Blank, method for producing structural component, and structural component

Abstract

A blank (20, 20A, 20B, 20C) for hot stamping is provided with a plurality of steel plates. The plurality of steel plates are arranged and joined so as to have an annular shape in plan view of the blank (20, 20A, 20B, 20C). The plurality of steel plates includes steel plates (21, 22). The first steel plate (21) has a minimum plate thickness (tmin). The plate thickness of the second steel plate (22) is greater than the plate thickness (tmin) of the first steel plate (21). The steel sheet (21, 22) is a plated steel sheet having a base steel sheet (21a, 22a) and an aluminum-based plating layer (21b, 22b). The deposition amount (W1) of the plating layer (21b) on the first steel sheet (21) is less than the deposition amount (W2) of the plating layer (22b) on the second steel sheet (22).

Description

Technical Field

[0001] This disclosure relates to blanks for hot stamping. Additionally, this disclosure relates to a method for manufacturing structural components using the blanks, and to structural components thereof. Background Technology

[0002] Automobile bodies and other structural components are formed from multiple structural parts. These structural parts are manufactured, for example, by stamping blanks. To ensure high strength and good dimensional accuracy, structural parts are sometimes manufactured using a stamping method known as hot stamping. Hot stamping is a technique in which a blank, made of steel sheet, is heated to a temperature within the austenitic region, then stamped using a die, and the blank is held within the die and subjected to heat dissipation (rapid cooling), thereby achieving quenching.

[0003] Patent Document 1 discloses an overlapping blank for hot stamping. The overlapping blank in Patent Document 1 includes a first steel plate and a second steel plate with an area smaller than the first steel plate. The second steel plate overlaps the surface of the first steel plate and is welded to the first steel plate. Both the first and second steel plates are aluminized steel plates, and the coating thickness on both surfaces is 20 g / m². 2 Above and 120g / m 2 The following applies. When the average adhesion amount of the aluminum-based coating on both surfaces of the first steel plate is defined as W1, the adhesion amount of the aluminum-based coating on the surface of the second steel plate that is not in contact with the first steel plate is defined as W2, the thickness of the first steel plate is defined as t1, and the thickness of the second steel plate is defined as t2, the overlapping blank in Patent Document 1 satisfies 30 ≤ (W1 - W2) ≤ 100 and (W1 / W2). 2 The relationship is ×(t1 / t2)≥1.5. According to Patent Document 1, by satisfying these relationships, for the overlapping portion of the first steel plate and the second steel plate, the alloying reaction of the coating that increases emissivity during hot stamping can be rapidly carried out on the surface.

[0004] Patent Document 2 discloses a method for manufacturing a vehicle body side structure frame from multiple blanks. In Patent Document 2, multiple blanks are joined to form a composite blank, and the vehicle body side structure frame is manufactured by stamping the composite blank. Patent Document 2 describes the hot forming (hot stamping) of the composite blank.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent No. 6642777

[0008] Patent Document 2: Japanese Patent Publication No. 2021-528248 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In recent years, to simplify the manufacturing process of structures, the integration of two or more components from the blank stage has been studied. Patent Document 2 discloses, for example, the hot stamping of a composite blank having a ring shape when viewed from above, and the forming of a ring-shaped vehicle body side structure frame integrally formed from pillars, sill beams, etc. However, when the composite blank contains steel plates of different thicknesses, the performance of the formed structural component may be reduced. Specifically, during hot stamping, the blank is heated in a furnace until its microstructure becomes austenitic, and then formed by a die. However, the thinner steel plate is cooled more easily than the thicker steel plate, so in the portion of the blank containing the thinner steel plate, the phase transformation to ferrite begins before the blank is removed from the furnace and forming begins, and the hardenability may deteriorate. Due to the localized deterioration of the hardenability of the blank, uneven hardness occurs in the structural component formed from the blank, and its impact absorption performance may be reduced. In addition, due to the localized deterioration of hardenability, uneven stress occurs in the structural component. Therefore, especially in the case of ring-shaped structural components, twisting is likely to occur, and dimensional accuracy may deteriorate. The larger the ring-shaped structural component, the more significant the reduction in impact absorption performance (collision resistance) caused by the deterioration of hardenability or dimensional accuracy.

[0011] The problem of this disclosure is to provide a blank for hot stamping that can improve the performance of annular structural components, particularly large annular structural components, when forming annular structural components containing steel plates with a thickness smaller than that of other steel plates.

[0012] Solution for solving the problem

[0013] The hot stamping blank disclosed herein comprises multiple steel plates. The multiple steel plates are arranged and joined in a ring-like manner when the blank is viewed from above. The multiple steel plates include a first steel plate and a second steel plate. The first steel plate has the smallest thickness among the multiple steel plates. The second steel plate has a thickness greater than that of the first steel plate. The first and second steel plates are respectively clad steel plates. The clad steel plates have a base steel plate and an aluminum-based coating. The aluminum-based coating covers both surfaces of the base steel plate. The amount of aluminum-based coating on the first steel plate relative to both surfaces of the base steel plate (g / m²) is... 2 The amount of aluminum coating in the second steel plate adhered to both surfaces of the base steel plate (g / m²) 2 )few.

[0014] Invention Effects

[0015] According to the hot stamping blank disclosed herein, when forming annular structural components, particularly large and annular structural components, which contain steel plates with a thickness smaller than other steel plates, the performance of the component can be improved. Attached Figure Description

[0016] Figure 1 This is a top view of the structural components of the first embodiment.

[0017] Figure 2 yes Figure 1 Sectional view II-II.

[0018] Figure 3A This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment, and a diagram showing the blank of the first embodiment.

[0019] Figure 3B This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment, and a diagram showing the blank of the first embodiment.

[0020] Figure 3C This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment, and a diagram showing the blank of the first embodiment.

[0021] Figure 3D This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment, and a diagram showing the blank of the first embodiment.

[0022] Figure 3E This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0023] Figure 3F This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0024] Figure 3G This is a schematic diagram illustrating the manufacturing method of the structural component of the first embodiment.

[0025] Figure 4A This is a cross-sectional view of a structural component manufactured by the manufacturing method of the first embodiment.

[0026] Figure 4B This is another cross-sectional view of a structural component manufactured by the manufacturing method of the first embodiment.

[0027] Figure 4C This is another cross-sectional view of a structural component manufactured by the manufacturing method of the first embodiment.

[0028] Figure 5 This is a top view of the blank in the second embodiment.

[0029] Figure 6 yes Figure 5 Sectional view VI-VI.

[0030] Figure 7This is a top view of the structural components of the second embodiment.

[0031] Figure 8 This is a cross-sectional view of the blank in the third real mode.

[0032] Figure 9 This is a cross-sectional view of the blank in the fourth embodiment.

[0033] Figure 10 This is a top view of the structural components in the variations of each embodiment.

[0034] Figure 11A This is a diagram showing the segmentation pattern of the structural components in the first embodiment.

[0035] Figure 11B This is a diagram showing other partitioning patterns of the structural components in the first embodiment.

[0036] Figure 11C This is a diagram showing other partitioning patterns of the structural components in the first embodiment.

[0037] Figure 11D This is a diagram showing other partitioning patterns of the structural components in the first embodiment.

[0038] Figure 11E This is a diagram showing other partitioning patterns of the structural components in the first embodiment.

[0039] Figure 11F This is a diagram showing other partitioning patterns of the structural components in the first embodiment.

[0040] Figure 11G This is a diagram showing other partitioning patterns of the structural components in the first embodiment.

[0041] Figure 12A This is a diagram showing the segmentation pattern of the structural components in the second embodiment.

[0042] Figure 12B This is a diagram showing other partitioning patterns of the structural components in the second embodiment.

[0043] Figure 12C This is a diagram showing other partitioning patterns of the structural components in the second embodiment.

[0044] Figure 12D This is a diagram showing other partitioning patterns of the structural components in the second embodiment. Detailed Implementation

[0045] The hot stamping blank of the embodiment comprises multiple steel plates. The multiple steel plates are arranged and joined in a ring-like manner when the blank is viewed from above. The multiple steel plates include a first steel plate and a second steel plate. The first steel plate has the smallest thickness among the multiple steel plates. The second steel plate has a thickness greater than that of the first steel plate. The first and second steel plates are respectively coated steel plates. The coated steel plates have a base steel plate and an aluminum-based coating. The aluminum-based coating covers both surfaces of the base steel plate. The amount of aluminum-based coating on the first steel plate relative to both surfaces of the base steel plate (g / m²) is... 2 The amount of aluminum coating in the second steel plate adhered to both surfaces of the base steel plate (g / m²) 2 Less (the first component).

[0046] The blank of the first composition includes a first steel plate with the smallest thickness and a second steel plate with a thickness greater than that of the first steel plate. Both the first and second steel plates are coated steel plates with an aluminum-based coating. However, the first steel plate has less aluminum-based coating adhering to both surfaces of the base steel plate than the second steel plate. Therefore, when the blank is heated during hot stamping, the alloying of the aluminum-based coating with iron occurs on the surface of the thinner-walled first steel plate before that of the relatively thicker-walled second steel plate, causing both surfaces of the first steel plate to change from silvery-white to black or near-black. Consequently, the emissivity of both surfaces of the first steel plate is higher than that of the second steel plate. Therefore, the first steel plate can be heated to the temperature of the austenitic region more quickly, ensuring a longer holding time at that temperature. Consequently, the austenite grains in the first steel plate can be coarsened. As a result, the ferrite transformation region (ferrite nose) in the CCT line diagram shifts towards the long-time side. Therefore, after the blank heating is completed, the start of the ferrite transformation of the first steel plate can be delayed, and the blank forming can begin while maintaining the microstructure of the first steel plate in an austenitic state. That is, the hardenability of the thinner first steel plate can be improved.

[0047] In the first-component blank, the hardenability of the thinner first steel plate is improved, allowing for effective quenching of the first steel plate during hot stamping of the structural component. This results in more uniform hardness of the structural component, suppressing localized strength reduction. Furthermore, stress unevenness is less likely to occur within the structural component, minimizing distortion even when the formed component is annular, ensuring good dimensional accuracy. Therefore, when forming annular structural components, particularly large annular components, from a blank containing a first steel plate thinner than the second steel plate, it reduces strength and dimensional inaccuracies and improves impact absorption (collision resistance).

[0048] In the first-component blank, the amount of aluminum-based coating adhering in the first steel plate with the smallest plate thickness is less than that in the second steel plate with the larger plate thickness. In this case, the first steel plate heats up faster than the second steel plate, and compared to the case where the amount of aluminum-based coating is the same in both plates, the high-temperature holding time of the first steel plate—that is, the time from when the first steel plate reaches the austenitic region until the second steel plate and the entire blank reach the austenitic region—is longer. Therefore, the inhomogeneity of the phase transformation caused by the difference in cooling rates between the steel plates is reduced after the blank heating is complete. Specifically, for the first steel plate with the smallest plate thickness, the start of the phase transformation from austenite to ferrite can be delayed, and the difference in phase transformation start time between the first steel plate with the smallest plate thickness and other steel plates becomes smaller. As a result, hardenability can be homogenized between the first steel plate with the smallest plate thickness and other steel plates.

[0049] In the first-formed blank, it is preferable to set the thickness of the first steel plate to t. min Let the thickness of the steel plate with the largest thickness among multiple steel plates be t. max At that time, 1.0 <t max / t min ≤3.2 (second component).

[0050] The blank contains multiple steel plates with the smallest plate thickness t. min The first steel plate and the one with the largest plate thickness t max When the thickness difference of other steel plates is large, it is difficult to ensure the process window during the manufacturing of structural components. For example, with the minimum plate thickness t min With maximum plate thickness t max When the difference is large, during hot stamping, while heating the blank, wait for the maximum plate thickness t. max During the period when the steel sheet reaches the temperature of the austenitic region, in the first steel sheet that is first heated to the temperature of the austenitic region, the alloying of the aluminum-based coating is over-alloyed, and the diffusion layer becomes thicker, sometimes making it impossible to ensure the corrosion resistance or weldability of the first steel sheet based on this coating. Therefore, in the second configuration, the maximum plate thickness t is... max Relative to minimum plate thickness t min The ratio is set to 3.2 or less. Therefore, the maximum plate thickness t is achieved. max The heating rate of the steel plate is related to the minimum plate thickness t min The heating rate of the first steel plate does not deviate excessively, thus allowing the heating of other steel plates to be completed before the alloying of the aluminum-based coating on the first steel plate proceeds. Therefore, structural components can be manufactured while maintaining the corrosion resistance or weldability of the first steel plate, ensuring a process window during the manufacturing process.

[0051] The blank of the first or second configuration may also have an overlapping portion. The overlapping portion is formed by overlapping the ends of two adjacent steel plates from a plurality of steel plates. The overlapping portion has, for example, a total plate thickness of 4.0 mm or less. The two steel plates may also be coated steel plates having a base steel plate and an aluminum-based coating covering both surfaces of the base steel plate, respectively. In this case, it is preferable that the amount of aluminum-based coating on each of the two steel plates relative to the two surfaces of the base steel plate (g / m²) is... 2 The amount of aluminum coating in the second steel plate adhered to both surfaces of the base steel plate (g / m²) 2 Less (the third component).

[0052] In cases where an overlap exists in the blank formed by the ends of two steel plates overlapping each other, it is sometimes difficult to ensure the process window during the manufacturing of structural components. Specifically, during hot stamping, while the blank is being heated and the overlap is waiting to reach the temperature of the austenitic region, the aluminum-based coating of the first steel plate with the smallest plate thickness is alloyed, resulting in a thicker diffusion layer. This can sometimes compromise the corrosion resistance or weldability of the first steel plate based on this coating. Therefore, in the third configuration, for each steel plate forming the overlap, the amount of aluminum-based coating adhering to both surfaces of the base steel plate is less than that of the second steel plate. This promotes the heating of the overlap, allowing the heating of the overlap to be completed before the alloying of the coating on the first steel plate becomes excessive, enabling the manufacturing of structural components while maintaining the corrosion resistance or weldability of the first steel plate. In other words, the process window during the manufacturing of structural components is easily ensured. Furthermore, in the third configuration, the total plate thickness of the overlap is limited to 4.0 mm or less, so the heating of the overlap relative to the first steel plate does not become too slow, further ensuring the process window.

[0053] In the blank of the third configuration, the outer surface of at least one of the two steel plates located at the overlap may be covered with a black coating (fourth configuration).

[0054] In the fourth configuration, a black coating is applied to the outer surface of at least one of the two steel plates forming the overlapping section. This increases the emissivity of the overlapping section, thereby accelerating the heating process. Therefore, it is easier to ensure the process window during the manufacturing of the structural component.

[0055] In the blank according to any one of the first to fourth configurations, at least one surface of the first steel plate may be covered with a black coating (fifth configuration).

[0056] In the fifth configuration, a black coating is applied to at least one surface of the first steel plate with the smallest plate thickness. This increases the emissivity of the surface of the first steel plate beforehand, thus allowing for faster heating of the first steel plate when heating the blank during hot stamping. Consequently, a longer high-temperature holding time for the first steel plate is ensured, further promoting the coarsening of austenite grains in the first steel plate. As a result, the hardenability of the thinner first steel plate can be further improved.

[0057] The manufacturing method of the structural component in the embodiment includes: a step of preparing a blank of any one of the first to fifth components; a step of heating the plurality of steel plates contained in the blank to a temperature above the austenitic phase transformation completion temperature; and a step of forming the heated blank into a ring-shaped structural component in plan view using a mold and then quenching it (sixth component).

[0058] The structural component of the embodiment includes a component body. The component body is formed of multiple steel plates joined together and has a ring shape when viewed from above. The multiple steel plates include a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate. The first steel plate and the second steel plate are coated steel plates having an aluminum-based coating on both surfaces of the base steel plate. The thickness of the aluminum-based coating in the first steel plate is smaller than the thickness of the aluminum-based coating in the second steel plate (seventh configuration).

[0059] The structural component of the 7th component can also be a door ring component of an automobile. The main body of the component can include the front pillar, the middle pillar, and the sill beam (8th component) that connects the front pillar and the middle pillar.

[0060] The following is a reference to the appendix. Figure 1 The embodiments of this disclosure will be described below. In each figure, the same or equivalent components are labeled with the same reference numerals, and the same descriptions are not repeated.

[0061] <First Implementation>

[0062] [Structural components]

[0063] Figure 1 This is a top view (top view) of the structural component 10 of this embodiment placed on a horizontal plane. The structural component 10 is, for example, used in the body of a car. Typically, the structural component 10 is a door ring component of a car. In this embodiment, an example of the structural component 10 being a door ring component will be described.

[0064] Structural component 10 is a hot-stamped component. That is, structural component 10 is formed by hot stamping (hot pressing) a blank composed of multiple steel plates. Structural component 10 includes a component body 11. The component body 11 has a ring shape when viewed from above. The component body 11 includes a front pillar 111, a center pillar 112, and a door sill beam 113. When structural component 10 is assembled into the body of a vehicle, the center pillar 112 is positioned behind the front pillar 111. The center pillar 112 extends generally along the vertical direction of the vehicle body. The front pillar 111 extends toward the center pillar 112. When structural component 10 is assembled into the body of a vehicle, the door sill beam 113 is positioned below the front pillar 111 and the center pillar 112. The door sill beam 113 connects the front pillar 111 and the center pillar 112.

[0065] In this embodiment, the main body 11 of the component is formed by a plurality of steel plates 21, 22, and 23 that are joined together. Figure 1 In the example, the front pillar 111 is mainly composed of steel plates 21 and 22. The middle pillar 112 is mainly composed of steel plate 23. The sill beam 113 is composed of steel plates 21 and 23.

[0066] Figure 2 yes Figure 1 Sectional view II-II. Figure 2 The image shows a cross-section obtained by cutting the structural member 10 along the thickness direction of the steel plate 21 at the location of the steel plate 21. Figure 2 As shown, steel plate 21 has an open cross-section. In cross-section of structural member 10, steel plate 21 has, for example, a generally cap-shaped form. More specifically, steel plate 21 includes a top plate 211, longitudinal walls 212 and 213, and flanges 214 and 215. Longitudinal walls 212 are located on the side opposite to longitudinal wall 213 relative to the top plate 211. In cross-section of structural member 10, one end of longitudinal walls 212 and 213 is connected by the top plate 211. In cross-section of structural member 10, flanges 214 and 215 are connected to the other ends of longitudinal walls 212 and 213, respectively. Flanges 214 and 215 project outwards from longitudinal walls 212 and 213, respectively, towards the outside of structural member 10.

[0067] In structural component 10, the width W of steel plate 21 can be 30 mm or more and 750 mm or less. The height H of steel plate 21 can be 25 mm or more and 150 mm or less. Width W is the distance in the cross-section of structural component 10 from the rounded end of the corner between top plate 211 and longitudinal wall 212 on the side of longitudinal wall 212 to the rounded end of the corner between top plate 211 and longitudinal wall 213 on the side of longitudinal wall 213. Height H is the distance along the thickness direction of top plate 211 from top plate 211 to flanges 214 and 215.

[0068] Although the illustration is omitted, the other steel plates 22 and 23 also have open sections, similar to steel plate 21. Steel plates 22 and 23 may also have, for example, a generally cap-shaped section when viewed in section of structural member 10. The widths of steel plates 22 and 23 may be 15 mm or more and 300 mm or less, respectively. The heights of steel plates 22 and 23 may be 10 mm or more and 150 mm or less, respectively.

[0069] The size of the ring-shaped structural component 10 when viewed from above is, for example, 1.0m or more. The size of the structural component 10 may also be, for example, 4.0m or less. The size of the structural component 10 refers to the length of the line segment connecting the two furthest points on the outer periphery of the structural component 10 when viewed vertically while the structural component 10 is placed on a horizontal plane.

[0070] [Manufacturing methods for structural components]

[0071] The following is for reference Figures 3A-3G The manufacturing method of the structural component 10 will be described. The manufacturing method of the structural component 10 in this embodiment includes: a step of preparing a blank 20; a step of heating the blank 20; and a step of forming the heated blank 20 into the structural component 10.

[0072] [Preparation Process]

[0073] like Figure 3A As shown, in the preparation process, a blank 20 with a shape formed by unfolding the structural component 10 is prepared. The blank 20 includes a plurality of steel plates 21, 22, and 23. The steel plates 21, 22, and 23 are arranged and joined in a ring-like manner when the blank 20 is viewed from above.

[0074] Figure 3B , Figure 3C and Figure 3D This is a cross-sectional view of the blank 20 showing the joint of steel plates 21, 22, and 23. Figure 3B , Figure 3C and Figure 3D They are respectively Figure 3A Sectional views IIIB-IIIB, IIIC-IIIC, and IIID-IIID. (Refer to...) Figure 3B and Figure 3C Steel plate 21 is butt-joined with steel plates 22 and 23 respectively. That is, these end faces are joined while the end face of steel plate 21 is in contact with the end face of steel plate 22, and these end faces are joined while the other end faces of steel plate 21 are in contact with the end face of steel plate 23. (Refer to...) Figure 3DIn addition to butt-joining with steel plate 21, steel plate 22 is also butt-joined with steel plate 23. The end face of steel plate 22 is joined to the end face of steel plate 23 in an abutting state. Steel plates 21, 22, and 23 are joined, for example, by laser welding. In this embodiment, blank 20 is a so-called welded plate.

[0075] Reference Figure 3B and Figure 3C Among steel plates 21, 22, and 23, steel plate 21 has the smallest plate thickness t. min Steel plate 22 has a thickness t greater than that of steel plate 21. min Large plate thickness. Steel plate 23 has the same plate thickness t as steel plate 21. min The above refers to the plate thickness. In this embodiment, the thickness of each of steel plates 22 and 23 is greater than the thickness t of steel plate 21. min Large. In this embodiment, steel plate 23 has the largest plate thickness t among steel plates 21, 22, and 23. max Steel plate 22 has a thickness t greater than that of steel plate 21. min Larger and thicker than steel plate 23 t max Small plate thickness t mid However, steel plate 22 can also have a thickness greater than that of steel plate 23. That is, among steel plates 21, 22, and 23, steel plate 22 can also have the largest thickness t. max .

[0076] In a typical case, the plate thickness t of steel plate 21 min Less than 1.4mm. Plate thickness t min For example, it can be 0.8mm or more. The plate thickness t of steel plate 21 min And the thickness t of steel plate 23 max Preferably, it satisfies 1.0. <t max / t min ≤3.2, more preferably 1.3≤t max / t min ≤3.2.

[0077] Steel plates 21, 22, and 23 are clad steel plates, more specifically, aluminized steel plates. Steel plate 21 has a base steel plate 21a and an aluminum-based coating 21b. Steel plate 22 has a base steel plate 22a and an aluminum-based coating 22b. Steel plate 23 has a base steel plate 23a and an aluminum-based coating 23b. The thickness t of steel plate 21 is... min This is the total thickness of the base steel plate 21a and the aluminum coating 21b, representing the average thickness of steel plate 21. The thickness t of steel plate 22... mid This is the total thickness of the base steel plate 22a and the aluminum coating 22b; it is the average thickness of steel plate 22. The thickness t of steel plate 23... max It is the total thickness of the base steel plate 23a and the aluminum coating 23b, and is the average thickness of the steel plate 23.

[0078] There are no particular restrictions on the types of base steel plates 21a, 22a, and 23a. Base steel plates 21a, 22a, and 23a can be the same as or different from other base steel plates.

[0079] In steel plate 21, an aluminum-based coating 21b covers both surfaces of the base steel plate 21a. The aluminum-based coating 21b is applied to the entirety or substantially throughout both surfaces of the base steel plate 21a. Similarly, in steel plate 22, an aluminum-based coating 22b covers both surfaces of the base steel plate 22a. The aluminum-based coating 22b is applied to the entirety or substantially throughout both surfaces of the base steel plate 22a. Furthermore, in steel plate 23, an aluminum-based coating 23b covers both surfaces of the base steel plate 23a. The aluminum-based coating 23b is applied to the entirety or substantially throughout both surfaces of the base steel plate 23a.

[0080] The chemical composition of the aluminum-based coatings 21b, 22b, and 23b is not particularly limited. Known aluminum-based coatings (coatings with aluminum as the main component) can be used as the aluminum-based coatings 21b, 22b, and 23b. Although not particularly limited, the aluminum-based coatings 21b, 22b, and 23b can be, for example, Al-Si based coatings. The aluminum-based coatings 21b, 22b, and 23b can be the same as or different from the aluminum-based coatings of other steel plates 21, 22, and 23, respectively.

[0081] Reference Figure 3B In the case of having the minimum plate thickness t min The amount of aluminum-based coating 21b in steel plate 21 adhered to both surfaces of the base steel plate 21a is set as W1 (g / m). 2 ), will have a larger plate thickness t mid The amount of aluminum-based coating 22b in steel plate 22 adhering to both surfaces of the base steel plate 22a is set as W2 (g / m). 2 When the aluminum-based coating 21b in steel plate 21 is less than the aluminum-based coating 22b in steel plate 22, the adhesion amount W1 is less than the adhesion amount W2 of the aluminum-based coating 22b in steel plate 22. The adhesion amount W1 of the aluminum-based coating 21b in steel plate 21 is the average adhesion amount on both surfaces of the base steel plate 21a. Typically, the adhesion amount (g / m²) of the aluminum-based coating 21b relative to one surface of the base steel plate 21a is... 2 The amount of aluminum-based coating 21b adhering to the other surface of the base steel plate 21a (g / m²) 2 The amounts of aluminum-based coating 21b are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating 21b may vary between the surface and the back of the base steel plate 21a. The amount of aluminum-based coating 21b may also differ between one and the other surface of the base steel plate 21a. The amount of aluminum-based coating 22b W2 in the steel plate 22 is the average amount of aluminum-based coating 22b on both surfaces of the base steel plate 22a. The amount of aluminum-based coating 22b relative to one surface of the base steel plate 22a (g / m²)2 The amount of aluminum-based coating 22b typically adhered to the other surface of the base steel plate 22a (g / m²). 2 They are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating 22b may vary between the surface and the back of the base steel plate 22a. The amount of aluminum-based coating 22b may also differ between one surface and the other.

[0082] The adhesion amount W1 of the aluminum-based coating 21b in steel plate 21 and the adhesion amount W2 of the aluminum-based coating 22b in steel plate 22 can also be 20 g / m². 2 Above and 120g / m 2 The following are preferred adhesion amounts: W1 and W2 are both 30 g / m². 2 The above, preferably 35g / m 2 The above. The preferred adhesion amounts W1 and W2 are 115 g / m². 2 The following is more preferably 100g / m 2 The following is the difference between the adhesion amounts W1 and W2: W2 - W1 is, for example, 10 (g / m³). 2 ) or above. W2-W1 is preferably 20 (g / m³). 2 ) or more, more preferably 30 (g / m 2 W2-W1 can also be 80 (g / m³). 2 Below ) . W2-W1 is preferably 70 (g / m 2 ) or less, more preferably 60 (g / m 2 Below that. Furthermore, the adhesion amounts W1 and W2 satisfy the relationship W2 / W1>1.0. Preferably, the adhesion amounts W1 and W2 satisfy the relationship W2 / W1≥1.2, and more preferably W2 / W1≥1.5.

[0083] Reference Figure 3D In the case of the plate with the maximum thickness t max The adhesion amount of the aluminum-based coating 23b in the steel plate 23 relative to the two surfaces of the base steel plate 23a is set as W3 (g / m). 2 When the aluminum-based coating 23b in steel plate 23 is less than the aluminum-based coating 22b in steel plate 22, the adhesion amount W3 can also be less. The adhesion amount W3 of the aluminum-based coating 23b is the average adhesion amount on both surfaces of the base steel plate 23a. Typically, the adhesion amount (g / m²) of the aluminum-based coating 23b relative to one surface of the base steel plate 23a is... 2 The amount of aluminum-based coating 23b adhering to the other surface of the base steel plate 23a (g / m²) 2They are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating 23b may vary between the surface and the back of the base steel plate 23a. The amount of aluminum-based coating 23b may also differ between one surface and the other surface of the base steel plate 23a.

[0084] The amount of aluminum coating 23b in steel plate 23 can also be the same as that in steel plates 21 and 22, for example, 20 g / m³. 2 Above and 120g / m 2 The following is a preferred adhesion amount W3: 30 g / m³. 2 The above, preferably 35g / m 2 The above. The preferred adhesion amount W3 is 115 g / m³. 2 The following is more preferably 100g / m 2 The following applies when W2 > W3, the difference between the adhesion amounts W2 and W3: W2 - W3 is, for example, 10 (g / m³). 2 ) or above. W2-W3 is preferably 20 (g / m³). 2 ) or more, more preferably 30 (g / m 2 W2-W3 can also be 80 (g / m³). 2 Below ) . W2-W3 is preferably 70 (g / m 2 ) or less, more preferably 60 (g / m 2 The following applies. The amount W3 of aluminum-based coating 23b adhering to steel plate 23 can be compared with the minimum plate thickness t. min The amount of aluminum coating 21b on the steel plate 21 is equal to or greater than the amount of aluminum coating 21b.

[0085] The method for forming aluminum-based coatings 21b, 22b, and 23b on base steel plates 21a, 22a, and 23a is not particularly limited; for example, a conventional hot-dip galvanizing method can be used. Specifically, by immersing the base steel plate 21a in a hot-dip aluminizing bath and wiping it with nitrogen, atmosphere, or other gases, an aluminized steel plate 21 with an adjusted adhesion amount W1 of the aluminum-based coating 21b can be obtained. Similarly, by immersing the base steel plate 22a in a hot-dip aluminizing bath and wiping it with nitrogen, atmosphere, or other gases, an aluminized steel plate 22 with an adjusted adhesion amount W2 of the aluminum-based coating 22b can be obtained. Furthermore, by immersing the base steel plate 23a in a hot-dip aluminizing bath and wiping it with nitrogen, atmosphere, or other gases, an aluminized steel plate 23 with an adjusted adhesion amount W3 of the aluminum-based coating 23b can be obtained. When an aluminum-based coating is formed by hot-dip galvanizing, an Al-Fe alloy layer is formed at the interface between the base steel plate and the aluminum-based coating by the dissolution of Fe during the hot-dip galvanizing process.

[0086] As a method for determining the adhesion amounts W1, W2, and W3 of aluminum-based coatings 21b, 22b, and 23b, for example, the sodium hydroxide-hexamethylenetetramine-hydrochloric acid peeling gravimetric method described in JIS G3314:2019 can be cited. Specifically, according to JIS G3314:2019, at least five specified surface areas S (mm²) are collected from the steel plates 21, 22, and 22 of the blank 20. 2 Test pieces (e.g., 50mm × 50mm) were used, and the weight w1 (g) of each test piece was measured. Then, each test piece was immersed in a sodium hydroxide aqueous solution. After confirming that the foaming caused by the dissolution of the coating had disappeared, the test pieces were removed from the sodium hydroxide aqueous solution and washed with water. Next, the wetted test pieces were immersed in a hydrochloric acid aqueous solution containing hexamethylenetetramine until the foaming caused by the dissolution of the coating disappeared. The test pieces removed from the hexamethylenetetramine hydrochloric acid aqueous solution were immediately washed with water and dried, and the weight w2 (g) of the test pieces was measured again. The adhesion amount W (g / m²) of the aluminum-based coating on each test piece was determined. 2 It can be achieved through {(w1-w2) / S}×10 6 The average adhesion amount W of five or more test pieces collected from each steel plate is taken as the adhesion amount of the aluminum-based coating in that steel plate.

[0087] However, when the test pieces collected from each of the steel plates 21, 22, and 22 are relatively small, the thickness (μm) of each aluminum-based coating 21b, 22b, and 23b is measured using an optical microscope (area: 100μm × 100μm) in three fields of view. The average thickness measured in the three fields of view is multiplied by three to convert it into the adhesion amount. At this time, for each of the steel plates 21, 22, and 22, the adhesion amount is calculated for each single side of the base steel plate, and the average of the obtained adhesion amounts (average of both sides) is taken as the adhesion amount of the aluminum-based coating. When an Al-Fe alloy layer exists at the interface between the base steel plate and the aluminum-based coating, the thickness of the aluminum-based coating also includes the thickness of the Al-Fe alloy layer. The thickness of the aluminum-based coating 21b on the thinnest steel plate 21 is smaller than the thickness of the aluminum-based coating 22b on the other steel plates 22. In this embodiment, the thickness of the aluminum-based coating 23b on the thickest steel plate 23 is also smaller than the thickness of the aluminum-based coating 22b on the steel plate 22. The thicknesses of the aluminum-based coatings 21b and 23b can be different from each other or the same.

[0088] (Heating process)

[0089] The prepared blank 20 is formed into structural component 10 by hot stamping (hot pressing). Figure 1 and Figure 2 During hot stamping, blank 20 is supplied to the heating process. (Refer to...) Figure 3EIn the heating process, for example, the blank 20 is heated using a heating furnace 30. The multiple steel plates 21, 22, and 23 contained in the blank 20 are heated to the austenitic phase transformation completion temperature (A). c3 (Points) or above. Steel plates 21, 22, and 23 are, for example, heated to above 900°C. As a result, the microstructure of steel plates 21, 22, and 23 is, for example, wholly or substantially transformed into the austenitic phase.

[0090] (Forming process)

[0091] Reference Figure 3F In the forming process, the heated blank 20 is formed into a ring-shaped structural component 10 when viewed from above using a mold 40. Figure 1 and Figure 2 The blank 20, after being heated through the heating process, is then removed from the heating furnace 30 (and quenched). Figure 3E The blank 20 is removed and conveyed to the die 40. The die 40 is mounted on a known stamping device. The die 40 includes, for example, a punch 41 and a die 42. The blank 20 is disposed between the punch 41 and the die 42.

[0092] Reference Figure 3G After the blank 20 is positioned between the punch 41 and the die 42, the die 42 is relatively close to the punch 41. The blank 20 is clamped (stamped) by the punch 41 and the die 42, forming a shape along the forming surfaces of the punch 41 and the die 42. The blank 20 is held in the clamped state by the punch 41 and the die 42. The blank 20 dissipates heat through the die 40 (quenching), and its microstructure transforms into martensite. Thus, structural component 10 can be manufactured from the blank 20.

[0093] Figures 4A-4C This is a cross-sectional view of the structural component 10 after hot stamping. Figure 4A The figure shows the plate with minimum thickness t. min The cross section of structural component 10 at the location of steel plate 21. Figure 4B This indicates a plate thickness t greater than that of steel plate 21. mid The cross section of structural component 10 at the location of steel plate 22. Figure 4C Indicates the maximum plate thickness t max The cross section of structural component 10 at the location of steel plate 23.

[0094] Reference Figure 4A In the hot-stamped structural component 10, the steel plate 21 is also a coated steel plate with an aluminum-based coating 21b on both surfaces of the base steel plate 21a. (Refer to...) Figure 4B Steel plate 22 is a coated steel plate having an aluminum-based coating 22b on both surfaces of the base steel plate 22a. (Refer to...) Figure 4CSteel plate 23 is a coated steel plate having an aluminum-based coating 23b on both surfaces of the base steel plate 23a. However, compared with the blank 20 ( Figures 3B-3D Compared to the state of the previous one, the aluminum-based coatings 21b, 22b, and 23b in the structural component 10 are alloyed with iron through a heating process.

[0095] Reference Figure 4A and Figure 4B When the average thickness (plating thickness) of the aluminum-based coating 21b on both surfaces of the steel plate 21 is set as K1 (μm), and the average thickness (plating thickness) of the aluminum-based coating 22b on both surfaces of the steel plate 22 is set as K2 (μm), the plating thickness K1 of the steel plate 21 is smaller than the plating thickness K2 of the steel plate 22. The difference between plating thicknesses K1 and K2 is, for example, 7 (μm) or more. K2-K1 can also be 33 (μm) or less. In addition, the plating thicknesses K1 and K2 can satisfy the relationship that K2 / K1>1.0. K2 / K1 is preferably 1.2 or more, and more preferably 1.5 or more.

[0096] Reference Figure 4B and Figure 4C In this embodiment, when the average thickness (plating thickness) of the aluminum-based coating 23b on both surfaces of the steel plate 23 is set to K3 (μm), the plating thickness K3 of the steel plate 23 is smaller than the plating thickness K2 of the steel plate 22. The difference between plating thicknesses K2 and K3: K2-K3 is, for example, 7 (μm) or more. K2-K3 may also be 33 (μm) or less.

[0097] The coating thicknesses K1, K2, and K3 of the aluminum-based coatings 21b, 22b, and 23b in the structural component 10 can be measured as follows: The body component is disassembled to obtain a ring-shaped structural component 10, and an analytical sample is obtained from this structural component 10, for example, by laser cutting. For example, analytical samples are obtained from multiple steel plates included in the structural component 10. The analytical samples are obtained at or near the center of the top plate of each steel plate with an open cross-section. For the test pieces obtained from multiple steel plates, the cross-section of the aluminum-based coating can be etched with nitric acid ethanol and observed using an optical microscope (area: 100 μm × 100 μm). The coating thickness is measured in three fields of view, and the average of the coating thickness measured in the three fields of view is taken as the coating thickness. It is common for the outermost layer of the structural component 10 to have, for example, an electrodeposited coating. In this case, the coating layer existing below the electrodeposited coating layer and above the base steel plate is observed.

[0098] With minimum plate thickness t minIn the cross-section of the structural member 10 at the location of steel plate 21, the value obtained by subtracting the minimum martensite fraction from the maximum martensite fraction (%) is used as the deviation of the martensite fraction. For example, the deviation of the martensite fraction is 20% or less. Preferably, the deviation of the martensite fraction is 15% or less, more preferably 10% or less. The deviation of the martensite fraction can be measured as follows: that is, in the case of the minimum plate thickness t... min In the cross-section of the structural component 10 at the location of the steel plate 21, at least 10 analytical samples (e.g., approximately 10 mm in size on the long side) are cut out at positions at least 20 mm away from the end and at least 10 mm apart on each side. Each analytical sample is then mirror-polished with the plate thickness direction as the observation surface, and etched using Lepera reagent. Then, for a region at a depth of 1 / 4 of the plate thickness from the steel plate surface (from 1 / 8 to 3 / 8 of the plate thickness from the steel plate surface), 30 tissue photographs are taken at 1000x magnification using an optical microscope, with each field of view being 2400 μm. 2 The above describes the image analysis of the obtained tissue photographs.

[0099] As an image analysis method, the maximum brightness value Lmax and minimum brightness value Lmin of the image are obtained. Pixels with brightness values ​​between Lmax-0.3(Lmax-Lmin) and Lmax are designated as white regions. The proportion of pixels in the white regions to the total number of pixels is calculated to determine the martensite fraction. This image analysis is performed on a total of 30 observation fields for each analytical sample to determine the martensite fraction, and the average value is taken as the martensite fraction of each analytical sample. Furthermore, the difference between the maximum and minimum martensite fractions among 10 or more analytical samples is defined as the value with the minimum plate thickness t. min The deviation of the martensite fraction in the cross-section of structural component 10 at the location of steel plate 21. Multiple components with a minimum plate thickness t exist within structural component 10. min In the case of steel plates, the martensite fraction is calculated by performing such analysis on each steel plate, and the deviation of the largest martensite fraction among these steel plates is taken as the deviation of the martensite fraction in the structural component 10.

[0100] Furthermore, depending on the steel plate, the martensite area ratio obtained through image analysis, i.e., the area ratio of the white region, sometimes contains a few percent of the area ratio of retained austenite. However, since the deviation in the martensite fraction is calculated using differentials, its impact is negligible.

[0101] After the forming process (hot stamping), steel plates 21, 22, and 23 can, for example, have a tensile strength of 0.5 GPa or more, preferably 1.0 GPa or more. At least one of the steel plates 21, 22, and 23 can also have a tensile strength of 1.5 GPa or more after the forming process. The tensile strength of each of the steel plates 21, 22, and 23 can be the same as or different from the tensile strength of the other steel plates.

[0102] [Effect]

[0103] In the blank 20 of this embodiment, the minimum plate thickness t is... min The amount W1 of the aluminum-based coating 21b on the steel plate 21 is less than the amount W2 of the aluminum-based coating 22b on the steel plate 22, which has a greater plate thickness. Therefore, when heating the blank 20 during hot stamping, the heating rate of the steel plate 21 is significantly higher than that of the steel plate 22. Specifically, because the aluminum-based coating 21b on the surface of the steel plate 21 is thinner, when the blank 20 is heated, the alloying of the aluminum-based coating 21b with the iron contained in the base steel plate 21a proceeds rapidly to the surface of the steel plate 21, turning both surfaces of the steel plate 21 black or nearly black. That is, the emissivity of both surfaces of the steel plate 21 increases during the heating process. Therefore, the steel plate 21 can be heated to the temperature in the austenitic region more quickly, ensuring a longer high-temperature holding time for the steel plate 21. As a result, the austenite grains in the microstructure of the steel sheet 21 become coarser, and the ferrite phase transformation region (ferrite nose) in the CCT diagram shifts towards the longer-term side. Therefore, it is possible to prevent the austenite phase from transforming into ferrite in the steel sheet 21 from the time it is removed from the furnace 30 until forming with the die 40 begins. Thus, forming of the blank 20 with the die 40 can begin while maintaining the microstructure of the steel sheet 21 in an austenitic state, improving the minimum plate thickness t. min The hardenability of steel plate 21.

[0104] In this embodiment, the hardenability of the relatively thin-walled steel plate 21 is improved, thereby enabling the uniformity of hardness in the structural component 10 formed from the blank 20. More specifically, due to the minimum plate thickness t... min The steel plate 21 is also well quenched, thus ensuring that the deviation of the martensite fraction in the steel plate 21 is less than 20%. Therefore, for example, when a collision load is applied to the structural member 10, deformation concentration is less likely to occur, and the structural member 10 can easily exhibit high impact absorption performance. Therefore, even when a ring-shaped structural member 10, particularly a large and ring-shaped structural member 10, is formed from a blank 20 containing a thin steel plate 21, the strength defects of the structural member 10 can be reduced, and the impact absorption performance of the structural member 10 can be improved.

[0105] The smaller the deviation in martensite fraction, the less uneven the mechanical properties within the structural component 10, which is preferable from the viewpoint of the function of the structural component 10. On the other hand, if the deviation in martensite fraction is large, it means that there are parts with insufficient hardenability, i.e., insufficient hardness, within the structural component 10. When the structural component 10 undergoes collision deformation, the deformation tends to concentrate in the parts with insufficient hardness, thus reducing the function of the structural component 10.

[0106] In this embodiment, by improving the hardenability of the relatively thin-walled steel plate 21, it is difficult to generate stress unevenness in the structural component 10. Therefore, even when the annular structural component 10 is formed from the annular blank 20, the structural component 10 is less prone to twisting. Therefore, even when the annular structural component 10, which includes a steel plate 21 with a small plate thickness, is formed from the blank 20, especially a large and annular structural component 10, dimensional inaccuracies of the structural component 10 can be reduced, and the impact absorption performance of the structural component 10 can be improved.

[0107] In the blank 20 of this embodiment, the minimum plate thickness t min The amount W1 of aluminum-based coating 21b in steel plate 21 is less than the amount W2 of aluminum-based coating 22b in steel plate 22, which has a greater plate thickness than steel plate 21. Therefore, steel plate 21 can heat up faster than steel plate 22, and thus the high-temperature holding time of steel plate 21 is longer compared to cases where the amount W1 of aluminum-based coating 21b in steel plate 21 is the same as or greater than the amount W2 of aluminum-based coating 22b in steel plate 22. Therefore, after the blank 20 is heated, the unevenness of phase transformation caused by the difference in cooling rates between steel plates 21, 22, and 23 can be reduced. Specifically, for the minimum plate thickness t... min The steel plate 21 can delay the start of the phase transformation from austenite to ferrite, thus reducing the difference in phase transformation start time between steel plate 21 and other steel plates 22 and 23. As a result, the hardenability of the steel plates 21, 22, and 23 contained in the blank 20 can be homogenized.

[0108] In this embodiment, during the heating process, the plate with the minimum thickness t is first... min The steel plate 21 reaches the temperature of the austenitic region, and then, with an intermediate plate thickness t... mid Steel plate 22 and with the maximum plate thickness t max The steel plates 23 sequentially reach the temperatures of the austenitic region. Here, the minimum plate thickness t min With maximum plate thickness t max The ratio: t max / t min Preferably, it is 3.2 or less. Therefore, it is possible to achieve a plate thickness t by heating. minBefore the alloying of the aluminum-based coating 21b on the steel plate 21 is excessive, and the diffusion layer grows, thereby losing the corrosion resistance or weldability of the coating 21b, the plate will have a thickness t. max The steel plate 23 is heated sufficiently until the austenitic phase transformation is complete. Therefore, a process window can be ensured during the manufacturing of the structural component 10.

[0109] <Second Implementation Method>

[0110] Figure 5 This is a top view of the blank 20A of the second embodiment. The blank 20 of the first embodiment is a welded plate formed by butt jointing steel plates 21, 22, and 23. The blank 20A of this embodiment differs from that of the first embodiment mainly in the way the steel plates are joined.

[0111] Reference Figure 5 The blank 20A comprises multiple steel plates 21, 22, 23, 24, and 25. The steel plates 21, 22, 23, 24, and 25 are arranged and joined in a ring-like manner when viewed from above. Similar to the first embodiment, the steel plate 21 has a minimum plate thickness t. min The amount of aluminum coating adhered to the blank 20A is less than that of the other steel plates 22. Therefore, the blank 20A of this embodiment can also achieve the same effect as the first embodiment.

[0112] The blank 20A has an overlapping portion 26. Figure 6 yes Figure 5 The cross-sectional view VI-VI shows the cross-section of the overlapping portion 26. In this embodiment, the overlapping portion 26 is formed by overlapping the ends of two adjacent steel plates 23 and 24. The ends of steel plate 23 are joined to the ends of steel plate 24 in an overlapping state. The steel plates 23 and 24 are joined together, for example, by spot welding or laser welding.

[0113] In this embodiment, steel plates 23 and 24 are clad steel plates. That is, steel plate 23, like in the first embodiment, has a base steel plate 23a and an aluminum-based coating 23b. Similarly, steel plate 24 has a base steel plate 24a and an aluminum-based coating 24b. The base steel plates 23a and 24a can be of the same type or different types. Similarly, the aluminum-based coatings 23b and 24b can be of the same type or different types.

[0114] The overlapping portion 26 has a total plate thickness t. The total plate thickness t is the thickness obtained by adding the plate thickness t3 of steel plate 23 to the plate thickness t4 of steel plate 24. The total plate thickness t also includes the thickness of the aluminum-based coatings 23b and 24b of steel plates 23 and 24. The total plate thickness t of the overlapping portion 26 is, for example, greater than 2.5 mm. The total plate thickness t of the overlapping portion 26 is preferably 4.0 mm or less. In this case, the adhesion amount of the aluminum-based coating 23b in steel plate 23 relative to both surfaces of the base steel plate 23a is set to W3 (g / m²). 2 The adhesion amount of the aluminum-based coating 24b in steel plate 24 relative to the two surfaces of the base steel plate 24a is set as W4 (g / m). 2 When the adhesion amounts W3 and W4 are greater than the adhesion amount W2 of the aluminum-based coating 22b in steel plate 22 relative to the two surfaces of the base steel plate 22a, the adhesion amounts W3 and W4 are greater than the adhesion amounts W2 of the aluminum-based coating 22b in steel plate 22 relative to the two surfaces of the base steel plate 22a. Figure 3B and Figure 3D )few.

[0115] The adhesion amount W3 of the aluminum-based coating 23b in the steel plate 23 is the average adhesion amount on both surfaces of the base steel plate 23a. Typically, the adhesion amount (g / m²) of the aluminum-based coating 23b relative to one surface of the base steel plate 23a is... 2 The amount of aluminum-based coating 23b adhering to the other surface of the base steel plate 23a (g / m²) 2 The amounts of aluminum-based coating 23b are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating 23b may vary between the surface and the back surface of the base steel plate 23a. The amount of aluminum-based coating 23b may also differ between one and the other surface of the base steel plate 23a. The amount of aluminum-based coating 24b W4 in the steel plate 24 is the average amount of aluminum-based coating 24b on both surfaces of the base steel plate 24a. Typically, the amount of aluminum-based coating 24b relative to one surface of the base steel plate 24a (g / m²) is... 2 The amount of aluminum-based coating 24b adhering to the other surface of the base steel plate 24a (g / m²) 2 They are essentially equal. However, due to factors such as manufacturing conditions, the amount of aluminum-based coating 24b may vary between the surface and the back of the base steel plate 24a. The amount of aluminum-based coating 24b may also differ between one and the other surface of the base steel plate 24a. The amounts W3 and W4 may also be 20 g / m². 2 Above and 120g / m 2 The following are preferred adhesion amounts: W3 and W4 are each 30 g / m³. 2 The above, preferably 35g / m 2 The above. The preferred adhesion amounts W3 and W4 are 115 g / m³. 2 The following is more preferably 100g / m 2 The following is the difference between the adhesion amounts W2 and W3 between steel plates 22 and 23: W2-W3 is, for example, 20 (g / m²). 2W2-W3 can be 80 (g / m³) or above. 2 Similarly, the difference between the adhesion amounts W2 and W4 between steel plates 22 and 24: W2-W4 is, for example, 20 (g / m²). 2 Above 80 (g / m³). W2-W4 can be 80 (g / m³). 2 The following applies: The amount of aluminum-based coating 23b on steel plate 23 and the amount of aluminum-based coating 24b on steel plate 24 may be the same or different. Furthermore, the thickness t3 of steel plate 23 and the thickness t4 of steel plate 24 may be the same or different. The thickness t3 of steel plate 23 and the thickness t4 of steel plate 24 are the average thicknesses of steel plates 23 and 24, respectively, and also include the thicknesses of the aluminum-based coatings 23b and 24b.

[0116] The amount of aluminum-based coating 23b adhering to steel plate 23 and the amount of aluminum-based coating 24b adhering to steel plate 24 can be measured by the method described in the first embodiment.

[0117] When the total thickness t of the overlapping portion 26 exceeds, for example, 2.5 mm, the overlapping portion 26 is difficult to heat up. Therefore, during the heating of the blank 20A in hot stamping, the overlapping portion 26 has a minimum thickness t during the period until it reaches the temperature of the austenitic region. min The aluminum coating 21b of the steel plate 21 ( Figure 3B and Figure 3C When alloying is performed, the diffusion layer becomes thicker, which sometimes compromises the corrosion resistance or weldability of the steel plate 21. However, in this embodiment, since the emissivity of the overlapping portion 26 can be increased to promote heating, even when the total thickness t of the overlapping portion 26 is, for example, greater than 2.5 mm, the overlapping portion 26 can be sufficiently heated until the austenitic phase transformation is complete before the alloying of the aluminum-based coating 21b of the steel plate 21 occurs and the diffusion layer overgrows, thereby losing corrosion resistance or weldability. Therefore, a process window can be ensured during the manufacturing of the structural component.

[0118] In the blank 20A of this embodiment, the steel plate 21 can be butt-joined with the steel plates 22 and 23, or it can form an overlapping portion 26 with one or both of the steel plates 22 and 23. The steel plate 25 can be butt-joined with the steel plates 22 and 24, or it can form an overlapping portion 26 with one or both of the steel plates 22 and 24.

[0119] Figure 7 This is a top view of structural component 10A manufactured from blank 20A. Structural component 10A has the same characteristics as structural component 10 in the first embodiment (…). Figure 1 and Figure 2The structure is roughly the same. However, in structural component 10A, the main body 11 is formed from five steel plates 21, 22, 23, 24, and 25. The method for manufacturing structural component 10A from blank 20A is the same as in the first embodiment.

[0120] Structural member 10A can have the same size as structural member 10 in the first embodiment. That is, the size of structural member 10A, which is ring-shaped when viewed from above, is, for example, 1.0m or more and 4.0mm or less. In structural member 10A, steel plates 21, 22, 23, 24, and 25 each have an open cross-section, similar to those in the first embodiment. Each of steel plates 21, 22, 23, 24, and 25 can, for example, have a generally cap-shaped cross-section when the structural member 10A is viewed from above.

[0121] Although the illustrations are omitted, in structural component 10A, the width of the steel plate 21 disposed at the upper part of the front pillar 111 is, for example, 15 mm or more and 300 mm or less. The height of the steel plate 21 may also be 10 mm or more and 150 mm or less. In structural component 10A, the width of the steel plate 22 disposed at the lower part of the front pillar 111 is, for example, 30 mm or more and 750 mm or less. The height of the steel plate 22 may also be 25 mm or more and 150 mm or less. In structural component 10A, the width of the steel plates 23 and 24 disposed at the position of the middle pillar 112 is, for example, 15 mm or more and 300 mm or less. The height of the steel plates 23 and 24 may be 10 mm or more and 150 mm or less. In structural component 10A, the width of the steel plate 25 disposed at the position of the sill beam 113 is, for example, 30 mm or more and 300 mm or less. The height of the steel plate 25 may also be 25 mm or more and 150 mm or less.

[0122] <Third Implementation Method>

[0123] Figure 8 This is a cross-sectional view of the blank 20B according to the third embodiment. Figure 8 The figure shows the blank 20B with the minimum plate thickness t. min The joint between the steel plate 21 and the steel plate 22 with a greater plate thickness t2. Figure 8 The example shown is similar to that in the first embodiment. Figure 3B The only difference in the example shown is the structure of steel plate 21.

[0124] In this embodiment, one surface of the steel plate 21 is substantially covered by a black coating 27. On the other hand, the black coating 27 is not substantially applied to the steel plate 22. For example, the brightness L of the surface from the coating 27... * The value (CIE 1976 Luminance Index L as specified in JIS Z 8781-4:2013) *When the emissivity is below 60, it can be determined that the coating 27 is black. The coating 27 is applied to the entire surface of the steel plate 21. The coating 27 can also be a carbon-based surface treatment coating (a coating containing carbon (C)). By applying such a black coating 27, the emissivity of the surface of the steel plate 21 is higher than that of both surfaces of the steel plate 22. For example, at a measurement temperature of 25°C and a wavelength of 8.0 μm, the emissivity of the surface of the steel plate 21 is greater than that of both surfaces of the steel plate 22. The difference in emissivity between the steel plate 21 and the steel plate 22 at 25°C and a wavelength of 8.0 μm is preferably greater than 5%, more preferably greater than 10%, and even more preferably greater than 20%.

[0125] As the coating 27, for example, a surface treatment coating described in International Publication No. 2022 / 215229 can be used. That is, the coating 27 can contain carbon black, for example. The coating 27 can further contain a metal oxide. The metal oxide is, for example, one or more oxides selected from the group consisting of Zr oxide, Zn oxide and Ti oxide. The coating 27 may also contain silicon dioxide.

[0126] The coating 27 can contain graphite or soot instead of carbon black, or contain graphite or soot in addition to carbon black. Alternatively, to improve the emissivity of the steel plate 21, the coating 27 can also contain, for example, needle-like compounds with an aspect ratio of 4 or more and 50 or less and a hexagonal crystal structure. Typically, the compound with a hexagonal crystal structure is graphite (C), but it can also be lanthanum silicate, magnesium diboride, beryllium oxide, zinc oxide, β-quartz, goethite (NiS), wurtzite (ZnS), etc.

[0127] In this embodiment, for the minimum plate thickness t min A black coating 27 is applied to one surface of the steel plate 21. This increases the emissivity of the steel plate 21 beforehand, resulting in faster heating of the steel plate 21 when the blank 20B is heated during hot stamping. This ensures a longer holding time at high temperatures for the steel plate 21. Consequently, the hardenability of the thinnest steel plate 21 can be further improved.

[0128] In this embodiment, only one side of the steel plate 21 is covered by the coating 27. However, the coating 27 may also cover both sides of the steel plate 21. The thickness of the coating 27 is, for example, 0.5 μm or more and 5.0 μm or less. Preferably, the thickness of the coating 27 is 1.0 μm or more and 3.0 μm or less. (The last sentence appears to be incomplete and possibly refers to a different embodiment.) min In comparison, the thickness of the coating 27 is negligible. Therefore, the thickness of the steel plate 21 measured including the coating 27 can be taken as the thickness t of the steel plate 21. min Treat it as such.

[0129] <Fourth Implementation>

[0130] Figure 9 This is a cross-sectional view of the blank 20C according to the fourth embodiment. Figure 9 The overlapping portion 26 formed by the steel plates 23 and 24 in the blank 20C is shown. Figure 9 The example shown is the same as the example shown in the second embodiment ( Figure 6 The difference is that the overlapping portion 26 is coated with the film 27 described in the third embodiment.

[0131] In this embodiment, the outer surfaces of the overlapping portions 26 in each of the steel plates 23 and 24 are substantially covered by a black coating 27. In the steel plate 23, the entire surface opposite to the target steel plate 24 is covered by the coating 27. The entire surface of the steel plate 24 opposite to the target steel plate 23 is also covered by the coating 27. That is, the surfaces of the steel plates 23 and 24 constituting the back surface of the overlapping portion 26 are each covered by the coating 27. This increases the emissivity of the overlapping portion 26, thus accelerating the heating of the overlapping portion 26 when heating the blank 20°C during hot stamping. Therefore, it is possible to achieve a higher emissivity in the steel plate 21 with a thickness of t. min ( Figure 3B and Figure 3C Before the alloying transition of the aluminum-based coating 21b is carried out, the overlapping portion 26 is heated to the temperature of the austenitic region, which allows the structural component 10 to be manufactured while maintaining the corrosion resistance or weldability of the steel plate 21. Therefore, it is easy to ensure the process window during the manufacturing of the structural component 10.

[0132] exist Figure 9 In the example, the outer surfaces of the overlapping portions 26 of each of the steel plates 23 and 24 are substantially covered by a black coating 27. However, it is also possible that the outer surface of one of the steel plates 23 and 24 located at the overlapping portion 26 is covered by the coating 27, while the outer surface of the other of the steel plates 23 and 24 located at the overlapping portion 26 is not covered by the coating 27. Additionally, in Figure 9 In the example, the surfaces of the individual steel plates 23 and 24 located inside the overlapping portion 26 are not substantially covered by the black coating 27. However, it is also possible that the surfaces of the individual steel plates 23 and 24 located inside the overlapping portion 26 are also covered by the coating 27. However, from the viewpoint of homogenizing the heating of the blank 20C during hot stamping, it is preferable that the surfaces of the individual steel plates 23 and 24 located outside the overlapping portion 26 are covered by the coating 27, while the surfaces located inside the overlapping portion 26 are not covered by the coating 27.

[0133] The embodiments of this disclosure have been described above, but this disclosure is not limited to the above embodiments. Various modifications can be made as long as they do not depart from its spirit.

[0134] In the first embodiment described above, it was explained that not only does it have a minimum plate thickness t min The steel plate 21, and has the largest plate thickness t max The amount of aluminum-based coating 23b adhering to steel plate 23 is less than that of aluminum-based coating 22b adhering to steel plate 22 in other examples. However, the maximum plate thickness t max The amount W3 of the aluminum-based coating 23b in the steel plate 23 can also be set to be greater than or equal to the amount W2 of the aluminum-based coating 22b in the steel plate 22. In this case, in the structural component 10 after hot stamping, the coating thickness K3 of the steel plate 23 is also greater than or equal to the coating thickness K2 of the steel plate 22. Among the multiple steel plates 21, 22, and 23 constituting the blank 20, as long as they have at least a minimum plate thickness t min The amount of aluminum coating 21b in steel plate 21 should be less than the amount of aluminum coating 22b in steel plate 22, i.e., W1.

[0135] In the first embodiment described above, the blank 20 comprises three steel plates 21, 22, and 23. In the second embodiment described above, the blank 20A comprises five steel plates 21, 22, 23, 24, and 25. However, the number of steel plates included in the blanks 20 and 20A is not limited to these. The blanks 20 and 20A are only required to include at least one steel plate with a minimum thickness t. min Steel plate 21 and having a thickness t greater than the plate thickness min A steel plate of thickness 22 is sufficient. Additionally, as long as the minimum plate thickness t is met... min The amount W1 of the aluminum-based coating 21b in steel plate 21 should be smaller than the amount W2 of the aluminum-based coating 22b in steel plate 22. Steel plate 21 is directly or indirectly bonded to steel plate 22. The annular blanks 20 and 20A, when viewed from above, typically contain more than three steel plates. The amount of aluminum-based coating on the steel plates other than steel plates 21 and 22 in blanks 20 and 20A is not particularly limited. The steel plates other than steel plates 21 and 22 can be aluminized steel plates, other coated steel plates, or even bare steel plates (bare material) without any coating. The arrangement of multiple steel plates including steel plates 21 and 22 in the annular blanks 20 and 20A is not particularly limited.

[0136] In either blank 20 or 20A, there exist multiple blanks with a minimum thickness t. min In the case of steel plate 21, it is preferable that the amount W1 of aluminum-based coating 21b is smaller in all steel plates 21 than the amount W2 of aluminum-based coating 22b in other steel plates 22. The amount W1 of aluminum-based coating 21b in these steel plates 21 can be the same, or it can be different. In the presence of multiple minimum plate thicknesses t... minIn the case of steel plate 21, the difference between the adhesion amounts W1 and W2 of aluminum-based coatings 21b and 22b of steel plates 21 and 22 is calculated by referring to the steel plate with the largest adhesion amount W1 of aluminum-based coating 21b among multiple steel plates 21: W2-W1.

[0137] In the first embodiment described above, the die 40 for hot stamping of the blank 20 includes a punch 41 and a die 42. However, the structure of the die 40 is not limited to the example described in the first embodiment. The die 40 may also include, for example, a liner and a pressure plate.

[0138] In the above embodiments, the main body 11 of structural components 10 and 10A includes a front pillar 111, a middle pillar 112, and a sill beam 113. However, the main body 11 may also include other constituent elements. For example, such as... Figure 10 As shown, the main body 11 of the component may also include a rear pillar 114. The structural components 10 and 10A of the above embodiment are door ring components (single door ring components) having a single-ring shape. On the other hand, Figure 8 The structural component shown is a door ring component with a double-ring shape (double door ring component). When manufacturing a double door ring component, the blank used as its raw material also has a double-ring shape.

[0139] Example

[0140] The present disclosure will be further described in detail below through embodiments. However, the present disclosure is not limited to the following embodiments.

[0141] [First Embodiment]

[0142] To confirm the effectiveness of this disclosure, CAE analysis was performed on the stamping (hot stamping) of the structural component as a bicycle door ring component, while changing the type (blank type) and thickness of the steel sheet included in the structural component and the segmentation pattern of the structural component, using commercially available software (AUTOFORM R.10, manufactured by AUTOFORM Corporation).

[0143] The steel plates used in this analysis are shown in Table 1.

[0144] [Table 1]

[0145]

[0146] In Table 1, the billet types are listed in the order of plating type, tensile strength, and application (hot stamping). However, for cases where a black coating containing carbon (C) is applied to the plating, the billet type is marked with the words "Black Coating (Single Side)" or "Black Coating (Both Sides)". "Black Coating (Single Side)" means that one side of the plating sheet is entirely covered by the black coating. "Black Coating (Both Sides)" means that both sides of the plating sheet are entirely covered by the black coating. Table 1 shows the coating adhesion amount for each side, but in this analysis, the coating adhesion amount is the same on both sides of the billet.

[0147] The segmentation pattern of the structural components is shown in Figures 11A-11G .exist Figures 11A-11G The diagram shows the number of steel plates (blanks) included in the structural component of the single-vehicle door ring assembly and the positions of the joints between the steel plates in the structural component. Figures 11A-11G In the diagram, numbers are marked in parentheses for each steel plate.

[0148] about Figure 11A and Figure 11B The segmentation patterns 1 and 2 shown are illustrated in Table 2, with the parsing conditions and results presented therein. Figure 11A and Figure 11B In the middle, the structural components are formed from 3 blanks (1) to (3).

[0149] [Table 2]

[0150]

[0151] Referring to Table 2, in Example 1, the amount of aluminum coating adhering to both surfaces of the base steel sheet has the minimum thickness t in the billets (1) to (3). min The amount of aluminum coating is less in the 1.2mm blank (3), and more in the other blanks (1) and (2) with a thickness greater than that of blank (3). In Example 2, the amount of aluminum coating has the smallest thickness t among the blanks (1) to (3). min The amount of aluminum coating is less in the 1.2mm blank (1) and more in other blanks (3) with a thickness greater than that of blank (1). In Example 3, the amount of aluminum coating has the smallest thickness t among blanks (1) to (3). min The amount of aluminum coating on the blanks (1) and (3) is less than that on the blank (2) which has a thickness greater than that on the blank (2). On the other hand, in Comparative Examples 1 and 2, the amount of aluminum coating on the blanks (1) to (3) is equal to that on each other.

[0152] In Table 2, "Time to reach 910℃" refers to the earliest temperature reached by any component of the billet contained in the blank (A). c3For billets (above 920°C), the time required from the start of heating the billet until it reaches 910°C is defined as follows: "Phase transformation start time" refers to the shortest time from when the billet is removed from the furnace after being heated at 920°C for 5 minutes and 30 seconds until the phase transformation to ferrite begins. "Painting thickness difference" refers to the minimum time required for the minimum plate thickness t... min The amount of aluminum-based coating adhered to the blank and the amount of aluminum-based coating adhered to the blank with a larger plate thickness (in the presence of multiple blanks with a thickness greater than t). min The difference (maximum adhesion amount) is calculated when the thickness of the blank is large and the amount of aluminum coating varies among these blanks. Table 2 shows that in Examples 1-3, where the amount of aluminum coating on the thinnest blank is less than that on more than one other blank, the time to reach 910°C is shortened by more than 20 seconds compared to Comparative Examples 1 and 2, and the heating rate of the thinnest blank in the heating process is higher. Furthermore, in Examples 1-3, the phase transformation start time exceeds 20 seconds, which is delayed compared to Comparative Examples 1 and 2. Therefore, it is easy to start blank forming before the ferrite phase transformation begins, and the blank can be uniformly quenched during the forming process.

[0153] about Figure 11C and Figure 11D The segmentation patterns 3 and 4 shown are illustrated in Table 3, with the parsing conditions and results presented therein. Figure 11C and Figure 11D In the middle, the structural components are formed from 4 blanks (1) to (4).

[0154] [Table 3]

[0155]

[0156] Referring to Table 3, in Examples 4-10, the blanks (1)-(4) have the smallest plate thickness t. min The amount of aluminum-based coating adhering in the blank is less than the amount of aluminum-based coating adhering in any other blank or more. In the presence of multiple sheets with a minimum plate thickness t... min In the case of blanks with smaller plate thicknesses, the amount of aluminum-based coatings adhering to all blanks is less than that in blanks with larger plate thicknesses. On the other hand, in Comparative Examples 3 to 7, the blanks (1) to (4) with the smallest plate thickness t min The amount of aluminum coating adhering in the billet is greater than that in other billets. In addition, in Examples 6 and 9 and Comparative Example 5, the billet (1) is alloyed hot-dip galvanized steel sheet (GA coated steel sheet).

[0157] As shown in Table 3, in Examples 4-10, compared to Comparative Examples 3-7, the time to reach 910°C was shortened by more than 20 seconds, and the heating rate of the thinnest billet in the heating process was increased. Furthermore, in Examples 4-10, the phase transformation initiation time exceeded 20 seconds, which was delayed compared to Comparative Examples 3-7. Therefore, it is easier to begin forming the blank before the ferrite phase transformation begins, and the blank can be uniformly quenched during the forming process.

[0158] In Examples 4, 5, and 10, the minimum plate thickness t is... min Both surfaces of the blank are covered with a black coating. In Examples 4, 5, and 10, the blank with the minimum plate thickness t was not... min Compared to Examples 6-9, where a black coating was applied to the billet, the time to reach 910°C was shortened by more than 20 seconds, and the heating of the thinnest billet in the heating process was further accelerated. Furthermore, in Examples 4, 5, and 10, the phase transformation initiation time was also delayed compared to Examples 6-9. Therefore, by utilizing a black coating to pre-enhance the temperature of the billet with the minimum plate thickness t... min The surface emissivity of the billet can further accelerate the heating of the billet and further delay the start of the phase transformation to the ferrite phase.

[0159] about Figures 11E-11G The segmentation patterns 5-7 shown are illustrated in Table 4, with the parsing conditions and results listed below. Figures 11E-11G In the middle, the structural components are formed from 5 blanks (1) to (5).

[0160] [Table 4]

[0161]

[0162] Referring to Table 4, in Examples 11-15, the blanks (1) to (5) have the smallest plate thickness t. min The amount of aluminum-based coating adhering in the blank is less than the amount of aluminum-based coating adhering in any other blank or more. In the presence of multiple sheets with a minimum plate thickness t... min In the case of blanks, the amount of aluminum coating on all blanks is less than the amount of aluminum coating on blanks with greater plate thickness. On the other hand, in Comparative Examples 8 to 11, the amount of aluminum coating on blanks (1) to (5) is equal to each other.

[0163] As shown in Table 4, in Examples 11-15, compared with Comparative Examples 8-11, the time to reach 910°C was shortened by more than 20 seconds, and the heating rate of the thinnest billet in the heating process was increased. Furthermore, in Examples 11-15, the phase transformation initiation time was delayed compared to Comparative Examples 8-11. Therefore, it is easier to start forming the blank before the ferrite phase transformation begins, and the blank can be uniformly quenched during the forming process.

[0164] In Examples 12 and 14, the minimum plate thickness t is... min The blank (1) is covered on one or both sides with a black coating. In Example 12, the minimum plate thickness t is... min One side of the blank (5) is also covered with a black coating. For example, if Example 12 is compared with Comparative Example 9, which has the same combination of cutting pattern, blank type (except for plating amount), and plate thickness, then in Example 12, the time to reach 910°C is shortened by more than 40 seconds, and the heating of the thinnest blank in the heating process is significantly faster. In addition, in Example 12, the phase transformation start time is also significantly delayed compared with Comparative Example 9. Therefore, by utilizing the black coating to pre-enhance the thickness of the blank with the minimum plate thickness t, min The surface emissivity of the billet can further accelerate the heating of the billet and further delay the start of the phase transformation to the ferrite phase.

[0165] In the embodiments and comparative examples shown in Tables 2 to 4, the blanks are joined together by laser joining (butt joining) after butt welding. On the other hand, in the embodiments shown in Table 5 below, a portion of the blanks is joined, for example, by spot welding to form an overlap.

[0166] [Table 5]

[0167]

[0168] Refer to Table 5 and Figure 11F In Examples 16, 18, and Comparative Example 12, blanks (2) and (5), blanks (3) and (4), and blanks (4) and (5) respectively form overlapping portions at their joints. Refer to Table 5 and... Figure 11E In Examples 17, 19 and Comparative Examples 13, 14, blanks (2) and (5), and blanks (3) and (4) respectively form overlapping portions at their joints.

[0169] Referring to Table 5, in Examples 16-19, the blanks (1) to (5) have the smallest plate thickness t. min The amount of aluminum-based coating adhering in the billet is less than that in other billets with greater plate thickness. In Examples 16 and 17, the coating thickness difference between the thinnest billet and other billets is 40 g / m. 2 In Examples 18 and 19, the difference in plating thickness between the thinnest blank and the other blanks was 60 g / m. 2 20g / m 2 On the other hand, in Comparative Examples 12 and 13, the amount of aluminum coatings in the blanks (1) to (5) was equal to that in each other. In Comparative Example 14, the minimum plate thickness t was... minThe aluminum coating on billet (4) was more abundant than that on other billets (1), (2), and (5) which had greater plate thickness. In Comparative Example 14, the coating thickness difference between the thinnest billet and the other billets was -20 g / m. 2 .

[0170] According to Table 5, in Examples 16-19, compared to Comparative Examples 12-14, the time to reach 910°C was shortened by more than 20 seconds, and the phase transformation initiation time was also delayed. Therefore, it was confirmed that even when there is overlap in the blank, by reducing the amount of aluminum-based coating applied to the thinnest blank, the same effect as in butt joint cases can be obtained. In particular, in Examples 16 and 18, where a black coating was applied to both sides of the thinnest blank, compared to Comparative Examples 12-14, the time to reach 910°C was shortened by more than 40 seconds, and the phase transformation initiation time was further delayed.

[0171] In Example 19, the difference in plating thickness between the thinnest blank and the other blanks was 20 g / m. 2 The temperature is relatively small. For this Example 19, it was also confirmed that compared with Comparative Examples 12-14, the time to reach 910°C was significantly shorter, and the phase transition start time was also significantly delayed.

[0172] [Second Embodiment]

[0173] Regarding the stamping (hot stamping) of the structural component as the double door ring component, the same analysis as in the first embodiment was performed while changing the type and thickness of the blank included in the structural component and the segmentation pattern of the structural component.

[0174] The steel plates used as blanks are selected from those shown in Table 1, similar to those in the first embodiment. The segmentation pattern of the structural components is as follows: Figures 12A-12D As shown. In Figures 12A-12D The diagram shows the number of steel sheets (blanks) included in the structural component of the double door ring assembly and the positions of the joints between the steel sheets in the structural component. Figures 12A-12D In the text, the numbers for each steel plate used as a billet are marked in parentheses.

[0175] about Figure 12A and Figure 12B The segmentation patterns 8 and 9 shown are illustrated in Table 6, with the parsing conditions and results presented therein. Figure 12A and Figure 12B In the middle, the structural components are formed from 6 blanks (1) to (6).

[0176] [Table 6]

[0177]

[0178] Referring to Table 6, in Examples 20-22, the blanks (1) to (6) have the smallest plate thickness t. min The amount of aluminum-based coating adhering in the blank is less than the amount of aluminum-based coating adhering in one or more blanks with greater plate thickness. In Examples 20-22, the coating thickness difference is 20 g / m. 2 That's all. On the other hand, in Comparative Example 15, the amount of aluminum coating on the blanks (1) to (6) was equal to each other. In Comparative Example 16, the amount of aluminum coating on the other blanks was greater than that on the blank with the smallest plate thickness t. min The blanks are numerous, and the coating thickness difference is -20g / m 2 .

[0179] As shown in Table 6, in Examples 20-22, compared to Comparative Examples 15 and 16, the time to reach 910°C was shortened by approximately 20 seconds, and the heating rate of the thinnest billet in the heating process was increased. Furthermore, in Examples 20-22, the phase transformation initiation time was delayed compared to Comparative Examples 15 and 16. Therefore, it can be said that by reducing the amount of aluminum-based coating adhering to the thinnest billet, it is easier to begin billet forming before the ferrite phase transformation begins, and the billet can be uniformly quenched during the forming process.

[0180] about Figure 12C and Figure 12D The segmentation patterns 10 and 11 shown are illustrated in Table 7, with the parsing conditions and results presented therein. Figure 12C and Figure 12D In the middle, the structural components are formed from 7 blanks (1) to (7).

[0181] [Table 7]

[0182]

[0183] Referring to Table 7, in Examples 23-25, the blanks (1) to (7) have the minimum plate thickness t. min The amount of aluminum coating attached to the blank is less than the amount of aluminum coating attached to one or more blanks with a larger plate thickness. On the other hand, in Comparative Examples 17 and 18, the amount of aluminum coating attached to the blanks (1) to (7) is equal to that of each other.

[0184] As shown in Table 7, in Examples 23-25, compared with Comparative Examples 17 and 18, the time to reach 910°C was shorter, and the heating rate of the thinnest billet in the heating process was higher. Furthermore, in Examples 23-25, the phase transformation initiation time was delayed compared to Comparative Examples 17 and 18. Therefore, it is easier to start forming the blank before the ferrite phase transformation begins, and the blank can be uniformly quenched during the forming process.

[0185] [Third Embodiment]

[0186] Regarding the stamping (hot stamping) of the structural component as a single-vehicle door ring, in order to confirm the influence of sheet thickness, the same analysis as in the first embodiment was performed while changing the combination and joining method of the blanks. The conditions and results of the analysis are shown in Table 8.

[0187] [Table 8]

[0188]

[0189] The segmentation patterns of Experiments 1 and 5 are Figure 11G The segmentation pattern shown is 7. The segmentation pattern of Experimental Example 4 is... Figure 11E The shown segmentation pattern is 5. In test examples 1, 4, and 5, a portion of the billet forms an overlapping portion at the joint. More specifically, in test examples 1 and 5, billets (1) and (2), billets (1) and (3), billets (2) and (5), and billets (4) and (5) respectively form overlapping portions at their joints. In test example 4, billets (1) and (2), billets (1) and (3), billets (3) and (4), and billets (2) and (5) respectively form overlapping portions at their joints. In these test examples, the minimum plate thickness t is... min The amount of aluminum coating attached to the billet is less than that attached to one or more billets with greater plate thickness.

[0190] The segmentation patterns of Experiments 2, 3, and 6 are Figure 11G The segmentation pattern 7 is shown. In tests 2, 3, and 6, the billets were joined together by butt joint. In these tests, the minimum plate thickness t is... min The amount of aluminum coating attached to the billet is less than that attached to one or more billets with greater plate thickness.

[0191] The "Process Window (PW)" in Table 8 is calculated by subtracting the time until the entire billet reaches 910°C from the allowable heating time of the earliest billet reaching 910°C. A process window of less than 5 seconds means that alloying of the coating occurs only in the earliest billet reaching 910°C during the heating process, compromising the coating's corrosion resistance and hindering the manufacture of structural components.

[0192] As shown in Table 8, at the maximum plate thickness t max Relative to minimum plate thickness t min The ratio: t max / t min In tests 5 and 6, exceeding 3.2, the process window was negative, failing to ensure the process window required for the proper manufacture of structural components. On the other hand, in t... max / t minIn test examples 1 to 4 with a value of 3.2 or less, a process window of more than 5 seconds can be ensured.

[0193] As shown in Table 8, in Test Example 5, where the maximum total plate thickness t of the overlapping section exceeds 4.0 mm, the process window is negative, and the process window required for good manufacturing of the structural component cannot be ensured. On the other hand, in Test Examples 1 and 4, where the maximum total plate thickness t of the overlapping section is less than 4.0 mm, a process window of more than 5 seconds can be ensured.

[0194] Reference Example 1 is an example of the same segmentation pattern 5 as Experimental Example 4, but there is no difference in the amount of aluminum-based coatings adhering between the blanks. However, in Reference Example 1, there is also no difference in plate thickness between the blanks, so there is no problem with the alloying of the coating in the thinnest blank, thus ensuring a process window of more than 5 seconds.

[0195] For Test Examples 1-4 and Comparative Examples 11 and 13A, after heating the blanks at a furnace temperature of 920°C until the entire blank reached 910°C, they were conveyed to a stamping device for 17 seconds and hot-stamped at a forming speed of 40 mm / s. While being pressurized with 3000 kN, the blanks were held at the bottom dead center for 20 seconds to obtain hot-stamped structural components. Samples were collected from the thinnest part of these structural components using the method described in the above embodiments, and the deviation of the martensite fraction was measured. Furthermore, shape accuracy and impact absorption performance were measured for these structural components. The evaluation results are shown in Table 9.

[0196] [Table 9]

[0197]

[0198] In Table 9, the deviation of the martensite fraction refers to, as described in the above embodiments, the deviation within the minimum plate thickness t. min The value obtained by subtracting the minimum martensite fraction (%) from the maximum martensite fraction (%) in the cross section of the structural component at the location of the billet.

[0199] Regarding shape accuracy, it is evaluated by assessing the degree to which the structural component, which appears roughly cap-shaped in cross-section, is separated from the target component at the overlap between the structural component and the target component when the structural component is mounted on top of other components. In Table 9, ○ indicates a distance of ±2.0 mm or less from the surface of the target component, △ indicates a distance greater than ±2.0 mm but less than ±3.0 mm, and × indicates a distance greater than ±3.0 mm.

[0200] Regarding impact absorption performance, we simulated SOL (Small Overlap) and side impacts with the structural components assembled in the vehicle. The impactor of the simulated vehicle collided with the structural components, and the maximum intrusion during the SOL impact (maximum SOL intrusion) and the maximum intrusion during the side impact (maximum side impact intrusion) were evaluated respectively. For impact absorption performance, door ring components were formed by joining separately hot-stamped blanks. The impact absorption performance of this door ring component was used as a benchmark, and the evaluation was conducted by comparing it with the benchmark. In Table 9, "good" indicates impact absorption performance equivalent to the benchmark, "better" indicates impact absorption performance superior to the benchmark, "marginal" indicates impact absorption performance slightly lower than the benchmark, and "poor" indicates even lower impact absorption performance.

[0201] Comparative Example 11 is Comparative Example 11 of the First Embodiment, and the blanks were butt-laminated laser-bonded together in the same manner as in Test Example 2. Comparative Example 13A is the same plate assembly as Comparative Example 13 of the First Embodiment, but the blanks were partially overlapped and bonded together in the same manner as in Test Example 4. In Comparative Examples 11 and 13A, unlike the Test Examples, the amount of plating in the thinnest blank was equal to the amount of plating in the other blanks. As shown in Table 9, in Test Examples 1 to 4, the deviation of the martensite fraction was less than 20%, and the deviation of the martensite fraction was significantly reduced compared to Comparative Examples 11 and 13A. In Test Examples 1 to 4, the shape accuracy was also good compared to Comparative Examples 11 and 13A.

[0202] In Test Examples 1-4, where the deviation in martensite fraction was small, the impact absorption performance was also improved compared to Comparative Examples 11 and 13A. Particularly in Test Examples 1, 2, and 4, where the deviation in martensite fraction was less than 15%, impact absorption performance above the baseline was ensured. That is, although multiple blanks were integrally formed into a ring-shaped structural component during the blanking stage, impact absorption performance equal to or better than that of a structural component formed by stamping and joining blanks separately was ensured. Among Test Examples 1-4, Test Example 2 exhibited the best impact absorption performance. Test Example 2, in particular, demonstrated high impact absorption performance in relation to side impacts.

[0203] Explanation of reference numerals in the attached figures

[0204] 10, 10A, Structural components; 11, Component body; 20, 20A, 20B, 20C, Blank; 21, Steel plate (first steel plate); 21a, Base steel plate; 21b, Aluminum coating; 22, Steel plate (second steel plate); 22a, Base steel plate; 22b, Aluminum coating; 23, Steel plate (third steel plate); 23a, Base steel plate; 23b, Aluminum coating; 24, Steel plate; 24a, Base steel plate; 24b, Aluminum coating; 25, Steel plate; 26, Overlapping part; 27, Coating; 40, Mold; 111, Front pillar; 112, Middle pillar; 113, Sill beam.

Claims

1. A blank, which is a blank for hot stamping. The blank comprises multiple steel plates arranged and joined in a ring-like manner when viewed from above. The plurality of steel plates includes a first steel plate having the smallest thickness and a second steel plate having a thickness greater than that of the first steel plate. The first steel plate and the second steel plate are respectively coated steel plates having a base steel plate and an aluminum-based coating covering both surfaces of the base steel plate. The amount of aluminum-based coating adhering to both surfaces of the base steel plate in the first steel plate is less than the amount of aluminum-based coating adhering to both surfaces of the base steel plate in the second steel plate. in, The amount of aluminum coating on the first steel plate relative to both surfaces of the base steel plate is measured in g / m². 2 The amount of aluminum-based coating adhering to both surfaces of the base steel plate in the second steel plate is measured in g / m². 2 .

2. The blank according to claim 1, wherein, Let the thickness of the first steel plate be t. min Let the thickness of the steel plate with the largest thickness among the plurality of steel plates be t. max At that time, 1.0 <t max / t min ≤3.

2.

3. The blank according to claim 1, wherein, The blank also includes an overlapping portion, which is formed by overlapping the ends of two adjacent steel plates among the plurality of steel plates, and the overlapping portion has a total plate thickness of less than 4.0 mm. The two steel plates are respectively a base steel plate and an aluminum-based coating covering both surfaces of the base steel plate. The amount of aluminum-based coating adhering to the two surfaces of the base steel plate in each of the two steel plates is less than the amount of aluminum-based coating adhering to the two surfaces of the base steel plate in the second steel plate. The unit for the amount of aluminum-based coating on each of the two steel plates relative to the two surfaces of the base steel plate is g / m². 2 The amount of aluminum-based coating adhering to both surfaces of the base steel plate in the second steel plate is measured in g / m². 2 .

4. The blank according to claim 3, wherein, The outer surface of at least one of the two steel plates located at the overlapping portion is covered with a black coating.

5. The blank according to claim 1, wherein, At least one surface of the first steel plate is covered with a black coating.

6. A method for manufacturing a structural component, comprising: The process of preparing the blank according to any one of claims 1 to 5; The process of heating the plurality of steel plates contained in the blank to above the temperature at which the austenitic phase transformation is completed; and The process of using a mold to shape the heated blank into a ring-shaped structural component when viewed from above, and then quenching it.

7. A structural component comprising a component body, the component body including a first steel plate having a minimum thickness and a second steel plate having a thickness greater than that of the first steel plate, the component body being formed of a plurality of interlocking steel plates and having a ring shape when viewed from above. The first steel plate and the second steel plate are coated steel plates with aluminum-based coatings on both surfaces of the base steel plate. The thickness of the aluminum-based coating in the first steel plate is smaller than the thickness of the aluminum-based coating in the second steel plate.

8. The structural component according to claim 7, wherein, The structural component is a car door ring component. The main body of the component includes a front pillar, a middle pillar, and a sill beam connecting the front pillar and the middle pillar.

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