Hot-stamped member

Abstract

This hot-stamped member comprises: a base steel sheet; an alloy plating layer that is positioned on the surface of the base steel sheet; and an oxide film that is positioned on the surface of the alloy plating layer. The alloy plating layer has a chemical composition containing, in mass%, 2.0-20.0% of Si and 35.0-80.0% of Fe, with the balance being Al and impurities. The average value of the thickness of the alloy plating layer is 10-60 μm. The oxide film contains a total of 0.01-45.00 mass% or more of one or more elements from among group A elements and group B elements.

Description

Hot stamping components

[0001] This disclosure relates to a hot stamping component. This application claims priority under Japanese Patent Application No. 2025-055517, filed in Japan on 28 March 2025, the contents of which are incorporated herein by reference.

[0002] Hot stamping (hot pressing) is a well-known technique for press-forming materials that are difficult to form, such as high-strength steel sheets. Hot stamping is a hot forming technique in which the material to be formed is heated before forming. In this technique, because the material is heated before forming, the steel is soft and has good formability during the forming process. Therefore, even high-strength steel can be formed into complex shapes with high precision, and since quenching is performed simultaneously with forming using a press die, the formed steel is known to have sufficient strength.

[0003] When hot stamping is applied to steel sheets, the high temperatures required for heating the sheets led to the formation of iron-based oxides on the surface. These iron-based oxides negatively affect weldability, necessitating a removal process after press forming. To address this problem, aluminum-plated steel sheets are used. In aluminum-plated steel sheets, the presence of an aluminum plating layer on the surface suppresses the formation of iron-based oxides during heating. Furthermore, hot-stamped components produced by applying hot stamping to aluminum-plated steel sheets exhibit excellent corrosion resistance after painting.

[0004] When hot stamping is applied to aluminum-plated steel sheets, hydrogen penetrates into the base steel sheet during heating in the hot stamping process. More specifically, during heating in the hot stamping process (for example, Ac ３ During the heating process to a temperature range higher than 2.5°C, the reaction shown in formula (1) below occurs on the surface of the Al-based plating layer, generating an oxide film on the surface of the Al-based plating layer and simultaneously generating hydrogen. This hydrogen diffuses through the oxide film and the plating layer, penetrating into the base steel sheet. When hot-stamped members obtained by hot-stamping Al-based plated steel sheets are made high-strength, there is a concern that the hydrogen that penetrates into the base steel sheet during heating may adversely affect the hot-stamped members. 2Al + 3H ２ O→Al２ O ３ +6H ... (1)

[0005] For example, Patent Document 1 discloses that hydrogen adsorption to a carbon steel sheet can be prevented by coating the carbon steel sheet with a barrier precoat containing nickel and chromium, with a weight ratio of Ni / Cr between 1.5 and 9.

[0006] Patent Document 2 discloses that a protective coating contains at least one alkaline earth metal or transition metal in a total of 0.1% to 0.5% by weight, and that an oxide of the alkaline earth metal or transition metal is formed on the outer surface of the protective coating during the hot forming of the flat steel product, thereby minimizing hydrogen absorption during the heating required for hot forming.

[0007] Japan Special Table No. 2019-518136 Publication Japanese Special Table No. 2017-536472

[0008] As the strength of the hot-stamped component increases, it becomes necessary to further reduce the amount of hydrogen that penetrates the base steel sheet. The technologies disclosed in Patent Documents 1 and 2 are unable to sufficiently reduce the amount of hydrogen that penetrates the base steel sheet (hydrogen storage capacity), and there is room for improvement in reducing hydrogen storage capacity.

[0009] This disclosure is made in view of the circumstances described above. The purpose of this disclosure is to provide a hot-stamped member that has high strength and excellent post-coating corrosion resistance, and has reduced hydrogen storage capacity.

[0010] The gist of this disclosure is as follows: [1] A hot-stamped member comprising a base steel sheet, an alloy plating layer located on the surface of the base steel sheet, and an oxide film located on the surface of the alloy plating layer, wherein the alloy plating layer has a chemical composition consisting of, by mass%, Si: 2.0 to 20.0% and Fe: 35.0 to 80.0%, with the remainder being Al and impurities, the average thickness of the alloy plating layer is 10 to 60 μm, the oxide film contains a total of 0.01 to 45.00 mass% of one or more elements from group A elements consisting of Ni, Cu, V, Mo, W, and Nb, and group B elements consisting of Li, Na, K, Rb, and Cs, and the Vickers hardness at a position 1 / 4 of the way from the surface of the base steel sheet is 242.4 HV or higher. [2] The hot stamping member according to [1], characterized in that the oxide film contains a total of 0.10 to 45.00% by mass of one or more elements from the elements of group A and the elements of group B. [3] The hot stamping member according to [1] or [2], characterized in that the average thickness of the oxide film is 10 to 2000 nm.

[0011] According to the above embodiment, it is possible to provide a hot-stamped member that has high strength and excellent corrosion resistance after painting, and also has reduced hydrogen storage capacity.

[0012] This is a schematic diagram showing the cross-section of an aluminum-plated steel sheet. This is a schematic diagram showing the cross-section of a hot-stamped component.

[0013] The inventors investigated hot-stamped members with reduced hydrogen storage capacity and obtained the following findings. Figure 1 is a schematic diagram showing the thickness cross-section of an Al-plated steel sheet. After hot stamping, a hot-stamped member 11 comprising a base steel sheet 1, an alloy plating layer 4, and an oxide film 5 can be obtained, as shown in Figure 2. When hot stamping is applied to an Al-plated steel sheet 10 comprising a base steel sheet 1, an Al-plated layer 2, and a film 3, hydrogen penetrates the base steel sheet 1 during heating in hot stamping. More specifically, during heating in hot stamping (for example, Ac ３During the heating process to a temperature range higher than the above point), the Al-based plating layer 2 transforms into an alloy plating layer 4, and a reaction represented by the following formula (1) occurs on the surface of the alloy plating layer 4. As a result, an oxide film 5 is formed on the surface of the alloy plating layer 4 and hydrogen is generated at the same time. Hydrogen diffuses through the oxide film 5 and the alloy plating layer 4 and penetrates into the base steel sheet 1. 2Al + 3H ２ O → Al ２ O ３ + 6H ··· (1)

[0014] In order to reduce the amount of hydrogen penetrating into the base steel sheet 1, it is considered effective to suppress hydrogen diffusion in one or both of the alloy plating layer 4 and the oxide film 5. In the present disclosure, the present inventors studied incorporating various elements into the oxide film 5 for the purpose of reducing the diffusion rate of hydrogen in the oxide film 5. As a result, it was found that incorporating Group A elements (Ni, Cu, V, Mo, W and Nb) and / or Group B elements (Li, Na, K, Rb and Cs) into the oxide film 5 is effective in reducing the hydrogen absorption amount of the base steel sheet 1 after hot stamping. Group A elements have a monovalent valence, and Group B elements have a divalent valence, which are different from the valence of Al (trivalent). When Group A elements or Group B elements replace Al in Al ２ O ３ in the oxide film 5, the substitution of Al in Al ２ O ３ in the oxide film 5 reduces lattice defects in the oxide film 5 to maintain charge balance, which reduces hydrogen diffusion paths and thus reduces the diffusion rate of hydrogen in the oxide film 5.

[0015] Hereinafter, a hot stamping member according to an embodiment of the present disclosure will be described in detail. Note that the lower limit and upper limit are included in the numerical limitation ranges described with "~" between them. Values indicated as "less than" and "more than" are not included in the numerical range. In addition, all percentages regarding chemical composition indicate mass percent%. In the following description, reference numerals from the drawings are omitted.

[0016] <Hot Stamping Member> The hot stamping member according to the present embodiment includes a base steel sheet, an alloy plating layer located on the surface of the base steel sheet, and an oxide film located on the surface of the alloy plating layer. First, the alloy plating layer will be described in detail.

[0017] [Alloy Plating Layer] The alloy plating layer has a chemical composition consisting of Si: 2.0 to 20.0% and Fe: 35.0 to 80.0% by mass, with the remainder being Al and impurities. The alloy plating layer is not particularly limited, but it is preferably a hot-dip plating layer. The following describes each element.

[0018] Si: 2.0-20.0% Si is an effective element for reducing the amount of hydrogen absorbed by the alloy plating layer. To obtain this effect fully, the Si content should be 2.0% or more. The Si content may also be 9.0% or more, or 12.0% or more. On the other hand, if the Si content is excessive, the corrosion resistance after coating will decrease. Therefore, the Si content should be 20.0% or less. The Si content may also be 15.0% or less.

[0019] Fe: 35.0-80.0% During heating in hot stamping, Fe diffuses from the base steel sheet into the Al-based plating layer and alloys with Al, etc. If the Fe content is less than 35.0%, the corrosion resistance after painting will decrease. Therefore, the Fe content should be 35.0% or more. Preferably, the Fe content is 45.0% or more, 50.0% or more, 55.0% or more, or 60.0% or more. On the other hand, if the Fe content is too high, the corrosion resistance may decrease due to excessive alloying of the alloy plating layer. Therefore, the Fe content should be 80.0% or less. Preferably, the Fe content is 70.0% or less or 60.0% or less.

[0020] The alloy plating layer may contain the following optional elements in place of a portion of the remaining Al. Since the optional elements do not need to be included, the lower limit is 0%. The content of the optional elements is preferably 5.000% or less in total. The content of the optional elements may be 4.500% or less, 4.000% or less, 3.500% or less, 3.000% or less, 2.500% or less, 2.000% or less, 1.500% or less, 1.000% or less, 0.800% or less, 0.500% or less, 0.100% or less, or 0.050% or less in total.

[0021] Zn: 0-0.500% Zn has a sacrificial corrosion protection effect and is an effective element for improving the corrosion resistance of the alloy plating layer. The Zn content may be 0%, but to obtain this effect, it is preferable that the Zn content be 0.001% or more. The Zn content may be 0.003% or more, 0.005% or more, 0.008% or more, 0.010% or more, or 0.020% or more. There is no particular upper limit, but from the viewpoint of manufacturing costs, etc., the Zn content may be 0.500% or less. The Zn content may be 0.400% or less, 0.300% or less, 0.100% or less, 0.050% or less, or 0.030% or less.

[0022] Ni: 0 to 0.500% Ni is an effective element for improving the corrosion resistance of the alloy plating layer. The Ni content may be 0%, but to obtain this effect, it is preferable that the Ni content be 0.001% or more. The Ni content may be 0.003% or more, 0.005% or more, 0.008% or more, 0.010% or more, or 0.020% or more. There is no particular upper limit, but from the viewpoint of manufacturing costs, etc., the Ni content may be 0.500% or less. The Ni content may be 0.400% or less, 0.300% or less, 0.100% or less, 0.050% or less, or 0.030% or less.

[0023] Mg: 0-3.000% Mg is an effective element for improving the corrosion resistance of the alloy plating layer. The Mg content may be 0%, but to obtain this effect, it is preferable that the Mg content be 0.001% or more. The Mg content may be 0.003% or more, 0.005% or more, or 0.010% or more. On the other hand, from the viewpoint of uniformity of the plating appearance, the Mg content may be 3.000% or less. The Mg content may be 2.000% or less, 1.000% or less, 0.500% or less, 0.300% or less, 0.100% or less, 0.050% or less, or 0.020% or less.

[0024] Ca: 0-3.000% Ca is an effective element for improving the corrosion resistance of the alloy plating layer. The Ca content may be 0%, but to obtain this effect, it is preferable that the Ca content be 0.001% or more. The Ca content may be 0.003% or more, 0.005% or more, or 0.010% or more. On the other hand, from the viewpoint of uniformity of the plating appearance, the Ca content may be 3.000% or less. The Ca content may be 2.000% or less, 1.000% or less, 0.500% or less, 0.300% or less, 0.100% or less, 0.050% or less, or 0.020% or less.

[0025] Sb: 0-0.500%, Pb: 0-0.500%, Cu: 0-1.000%, Sn: 0-1.000%, Ti: 0-1.000%, Cr: 0 ~1.000%, Nb: 0~1.000%, Zr: 0~1.000%, Mn: 0~1.000%, Mo: 0~1.000%, Ag: 0~1.00 0%, Li: 0-1.000%, La: 0-0.500%, Ce: 0-0.500%, B: 0-0.500%, Y: 0-0.500%, Sr: 0-0.500%, In: 0-0.500%, Co: 0-0.500%, Bi: 0-0.500%, P: 0-0.500%, W: 0-0.500% Sb, Pb, Cu, Sn, Ti, Cr, Nb, Zr, Mn, Mo, Ag, Li, La, Ce, B, Y, Sr, In, Co, Bi, P and W do not need to be included in the alloy plating layer, but may be included in amounts of 0.0001% or more, 0.001% or more, or 0.01% or more. These elements, within a predetermined content range, do not adversely affect the hot-stamped member according to this embodiment. However, if the content of each element is excessive, it may reduce the corrosion resistance of the hot-stamped member after painting. Therefore, the content of Sb, Pb, La, Ce, B, Y, Sr, In, Co, Bi, P, and W is preferably 0.500% or less, and may be 0.300% or less, 0.100% or less, 0.050% or less, or 0.020% or less. The content of Cu, Sn, Ti, Cr, Nb, Zr, Mn, Mo, Ag, and Li is preferably 1.000% or less, and may be 0.800% or less, 0.500% or less, 0.100% or less, 0.050% or less, or 0.020% or less.

[0026] In the chemical composition of the alloy plating layer, the remainder consists of Al and impurities. In this embodiment, impurities refer to components that are mixed in during the plating process when manufacturing Al-based plated steel sheets, due to various factors in the manufacturing process, including the raw materials.

[0027] The chemical composition of the alloy plating layer is measured by the following method. A sample is cut from the hot-stamped member from the location described later, embedded in resin, and the cross-section in the thickness direction of the hot-stamped member is polished to create an observation surface. Next, carbon is deposited on the sample to facilitate current flow, and then, using an FE-EPMA at an acceleration voltage of 10 kV and a magnification of 1500x or more, the content of each element is analyzed at 1 μm intervals from the surface of the hot-stamped member toward the center of the thickness. The region in which the combined content of Al and Si in the total content of elements excluding carbon is 20% or more, and the content of O (oxygen) is 30% or less is identified as the alloy plating layer. Note that carbon is excluded here to exclude the carbon contained in the resin in which the sample is embedded from the measurement. Point analysis is performed at 1 μm intervals from the surface of the alloy plating layer (i.e., the interface between the oxide film and the alloy plating layer) toward the center of the thickness to measure the content of the target element. These operations are performed at other locations at a distance of 100 nm or more in a direction perpendicular to the thickness direction of the plate, for a total of five locations. By calculating the average content of the target element, the chemical composition of the alloy plating layer is obtained.

[0028] The hot-stamped member according to this embodiment can be used as various automotive parts as described above, for example, after a chemical conversion coating or paint film is arbitrarily formed on its surface. In this embodiment, when taking a sample from the hot-stamped member, the sampling locations are as follows. Furthermore, if the alloy plating layer cannot be identified by the method described above, or if the oxide film cannot be identified by the method described later, the paint film or chemical conversion coating is removed by the method described below before measurement.

[0029] When taking samples from hot-stamped members for various measurements and analyses, avoid taking samples from the following locations: (i) Welded areas: within 20 mm of the toe of spot welds and within 20 mm of the toe of arc / laser welds. (ii) Machined areas: machined areas with a radius of curvature of less than 15 mm, and within 5 mm of the said machined areas. (iii) Ends: ends within 5 mm of the cut end face of the part. (iv) Corroded areas: within 5 mm of areas where rust is visible.

[0030] Coating Removal Process: Apply a coating remover (Neoriver #160, manufactured by Sansai Chemical Co., Ltd., or CS500K, manufactured by Neos Co., Ltd.) to the surface of the cut-out sample at room temperature and let it stand for 5 minutes. Then, rub the surface of the sample to which the coating remover has been applied using a hard sponge (for example, "Kanefeel," manufactured by AION Co., Ltd.) to remove the coating from the surface of the sample.

[0031] Next, the surface of the sample after the coating has been removed is washed with water and dried. At this time, the remaining state of the coating is confirmed by SEM-EPMA measurement of the surface of the sample (100 μm square, 5 fields of view) after washing and drying. In the elemental distribution image obtained by EPMA, a region in which the C concentration is 10 mass% or more is identified, and if the area ratio of this region is 5% or more, it is determined that the coating has not been removed sufficiently.

[0032] To measure the area fraction of the region where the C concentration is 10% by mass or more, first, an elemental distribution image of C is obtained using EPMA with the C concentration range set to 10-30% by mass. The preferred measurement conditions for EPMA are as follows: Apparatus: JXA-8230 electron probe microanalyzer manufactured by JEOL Ltd. Acceleration voltage: 15 kV Irradiation current: 0.05 μA Surface analysis: WDS Analysis interval: 300 μm or more Area fraction: Average value of 5 fields

[0033] Next, the area ratio is measured by performing image processing on the obtained elemental distribution image of C. Image analysis software "ImageJ" is used for the image processing. Specifically, after loading the elemental distribution image of C described above into ImageJ, binarization is performed by "Make Binary" under "Binary" of "Process" such that a region with a C concentration of 10% by mass or more is displayed in black, and a region with a C concentration of less than 10% by mass is displayed in white. After binarization, "Measure" of "Analyze" is used to read the numerical value of "Area fraction" in "Results". This read numerical value is determined as the area ratio of the region where the C concentration is 10% by mass or more.

[0034] If peeling of the coating film is insufficient, removal of the coating film is repeated until the area ratio of the region where the C concentration is 10% by mass or more becomes less than 5%.

[0035] The chemical conversion coating is removed from the surface of the sample by performing a method in accordance with JIS K 3151:1996 on a sample that has been cut out from the component after the chemical conversion coating removal step and from which the coating film has been removed. Specifically, the chemical conversion coating is removed from the surface of the sample by immersing the sample after coating film removal in a 5% by mass chromic acid aqueous solution heated to 75°C for 15 minutes.

[0036] Next, the surface of the sample after removal of the chemical conversion coating is washed with water and dried. At this time, the residual state of the chemical conversion coating is confirmed by performing SEM-EPMA measurement on the surface (100 µm square, 5 fields of view) of the sample after washing with water and drying.

[0037] In the elemental distribution image obtained by EPMA, regions where the P concentration is 5% by mass or higher are identified, and if the area fraction of these regions is 5% or higher, it is determined that the chemical conversion coating has not been sufficiently removed. To measure the area fraction of regions where the P concentration is 5% by mass or higher, first, an elemental distribution image of P is obtained using EPMA with the P concentration range set to 5-10%. Next, the area fraction is measured by image processing of the obtained elemental distribution image of P. The image analysis software "ImageJ" is used for image processing. Specifically, after loading the above elemental distribution image of P into ImageJ, the image is binarized using "Make Binary" in "Binary" under "Process" so that regions where the P concentration is 5% by mass or higher are displayed in black and regions where it is less than 5% by mass are displayed in white. After binarization, the value of "Area fraction" in "Results" is read using "Measure" under "Analyze". This read value is determined as the area percentage of the region where the P concentration is 5% by mass or higher.

[0038] If the chemical conversion coating is not sufficiently removed, the removal of the chemical conversion coating is repeated until the area ratio of the region where the P concentration is 5% by mass or more is less than 5%.

[0039] Average thickness of alloy plating layer: 10 to 60 μm If the average thickness of the alloy plating layer is less than 10 μm, the corrosion resistance of the hot-stamped member after painting will be insufficient. Therefore, the average thickness of the alloy plating layer should be 10 μm or more. Preferably, the average thickness of the alloy plating layer is 13 μm or more, more preferably 15 μm or more, and even more preferably 25 μm or more. On the other hand, if the average thickness of the alloy plating layer is greater than 60 μm, there is a possibility that the area near the surface of the alloy plating layer is not alloyed with the base steel plate, and the corrosion resistance of the hot-stamped member after painting will be insufficient. Therefore, the average thickness of the alloy plating layer should be 60 μm or less. Preferably, the average thickness of the alloy plating layer is 50 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less.

[0040] The average thickness of the alloy plating layer is obtained by the following method. A sample is cut from the hot-stamped member from the location described above, embedded in resin, and the cross-section in the thickness direction of the hot-stamped member is polished to create an observation surface. Next, carbon is deposited on the sample to facilitate current flow, and then point analysis is performed using FE-EPMA at an acceleration voltage of 10 kV and a magnification of 1500x or more to quantitatively analyze the content of each element. Point analysis is performed at 1 μm intervals from the surface of the hot-stamped member (i.e., the surface of the oxide film) toward the center of the thickness, and the region in which the sum of the content of Al and Si in the total content of elements excluding carbon is 20 mass% or more, and the content of O (oxygen) in the total content of elements excluding carbon is 30 mass% or less is identified as the alloy plating layer. The thickness of the alloy plating layer is measured at a total of 5 locations, separated by 10 μm or more in a direction perpendicular to the thickness direction. The average value of these measurements is calculated to obtain the average thickness of the alloy plating layer.

[0041] [Oxide Film] The oxide film is located on the surface of the alloy plating layer. The oxide film contains one or more elements from Group A elements consisting of Ni, Cu, V, Mo, W, and Nb, and Group B elements consisting of Li, Na, K, Rb, and Cs.

[0042] Total content of Group A and Group B elements: 0.01 to 45.00% by mass. If the total content of Group A and Group B elements in the oxide film of the hot stamping member is 0.01% by mass or more, hydrogen diffusion can be sufficiently suppressed during heating in hot stamping by the Group A and / or Group B elements sufficiently contained in the oxide film. In this embodiment, from the viewpoint of further reducing the hydrogen storage capacity of the hot stamping member, it is preferable that the oxide film contains Group B elements. Furthermore, if Group A elements are included, from the same viewpoint, it is preferable that one or more of Mo, W, and Nb are included.

[0043] If the total content of Group A and Group B elements in the oxide film is less than 0.01% by mass, the total content of Group A and Group B elements in the oxide film is insufficient, and the hydrogen storage capacity of the hot-stamped member increases. Therefore, the total content of Group A and Group B elements in the oxide film should be 0.01% by mass or more. It is not necessary to include both Group A and Group B elements; it may include at least one of Group A elements or at least one of Group B elements, with a content of 0.01% by mass or more. The total content of Group A and Group B elements in the oxide film is preferably 0.10% by mass or more, more preferably 0.30% by mass or more, or 1.00% by mass or more. There is no particular upper limit specified for the total content of Group A and Group B elements in the oxide film, but it should be 45.0% by mass or less. This upper limit may be 20.00% by mass or less, 15.00% by mass or less, 10.00% by mass or less, 7.00% by mass or less, 1.50% by mass or less, or 1.00% by mass or less.

[0044] The chemical composition of the oxide film is measured by the following method. For the hot-stamped member, a sample with a width of 10 μm and a depth of 5 to 35 μm is taken using a FIB (Focused Ion Beam) from the location described above so that the cross-section of the oxide film present on the surface of the alloy plating layer can be observed. Next, an elemental distribution image of the cross-section is obtained using TEM-EDS. Based on this elemental distribution image and the measurement results of the content of the elements targeted for point analysis by TEM-EDS, the region in which the combined content of Al and Si in the total content of elements excluding carbon is 20% by mass or more, and the content of O (oxygen) in the total content of elements excluding carbon is 30% by mass or less is identified as the alloy plating layer. In addition, the region on the surface of the alloy plating layer in which the combined content of Al and Si in the total content of elements excluding carbon is 20% by mass or more, and the content of O (oxygen) in the total content of elements excluding carbon is more than 30% by mass and 80% by mass or less is identified as the oxide film. Using TEM-EDS, the content of Group A and Group B elements is measured at a total of 10 locations in the oxide film, at the center of the thickness direction, with each location separated by at least 1 μm in a direction perpendicular to the thickness direction. The total content of Group A and Group B elements in the oxide film is obtained by calculating the average value of the 10 locations.

[0045] Average value of oxide film thickness: 10 to 2000 nm By setting the average value of the oxide film thickness to 10 nm or more, the amount of hydrogen absorbed by the hot-stamped member can be further reduced. Therefore, it is preferable that the average value of the oxide film thickness be 10 nm or more. More preferably, the average value of the oxide film thickness is 50 nm or more, 100 nm or more, 200 nm or more, or 300 nm or more. Furthermore, by setting the average value of the oxide film thickness to 2000 nm or less, deterioration of the weldability of the hot-stamped member can be suppressed. Therefore, it is preferable that the average value of the oxide film thickness be 2000 nm or less. The average value of the oxide film thickness may also be 1500 nm or less, 1000 nm or less, or 500 nm or less.

[0046] The average thickness of the oxide film is obtained by the following method: The oxide film is identified using the same method as when analyzing its chemical composition. The thickness of the oxide film is measured at a total of five locations, separated by at least 1 μm in the direction perpendicular to the thickness of the plate. The average thickness of the oxide film is obtained by calculating the average of these measurements.

[0047] [Base Steel Sheet] The chemical composition of the base steel sheet will be described below. Note that the chemical composition of the base steel sheet is not a technical feature essential for achieving the objectives of this disclosure. The following description is merely an example of a preferred chemical composition of the base steel sheet applied to the hot-stamped member and does not limit the base steel sheet of this disclosure.

[0048] The chemical composition of the base steel sheet is as follows (in mass%): C: 0.10-0.60%, Si: 0.01-0.60%, Mn: 0.001-3.000%, Al: 0.0002-2.000%, P: 0.100% or less, S: 0.1000% or less, N: 0.0200% or less, O: 0.0100% or less, Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.000%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, W: 0-1.000%. Preferably, the mixture consists of Hf: 0-0.050%, Mg: 0-0.050%, Zr: 0-0.050%, Ca: 0-0.500%, REM: 0-0.30%, Zn: 0-0.20%, Bi: 0-0.10%, Zr: 0-0.50%, Co: 0-3.00%, Sb: 0-0.50%, As: 0-0.10%, Sn: 0-0.10%, Hf: 0-0.10%, Te: 0-0.10%, Sr: 0-0.10%, Ta: 0-0.10%, Ir: 0-1.000%, with the remainder being Fe and impurities. Each element will be described in detail below.

[0049] C: 0.10-0.60% Carbon (C) is an element that increases tensile strength inexpensively and is an important element for controlling the strength of steel. To obtain this effect sufficiently, it is preferable that the C content be 0.10% or more. The C content may be 0.15% or more, 0.20% or more, 0.30% or more, or 0.35% or more. On the other hand, if the C content is excessive, it may cause a decrease in elongation. For this reason, it is preferable that the C content be 0.60% or less. The C content may be 0.50% or less, or 0.40% or less.

[0050] Si: 0.01-0.60% Si is an element that improves tensile strength and, like C, is an important element for controlling the strength of steel. If the Si content is less than 0.01%, the effect of improving strength is difficult to exert, and the tensile strength may not improve sufficiently. For this reason, it is preferable that the Si content be 0.01% or more. Also, Si is an easily oxidizable element. If the Si content exceeds 0.60%, the wettability may decrease during hot-dip plating due to the influence of Si-based oxides formed on the surface of the base steel sheet, which may result in non-plating. For this reason, it is preferable that the Si content be 0.60% or less. The Si content may also be 0.50% or less or 0.40% or less.

[0051] Mn: 0.001 to 3.000% Mn is an element that enhances the hardenability of steel and is effective in improving its strength. To fully obtain this effect, it is preferable that the Mn content be 0.001% or more. The Mn content may be 0.01% or more, 0.10% or more, or 0.20% or more. On the other hand, if Mn is included in excess, it may cause a decrease in elongation along with an increase in steel strength. For this reason, it is preferable that the Mn content be 3.000% or less. The Mn content may be 2.800% or less, 2.500% or less, or 2.000% or less.

[0052] Al: 0.0002 to 2.000% Al is an element that acts as a deoxidizing agent for steel and has the effect of sounding down steel. To obtain this effect to the fullest extent, it is preferable that the Al content be 0.0002% or more. The Al content may be 0.001% or more, 0.010% or more, 0.050% or more, or 0.100% or more. On the other hand, if Al is present in excess, coarse Al oxide may be generated, which may reduce the elongation of the steel sheet. For this reason, it is preferable that the Al content be 2.000% or less. The Al content may be 1.500% or less, 1.000% or less, 0.800% or less, or 0.500% or less.

[0053] P: 0.100% or less. P is an element that segregates at grain boundaries and promotes steel embrittlement. A lower P content is preferable, so 0% is preferable. However, excessive reduction of the P content causes a significant increase in cost. Therefore, it is preferable that the P content be 0.0001% or more. The P content may be 0.001% or more or 0.005% or more. On the other hand, if there is an excess of P, it may cause steel embrittlement due to grain boundary segregation. Therefore, it is preferable that the P content be 0.100% or less. The P content may be 0.050% or less, 0.030% or less or 0.010% or less.

[0054] S: 0.1000% or less. S is an element that generates nonmetallic inclusions such as MnS in steel, causing a decrease in the elongation of hot-stamped members. A lower S content is preferable, so 0% is preferable. However, excessive reduction of the S content causes a significant increase in cost. Therefore, the S content may be 0.0001% or more. The S content may be 0.0002% or more, 0.0010% or more, or 0.0050% or more. On the other hand, if there is an excessive amount of S, cracks may occur during cold forming, starting from nonmetallic inclusions. Therefore, it is preferable that the S content be 0.1000% or less. The S content may be 0.0500% or less, 0.0200% or less, or 0.0100% or less.

[0055] N: 0.0200% or less. N is an element that forms coarse nitrides in steel sheets, reducing the workability of the steel sheet. A lower N content is preferable, so 0% is preferable. However, excessive reduction of the N content causes a significant increase in manufacturing costs. Therefore, it is preferable that the N content be 0.0001% or more. The N content may be 0.0005% or more or 0.0010% or more. On the other hand, if N is included in excess, as described above, it may form coarse nitrides and reduce the workability of the steel sheet. Therefore, it is preferable that the N content be 0.0200% or less. The N content may be 0.0150% or less, 0.0100% or less, 0.0080% or less or 0.0050% or less.

[0056] O: 0.0100% or less. O is an element that, when present in large quantities in steel, forms coarse oxides that act as fracture initiation points, causing brittle fracture and hydrogen-induced cracking. If the O content exceeds 0.0100%, brittle fracture and hydrogen-induced cracking are more likely to occur in the base steel sheet. Therefore, the O content should be 0.0100% or less. Preferably, the O content is 0.0080% or less, 0.0060% or less, 0.0050% or less, 0.0040% or less, or 0.0035% or less. Since a lower O content is preferable, the O content may be 0%. In order to disperse a large number of fine oxides during the deoxidation of molten steel, the O content may be 0.0005% or more, or 0.0010% or more.

[0057] The preferred chemical composition of the base steel sheet is, if necessary, to replace a portion of the remaining Fe with an optional element, such as Nb: 0-0.15%, Ti: 0-0.15%, V: 0-0.15%, Mo: 0-1.0%, Cr: 0-1.000%, Cu: 0-1.0%, Ni: 0-1.0%, B: 0-0.0100%, W: 0-1.000%, Hf: 0-0.050%, Mg: 0-0.050%, and Zr: 0-0.05%. It may contain one or more of the following elements: 0%, Ca: 0-0.500%, REM: 0-0.30%, Zn: 0-0.20%, Bi: 0-0.10%, Zr: 0-0.50%, Co: 0-3.00%, Sb: 0-0.50%, As: 0-0.10%, Sn: 0-0.10%, Hf: 0-0.10%, Te: 0-0.10%, Sr: 0-0.10%, Ta: 0-0.10%, and Ir: 0-1.000%. Each of these optional elements may be present in amounts of 0.0001% or more, 0.0005% or more, 0.001% or more, or 0.01% or more. In this embodiment, REM refers to the collective term for 17 elements consisting of Sc, Y, and lanthanides, and the REM content refers to the total content of these elements. In the case of lanthanides, they are added industrially in the form of mischmetal.

[0058] In the base steel sheet, the remainder other than the elements mentioned above consists of Fe and impurities. Impurities in the base steel sheet refer to components that are mixed in during the industrial production of the base steel sheet due to various factors in the manufacturing process, including raw materials such as ore and scrap.

[0059] The chemical composition of the base steel sheet can be measured using general analytical methods. The chemical composition of the base steel sheet can be measured by removing the oxide film and alloy plating layer by mechanical grinding, and then measuring the chips by ICP emission spectrometry (ICP-AES: Inductively Coupled Plasma-Atomic Emission Spectrometry) in accordance with JIS G 1201:2022. Specifically, a 35 mm square test piece is obtained from around the 1 / 2 thickness point of the base steel sheet, and the elemental content can be determined by measuring it using a Shimadzu ICPS-8100 or similar (measuring device) under conditions based on a pre-prepared calibration curve. C and S, which cannot be measured by ICP-AES, can be measured using combustion-infrared absorption spectroscopy, N can be measured using inert gas fusion-thermal conductivity spectroscopy, and O can be measured using inert gas fusion-nondispersive infrared absorption spectroscopy.

[0060] The thickness of the base steel sheet is not particularly limited, but for example, 0.2 mm or more is preferred. The thickness of the base steel sheet may be 0.3 mm or more, 0.6 mm or more, 1.0 mm or more, or 2.0 mm or more. Alternatively, the thickness of the base steel sheet may be 6.0 mm or less. The thickness of the base steel sheet may be 5.0 mm or less, or 4.0 mm or less.

[0061] Vickers hardness: 242.4 HV or higher In the hot-stamped member according to this embodiment, the Vickers hardness at a position 1 / 4 of the thickness of the base steel sheet from the surface of the base steel sheet is 242.4 HV or higher. If the Vickers hardness is 242.4 HV or higher, it can be determined that the member has high strength. Preferably, the Vickers hardness is 300.0 HV or higher, 400.0 HV or higher, 500 HV or higher, or 600 HV or higher. There is no particular upper limit, but it may be 1000.0 HV or lower or 900 HV or lower. The surface of the base steel sheet referred to here means, in other words, the interface between the base steel sheet and the alloy plating layer. The interface between the base steel sheet and the alloy plating layer can be determined by the method using FE-EPMA described above. Specifically, the content of each element is analyzed at 1 μm intervals from the surface of the hot-stamped member (i.e., the surface of the oxide film) toward the center of the plate thickness, and the position where the Fe content first exceeds 95% of the total content of elements excluding carbon is identified as the interface between the base steel plate and the alloy plating layer.

[0062] Vickers hardness is measured by the following method. The Vickers hardness test is performed in accordance with JIS Z 2244-1:2024. In the Vickers hardness test, five Vickers hardness points are measured at a position 1 / 4 of the way from the surface of the base steel plate on the cross section (thickness section) of the polished test piece, specifically at a position 1 / 4 of the thickness from the surface of the base steel plate in the thickness direction, with a load of 9.8 N and a load holding time of 10 seconds. The Vickers hardness at a position 1 / 4 of the way from the surface of the base steel plate is obtained by calculating the average of three of the obtained measurements, excluding the maximum and minimum values. Alternatively, the tensile strength may be measured by the method described later, and the tensile strength (MPa) may be converted to Vickers hardness by dividing it by 3.3 (tensile strength / 3.3).

[0063] In the base steel sheet of the hot-stamped member according to this embodiment, the microstructure is preferably mainly composed of martensite. Specifically, it is preferable that 70% or more of the area is martensite. If the area ratio of martensite in the microstructure of the base steel sheet is 70% or more, the hot-stamped member including the base steel sheet can be identified as having been hot-stamped. Furthermore, it is more preferable that the area ratio of martensite be 80% or more, 90% or more, 95% or more, or 100%. The remaining microstructure may include one or more of retained austenite, bainite, ferrite, and pearlite. Note that martensite also includes tempered and auto-tempered martensite. Auto-tempered martensite is tempered martensite that is generated during cooling during quenching without heat treatment for tempering, and is generated when the martensite generated by the heat generated accompanying the martensitic transformation is tempered on the spot.

[0064] <Method for Manufacturing Al-Plated Steel Sheets> A preferred method for manufacturing Al-Plated steel sheets for producing hot-stamped members according to this embodiment will be described below. The following description is intended to illustrate characteristic methods for manufacturing Al-Plated steel sheets for producing hot-stamped members according to this embodiment, and is not intended to limit the manufacturing to those produced by the manufacturing methods described below.

[0065] Al-plated steel sheets can be manufactured, for example, by a casting process in which molten steel with an adjusted chemical composition is cast to form a steel billet; a hot rolling process in which the steel billet is hot-rolled to obtain a hot-rolled steel sheet; a cold rolling process in which the hot-rolled steel sheet is cold-rolled to obtain a cold-rolled steel sheet; an annealing process in which the cold-rolled steel sheet is annealed to obtain a cold-rolled and annealed steel sheet; a plating process in which an Al-plated layer is formed on the cold-rolled and annealed steel sheet; and a film formation process in which a film is formed on the surface of the Al-plated layer. Alternatively, the sheet may be pickled after the hot-rolling process and then immediately subjected to the cold-rolling process without being wound up. Each process will be explained in detail below.

[0066] [Casting Process] The conditions for the casting process are not particularly limited. For example, after melting in a blast furnace or electric furnace, various secondary smelting processes may be carried out, followed by casting using methods such as conventional continuous casting or ingot casting.

[0067] [Hot Rolling Process] Hot-rolled steel sheets can be obtained by hot-rolling cast steel billets. The hot-rolling process is carried out by hot-rolling the cast steel billet either directly or after it has been cooled and then reheated. When reheating is performed, the heating temperature of the steel billet may be, for example, 1100 to 1250°C. In the hot-rolling process, rough rolling and finish rolling are usually performed. The temperature and reduction ratio of each rolling can be appropriately determined according to the desired metal structure and sheet thickness. For example, the end temperature of finish rolling (the exit temperature of the final stand) may be 900 to 1050°C, and the reduction ratio of finish rolling may be 10 to 50%. Note that the reduction ratio of finish rolling referred to here is the total reduction ratio in finish rolling, and the sheet thickness before finish rolling is t ０ The thickness of the sheet after finish rolling is t １ When this is the case, (1-t １ / t ０ It can be expressed as ) × 100 (%).

[0068] Hot-rolled steel sheets can be wound at a predetermined temperature. The winding temperature can be appropriately determined according to the desired metal structure, etc., and may be, for example, 500 to 800°C. Before or after winding, the hot-rolled steel sheet may be unwound and subjected to a predetermined heat treatment. After the hot-rolling process, it is also possible to pickle the sheet and then perform the cold-rolling process described later.

[0069] [Cold Rolling Process] Cold-rolled steel sheets can be obtained by cold-rolling hot-rolled steel sheets. The reduction ratio in cold rolling can be appropriately determined according to the desired metal structure and sheet thickness, and may be, for example, 20 to 80%. After the cold rolling process, the sheet may be cooled to room temperature by air cooling, for example. Note that the reduction ratio in cold rolling referred to here is the total reduction ratio in cold rolling, and the sheet thickness before cold rolling is t ２ Let the plate thickness after cold rolling be t ３ When this is the case, (1-t ３ / t ２ It can be expressed as ) × 100 (%).

[0070] [Annealing Process] Cold-rolled annealed steel sheets can be obtained by annealing cold-rolled steel sheets. The annealing process includes heating the cold-rolled steel sheet to a temperature range of 730 to 900°C in an atmosphere with a dew point of -50 to 20°C and holding it for 10 to 300 seconds. Cooling after annealing should be carried out at a cooling rate suitable for obtaining the desired metal structure from the holding temperature down to the immersion temperature of the plate in the subsequent plating process. Although not particularly limited, for example, the cooling process may be carried out at an average cooling rate of 10°C / s or more from the heating temperature of the annealing process down to the immersion temperature of the plate in the plating process.

[0071] [Plating Process] In the plating process, an Al-based plating layer having the chemical composition and form described above is formed on at least one, preferably both, surfaces of the cold-rolled annealed steel sheet (base steel sheet). The plating process is carried out, for example, by hot-dip galvanizing. The conditions of the plating process can be appropriately set considering the thickness and amount of the Al-based plating layer, etc. For example, after immersing the cold-rolled annealed steel sheet in the plating bath, it is removed and immediately treated with N by the gas wiping method. ２ By blowing gas or air onto the plate and then cooling it, the thickness of the Al-based plating layer can be adjusted to a predetermined range, for example, within the range of 10 to 60 μm.

[0072] During the cooling process after plating, powder spraying is performed from the time of plating until the temperature reaches 600°C. The powder spraying involves spraying aluminum oxide with an average particle size of 10 μm or less along with gas at a speed of 1 to 25 m / s. This allows for the presence of a desired amount of Si near the surface of the Al-based plating layer. This is because the sprayed powder acts as a nucleus for Si crystallization, and the rapid cooling of the Al-based plating layer surface promotes Si crystallization near the surface of the Al-based plating layer.

[0073] If the powder spraying speed is less than 1 m / s, the surface of the Al-based plating layer is not sufficiently cooled, and the Si phase does not crystallize sufficiently near the surface of the Al-based plating layer. In this case, the Si phase crystallizes using the surface of the base steel sheet or the Fe-Al alloy layer, which is an alloy of the Al-based plating layer and the base steel sheet, as a nucleus. As a result, it is not possible to suppress the reduction of Si near the surface of the Al-based plating layer, and this Si amount cannot be controlled to the desired range. Therefore, if the powder spraying speed is less than 1 m / s, even if the Si content in the chemical composition of the Al-based plating layer is high, for example, 25.0%, it is not possible to make the Si near the surface of the Al-based plating layer greater than the desired amount. As a result, it is not possible to form an oxide film containing the desired amount of Group A elements and / or Group B elements. If the powder spraying speed is greater than 25 m / s, not only the surface of the Al-based plating layer but also the base steel sheet is cooled, which promotes the crystallization of Si using the surface of the base steel sheet or the Fe-Al alloy layer, which is an alloy of the Al-based plating layer and the base steel sheet, as a nucleus. As a result, it is not possible to control the amount of Si near the surface of the Al-based plating layer to the desired range.

[0074] By concentrating Si near the surface of the Al-based plating layer, the reaction between the Group A and / or Group B elements in the coating and the oxide film can be sufficiently promoted during heating in hot stamping. When Si is concentrated near the surface of the Al-based plating layer, both Al and Si are oxidized during heating in hot stamping. As a result, the presence of Si-based oxides suppresses the coarsening of the oxide film grains, refines the oxide film, and increases the number of grain boundaries that serve as diffusion paths. This promotes the reaction between the oxide film and the coating. Consequently, an oxide film containing Group A and / or Group B elements can be generated during heating in hot stamping, and this oxide film suppresses hydrogen diffusion, thereby reducing the hydrogen storage capacity of the hot stamped component.

[0075] [Film Formation Process] In the film formation process, a film is formed on the surface of the Al-based plating layer. The method of forming the film is not particularly limited, but for example, the film can be formed by the following method.

[0076] A solution containing a desired amount of Group A elements and / or Group B elements is applied to the surface of an Al-based plating layer, and drying is performed as necessary to form a coating film. Here, the solution preferably contains an organic and / or inorganic binder. Examples of organic binders include polyurethane resins, polyester resins, acrylic resins, epoxy resins, polyamide resins, polyolefin resins, silane coupling agents, etc. Most of these organic binders disappear during heating in hot stamping. Examples of inorganic binders include Zr oxides, bromides, chlorides, fluorides, hydroxides, carbides, nitrides; Ti oxides, bromides, chlorides, fluorides, hydroxides, carbides, nitrides; Zn oxides, bromides, chlorides, fluorides, hydroxides, carbides, nitrides; colloidal silica, etc.

[0077] A film with an amorphous content of 90% or more can be formed by applying an aqueous solution containing Group A elements and / or Group B elements to the surface of an Al-based plating layer, and then heating the coating to 100°C at an average heating rate of 5.0 to 100°C / s during drying. Heating to 100°C at an average heating rate of 5.0 to 100°C / s rapidly evaporates the water, increasing the frequency of nucleation of solid components in the film, thereby refining the crystal grains and promoting amorphous formation. To prevent the Al-based plating layer from alloying with the base metal and reducing adhesion, it is preferable to limit the heating at the above average heating rate to an upper limit of 600°C. Furthermore, the temperature at which heating begins, i.e., the temperature at which coating takes place, is preferably, for example, 5 to 40°C, in order to prevent the water in the aqueous solution containing Group A elements and / or Group B elements from solidifying or evaporating during coating. Note that the atmosphere during heating is not limited to air or vacuum. Typical methods for applying the solution include bar coating, roller coating, and spraying, but the method is not limited to these techniques.

[0078] By making a portion of the coating amorphous, the diffusion paths of the substance increase compared to crystalline coatings, and the reaction between the Group A elements and / or Group B elements in the coating and the oxide film is further promoted during heating in hot stamping. As a result, the oxide film can further suppress hydrogen diffusion, and the hydrogen storage capacity of the hot stamped member is further reduced.

[0079] [Hot Stamping Process] Hot stamped components can be obtained by performing hot stamping on Al-plated steel sheets. In hot stamping, Al-plated steel sheets are blanked (punched) as needed, and then Ac ３ The material is heated to a temperature above 15°C to soften it. After the softened Al-plated steel sheet is pressed, it is cooled (quenched). In addition to conventional electric furnaces and radiant tube furnaces, far-infrared heating can also be used as a heating method.

[0080] In hot stamping, heating is preferably performed in a furnace at a temperature of 800 to 1000°C for at least 3 minutes. If the heating time is shorter than 3 minutes, the tensile strength of the hot stamped material may not be sufficiently high. While there is no need to limit the upper limit of the heating time, it is preferable to keep it to 10 minutes or less from the viewpoint of corrosion resistance after painting. If the heating temperature is lower than 800°C, the tensile strength may be insufficient. Therefore, the heating temperature should be 800°C or higher. While there is no need to limit the upper limit of the heating temperature, it should be kept below 1000°C from the viewpoint of equipment load.

[0081] The heating atmosphere in hot stamping is not particularly limited and can be any normal conditions, such as air, a gas combustion atmosphere with a controlled air-fuel ratio, or a nitrogen atmosphere, and the dew point may be controlled in these atmospheres.

[0082] Next, embodiments of the present invention will be described. The conditions in the embodiments are merely examples of conditions adopted to confirm the feasibility and effectiveness of the present disclosure, and the present disclosure is not limited to these examples of conditions. The present disclosure may adopt various conditions insofar as they do not depart from the gist of the present disclosure and achieve the objectives of the present disclosure.

[0083] Steel having the chemical composition shown in Table 1 was melted and continuously cast. Subsequently, Al-plated steel sheets shown in Table 2 were obtained under the conditions of the Al-plated steel sheet manufacturing method described above. However, the thickness of the Al-plated layer was N ２ The formation of the Al-based plating layer and film was controlled by the gas wiping method, and various changes were made to the composition of the plating bath and the composition of the film-forming solution. In some cases, the average particle size and spraying speed of the sprayed powder were outside the ranges described above during the formation of the plating layer.

[0084] Furthermore, the chemical composition of the Al-based plating layer, the average thickness of the Al-based plating layer, the average Si content at a depth of 3 μm from the surface of the Al-based plating layer (Si content at a depth of 3 μm from the surface), the total content of Group A and Group B elements in the film (total content of Group A and Group B), the average thickness of the film (thickness), and the amorphous ratio of the film were measured using the following methods.

[0085] Chemical Composition of Al-Plated Layers A sample was cut from a portion of an Al-plated steel sheet at least 10 mm away from the edge, embedded in resin, and the cross-section of the Al-plated steel sheet was polished to create an observation surface. Next, carbon was deposited onto the sample to facilitate current flow, and then, using an FE-EPMA at an acceleration voltage of 10 kV and a magnification of 1500x or more, the content of each element was analyzed at 1 μm intervals from the surface toward the center of the thickness of the Al-plated steel sheet. Regions where the combined content of Al and Si in the total content of elements excluding carbon was 30% or more were identified as Al-plated layers. Carbon was excluded here to remove the carbon contained in the resin in which the sample was embedded from the measurement values. Point analysis was performed at 1 μm intervals from the surface of the Al-plated layer toward the center of the thickness to measure the content of the target element. These operations were performed at another location at a distance of at least 100 nm perpendicular to the thickness direction, for a total of five locations, and the average value of the content of the target element was calculated to obtain the chemical composition of the Al-plated layer.

[0086] Average Thickness of Al-Plated Plating Layer A sample was cut from a portion of the Al-plated steel sheet at least 10 mm away from the edge, embedded in resin, and the cross-section of the Al-plated steel sheet was polished to create an observation surface. Next, carbon was deposited onto the sample to facilitate current flow, and then point analysis was performed using FE-EPMA at an acceleration voltage of 10 kV and a magnification of 1500x or more to quantitatively analyze the content of each element. Point analysis was performed at 1 μm intervals from the surface of the Al-plated steel sheet toward the center of the sheet thickness. Regions where the sum of the content of Al and Si in relation to the total content of elements excluding carbon was 30 mass% or more were identified as the Al-plated layer, and regions where the sum of the content of Al and Si in relation to the total content of elements excluding carbon was less than 30 mass% were identified as regions other than the Al-plated layer. The thickness of the Al-plated layer was measured at a total of five locations, at least 10 μm apart in a direction perpendicular to the sheet thickness direction. The average value of these measurements was calculated to obtain the average thickness of the Al-plated layer.

[0087] The average Si content at a depth of 3 μm from the surface of the Al-based plating layer (Si content at a depth of 3 μm from the surface) was determined using the same method as when measuring the thickness of the Al-based plating layer. Next, at a depth of 3 μm from the surface of the Al-based plating layer, the Si content was measured by performing point analysis every 1 μm over a length of 30 μm in a direction perpendicular to the thickness direction. The same operation was performed at seven locations (a total length of 210 μm), and the average value of the obtained Si content was calculated to obtain the average Si content at a depth of 3 μm from the surface of the Al-based plating layer.

[0088] The total content of Group A and Group B elements in the coating (total content of Group A and Group B) was determined. Samples with a width of 10 μm and a depth of 5 to 35 μm were taken using a FIB (Focused Ion Beam) from a portion at least 10 mm away from the edge of the Al-plated steel sheet, specifically from a portion 15 mm away from the edge, so that the cross-section of the coating present on the surface of the Al-plated layer could be observed. Next, an elemental distribution image of the cross-section was obtained using TEM-EDS. Based on this elemental distribution image and the measurement results of the content of elements targeted for point analysis using TEM-EDS, the region where the total content of Al and Si in the total content of elements excluding carbon was 30 mass% or more was identified as the Al-plated layer, and the region where the total content of Al and Si in the total content of elements excluding carbon was less than 30 mass% and which was located on the surface of the Al-plated layer was identified as the coating. Using TEM-EDS, the content of Group A and Group B elements was measured at 10 locations in the film, at the center of the film's thickness direction, with each location separated by at least 100 nm in a direction perpendicular to the film's thickness direction. The total content of Group A and Group B elements in the film was obtained by calculating the average value across the 10 locations.

[0089] Average film thickness (thickness) The film was identified using the same method as when analyzing the chemical composition of the film. The film thickness was measured at a total of five locations, at a distance of 100 nm or more from each other in a direction perpendicular to the plate thickness direction. The average value of these measurements was calculated to obtain the average film thickness.

[0090] Amorphous Ratio of the Coating A sample with a width of 10 μm and a depth of 5 to 35 μm was taken from a portion of the Al-plated steel sheet at least 10 mm away from the edge, specifically at a portion 15 mm away from the edge, using a Focused Ion Beam (FIB) so that the cross-section of the coating present on the surface of the Al-plated layer could be observed. Next, the sample surface corresponding to the cross-section of the coating was subjected to electron diffraction using a TEM ("JEM-2100F", manufactured by JEOL Ltd.) with an electron beam probe diameter of 10 nm. The crystalline structure of the coating was determined by examining the obtained diffraction pattern.

[0091] The proportion of amorphous material in the coating was calculated using the following method: Diffraction patterns were obtained by electron diffraction at 10 points on the surface of the sample using a transmission electron microscope (TEM). If 9 or more of the 10 obtained diffraction patterns showed a ring-shaped pattern, it was determined that the proportion of amorphous material in the coating was 90% or more by area. The acceleration voltage during TEM observation was 200 kV. Furthermore, if the plated layer was included in the sample for analysis, it was excluded from the measurement, and only the coating was measured.

[0092] Hot stamping was performed on Al-plated steel sheets under the conditions shown in Table 3 to obtain the hot-stamped members shown in Table 4. The tensile strength and hydrogen storage capacity of the hot-stamped members were evaluated using the method described later. The results are shown in Table 4. Underlined text in the table indicates that the product is outside the scope of this disclosure or that the manufacturing conditions are undesirable.

[0093] Tensile strength was obtained by taking a No. 5 test specimen in accordance with JIS Z 2241:2022 and performing a tensile test. The tensile test specimen was taken from the 1 / 4 portion from the end of the hot-stamped member. The tensile test was performed twice, and the average value was used as the representative value. If it is not possible to take a No. 5 test specimen due to the small size or complex shape of the hot-stamped member, the Vickers hardness may be measured using the method described above, and the Vickers hardness may be converted to tensile strength by multiplying it by 3.3 (Vickers hardness × 3.3). Alternatively, the value obtained by dividing the tensile strength by 3.3 (tensile strength / 3.3) is used as the converted Vickers hardness value (HV) and is listed in the table.

[0094] If the tensile strength was 800 MPa or higher, i.e., if the Vickers hardness equivalent value was 242.2 HV or higher, it was judged to have high strength and was deemed acceptable. On the other hand, if the tensile strength was less than 800 MPa, i.e., if the Vickers hardness equivalent value was less than 242.2 HV, it was judged to not have high strength and was deemed unacceptable.

[0095] Hydrogen storage capacity was evaluated using the temperature-induced desorption method. The temperature was increased at 100°C / h, and the amount of hydrogen released up to 250°C was measured. The samples were stored at -70°C or below from the time of hot stamping until the start of measurement, and the evaluation was performed within 30 days of storage. Hydrogen storage capacity was defined as the mass of hydrogen relative to the mass of the hot-stamped material. If the hydrogen storage capacity was 0.80 ppm by mass or less, it was judged as a pass, indicating that the hydrogen storage capacity had been reduced. On the other hand, if the hydrogen storage capacity was greater than 0.80 ppm by mass, it was judged as a fail, indicating that the hydrogen storage capacity had not been reduced. Furthermore, if the hydrogen storage capacity was 0.60 ppm by mass or less, it was judged that the hydrogen storage capacity had been further reduced.

[0096] The corrosion resistance after painting was evaluated by the following method. A 100 mm x 50 mm x 1.4 mm test piece was taken from the hot-stamped material, chemically treated with a chemical conversion solution (PB-SX35) manufactured by Nippon Parkerizing Co., Ltd., and then coated with electrodeposition paint (Powernix 110) manufactured by Nippon Paint Co., Ltd. to a film thickness of 20 μm after baking. The baking treatment was performed by heating at 170°C for 20 minutes. Next, a straight cut defect reaching the plating layer was introduced in the center of the test piece. Then, a combined cycle corrosion test in accordance with JASO (M609-91) was performed for 120 cycles, and the film blister width (maximum value on one side) was measured, and the corrosion resistance after painting was evaluated according to the following criteria. If the evaluation was A, it was judged to be a pass, indicating that it has excellent corrosion resistance after painting. If the evaluation was B, it was judged to be a fail, indicating that it does not have excellent corrosion resistance after painting. A: 6 mm or less B: Greater than 6 mm

[0097]

[0098]

[0099]

[0100]

[0101] As can be seen from the above, the hot-stamped member according to the present invention has high strength and excellent corrosion resistance after painting, and its hydrogen storage capacity is reduced.

[0102] According to the above embodiment, it is possible to provide a hot-stamped member that has high strength and excellent corrosion resistance after painting, and also has reduced hydrogen storage capacity.

[0103] 1. Base material steel sheet 2. Al-based plating layer 3. Coating 4. Alloy plating layer 5. Oxide film 10. Al-based plated steel sheet 11. Hot stamping component

Claims

1. A hot-stamping member comprising a base steel sheet, an alloy plating layer located on the surface of the base steel sheet, and an oxide film located on the surface of the alloy plating layer, wherein the alloy plating layer has a chemical composition consisting of, by mass%, Si: 2.0 to 20.0% and Fe: 35.0 to 80.0%, with the remainder being Al and impurities, the average thickness of the alloy plating layer is 10 to 60 μm, the oxide film contains a total of 0.01 to 45.00 mass% of one or more elements from group A elements consisting of Ni, Cu, V, Mo, W, and Nb, and group B elements consisting of Li, Na, K, Rb, and Cs, and the Vickers hardness at a position 1 / 4 of the way from the surface of the base steel sheet is 242.4 HV or higher.

2. The hot stamping member according to claim 1, characterized in that the oxide film contains a total of 0.10 to 45.00% by mass of one or more elements from the elements of group A and the elements of group B.

3. The hot stamping member according to claim 1 or 2, characterized in that the average thickness of the oxide film is 10 to 2000 nm.

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