Al-PLATED STEEL SHEET

Abstract

This Al-plated steel sheet comprises: a base steel sheet; an Al-plating layer that is positioned on the surface of the base steel sheet; and a coating film that is positioned on the surface of the Al-plating layer. The Al-plating layer has a chemical composition containing, in mass%, 7.0-25.0% of Si and 25.0% or less of Fe, with the balance being Al and impurities. The average value of the thickness of the Al-plating layer is 10-60 μm. The average value of the Si content at a position at a depth of 3 μm from the surface of the Al-plating layer is 3-70 mass%. The coating film contains a total of 0.1 mass% or more of one or more elements from among group A elements and group B elements. The average value of the thickness of the coating film is 0.01-30.0 μm.

Description

Al-plated steel sheet

[0001] This disclosure relates to an Al-plated steel sheet. This application claims priority under Japanese Patent Application No. 2025-055487, filed in Japan on March 28, 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 an Al-based plated steel sheet that can be used to manufacture hot-stamped members having excellent post-coating corrosion resistance and reduced hydrogen storage capacity.

[0010] The gist of this disclosure is as follows: [1] An Al-plated steel sheet comprising a base steel sheet, an Al-based plating layer located on the surface of the base steel sheet, and a film located on the surface of the Al-based plating layer, wherein the Al-based plating layer has a chemical composition consisting of, by mass%, Si: 7.0 to 25.0%, Fe: 25.0% or less, with the remainder being Al and impurities, the average thickness of the Al-based plating layer is 10 to 60 μm, the average Si content at a depth of 3 μm from the surface of the Al-based plating layer is 3 to 70% by mass, the film contains a total of 0.1% by mass or more 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 average thickness of the film is 0.01 to 30.0 μm. [2] The Al-plated steel sheet according to [1], characterized in that the coating is amorphous.

[0011] According to the above embodiment, it is possible to provide an Al-plated steel sheet that has excellent post-coating corrosion resistance and reduced hydrogen storage capacity, enabling the manufacture of hot-stamped members.

[0012] This is a schematic diagram showing the cross-section of an Al-plated steel sheet. This is a schematic diagram showing the cross-section of a hot-stamped member. This figure shows an example of electron diffraction patterns of the cross-section of the Al-plated layer and film on an Al-plated steel sheet, obtained by TEM.

[0013] The inventors investigated an Al-based plated steel sheet that can be used to manufacture 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-based 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-based plated steel sheet 10 comprising a base steel sheet 1, an Al-based plating 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 ３In the heating process to a temperature range higher than the melting 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. The hydrogen diffuses through the oxide film 5 and the alloy plating layer 4 and penetrates into the base steel sheet 1. 2Al+3H ２ 2O→Al2 ２ O3 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 the diffusion of hydrogen in either 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 for reducing the hydrogen absorption amount of the base steel sheet 1 after hot stamping. The group A elements have a monovalent valence, and the group B elements have a divalent valence, which are different from the valence (trivalent) of Al. Group A elements or group B elements are incorporated into Al2 ２ O3 ３ by substituting Al in the oxide film 5, in order to maintain charge balance, Al2 ２ O3 ３ lattice defects in the oxide film 5 are reduced, hydrogen diffusion paths are decreased, and the diffusion rate of hydrogen in the oxide film 5 can be reduced.

[0015] In the Al-based plated steel sheet 10 to be subjected to hot stamping, a film containing group A elements and / or group B elements is provided on the surface of the Al-based plating layer 2, and a desired amount of Si is allowed to exist near the surface of the Al-based plating layer 2. Thereby, during heating in hot stamping, the oxide film 5 sufficiently containing group A elements and / or group B elements can be formed on the surface of the alloy plating layer 4. As a result, during heating in hot stamping, the diffusion of hydrogen in the oxide film 5 can be suppressed, and a hot stamped member with a reduced hydrogen absorption amount can be manufactured.

[0016] In the Al-based plated steel sheet, the film 3 acts as a source of Group A elements and / or Group B elements for the oxide film 5. However, simply applying the film is not enough to generate the oxide film 5 containing Group A elements and / or Group B elements on the surface of the alloy plating layer 4 by heating in hot stamping. By applying the film 3 containing Group A elements and / or Group B elements, and by providing a desired amount of Si near the surface of the Al-based plating layer 2, the reaction between the Group A elements and / or Group B elements in the film 3 and the oxide film 5 can be promoted during heating in hot stamping.

[0017] If a desired amount of Si is present near the surface of the Al-based plating layer 2, both Al and Si will be oxidized during heating in hot stamping. As a result, the presence of Si-based oxides refines the crystal grains of the oxide film 5, increasing the number of grain boundaries that serve as diffusion paths for group A elements and / or group B elements in the film 3. This promotes the reaction between the oxide film 5 and the film 3. Consequently, an oxide film 5 containing group A elements and / or group B elements can be generated during heating in hot stamping, and this oxide film 5 suppresses hydrogen diffusion, thereby reducing the amount of hydrogen absorbed by the hot stamping member 11.

[0018] More preferably, by making the coating 3 of the Al-plated steel sheet 10 amorphous, the reaction between the group A elements and / or group B elements in the coating 3 and the oxide film 5 can be further promoted during heating in hot stamping. The amorphous coating 3 contains more diffusion paths for substances than the crystalline coating 3. As a result, the oxide film 5 can further suppress hydrogen diffusion, and the amount of hydrogen absorbed by the hot stamping member 11 can be further reduced.

[0019] The following describes in detail an Al-based plated steel sheet according to one embodiment of this disclosure. Note that the numerical limit ranges indicated by "~" below include both a lower limit and an upper limit. Numbers indicated as "less than" or "greater than" do not include the numerical range. Furthermore, all percentages for chemical composition represent mass percentages. Reference numerals in the drawings are omitted in the following description.

[0020] <Al-based plated steel sheet> The Al-based plated steel sheet according to this embodiment comprises a base steel sheet, an Al-based plating layer located on the surface of the base steel sheet, and a film located on the surface of the Al-based plating layer. First, the Al-based plating layer will be described in detail.

[0021] [Al-based plating layer] The Al-based plating layer has a chemical composition consisting of Si: 7.0 to 25.0% and Fe: 25.0% or less by mass, with the remainder being Al and impurities. The Al-based plating layer is not particularly limited, but it is preferably a hot-dip plating layer. The following describes each element.

[0022] Si: 7.0-25.0% Si is an effective element for reducing the hydrogen storage capacity of hot-stamped components. To fully obtain this effect, the Si content should be 7.0% or more. The Si content may also be 9.0% or more, 12.0% or more, or 15.0% or more. On the other hand, if the Si content exceeds 25.0%, the corrosion resistance of the hot-stamped component after painting will decrease. Therefore, the Si content should be 25.0% or less. The Si content may also be 20.0% or less.

[0023] Fe: 25.0% or less. Fe is an element that can be included in the Al-based plating layer, for example, by dissolving from the base steel sheet into the plating bath or by reacting with Al in the Al-based plating layer during the plating process to form an alloy phase containing Fe and Al. Since it is difficult to make the Fe content 0%, it is preferable that the Fe content be 0.1% or more. The Fe content may be 1.0% or more, 5.0% or more, or 7.0% or more. On the other hand, if the Fe content exceeds 25.0%, the adhesion of the Al-based plating layer decreases. Therefore, the Fe content should be 25.0% or less. Preferably, the Fe content is 20.0% or less, 15.0% or less, or 10.0% or less.

[0024] The Al-based plating layer may contain the following optional elements in place of a portion of the remaining Al. Since the optional elements are not required to be present, the lower limit is 0%. The total content of the optional elements is preferably 5.000% or less. The total 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.

[0025] Zn: 0 to 0.500% Zn has a sacrificial corrosion protection effect and is an effective element for improving the corrosion resistance of Al-based plating layers. 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.

[0026] Ni: 0 to 0.500% Ni is an effective element for improving the corrosion resistance of the Al-based 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.

[0027] Mg: 0-3.000% Mg is an effective element for improving the corrosion resistance of the Al-based 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 improving processability, 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.

[0028] Ca: 0-3.000% Ca is an effective element for improving the wettability of the plating bath. 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, if Ca is present in excess, a large amount of hard intermetallic compounds may be formed in the Al-based plating layer, making the Al-based plating layer brittle and reducing its adhesion to the base steel sheet. Therefore, it is preferable that the Ca content 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.

[0029] 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 have to be included in the Al-based plating layer, but they may be included in amounts of 0.0001% or more, 0.001% or more, or 0.01% or more. These elements do not adversely affect the Al-based plated steel sheet according to this embodiment as long as they are within a predetermined content range. 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.

[0030] In the chemical composition of the Al-based plating layer, the remainder consists of Al and impurities. In this embodiment, impurities refer to components that are mixed in during the formation of the Al-based plating layer due to various factors in the manufacturing process, including the raw materials.

[0031] The chemical composition of the Al-based plating layer is measured by the following method. A sample is cut from a portion of the Al-based plated steel sheet at least 10 mm away from the edge, and the sample is embedded in resin. The cross-section of the Al-based plated steel sheet is then polished to create an observation surface. Next, carbon is 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, point analysis is performed to determine the content of each element at 1 μm intervals from the surface toward the center of the thickness of the Al-based plated steel sheet. The region where the combined content of Al and Si accounts for 30% or more of the total content of elements excluding carbon is identified as the Al-based plating layer. Carbon is excluded here to remove 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 toward the center of the thickness of the Al-based plating layer 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 Al-based plating layer is obtained.

[0032] Average thickness of the Al-based plating layer: 10 to 60 μm If the average thickness of the Al-based 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 Al-based plating layer should be 10 μm or more. Preferably, the average thickness of the Al-based 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 Al-based plating layer exceeds 60 μm, the area near the surface of the Al-based plating layer will not alloy with the base steel plate during heating in hot stamping, and the corrosion resistance of the hot-stamped member after painting will be insufficient. Therefore, the average thickness of the Al-based plating layer should be 60 μm or less. Preferably, the average thickness of the Al-based plating layer is 50 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less.

[0033] The average thickness of the Al-based plating layer is obtained by the following method. Cut a sample from a portion at least 10 mm away from the end of the Al-based plated steel sheet, embed the sample in resin, polish the thickness cross-section of the Al-based plated steel sheet to obtain an observation surface. Then, after vapor-depositing carbon on the sample to facilitate energization, point analysis is performed using FE-EPMA at an acceleration voltage of 10 kV and a magnification of 1500× or higher to quantitatively analyze the content of each element. Point analysis is performed every 1 μm from the surface of the Al-based plated steel sheet toward the center of the sheet thickness, and a region where the total content of Al and Si accounts for 30 mass% or more of the total content of elements excluding carbon is identified as the Al-based plating layer. Additionally, a region where the total content of Al and Si accounts for less than 30 mass% of the total content of elements excluding carbon is identified as a region other than the Al-based plating layer. The thickness of the Al-based plating layer is measured at a total of 5 locations, with each location separated by 10 μm or more in the direction perpendicular to the sheet thickness direction. The average value of these measurements is calculated to obtain the average thickness of the Al-based plating layer.

[0034] Average Si content at a position 3 μm deep from the surface of the Al-based plating layer: 3 to 70 mass% Generally, during the cooling process after plating using an Al-based plating bath containing Si, Si crystallizes in the Al-based plating layer. In the present embodiment, the average Si content at a position near the surface of the Al-based plating layer (a position 3 μm deep from the surface) is set to 3 to 70 mass%. In the present embodiment, the surface of the Al-based plating layer refers, in other words, to the interface between the Al-based plating layer and the coating film.

[0035] In this embodiment, the reduction of Si content near the surface of the Al-based plating layer is suppressed, and a desired amount of Si is present. This promotes the reaction between the Group A elements and / or Group B elements in the film and the oxide film during heating in hot stamping, making it possible to form an oxide film containing the desired amount of Group A elements and / or Group B elements. Although not intended to be bound by any particular theory, the inventors speculate that the reason is as follows: When a desired amount of Si is present 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 crystal grains of the oxide film, and the oxide film becomes finer, increasing the number of crystal grain boundaries that serve as diffusion paths. This promotes the reaction between the oxide film and the coating.

[0036] If the average Si content at a depth of 3 μm from the surface of the Al-based plating layer is less than 3 mass%, it is not possible to form an oxide film containing the desired amount of Group A elements and / or Group B elements after hot stamping. As a result, the hydrogen storage capacity of the hot-stamped member increases. Therefore, the average Si content at a depth of 3 μm from the surface of the Al-based plating layer should be 3 mass% or more. Preferably, the average Si content is 5 mass% or more, 9 mass% or more, 12 mass% or more, 15 mass% or more, 20 mass% or more, 30 mass% or more, or 50 mass% or more. If the average Si content at a depth of 3 μm from the surface of the Al-based plating layer exceeds 70 mass%, the Si content of the Al-based plating layer must be greater than 25.0 mass%. As described above, if the Si content in the Al-based plating layer exceeds 25.0 mass%, the corrosion resistance of the hot-stamped member after painting decreases. Therefore, the average Si content at a depth of 3 μm from the surface of the Al-based plating layer should be 70 mass or less. The average Si content is preferably 65% ​​by mass or less, or 60% by mass or less.

[0037] The average value of Si content at a position 3 µm deep from the surface of the Al-based plating layer is obtained by the following method. The Al-based plating layer is identified by the same method as that used when measuring the thickness of the Al-based plating layer. Then, at a position 3 µm deep from the surface of the Al-based plating layer, point analysis is performed every 1 µm over a length of 30 µm in a direction perpendicular to the plate thickness direction to measure the Si content. The same operation is performed at 7 locations (total length of 210 µm), and the average value of the obtained Si content is calculated, thereby obtaining the average value of Si content at a position 3 µm deep from the surface of the Al-based plating layer.

[0038] [Coating Film] The coating film is located on the surface of the Al-based plating layer. The coating film contains one or more elements selected from the group A elements consisting of Ni, Cu, V, Mo, W and Nb, and the group B elements consisting of Li, Na, K, Rb and Cs. From the viewpoint of further reducing the hydrogen absorption amount of the hot stamped member, the coating film preferably contains a group B element.

[0039] Total content of group A elements and group B elements: 0.1 mass% or more When the total content of group A elements and group B elements in the coating film is less than 0.1 mass%, the reaction between the group A elements and / or group B elements in the coating film and the oxide film composed of Al-Si-Fe oxide becomes insufficient during heating in hot stamping, so that a desired amount of group A elements and / or group B elements cannot be secured in the oxide film of the hot stamped member. As a result, the diffusion of hydrogen in the oxide film of the hot stamped member is not suppressed, and the hydrogen absorption amount of the hot stamped member increases. Therefore, the total content of group A elements and group B elements in the coating film is set to 0.1 mass% or more. It is not necessary to contain both group A elements and group B elements; the coating may contain at least one of group A elements or at least one of group B elements, and the content thereof may be 0.1 mass% or more. The total content of group A elements and group B elements in the coating film is preferably 1.0 mass% or more, 5.0 mass% or more, or 10.0 mass% or more. The upper limit of the total content of group A elements and group B elements in the coating film is not particularly limited, and may be 95.0 mass% or less, 80.0 mass% or less, 70.0 mass% or less, 50.0 mass% or less, 30.0 mass% or less, or 20.0 mass% or less.

[0040] The chemical composition of the coating is measured by the following method. 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 a portion of the Al-plated steel sheet that is 10 mm or more away from the edge, preferably 15 mm away from the edge, so that the cross-section of the coating present on the surface of the Al-plated 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 total content of Al and Si in relation to the total content of elements excluding carbon is 30 mass% or more is identified as the Al-plated layer. In addition, the region in which the total content of Al and Si in relation to the total content of elements excluding carbon is less than 30 mass% and which is located on the surface of the Al-plated layer is identified as a coating. Using TEM-EDS, the content of Group A and Group B elements is measured at 10 locations, each at a distance of 100 nm or more in a direction perpendicular to the thickness direction, at the center of the film's thickness direction. The total content of Group A and Group B elements in the film is obtained by calculating the average value of the 10 locations.

[0041] Average film thickness: 0.01 to 30.0 μm If the average film thickness is less than 0.01 μm, the film cannot completely cover the surface of the plating layer, resulting in insufficient reaction between the Group A and / or Group B elements in the film and the oxide film during heating in hot stamping. As a result, it is not possible to form an oxide film containing the desired amount of Group A and / or Group B elements, and the hydrogen storage capacity of the hot stamping member cannot be reduced. Therefore, the average film thickness should be 0.01 μm or more. Preferably, the average film thickness is 0.05 μm or more, 0.1 μm or more, or 0.5 μm or more. On the other hand, if the average film thickness exceeds 30.0 μm, the adhesion of the film decreases, so the average film thickness should be 30.0 μm or less. The average film thickness may also be 20.0 μm or less, 10.0 μm or less, 5.0 μm or less, or 1.0 μm or less.

[0042] The average thickness of the coating is obtained by the following method: The coating is identified using the same method as when analyzing its chemical composition. The thickness of the coating is measured at a total of five locations, at a distance of 100 nm or more from each other in a direction perpendicular to the thickness direction of the plate. The average thickness of the coating is obtained by calculating the average of these measurements.

[0043] The coating is preferably amorphous. Specifically, it is preferable that the crystalline structure of the coating contains amorphous material by area percentage of 90% or more. By containing amorphous material by area percentage of 90% or more, the amount of hydrogen absorbed in the hot-stamped member can be further reduced. The inventors speculate that the reason for this is as follows.

[0044] Amorphous coatings contain more diffusion paths for substances than crystalline coatings. Therefore, by making the coating amorphous, the reaction between the Group A elements and / or Group B elements in the coating and the Al-Si-Fe 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 component is further reduced.

[0045] The crystalline structure of the film is determined by electron diffraction patterns obtained using a transmission electron microscope (TEM). A crystalline structure is defined as one in which clear crystalline diffraction spots are obtained in the electron diffraction pattern, while an amorphous structure is defined as one in which no crystalline diffraction spots are obtained and only a continuous ring-shaped diffraction pattern (halo pattern) is obtained.

[0046] Figure 3 shows an example of electron diffraction patterns of cross-sections of the Al-based plating layer and film on an Al-based plated steel sheet, obtained by TEM (transmission electron microscope). Figure 3(a) is the electron diffraction pattern corresponding to the Al-based plating layer. In Figure 3(a), crystalline diffraction spots are observed, indicating that the Al-based plating layer contains a metallic phase with a crystalline structure. On the other hand, Figures 3(b) to (d) are electron diffraction patterns corresponding to the film, and are examples of halo patterns (electron diffraction patterns) indicating amorphousness. In the cases of Figures 3(b) to (d), ring-shaped diffraction patterns (halo patterns) are observed, indicating that the structure contained in the film is amorphous.

[0047] This section describes in detail the method for observing and determining the crystalline structure of the coating. A sample with a width of 10 μm and a depth of 5 to 35 μm is taken using a Focused Ion Beam (FIB) from a portion of the Al-plated steel sheet that is 10 mm or more away from the edge, preferably 15 mm away from the edge, so that the cross-section of the coating present on the surface of the Al-plated layer can be observed. Next, the sample surface corresponding to the cross-section of the coating is subjected to electron diffraction using a TEM ("JEM-2100F", manufactured by JEOL Ltd.) with an electron beam probe diameter of 10 nm. By examining the obtained diffraction pattern, the crystalline structure of the coating can be determined.

[0048] The proportion of amorphous material in the coating is calculated by the following method: Using a transmission electron microscope (TEM), electron diffraction is performed on 10 points on the surface of the sample to obtain diffraction patterns. If 9 or more of the 10 diffraction patterns obtained show a ring-shaped diffraction pattern, it is determined that the proportion of amorphous material in the coating is 90% or more by area. The acceleration voltage during TEM observation is set to 200 kV. If the plated layer is also included in the sample for analysis, it is excluded from the measurement, and only the coating is measured.

[0049] [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 for application to hot stamping and does not limit the base steel sheets of this disclosure.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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 mentioned 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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 coating and Al-based plating layer by mechanical grinding, and then measuring the chips using 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-established 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.

[0062] 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.

[0063] <Method for Manufacturing Al-Plated Steel Sheets> A preferred method for manufacturing Al-Plated steel sheets according to this embodiment will be described below. The following description is intended to illustrate characteristic methods for manufacturing the plated steel sheets according to this embodiment, and is not intended to limit the Al-Plated steel sheets according to this embodiment to those manufactured by the manufacturing methods described below.

[0064] The Al-plated steel sheet according to this embodiment can be manufactured by, for example, 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 forming process in which a film is formed on the surface of the Al-plated layer. Alternatively, the sheet may be pickled and then immediately subjected to the cold rolling process without being wound after the hot-rolling process. Each process will be described in detail below.

[0065] [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.

[0066] [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 (%).

[0067] 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.

[0068] [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 (%).

[0069] [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.

[0070] [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. For example, after immersing the cold-rolled annealed steel sheet in an Al plating bath containing 7.0 to 25.0% Si, it is removed and immediately treated with N by the gas wiping method. ２ By blowing gas or air onto the Al-based plating layer 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. However, if the immersion time in the Al-plating bath is prolonged, the formation of the Fe-Al phase near the surface of the base steel sheet is promoted, and this Fe-Al phase is incorporated into the Al-based plating layer, which may increase the Fe concentration in the Al-based plating layer to over 25.0%. Therefore, an immersion time of 10 seconds or less is preferable.

[0071] 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.

[0072] 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 it is not possible to control this Si amount within 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 above the desired amount. 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, and the crystallization of Si is promoted 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 Si amount near the surface of the Al-based plating layer within the desired range. If the average particle size of the sprayed powder exceeds 10 μm, it is not possible to promote the crystallization of Si near the surface of the Al-based plating layer.

[0073] [Film Formation Process] In the film formation process, a film having the chemical composition and form described above 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.

[0074] 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, it is preferable that the solution contains an organic and / or inorganic binder. The thickness of the coating can be controlled by adjusting the solid content concentration of the solution. The content of Group A elements and / or Group B elements in the coating can be controlled by adjusting the content of Group A elements and / or Group B elements in the solid content of the solution. 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 oxides, bromides, chlorides, fluorides, hydroxides, carbides, and nitrides of Zr; oxides, bromides, chlorides, fluorides, hydroxides, carbides, and nitrides of Ti; oxides, bromides, chlorides, fluorides, hydroxides, carbides, and nitrides of Zn; and colloidal silica.

[0075] 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.

[0076] 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.

[0077] Steel having the chemical composition shown in Table 1 was melted and continuously cast. Subsequently, Al-plated steel sheets with a thickness of 1.4 mm, as shown in Table 3, were obtained under the conditions shown in Tables 2A and 2B. The thickness of the Al-plated layer was N ２ The process was controlled by the gas wiping method. In addition, various changes were made to the composition of the plating bath and the solution for film formation during the formation of the Al-based plating layer and film.

[0078] Manufacturing methods No. B1 to B23 are examples of production using the preferred manufacturing method. On the other hand, manufacturing methods No. b1 to b16 are examples of production using a manufacturing method that deviates from the conditions of the preferred manufacturing method. In the plating process, manufacturing method No. b4 is an example where the Si content of the Al plating bath was low at 4.7%, manufacturing method No. b5 is an example where the Si content of the Al plating bath was high at 27.5%, manufacturing method No. b6 is an example where the immersion time of the Al plating bath was excessively long, manufacturing method No. b7 is an example where the gas pressure during wiping was excessively low, and manufacturing method No. b8 is an example where the gas pressure during wiping was excessively high. Furthermore, in the film formation process, manufacturing method No. b9 is an example where the total content of group A elements and / or group B elements in the solid content of the solution was excessively low at 0.01%, manufacturing method No. b10 is an example where the solid content concentration of the solution was low, and manufacturing method No. b11 is an example where the solid content concentration of the solution was excessively high. Also, in manufacturing method No. 14, particle spraying was not performed. In manufacturing method No. 15, instead of particle spraying, cold rolling was performed to achieve a total reduction ratio of 50%. In manufacturing method No. 16, unlike the other examples, zinc powder was sprayed instead of aluminum oxide during particle spraying.

[0079] Al-plated steel sheets cut to 100 mm x 100 mm x 1.4 mm were placed in a heating furnace at 910°C with a dew point of +40°C for 7 minutes, then molded in a die and rapidly cooled in the same die to obtain hot-stamped members. The tensile strength, corrosion resistance after coating, and hydrogen storage capacity of the hot-stamped members were evaluated using the method described later. The results are shown in Table 4. In No. c3, partial peeling of the Al-plated layer was observed, so only the chemical composition of the Al-plated layer was analyzed, and no further evaluation was performed. Also, in No. c10, the coating peeled off, so the properties of the hot-stamped member were not evaluated. Underlined text in the table indicates that it is outside the scope of this disclosure or that the manufacturing conditions are undesirable.

[0080] 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.

[0081] 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.

[0082] 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 member, 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 was introduced in the center of the test piece, reaching the alloy plating layer. 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 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: Over 6 mm

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] As can be seen from the above, the Al-plated steel sheet according to the present invention can be used to manufacture hot-stamped members that have excellent corrosion resistance after painting and reduced hydrogen storage capacity.

[0089] According to the above embodiment, it is possible to provide an Al-plated steel sheet that has excellent post-coating corrosion resistance and reduced hydrogen storage capacity, enabling the manufacture of hot-stamped members.

[0090] 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. An Al-plated steel sheet comprising a base steel sheet, an Al-based plating layer located on the surface of the base steel sheet, and a film located on the surface of the Al-based plating layer, wherein the Al-based plating layer has a chemical composition consisting of, by mass%, Si: 7.0 to 25.0% and Fe: 25.0% or less, with the remainder being Al and impurities, the average thickness of the Al-based plating layer is 10 to 60 μm, the average Si content at a depth of 3 μm from the surface of the Al-based plating layer is 3 to 70% by mass, the film contains a total of 0.1% by mass or more 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 average thickness of the film is 0.01 to 30.0 μm.

2. The Al-based plated steel sheet according to claim 1, characterized in that the coating is amorphous.

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