have, for example, a generally hat shape in a cross-sectional view of the structural member B3-10. The width of the steel plates B3-22 and B3-23 may be 15 mm or more and 300 mm or less respectively. The height of the steel plates B3-22 and B3-23 may be 10 mm or more and 150 mm or less respectively.

[0364] In a plan view, the size of the annular structural member B3-10 is, for example, 1.0 m or more. The size of the structural member B3-10 may be, for example, 4.0 m or less. The size of the structural member B3-10 refers to the length of a line segment connecting two points that are the farthest apart among any two points on the outer periphery of the structural member B3-10 when viewed along the vertical direction with the structural member B3-10 placed on a horizontal plane.

[0365] [Manufacturing method of structural member] Hereinafter, the manufacturing method of the structural member B3-10 will be described with reference to FIGS. 18A to 18G. The manufacturing method of the structural member B3-10 according to the present embodiment includes a step of preparing a blank B3-20, a step of heating the blank B3-20, and a step of shaping the heated blank B3-20 into the structural member B3-10.

[0366] (Preparation step) As shown in FIG. 18A, in the preparation step, a blank B3-20 having a shape in which the structural member B3-10 is developed is prepared. The blank B3-20 includes a plurality of steel plates B3-21, 22, 23. The steel plates B3-21, 22, 23 are arranged and joined so as to have an annular shape in a plan view of the blank B3-20.

[0367] Figures 18B, 18C, and 18D are cross-sectional views of blank B3-20 showing the joints of steel plates B3-21, 22, and 23. Figures 18B, 18C, and 18D are the IIIB-IIIB cross-sectional view, the IIIC-IIIC cross-sectional view, and the IIID-IIID cross-sectional view of Figure 18A, respectively. Referring to Figures 18B and 18C, steel plate B3-21 is butt-joined to each of steel plates B3-22 and B3-23. That is, these end faces are joined in a state where the end face of steel plate B3-21 abuts against the end face of steel plate B3-22, and these end faces are joined in a state where the other end face of steel plate B3-21 abuts against the end face of steel plate B3-23. Referring to Figure 18D, steel plate B3-22 is butt-joined to steel plate B3-23 in addition to steel plate B3-21. The end face of steel plate B3-22 is joined to the end face in a state where it abuts against the end face of steel plate B3-23. Steel plates B3-21, 22, and 23 are joined by, for example, laser welding. In the present embodiment, blank B3-20 is a so-called tailor-welded blank.

[0368] Referring to FIGS. 18B and 18C, in steel plates B3-21, B3-22, and B3-23, steel plate B3-21 has the smallest plate thickness t min having. Steel plate B3-22 has a plate thickness greater than the plate thickness t min of steel plate B3-21. Steel plate B3-23 has a plate thickness equal to or greater than the plate thickness t min of steel plate B3-21. In the example of the present embodiment, the respective plate thicknesses of steel plates B3-22 and B3-23 are greater than the plate thickness t min of steel plate B3-21. In the present embodiment, steel plate B3-23 has the largest plate thickness t max among steel plates B3-21, B3-22, and B3-23. Steel plate B3-22 has a plate thickness greater than the plate thickness t min of steel plate B3-21 and smaller than the plate thickness t max of steel plate B3-23, having a plate thickness t mid . However, steel plate B3-22 can also have a plate thickness equal to or greater than that of steel plate B3-23. That is, in steel plates B3-21, B3-22, and B3-23, steel plate B3-22 can also have the largest plate thickness t max .

[0369] The plate thickness t of steel plate B3-21min is typically less than 1.4 mm. The plate thickness t min may be, for example, 0.8 mm or more. The plate thickness t of the steel plate B3-21 min and the plate thickness t of the steel plate B3-23 max satisfy 1.0 < t max / t min ≦ 3.2, and preferably satisfy 1.3 ≦ t max / t min ≦ 3.2.

[0370] The steel plate B3-21 having the minimum plate thickness t in the blank B3-20 min is configured such that the emissivity on at least one of its both surfaces is greater than the emissivity on both surfaces of the steel plate B3-22. For example, the emissivity at a wavelength of 8.0 μm at 25 °C is 60% or more on one or both surfaces of the steel plate B3-21 and less than 60% on both surfaces of the steel plate B3-22. The emissivity at a wavelength of 8.0 μm at 25 °C on one or both surfaces of the steel plate B3-21 is more preferably 70% or more, and even more preferably 80% or more. The difference in emissivity at a wavelength of 8.0 μm at 25 °C between the steel plate B3-21 having the minimum plate thickness t min and the other steel plate B3-22 is preferably greater than 5%, more preferably greater than 10%, and even more preferably greater than 20%. The emissivity can be measured in accordance with JIS R 1801 (2002). In this case, a sample collected from the steel plate to be measured is set in a Fourier transform infrared spectrophotometer, and the emissivity is calculated by measuring the radiation intensity at a wavelength of 8.0 μm at 25 °C. Alternatively, it is also possible to calculate the emissivity from the ratio of the radiation intensity of the site of interest at 25 °C to the radiation intensity of a blackbody by using a radiation thermometer with the measurement wavelength set to 8.0 μm.

[0371] In this embodiment, one surface of the steel plate B3-21 is covered with the film B3-26. On the other hand, the film B3-26 is not provided on the steel plate B3-22. As a result, the emissivity of one surface of the steel plate B3-21 is higher than the emissivity of both surfaces of the steel plate B3-22.

[0372] The film B3-26 is, for example, a black film. For example, the lightness L from the surface of the film B3-26 * value (CIE 1976 lightness index L defined in JIS Z8781-4(2013) * ) is 60 or less, the film B3-26 can be determined to be black. The film B3-26 may be a carbon-based surface treatment film (a film containing carbon (C)). The emissivity of the film B3-26 at a wavelength of 8.0 μm at 25°C is 60% or more, preferably 70% or more, more preferably 80% or more. That is, the emissivity of the surface of the steel sheet B3-21 to which the film B3-26 is applied at a wavelength of 8.0 μm at 25°C is 60% or more, preferably 70% or more, more preferably 80% or more. The film B3-26 may have an emissivity of 60% or more at a wavelength of 8.0 μm at 700°C. As the film B3-26, for example, the surface treatment film described in Patent Document 1 can be used. Specifically, the film B3-26 can contain carbon black and one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide. The film B3-26 may or may not contain silica. That is, the content of silica in the film B3-26 is 0 g / m 2 or more. The content of silica in the film B3-26 may be 0.30 g / m 2 or less. The content of silica is more preferably 0.10 g / m 2 or less, and even more preferably 0.05 g / m 2 or less.

[0373] Carbon black and the oxide can be dispersed and present throughout the surface of the film B3-26 perpendicular to the thickness direction of the steel sheet B3-21. Let the content of carbon black be X CB (g / m 2 ), and the content of one or more oxides (metal oxides) selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide be X Oxide (g / m 2 ). When CB and XOxide preferably satisfies the following formula (1). 118.9 ≦ 24280 / {6700 / (100 + 76×X CB ) + 18000 / (130 + 65×X Oxide )} ≦ 332.0 (1)

[0374] In formula (1), for the central formula: 24280 / {6700 / (100 + 76×X CB ) + 18000 / (130 + 65×X Oxide )}, the value calculated is preferably 119.0 or more, more preferably 170.0 or more, and even more preferably 220.0 or more. The value calculated by the central formula is preferably 330.0 or less, more preferably 310.0 or less, and even more preferably 300.0 or less.

[0375] The dispersion state of carbon black and metal oxide in film B3-26 can be confirmed by performing surface analysis of film B3-26 with an Electron Probe Micro Analyzer (EPMA) for elements derived from carbon black (e.g., C) and elements derived from oxides (Zr, Zn, and Ti). The carbon black content X CB can be measured by cross-section analysis of film B3-26 using a Transmission Electron Microscope (TEM). That is, cross-section analysis of film B3-26 is performed by TEM-EDS analysis on a region of a predetermined size (film thickness of film B3-26 × 5 μm), and the film thickness of film B3-26 and the area ratio occupied by particles with a carbon content of 70 mass% or more in the region are measured. When the density of carbon black is ρ (ton / m 3 ), the film thickness is d (μm), and the area ratio is a (%), the value represented by ρ × d × a is the carbon black content X CB (g / m 2 ). The oxide content X OxideIt can be determined by performing elemental analysis from the surface of the film B3-26 using a fluorescent X-ray analyzer (manufactured by Rigaku, ZSX Primus) and quantifying metallic Zr, metallic Zn, and metallic Ti.

[0376] The content X of carbon black in the film B3-26 CB is preferably 0.030 g / m 2 or more, and more preferably 0.100 g / m 2 or more. The content X CB may be set within the range that satisfies formula (1), but is preferably 0.800 g / m 2 or less, and more preferably 0.600 g / m 2 or less.

[0377] The film B3-26 can contain 5.0% or more of carbon black by volume, preferably 8.0% or more of carbon black by volume. Further, the film B3-26 can contain 40.0% or less of carbon black by volume, preferably 30.0% or less of carbon black by volume.

[0378] The content X of metal oxide in the film B3-26 Oxide is preferably 0.030 g / m 2 or more, and more preferably 0.060 g / m 2 or more. The content X Oxide may be set within the range that satisfies formula (1), but is preferably 0.500 g / m 2 or less, and more preferably 0.300 g / m 2 or less.

[0379] The film B3-26 can contain 1.0% or more of metal oxide by volume. Further, the film B3-26 can contain 30.0% or less of metal oxide by volume, preferably 25.0% or less of metal oxide by volume.

[0380] The content X of carbon black CB (g / m 2) and the content X of the metal oxide Oxide (g / m 2 ) and the ratio: X Oxide / X CB is preferably 0.20 or more and 200.00 or less. X Oxide / X CB is more preferably 0.40 or more and 10.00 or less, and even more preferably 0.60 or more and 5.00 or less.

[0381] In addition to the above carbon black and metal oxide, the film B3-26 can contain various binder components and additives.

[0382] The binder component is preferably a water-dispersible or water-soluble resin. The content of the binder component is preferably 40% by volume or more based on the total volume of the film B3-26. As the binder component selected from water-dispersible or water-soluble resins, various known resins showing water-dispersibility or water-solubility can be used. Examples of such resins showing water-dispersibility or water-solubility include polyurethane resins, polyester resins, acrylic resins, epoxy resins, fluororesins, polyamide resins, polyolefin resins, polymer compounds obtained by hydrolysis and polycondensation of silane coupling agents, and the like. The binder component is more preferably one or more selected from the group consisting of polyester resins, polyurethane resins, polyolefin resins, acrylic resins, epoxy resins, fluororesins, and polyamide resins. When a polyurethane resin is used as the binder component, the polyurethane resin is preferably a polyether-based polyurethane resin.

[0383] The additives are, for example, leveling agents, water-soluble solvents, metal stabilizers, etching inhibitors, etc. The leveling agent is, for example, a nonionic or cationic surfactant. Examples of the nonionic or cationic surfactant include polyethylene oxide or polypropylene oxide adducts, acetylene glycol compounds, etc. Examples of the water-soluble solvent include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol, and propylene glycol, cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether, esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, etc. Examples of the metal stabilizer include chelate compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid). Examples of the etching inhibitor include amine compounds such as ethylenediamine, triethylenetetramine, guanidine, and pyrimidine.

[0384] The film B3-26 can be formed, for example, by applying an organic or inorganic treatment liquid containing carbon black and metal oxide to the entire surface of the steel sheet B3-21 and then drying the volatile components in the treatment liquid. The treatment liquid can be applied to the surface of the steel sheet B3-21, for example, by a roll coater, a curtain coater, or an inkjet. In the case of an inkjet, the film thickness of the film B3-26 can also be continuously changed. The film thickness of the film B3-26 is, for example, 0.5 μm or more and 5.0 μm or less. Preferably, the film thickness of the film B3-26 is 1.0 μm or more and 3.0 μm or less. The film thickness of the film B3-26 is negligibly small compared to the plate thickness t min of the steel sheet B3-21. Therefore, the plate thickness of the steel sheet B3-21 measured including the film B3-26 can be treated as the plate thickness t min of the steel sheet B3-21.

[0385] The steel sheet B3-21 may be a plated steel sheet. In this case, the steel sheet B3-21 has a base metal steel sheet B3-216 and a plating layer B3-217. The type of the base metal steel sheet B3-216 is not particularly limited. The plating layer B3-217 is provided on the base metal steel sheet B3-216. The plating layer B3-217 covers the whole or substantially the whole of both surfaces of the base metal steel sheet B3-216. The plating layer B3-217 is a metal plating layer. The plating layer B3-217 may be, for example, a molten aluminum plating, or may be a molten zinc plating, an alloyed molten zinc plating, or an electrogalvanized plating. As the steel sheet B3-21, known aluminum-plated steel sheets, zinc-plated steel sheets, etc. can be used.

[0386] The plating layer B3-217 is typically a plating layer (aluminum-based plating layer) mainly composed of aluminum. The constitution of the aluminum-based plating layer is not particularly limited. As the plating layer B3-217, a known aluminum-based plating layer can be adopted. When the steel sheet B3-21 is a plated steel sheet, the plate thickness t of the steel sheet B3-21 min is the combined plate thickness of the base metal steel sheet B3-216 and the plating layer B3-217.

[0387] The steel sheets B3-22, 23 may be known plated steel sheets, similar to the steel sheet B3-21. The steel sheets B3-22, 23 may be aluminum-plated steel sheets or zinc-plated steel sheets. The steel sheets B3-22, 23 may be plated steel sheets of the same type as the steel sheet B3-21 or may be plated steel sheets of a different type from the steel sheet B3-21. Also, the steel sheet B3-22 may be a plated steel sheet of the same type as the steel sheet B3-23 or may be a plated steel sheet of a different type from the steel sheet B3-23. When the steel sheet B3-22 is a plated steel sheet, the plate thickness t of the steel sheet B3-22 mid is the combined plate thickness of the base metal steel sheet and the plating layer. Similarly, when the steel sheet B3-23 is a plated steel sheet, the plate thickness t of the steel sheet B3-23 max is the combined plate thickness of the base metal steel sheet and the plating layer. When two or more of the steel sheets B3-21, 22, 23 are plated steel sheets, the plating weight per unit area of each steel sheet may be the same as or different from that of the other steel sheets.

[0388] (Heating process) The prepared blank B3-20 is formed into the structural member B3-10 (Figs. 16 and 17) by hot stamping (hot press working). During hot stamping, the blank B3-20 is subjected to a heating process. Referring to Fig. 18E, in the heating process, the blank B3-20 is heated by, for example, a heating furnace B3-30. The plurality of steel plates B3-21, 22, 23 included in the blank B3-20 are heated to a temperature equal to or higher than the austenite transformation completion temperature (A c3 point). The steel plates B3-21, 22, 23 are heated to, for example, 900°C or higher. As a result, the microstructure of the steel plates B3-21, 22, 23 is transformed entirely or almost entirely into the austenite phase.

[0389] (Forming process) Referring to Fig. 18F, in the forming process, using a mold B3-40, the heated blank B3-20 is formed into an annular structural member B3-10 (Figs. 16 and 17) in plan view and quenched. The blank B3-20 heated by the heating process is taken out from the heating furnace B3-30 (Fig. 18E) and conveyed to the mold B3-40. The mold B3-40 is attached to a known press device. The mold B3-40 includes, for example, a punch B3-41 and a die B3-42. The blank B3-20 is disposed between the punch B3-41 and the die B3-42.

[0390] Referring to Fig. 18G, after the blank B3-20 is disposed between the punch B3-41 and the die B3-42, the die B3-42 approaches the punch B3-41 relatively. The blank B3-20 is clamped (pressed) by the punch B3-41 and the die B3-42 and formed into a shape along the forming surfaces of the punch B3-41 and the die B3-42. The blank B3-20 is held while being clamped by the punch B3-41 and the die B3-42. The blank B3-20 is heat-extracted (quenched) by the mold B3-40, and its microstructure is transformed into martensite. Thereby, the structural member B3-10 can be manufactured from the blank B3-20.

[0391] FIG. 19 is a cross-sectional view of the structural member B3-10 after hot stamping. In FIG. 19, a cross-section of the structural member B3-10 is shown at the position of the steel plate B3-21 (FIGS. 18B and 18C) where the black film B3-26 was applied at the stage of the blank B3-20. This structural member B3-10 includes a member main body B3-11 and a film B3-12. The film B3-12 is provided on the steel plate B3-21. The black film B3-26 (FIGS. 18B and 18C) applied to the steel plate B3-21 in the blank B3-20 becomes the film B3-12 after hot stamping. When the film B3-26 contains carbon black, this carbon black almost disappears due to high-temperature heating during hot stamping, but may remain on the member main body B3-11. When the film B3-26 before hot stamping satisfies the above formula (1), the film B3-12 after hot stamping may not contain carbon black, or 0.500 g / m 2 It may also contain the following carbon black. When the film B3-12 after hot stamping contains carbon black, the carbon black content in the film B3-12 is 0 g / m 2 Above. Also, when the film B3-26 before hot stamping satisfies the above formula (1), in the film B3-12 after hot stamping, the value calculated by the central formula: 24280 / {6700 / (100 + 76×X CB ) + 18000 / (130 + 65×X Oxide )} is, for example, 120.0 or more and 150.0 or less.

[0392] When the film B3-26 (FIGS. 18B and 18C) before hot stamping satisfies the above formula (1), the film B3-12 after hot stamping contains, for example, 0 g / m of one or more oxides (metal oxides) selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide 2 Above, more desirably 0.001 g / m 2 Or more. The metal oxide content of the film B3-12 is, for example, 0.500 g / m 2 Or less. Thus, when the metal oxide remains in the structural member B3-10, that is, when the film B3-12 is 0 g / m 2When containing a super metal oxide, it is more desirable because the corrosion resistance of the structural member B3-10 is improved. When the film B3-26 before hot stamping satisfied the above formula (1), the film B3-12 after hot stamping contains 0 to 0.30 g / m 2 of silica.

[0393] The content of carbon black, the content of metal oxide, and the content of silica in the film B3-12 can be measured in the same manner as the film B3-26 at the stage of the blank B3-20. Specifically, the vehicle body part is disassembled to obtain the annular structural member B3-10, and an analysis sample is obtained from this structural member B3-10 by, for example, laser cutting or the like. For example, analysis samples are obtained from each of the plurality of steel plates included in the structural member B3-10. The acquisition position of the analysis sample is the center or the vicinity of the top plate of each steel plate having an open cross section. The obtained analysis sample is adjusted by polishing the cross section to outside the heat affected zone during laser cutting or the like to prepare a film analysis sample. For this sample, by performing surface analysis of the film B3-12 for elements derived from carbon black (for example, C) and elements derived from oxides (Zr, Zn, and Ti) by EPMA, the dispersion states of carbon black and metal oxide in the film B3-12 can be confirmed.

[0394] In many cases, there is, for example, an electrodeposition coating film on the outermost surface of the structural member B3-10. In that case, the film layer existing under the electrodeposition coating film layer and above the alloyed metal plating layer is analyzed. The content X CB of carbon black in the film B3-12 can be measured by cross-sectional analysis of the film B3-26 using TEM. That is, cross-sectional analysis of the film B3-12 is performed by TEM-EDS analysis for a region of a predetermined size (film thickness of the film B3-12 × 5 μm), and the film thickness of the film B3-12 and the area ratio occupied by particles having a carbon content of 70 mass% or more in the region are measured. When the density of carbon black is ρ (ton / m 3 ), the film thickness is d (μm), and the area ratio is a (%), the value represented by ρ × d × a is the content X CB (g / m 2) becomes the oxide content X Oxide can be determined by performing elemental analysis on the coating layer present in the lower layer of the electrodeposited coating film layer and the upper layer of the alloyed metal plating layer using the above-described fluorescent X-ray analyzer and quantifying metallic Zr, metallic Zn, and metallic Ti.

[0395] The minimum plate thickness t min In the cross-section of the structural member B3-10 at the position of the steel plate B3-21 having the minimum plate thickness t, when the value obtained by subtracting the minimum martensite fraction (%) from the maximum martensite fraction (%) is defined as the variation in the martensite fraction, the variation in the martensite fraction is, for example, 20% or less. The variation in the martensite fraction is preferably 15% or less, and more preferably 10% or less. The variation in the martensite fraction can be measured as follows. That is, the minimum plate thickness t min In the cross-section of the structural member B3-10 at the position of the steel plate B3-21 having the minimum plate thickness t, after cutting out 10 or more analysis samples (for example, having a size of about 10 mm on the long side) from positions separated by 20 mm or more from the end and each separated by 10 mm or more, each is mirror-polished and etched with a lepera reagent so that the plate thickness direction becomes the observation surface. Then, for the region from 1 / 8 of the plate thickness from the steel plate surface to 3 / 8 of the plate thickness from the steel plate surface (1 / 4 depth of the plate thickness from the steel plate surface), using an optical microscope, a tissue photograph with a magnification of 1000 times and a field of view of 2,400 μm 2 or more is taken for 30 fields of view, and image analysis is performed on the obtained tissue photographs.

[0396] As the image analysis method, the maximum brightness value Lmax and the minimum brightness value Lmin of the image are obtained from the image, the portion having pixels with brightness from Lmax - 0.3(Lmax - Lmin) to Lmax is defined as the white region, and the ratio of the number of pixels in the white region to the total number of pixels is calculated to measure the martensite fraction. For a total of 30 observation fields of each analysis sample, such image analysis is performed to obtain the martensite fraction, and the average value is taken as the martensite fraction of each analysis sample. Further, the difference between the maximum value and the minimum value of the martensite fraction in 10 or more analysis samples is the minimum plate thickness t minIt is defined as the variation in the martensite fraction in the cross-section of the structural member B3-10 at the position of the steel plate B3-21 having [the minimum plate thickness t in the structural member B3-10]. min When there are multiple steel plates having [the minimum plate thickness t], such analysis is performed for each steel plate to obtain the martensite fraction, and the maximum variation in the martensite fraction among these steel plates is taken as the variation in the martensite fraction in the structural member B3-10.

[0397] Note that depending on the steel plate, the area ratio of martensite obtained by image analysis, that is, the area ratio of the white region, may contain several percent of the area ratio of retained austenite. However, since the variation in the martensite fraction is calculated by difference, its influence is minor.

[0398] After the forming process (hot stamping), the steel plate B3-21 can have a tensile strength of, for example, 0.5 GPa or more, preferably 1.0 GPa or more. Similarly, after the forming process (hot stamping), the steel plates B3-22, 23 (Fig. 16) can have a tensile strength of, for example, 0.5 GPa or more, preferably 1.0 GPa or more. At least one of the steel plates B3-21, 22, 23 may have a tensile strength of 1.5 GPa or more after the forming process. The tensile strength of each of the steel plates B3-21, 22, 23 may be the same as or different from the tensile strength of other steel plates.

[0399] [Effect] In the blank B3-20 according to the present embodiment, the minimum plate thickness t minThe emissivity of one surface of the steel sheet B3-21 having [a certain property] is greater than the emissivities of both surfaces of the steel sheet B3-22 having a greater plate thickness. That is, the surface of the steel sheet B3-21 is subjected to a treatment for increasing the emissivity. As a result, when the blank B3-20 is heated during hot stamping, the heating rate of the steel sheet B3-21 becomes significantly higher compared to the steel sheet B3-22. Therefore, in the heating process, the steel sheet B3-21 can be quickly heated to the temperature in the austenite region, and a long holding time at high temperature of the steel sheet B3-21 can be ensured. As a result, the austenite crystal grains in the microstructure of the steel sheet B3-21 coarsen, and the ferrite transformation region (ferrite nose) in the CCT diagram shifts to the long-time side. Thus, it is possible to prevent the austenite in the steel sheet B3-21 from transforming into ferrite after being taken out from the heating furnace B3-30 until the forming by the mold B3-40 is started. Therefore, the forming of the blank B3-20 by the mold B3-40 can be started while maintaining the microstructure of the steel sheet B3-21 in the austenite phase, with the minimum plate thickness t min the hardenability of the steel sheet B3-21 having [a certain property] can be improved.

[0400] In this embodiment, since the hardenability of the relatively thin steel sheet B3-21 is improved, the hardness of the structural member B3-10 formed from the blank B3-20 can be made uniform. More specifically, for the steel sheet B3-21 having the minimum plate thickness t min since it can be well hardened even in the steel sheet B3-21 having [a certain property], the variation in the martensite fraction in the steel sheet B3-21 can be made 20% or less. As a result, for example, when a collision load is input to the structural member B3-10, deformation concentration is less likely to occur, and the structural member B3-10 is more likely to exhibit high impact absorption performance. Therefore, even when forming the annular structural member B3-10 including the steel sheet B3-21 with a small plate thickness, particularly a large and annular structural member B3-10 from the blank B3-20, the strength defect of the structural member B3-10 can be reduced, and the impact absorption performance of the structural member B3-10 can be improved.

[0401] The smaller the variation in the martensite fraction, the less non-uniformity in mechanical properties within the structural member B3-10, which is preferable from the perspective of the function of the structural member B3-10. On the other hand, when the variation in the martensite fraction is large, it indicates that the quenching insufficient parts, that is, the insufficient hardness parts, are unevenly distributed within the structural member B3-10. When the structural member B3-10 undergoes collision deformation, deformation is likely to concentrate on the insufficient hardness parts, resulting in a decline in the function of the structural member B3-10.

[0402] In this embodiment, by improving the hardenability of the relatively thin steel plate B3-21, it becomes less likely for stress non-uniformity to occur in the structural member B3-10. Therefore, even when forming the annular structural member B3-10 from the annular blank B3-20, it is less likely for the structural member B3-10 to twist. Thus, even when forming the annular structural member B3-10 including the steel plate B3-21 with a small thickness, particularly a large-sized and annular structural member B3-10 from the blank B3-20, it is possible to reduce the dimensional accuracy defect of the structural member B3-10 and improve the impact absorption performance of the structural member B3-10.

[0403] In the blank B3-20 according to this embodiment, the surface of the steel plate B3-21 with the minimum plate thickness t min is substantially covered with the black film B3-26, while the steel plate B3-22 with a larger plate thickness than the steel plate B3-21 is not provided with the film B3-26. Therefore, the emissivity of the surface of the steel plate B3-21 is larger than the emissivities of both surfaces of the steel plate B3-22. In this case, since the steel plate B3-21 heats up faster than the steel plate B3-22, the high-temperature holding time of the steel plate B3-21 becomes longer compared to the case where the steel plate B3-21 has the same emissivity as the steel plate B3-22. Thereby, after the heating of the blank B3-20 is completed, it is possible to reduce the non-uniformity of the phase transformation caused by the difference in the cooling rate among the steel plates B3-21, 22, 23. Specifically, the minimum plate thickness t minSince the start of the phase transformation from austenite to ferrite can be delayed for the steel sheet B3-21, the difference in the start time of the phase transformation between the steel sheet B3-21 and the other steel sheets B3-22 and 23 is reduced. As a result, the hardenability of the steel sheets B3-21, B3-22, and B3-23 included in the blank B3-20 can be made uniform.

[0404] For example, when the plating layer B3-217 of the steel sheet B3-21 is an aluminum-based plating layer, the heating rate of the steel sheet B3-21 tends to be low in the heating process. Since the aluminum-based plating layer is white, it easily reflects thermal energy and inhibits the temperature rise of the steel sheet B3-21. However, in the blank B3-20 according to the present embodiment, a treatment for increasing the emissivity is performed on the surface of the steel sheet B3-21. Therefore, even if the steel sheet B3-21 is a plated steel sheet having an aluminum-based plating layer, the temperature rise of the steel sheet B3-21 in the heating process can be promoted, and the high-temperature holding time of the steel sheet B3-21 can be ensured for a long time. Therefore, the hardenability in the thin steel sheet B3-21 can be ensured.

[0405] In the present embodiment, in the heating process, first, the steel sheet B3-21 having the minimum plate thickness t min reaches the temperature in the austenite region, and then, the steel sheet B3-22 having the intermediate plate thickness t mid and the steel sheet B3-23 having the maximum plate thickness t max reach the temperature in the austenite region in order. Here, the ratio of the minimum plate thickness t min to the maximum plate thickness t max : t max / t min is preferably 3.2 or less. Thereby, before the alloying of the plating layer B3-217 of the steel sheet B3-21 having the plate thickness t min progresses excessively due to heating and the diffusion layer grows and the corrosion resistance or weldability is lost, the steel sheet B3-23 having the plate thickness t max can be sufficiently heated until the phase transformation to austenite is completed. Therefore, a process window can be ensured in the manufacture of the structural member B3-10.

[0406] In this embodiment, in order to increase the emissivity of the steel sheet B3-21, a film B3-26 can be applied to the steel sheet B3-21. The emissivity (at a temperature of 25°C and a wavelength of 8.0 μm) of the film B3-26 is, for example, 60% or more. Thereby, the steel sheet B3-21 can be efficiently radiatively heated, and the rate of temperature increase of the steel sheet B3-21 in the heating process is more likely to increase.

[0407] In this embodiment, the film B3-26 can contain carbon black, one or more oxides selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide, and 0 to 0.30 g / m 2 of the following silica. The content X CB (g / m 2 ) of carbon black and the content X Oxide (g / m 2 ) of the oxide preferably satisfy the above formula (1). Formula (1) is a formula that defines the relationship between the magnification (%) of the increase in the rate of temperature increase (°C / s) and the content X CB of carbon black and the content X Oxide of the oxide. Formula (1) shows that in the range up to 700°C, carbon black mainly functions as a heat absorber, and in the range above 700°C, the oxide mainly functions as a heat absorber. When the film B3-26 satisfies formula (1), the emissivity at a wavelength of 8.0 μm at 25°C on the surface of the steel sheet B3-21 to which the film B3-26 is applied is likely to be 60% or more.

[0408] Carbon black and the oxide can be dispersed throughout the film B3-26 on the plane perpendicular to the thickness direction of the steel sheet B3-21. Thereby, the emissivity of the surface of the steel sheet B3-21 is likely to be made uniform. Therefore, in the heating process, the steel sheet B3-21 having the minimum plate thickness t min can be heated quickly and uniformly.

[0409] However, the configuration of the film B3-26 is not limited to this. The film B3-26 may be a substantially black film in order to increase the emissivity of the steel plate B3-21 as compared with the untreated case. For example, the film B3-26 may contain graphite or soot instead of or in addition to carbon black. Alternatively, the film B3-26 may contain, for example, a needle-like compound having a hexagonal crystal structure with an aspect ratio of 4 or more and 50 or less in order to increase the emissivity of the steel plate B3-21. The compound having a hexagonal crystal structure is typically graphite (C), but may also be lanthanum silicate, magnesium diboride, beryllium oxide (beryllia), zinc oxide, β-quartz, acicular nickel ore (NiS), wurtzite (ZnS), or the like.

[0410] <Second Embodiment> FIG. 20 is a plan view of the blank B3-20A according to the second embodiment. The blank B3-20 according to the first embodiment is a tailored blank in which the steel plates B3-21, 22, and 23 are butt-joined to each other. The blank B3-20A according to the present embodiment is mainly different from the first embodiment in the aspect of the joint portion of the steel plates.

[0411] Referring to FIG. 20, the blank B3-20A includes a plurality of steel plates B3-21, 22, 23, 24, and 25. The steel plates B3-21, 22, 23, 24, and 25 are arranged and joined so as to have an annular shape in a plan view of the blank B3-20. Similar to the first embodiment, the steel plate B3-21 has the minimum plate thickness t min and is configured such that the emissivity of at least one surface thereof is greater than the emissivity of both surfaces of the steel plate B3-22. Therefore, the blank B3-20A according to the present embodiment can also achieve the same effect as the first embodiment.

[0412] The blank B3-20A includes an overlap portion B3-27. FIG. 21 is a cross-sectional view taken along line VI-VI of FIG. 20 and shows the cross-section of the overlap portion B3-27. In the present embodiment, the overlap portion B3-27 is formed by overlapping the ends of two adjacent steel plates B3-23 and B3-24. The end of the steel plate B3-23 is joined in a state of being overlapped with the end of the steel plate B3-24. The steel plates B3-23 and B3-24 are joined to each other by, for example, spot welding or laser welding.

[0413] The overlap portion B3-27 has an overall plate thickness t. The overall plate thickness t is the sum of the plate thickness of the steel plate B3-23 and the plate thickness of the steel plate B3-24. When at least one of the steel plates B3-23 and B3-24 is a plated steel plate, the overall plate thickness t also includes the thickness of the plating layer. The overall plate thickness t of the overlap portion B3-27 is, for example, greater than 2.5 mm and 4.0 mm or less. In this case, the steel plate B3-23 is configured such that the emissivity of the surface located outside the overlap portion B3-27, that is, the surface on the side opposite to the steel plate B3-24, is greater than the emissivity of both surfaces of the steel plate B3-22 (Fig. 20). The steel plate B3-24 is configured such that the emissivity of the surface located outside the overlap portion B3-27, that is, the surface on the side opposite to the steel plate B3-23, is greater than the emissivity of both surfaces of the steel plate B3-22. That is, in each of the steel plates B3-23 and B3-24, the surface located outside the overlap portion B3-27 is subjected to a treatment for increasing the emissivity over the entire surface. For example, the emissivity at a wavelength of 8.0 μm at 25°C is 60% or more, preferably 70% or more, more preferably 80% or more, on the surface of the steel plates B3-23 and B3-24 located outside the overlap portion B3-27. The difference in emissivity at a wavelength of 8.0 μm at 25°C between the surface of the steel plates B3-23 and B3-24 located outside the overlap portion B3-27 and both surfaces of the other steel plate B3-22 is preferably greater than 5%, more preferably greater than 10%, and even more preferably greater than 20%. In the steel plates B3-23 and B3-24, the emissivity of the surface located inside the overlap portion B3-27 may be greater than the emissivity of both surfaces of the steel plate B3-22 or may be equal to or less than the emissivity of both surfaces of the steel plate B3-22.

[0414] In steel plates B3-23 and B3-24, the surface located outside the overlap portion B3-27 may be covered by a film B3-26, so that the emissivity of the surface may be greater compared to the steel plate B3-22 (FIG. 20). The film B3-26 used for the steel plates B3-23 and B3-24 can have the same configuration as the film B3-26 used for the steel plate B3-21. Since the film thickness of the film B3-26 is very small as described above, the total plate thickness t of the overlap portion B3-27 can be the plate thickness measured including the film B3-26.

[0415] When the total plate thickness t of the overlap portion B3-27 exceeds, for example, 2.5 mm, since the overlap portion B3-27 is difficult to heat up, when the blank B3-20A is heated during hot stamping, until the overlap portion B3-27 reaches the temperature in the austenite region, the minimum plate thickness t min of the plating layer B3-217 (FIGS. 18B and 18C) of the steel plate B3-21 having it may be alloyed and the diffusion layer may grow, and the corrosion resistance or corrosion resistance of the steel plate B3-21 may not be ensured. However, in the present embodiment, since the emissivity of the overlap portion B3-27 is increased to promote heating, even when the total plate thickness t of the overlap portion B3-27 is greater than 2.5 mm, the overlap portion B3-27 can be sufficiently heated until the phase transformation to austenite is completed before the alloying of the plating layer B3-217 of the steel plate B3-21 progresses and the diffusion layer becomes thick and the corrosion resistance or weldability is lost. Therefore, a process window in the manufacture of the structural member can be ensured.

[0416] In the blank B3-20A according to the present embodiment, the steel plate B3-21 may be butt-joined to the steel plates B3-22 and ...

Claims

1. An automobile side module for reinforcing an outer side of an automobile, the automobile side module being formed by hot stamping a plurality of integrated steel plates, The minimum circumscribed rectangle area when viewed from the perpendicular direction of the reference plane is S (m ２ ), Among the components of the automobile side module, The total weight of components weighing 0.200 kg or more is W ０．２ (kg), The total weight of the components with a minimum Vickers hardness of HV510 or more is W ５１０ Then, W ０．２ / S is 7.7 or less, W ５１０ / W ０．２ is greater than 0.10 An automobile side module comprising:

2. Elemental technology A1; Elemental technology A2; At least one of the following: Elemental technology B1; Elemental technology B2; Elemental technology B3a; and Elemental technology B3b; and Elemental technology B4; Elemental technology B5a; Elemental technology B5b; and Elemental technology B6; At least one of the following: Equipped with The elemental technology A1 is The chemical composition, in mass%, is C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0 to 0.15%, Ti: 0 to 0.15%, V: 0 to 0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0 to 1.0%, Ni: 0-1.0%, B: 0 to 0.0100%, Ca: 0 to 0.010%, and REM: 0-0.30% with the remainder being Fe and impurities, The metal structure contains martensite, bainite and tempered martensite in a total of 90% or more by area ratio, In a texture from the surface to a position 1 / 4 of the sheet thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1-10> to {001}<-1-10> to the pole density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 1.8; In a texture from the surface at a position that is 1 / 4 of the sheet thickness to a position that is 1 / 2 of the sheet thickness from the surface, the ratio of the pole density of an orientation group consisting of {001}<1-10> to {001}<-1-10> to the pole density of an orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 2.

3. A hot stamped compact characterized by: The elemental technology A2 is The chemical composition, in mass%, is C: 0.15-0.50%, Si: 0.0010-3.000%, Mn: 0.30-3.00%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0100% or less, Nb: 0 to 0.15%, Ti: 0 to 0.15%, V: 0 to 0.15%, Mo: 0-1.0%, Cr: 0-1.0%, Cu: 0 to 1.0%, Ni: 0-1.0%, B: 0 to 0.0100%, Ca: 0 to 0.010%, and REM: 0-0.30% with the remainder being Fe and impurities, The steel has a metal structure including a total of 10 to 30% by area of ​​ferrite and granular bainite, and a balance including at least one of martensite, bainite, and tempered martensite, In a texture from the surface to a position 1 / 4 of the sheet thickness from the surface, the ratio of the pole density of the orientation group consisting of {001}<1-10> to {001}<-1-10> to the pole density of the orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 1.8; In a texture from the surface at a position that is 1 / 4 of the sheet thickness to a position that is 1 / 2 of the sheet thickness from the surface, the ratio of the pole density of an orientation group consisting of {001}<1-10> to {001}<-1-10> to the pole density of an orientation group consisting of {111}<1-10> to {111}<-1-12> is less than 2.

3. A hot stamped compact characterized by: The elemental technology B1 is A hot stamped laminated product comprising: a first Al-Fe alloy plated steel sheet having a sheet thickness T1; and a second Al-Fe alloy plated steel sheet having a sheet thickness T2 and having an area smaller than that of the first Al-Fe alloy plated steel sheet, the second Al-Fe alloy plated steel sheet being overlapped on and welded to the first Al-Fe alloy plated steel sheet, A laminated hot stamped compact that satisfies the relationships of the following formulas (7) to (9), 25≦K1≦60...Formula (7) 25≦K2≦60...Formula (8) 0≦(D1-D2)×(K1 / K2)2≦5.0 ...Formula (9) Where: K1: an average value of a plating thickness of the Al-Fe-based alloy plating layer on a side in contact with the second Al-Fe-based alloy plated steel sheet and a plating thickness of the Al-Fe-based alloy plating layer on a side not in contact with the second Al-Fe-based alloy plated steel sheet in a non-overlapping portion of the first Al-Fe-based alloy plated steel sheet K2: plating thickness of the Al-Fe-based alloy plating layer on a side not in contact with the first Al-Fe-based alloy plated steel sheet in the overlapping portion of the second Al-Fe-based alloy plated steel sheet; D1: thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on a side in contact with the second Al-Fe-based alloy plated steel sheet in the first Al-Fe-based alloy plated steel sheet so as to be in contact with a steel sheet substrate, and thickness of a diffusion layer located in the Al-Fe-based alloy plating layer on a side not in contact with the second Al-Fe-based alloy plated steel sheet so as to be in contact with a steel sheet substrate; The average value of D2: a thickness of a diffusion layer located in the Al-Fe-based alloy plating layer so as to be in contact with a steel sheet substrate on a side of the second Al-Fe-based alloy plated steel sheet not in contact with the first Al-Fe-based alloy plated steel sheet, The units of the plate thickness T1 and the plate thickness T2 are mm, and the units of the K1, the K2, the D1, and the D2 are μm. The elemental technology B2 is A base steel plate; An aluminum plating layer having an Al content of 80 mass% or more provided on at least one surface of the base steel sheet; and a surface treatment film provided on the aluminum plating layer, The surface treatment film is A compound A containing carbon; A compound B which is an oxide or fluoride of a metal element M and has a rutile structure; The carbon concentration of the compound A is 80% by mass or more, A hot stamped product formed using an aluminum-plated steel sheet for hot stamping, characterized in that a concentration of the metal element M satisfies the following formula (1) and the following formula (2), 1≦C ｂＭ ≦40・・・Formula (1) 1.5≦C ｂＭ / C ｔＭ ≦10.0・・・Formula (2) Here, when the average thickness of the surface treatment film is H, C in the above formula (2) ｔＭ is the concentration, in mass %, of the metal element M at a position 0.05H from the surface of the surface treatment film, C in the above formula (1) and the above formula (2) ｂＭ is the concentration, in mass %, of the metal element M at a position 0.95H from the surface of the surface treatment film, The elemental technology B3a is A structural member, A member body formed by a plurality of steel plates joined together, including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than the plate thickness of the first steel plate, and having an annular shape in a plan view; A coating layer is provided on the first steel plate, and contains at least one oxide selected from the group consisting of Zr oxide, Zn oxide, and Ti oxide in an amount of 0.001 g / m ２ A coating containing the above, A structural member comprising: The elemental technology B3b is A structural member, A member body formed by a plurality of steel plates joined together, including a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than the plate thickness of the first steel plate, and having an annular shape in a plan view; A carbon black layer having a thickness of 0.500 g / m2 is provided on the first steel plate. ２ A coating containing the following: A structural member comprising: The elemental technology B4 is A structural member, The member body includes a first steel plate having a minimum plate thickness and a second steel plate having a plate thickness greater than the plate thickness of the first steel plate, and is formed by a plurality of steel plates joined to each other and has an annular shape in a plan view; The first steel sheet and the second steel sheet are each a plated steel sheet having an aluminum-based plating layer on both surfaces of a base steel sheet, a thickness of the aluminum-based plating layer on the first steel plate is smaller than a thickness of the aluminum-based plating layer on the second steel plate; The elemental technology B5a is A structural member, A member body including a first steel plate and a second steel plate having an end portion that is overlapped and joined to an end portion of the first steel plate to form an overlap portion together with the end portion of the first steel plate, the member body being formed by a plurality of steel plates joined to each other and having an annular shape in a plan view; a first steel plate and a second steel plate, the first steel plate and the second steel plate being provided on a surface located outside the overlap portion ... ２ A coating containing the above, A structural member comprising: The elemental technology B5b is A structural member, A member body including a first steel plate and a second steel plate having an end portion that is overlapped and joined to an end portion of the first steel plate to form an overlap portion together with the end portion of the first steel plate, the member body being formed by a plurality of steel plates joined to each other and having an annular shape in a plan view; a carbon black layer of 0.500 g / m2 is provided on a surface of each of the first steel plate and the second steel plate that is positioned outside the overlap portion; ２ A coating containing the following: A structural member comprising: The elemental technology B6 is A structural member, The member body is formed of a plurality of steel plates joined together and has an annular shape in a plan view; The plurality of steel plates include a first steel plate, a second steel plate, and a third steel plate, The end of the first steel plate is overlapped and joined to the end of the second steel plate to form an overlap portion having the maximum plate thickness in the member body together with the end of the second steel plate, At least one of the first steel plate and the second steel plate, and the third steel plate, A plated steel sheet having an aluminum-based plating layer on both surfaces of a base steel sheet, a thickness of the aluminum-based plating layer on at least one of the first steel plate and the second steel plate is smaller than a thickness of the aluminum-based plating layer on the third steel plate, which is a structural member; 2. The vehicle side module according to claim 1.

3. At least one of elemental technology A1 and elemental technology A2, At least one of elemental technology B1 and elemental technology B2; 3. The vehicle side module according to claim 2, further comprising:

4. At least one of elemental technology A1 and elemental technology A2, At least one of element technology B3a, element technology B3b, element technology B4, element technology B5a, element technology B5b, and element technology B6; 3. The vehicle side module according to claim 2, further comprising:

5. At least one of elemental technology A1 and elemental technology A2, At least one of elemental technology B1 and elemental technology B2; At least one of element technology B3a, element technology B3b, element technology B4, element technology B5a, element technology B5b, and element technology B6; 3. The vehicle side module according to claim 2, further comprising: