Hot stamped compact

Abstract

This hot-stamp-formed article has a specified chemical composition, in which the area ratio of bainite in a surface layer region is more than 10%, the maximum value of a pole density in a texture is 4.0 or less, and the de-B index is 0.05 or more.

Description

[Technical Field]

[0001] The present invention relates to a hot stamped product. This application claims priority based on Japanese Patent Application No. 2022-067023, filed on April 14, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, there has been a demand for lighter automobile bodies from the perspectives of environmental protection and resource conservation, and high-strength steel sheets are being used in automobile components. Automotive components are manufactured by press forming, but as the strength of steel sheets increases, not only do the forming loads increase but also formability decreases. Therefore, the formability of high-strength steel sheets into components with complex shapes becomes an issue.

[0003] To solve the above-mentioned problems, the application of hot stamping technology, in which steel sheets are heated to a high temperature in the austenite region where they soften and then press-formed, is being promoted. Hot stamping is attracting attention as a technology that achieves both formability into automotive parts and strength by performing quenching treatment in a die simultaneously with press working.

[0004] For example, Patent Document 1 discloses a high-strength electrogalvanized steel sheet with a high yield ratio and excellent bendability, in which the amount of diffusible hydrogen in the steel is 0.20 mass ppm or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 079925 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to further reduce the weight of automobile bodies compared to conventional models, it is effective to increase the strength of steel sheets. To increase the strength of steel sheets, it is effective to make the metallographic structure of the steel sheet a metallographic structure in which martensite with a high dislocation density is the main phase. However, a metallographic structure in which martensite with a high dislocation density is the main phase traps a large amount of hydrogen that penetrates from the outside, making automobile components more susceptible to hydrogen embrittlement cracking.

[0007] Hydrogen embrittlement cracking is a phenomenon in which a steel component subjected to high stress during use is destroyed due to hydrogen that penetrates into the steel from the external environment. This phenomenon is also called delayed fracture due to the type of fracture that occurs. It is generally known that hydrogen embrittlement cracking in steel plate is more likely to occur as the tensile strength of the steel plate increases. This is thought to be because the higher the tensile strength of the steel plate, the greater the residual stress in the steel plate after part formation. The susceptibility to this hydrogen embrittlement cracking (delayed fracture) is called hydrogen embrittlement resistance.

[0008] In Patent Document 1, bendability is taken into consideration, but hydrogen embrittlement resistance is not taken into consideration.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hot-stamped steel sheet having high strength and excellent resistance to hydrogen embrittlement. [Means for solving the problem]

[0010] The gist of the present invention is as follows. (1) A hot-stamped steel according to one aspect of the present invention has a chemical composition, in mass%, of C: more than 0.40%, less than 0.70%, Si: 0.010 to 3.000%, Mn: 0.10% or more, less than 0.60% P: 0.100% or less, S: 0.0100% or less, N: 0.0200% or less, O: 0.0200% or less, Al: 0.0010~0.5000%, Nb: 0.0010~0.1000%, Ti: 0.010 to 0.200%, Cr: 0.010~0.800%, Mo: 0.0010 to 1.0000%, B: 0.0005~0.0200%, Co: 0-4.00%, Ni: 0-3.00% Cu: 0-3.00% V: 0~3.00%, W: 0~3.00%, Ca: 0 to 1.0000%, Mg: 0 to 1.0000%, REM: 0 to 1.0000%, Sb: 0 to 1.000%, Sn: 0 to 1.000%, Zr: 0 to 1.000%, As: 0 to 0.100%, and The balance is Fe and impurities. In a surface layer region which is a region from the surface of the hot stamped body to a depth of 1 / 25 of the plate thickness from the surface, The area fraction of bainite is more than 10%, The maximum value of the pole density of the texture is 4.0 or less, It is an index that quantitatively shows the decrease in the concentration of B. The de-B index is 0.05 or higher. (2) The hot stamped steel according to (1) above, wherein the chemical composition is, in mass%, Co: 0.01 to 4.00%, Ni: 0.01 to 3.00% Cu: 0.01 to 3.00%, V: 0.01~3.00%, W: 0.01 to 3.00%, Ca: 0.0001 to 1.0000%, Mg: 0.0001 to 1.0000%, REM: 0.0001 to 1.0000%, Sb: 0.001 to 1.000%, Sn: 0.001 to 1.000%, Zr: 0.001 to 1.000%, and As: 0.001 to 0.100% The compound may contain one or more selected from the group consisting of: [Effects of the Invention]

[0011] According to the above aspects of the present invention, it is possible to provide a hot stamped steel sheet having high strength and excellent resistance to hydrogen embrittlement. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 10 is a diagram for explaining how to determine the de-B index. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present inventors have found that the hydrogen embrittlement resistance of a hot-stamped steel can be improved by generating a desired amount of bainite in the surface layer region, forming a texture with a desired crystal orientation, and achieving a desired deboronation index.

[0014] The present inventors have found that, in order to obtain a hot stamped steel sheet having the above-described characteristics, it is particularly effective to perform annealing under desired conditions during the production of a steel sheet to be subjected to hot stamping.

[0015] The hot stamped steel according to this embodiment will be described in detail below. First, the reasons for limiting the chemical composition of the hot stamped steel according to this embodiment will be described.

[0016] In the following, the numerical ranges indicated by "to" include the lower and upper limits. Numerical values ​​indicated as "less than" and "greater than" are not included in the numerical range. All % in chemical compositions indicate mass %.

[0017] The hot stamped steel according to this embodiment has a chemical composition, in mass%, of C: more than 0.40% but not more than 0.70%, Si: 0.010 to 3.000%, Mn: 0.10% or more but less than 0.60%, P: 0.100% or less, S: 0.0100% or less, N: 0.0200% or less, O: 0.0200% or less, Al: 0.0010 to 0.5000%, Nb: 0.0010 to 0.1000%, Ti: 0.010 to 0.200%, Cr: 0.010 to 0.800%, Mo: 0.0010 to 1.0000%, B: 0.0005 to 0.0200%, and the balance: Fe and impurities. Each element will be explained below.

[0018] C: More than 0.40%, less than 0.70% C is an element that improves the strength of a hot-stamped steel sheet. If the C content is 0.40% or less, the desired strength cannot be obtained in the hot-stamped steel sheet. Therefore, the C content is set to more than 0.40%. The C content is preferably 0.42% or more or 0.44% or more. On the other hand, if the C content exceeds 0.70%, the amount of hydrogen trapped in martensite increases, making it impossible to obtain excellent hydrogen embrittlement resistance. Therefore, the C content is set to 0.70% or less. Preferably, the C content is 0.65% or less or 0.60% or less.

[0019] Si: 0.010 to 3.000% Silicon is an element that improves the strength of a hot stamped steel sheet through solid solution strengthening. If the Si content is less than 0.010%, the desired strength cannot be obtained. Therefore, the Si content is set to 0.010% or more. The Si content is preferably 0.050% or more, 0.100% or more, or 0.150% or more. On the other hand, if the Si content exceeds 3.000%, the amount of ferrite increases and the desired metal structure cannot be obtained. Therefore, the Si content is set to 3.000% or less. The Si content is preferably 2.000% or less, 1.000% or less, or 0.600% or less.

[0020] Mn: 0.10% or more, less than 0.60% Mn is an element that improves the hardenability of steel and increases the strength of hot-stamped steel. To obtain the desired strength, the Mn content is set to 0.10% or more. The Mn content is preferably 0.20% or more or 0.25% or more. On the other hand, if the Mn content is 0.60% or more, the desired texture cannot be obtained. Therefore, the Mn content is set to less than 0.60%. Preferably, the Mn content is 0.55% or less, 0.50% or less, or 0.45% or less.

[0021] P:0.100% or less P is an impurity element that segregates at grain boundaries, thereby reducing grain boundary strength. This reduces the hydrogen embrittlement resistance of the hot-stamped steel. If the P content exceeds 0.100%, the above effect becomes significant. Therefore, the P content is set to 0.100% or less. The P content is preferably 0.050% or less or 0.010% or less. The lower limit of the P content is not particularly limited, but may be 0%. However, if the P content is reduced to less than 0.0001%, the dephosphorization cost increases significantly, which is economically undesirable. Therefore, the P content may be set to 0.0001% or more, 0.001% or more, or 0.005% or more.

[0022] S: 0.0100% or less S is an impurity element that forms inclusions in steel. These inclusions trap large amounts of hydrogen, forming regions with locally high hydrogen concentrations, which deteriorates the hydrogen embrittlement resistance of the hot-stamped steel. If the S content exceeds 0.0100%, the above effect becomes significant. Therefore, the S content is set to 0.0100% or less. The S content is preferably 0.0080% or less, 0.0050% or less, or 0.0030% or less. The lower limit of the S content is not particularly limited, but may be 0%. However, reducing the S content to less than 0.0001% significantly increases the desulfurization cost, which is economically undesirable. Therefore, the S content may be 0.0001% or more, 0.0002% or more, 0.0003% or more, or 0.0010% or more.

[0023] N: 0.0200% or less N is an impurity element that forms nitrides in steel. These nitrides trap large amounts of hydrogen, forming regions with locally high hydrogen concentrations, which deteriorates the hydrogen embrittlement resistance of the hot-stamped steel. If the N content exceeds 0.0200%, the above effect becomes significant. Therefore, the N content is set to 0.0200% or less. The N content is preferably 0.0150% or less, 0.0100% or less, 0.0060% or less, or 0.0040% or less. The lower limit of the N content is not particularly limited, but may be 0%. However, if the N content is reduced to less than 0.0001%, the cost of denitrification increases significantly, which is economically undesirable. Therefore, the N content may be set to 0.0001% or more or 0.0010% or more.

[0024] O: 0.0200% or less When a steel contains a large amount of O, it forms coarse oxides. These oxides trap a large amount of hydrogen, forming regions with locally high hydrogen concentrations, which deteriorates the hydrogen embrittlement resistance of the hot-stamped steel. If the O content exceeds 0.0200%, the above effect becomes significant. Therefore, the O content is set to 0.0200% or less. The O content is preferably set to 0.0100% or less, 0.0070% or less, or 0.0040% or less. The O content may be 0%, but in order to disperse a large number of fine oxides during deoxidation of molten steel, the O content may be 0.0005% or more or 0.0010% or more.

[0025] Al: 0.0010 to 0.5000% Al is an element that has the effect of deoxidizing molten steel to improve the soundness of the steel. If the Al content is less than 0.0010%, deoxidation is insufficient, and coarse oxides are formed. These oxides trap a large amount of hydrogen, forming regions with locally high hydrogen concentrations, which deteriorate the hydrogen embrittlement resistance of the hot-stamped steel. Therefore, the Al content is set to 0.0010% or more. The Al content is preferably 0.0050% or more, 0.0100% or more, or 0.0300% or more. On the other hand, if the Al content exceeds 0.5000%, coarse oxides are formed in the steel. These oxides trap a large amount of hydrogen, forming regions with locally high hydrogen concentrations, which deteriorates the hydrogen embrittlement resistance of the hot-stamped steel. Therefore, the Al content is set to 0.5000% or less. The Al content is preferably 0.4000% or less, 0.3000% or less, 0.2000% or less, or 0.1000% or less.

[0026] Nb: 0.0010 to 0.1000% Nb is an element that forms carbonitrides in steel and improves the strength of hot-stamped steel through precipitation strengthening. If the Nb content is less than 0.0010%, the desired strength cannot be obtained. Therefore, the Nb content is set to 0.0010% or more. The Nb content is preferably 0.0050% or more, 0.0090% or more, or 0.0150% or more. On the other hand, if the Nb content exceeds 0.1000%, a large amount of carbonitrides is formed in the steel, deteriorating the hydrogen embrittlement resistance of the hot-stamped steel. Therefore, the Nb content is set to 0.1000% or less. The Nb content is preferably 0.0800% or less or 0.0600% or less.

[0027] Ti: 0.010 to 0.200% Ti is an element that forms carbonitrides in steel and improves the strength of hot-stamped steel through precipitation strengthening. If the Ti content is less than 0.010%, the desired strength cannot be obtained. Therefore, the Ti content is set to 0.010% or more. The Ti content is preferably 0.020% or more or 0.025% or more. On the other hand, if the Ti content exceeds 0.200%, a large amount of coarse carbonitrides are formed in the steel, which creates sites where the hydrogen concentration increases locally, deteriorating the hydrogen embrittlement resistance of the hot-stamped steel. Therefore, the Ti content is set to 0.200% or less. The Ti content is preferably 0.150% or less, 0.090% or less, 0.080% or less, 0.070% or less, 0.060% or less, or 0.050% or less.

[0028] Cr: 0.010~0.800% Cr is an element that dissolves in prior austenite grains during heating before hot stamping, thereby increasing the strength of the hot stamped steel. If the Cr content is less than 0.010%, the desired strength cannot be obtained. Therefore, the Cr content is set to 0.010% or more. The Cr content is preferably set to 0.100% or more, 0.150% or more, or 0.200% or more. On the other hand, if the Cr content exceeds 0.800%, the desired texture cannot be obtained in the hot stamped steel, and hydrogen embrittlement resistance deteriorates. Therefore, the Cr content is set to 0.800% or less. The Cr content is preferably 0.700% or less, 0.500% or less, or 0.400% or less.

[0029] Mo: 0.0010 to 1.0000% Mo is an element that dissolves in prior austenite grains during heating before hot stamping, thereby increasing the strength of the hot stamped steel. If the Mo content is less than 0.0010%, the desired strength cannot be obtained. Therefore, the Mo content is set to 0.0010% or more. The Mo content is preferably set to 0.0100% or more, 0.0500% or more, or 0.1000% or more. On the other hand, if the Mo content exceeds 1.0000%, the desired texture cannot be obtained in the hot stamped steel, and hydrogen embrittlement resistance deteriorates. Therefore, the Mo content is set to 1.0000% or less. The Mo content is preferably 0.8000% or less, 0.6000% or less, or 0.4000% or less.

[0030] B: 0.0005 to 0.0200% B is an element that improves the hardenability of steel. If the B content is less than 0.0005%, the desired strength cannot be obtained. Therefore, the B content is set to 0.0005% or more. The B content is preferably set to 0.0010% or more or 0.0015% or more. On the other hand, if the B content exceeds 0.0200%, coarse intermetallic compounds are formed in the hot-stamped steel. These intermetallic compounds become sites where the hydrogen concentration increases locally, deteriorating the hydrogen embrittlement resistance of the hot-stamped steel. Therefore, the B content is set to 0.0200% or less. The B content is preferably 0.0150% or less, 0.0100% or less, 0.0080% or less, 0.0040% or less, or 0.0030% or less.

[0031] The remainder of the chemical composition of the hot stamped steel may be Fe and impurities. Examples of impurities include elements that are inevitably mixed in from steel raw materials or scrap and / or during the steelmaking process and are permissible within a range that does not impair the properties of the hot stamped steel according to this embodiment.

[0032] The hot stamped steel may contain the following elements as optional elements. When the following optional elements are not contained, the content is 0%.

[0033] Co: 0-4.00% Co is an element that improves the strength of the hot stamped steel by solid solution strengthening. To ensure this effect, the Co content is preferably 0.01% or more, and more preferably 0.05% or more. On the other hand, since the above effects are saturated even when Co is contained in a large amount, the Co content is set to 4.00% or less. If necessary, the upper limit of the Co content may be set to 1.00%, 0.50%, 0.10%, 0.05%, or 0.02%.

[0034] Ni: 0 to 3.00% Ni has the effect of increasing the strength of the hot stamped body by dissolving in prior austenite grains during heating before hot stamping. To ensure this effect, the Ni content is preferably 0.01% or more. On the other hand, since the above effects are saturated even if the Ni content is large, the Ni content is preferably 3.00% or less. If necessary, the upper limit of the Ni content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05%, or 0.02%.

[0035] Cu: 0 to 3.00% Cu dissolves in prior austenite grains during heating before hot stamping, thereby enhancing the strength of the hot stamped steel. To ensure this effect, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.05% or more. On the other hand, since the above effects are saturated even when Cu is contained in a large amount, the Cu content is preferably set to 3.00% or less. If necessary, the upper limit of the Cu content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05%, or 0.02%.

[0036] V: 0~3.00% V forms carbonitrides in steel and has the effect of improving the strength of the hot-stamped steel by precipitation strengthening. To ensure this effect, the V content is preferably 0.01% or more, and more preferably 0.05% or more. On the other hand, if the V content exceeds 3.00%, a large amount of coarse carbonitrides are formed in the steel. These carbonitrides become sites that locally increase the hydrogen concentration, deteriorating the hydrogen embrittlement resistance of the hot-stamped steel. Therefore, the V content is set to 3.00% or less. If necessary, the upper limit of the V content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05%, or 0.02%.

[0037] W: 0~3.00% W has the effect of improving the strength of the hot-stamped steel. To reliably obtain this effect, the W content is preferably 0.01% or more, and more preferably 0.05% or more. On the other hand, since the above effect saturates even if W is contained in a large amount, the W content is set to 3.00% or less. If necessary, the upper limit of the W content may be set to 1.50%, 1.00%, 0.50%, 0.10%, 0.05%, or 0.02%.

[0038] Ca: 0 to 1.0000% Ca is an element that suppresses the generation of oxides that serve as fracture initiation sites, and contributes to improving the hydrogen embrittlement resistance of the hot-stamped steel. To reliably obtain this effect, the Ca content is preferably 0.0001% or more. On the other hand, since the above effect saturates even if a large amount of Ca is added, the Ca content is set to 1.0000% or less. If necessary, the upper limit of the Ca content may be set to 0.1000%, 0.0100%, 0.0050%, 0.0010%, 0.0005%, or 0.0002%.

[0039] Mg: 0 to 1.0000% Mg forms oxides and sulfides in molten steel, suppressing the formation of coarse MnS and dispersing many fine oxides, thereby refining the metal structure. This contributes to improving the hydrogen embrittlement resistance of the hot-stamped steel. To ensure these effects, the Mg content is preferably 0.0001% or more. On the other hand, since the above effect saturates even when Mg is added in a large amount, the Mg content is set to 1.0000% or less. If necessary, the upper limit of the Mg content may be set to 0.1000%, 0.0100%, 0.0050%, 0.0010%, 0.0005%, or 0.0002%.

[0040] REM: 0 to 1.0000% REM suppresses the formation of coarse oxides that become sites for localized increases in hydrogen concentration. This contributes to improving the hydrogen embrittlement resistance of the hot-stamped steel. To ensure this effect, the REM content is preferably 0.0001% or more. On the other hand, since the above effect saturates even if the REM content is contained in a large amount, the REM content is set to 1.0000% or less. If necessary, the upper limit of the REM content may be set to 0.1000%, 0.0100%, 0.0050%, 0.0010%, 0.0005%, or 0.0002%. In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the content of REM refers to the total content of these elements.

[0041] Sb: 0 to 1.000% Sb suppresses the formation of coarse oxides that become sites that accompany local increases in hydrogen concentration. This contributes to improving the hydrogen embrittlement resistance of the hot-stamped steel. To reliably obtain this effect, the Sb content is preferably 0.001% or more. On the other hand, since the above effect saturates even if Sb is added in a large amount, the Sb content is set to 1.000% or less. If necessary, the upper limit of the Sb content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005%, or 0.002%.

[0042] Sn: 0 to 1.000% Sn suppresses the formation of coarse oxides that become sites for localized increases in hydrogen concentration, thereby contributing to improved hydrogen embrittlement resistance of the hot-stamped steel. To ensure this effect, the Sn content is preferably 0.001% or more. On the other hand, since the above effect saturates even if Sn is contained in a large amount, the Sn content is set to 1.000% or less. If necessary, the upper limit of the Sn content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005%, or 0.002%.

[0043] Zr: 0 to 1.000% Zr suppresses the formation of coarse oxides that become sites for localized increases in hydrogen concentration, thereby contributing to improving the hydrogen embrittlement resistance of the hot-stamped steel. To ensure this effect, the Zr content is preferably 0.001% or more. On the other hand, since the above effect saturates even if the Zr content is large, the Zr content is set to 1.000% or less. If necessary, the upper limit of the Zr content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005%, or 0.002%.

[0044] As: 0 to 0.100% As reduces the austenite single-phase temperature, thereby refining prior austenite grains. This contributes to improving the hydrogen embrittlement resistance of the hot-stamped steel. To reliably obtain this effect, the As content is preferably 0.001% or more. On the other hand, since the above effect saturates even if the As content is large, the As content is set to 0.100% or less. If necessary, the upper limit of the As content may be set to 0.100%, 0.050%, 0.020%, 0.010%, 0.005%, or 0.002%.

[0045] The chemical composition of the hot-stamped body can be measured by a common analytical method, such as inductively coupled plasma-atomic emission spectrometry (ICP-AES). C and S can be measured using a combustion-infrared absorption method, N can be measured using an inert gas fusion-thermal conductivity method, and O can be measured using an inert gas fusion-non-dispersive infrared absorption method. When the surface of the hot stamped body is provided with a plating layer, a paint film, etc., the plating layer, paint film, etc. is removed by mechanical grinding before analyzing the chemical composition.

[0046] Next, the metal structure of the hot stamped steel according to this embodiment will be described. In the hot-stamped steel according to this embodiment, in a surface layer region extending from the surface of the hot-stamped steel to a depth of 1 / 25 of the plate thickness (thickness of the hot-stamped steel), the area fraction of bainite exceeds 10%, the maximum value of the pole density of the texture is 4.0 or less, and the de-B index is 0.05 or more.

[0047] In this embodiment, the surface layer region refers to a region extending from the surface of the hot-stamped steel to a depth of 1 / 25 of the plate thickness (thickness of the hot-stamped steel). In addition, when the hot-stamped product has a plating layer, a paint film, etc. on its surface, the term "surface" here refers to the interface between the plating layer and the base steel sheet, and for convenience, the plating layer, paint film, etc. are excluded from the hot-stamped product. Specifically, when the hot-stamped product has a plating layer, paint film, etc. on its surface, as described below, for convenience, the region where the iron concentration is less than 90 mass% in GD-OES measurement, that is, the plating layer, paint film, etc., is excluded from the hot-stamped product, and the measurement point where the iron concentration is 90 mass% (that is, the interface between the base steel material and the plating layer, etc.) is considered to be the surface of the hot-stamped product. As mentioned above, the plated layer, paint film, etc. are excluded from the hot-stamped body. However, if the thickness of the plated layer, paint film, etc. is so small as to be negligible compared to the thickness of the hot-stamped body (however, if only the plated layer is present, the thickness of the plated layer is often so small that it can be ignored in most cases), then when measuring the thickness of the hot-stamped body, the thickness of the hot-stamped body may be taken as the thickness including the plated layer, paint film, etc.

[0048] (Surface region) Area ratio of bainite: over 10% By forming bainite in the surface layer region, the dislocation density in the surface layer region can be reduced. As a result, hydrogen penetration from the external environment can be suppressed, and the hydrogen embrittlement resistance of the hot-stamped body can be improved. Furthermore, by forming bainite in the surface layer region, excessive softening of the surface layer can be suppressed, thereby further improving the hydrogen embrittlement resistance while maintaining the load-bearing capacity of the member. If the area fraction of bainite in the surface layer region is 10% or less, the hydrogen embrittlement resistance of the hot-stamped body will deteriorate. Therefore, the area fraction of bainite is set to more than 10%. Preferably, it is 20% or more, 40% or more, or 60% or more. The upper limit of the area ratio of bainite is not particularly limited, but may be 100%, 90%, or 80%.

[0049] The metal structure of the surface layer region may contain, in addition to bainite, 0 to 90% (0% or more and 90% or less) martensite, and a total of 0 to 65% (0% or more and 65% or less) ferrite and retained austenite. Note that martensite in this embodiment includes untempered martensite (fresh martensite) and tempered martensite. The area ratio of the metal structure is calculated for the surface region (the region from the surface to a depth of 1 / 25 of the plate thickness) by the following method.

[0050] A sample is cut out from any position at least 50 mm away from the end face of the hot-stamped product (if a sample cannot be taken from this position, a position avoiding the end) so that a thickness cross section parallel to the rolling direction can be observed. The size of the sample depends on the measuring device, but it should be large enough to allow observation of about 10 mm in the rolling direction.

[0051] The cross section of the sample is polished using #600 to #1500 silicon carbide paper, and then mirror-finished using a liquid in which diamond powder with a grain size of 1 to 6 μm is dispersed in a diluent such as alcohol or pure water. The observation surface is then polished by electrolytic polishing. At any position along the longitudinal direction of the sample cross section, a 50 μm long region extending from the surface of the hot-stamped compact to a depth of 1 / 25 of the plate thickness is measured using electron backscatter diffraction at 0.1 μm measurement intervals to obtain crystal orientation information. An EBSD analyzer consisting of a thermal field emission scanning electron microscope and an EBSD detector can be used for the measurement. For example, an EBSD analyzer consisting of a JEOL JSM-7001F and a TSL DVC5 detector can be used. The vacuum level inside the EBSD analyzer is 9.6 × 10 -5 The acceleration voltage may be 15 kV and the probe current level may be 13.

[0052] The obtained crystal orientation information is used with the "Phase Map" function of the "OIM Analysis®" software attached to the EBSD analyzer to determine that the crystal structure is fcc and to determine the area fraction of retained austenite. The area fraction of this retained austenite is then calculated to obtain the area fraction of retained austenite. Next, in the region with a bcc crystal structure, the "Grain Average Misorientation" function of the "OIM Analysis®" software attached to the EBSD analyzer is used to extract, as bainite, regions where the "Grain Average Misorientation" is greater than 0.50° and less than 0.75° under the condition that 5° grain boundaries are considered to be grain boundaries. The area fraction of bainite is then calculated to obtain the area fraction of bainite. Next, the area where "Grain Average Misorientation" is 0.5° or less is extracted as ferrite. The area ratio of the extracted ferrite is calculated to obtain the ferrite area ratio. The remaining area (the area where "Grain Average Misorientation" is over 0.75°) is extracted as martensite, and the area ratio of martensite is calculated to obtain the martensite area ratio. In this embodiment, the rolling direction of the hot-stamped steel is determined by the following method. First, a test piece is taken from any position at least 50 mm away from the end of the hot-stamped product so that the thickness cross section can be observed. The thickness cross section of the taken test piece is mirror-polished and then observed using an optical microscope at magnifications of 100x, 200x, 500x, and 1000x. An appropriate magnification at which the dimensions of the inclusions can be measured is selected depending on the size of the inclusions. The observation range is 500 μm or more in width and across the entire thickness of the product, and dark areas are determined to be inclusions. Observation may be performed using multiple fields of view. Next, using the thickness cross section initially observed using the above method as a reference, the test piece is rotated in 5° increments in the range of 0° to 180° around the thickness direction, and the cross sections parallel to the plane are observed using the same method. The average length of the major axes of the multiple inclusions in each cross section is calculated for each cross section. The cross section with the largest average value of the major axis length of the inclusions obtained is identified. The direction parallel to the longitudinal axis of the inclusions in the cross section is determined to be the rolling direction.

[0053] (Surface region) Crystal orientation in the surface region: Maximum value of the pole density of the texture is 4.0 or less By controlling the texture in the surface layer region, it is possible to suppress the penetration of hydrogen into the surface layer region from the external environment, thereby improving the hydrogen embrittlement resistance of the hot-stamped body. If the maximum value of the pole density of the texture in the surface layer region exceeds 4.0, the hydrogen embrittlement resistance of the hot-stamped body deteriorates. Therefore, the maximum value of the pole density of the texture in the surface layer region is set to 4.0 or less. Preferably, it is 3.5 or less, 3.0 or less, or 2.5 or less. The lower limit of the pole density of the texture in the surface layer region is not particularly limited, but may be 1.0 or 1.2.

[0054] The texture in the surface region (the region from the surface to a depth of 1 / 25 of the plate thickness) is obtained by the following method. A sample is cut out from any position at least 50 mm away from the end face of the hot-stamped product (if a sample cannot be taken from this position, a position avoiding the end) so that a thickness cross section parallel to the rolling direction can be observed. The size of the sample depends on the measuring device, but it should be large enough to allow observation of about 10 mm in the rolling direction.

[0055] The cross section of the sample is polished using #600 to #1500 silicon carbide paper, then polished to a mirror finish using a liquid in which diamond powder with a grain size of 1 to 6 μm is dispersed in a diluted solution such as alcohol or pure water. It is then finished by electrolytic polishing. At any position along the longitudinal direction of the sample cross section, a region 1000 μm long, extending from the surface to a depth of 1 / 25 of the plate thickness, is measured using electron backscatter diffraction at 5.0 μm measurement intervals to obtain crystal orientation information. Measurements can be performed using an EBSD analyzer consisting of a thermal field emission scanning electron microscope and an EBSD detector, such as a JEOL JSM-7001F and a TSL DVC5 detector. The vacuum level inside the EBSD analyzer is 9.6 × 10 -5 The acceleration voltage may be 15 kV and the probe current level may be 13.

[0056] The obtained crystal orientation information is used with the "Texture" function of the "OIM Analysis (registered trademark)" software attached to the EBSD analyzer to perform intensity calculations using harmonic series expansion for crystal grains with a bcc crystal structure. In this case, the expansion order is set to 16, and the half-width when applying a Gaussian distribution is set to 5°. Next, the "Texture Plot" function is used for the output file after intensity calculation to output the φ2 = 45° cross section in the crystal orientation distribution function (ODF). The maximum value of the pole density in the φ2 = 45° cross section is taken as the pole density of the texture in the surface region.

[0057] (Surface area) B removal index: 0.05 or more The deB index is an index that quantitatively represents the amount of decrease in the B concentration in the surface layer region. By reducing the B concentration in the surface layer region, the strength of the prior austenite before transformation decreases, improving the deformability of the prior austenite grains and facilitating the generation of randomly oriented crystal grains in the surface layer region. If the deB index in the surface layer region is less than 0.05, it is not possible to obtain crystal grains with a desired texture in the surface layer region. Therefore, the deB index is set to 0.05 or more. Preferably, it is 0.20 or more, 0.30 or more, or 0.35 or more. The upper limit of the de-B index is not particularly limited, but may be set to 1.00, 0.80, or 0.60.

[0058] The de-B index in the surface layer region can be obtained by the following method. The element concentration distribution in the thickness direction of the hot-stamped compact is measured using a glow discharge optical emission spectrometer (GD-OES: a Marcus-type high-frequency glow discharge optical emission spectrometer, GD-PROFILER-HR, manufactured by HORIBA, Ltd.). The measurement conditions are an analysis diameter of 4 mm, a sputtering rate of 4 μm / min, an argon pressure of 600 Pa, an RF output of 35 W, and a measurement interval of 0.02 μm or less. Measurements are performed for all elements contained in the hot-stamped compact.

[0059] In addition, when the hot-stamped product has a plating layer or the like on its surface, the "surface" here refers to the interface between the plating layer or the like and the base steel sheet. In cases where the surface has a plating layer, paint film, or the like, the plating layer or paint film is partially or completely removed by mechanical polishing or chemical polishing so that measurements can be made up to a depth of 200 μm from the surface of the base steel sheet (the interface between the base steel sheet and the plating layer or paint film, etc.) before GD-OES measurement. In GD-OES measurement, the measurement point where the iron concentration is 90 mass% is considered to be the surface of the hot-stamped product. In the following explanation, for convenience of explanation, the hot-stamped product may also be referred to as the base steel sheet.

[0060] Next, the B concentration is measured from the surface of the hot-stamped body to a depth of at least 100 μm from the surface. After measuring the B concentration at a depth of 100 μm from the surface, if the absolute value of the difference between the average B concentration in a region 80 to 100 μm and the maximum measured B concentration in the region 80 to 100 μm is 0.0006 mass% or less, and the absolute value of the difference between the average B concentration in the region 80 to 100 μm and the minimum measured B concentration in the region 80 to 100 μm is 0.0006 mass% or less, the measurement of the B concentration in the depth direction is terminated at a depth of 100 μm from the surface. If this requirement for ending measurement is not met, measurement of the B concentration in the depth direction is continued. Then, each time a new measurement value of the B concentration in the depth direction is obtained, the average B concentration in the region from the deepest point to 20 μm from the deepest point toward the surface is calculated, and if the absolute value of the difference between the average B concentration in the region from the deepest point to 20 μm from the deepest point toward the surface and the maximum measurement value of the B concentration in the region from the deepest point to 20 μm from the deepest point toward the surface is 0.0006 mass% or less, and the absolute value of the difference between the average B concentration in the region from the deepest point to 20 μm from the deepest point toward the surface and the minimum measurement value of the B concentration in the region from the deepest point to 20 μm from the deepest point toward the surface is 0.0006 mass% or less, measurement of the B concentration in the depth direction is ended at that position. For example, when a measurement value of the B concentration is obtained at a depth of 150 μm from the surface, if the absolute value of the difference between the average B concentration in a region 130 to 150 μm deep from the surface and the maximum measured B concentration value in the region 130 to 150 μm deep from the surface is 0.0006 mass% or less, and if the absolute value of the difference between the average B concentration in the region 130 to 150 μm deep from the surface and the minimum measured B concentration value in the region 130 to 150 μm deep from the surface is 0.0006 mass% or less, the measurement of the B concentration in the depth direction is terminated at a depth of 150 μm from the surface. Even if the requirements for ending measurement are not met and measurement of the B concentration in the depth direction cannot be completed, measurement of the B concentration in the depth direction is completed when measurement of the B concentration at a depth of 200 μm from the surface is completed. Then, when measurement of the B concentration in the depth direction is completed, the average value of the B concentration in the region from the deepest part (the deepest position where the B concentration used to calculate the B removal index was obtained) to a position 20 μm toward the surface from the deepest part (hereinafter, the average value of the B concentration in this region is referred to as the average B concentration in the deepest 20 μm) is used to calculate the B removal index below. For convenience of measurement, for example, the B concentration may be measured from the surface to a depth of 200 μm, and then the shallowest depth position that satisfies the above-mentioned condition for ending the B concentration measurement in the depth direction may be found in the region from the surface to a depth of 100 to 200 μm, and if such a position is found, the B desorption index may be calculated without using the B concentration measurement results at positions deeper than that depth position. For example, the B concentration may be measured from the surface to a depth of 200 μm, and in this case, if the shallowest depth position that satisfies the above-mentioned condition for ending the B concentration measurement in the depth direction is found in the region 100 μm or more from the surface, the measurement may be considered to have ended at that depth position, and the B desorption index may be calculated.

[0061] Hot stamped compact Surface to deepest part In this region, the decrease in B concentration per unit depth (the average B concentration in the deepest 20 μm minus the B concentration at each measurement point) is calculated, and the integral of the product of the decrease in B concentration and unit depth is calculated to determine the area of ​​the B-deficient region (area of ​​region A in Figure 1). However, if the value obtained by subtracting the B concentration at each measurement point from the average B concentration in the deepest 20 μm is negative, the integral is set to 0 (due to the de-B phenomenon near the surface, the B concentration at each measurement point is almost always lower than the average B concentration in the deepest 20 μm, and this integral value is positive). Next, the product of the average B concentration in the deepest 20 μm and the length of 200 μm is calculated as the reference area (area of ​​the rectangular region B in Figure 1). The B-deficient area (area of ​​region A) divided by the reference area (area of ​​region B) is determined to be the de-B index (area of ​​region A / area of ​​region B). Even when the requirement for measurement to be completed within 200 μm from the surface is met as described above, the length by which the average B concentration in the deepest 20 μm is multiplied is set to 200 μm to calculate the reference area (area of ​​region B).

[0062] The metal structure of regions other than the surface region of the hot stamped body (for example, the region from a depth of 4 / 16 of the plate thickness from the surface of the hot stamped body to a depth of 5 / 16 of the plate thickness from the surface) is not particularly limited as long as the desired strength and hydrogen embrittlement resistance can be obtained, but for example, it may be composed of a total of 90 to 100% (90% or more and 100% or less) of martensite and bainite, and 0 to 10% (0% or more and 10% or less) of ferrite and retained austenite, by area %. The metallographic structure of the region other than the surface layer region is measured by the following method. Note that the metallographic structure of the region other than the surface layer region is measured from a depth of 1 / 8 of the sheet thickness from the surface to a depth of 3 / 8 of the sheet thickness from the surface. The reason for this is that the metallographic structure in this region represents a typical metallographic structure of a hot stamped steel.

[0063] A sample is cut out from any position at least 50 mm away from the end face of the hot-stamped product (if a sample cannot be taken from this position, a position avoiding the end) so that a thickness cross section parallel to the rolling direction can be observed. The size of the sample depends on the measuring device, but it should be large enough to allow observation of about 10 mm in the rolling direction.

[0064] The cross section of the sample is polished using #600 to #1500 silicon carbide paper, then polished to a mirror finish using a liquid in which diamond powder with a grain size of 1 to 6 μm is dispersed in a diluted solution such as alcohol or pure water. The observation surface is then polished by electrolytic polishing. At any position along the longitudinal direction of the sample cross section, a 50 μm long region extending from 1 / 8 of the plate thickness depth to 3 / 8 of the plate thickness depth from the surface is measured using electron backscatter diffraction at 0.1 μm measurement intervals to obtain crystal orientation information. Measurements can be performed using an EBSD analyzer consisting of a thermal field emission scanning electron microscope and an EBSD detector, such as a JEOL JSM-7001F and a TSL DVC5 detector. The vacuum level inside the EBSD analyzer is 9.6 × 10 -5The acceleration voltage may be 15 kV and the probe current level may be 13.

[0065] The obtained crystal orientation information is used with the "Phase Map" function of the "OIM Analysis®" software provided with the EBSD analyzer to determine whether the crystal structure is fcc or retained austenite. The area fraction of this retained austenite is calculated to determine the area fraction of retained austenite. Next, regions with a bcc crystal structure are determined to be bainite, martensite, and ferrite. For these regions, the "Grain Average Misorientation" function of the "OIM Analysis®" software provided with the EBSD analyzer is used to extract regions with a "Grain Average Misorientation" of 0.5° or less as ferrite, under the condition that 5° grain boundaries are considered to be grain boundaries. The area fraction of the extracted ferrite is then calculated to determine the area fraction of ferrite.

[0066] Next, the remaining region (the region where "Grain Average Misorientation" exceeds 0.5°) is taken as the total area ratio of martensite and bainite.

[0067] The hot-stamped product according to this embodiment may have a plating layer on its surface. By having a plating layer on its surface, corrosion resistance can be improved after hot stamping. Examples of the plating layer include an aluminum plating layer, an aluminum-zinc plating layer, an aluminum-silicon plating layer, a hot-dip galvanized layer, an electrogalvanized layer, a galvannealed hot-dip galvanized layer, a zinc-nickel plating layer, and an aluminum-magnesium-zinc based plating layer.

[0068] Next, a steel sheet for hot stamping for obtaining the hot stamped steel according to this embodiment will be described. The steel sheet for hot stamping has the above-mentioned chemical composition. The metal structure of the steel sheet for hot stamping is not particularly limited as long as it can obtain the desired strength and hydrogen embrittlement resistance after hot stamping, but may, for example, be composed of, in area ratios, ferrite: 5 to 90%, bainite and martensite: 0 to 100%, pearlite: 10 to 95%, and retained austenite: 0 to 5%. In addition, iron carbides, alloy carbides, intermetallic compounds, and inclusions may be included.

[0069] Furthermore, the steel sheet for hot stamping may have a plating layer on its surface. By having a plating layer on its surface, corrosion resistance can be improved after hot stamping. Examples of the plating layer include an aluminum plating layer, an aluminum-zinc plating layer, an aluminum-silicon plating layer, a hot-dip galvanized layer, an electrogalvanized layer, a galvannealed hot-dip galvanized layer, a zinc-nickel plating layer, and an aluminum-magnesium-zinc based plating layer.

[0070] Manufacturing method of steel sheet for hot stamping Hereinafter, a method for producing a steel sheet for hot stamping for obtaining the hot-stamped steel according to this embodiment will be described. In order to obtain the hot-stamped steel described above, it is particularly effective to control the annealing conditions in the method for producing a steel sheet for hot stamping.

[0071] The conditions for the casting method of molten steel, heating before hot rolling, rough rolling, finish rolling, coiling and cold rolling are not particularly limited, and may be general conditions. Furthermore, in order to soften the hot-rolled steel sheet, the coil after coiling may be subjected to a softening heat treatment. The method of the softening heat treatment is not particularly limited, and general conditions may be used.

[0072] annealing After cold rolling, it is preferable to perform annealing by heating in an oxidizing atmosphere for 15 seconds or more. Normally, annealing is preferably performed in a reducing atmosphere to suppress scale formation, but in this embodiment, annealing is performed in an oxidizing atmosphere to promote scale formation on the steel sheet surface. During heating for hot stamping, the scale formed on the steel sheet surface acts as an oxidation source, oxidizing C and B in the surface layer region. The oxidized C and B are removed from the steel sheet surface, reducing the amounts of C and B in the surface layer region. As a result, the strength of prior austenite grains decreases, making them more susceptible to deformation, and randomly oriented crystal grains are more likely to be generated. This allows crystal grains with a desired texture to be generated in the surface layer region.

[0073] The heating temperature during annealing may be in the range of 730 to 900°C, and by retaining the steel within this heating temperature range for 15 seconds or longer, it is possible to promote scale formation while suppressing scale spalling. The annealing time is preferably 100 seconds or longer, more preferably 200 seconds or longer, and even more preferably 300 seconds or longer. On the other hand, annealing for more than 3600 seconds is not preferred because the prior austenite grain size becomes coarse, the grain boundary diffusion rate of B decreases, deboronation does not progress, and the deboronation index does not reach 0.05 or more. Therefore, the annealing time is preferably 3600 seconds or shorter. After annealing in an oxidizing atmosphere, the steel sheet may be subjected to another annealing step in an oxidizing or non-oxidizing atmosphere, as long as no treatment (such as pickling) for removing oxide scale is performed.

[0074] In this embodiment, the oxidizing atmosphere may be any heating atmosphere in which oxide scale is formed on the surface of the steel sheet, and may be any general condition. For example, in a gas combustion atmosphere, the mixture ratio of air to fuel (air-fuel ratio) is preferably controlled to 1.00 or more, and more preferably 1.10 or more. Annealing in an oxidizing atmosphere preferably forms oxide scale of 15 μm or more on the surface of the steel sheet. It is preferable that the oxide scale on the steel sheet surface is left in subsequent processes. That is, it is preferable to perform the hot stamping described below with the oxide scale remaining. The oxide scale is removed by shot blasting after hot stamping. Furthermore, even when a plating layer is formed on the surface of a steel sheet for hot stamping, an oxide scale remains at the interface between the base steel sheet and the plating layer. When a plating layer is formed, the oxide scale disappears after hot stamping due to an alloying reaction during heating before hot stamping.

[0075] Hot stamping The hot stamped steel sheet manufactured by the above-mentioned method is hot stamped to obtain a hot stamped product according to this embodiment. The hot stamping conditions are not particularly limited, but for example, it is preferable to heat the hot stamping steel sheet to a temperature range of 800°C to 1000°C and hold it at this temperature range for 60 to 1200 seconds.

[0076] If the heating temperature is less than 800°C, austenitization will be insufficient, and the hydrogen embrittlement resistance of the hot-stamped steel may be deteriorated or the desired strength may not be obtained. On the other hand, if the heating temperature exceeds 1000°C, the prior austenite will undergo excessive grain growth, and the hydrogen embrittlement resistance of the hot-stamped steel may be deteriorated or the desired strength may not be obtained. If the holding time is less than 60 seconds, austenitization will be insufficient, and the hydrogen embrittlement resistance of the hot-stamped steel may be deteriorated or the desired strength may not be obtained. If the holding time exceeds 1200 seconds, the prior austenite will undergo excessive grain growth, and the hydrogen embrittlement resistance of the hot-stamped steel may be deteriorated or the desired strength may not be obtained.

[0077] The heating atmosphere is not particularly limited and may be under normal conditions, such as in the atmosphere, a gas combustion atmosphere in which the ratio of air to fuel is controlled, or a nitrogen atmosphere, and the dew point of these gases may be controlled. After holding the material in this temperature range, it is hot stamped. After hot stamping, it is sufficient to cool the material to a temperature range of 250°C or lower at an average cooling rate of 20°C / s or more.

[0078] Examples of the heating method before hot stamping include heating with an electric furnace or gas furnace, flame heating, electrical heating, high frequency heating, and induction heating.

[0079] The hot-stamped product according to this embodiment is obtained by the above method. To soften the product, tempering at 130 to 600°C may be performed after hot stamping, or baking hardening may be performed after painting. Furthermore, a portion of the hot-stamped product may be tempered by laser irradiation or the like to provide a partially softened region. [Example]

[0080] Next, examples of the present invention will be described, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0081] Slabs produced by casting molten steel having the chemical compositions shown in Tables 1A to 2C were held at a temperature of 1200°C or higher for 20 minutes or longer, and then rough rolling, finish rolling, cold rolling, and coiling were carried out under general conditions. Annealing was then carried out under the conditions shown in Tables 3A to 3C. Annealing was carried out in an oxidizing atmosphere. In the annealing in an oxidizing atmosphere, the mixture ratio of air to fuel (air-fuel ratio) was controlled to 1.05 in a gas combustion atmosphere.

[0082] The obtained steel sheets for hot stamping were heated to the temperature ranges shown in Tables 3A to 3C in a furnace to which nitrogen gas was continuously supplied, and after holding at the temperature ranges, hot stamped, and then hot stamped under the conditions of cooling at an average cooling rate of 20°C / s or more to a temperature range of 250°C or less. As a result, hot stamped products shown in Tables 4A to 4C were obtained. However, some examples were subjected to re-annealing, plating, or heat treatment for softening, as indicated in the table.

[0083] Note that underlines in the table indicate values ​​outside the scope of the present invention, outside the preferred manufacturing conditions, or unfavorable characteristic values. Furthermore, the metallographic structure of the surface region of the hot-stamped steel according to the present invention example contained, in addition to bainite, 90% or more of martensite, and a total of 65% or less of ferrite and retained austenite, in terms of area percentage. Furthermore, the metallographic structure of the region other than the surface region of the hot-stamped steel according to the present invention example consisted, in terms of area percentage, of 90% or more of martensite and bainite, and 10% or less of ferrite and retained austenite.

[0084] The metallographic structure, de-B index, and pole density of the texture of the hot-stamped body were measured by the methods described above. The mechanical properties of the hot-stamped body were evaluated by the following methods.

[0085] Tensile strength The tensile (maximum) strength TS of the hot-stamped compact was measured by preparing a No. 5 test piece from any position on the hot-stamped compact and conducting a tensile test in accordance with JIS Z 2241:2011. The crosshead speed was 1 mm / min. A tensile strength TS of 2200 MPa or more was judged to be high strength and pass, while a tensile strength of less than 2200 MPa was judged to be low strength and fail.

[0086] Hydrogen embrittlement resistance The hydrogen embrittlement resistance of the hot-stamped compact was evaluated using the following method. A test piece measuring 68 mm in length and 6 mm in width was taken from a random position on the hot-stamped compact. The edges of the test piece were polished using #200 to #1500 silicon carbide paper, and then polished to a mirror finish using a liquid in which diamond powder with a particle size of 1 to 6 μm was dispersed in a diluted solution such as alcohol or pure water. The corners of the test piece were then chamfered using #200 to #1500 silicon carbide paper. A stress of 800 MPa or more was applied to the test piece, and it was immersed in 1 liter of hydrochloric acid adjusted to pH 4 at room temperature for 48 hours, and the presence or absence of cracks was evaluated.

[0087] A specimen that did not crack even under a load stress of 800 MPa or more was judged to have passed. A specimen with no cracks at 800 MPa was marked "Fair," a specimen with no cracks at 900 MPa was marked "Good," a specimen with no cracks at 1000 MPa was marked "Very Good," and a specimen with no cracks at 1100 MPa or more was marked "Excellent." On the other hand, a specimen with cracks at a load stress of 800 MPa was judged to have failed and marked "Bad" in the table.

[0088] [Table 1A]

[0089] [Table 1B]

[0090] [Table 1C]

[0091] [Table 2A]

[0092] [Table 2B]

[0093] [Table 2C]

[0094] [Table 3A]

[0095] [Table 3B]

[0096] [Table 3C]

[0097] [Table 4A]

[0098] [Table 4B]

[0099] [Table 4C]

[0100] Tables 4A to 4C show that the hot-stamped steels of the examples of the present invention have high strength and excellent hydrogen embrittlement resistance, while the hot-stamped steels of the comparative examples are inferior in one or more properties. [Industrial Applicability]

[0101] According to the above aspects of the present invention, it is possible to provide a hot stamped steel sheet having high strength and excellent resistance to hydrogen embrittlement.

Claims

1. The chemical composition, in mass%, is C: more than 0.40%, less than 0.70%, Si: 0.010-3.000%, Mn: 0.10% or more and less than 0.60%; P: 0.100% or less, S: 0.0100% or less, N: 0.0200% or less, O: 0.0200% or less, Al: 0.0010-0.5000%, Nb: 0.0010-0.1000%, Ti: 0.010-0.200%, Cr: 0.010-0.800%, Mo: 0.0010-1.0000%, B: 0.0005-0.0200%, Co: 0-4.00%, Ni: 0-3.00%, Cu: 0-3.00%, V: 0 to 3.00%, W: 0-3.00%, Ca: 0-1.0000%, Mg: 0 to 1.0000%, REM: 0-1.0000%, Sb: 0 to 1.000%, Sn: 0-1.000%, Zr: 0 to 1.000%, As: 0 to 0.100%, and The balance is Fe and impurities. In a surface layer region which is a region from the surface of the hot stamped body to a depth of 1 / 25 of the plate thickness from the surface, The area ratio of bainite is more than 10%, The maximum value of the pole density of the texture is 4.0 or less, The B removal index, which is an index that quantitatively indicates the amount of decrease in B concentration, is 0.05 or more. A hot stamped product characterized by:

2. The chemical composition is, in mass %, Co: 0.01-4.00%, Ni: 0.01 to 3.00%, Cu: 0.01-3.00%, V: 0.01 to 3.00%, W: 0.01-3.00%, Ca: 0.0001-1.0000%, Mg: 0.0001 to 1.0000%, REM: 0.0001-1.0000%, Sb: 0.001 to 1.000%, Sn: 0.001 to 1.000%, Zr: 0.001 to 1.000%, and As: 0.001-0.100% The hot-stamped product according to claim 1, characterized in that it contains one or more selected from the group consisting of

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