Hot stamped parts

Abstract

This hot-stamped part comprises a first steel sheet and a second steel sheet superimposed thereon, wherein the first steel sheet has a first base steel sheet and a first Al-Fe alloy plating layer located on the surface of the first base steel sheet, and the second steel sheet has a second base steel sheet, a second Al-Fe alloy plating layer located on the surface of the second base steel sheet, and a surface treatment film on the second Al-Fe alloy plating layer on the side not in contact with the first base steel sheet, wherein the surface treatment film contains an oxide of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn, and in electron beam microanalyzer analysis of the surface treatment film, when the operation of measuring the average concentration of the metal element in a 20 mm × 20 mm area is repeated 10 times, the ratio Emax / Emin of the maximum value Emax of the average concentration is 1.25 or less.

Description

[Technical Field]

[0001] This disclosure relates to hot-stamped parts. This application claims priority based on Japanese Patent Application No. 2025-075450, filed in Japan on April 30, 2025, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] In recent years, there has been a growing demand to reduce the consumption of chemical fuels in order to protect the environment and prevent global warming, and this demand is affecting various manufacturing industries.

[0003] For example, automobiles, which are indispensable for daily life and activities as a means of transportation, are no exception, and improvements in fuel efficiency through measures such as reducing the weight of the vehicle body are required. However, simply reducing the weight of an automobile can lead to a decrease in safety. Therefore, when reducing the weight of a vehicle, it is necessary to ensure safety to an even greater extent.

[0004] Much of an automobile's structure is made of iron, especially steel plates. Therefore, reducing the weight of these steel plates is extremely effective in making the vehicle lighter. Furthermore, the demand for weight reduction in such steel plates is increasing not only in the automobile industry but also in various other manufacturing industries.

[0005] In response to such demands, simply reducing the weight of the steel plate might be considered by making the steel plate thinner. However, thinning the steel plate leads to a decrease in the strength of the structure made up of that steel plate. Therefore, in recent years, research and development has been conducted on steel plates that can maintain or increase the mechanical strength of structures even when made thinner than the steel plates used previously, by increasing the mechanical strength of the steel plate.

[0006] Generally, materials with high mechanical strength tend to have reduced shape retention during forming processes such as bending. Therefore, processing materials with high mechanical strength into complex shapes becomes difficult.

[0007] One way to solve the problems of formability is the so-called "hot stamping method" (also known as the hot pressing method, hot press method, high-temperature pressing method, or die quenching method). In this hot stamping method, the material to be formed is heated to a high temperature to transform it into a structure called austenite (austenitization), and the softened steel sheet is pressed to form it, and then rapidly cooled during forming (cooled by a low-temperature die during pressing, the steel sheet is rapidly cooled). With this hot stamping method, the material is first heated to a high temperature and softened, so it can be easily pressed. Furthermore, the quenching effect due to rapid cooling after forming can increase the mechanical strength of the material. Therefore, this hot stamping method makes it possible to obtain molded products with good shape retention and high mechanical strength.

[0008] For example, Patent Document 1 discloses a technology for manufacturing molded products usable as automotive parts by processing alloyed hot-dip galvanized steel sheets using a hot stamping method. Patent Document 2 also discloses a technology for improving the corrosion resistance of hot-stamped parts after painting. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2003-126921 [Patent Document 2] International Publication No. 2009 / 131233 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The hot stamping method described in Patent Document 1 requires heating the steel sheet to be processed to an Ac3 point or higher. Therefore, time must be allocated to heat the steel sheet to this temperature, leaving room for improvement in productivity. Furthermore, although the method described in Patent Document 2 shows good reactivity with the chemical treatment agent applied to the steel sheet, the relatively large amount of agent adhering to it leaves room for economic improvement. In addition, when a part is constructed by overlapping a first steel sheet and a second steel sheet with different areas, the corrosion resistance after painting may decrease at the boundary between the overlapping area and the other areas (hereinafter referred to as the boundary).

[0011] This disclosure has been made in view of the above-mentioned problems, and aims to provide a hot-stamped part that has excellent post-painting corrosion resistance even at the boundary between the area where the steel plates are overlapped and the other areas. [Means for solving the problem]

[0012] To solve the above problems, the inventors conducted diligent research and discovered that, in order to improve the post-painting corrosion resistance of hot-stamped parts in areas where the coating film is thin at the boundary when electrodeposition coating is applied, a surface treatment film containing an oxide of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn, and having little variation in the concentration of the metal element, can be formed on the Al-Fe alloy plating layer of the small steel sheet (second steel sheet) on the opposite side of the overlapping surface, thereby improving the post-painting corrosion resistance of hot-stamped parts.

[0013] Based on these findings, the summary of this disclosure is as follows: (1) A hot-stamped part comprising a first steel sheet and a second steel sheet superimposed on the first steel sheet and having a smaller area than the first steel sheet, wherein the first steel sheet comprises a first base steel sheet and a first Al-Fe alloy plating layer located on the surface of the first base steel sheet, and the second steel sheet comprises a second base steel sheet, a second Al-Fe alloy plating layer located on the surface of the second base steel sheet, and a surface treatment film on the second Al-Fe alloy plating layer on the side not in contact with the first base steel sheet, wherein the surface treatment film contains an oxide of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn, and in electron beam microanalyzer analysis of the surface treatment film, when the operation of measuring the average concentration of the metal element in a 20 mm × 20 mm area is repeated 10 times, the ratio of the maximum value Emax to the minimum value Emin of the average concentration, Emax / Emin, is 1.25 or less. (2) The hot stamped part according to (1), characterized in that the arithmetic mean roughness Ra of the surface of the second steel plate that is not in contact with the surface of the first steel plate is 0.8 to 2.5 μm. (3) The amount of one or more of the metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn deposited on the surface treatment film is 0.05 g / m 2 The hot stamping part according to (1) or (2), characterized in that it is as described above. (4) The chemical composition of the first base steel sheet and the second base steel sheet is, in mass%, C: 0.10~0.60%, Si: 0.01~0.60%, Mn: 0.50~3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.001~0.100%, Ti: 0.01~0.10%. B: 0.0001 to 0.0100%, N: 0.0150% or less, Cr: 0 to 1.00%, Cu: 0 to 1.000%, Ni: 0 to 2.00%, Nb: 0 to 1.00%, V: 0 to 1.00%, Mo: 0 to 1.00%, W: 0 to 1.00%, Sn: 0 to 1.00%, Ca: 0 to 0.0100%, Mg: 0 to 0.05%, Zr: 0 to 0.05%, REM: 0 to 0.3000%, and the balance: Fe and impurities, characterized by the hot stamping part according to (1) or (2). (5) The chemical compositions of the first base steel plate and the second base steel plate are, in mass %, Cr: 0.01 to 1.00%, Cu: 0.001 to 1.000%, Ni: 0.01 to 2.00%, Nb: 0.01 to 1.00%, V: 0.01 to 1.00%, Mo: 0.01 to 1.00%, W: 0.01 to 1.00%, Sn: 0.01 to 1.00%, Ca: 0.0001 to 0.0100%, Mg: 0.001 to 0.05%, and Zr: 0.001 to 0.05%, containing one or more selected from the group consisting of, characterized by the hot stamping part according to (4).

Advantages of the Invention

[0014] According to the above aspect of the present disclosure, it is possible to provide a hot stamping part having excellent corrosion resistance after painting even at the boundary between the region where the steel plates are overlapped and the other regions in the hot stamping part.

Brief Description of the Drawings

[0015] [Figure 1] The cross-sectional schematic view along the plate thickness direction of the hot stamping part according to the present embodiment is shown. [Figure 2] [Figure 2] The cross-sectional schematic view along the plate thickness direction when electrodeposition coating is applied to the hot stamping part according to the present embodiment is shown.

Modes for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present disclosure will be described in detail. (Hot Stamping Part 1) Figure 1 is a schematic cross-sectional view of the hot-stamped part 1 according to this embodiment, along the thickness direction. The hot-stamped part 1 according to this embodiment represents the part after hot-stamping (hot-stamped molded body), and is formed by overlapping a first Al-plated steel sheet (also called the first aluminum-plated steel sheet) and a second Al-plated steel sheet (also called the second aluminum-plated steel sheet) and hot-stamping them. The hot-stamped part is also called a "hot-stamped molded body" or "hot-stamped molded product". In the case of cold forming, processing structures such as elongated crystal grains can be observed in the cross-sectional microstructure of the bent portion. In contrast, with hot stamping, the structure after hot stamping is the same as the microstructure after quenching, and the crystal grain elongation observed in cold-worked products is not seen. Therefore, hot-stamped components or molded products can be distinguished from cold-formed components or molded products such as cold-pressed products. In this specification, the "~" symbol indicating a numerical range, unless otherwise specified, means that the numbers before and after it are included as the lower and upper limits. However, if "greater than" or "less than" is appended to a number, that number is not included. Unless otherwise specified, the units of the chemical composition of the base steel sheet and the Al-Fe alloy plating layer are in mass percent.

[0017] The first steel sheet 10 comprises a first base steel sheet 11 and a first Al-Fe alloy plating layer 12 located on the surface of the first base steel sheet 11.

[0018] The second steel sheet 20 comprises a second base steel sheet 21, a second Al-Fe alloy plating layer 22 located on the second base steel sheet 21, and a surface treatment film Y provided on the second Al-Fe alloy plating layer 22.

[0019] The surface treatment film Y contains an oxide E of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn. In other words, the surface treatment film Y contains at least one oxide E from among Sc oxide, V oxide, Cr oxide, Ni oxide, Cu oxide, Zn oxide, Zr oxide, Ti oxide, and Mn oxide.

[0020] In the present embodiment, terms such as "steel plate" are used for the first steel plate 10, the second steel plate 20, the first base steel plate 11, or the second base steel plate 21. However, since they are formed by hot stamping, some or all of their shapes are curved. However, it is not necessary to exclude flat shapes from the "steel plate".

[0021] The surface treatment film Y has an oxide E of any one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn. According to the hot stamping part 1 having such a configuration, good corrosion resistance after painting can be obtained even at the boundary 40 between the region where the steel plates are overlapped and the other regions in the hot stamping part 1.

[0022] Here, the "corrosion resistance after painting" is the corrosion resistance after forming an electrodeposition coating film 50 on the hot stamping part, as described in the examples below.

[0023] <Al-Fe alloy plating layer> The Al-Fe alloy plating layer (plating layer) in the hot stamping part 1 according to the present embodiment will be described in detail. The hot stamping part 1 according to the present embodiment has an Al-Fe alloy plating layer on the surface of the steel plate. The Al-Fe alloy plating layer (the first Al-Fe alloy plating layer 12 and the second Al-Fe alloy plating layer 22) may be provided on the entire surface of the steel plate, or may be provided on one or both sides of the steel plate.

[0024] By having Al-Fe alloy plating layers (first Al-Fe alloy plating layer 12 and second Al-Fe alloy plating layer 22) on the base steel sheets (first base steel sheet 11 and second base steel sheet 21), the corrosion resistance after painting following hot stamping can be further improved. In addition, the presence of an Al-Fe alloy plating layer on each base steel sheet improves the corrosion resistance of the hot-stamped part 1 and prevents the formation of iron scale on its surface due to heating during hot stamping (Note: As will be described later, when an Al-plated steel sheet S with an Al plating layer formed on it is hot-stamped, the Al plating layer on the surface of the Al-plated steel sheet S is alloyed (during heating) to become an Al-Fe alloy plating layer). Iron scale contaminates the heating furnace and adheres to the rolls used for conveying, thus creating a manufacturing burden. Therefore, if iron scale is formed, processes such as shot blasting are required to remove it, which is economically undesirable. For this reason, Al-plated steel sheets S with an Al plating layer formed on them are often used as the material for the hot-stamped part 1.

[0025] The thickness of the Al-Fe alloy plating layer is not limited, but is preferably 10.0 μm or more. If the thickness of the Al-Fe alloy plating layer is less than 10.0 μm, the corrosion resistance after painting may decrease. The thickness of the Al-Fe alloy plating layer is more preferably 15.0 μm or more, and even more preferably 20.0 μm or more.

[0026] While there is no upper limit to the thickness of the Al-Fe alloy plating layer, if the thickness exceeds 45.0 μm, the shear force and compressive stress exerted on the plating layer by the mold during hot stamping will increase. In this case, the plating layer may become more prone to peeling, and there is a concern that the corrosion resistance after painting will decrease. Therefore, the thickness of the Al-Fe alloy plating layer is preferably 45.0 μm or less. More preferably, the thickness of the Al-Fe alloy plating layer is 40.0 μm or less or 35.0 μm or less.

[0027] The thickness of the Al-Fe alloy plating layer is determined by the following method. After etching a sample embedded in resin so that the cross-section of the Al-Fe alloy plating layer is exposed using Nital, it is observed using a scanning electron microscope (SEM). The boundary between the base steel sheet and the Al-Fe alloy plating layer is defined as the outermost surface location where the base material structure appears in the secondary electron image on the obtained SEM image. Next, the thickness of the Al-Fe alloy plating layer is measured. This measurement is repeated at five locations at 500 nm intervals perpendicular to the thickness of the base steel sheet, and the average of the five measurement results is taken as the "thickness of the Al-Fe alloy plating layer." The cross-sectional image of the Al-Fe alloy plating layer is selected from areas without obvious defects such as scratches or corrosion, and from areas that have not been processed.

[0028] The Al-Fe alloy plating layer may consist of Al, Fe, and impurities. In addition to Al and Fe, the Al-Fe alloy plating layer may also contain one or more elements selected from Si, Mn, B, W, Mo, Sb, Sn, Cr, Co, Cu, Ni, Ta, Ca, Mg, Sr, Se, Re, Hf, Li, and Zn, which have the effect of improving corrosion resistance (corrosion-enhancing elements).

[0029] The Al content of the Al-Fe alloy plating layer is 30.0% or more, and the sum of the Al and Fe content is 80.0% or more. More preferably, the sum of the Al and Fe content is 90.0% or more or 92.0% or more. The total content (mass%) of the above corrosion-resistant elements is preferably 0.005 to 10.0%, and more preferably 0.005 to 8.0%. Examples of impurities contained in the Al-Fe alloy plating layer include elements that make up stainless steel, ceramics, and thermal spray coatings commonly used in hot-dip plating equipment. The chemical composition of the Al-Fe alloy plating layer is measured as follows. A test specimen is taken from the second steel plate 20 (overlapping section). The test specimen is embedded in resin so that the cross-section in the thickness direction can be observed, and the cross-section is mirror-polished. Then, the cross-section (polished surface) of the sample embedded in resin is analyzed using an electron probe microanalyzer (EPMA) to measure the concentration of each element at 10 points in the thickness direction of the Al-Fe alloy plating layer. However, the starting point is at a distance of 1 / 11 of the "thickness of the Al-Fe alloy plating layer" (i.e., "thickness of the Al-Fe alloy plating layer" × 1 / 11) from the boundary between the Al-Fe alloy plating layer and the base steel material, and the 10 points include the start and end points at intervals of 1 / 11 of the "thickness of the Al-Fe alloy plating layer" from the starting point. In this case, the end point is at a distance of 1 / 11 of the "thickness of the Al-Fe alloy plating layer" from the outermost surface of the Al-Fe alloy plating layer. The analysis is performed at these 10 points, and the average concentration of each element (Fe, Al, Si, Mn, B, W, Mo, Sb, Sn, Cr, Co, Cu, Ni, Ta, Ca, Mg, Sr, Se, Re, Hf, Li, Zn) at these 10 points is taken as the chemical composition of the Al-Fe alloy plating layer. In other words, the arithmetic mean of the concentrations of each element measured at 10 points in the thickness direction using EPMA at intervals of "thickness of the Al-Fe alloy plating layer" × 1 / 11 is taken as the chemical composition (concentration of each element) of the Al-Fe alloy plating layer.

[0030] The Al-Fe alloy plating layer preferably contains one or more intermetallic compounds. The inclusion of one or more intermetallic compounds in the Al-Fe alloy plating layer improves its corrosion resistance. While the exact reason is unclear, it is presumed that because the potential of the intermetallic compounds is lower than that of iron, they dissolve first, thus preventing corrosion of the underlying steel plate. More preferably, the Al-Fe alloy plating layer consists of one or more intermetallic compounds and impurities.

[0031] Examples of the above intermetallic compounds include Fe2Al5, FeAl2, FeAl (also called ordered BCC), α-Fe (also called disordered BCC), Al-Soluble α-Fe, and compositions in which Si is dissolved in these materials. Furthermore, examples of the above intermetallic compounds include Al-Fe-Si ternary alloy compositions (12 types of τ1 to τ12 have been identified, with τ5 being called the α phase and τ6 being called the β phase).

[0032] The presence of the above-mentioned intermetallic compounds in the Al-Fe alloy plating layer can be confirmed using the limited-field electron diffraction function and energy-dispersive X-ray spectroscopy (EDS) function of a field emission-transmission electron microscope (FE-TEM).

[0033] Specifically, first, the cross-section of the Al-Fe alloy plating layer of the hot-stamped part 1 along the thickness direction is processed into a thin piece with a thickness of approximately 100 nm, and then the thin piece is measured using FE-TEM. If a diffraction pattern of the above compound is detected as a result of the measurement, it can be determined that the intermetallic compound is present at that location. Even if no diffraction pattern originating from crystals is measured in the above measurement, the compound can be identified from the ratio of each element by analyzing the same location using the EDS function. Furthermore, if five locations are measured randomly in the manner described above, and an intermetallic compound is present at all of these locations, in this embodiment, it is determined that the Al-Fe alloy plating layer is substantially composed of one or more intermetallic compounds.

[0034] An Al2O3 layer may be further arranged on the surface of the Al-Fe alloy plating layer. Having an Al2O3 layer on the Al-Fe alloy plating layer can improve the adhesion of the surface treatment film Y, thereby improving the adhesion of the coating film. The presence of an Al2O3 layer on the surface of the Al-Fe alloy plating layer promotes the formation of the surface treatment film Y on the Al2O3 layer, thus improving the adhesion of the coating film.

[0035] The Al2O3 layer may contain Mg and / or Ca, the Mg oxide may be a composite oxide of Mg and Al, and the Ca oxide may be a composite oxide of Ca and Al.

[0036] The thickness of the Al2O3 layer may be less than 0.05 μm, with a lower limit of 0 μm. The thickness of the Al2O3 layer is preferably 0.02 μm or more, or 0.05 μm or more, and more preferably 0.10 μm or more. On the other hand, if the thickness of the Al2O3 layer exceeds 3.00 μm, the adhesion of the Al2O3 layer to the Al-Fe alloy plating layer decreases, which may lead to the peeling of the electrodeposited coating 50 formed on the hot-stamped part 1. For this reason, the thickness of the Al2O3 layer is preferably 3.00 μm or less. The thickness of the Al2O3 layer is preferably 2.50 μm or less, 2.00 μm or less, 1.50 μm or less, or 0.80 μm or less, and more preferably 0.50 μm or less.

[0037] The thickness of the Al2O3 layer can be determined by the following method. The sample, embedded in resin so that the cross-section of the Al2O3 layer is exposed, is etched with Nital and then observed using a scanning electron microscope (SEM). The boundary between the Al-Fe alloy plating layer and the Al2O3 layer is defined as the position where the Al-Fe alloy plating layer appears in the secondary electron image on the obtained SEM image. Next, the thickness of the Al2O3 layer is measured at five points at 500 nm intervals perpendicular to the thickness of the base steel plate, and the average value is defined as the "thickness of the Al2O3 layer." The cross-sectional image of the Al2O3 layer is selected from areas without obvious defects such as scratches or corrosion, and from areas that have not been processed.

[0038] The above method for measuring the thickness of the Al2O3 layer presents challenges in accuracy when the Al2O3 layer is relatively small (for example, less than 0.1 μm). Without a skilled technician, the measurement accuracy may be significantly reduced, or the Al2O3 layer thickness may be incorrectly determined to be 0 μm. Therefore, instead of measuring the thickness of the Al2O3 layer, the presence of the Al2O3 layer can be confirmed using the following method.

[0039] A test specimen is taken from the second steel plate (overlapping section). The collected test specimen is processed using a cryo-FIB (Focused Ion Beam)-μ sampling method with a focused ion beam apparatus (Hitachi High-Technologies "NB5000") to prepare a sample with the cross-section of the Al-Fe alloy plating layer as the measurement surface.

[0040] Using a scanning transmission electron microscope (STEM), elemental analysis by EDS and electron diffraction patterns are obtained for the phase observed on the outermost surface of the specimen, and structural analysis is performed. If Al and O are identified from the elemental analysis results of the observed phase, and a phase identified as the Al2O3 phase is found in the electron diffraction pattern by comparison with a crystal database, then it can be determined that an Al2O3 layer exists. The observation conditions using STEM and the elemental analysis conditions using EDS are as follows: - Observation conditions using STEM - • Equipment: JEOL Ltd. "Spherical Aberration-Corrected Transmission Electron Microscope (Cs-TEM): NEOARM" ·Magnification: 100,000 times • Acceleration voltage: 200 keV Other conditions: Observations will be performed at -160°C using a cryoholder. -Elemental analysis conditions using EDS- • Equipment: JEOL Ltd. "JED-2300T" • Acceleration voltage: 200 keV Other conditions: During analysis, a cryoholder will be used, and observations will be performed at -160°C.

[0041] In this embodiment, the presence of the Al2O3 layer is almost always confirmed using the method described above. However, even if the presence of the Al2O3 layer is confirmed by a skilled technician, a different technician may not be able to confirm its presence, even with the same test piece (a test piece taken from the same second steel plate (overlapping section)). Considering the difficulty of the aforementioned method for measuring the thickness of the Al2O3 layer and the method for confirming the presence of the Al2O3 layer, it is not desirable in this embodiment to specify the thickness of the Al2O3 layer as, for example, 0.05 μm or more, or to make the presence of the Al2O3 layer mandatory. If the Al2O3 layer is present, its location is directly above (on the surface side of) the Al-Fe alloy plating layer, and (if surface treatment film Y is present) between the Al-Fe alloy plating layer and surface treatment film Y.

[0042] <Surface treatment coating Y> In this embodiment, the surface treatment film Y is provided on the Al-Fe alloy plating layer (on the surface side). In this disclosure, corrosion resistance after painting can be improved by adjusting the metal oxides contained in the surface treatment film Y. Specifically, first, the surface treatment film Y contains an oxide E of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn.

[0043] [Oxides of one or more metallic elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn] The surface treatment film Y contains an oxide E of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn. This improves corrosion resistance after painting. The mechanism by which the inclusion of oxide E of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn in the surface treatment film Y results in improved corrosion resistance after painting is not clear, but it is thought to be as follows.

[0044] When a painted Al-Fe alloy plated steel sheet is exposed to a corrosive environment, the metal (Al-Fe) in the Al-Fe alloy plating layer dissolves, causing a decrease in pH due to the hydrolysis reaction of ions present in the dissolved area. This shift to an acidic pH creates conditions that make the metal more susceptible to dissolution. In contrast, oxides of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn in the surface treatment film Y act as bases to HCl in an acidic environment, i.e., in the presence of an acid (e.g., HCl). Therefore, it is conceivable that HCl can suppress the shift to an acidic pH. Furthermore, these oxides themselves are thought to play a role in reducing the activity of chloride ions, which are corrosive factors.

[0045] As a result, it is possible to prevent the dissolution of the metal in the Al-Fe alloy plating layer, which is expected to improve corrosion resistance after painting.

[0046] Figure 2 is a schematic cross-sectional view along the thickness direction of the hot-stamped part 1 obtained in this embodiment after the electrodeposited coating 50, described later, has been applied. As shown in Figure 2, the surface edges of the second steel plate 20 that are not in contact with the first steel plate 10 are areas where the electrodeposited coating 50 is thin, which is a factor in reducing corrosion resistance after painting. In contrast, the presence of the above-mentioned oxide E uniformly dispersed throughout the surface treatment film Y makes it possible to improve the corrosion resistance of the hot-stamped part 1 after painting.

[0047] The presence or absence of oxide E can be determined, for example, as follows: A test specimen is taken from the second steel sheet (overlapping section). However, if there is a coating or chemical conversion coating, the coating or chemical conversion coating is removed from the sampled test specimen beforehand by performing the method described later (coating removal step or chemical conversion coating removal step). After that, one SEM-EPMA analysis is performed on the surface of the second steel sheet. The SEM-EPMA analysis is performed on an analysis area of ​​20 mm × 20 mm for Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, Mn, Al, Si, Fe, and oxygen. In the EPMA elemental mapping (SEM-EPMA analysis) of the surface of the second steel sheet, if the total concentration of one or more metal elements from Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn is detected at the electron beam irradiation position (measurement point) where oxygen is detected at 1.0 mass% or more, it is determined that oxide E of the detected metal element is present on the surface of the second steel sheet. Furthermore, if the number of measurement points where oxide E is determined to be present on the surface of the second steel sheet using this method (measurement points where oxygen ≥ 1.0 mass% and the total concentration of metal elements ≥ 3.0 mass%) is 70% or more of all measurement points (400 × 400) within the analysis range, then it is determined that a surface treatment film Y containing oxide E exists. The measurement conditions for EPMA elemental mapping analysis are as follows: Equipment: JEOL Ltd. JXA-8230 Electron Probe Microanalyzer Acceleration voltage: 15kV Irradiation current: 0.05μA Irradiation time: 50 milliseconds Score: 400 x 400 Irradiation interval (X direction): 50μm Irradiation interval (Y direction): 50μm

[0048] [Ratio of the maximum value Emax to the minimum value Emin of the average concentration of a metallic element: Emax / Emin ≤ 1.25] In this embodiment, it is necessary to uniformly contain oxides E of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn in the surface treatment film Y. Therefore, in electron beam microanalyzer (EPMA) analysis of the surface treatment film Y, when the process of measuring the average concentration of the metal element (the average value of the total concentration of the metal element) in a 20 mm × 20 mm area (analysis range) is repeated 10 times, the ratio Emax / Emin of the maximum value Emax to the minimum value Emin of the average concentration is 1.25 or less. When analyzing actual parts, the analysis will be performed after carrying out the coating removal process and chemical conversion coating removal process described later, as necessary.

[0049] The analysis method for Emax / Emin is as follows: For the metallic elements of oxide E contained in the surface treatment film—Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, Mn, as well as Al, Si, and Fe—EPMA surface analysis (analysis range 20 mm × 20 mm) is performed to measure the average concentration (mass %) of the metallic elements of oxide E. This measurement is repeated 10 times for different analysis ranges to obtain 10 measurement values ​​for the average concentration (mass %) of the metallic elements of oxide E. The EPMA analysis conditions are the same as those used to determine the presence or absence of oxide E. In this case, if two or more metallic elements of oxide E are present in the surface treatment film, the average concentration of the metallic elements of oxide E is the sum of the average concentrations of those two or more elements. Each analysis range is measured at a location at least 5 mm away from adjacent analysis ranges. Of the average concentrations of oxide E at the 10 analyzed locations, the highest value is taken as Emax, and the lowest value is taken as Emin. Emax / Emin is then calculated.

[0050] The total amount of oxide E of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn deposited on the surface treatment film Y is 0.05 g / m². 2 Preferably, the amount of oxides adhering to the surface treatment film is 0.05 g / m². 2By following these steps, good corrosion resistance after painting can be achieved. However, since an excessively large amount of oxide E is undesirable from a cost perspective, the amount of oxide adhering to the surface treatment film should be 3.0 g / m². 2 The following is preferable.

[0051] The total amount of oxide E deposited on a surface treatment film can be determined by creating a calibration curve using an X-ray fluorescence analyzer, comparing the detection intensity of oxides in a sample with a known amount of deposition with the amount of deposition. Specifically, for example, a test specimen is taken from the second steel plate (overlapping section). After the electrodeposition coating is removed, the metal elements constituting oxide E are analyzed using an X-ray fluorescence analyzer. Here, the amount of oxide E attached refers to the amount of metal elements of oxide E attached per unit area. The amount of oxide E attached is determined by performing elemental analysis from the surface using an X-ray fluorescence analyzer (RIGAKU Corporation, ZSX Primus) and quantifying the metal elements of oxide E.

[0052] The arithmetic mean roughness Ra of the side of the second steel plate 20 that is not in contact with the surface of the first steel plate 10 is 0.8 to 2.5 μm, which further improves corrosion resistance after painting. If the electrodeposited coating 50 is present on the surface of the second steel sheet 20 that is not in contact with the surface of the first steel sheet 10, the arithmetic mean roughness Ra can be measured by, for example, peeling off the electrodeposited coating 50 using the method described later. The surface of the second steel sheet 20 has a second Al-Fe alloy plating layer 22 and a surface treatment film Y (on the surface of the second Al-Fe alloy plating layer 22). The arithmetic mean roughness Ra is measured without removing the second Al-Fe alloy plating layer 22 or the surface treatment film Y.

[0053] The arithmetic mean roughness Ra is the arithmetic mean roughness Ra specified in JIS B0601:2013. This is because setting the arithmetic mean roughness Ra to 0.8 μm or higher improves the adhesion between the electrodeposited coating 50 and the second steel plate 20, further enhancing corrosion resistance after painting. Furthermore, setting it to 2.5 μm or less ensures uniformity of the thickness of the electrodeposited coating 50, making it difficult for corrosion-promoting components such as saltwater and oxygen to penetrate beneath the coating, thus further improving corrosion resistance after painting. To improve corrosion resistance, the arithmetic mean roughness Ra is more preferably 1.3 μm or more, and even more preferably 1.5 μm or more. On the other hand, if the arithmetic mean roughness Ra is too high, the corrosion resistance after painting will decrease, so it is more preferably 2.3 or less, and even more preferably 2.1 or less.

[0054] In accordance with JIS B0601:2013, the hot-stamped part 1 was measured in one direction with a cutoff of 0.8 mm and a measurement distance of 4 mm. The average value of three measurements was calculated and defined as the arithmetic mean roughness Ra.

[0055] The hot-stamped part 1 according to this embodiment can obtain excellent post-painting corrosion resistance by applying a configuration having the above-described features.

[0056] <Base material steel plate> The steel sheets that serve as the base material for the hot-stamped part 1 according to this embodiment (first base material steel sheet 11 and second base material steel sheet 21), that is, the original sheet of Al-plated steel sheet S which is the material for the hot-stamped part 1, are not particularly limited as long as they are steel sheets that can be suitably used in the hot-stamping method.

[0057] The chemical composition of the base steel sheets (first base steel sheet 11 and second base steel sheet 21) of the hot stamped part 1 according to this embodiment is, for example, in mass%, C: 0.10~0.60%, Si: 0.01~0.60%, Mn: 0.50~3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.001~0.100%, Ti: 0.01~0.10%, B: 0.0001~0.01% Examples of chemical compositions include those containing 00%, N: 0.0150% or less, Cr: 0-1.00%, Cu: 0-1.000%, Ni: 0-2.00%, Nb: 0-1.00%, V: 0-1.00%, Mo: 0-1.00%, W: 0-1.00%, Sn: 0-1.00%, Ca: 0-0.0100%, Mg: 0-0.05%, Zr: 0-0.05%, with the remainder being Fe and impurities.

[0058] The base material (the portion of the Al-plated steel sheet S that is hot-stamped, excluding the Al plating) can be exemplified by steel sheets such as hot-rolled steel sheets or cold-rolled steel sheets. The chemical composition of the base material is the same as that of the base material, and will be explained in detail below.

[0059] [C:0.10~0.60%] Carbon (C) is an element effective in improving tensile strength. A C content of 0.10% or more is preferable because it improves tensile strength. Therefore, a C content of 0.10% or more is preferable. A C content of 0.20% or more is more preferable, and even more preferable is 0.25% or more. On the other hand, a C content of 0.60% or less can improve the strength of the steel sheet while suppressing a decrease in elongation and reduction of area. Therefore, a C content of 0.60% or less is preferable. A C content of 0.40% or less is more preferable, and even more preferable is 0.30% or less.

[0060] [Si: 0.01~0.60%] Si, like C, is one of the elements that improves tensile strength. When the Si content is 0.01% or more, the strength-improving effect is fully exhibited, and a sufficient improvement in tensile strength is obtained. For this reason, a Si content of 0.01% or more is preferable. The Si content is more preferably 0.05% or more, 0.10% or more, and even more preferably 0.15% or more. On the other hand, since Si is also an easily oxidizable element, when the Si content is 0.60% or less, the decrease in wettability due to the influence of Si oxides formed on the surface layer of the steel sheet during hot-dip Al plating is suppressed, and the occurrence of unplated areas can be suppressed. For this reason, a Si content of 0.60% or less is preferable. The Si content is more preferably 0.40% or less, and even more preferably 0.30% or less.

[0061] [Mn: 0.50~3.00%] Mn is one of the strengthening elements that enhance steel, and it is also one of the elements that improve hardenability. Furthermore, Mn is an effective element in preventing hot brittleness caused by the impurity sulfur (S). These effects can be fully obtained when the Mn content is 0.50% or more. Therefore, in order to reliably exhibit the above effects, the Mn content is preferably 0.50% or more. More preferably, the Mn content is 0.80% or more, and even more preferably 1.00% or more. On the other hand, Mn is an austenite-forming element. When the Mn content is 3.00% or less, the amount of retained austenite phase does not become too large, and the decrease in strength can be suppressed. Therefore, the Mn content is preferably 3.00% or less. More preferably, the Mn content is 1.50% or less, and even more preferably 1.20% or less.

[0062] [P:0.050% or less] P is an impurity contained in steel. When the P content is 0.050% or less, the P contained in the steel sheet can suppress the reduction in the toughness of the base material of the hot-stamped molded body by segregation at the grain boundaries of the steel sheet, thereby suppressing the reduction in the delayed fracture resistance of the steel sheet. For this reason, a P content of 0.050% or less is preferable. It is preferable to keep the P content as low as possible, more preferably 0.03% or less, and even more preferably 0.01% or less. The phosphorus (P) content may be 0%. However, reducing the P content to less than 0.001% significantly increases the cost of P removal, which is economically undesirable. Therefore, the P content may be 0.001% or more, or 0.005% or more.

[0063] [S:0.020% or less] S is an impurity contained in steel. When the S content is 0.020% or less, it is possible to suppress the formation of sulfides by the S contained in the steel sheet, which reduces the toughness of the steel sheet, and thus suppress the reduction in the delayed fracture resistance of the steel sheet. For this reason, the S content is preferably 0.020% or less, preferably as low as possible, more preferably 0.010% or less, and even more preferably 0.005% or less. The sulfur content may be 0%. However, reducing the sulfur content to less than 0.0001% significantly increases the cost of desulfurization, which is economically undesirable. Therefore, the sulfur content may be 0.0001% or more, or 0.0002% or more.

[0064] [Al:0.001~0.100%] Al is an element that generally has the effect of deoxidizing molten steel. Therefore, the Al content is preferably 0.001% or more. More preferably, the Al content is 0.005% or more, 0.010% or more, and even more preferably 0.020% or more. On the other hand, when the Al content is 0.100% or less, the rise in the Ac3 point of the steel sheet is suppressed, so the heating temperature required to ensure the hardenability of the steel during hot stamping can be reduced, which is desirable for hot stamping production. Accordingly, the Al content of the steel sheet is preferably 0.100% or less, more preferably 0.050% or less, and even more preferably 0.010% or less.

[0065] [Ti: 0.01~0.10%] Ti is one of the elements that enhances strength. When the Ti content is 0.01% or more, sufficient strength improvement and oxidation resistance improvement effects can be obtained. Therefore, in order to reliably exhibit the above effects, it is preferable that the Ti content be 0.01% or more. More preferably, the Ti content is 0.03% or more, and even more preferably 0.05% or more. On the other hand, when the Ti content is 0.10% or less, for example, the formation of carbides and nitrides is suppressed, the softening of the steel can be suppressed, and sufficient tensile strength can be obtained. Therefore, it is preferable that the Ti content be 0.10% or less. More preferably, the Ti content is 0.08% or less, and even more preferably 0.07% or less.

[0066] [B:0.0001~0.0100%] B acts during quenching to improve strength. If the B content is 0.0001% or less, this strength-improving effect cannot be sufficiently obtained. Therefore, it is preferable that the B content be 0.0001% or more. More preferably, the B content is 0.0005% or more, 0.0010% or more, and even more preferably 0.0020% or more. On the other hand, if the B content is 0.0100% or less, the formation of inclusions is reduced, embrittlement of the steel plate is suppressed, and a decrease in fatigue strength can be suppressed. Therefore, it is preferable that the B content be 0.0100% or less. More preferably, the B content is 0.0040% or less, and even more preferably 0.0030% or less.

[0067] [N:0.0150% or less] N is an impurity contained in steel. When the N content is 0.0150% or less, the formation of nitrides by N contained in the steel sheet is suppressed, thereby suppressing a decrease in the toughness of the steel sheet. Furthermore, when B is contained in the steel sheet, the N contained in the steel sheet is suppressed from bonding with B and reducing the amount of solid-solution B, thereby suppressing a decrease in the hardenability-improving effect of B. For this reason, the N content is preferably 0.0150% or less. It is even more preferable to keep the N content as low as possible, more preferably 0.0100% or less, and even more preferably 0.0050% or less. The lower limit of the N content is 0%. The N content may be 0.0001% or more, 0.0003% or more, or 0.0010% or more, as needed.

[0068] Furthermore, the base steel sheet of the hot-stamped part 1 according to this embodiment may also contain one or more of the following optional additive elements: Cr, Ni, Cu, Mo, V, Nb, Sn, W, Ca, and REM. The inclusion of these elements is not mandatory, and the lower limit of the content of each of these elements is 0%.

[0069] [Cr: 0~1.00%] Cr is an element that improves the hardenability of steel sheets. To fully obtain this effect, it is preferable to have a Cr content of 0.01% or more, more preferably 0.02% or more, or 0.10% or more. On the other hand, by having a Cr content of 1.00% or less, it is possible to fully obtain this effect while suppressing an increase in cost. Therefore, when Cr is included, it is preferable to have a Cr content of 1.00% or less. More preferably, the Cr content is 0.80% or less, and even more preferably 0.70% or less.

[0070] [Ni: 0~2.00%] Ni is an element that enhances the hardenability of steel and ensures stable strength of the hot-stamped part 1 after quenching. To fully exhibit these effects, it is preferable to have a Ni content of 0.01% or more or 0.10% or more. More preferably, the Ni content is 0.10% or more, and even more preferably 0.15% or more. On the other hand, by having a Ni content of 2.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Ni is included, it is preferable to have a Ni content of 2.00% or less. The Ni content is more preferably 1.50% or less, and even more preferably 1.00% or less, 0.60% or less, or 0.40% or less.

[0071] [Cu: 0~1.000%] Cu is an element that enhances the hardenability of steel and ensures stable strength of hot-stamped parts 1 after quenching. Cu also improves pitting corrosion resistance in corrosive environments. To fully exhibit these effects, a Cu content of 0.001% or more is preferable. More preferably, the Cu content is 0.100% or more, and even more preferably 0.200% or more. On the other hand, a Cu content of 1.000% or less allows for sufficient utilization of the above effects while maintaining economic efficiency. Therefore, when Cu is included, a Cu content of 1.000% or less is preferable. More preferably, the Cu content is 0.90% or less, even more preferably 0.80% or less, 0.60% or less, or 0.40% or less.

[0072] [Mo: 0~1.00%] Mo is an element that enhances the hardenability of steel and ensures stable strength of the hot-stamped part 1 after quenching. To fully exhibit these effects, it is preferable to have a Mo content of 0.01% or more. More preferably, the Mo content is 0.05% or more or 0.10% or more, and even more preferably 0.20% or more. On the other hand, by having a Mo content of 1.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Mo is included, it is preferable to have a Mo content of 1.00% or less. More preferably, the Mo content is 0.80% or less, and even more preferably 0.50% or less.

[0073] [V: 0~1.00%] V is an element that enhances the hardenability of steel and ensures stable strength of the hot-stamped part 1 after quenching. To fully exhibit these effects, it is preferable to have a V content of 0.01% or more. More preferably, the V content is 0.05% or more or 0.10% or more, and even more preferably 0.20% or more. On the other hand, by having a V content of 1.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when V is included, it is preferable to have a V content of 1.00% or less. More preferably, the V content is 0.80% or less, and even more preferably 0.50% or less or 0.30% or less.

[0074] [Nb: 0~1.00%] Nb is an element that enhances the hardenability of steel and ensures stable strength of the hot-stamped part 1 after quenching. To fully exhibit these effects, it is preferable to have an Nb content of 0.01% or more. More preferably, the Nb content is 0.05% or more or 0.10% or more, and even more preferably 0.20% or more. On the other hand, by having an Nb content of 1.00% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Nb is included, it is preferable to have an Nb content of 1.00% or less. More preferably, the Nb content is 0.80% or less, and even more preferably 0.50% or less, 0.30% or less, or 0.10% or less.

[0075] [Sn: 0~1.00%] Sn is an element that improves pitting corrosion resistance in corrosive environments. To fully exhibit this effect, it is preferable to have a Sn content of 0.01% or more. More preferably, the Sn content is 0.05% or more or 0.10% or more, and even more preferably 0.20% or more. On the other hand, a Sn content of 1.00% or less suppresses the decrease in grain boundary strength and the decrease in toughness. Therefore, when Sn is included, it is preferable to have a Sn content of 1.00% or less. More preferably, the Sn content is 0.80% or less, and even more preferably 0.50% or less, 0.30% or less, or 0.10% or less.

[0076] [W: 0~1.00%] W is an element that enhances the hardenability of steel and ensures stable strength of hot-stamped parts 1 after quenching. Furthermore, W improves pitting corrosion resistance in corrosive environments. To fully exhibit these effects, a W content of 0.01% or more is preferable. More preferably, the W content is 0.05% or more, or 0.10% or more, and even more preferably 0.20% or more. On the other hand, a W content of 1.00% or less allows for sufficient acquisition of the above effects while improving economic efficiency. Therefore, when W is included, a W content of 1.00% or less is preferable. More preferably, the W content is 0.80% or less, even more preferably 0.50% or less, 0.30% or less, or 0.10% or less.

[0077] [Ca: 0~0.0100%] Ca is an element that refines inclusions in steel and improves toughness and ductility after quenching. To fully exhibit this effect, it is preferable to have a Ca content of 0.0001% or more, more preferably 0.0010% or more, and even more preferably 0.0020% or more. On the other hand, by having a Ca content of 0.0100% or less, it is possible to obtain the effect fully while suppressing costs. Therefore, when Ca is included, it is preferable to have a Ca content of 0.0100% or less, more preferably 0.0040% or less, and even more preferably 0.0030% or less.

[0078] [Mg: 0~0.05%] Like Ca, Mg is an element that refines inclusions in steel and improves toughness and ductility after quenching. To fully exhibit this effect, it is preferable to have an Mg content of 0.001% or more. More preferably, the Mg content is 0.003% or more, 0.006% or more, or 0.01% or more, and even more preferably 0.02% or more. On the other hand, by having an Mg content of 0.05% or less, the above effects can be fully obtained while improving economic efficiency. Therefore, when Mg is included, it is preferable to have an Mg content of 0.05% or less. More preferably, the Mg content is 0.04% or less, and even more preferably 0.03% or less.

[0079] [Zr: 0~0.05%] Zr is an element that suppresses the occurrence of fracture by inhibiting the formation of oxides that serve as the starting point for fracture. To fully exhibit this effect, it is preferable to have a Zr content of 0.001% or more. More preferably, the Zr content is 0.003% or more, 0.006% or more, or 0.01% or more, and even more preferably 0.02% or more. On the other hand, by having a Zr content of 0.05% or less, the above effect can be fully obtained while improving economic efficiency. Therefore, when Zr is included, it is preferable to have a Zr content of 0.05% or less. More preferably, the Zr content is 0.04% or less, and even more preferably 0.03% or less.

[0080] [REM:0~0.3000%] REM, like Ca, is an element that refines inclusions in steel and improves toughness and ductility after quenching. To fully exhibit this effect, it is preferable to have a REM content of 0.0010% or more, and more preferably 0.002% or more. On the other hand, by having a REM content of 0.3000% or less, it is possible to obtain the full effect while suppressing costs. Therefore, when REM is included, it is preferable to have a REM content of 0.3000% or less, and more preferably 0.2000% or less. Here, REM refers to the total of 17 elements including Sc, Y, and lanthanides, and the REM content mentioned above means the sum of the content of these elements.

[0081] The remainder of the components other than those listed above consists of Fe and impurities. These impurities are, for example, elements that may be introduced during the manufacturing process.

[0082] The chemical composition of the steel sheet (base steel sheet) constituting the hot-stamped part 1 described above can be determined by taking a test piece from the steel sheet constituting the hot-stamped part 1, removing the plating layer and coating from the steel sheet, and then measuring the average elemental content over the entire sheet thickness using a general analytical method. For example, it can be measured using inductively coupled plasma atomic emission spectrometry (ICP-AES) or inductively coupled plasma mass spectrometry. C and S can be measured using combustion-infrared absorption spectrometry, and O and N can be measured using inert gas melting-infrared absorption spectrometry or inert gas melting-thermal conductivity spectrometry. Al can be measured by ICP-AES using the filtrate obtained after heating and decomposing the sample with acid. Furthermore, if analysis values ​​for molten steel, slabs, or other steel sheets manufactured from the same molten steel are available, the analysis of test pieces taken from the steel sheet may be omitted, and those analysis values ​​may be considered as the chemical composition of the steel sheet (base steel sheet).

[0083] (Manufacturing method for hot-stamped part 1) Next, a preferred manufacturing method for the hot-stamped part 1 of this embodiment will be described. The manufacturing method of the hot stamped part 1 in this embodiment is: (1) A plating process in which an Al plating layer is formed on the first material steel sheet and the second material steel sheet, respectively. (2) A coating process in which a surface treatment solution is applied to the Al plating layer of the second material steel sheet to form a film Y1, (3) A blank manufacturing process in which a second Al-plated steel sheet having an Al plating layer and film Y1 formed on it and a first Al-plated steel sheet that has not had a surface treatment solution applied are overlapped and spot-welded to produce a blank, (4) A hot stamping step in which a blank is hot stamped to obtain a hot stamped part 1 having an Al-Fe alloy plating layer and a surface treatment film, It holds.

[0084] <Plating Process> In the plating process, an Al plating layer is formed on the base steel sheet. Methods for forming the Al plating layer include, but are not limited to, hot-dip plating, electroplating, physical vapor deposition, and chemical vapor deposition. When forming the Al plating layer by the hot-dip plating method, the bath composition may be Al alone or a composition containing silicon (Si) in addition to Al. During plating, Fe in the base steel sheet diffuses into the hot-dip plating layer, forming the Al plating layer. Hereinafter, the steel sheet on which this Al plating layer has been formed will also be referred to as plated steel sheet.

[0085] <Coating process> Next, in the coating process, a surface treatment solution is applied to the steel sheet on which the Al plating layer has been formed to form a film Y1 (for the film Y of the hot-stamped part 1). Film Y1 becomes the surface treatment film Y of the hot-stamped part 1 after hot stamping. In this embodiment, the surface treatment film Y of the hot-stamped part 1 can be formed by applying a surface treatment solution prepared by an appropriate method to the surface of the Al plating layer to form film Y1, and then carrying out the hot-stamping process under the conditions described later. As a result, in the surface treatment film Y of the hot-stamped part 1 according to this embodiment, oxides E of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn can be dispersed throughout the surface treatment film Y. The Al2O3 layer of the hot-stamped part 1 according to this embodiment is often naturally formed when an Al plating layer is formed on the surface of the base steel sheet. Subsequently, the Al2O3 layer can be made thicker by performing a hot stamping process under the conditions described later. However, although it often depends on the hot stamping conditions, measuring the thickness of the Al2O3 layer or confirming the presence of the Al2O3 layer is not easy, as mentioned above, especially when the thickness of the Al2O3 layer is very small.

[0086] As a surface treatment solution applied to the entire surface of one side of the Al-plated steel sheet S (i.e., the base sheet for the hot-stamped part 1) on which the Al-plated layer is formed, an organic or inorganic surface treatment solution containing the above-mentioned elemental oxides (these are oxides present in the film Y1 on the surface of the Al-plated steel sheet S, hereinafter referred to as oxide E1) is used. After applying this surface treatment solution to the entire surface of the Al-plated steel sheet S using a roll coater, curtain coater, or inkjet printer, the volatile components in the surface treatment solution are dried to form the film Y1 on the surface of the Al-plated steel sheet S. Inkjet printing is particularly preferred because it allows for continuous changes in film thickness.

[0087] However, simply applying a surface treatment solution containing the oxide E1 of the above-mentioned metal element does not allow the oxide E1 to be uniformly dispersed throughout the film Y1 on the Al-plated steel sheet S, and the post-paint corrosion resistance at the surface edge of the second steel sheet 20 that is not in contact with the first steel sheet 10 of the hot-stamped part 1 does not improve. In other words, by applying the surface treatment solution and then heating and drying the treatment solution on the surface of the Al-plated steel sheet S under appropriate conditions, the oxide E1 can be uniformly dispersed throughout the film Y1, and the post-paint corrosion resistance at the surface edge of the second steel sheet 20 that is not in contact with the first steel sheet 10 of the hot-stamped part 1 can be improved.

[0088] When the mass fraction of oxide E1 in the surface treatment solution is Mm [mass%], the mass fraction of water in the surface treatment solution is Wm [mass%], the thickness of the second Al-plated steel sheet S before application of the surface treatment solution is ta [mm], the maximum temperature that the second Al-plated steel sheet S can reach is Tm [°C], and the heating rate when the temperature of the second Al-plated steel sheet S exceeds 50°C is SA [°C / s], the surface treatment solution is dried so that PA, shown in equation (1), is between 0.05 and 6.31. Note that the values ​​of Wm, SA, ta, Mm, and Tm are in the units indicated in the parentheses above, and the unit of PA calculated by equation (1) is considered to be dimensionless. PA = (Wm×SA×ta) / {Mm×(Tm+270)} … Equation (1)

[0089] If PA is less than 0.05, the oxide E1 cannot be uniformly dispersed throughout, and the corrosion resistance of the hot-stamped part 1 after painting cannot be improved. On the other hand, if PA exceeds 6.31, the amount of heating is too great, and the film is formed before the oxide E1 is dispersed throughout the entire film Y1, causing the oxide E1 to become localized. As a result, it is not possible to improve the corrosion resistance of the hot-stamped part 1 after painting.

[0090] Oxide E1 can be one or more oxides selected from Sc oxide, V oxide, Cr oxide, Ni oxide, Cu oxide, Zn oxide, Zr oxide, Ti oxide, or Mn oxide, and is not limited to a specific oxide among these. An example of oxide E1 is given below. Sc2O3: Fujifilm Wako Pure Chemical Corporation / Scandium Oxide V2O5: Manufactured by Taiyo Mining Co., Ltd. / Vanadium Pentoxide Cr2O3: Mitsuwa Chemical Co., Ltd. / Chromium(III) Oxide NiO: Fujifilm Wako Pure Chemical Corporation / Nickel Oxide CuO: Fujifilm Wako Pure Chemical Corporation / Copper Oxide ZnO: Hakusui Tech Co., Ltd. / ZINCOX SUPER F-1 ZrO2: Manufactured by Sakai Chemical Industry Co., Ltd. / Zirconium oxide dispersion SZR-W TiO2: Manufactured by Ishihara Sangyo Co., Ltd. / TTO-W-5 MnO2: Manufactured by Kishida Chemical Co., Ltd. / Manganese(IV) Oxide

[0091] (Surface treatment liquid) The temperature of the surface treatment liquid applied during the coating process is preferably between 10 and 40°C. If the temperature of the surface treatment liquid is below 10°C, it will take a long time to dry, resulting in insufficient improvement in corrosion resistance after coating. On the other hand, if the temperature of the surface treatment liquid exceeds 40°C, the dispersibility of oxides and resins in the surface treatment liquid decreases, leading to a decrease in paintability.

[0092] The heating rate SA when the temperature of the Al-plated steel sheet S exceeds 50°C is calculated by connecting thermocouples to the center in the length and width directions of the sheet in advance, and measuring the temperature of the Al-plated steel sheet S after applying a surface treatment solution to the second Al-plated steel sheet S and then heating and drying it. Specifically, the heating rate SA is the time it takes for the temperature of the Al-plated steel sheet S to reach 55°C from 45°C, divided by a temperature difference of 10°C. Preferably, the time tm for the temperature of the second Al-plated steel sheet S to reach the maximum temperature Tm from 25°C is 10 seconds or more. If it is less than 10 seconds, drying will be insufficient, the uniformity of the oxide E1 in the horizontal direction of the steel sheet will be impaired, and the improvement in corrosion resistance after painting may be insufficient.

[0093] Furthermore, in addition to the oxide E1 mentioned above, the surface treatment solution may contain various binder components, additives, and silica.

[0094] [Binder ingredients] The binder component that may be contained in the film Y1 according to this embodiment is preferably a water-dispersible or water-soluble resin. The content of the binder component selected from the water-dispersible or water-soluble resin is preferably 50% by volume or more of the total volume of the film Y1.

[0095] As the binder component selected from water-dispersible or water-soluble resins, various known resins exhibiting water dispersibility or water solubility can be used. Examples of such water-dispersible or water-soluble resins include polyurethane resins, polyester resins, acrylic resins, epoxy resins, fluororesins, polyamide resins, polyolefin resins, and polymer compounds obtained by hydrolysis and condensation polymerization of silane coupling agents. It is more preferable that the binder component be one or more selected from the group consisting of polyester resins, polyurethane resins, polyolefin resins, acrylic resins, epoxy resins, fluororesins, and polyamide resins. When multiple resins are used as the binder component, the total content of the multiple resins used is treated as the content of the binder component.

[0096] Furthermore, when using polyurethane resin as a binder component, it is preferable that the polyurethane resin be polyether-based. This is because, compared to polyester-based polyurethane resins, polyether-based polyurethane resins can prevent hydrolysis caused by acids and alkalis. Also, compared to polycarbonate-based polyurethane resins, they can suppress the formation of hard and brittle films, thus ensuring adhesion during processing and corrosion resistance of the processed area.

[0097] Whether or not polyurethane resin is contained can be determined by infrared spectroscopy, specifically by observing the infrared absorption spectrum at 3330 cm⁻¹. -1 (NH telescopic), 1730cm -1 (C=O expansion and contraction), 1530cm -1 (CN), 1250cm -1 This can be determined based on whether or not characteristic absorption of (CO) is observed.

[0098] The polyurethane resin content can be determined by the following method. First, a calibration curve is created using samples with known polyurethane resin content, showing the relationship between content and characteristic absorption intensity. Then, the content can be determined from the resulting characteristic absorption intensity.

[0099] For resins other than the polyurethane resins mentioned above, it is possible to determine their presence and content, similar to the polyurethane resins, by focusing on the absorption of properties derived from functional groups specific to each resin.

[0100] [Additives] The coating Y1 according to this embodiment may contain various additives, such as leveling agents, water-soluble solvents, metal stabilizers, etching inhibitors, etc., as additives used when preparing the processing solution before forming the coating Y1, to the extent that the effects of this disclosure are not impaired.

[0101] As the leveling agent, examples of nonionic or cationic surfactants include polyethylene oxide or polypropylene oxide adducts, acetylene glycol compounds, and the like.

[0102] Examples of the water-soluble solvent include alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol, and propylene glycol; cellosolves such as ethylene glycol monobutyl ether and ethylene glycol monoethyl ether; esters such as ethyl acetate and butyl acetate; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0103] Examples of the metal stabilizer include chelate compounds such as EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid).

[0104] Examples of the etching inhibitor include amine compounds such as ethylenediamine, triethylenetetramine, guanidine, and pyrimidine.

[0105] Regarding the content of the above additives, it is also possible to measure after creating a calibration curve with a fluorescent X-ray measuring device in the same manner as in the case of metal oxides.

[0106] Furthermore, for the purpose of reducing the temperature rise time during the heating of the hot stamp, carbon black, graphite, soot, or other carbon-derived pigments may be added as additives to enhance the absorption of radiant heat.

[0107] [Silica] The film Y1 according to this embodiment may contain silica. More specifically, in the film Y1 according to this embodiment, the content of silica is from 0 to 0.3 g / m 2 It is. When the silica content exceeds 0.3 g / m 2 it is not very desirable for the temperature rise effect in hot stamp heating, and it becomes costly, so it is not preferable from the viewpoint of economy. Also, silica is a substance with low electrical conductivity. Therefore, silica at 0.3 g / m2 If the silica content exceeds a certain amount, it is undesirable in terms of weldability after hot stamping. When silica is included, the smaller the silica content of the coating Y1, the better. The silica content of the coating Y1 is more preferably 0.10 g / m 2 The following, and more preferably 0.05 g / m 2 The following applies:

[0108] <Blank Manufacturing Process> In the blank manufacturing process, hot stamping steel sheets are obtained by subjecting plated steel sheets to various processes such as cutting and punching with a press. Alternatively, hot stamping steel sheets can also be obtained by applying coating Y1 after pre-cutting or punching the plated steel sheets with a press. A blank is manufactured by overlapping and welding a first steel plate without coating Y1 and a second steel plate with coating Y1 applied as described above.

[0109] The welding method is not particularly limited and can be selected from options such as spot welding, laser welding, projection welding, and gas welding. The area joined by welding is not particularly limited, but it is preferably 2% or more of the area of ​​the second steel plate. If it is less than 2%, gas may be present in the gap between the first and second steel plates during hot stamping, which will create resistance to heat transfer and may hinder productivity. On the other hand, if it exceeds 60%, welding will take longer, which will also hinder productivity.

[0110] <Hot stamping process> Next, the blank obtained above is hot-stamped. Suitable heating devices include electric furnaces, gas furnaces, far-infrared furnaces, and conventional heating devices equipped with infrared heaters. The specific heating conditions during hot stamping are not particularly limited; they should be appropriately controlled.

[0111] Subsequently, the heated hot-stamping steel sheet (Al-plated steel sheet S) can be formed and cooled to obtain the hot-stamped part 1 according to this embodiment. The parts heated to above the Ac3 point temperature, where the metal structure transforms into the austenite phase, are hardened to increase their strength. As a result, a hot-stamped part 1 with improved strength due to hardening can be obtained.

[0112] The heating method is not particularly limited and can include electric resistance furnaces or infrared heating furnaces that utilize radiant heat. The atmosphere can also be air or an atmospheric gas with an oxygen concentration of 20% to 50%.

[0113] By setting the parameter PB, represented by equation (2), to 1.5 to 4.5 during heating, the arithmetic mean roughness Ra of the surface of the second base steel sheet 21 that is not in contact with the surface of the first base steel sheet 11 can be set to 0.8 to 2.5 μm. The values ​​of ta, tb, and SB are in the units indicated in the parentheses below, and the unit of PB calculated by equation (2) is considered to be dimensionless. PB = (ta + tb) × SB ... Equation (2) First Steel Plate's plate thickness tb [mm] Thickness of the second steel plate ta [mm] Average heating rate SB [°C / s] of the second steel plate 20 from 750°C to 850°C

[0114] The SB (saturation bracing) is preferably 0.5 to 2.0°C / s. If it is less than 0.5°C / s, the arithmetic mean roughness Ra cannot be controlled within the range of 0.8 to 2.5 μm, and further improvement in corrosion resistance after painting cannot be expected. On the other hand, if it exceeds 2.0°C / s, similarly, the arithmetic mean roughness Ra cannot be controlled within the range of 0.8 to 2.5 μm, and further improvement in corrosion resistance after painting cannot be expected.

[0115] For cooling the hot-stamped part 1, in addition to cooling by the mold (if necessary, cooling water or the like may be circulated inside the mold to prevent the mold temperature from rising), the cooling rate may be increased by bringing it into contact with a liquid such as water.

[0116] The hot-stamped part 1 according to the embodiment of this disclosure can be used, for example, as one of the various automotive parts described above, after a chemical conversion coating or paint film is arbitrarily formed on its surface. In this case, when measuring the cross-section of the hot-stamped part 1 (for example, measuring the thickness or chemical composition of the Al-Fe alloy plating layer), the paint film removal step and the chemical conversion coating removal step are unnecessary. However, when measuring the surface of the hot-stamped part 1, for example, measuring Emax / Emin or the amount of oxide E attached, it is necessary to remove the paint film or chemical conversion coating beforehand. The paint film removal step and the chemical conversion coating removal step in this case are as follows. Furthermore, the sampling locations for all measurements are as follows.

[0117] [Sample collection location] When taking samples from parts, avoid the following locations (i) to (iv). (i) Within 20 mm of the toe of a spot weld, and within 20 mm of the bead toe of an arc / laser weld. (ii) Machining area with a radius of curvature of less than 15 mm, and areas within 5 mm of said machining area (iii) Ends within 5 mm from the cut end face of the part (iv) Areas within 5 mm of the area where red rust is visible to the naked eye

[0118] [Paint film removal process] For a sample cut from the main part, the coating is removed under the following conditions to expose the steel plate. A coating remover (Neoriver #160, manufactured by Sansai Chemical Co., Ltd.) is applied to the surface at room temperature and left to stand for about 5 minutes. Then, the coating is removed by rubbing with a hard sponge or the like (e.g., Kanefeel, manufactured by AION Co., Ltd.). After that, it is washed with water and dried. At this time, the remaining state of the coating is confirmed by SEM-EPMA measurement of the sample surface (100 μm square, 5 fields of view) after washing with water and drying. In the elemental distribution image obtained by EPMA, regions with a C concentration of 10 mass% or more are identified, and if the area ratio of these regions is 5% or more, it is judged that the coating has not been removed sufficiently. To measure the area ratio of regions with a C concentration of 10 mass% or more, first obtain an elemental distribution image of C in EPMA with the C concentration range set to 10-30%. The specific measurement conditions for EPMA are as follows. Equipment: JEOL Ltd. JXA-8230 Electron Probe Microanalyzer Acceleration voltage: 15kV Irradiation current: 0.05μA Surface analysis:WDS Analysis interval: 300 μm or longer Area ratio: Average value of 5 fields of view Next, the area fraction is measured by image processing of the obtained elemental distribution image. The image analysis software "ImageJ" is used for image processing. After loading the elemental distribution image of C into ImageJ, the image is binarized using "Make Binary" in "Process" > "Binary" so that areas with a C concentration of 10 mass% or more are displayed in black and areas with a C concentration of less than 10 mass% are displayed in white. After binarization, the value of "Area fraction" in "Results" is read using "Measure" in "Analyze" and this value is determined as the area fraction of the areas with a C concentration of 10 mass% or more. If the paint film is not sufficiently removed, the removal of the paint film is repeated until the area fraction of the areas with a C concentration of 10 mass% or more is less than 5%.

[0119] [Removal of chemical conversion coating] For samples cut from the main body of the part and with the coating removed, if the chemical conversion coating is, for example, a zinc phosphate coating, the chemical conversion coating is removed in accordance with JIS K3151:1996. Specifically, the chemical conversion coating is removed by immersion in a 5% chromic acid aqueous solution heated to 75°C for 15 minutes. After that, it is washed with water and dried. At this time, the remaining state of the chemical conversion crystals is confirmed by SEM-EPMA measurement of the sample surface (100 μm square, 5 fields of view) after washing with water and drying. In the elemental distribution image obtained by EPMA, regions where the P concentration is 5% by mass or more are identified, and if the area ratio of the region is 5% or more, it is judged that the chemical conversion coating has not been removed sufficiently. To measure the area ratio of regions where the P concentration is 5% by mass or more, first, an elemental distribution image of P is obtained in EPMA with the P concentration range set to 5-10%. Then, the area ratio is measured by image processing of the obtained elemental distribution image. Image processing is performed using the image analysis software "ImageJ". After loading the elemental distribution image of P into ImageJ, the image is binarized using "Make Binary" in "Process" > "Binary" so that areas with a P concentration of 5 mass% or more are displayed in black and areas with a P concentration of less than 5 mass% are displayed in white. After binarization, the value of "Area fraction" in "Results" is read using "Measure" in "Analyze" and this value is determined as the area percentage of areas with a P concentration of 5 mass% or more. If the chemical conversion coating is not sufficiently removed, the removal of the chemical conversion coating is repeated until the area percentage of areas with a P concentration of 5 mass% or more is less than 5%. [Examples]

[0120] The following describes embodiments of this disclosure. However, the conditions in these embodiments are merely examples of conditions adopted to confirm the feasibility and effectiveness of this disclosure, and this disclosure is not limited to these examples of conditions. This disclosure may adopt various conditions, provided that they do not depart from the gist of this disclosure and achieve the objectives of this disclosure.

[0121] As the base steel sheet, it is preferable to use a steel sheet that can obtain the desired mechanical properties (meaning various properties related to mechanical deformation and fracture, such as tensile strength, yield point, elongation, reduction of area, hardness, impact value, fatigue strength, etc.) after hot stamping. The chemical composition of the base steel sheet before plating used in the hot stamping steel sheets shown in the following examples is shown in Table 1 below.

[0122] [Table 1]

[0123] Al-plated steel sheets for hot stamping (steel sheet symbols A1-A21, a1-a3) were prepared by applying Al plating and film Y1 to base steel sheets (steel No. S1-S13) having the chemical compositions shown in Table 1, using the surface treatment methods shown in Table 2. More specifically, for each base steel sheet, for the first steel sheet, a sheet with a thickness of 0.8 mm to 2.3 mm was prepared, plated with Al-10 mass%Si plating by hot-dip galvanizing, and then cut to a size of 300 mm wide x 400 mm long. For the second steel sheet, a sheet with a thickness of 0.8 mm to 2.3 mm was prepared, plated with Al-10 mass%Si plating by hot-dip galvanizing, then film Y1 was applied to the entire surface of one side, and then heated while controlling the heating rate SA above 50°C to 7-20°C / s, and then cut to a size of 150 mm wide x 200 mm long.

[0124] A surface treatment solution containing at least one oxide E1 such as Sc2O3, V2O5, Cr2O3, NiO, CuO, ZnO, ZrO2, TiO2, or MnO2, in addition to a water-based urethane resin binder component, was applied to one side of the base steel sheet using a bar coater and dried to form a film. Some surface treatment solutions also contained silica and carbon black in addition to the above components. The total film adhesion per side was 0.2-5 g / m². 2 It was set within the range. The following raw materials were used as oxide E1. Sc2O3: Fujifilm Wako Pure Chemical Corporation / Scandium Oxide V2O5: Manufactured by Taiyo Mining Co., Ltd. / Vanadium Pentoxide Cr2O3: Mitsuwa Chemical Co., Ltd. / Chromium(III) Oxide NiO: Fujifilm Wako Pure Chemical Corporation / Nickel Oxide CuO: Fujifilm Wako Pure Chemical Corporation / Copper Oxide ZnO: Hakusui Tech Co., Ltd. / ZINCOX SUPER F-1 ZrO2: Manufactured by Sakai Chemical Industry Co., Ltd. / Zirconium oxide dispersion SZR-W TiO2: Manufactured by Ishihara Sangyo Co., Ltd. / TTO-W-5 MnO2: Manufactured by Kishida Chemical Co., Ltd. / Manganese(IV) Oxide

[0125] [Table 2]

[0126] The first and second steel plates were overlapped by spot welding, aligning their centers. The spot welds were placed 30 mm from the edge of the second steel plate, with welds spaced 30 mm apart. A chromium copper electrode was used, and a DC current of 10.0 kA was applied to create the hot stamping blanks shown in Table 3.

[0127] [Table 3]

[0128] Subsequently, a thermocouple was connected to the center of the surface of the second steel sheet coated with film Y1 that was not in contact with the first steel sheet, so that the temperature could be measured. Then, the steel sheet was heated in an electric heating furnace with the furnace temperature set so that the holding temperature was 890 to 970°C under the conditions shown in Table 4. The average heating rate SB from 750°C to 850°C was controlled to 0.5 to 2.0°C / s, and after reaching the holding temperature, it was held for 120 seconds, then cooled to obtain the hot-stamped part 1.

[0129] [Table 4]

[0130] The evaluation methods for each evaluation item were as follows. Measurements of features and properties not specifically described in this example paragraph were performed as described in this specification. The thickness of the Al2O3 layer measured by the SEM observation method after Nital etching, as described above, was 0.02 to 2.90 μm. Furthermore, the presence of the Al2O3 layer was confirmed in all examples by the STEM-EDS analysis described above. [Corrosion resistance after hot stamping (corrosion resistance after painting)] The corrosion resistance after coating was evaluated according to the method specified in JIS H8502:1999, 8.1 Neutral Salt Spray Cycle Test Method. Specifically, the evaluation was performed using the following method. Samples were taken from hot-stamped part 1 and coated with a 7 μm thick cationic electrodeposition coating at a baking temperature of 140°C for 8 minutes. These samples were then subjected to corrosion testing. After 120, 180, and 240 cycles, the samples were removed and visually inspected for the presence or absence of red rust. A score of B or higher was considered acceptable.

[0131] (Rating) A: No red rust up to 240 cycles B: No rust after 180 cycles, slight rust after 240 cycles. C: No rust after 120 cycles, slight rust after 180 cycles. The evaluation results for the hot-stamped part 1 obtained above are shown in Table 5.

[0132] [Table 5]

[0133] Examples D1 to D21, which satisfy the scope of this disclosure, exhibit excellent corrosion resistance of the hot-stamped part 1 after painting, while comparative examples d1 to d3, which do not satisfy the scope of this disclosure, exhibited inferior corrosion resistance of the hot-stamped part 1 after painting.

[0134] In Comparative Examples d1, d2, and d3, after applying the surface treatment solution to the surface of the Al-plated steel sheet of the second steel sheet, the drying parameter PA was less than 0.05 or exceeded 6.31, and the ratio Emax / Emin, which is the ratio of the maximum value Emax to the minimum value Emin of the average concentration of metal elements in the oxide, was 1.25 or higher, resulting in poor corrosion resistance after coating (rating C).

[0135] Examples D1-D6, D7, D11-D14, D16, and D19-D21, under the hot stamping conditions shown in Table 3, resulted in a parameter PB in the range of 1.5-4.5, leading to an arithmetic mean roughness Ra of the second steel sheet of 0.8-2.5. Furthermore, the amount of oxide adhesion and the thickness of the Al-Fe alloy plating layer also met the preferred range, resulting in superior corrosion resistance after painting (rating A). [Industrial applicability]

[0136] According to the above embodiments of this disclosure, it is possible to provide Al-plated hot-stamped parts having excellent corrosion resistance after painting. [Explanation of symbols]

[0137] 1 Hot stamped part 10 Daiichi Steel Plate 11 First base steel plate 12. First Al-Fe alloy plating layer 20 Second steel plate 21 Second base material steel plate 22 Second Al-Fe alloy plating layer 40 Boundary 50 Electrodeposition coating Y Surface treatment coating

Claims

1. First Steel Plate and A second steel plate is superimposed on the first steel plate and has a smaller area than the first steel plate, A hot-stamped part comprising, The first steel sheet comprises a first base steel sheet and a first Al-Fe alloy plating layer located on the surface of the first base steel sheet. The second steel sheet comprises a second base steel sheet, a second Al-Fe alloy plating layer located on the surface of the second base steel sheet, and a surface treatment film on the side of the second Al-Fe alloy plating layer that is not in contact with the first base steel sheet. The surface treatment film contains an oxide of one or more metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn. In electron beam microanalyzer analysis of the surface treatment film, when the process of measuring the average concentration of the metal element in a 20 mm x 20 mm area is repeated 10 times, the ratio Emax / Emin of the maximum and minimum average concentrations is 1.25 or less. A hot-stamped part characterized by the following features.

2. The arithmetic mean roughness Ra of the surface of the second steel sheet that is not in contact with the surface of the first steel sheet is 0.8 to 2.5 μm. The hot-stamped part according to feature 1.

3. The amount of one or more of the metal elements selected from the group consisting of Sc, V, Cr, Ni, Cu, Zn, Zr, Ti, and Mn deposited in the surface treatment film is 0.05 g / m². ２ That's all. The hot stamped part according to claim 1 or 2.

4. The chemical composition of the first base steel sheet and the second base steel sheet is, in mass%, C: 0.10-0.60%, Si: 0.01-0.60%, Mn: 0.50-3.00%, P: 0.050% or less, S: 0.020% or less, Al: 0.001-0.100%, Ti: 0.01 to 0.10%, B: 0.0001 to 0.0100%, N: 0.0150% or less, Cr: 0-1.00%, Cu: 0 to 1.000%, Ni: 0-2.00%, Nb: 0 to 1.00%, V: 0 to 1.00%, Mo: 0-1.00%, W: 0 to 1.00%, Sn: 0-1.00%, Ca: 0-0.0100%, Mg: 0 to 0.05%, Zr: 0 to 0.05%, REM: 0-0.3000%, and, Remainder: Contains Fe and impurities. The hot stamped part according to claim 1 or 2.

5. The chemical composition of the first base steel sheet and the second base steel sheet is, in mass%, Cr: 0.01-1.00%, Cu: 0.001 to 1.000%, Ni: 0.01-2.00%, Nb: 0.01 to 1.00%, V: 0.01 to 1.00%, Mo: 0.01-1.00%, W: 0.01-1.00%, Sn: 0.01-1.00%, Ca: 0.0001-0.0100%, Mg: 0.001-0.05%, and, Contains one or more of the group consisting of Zr: 0.001 to 0.05%. The hot-stamped part according to feature 4.

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