Technical field
[0001]The present invention is a hot stamping material used in the structural member and reinforcing member of intensity automobiles and structures required, in particular, hot stamping superior strength after hot stamping, ductility, resistance to the collision characteristics and resistance to hydrogen embrittlement body on.
BACKGROUND
[0002]Recently, weight reduction of automobile bodies from the viewpoint of environmental protection and resource saving has been required, therefore, the application of high-strength steel sheets to automobile members is accelerating. However, since the formability due to the high strength of the steel sheet deteriorates in the high-strength steel sheet, it becomes a problem formability into complex shaped members.
[0003]To solve such problems, the application of hot stamping to implement press molding after heating the steel to a high temperature of the austenite region is underway. Hot stamping, pressing and simultaneously, since carrying out the hardening process in the mold, it is possible to obtain a strength corresponding to the C content of the steel sheet, it is attracting attention as a technology to achieve both shaping and strength secured to automotive parts ing.
[0004]However, conventional hot pressed parts manufactured by press hardening, to the plate thickness throughout is formed of a hard tissue (mainly martensite), the bending deformation at the time of vehicle collision occurs, part of the buckling portion easy greatest distortion enters, progresses cracks starting from the vicinity of the surface layer of the steel sheet, and finally lead to breakage.
[0005]In the hot stamping member is not how to contact with the mold is necessarily uniform, for example, the cooling rate tends to decrease at such vertical wall portion of the hat member. Etc. If this is low hardenability of the steel sheet, it is possible to locally hardness lower region is formed on the steel sheet. Local softening unit deformation is concentrated at the time of a collision, to become a factor of cracking, variation in the hardness in the molding body is small, that is, to secure stable strength to ensure the anti-collision properties in is important. Furthermore, if the bending deformation at the time of vehicle collision occurs, localized deformation by hat member buckles, the load bearing of the member decreases. That member and the maximum load as well as members strength also affected the likelihood of buckling. Ductile and deformable region of the steel sheet is less likely localized in member states. That is hard to buckle.
[0006]Therefore it is important ductility in hot stamping member, generally ductility of martensite is low. Also, penetration of hydrogen is promoted due to the high density of the surface layer of the lattice defects of the steel sheet, it is a problem that becomes poor hydrogen embrittlement resistance of the member. For this reason, hot pressed parts manufactured by press hardening, application site in automotive parts has been limited.
[0007]To the above problem, a technology for suppressing cracks by increasing the deformability of the hot pressed part is proposed. In Patent Document 1, hot pressed parts while the hardness of the plate thickness center and more than 400Hv of, by forming the surface layer has a thickness of 20μm or more 200μm or less hardness 300Hv following soft layer, the tensile strength of 1300MPa or higher while ensuring the strength of a technology for suppressing cracking during automobile collision is disclosed. In Patent Document 2, by controlling the concentration of carbon sheet thickness surface layer to 1/5 of the carbon concentration of the thickness center portion, a technique for improving the resistance to hydrogen embrittlement by reducing the density of the surface layer of the lattice defects is disclosed ing. In Patent Document 3, the thickness center portion is a composite structure of ferrite and martensite, by increasing the structural fraction of the ferrite in the surface layer portion, technology capable relieve stress even when subjected to bending surface portion severe deformation is disclosed ing.
[0008]However, Patent Document 1 and Patent Document 2, the surface layer portion of the sheet thickness and soft tissue, by a central portion of the plate thickness composed of hard tissue, the gradient of the sudden stiffness in the thickness direction is generated Therefore, when subjected to bending deformation, cracking near the boundary of the soft slope of sudden hardness is occurring tissue and the hard tissue is a problem that tends to occur. In Patent Document 3, the surface portion of the sheet thickness and soft tissue, and a central portion of the plate thickness by the complex structure of the hard tissue and soft tissue, to reduce the gradient of the sudden stiffness in the thickness direction it is, but for the central portion of the plate thickness and the complex structure, the upper limit of the tensile strength becomes about 1300 MPa, it is difficult to ensure a higher tensile strength 1500MPa required for the hot pressed part.
CITATION
Patent Document
[0009]Patent Document 1: JP 2015-30890 JP
Patent Document 2: JP 2006-104546 Patent Publication
Patent Document 3: WO 2015/097882
Summary of the Invention
Problems that the Invention is to Solve
[0010]In view of the problems of the prior art, and has a tensile strength of 1500MPa or more strength to achieve both the high bending resistance and hydrogen embrittlement resistance to achieve the anti-collision properties and suppressing the hardness variation It was a problem, and an object thereof is to provide a hot stamp formed body to solve the problem. Further, the present invention aims at providing a hot stamping molded article to achieve both high ductility and high hydrogen embrittlement resistance.
Means for Solving the Problems
[0011]The present inventors have intensively studied how to solve the above problems. As a result, in order to improve the hydrogen embrittlement resistance, it is effective to reduce the density of the sheet thickness surface layer lattice defects, for this purpose, it is necessary to form a soft tissue surface. Meanwhile, in order to ensure a tensile strength of at least 1500MPa, it is necessary to configure the central portion of the thickness only hard tissue. Thus, the thickness of the surface layer and the soft tissue, when configured in hard tissue in the center of the plate thickness, reducing the gradient in the thickness direction of the abrupt stiffness that occurs near the boundary of the hard tissue and soft tissue if it is possible to, while ensuring the tensile strength 1500MPa or more strength and good resistance to hydrogen embrittlement was considered good bending properties are obtained.
[0012]Therefore, the inventors found that by performing the surface layer of the tissue control a soft tissue, an investigation will good bending properties resulting steel sheet metal structure, and made extensive studies. As a result, the metal structure that constitutes the softened layer is in a thickness cross section, when a region surrounded by the grain boundaries having a misorientation of 15 ° or more was defined as the crystal grain, the maximum crystal orientation difference of the inside of the crystal grains There was found to be 1 ° and less crystal grains and is composed of the crystal grains inside the maximum misorientation 8 ° ~ 15 ° of the crystal grains. Also, these measurements were found to be as measured in the region from a depth position of the surface layer of the subsurface 20μm depth position in the thickness 1/2 of the surface layer (surface layer center). Thus, the influence of surface properties of a hot stamping member has been found that it is possible to eliminate the influence of the transition portion from the mid-thickness portion in the surface layer.
[0013]Further, by controlling the addition amount of Mn and Si in the thickness of the central portion, thereby improving the ductility was ensured stably high strength by increasing hardenability. As a result, it is possible to bend suppress the occurrence of cracking during deformation, while ensuring the above tensile strength and good resistance to hydrogen embrittlement 1500 MPa, to achieve a good bendability and ductility, and hardness variation that succeeds in keeping, it was possible to obtain excellent hot stamping body crashworthiness properties and hydrogen embrittlement resistance.
[0014]
　The present invention has been completed based on the above findings and has as its gist is as follows.
(1) and the plate thickness center part, a hot stamping member and a softening layers disposed on both sides or one side of the plate thickness center part,
　the plate thickness central portion,
　by mass%,
C: 0. more than 20%, less than 0.70%
Si: less than
3.00%, Mn: 0.20% or more, less than 3.00%
P: 0.10% or
less, S: 0.10% or
less, sol. Al: 0.0002%, or more 3.0000% or less,
N: contains 0.01% or less,
　the balance being Fe and unavoidable impurities, having the following hardness above 500 Hv 800 Hv,
　below the surface of the softened layer metal structure from the depth of 20μm to a thickness 1/2 of the depth of the softened layer is in a cross section parallel to the thickness direction, a region surrounded by the grain boundaries having a misorientation of 15 ° or more and the crystal grain when defined, the crystal grains maximum crystal misorientation inside than 1 ° of the crystal grains, the grain interior Hot stamping molded maximum crystal orientation differences 8 ° or more and 15 ° or less grain total area ratio of the is equal to or less than 20% to 50%.
(2) a Si content of less 0.50%, Mn content is 0.20% or more, hot stamping molded article according to and less than 1.50% (1).
(3) a Si content of less 0.50% Mn content is 1.50% or more, and less than 3.00%, hot stamping molded article according to (1).
(4) Si content of 0.50 percent, less than 3.00% Mn content is 0.20% or more and less than 1.50%, the plate thickness central portion, an area fraction , 1.0% or more, hot stamping molded article according to (1) comprises a residual austenite of less than 5.0%.
(5) Si content of 0.50 percent, less than 3.00%, Mn content is 1.50% or more and less than 3.00%, the plate thickness central portion, an area fraction , 1.0% or more, hot stamping molded article according to (1) comprises a residual austenite of less than 5.0%.
(6) mid-thickness portion is further, in mass%, Ni: characterized by containing 0.01% or more 3.00% or less (1) hot stamping according to any one of the - (5) molded body.
(7) mid-thickness portion further contains, by mass%, Nb: 0.010% or more 0.150% or less, Ti: 0.010% or more 0.150% or less, Mo: 0.005% or more 1. 000% or less, B: to contain more than one or two of 0.0005% or more 0.0100% or less and wherein (1) hot stamping molded article according to any one of the - (6).
(8) hot stamping molded article according to any one of the plating layer to the softening layer is formed, characterized in (1) to (7).
The invention's effect
[0015]
　According to the present invention, bendability, ductility, crashworthiness characteristics, and can provide a small hot stamping member variation in excellent hydrogen embrittlement resistance, and hardness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016]
FIG. 1 is a schematic view for explaining the diffusion of C atoms in the production of hot stamping molding of the present invention.
It is a graph showing the dislocation density change after rolling pass about rough rolling used in the method for producing the hot stamping material of the present invention; FIG.
DESCRIPTION OF THE INVENTION
[0017]
(This structure of the hot stamping molded body according to the invention)
　hot stamping molded body according to the present invention has a structure in which both sides or one side softened layer on the surface of, are arranged. The softened layer is a region having a 10Hv or lower hardness than the hardness of the plate thickness center part.
[0018]
(Sheet thickness central part)
　mid-thickness portion of the hot stamping molded body according to the present invention involves the to have the following hardness above 500 Hv 800 Hv. To the hardness of the plate thickness central portion within the above range will be described as follows for the reason for limiting the composition of the plate thickness center part. Hereinafter,% of the component composition means mass%.
[0019]
(C: 0.20% or more and less than 0.70%)
　C is, 500 Hv or more at mid-thickness portion, is an important element for obtaining the following hardness 800 Hv. If it is less than 0.20%, since it is difficult to ensure a more 500Hv at mid-thickness portion, C is 0.20% or more. Preferably 0.30% or more. On the other hand, when it exceeds 0.70% hardness of the plate thickness central portion exceeds the 800 Hv, since bending resistance is reduced, C is a 0.70%. Preferably not more than 0.50%.
[0020]
(Si: less than
　3.00%) Si are the elements contributing to the improvement of strength in the solid solution strengthening, it may be added 0.50% as the upper limit from the viewpoint of improving the strength. On the other hand, the effect of the strength improved if added over 0.50% is the upper limit of 0.50% to saturation. Preferably not more than 0.30%.
[0021]
　Si also without compromising the hydrogen embrittlement resistance and bending resistance expressed by a surface layer of tissue control, is also an element having an effect of enhancing the ductility. In particular, when bending deformation at the time of vehicle collision occurs, localized deformation by hat member buckles, the load bearing of the member decreases. That member and the maximum load as well as members strength also affected the likelihood of buckling. Ductile and deformable region of the steel sheet is less likely localized in member states. That is hard to buckle.
[0022]
　It is important ductility in hot stamping member, generally ductility of martensite is low. By adding Si exceeds 0.50%, it is possible to secure more than 1.0% of residual austenite in area fraction, it is possible to improve the ductility. From this perspective, Si is preferably set to 0.50% super added. More preferably not less than 1.00%. On the other hand, the addition of more than 3.00%, residual austenite becomes an area fraction of 5.0% or more, because it causes bending of the deterioration, the upper limit is less than 3.00%. Preferably less than 2.00%.
[0023]
(Mn: 0.20% or more and less than
　3.00%) Mn is an element contributing to improving the strength in the solid solution strengthening. Effect of improving the strength of the steel sheet by solid solution Mn into the metal tissues is the amount of less than 0.20% the effect is not obtained, adding 0.20% or more. Preferably 0.70% or more. On the other hand, addition over 1.50%, the effect is saturated.
[0024]
　Moreover, Mn has the effect of enhancing the hardenability. By adding 1.50% or more, it is possible to obtain a stable high strength by increasing hardenability. The preferred addition amount for obtaining the effect of improving the hardenability, 1.70% or more. Be added 3.00% or more, the effect is to saturate, and 3.00% the upper limit of the Mn content. Preferably, less than 2.00%.
[0025]
(P: 0.10% or less)
　P segregates in the grain boundary, it is an element which inhibits the strength of grain boundaries. Exceeds 0.10%, significantly reduced the strength of the grain boundary, so hydrogen embrittlement resistance and bending resistance is lowered, P is at most 0.10%. Preferably 0.05% or less. The lower limit is not particularly limited, when reduced to less than 0.0001%, de P cost increases greatly, since economically disadvantageous, practically, 0.0001% is substantially the lower.
[0026]
(S: 0.10% or less)
　S is an element which forms inclusions. It exceeds 0.10%, since inclusions generated hydrogen embrittlement resistance and bending resistance is lowered, S is at most 0.10%. Preferably 0.0025% or less. The lower limit is not particularly limited, when reduced to less than 0.0015%, de S cost increases greatly, since economically disadvantageous, practically, 0.0001% is substantially the lower.
[0027]
(Sol.Al:0.0002Pasento, or 3.0000% or
　less) Al is an element which forms an action of sound of the steel by deoxidation of molten steel. In the present invention, in order to obtain a deoxidation effect, but not all of the Al contained in the steel, the range of the content of the aluminum (sol. Al) of the so-called acid-soluble is defined. sol. When the content of Al is less than 0.0002%, the deoxidation is insufficient, sol. Al is 0.0002% or more. Preferably is 0.0010% or more. On the other hand, even if added over 3.0000% since the effect is saturated, and less 3.0000%.
[0028]
(N: 0.01% or less)
　N is an impurity element, an element that inhibits bendability to form a nitride. Exceeds 0.01%, the bendability generates coarse nitrides is significantly reduced, N is the set to 0.01% or less. Preferably is less than or equal to 0.0075%. The lower limit is not particularly limited, when reduced to less than 0.0001%, de-N cost increases greatly, since economically disadvantageous, practically, 0.0001% is substantially the lower.
[0029]
(Ni: 0.01% or more, 3.00% or
　less) Ni are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect is obtained is less than 0.01%, adding 0.01% or more. Preferably 0.50% or more. On the other hand, even if added over 3.00% since the effect is saturated, and less 3.00%. Preferably not more than 2.50%.
[0030]
(Nb: 0.010% or more 0.150% or
　less) Nb are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect can be obtained with less than 0.010%, the addition of 0.010% or more. Preferably 0.035% or more. On the other hand, even if added over 0.150% of its effect will be saturated, 0.150% or less. Preferably is less than or equal to 0.120%.
[0031]
(Ti: 0.010% or more 0.150% or
　less) Ti are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect can be obtained with less than 0.010%, 0.010% or more. Preferably 0.020%. On the other hand, even if added over 0.150% of its effect will be saturated, 0.150% or less. Preferably is less than or equal to 0.120%.
[0032]
(Mo: 0.005% or more, 1.000% or
　less) Mo are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect can be obtained with less than 0.005%, 0.005% or more. Preferably it is greater than or equal to 0.0100%. On the other hand, even if added over 1.000%, the effect is to saturate, is 1.000% or less. Preferably is less than or equal to 0.800%.
[0033]
(B: 0.0005% or more, 0.0100% or less)
　B is an element that improves segregation and strength of grain boundaries in a grain boundary, it may be added as necessary. Since the addition effect is not sufficiently obtained is less than 0.0005% is added 0.0005% or more. Preferably is 0.0010% or more. On the other hand, its effect if added over 0.0100% in order to saturate, and 0.01% or less. Preferably is less than or equal to 0.0075%.
[0034]
　Balance of composition of the mid-thickness portion is Fe and unavoidable impurities. Unavoidable impurities inevitably mixed in steel raw material and / or steel manufacturing process, an element that is allowed in a range that does not inhibit the characteristics of the hot stamping molded body according to the present invention.
[0035]
(Hardness of the plate thickness central portion: 500 Hv or more, 800 Hv or less)
　the hardness of the plate thickness central portion If it is more than 500 Hv, can be secured over 1500MPa as the tensile strength of the hot stamping molding of the present invention. Preferably, it is greater than or equal to 600Hv. On the other hand, the hardness of the plate thickness central portion is more than 800 Hv, the difference in hardness of the softened layer is too large, because it causes bending of the deterioration, the upper limit 800 Hv. Preferably is less than or equal to 720Hv.
[0036]
　Method of measuring the hardness of the plate thickness central portion is as follows. Collected a cross section perpendicular to the plate surface of the hot stamping material, performs sample preparation of the measurement surface, subjected to hardness testing. Process for the preparation of the measurement surface may be carried out according to JI Z 2244, for example, after polishing the measurement surface using silicon carbide paper # 1500 and # 600, alcohols such as diamond powder 6μm from the particle size 1μm it Shiagere mirror using a liquid dispersed in a diluent or pure water. Hardness test may be carried out in the method described in JIS Z 2244, using a micro Vickers hardness tester, 1/2 position of the sheet thickness, a load 1 kgf, at least three times the spacing of the indentations 10 in point measured, and the average value and the hardness of the plate thickness central portion of the hot stamping molding.
[0037]
(Metal structure of the sheet thickness central part)
　mid-thickness portion, by inclusion of 1% or more of residual austenite in area fraction, it is possible to improve the ductility. Area fraction of retained austenite in the sheet thickness center portion is preferably at least 2%. However, when the area fraction of 5% or more, because it causes bending of the degradation, and the upper limit of less than 5%. Preferably less than 4.5%.
[0038]
　Area fraction of retained austenite in the sheet thickness central portion can be measured by the following method. A member after the hot stamping, samples were taken and scalped from the normal direction of the rolling surface to the half depth of the sheet thickness, subjecting the surface obtained by scalped to X-ray diffraction measurement. From an image obtained by X-ray diffraction using the Kα line of Mo, it is possible to determine the area ratio Vγ of retained austenite using the following equation.
　Vγ = (2/3) {100 / (0.7 × α (211) / γ (220) +1)} + (1/3) {100 / (0.78 × α (211) / γ (311) +1)}
　where, alpha (211) is X-ray diffraction intensity at (211) plane of the ferrite, gamma (220) is X-ray diffraction intensity at the (220) plane of the austenite, gamma (311) of the austenite (311) it is an X-ray diffraction intensity in a plane.
[0039]
(Softening layer)
　As described above, the softened layer in the present invention, in the plate thickness direction of the plate thickness cross section of the hot pressed bodies, the hardness of the plate thickness central portion (hardness at 1/2 position of the sheet thickness) from lowered position above 10Hv from a region to the surface of the molded product. The following describes the metal structure and the composition of the softened layer.
[0040]
(Metal structure of the softened layer)
　results inventors have made intensive studies, the results of the examination of the metallographic structure of the steel sheet excellent bendability is obtained, the metal constituting the softened layer tissue, in the thickness cross section, 15 when ° or more regions surrounded by grain boundaries with misorientation is defined as crystal grains, wherein the grains up to the crystal orientation difference of inside than 1 ° of the crystal grains, the maximum crystal orientation difference of the inside of the crystal grains it has been found that good is composed of 8 ° ~ 15 ° of the crystal grains. These measurements were found to be as measured in the region of from a depth position of the surface under 20μm softening layer to a depth position in the thickness 1/2 of the softened layer (softened layer center). The present inventors have studied intensively, in view of the effect of bending, etc., the fractions of the structures from the position of 20μm from the surface of the softened layer to a depth position in the thickness 1/2 of the softened layer is important. Thus, the influence of surface properties of a hot stamping member has been found that it is possible to eliminate the influence of the transition portion leading to the softened layer from a thickness center portion.
[0041]
　In the metal structure of the softened layer, the crystal grains and the maximum crystal misorientation inside than 1 ° of the crystal grains, the crystal grains inside the maximum misorientation 8 ° ~ 15 ° of the crystal grains total area ratio of the 20 It is less than%, because the effect is not sufficiently obtained, the lower limit is 20%. Preferred are the area ratio of 20% or more, more preferably may is 25% or more. Meanwhile, the total area ratio of the metal structure is 50% or more of the softened layer, reducing softening layer and the plate thickness central portion hardness difference becomes large, the gradient of the thickness direction of the abrupt stiffness that occurs when bending deformation since the effect of the not sufficiently obtained, and less than 50%. More preferably, it is preferable to 45% or less.
[0042]
　Note that while the depth position in the thickness 1/2 of the softened layer from (softened layer center) of the plate thickness center part, the hardness in the sheet thickness central portion of the softened layer (boundary between the mid-thickness portion) the HVA, certain hardness of the softened layer center When HVB, the relationship HvA-HvB ≧ 10Hv.
[0043]
　The method of determining the region from the softened layer subsurface 20μm to 1/2 position in the thickness of the softened layer is described below. Perform sample preparation of the measurement surface by taking a vertical cross-section (thickness cross-section) relative to the measurement object of the hot stamping surface, subjected to hardness testing. Process for the preparation of the measurement surface may be carried out according to JI Z 2244, for example, after polishing the measurement surface using silicon carbide paper # 1500 and # 600, alcohols such as diamond powder 6μm from the particle size 1μm it Shiagere mirror using a liquid dispersed in a diluent or pure water. To the sample prepared with the measuring surface, using a micro Vickers hardness tester according to the method of the JI Z 2244, wherein, performing the two measurements. First time, said the region within 20μm in the thickness direction from the surface of the hot stamping member to the center of plate thickness (thickness of 1/2 position), direction perpendicular to the surface (thickness direction) to, a load 0.3 kgf, measured at least three times the interval of the indentation. However, if the plating layer is present, plating, or measured from the region within just under 20μm alloy layer of a material of the plating and the softened layer. The mid-thickness portion hardness of determining a reduced start position than 10Hv from (hardness at 1/2 position of the sheet thickness) of the softened layer to the surface of the hot stamping member from its thickness position . If the softened layer is present on both surfaces, the second measurement of the is carried out in a similar manner at first and the opposite surface (back surface), the position starts to decrease more than 10Hv from the hardness of the plate thickness central portion to determine.
[0044]
　Next, a method of calculating the area ratio of the metal structure of the softened layer. Cutting out a sample so that it can be a cross section perpendicular to its surface from the hot stamping material (plate thickness cross-section) is observed. The length of the sample, depending on the measurement device, may be about 50 [mu] m. In the thickness direction of the sample, a region from the surface of the softened layer to a thickness of 1/2 position (softened layer center) of the softened layer, and EBSD analysis measurement interval 0.2μm obtain crystal orientation information. Here EBSD analysis, thermal field emission scanning electron microscope (JEOL Ltd. JSM-7001F) and EBSD detector using an apparatus comprised of (TSL manufactured DVC5 type detector), the analysis speed of 200 to 300 points / sec carry out.
[0045]
　Next, the obtained crystal orientation information, a region surrounded by the grain boundaries having a misorientation of 15 ° or more is defined as one crystal grain, to create a crystal orientation map of the plate surface direction. Using the obtained crystal orientation map, determine the point of intersection of the crystal grain of the long axis and the crystal grain boundary. Of the two intersections, and starting one of the one point, the other point as an end point, and calculates the azimuth difference between all the measurement points included in the long axis of the crystal grains. The maximum value of the resulting orientation difference, the maximum crystal orientation difference in the crystal grains, after executing all of the crystal grains contained the analysis measurement region, the average value of 15 ° or more of the grain boundary of the values It is defined as the maximum crystal orientation difference of the inner area surrounded by.
[0046]
　Maximum crystal misorientation as defined above, for example, be used mounted on the software that came with the EBSD analyzer "OIM Analysis (TM)" and "Inverse Pole Figure the Map" "Profile Vector" function, conveniently calculated it is possible to. The "Inverse Pole Figure the Map" function, it is possible to draw a grain boundary having a tilt angle of 15 ° or more as high angle grain boundary, further, it is possible to create a crystal orientation map of the plate surface direction. The "Profile Vector" function, can be calculated Misorientation Angle (misorientation) between all contained in any straight line of measuring points. All crystal grains contained in the measurement region for (not including the crystal grains at the end of the measurement region), and carrying out the analysis, the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries 1 ° following the crystal grains, the crystal orientation differences to calculate the total area ratio of crystal grains is 8 ° ~ 15 °. If the softened layer is formed on both sides, the above procedure was also performed on the back surface side of the hot stamping material, employing the average value of the obtained area ratio from the front side and back side.
[0047]
(Softened layer of composition)
　The composition of the softened layer, P is an unavoidable impurity element that inhibit the intensity and / or bending resistance, S, except N, is not particularly limited, strength and excellent bendability hot stamping member to ensure the steel showing a, it is preferable that the following composition.
[0048]
　The composition of the softened layer, C content, Si content, and any one of the Mn content or two or more, not more than 0.6 times the corresponding element content of the mid-thickness portion preferably, the preferred range of each component of such a case is as follows.
[0049]
(C: 0.05% or more and less than 0.42%)
　C may be added in an amount of 0.05% or more in order to increase the strength. In the viewpoint of improving the impact properties by increasing the load bearing as members, preferably, 0.10% or more. To the hardness of the softened layer lower than the hardness of the plate thickness center part, it is preferable to be less than the thickness center portion. A preferable content of C of the softening layer for this is less than 0.42%, more preferably not more than 0.35%.
[0050]
(Si: less than
　2.00%) Si are the elements contributing to the improvement of strength in the solid solution strengthening, it is added to improve the strength. However, since the hardness of the softened layer lower than the hardness of the plate thickness center part, it is preferable to be less than the thickness center portion.
[0051]
　If the Si content of the mid-thickness portion is less than 0.50%, preferably the Si content of the softened layer is less than 0.30%, preferably not more than 0.20%. Further, the plate thickness Si content in the central portion of 0.50 percent, of less than 3.00%, the content of the preferred Si softening layer is less than 2.00%, more preferably less 1.50% it is.
[0052]
(Mn: 0.01% or more, 1.80% or
　less) is Mn, since an element which contributes to improving the strength in the solid solution strengthening, are added to improve the strength. To the hardness of the surface layer lower than the hardness of the plate thickness center part, it is preferable to be less than the thickness center portion. Content less than 1.80% of the surface layer of the preferred Mn for this, preferably 1.40% or less, more preferably less than 0.90%, still more preferably 0.70%.
[0053]
　Mn content of the mid-thickness portion is 0.20% or more, is less than 1.50%, the content of the preferred Mn softening layer is less than 0.90%, more preferably below 0.70% is there. Also preferred Mn content of the softened layer is less than 0.12% to 0.90% and preferably 0.70%. Further, Mn content of the mid-thickness portion is 1.50% or more, is less than 3.00%, the content of the preferred Mn softening layer is less 1.80%.
[0054]
(P: 0.10% or less)
　P segregates in the grain boundary, it is an element which inhibits the strength of grain boundaries. Exceeds 0.10%, significantly reduced the strength of the grain boundary, so hydrogen embrittlement resistance and bending resistance is lowered, P is 0.1% or less. Preferably 0.05% or less. The lower limit is not particularly limited, when reduced to less than 0.0001%, de P cost increases greatly, since economically disadvantageous, practically, 0.0001% is substantially the lower.
[0055]
(S: 0.10% or less)
　S is an element which forms inclusions. It exceeds 0.10%, since inclusions generated hydrogen embrittlement resistance and bending resistance is lowered, S is at most 0.10%. Preferably 0.0025% or less. The lower limit is not particularly limited, when reduced to less than 0.0015%, de S cost increases greatly, since economically disadvantageous, practically, 0.0001% is substantially the lower.
[0056]
(Sol.Al:0.0002Pasento, or 3.0000% or
　less) Al is an element which forms an action of sound of the steel by deoxidation of molten steel. In the present invention, in order to obtain a deoxidation effect, but not all of the Al contained in the steel, the range of the content of the aluminum (sol. Al) of the so-called acid-soluble is defined. sol. When the content of Al is less than 0.0002%, the deoxidation is insufficient, sol. Al is preferably set to 0.0002% or more. More preferably 0.0010% or more. On the other hand, even if added over 3.0% since the effect is saturated, and 3.0% or less.
[0057]
(N: 0.01% or less)
　N is an impurity element, an element that inhibits bendability to form a nitride. Exceeds 0.01%, the bendability generates coarse nitrides is significantly reduced, N is the set to 0.01% or less. Preferably is less than or equal to 0.0075%. The lower limit is not particularly limited, when reduced to less than 0.0001%, de-N cost increases greatly, since economically disadvantageous, practically, 0.0001% is substantially the lower.
[0058]
　Note that the components of the softening layer, C content, Si content, and one or more Mn content, C content of mid-thickness portion, Si content and for Mn content is preferably not more than 0.6-fold, respectively, except that the strength and / or bending is unavoidable impurity element that inhibits property P, S, the upper limit of N is defined, there is no particular limitation on the other components. In general, the softening layer, C, in addition to Si and Mn, may optionally include one or more of the following components.
[0059]
(Ni: 0.01% or more, 3.00% or
　less) Ni are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect is obtained is less than 0.01%, adding 0.01% or more. Preferably not less than 0.5%. On the other hand, even if added over 3.00% since the effect is saturated, and less 3.00%. Preferably not more than 2.50%.
[0060]
(Nb: 0.010% or more 0.150% or
　less) Nb are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect can be obtained with less than 0.010%, the addition of 0.010% or more. Preferably 0.035% or more. On the other hand, even if added over 0.150% of its effect will be saturated, 0.150% or less. Preferably is less than or equal to 0.120%.
[0061]
(Ti: 0.010% or more 0.150% or
　less) Ti are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect can be obtained with less than 0.010%, 0.010% or more. Preferably 0.020%. On the other hand, even if added over 0.150% of its effect will be saturated, 0.150% or less. Preferably is less than or equal to 0.120%.
[0062]
(Mo: 0.005% or more, 1.000% or
　less) Mo are the elements contributing to the improvement of strength in solid solution strengthening may be added as necessary. Since no effect can be obtained with less than 0.005%, 0.005% or more. Preferably 0.010% or more. On the other hand, even if added over 1.000%, the effect is to saturate, is 1.000% or less. Preferably is less than or equal to 0.800%.
[0063]
: (B 0.0005% or more, 0.01% or less)
　of B, since an element for improving the segregation is strength of grain boundaries in a grain boundary, may be added as necessary. Since the addition effect is not sufficiently obtained is less than 0.0005% is added 0.0005% or more. Preferably is 0.0010% or more. On the other hand, its effect if added over 0.0100% in order to saturate, and 0.0100% or less. Preferably is less than or equal to 0.0075%.
[0064]
(Hard section of a hot stamping molded article distribution)
　in a cross section perpendicular to the surface of the hot stamping material, it is preferable hardness distribution is uniform. Hardly contacts the die in the vertical wall portion in the hat structure, hardness because the cooling rate is reduced is reduced in some cases. If 100HV than the hardness relative to the average hardness of the cross section perpendicular to the longitudinal direction of the hat shaped body there is a region to be reduced, a higher crashworthiness the deformation upon impact is broken at an early stage to concentrate the softened portion not be obtained. Thus the average value of the hardness distribution in the cross section perpendicular to the surface of the hot stamping member (hereinafter, referred to as "cross-sectional average hardness".) There shall be no point below 100HV from. Hardness distribution and cross-sectional average hardness in the cross section, using Vickers hardness tester (load 1 kgf), the cross section perpendicular to the longitudinal direction of the elongated hot stamping member, any position in the longitudinal direction in collected, the following equally spaced 1mm pitch, obtained by measuring the Vickers hardness between the ends of the cross-section.
[0065]
(Plating of layers)
　on the surface of the softened layer, for the purpose of improvement of corrosion resistance may be formed a plating layer. Plating layer may be either a electroplating layer and the molten plating layer. The electroplating layer, electro-galvanized layer, electric Zn-Ni alloy plating layer and the like. The melt coating layer, galvanized layer, galvannealed layer, molten aluminum plating layer, melt Zn-Al alloy plating layer, hot-dip Zn-Al-Mg alloy plating layer, hot-dip Zn-Al-Mg-Si alloy plating layer, and the like. Coating weight of the plating layer may be a common adhesion amount is not particularly limited.
[0066]
(Production method of hot stamping molded body according to the present invention)
　will now be described an embodiment of a manufacturing method for obtaining a hot stamp molded body according to the present invention, the present invention provides multi-layer steel sheet as described below but it is not limited to the form.
[0067]
　One embodiment of the production method of the present invention, first, after by grinding the surface and / or back surface of the steel sheet satisfying the requirements of the composition of the plate thickness center of the removal of the surface oxide was ground plane laminating the softened layer steel plate on the side. The fixing method of the steel sheet for softening layer steel plate and the plate thickness central portion is not particularly limited, may be performed by adhering with arc welding. Incidentally, C content, Si content, and any one or two or more corresponding softened layer steel plate is 0.6 times or less of the element content of the steel sheet for mid-thickness portion of the Mn content it is preferable to laminate.
[0068]
　Further, by controlling the speed casting in a continuous casting process of the softened layer for steel sheet more than 6 ton / min, is suppressed microscopic segregation of Mn in the softened layer steel sheet, the concentration distribution of Mn in the softened layer steel sheet it can be made uniform. Mn, by increasing the yield strength of the austenite, for influencing the generation behavior of the grain boundaries in the structure after transformation, the region surrounded by the grain boundaries having a misorientation of 15 ° or more was defined as the crystal grain Occasionally, have the effect of maximum misorientation of grains inside to promote the formation of grains is 8 ° ~ 15 °. Therefore, for the purpose of promoting the formation of the microstructure, the speed casting in a continuous casting process of the softened layer for steel sheet may be controlled to more than 6 ton / hr.
[0069]
　Also, a multi-layer steel sheet produced by the above method, further 1100 ° C. or more, those holding 1350 ° C. or less at a temperature of 60 minutes or more, is preferably used as a steel sheet for hot stamping molded article according to the present invention. Results inventors studied, 1100 ° C. or more, by performing heat treatment of holding 1350 ° C. or less at 60 minutes or more, the metal structure of the region up to the softening layer center from a depth position of the surface under 20μm softening layer 15 ° or more regions surrounded by grain boundaries with misorientation when defining the crystal grains, and grain maximum crystal misorientation inside than 1 ° of the crystal grains, the maximum crystal orientation difference of the inside of the crystal grains 8 ° ~ 15 total area ratio of a crystal grain ° 20% or more, and less than 50%, it was found that excellent bendability and hydrogen embrittlement resistance is obtained. The upper limit is not particularly limited and holds more than 300 minutes, the heating cost is significantly elevated economical disadvantage, the practical operation, 300 minutes is substantially upper limit.
[0070]
　Laminate produced in the above production method (multilayered steel) to hot rolling, cold rolling, by hot stamping, etc. continuous hot dipping is subjected, it is possible to obtain a hot stamp molded body according to the present invention.
[0071]
　Hot rolling may be hot rolled carried out at normal conditions. For example, the finishing temperature may be carried out in a temperature range of not lower than 810 ° C., cooling conditions followed is not particularly necessary to define, implement the coiling in a temperature range of 750 ° C. or less. Further, it is also possible to implement the re-heat treatment for softening of the multilayered steel sheet after hot rolling.
[0072]
　However, in order to further promote the formation of plate thickness center part, the hot rolling after the heat treatment of the multilayer steel includes rough rolling and finish rolling, the rough rolling is per pass at 1100 ° C. or more temperature the thickness reduction rate is less than 50% 5% or more, and interpass time is 2 times or more performed are preferably under the conditions of more than 3 seconds.
[0073]
　More specifically, in order to further promote the formation of plate thickness center in the present invention, it is necessary to control the alloying elements, in particular the concentration of C atoms distributed loosely. Distribution of C concentration obtained by the diffusion of C atoms, the diffusion frequency of C atoms is increased as the temperature rises. Therefore, in order to control the C concentration is controlled in the rough rolling it is important from the hot rolling heating. The hot rolling heating, in order to promote the diffusion of C atoms, it is necessary to high temperature heating temperature, preferably 1350 ° C. 1100 ° C. or higher, more preferably at most 1150 ° C. Ultra 1350 ° C.. The hot rolling heating, a change shown in FIG. 1 (i) and (ii) occurs. (I) is the diffusion of C atoms from a thickness center portion to the surface layer, (ii) is a decarburization of C desorbed to the outside from the surface layer. Distribution C concentration caused by balance of the diffusion and elimination reaction of the C atoms of the (i) and (ii). Is less than 1100 ° C., since the reaction of (i) is insufficient, not obtained preferably C concentration distribution. On the other hand, in the 1350 ° C. greater than the reactivity of (ii) it is excessively generated, can not be obtained likewise preferred concentration distribution.
[0074]
　After having controlled the preferred C concentration distribution by adjusting the hot rolling heating temperature, in order to obtain a more optimal C concentration distribution, the path control in the rough rolling is very important. Rough rolling the rough rolling temperature is 1100 ° C. or more, the thickness reduction rate per pass is 5% or more and less than 50%, and interpass time is performed twice or more under the conditions of more than 3 seconds. This is because the distortion introduced by the rough rolling, in order to promote the diffusion of C atoms of (i) in FIG. Assuming that a slab with a controlled C concentration in a preferable state in hot rolling heating rough rolling and finish rolling in the usual manner, so that the C atom plate thickness without being able to sufficiently diffuse within the surface layer is reduced. Accordingly, the slab having a thickness of more than 200 mm, when manufacturing a hot rolled steel sheet having a thickness of several mm by hot rolling of a conventional method, C concentration in the surface layer becomes rapidly changing steel, gradual change in hardness is obtained no. Found methods to solve this is the path control of the rough rolling. Diffusion of C atoms is greatly influenced by the strain (dislocation density) as well temperature. In particular, in comparison with the lattice diffusion, since the increasing spread frequency more than 10 times in the dislocation diffusion, while leaving the dislocation density, it is necessary to devise to reduce the sheet thickness by rolling. Curve 1 in Figure 2 is of the plate thickness reduction ratio per one pass of the rough rolling is small, it shows the dislocation density change after rolling pass, it can be seen that the strain remains for a long time. By thus leaving the strain on the surface layer for a long time, occur diffusion of C atoms in the surface layer is sufficient, it is possible to obtain an optimal C concentration distribution. On the other hand, the curve 2 is the change of the dislocation density of the plate thickness reduction ratio per one pass of the rough rolling is large, the amount of strain introduced by rolling is increased, the recovery is likely to be promoted, dislocation density rapidly descend. Therefore, in order to obtain an optimal concentration distribution of C, it is necessary not to cause a change of the dislocation density, such as curve 2. From this viewpoint, the upper limit of the sheet thickness reduction rate per one pass is less than 50%. In order to promote the diffusion of C atoms in the surface layer, because the secure dislocation density and the retention time of a quantity required, next to the lower limit of the sheet thickness reduction rate of 5%, secured over three seconds as the path between the time You need to have
[0075]
　Cold rolling the usual reduction ratio, for example, it is a cold rolling conducted at 30 to 90%. The hot-rolled steel sheet and cold-rolled steel sheet, as it is, or the heat and rolled steel sheet or steel sheet subjected to recrystallization annealing to the cold-rolled steel sheet in normal conditions, is also included steel sheet subjected to temper rolling under normal conditions.
[0076]
　Heating during hot stamping, molding, cooling process also may be carried out at normal conditions. For example, hot rolled steel sheet rewind wound hot rolled steel sheet in the hot rolling step, or cold-rolled steel sheet subjected to cold rolling rewind the hot-rolled steel sheet was wound, or a plated cold rolled steel sheet subjected to, 0.1 ° C. / s or higher, at a heating rate of 200 ℃ / s, 810 ℃ above, was heated to a temperature of 1000 ° C. or less, the steel sheet was maintained at this temperature, in a conventional hot stamping to the desired shape molding to.
[0077]
　Retention time, so may be set according to the molding aspect is not particularly limited. For example, 30 seconds or more, cooling the green compact after it hot stamp equal to or less than 600 seconds to room temperature.
[0078]
　Cooling speed may be set to a normal condition, for example, the average cooling rate in the temperature range from the heating temperature to 400 ° C. than can fall within 50 ° C. / s or higher. Mid-thickness Si content 0.50% in unit exceeds, less than 3.00% Mn content is 0.20% or more in the sheet thickness center part, and the steel plate is less than 1.50%, mid-thickness Si content 0.50% in unit exceeds, less than 3.00%, Mn content in the sheet thickness center portion is 1.50% or more, in the case of there steel sheet less than 3.00% is , in order to improve the ductility by increasing the production amount of residual austenite, the cooling after heating and holding, 200 ° C. or higher, controlling the average cooling rate in a temperature range of 400 ° C. or less to less than 50 ° C. / s It is preferred.
[0079]
　For the purpose of adjustment of the intensity may be subjected to tempering in the range of 0.99 ° C. ~ 600 ° C. in cooling the molded body to room temperature.
[0080]
　In the manufacturing method of hot stamping of the aforementioned embodiments, and constitutes a plate thickness central portion and softening layer in each separate steel. However, hot stamping molding of the present invention is not limited to multi-layer steel sheet obtained by laminating two steel plates as described above. Mid-thickness portion and the softened layer may be formed in a steel sheet of a single material, for example, by softening the surface layer of the single layer steel sheet with decarburization, softened layer and mid-thickness portion it is also possible to produce a high strength steel sheet consisting of a.
Example
[0081]
　Next, a description will be given of an embodiment of the present invention, conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is, in this single condition example the present invention is not limited. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0082]
Production Example A]
　surface in Table A-1-1 ~ TABLE A-1-2 mid-thickness portion for steel No.1 having chemical compositions shown in ~ 19 ( "steels No.1 ~ 19" in the table) to remove surface oxides by grinding. Thereafter, the softened layer formed steel plate having a chemical composition shown in Table A-1-1 ~ TABLE A-1-2 on both or one side of the respective plate thickness center part steel plate (hereinafter, referred to as "surface layer steel sheet". ) are laminated in arc welding, to produce a laminated steel sheet No.1 ~ 44 for hot stamping molded article. In the table, the column of component composition 0 indicates that the corresponding component is not intentionally added.
[0083]
　Incidentally, the thickness of the sum of the surface steel plate and the plate thickness center part for the steel sheet after arc welding and 200 mm ~ 300 mm, the thickness of the surface layer for steel sheet, about 1/3 of the thickness of the steel sheet mid-thickness portion ( If one side is approximately 1/4). Laminated steel plate No. 38 is a steel with a welded surface steel plate only on one side. Among TABLE A-1-1 ~ TABLE A-1-2 No.1 ~ 44 of the laminated steel sheet, steel sheet for plate thickness center portion satisfy the composition requirements of the mid-thickness portion of the hot stamping molded body according to the present invention nothing is indicated as "comparative steel" remarks.
[0084]
　For each of the laminated steel sheets No.1 ~ 44, in Table A-2-1 ~ Table A-2-2 are shown production conditions No.1 ~ 44 conditions, hot rolling before the heat treatment, rough rolling and heat during rolling, and the steel sheet is subjected to cold rolling. Then, heat treatment (in the table, "heat treatment of a hot stamping molded article") shown in Table A-2-1 ~ Table A-2-2 against the steel plate subjected to hot stamp by applying hot stamping body ( Table a-3 of the item "molded body") No. 1A ~ 44A were prepared, respectively. Incidentally, Nanba36A, the hot stamping of 37A, in hot-dip plating line, the steel sheet base metal surface, the adhesion amount 120 ~ 160 g / m 2 was aluminum plating.
[0085]
　In the table, "roughing" item "sheet thickness reduction rate" of means sheet thickness reduction rate per pass of rough rolling, the item "rolling count" rolling path between time under conditions of more than 3 seconds It means a number of times. Also, items in the table, "heating rate (° C. / s)" means heating rate to reach the heating temperature after cold rolling step "heat treatment during hot stamp". Further, in the table, the item "heating temperature (℃)" in "heat treatment during hot stamping" is the temperature during hot stamping, "average cooling rate (℃ / s) (400 ℃ greater)" is the heating temperature means an average cooling rate in the temperature range up to 400 ° C. greater (° C. / s), "average cooling rate (℃ / s) (400 ℃ or less)", the average cooling in the temperature region of 200 ° C. or higher 400 ° C. or less It refers to the rate (℃ / s). Further, in the table, symbol "-" is attached column indicates that has not been appropriate treatment.
[0086]
　Table A-3, showing the metal structure and characteristics of the hot stamping material No. 1A ~ 44A. Position and thickness 1/2 in samples taken from the hot stamping material, components of the analysis of the position of 20μm from the surface of the softened layer is laminated steel sheets in Table A-1-1 ~ TABLE A-1-2 No. steel and for mid-thickness of 1-44 was comparable to the components of the surface layer steel plate.
[0087]
　The metal structure of the steel sheet after the hot stamping, as measured by the foregoing method, the hardness of the plate thickness center portion for steel plates constituting the plate thickness center part, the surface of the thickness of the surface layer steel plate constituting the softened layer 1/2 in the metal structure until, over 15 ° maximum crystal orientation difference of the internal grain boundary enclosed area is 1 ° or less and the crystal grains, the total area ratio of the crystal orientation differences 8 ° ~ a 15 ° grain calculated. Maximum crystal and orientation difference 1 ° or less crystal grains, the maximum misorientation 8 ° ~ of 15 ° grain total area ratio of in the field "high angle grain boundaries in Table A-3 a calculated value of the area ratio (% ) is shown in ".
[0088]
　A tensile test was carried out of the hot stamping body. The results are described in Table A-3. Tensile test, to prepare a No. 5 test piece described in JIS Z 2201, was carried out according to the test method described in JIS Z 2241.
[0089]
　Hydrogen embrittlement resistance of a hot stamping molded article was evaluated using a test piece cut out from the molded body. Generally hot stamping body is other joining parts using bonding techniques, such as spot welding, depending part shape accuracy stress applied torsion hot stamping body is added. Stress depends on the location of the parts, it is difficult to accurately calculate this, it is believed that there is no practical problem to be delayed fracture in yield stress. Therefore, from the shaped body, cut out a test specimen having a thickness of 1.2 mm × width 6 mm × length 68mm, after applying the distortion of considerable yield stress at four-point bending test, and 100h immersed in pH3 hydrochloric acid, cracks It was to evaluate the resistance to hydrogen embrittlement in the occurrence or non-occurrence. Pass the case without a break (○), in the case of rupture there was judged as failure (×).
[0090]
　To evaluate the anti-collision properties of a hot stamping molded article were evaluated in the following measurement condition based on the VDA standard defined by the German Automobile Industry Association (VDA238-100). The displacement at maximum load obtained in the bending test in the present invention is converted into an angle in VDA standard, by determining the maximum bending angle, were evaluated crashworthiness properties of hot stamping molding.
[0091]
Specimen dimensions: 60 mm (rolling direction) × 60 mm (rolling direction perpendicular), or, 30 mm (rolling direction) × 60 mm (rolling direction perpendicular)
Bending ridgeline: rolling direction perpendicular
Test method: roll support, punches push
roll diameter: .phi.30 mm
punch shape: front end R = 0.4 mm
distance between the rolls: 2.0 × thickness (mm) + 0.5 mm
indentation speed: 20 mm / min
tester: Shimadzu AUTOGRAPH 20 kN
[0092]
　Tensile strength is at least 1500 MPa, yet, the maximum bending angle (°) is not less 90 (°) or more, yet, a case where hydrogen embrittlement resistance becomes accepted as excellent crashworthiness properties and hydrogen embrittlement resistance , it was the invention example. Of the above three performances, if not satisfied with any one sample of Comparative Example.
[0093]
　Both hot stamping molded article of the present invention embodiment, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries than 1 ° and the crystal grains, the total area ratio of the crystal orientation differences 8 ° ~ a 15 ° crystal grains was less than 20% or more 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0094]
　In contrast, hot stamping of No.5A the hardness of the plate thickness center portion is insufficient for the carbon content of the steel plate for plate thickness central portion was small, the tensile strength was insufficient. Hot stamping of No.9A, since the carbon content of the steel plate for plate thickness center part was excessive, the hardness of the plate thickness central portion becomes excessive, bending resistance of the target is not obtained. Also, the hot stamping of No.11A the hardness of the plate thickness center portion is insufficient for the Mn content of the steel sheet for plate thickness center portion is poor, the tensile strength was insufficient.
[0095]
　Hot stamping of No.30A ~ 32A are comparative examples manufactured by using the laminated steel sheet for hot stamping molded preferred heat treatment before hot stamping process was not applied. Hot stamping of No.30A because the heat treatment temperature before hot stamp process is too low, the growth of soft tissue and intermediate hardness of the metal structure is insufficient, the influence of surface properties of a hot stamping molded article, can not eliminate the influence of the transition portion leading to the softened layer from a thickness center part, it was not possible to obtain excellent bendability. Also, the hot stamping of No.31A because the heat treatment temperature before hot stamping process was excessively high, the growth of soft tissue and intermediate hardness of the metal structure becomes excessive, the hardness of the softened layer and mid-thickness portion the difference becomes too large, the effect of reducing an abrupt hardness gradient of the thickness direction generated during bending deformation could not be obtained. Therefore, hot stamping of No.31A could not obtain excellent bendability. Hot stamping of No.32A because the heat treatment time before the hot stamping process is too short, the metal structure of the softened layer to a thickness of 1/2 from the surface of the softened layer, soft tissues and intermediate hardness growth of the metal structure becomes insufficient, bendability of the target is not obtained.
[0096]
　No. Hot stamping of 41A is rolling temperature of the rough rolling was low. In addition, No. Hot stamping of 42A are sheet thickness reduction rate of the rough rolling it was low. In addition, No. Hot stamping of 43A, the path between the time a small rolling times under conditions of more than 3 seconds. These hot stamping body, because it is not manufactured in a suitable rough rolling conditions, the growth of soft tissue and intermediate hardness of the metal structure is insufficient, it is impossible to relieve the strain caused by bending deformation , it was not possible to obtain a bending of a target.
[0097]
　Hot stamping of No44A is a steel plate with a controlled speed casting in a continuous casting process of surface layer steel plates than 6 ton / min, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, 15 maximum crystal orientation difference of the inner area surrounded by ° or more grain boundaries and is 1 ° or less of crystal grains, it is possible to crystal orientation differences increase the total area ratio of crystal grains is 8 ° ~ 15 °, bending It is excellent in sex.
[0098]
[TABLE A-1-1]

[0099]
[TABLE A-1-2]

[0100]
[A-2-1 Table]

[0101]
[TABLE A-2-2]

[0102]
[Table A-3]

[0103]
[Production Example B]
　to remove the Table B-1-1 by grinding the surface of the steel sheet for mid-thickness portion having a chemical composition shown in through Table B-1-2 surface oxide. Then, by laminating a surface layer for steel sheet having the chemical compositions shown in Table B-1-3 ~ Table B-1-4 on both or one side of the respective plate thickness central portion for steel plates in arc welding, hot stamping member the laminated steel plate No.1 ~ 52 in use was produced. In the table, the column of component composition 0 indicates that the corresponding component is not intentionally added.
[0104]
　Incidentally, the thickness of the sum of the surface steel plate and the plate thickness center part for the steel sheet after arc welding and 200 mm ~ 300 mm, the thickness of the surface layer for steel sheet, about 1/3 of the thickness of the steel sheet mid-thickness portion ( If one side is approximately 1/4). Laminated steel plate No. 32 is a steel with a welded surface steel plate only on one side. Of Table B-1-1 ~ Table No.1 ~ 52 of laminated steel plates of the B-1-3, for a steel sheet thickness center portion satisfy the composition requirements of the mid-thickness portion of the hot stamping molded body according to the present invention nothing is indicated as "comparative steel" remarks.
[0105]
　For each of the laminated steel sheets No.1 ~ 52, in Table B-2-1 ~ Table B-2-2 are shown production conditions No.1 ~ 52 conditions, hot rolling before the heat treatment, rough rolling and heat during rolling, and the steel sheet is subjected to cold rolling. Then, heat treatment (in the table, "heat treatment of a hot stamping molded article") shown in Table B-2-1 ~ Table B-2-2 against the steel plate subjected to hot stamp by applying hot stamping body ( Table B-3-1 and Table B-3-2 of the item "molded body") No.1B ~ 52B were prepared, respectively. Incidentally, Nanba30B, the hot stamping of 31B, in hot-dip plating line, the steel sheet base metal surface, the adhesion amount 120 ~ 160 g / m 2 was aluminum plating. Incidentally, each item of the Table B-2-1 ~ Table B-2-2 correspond respectively to the items shown in Table A-2-1 ~ Table A-2-2. Further, in the table, symbol "-" is attached column indicates that has not been appropriate treatment.
[0106]
　Table B-3-1 and Table B-3-2, showing a metal structure and characteristics of the hot stamping body No.1B ~ 52B. Position and thickness 1/2 in samples taken from the hot stamping material, components of the analysis of the position of 20μm from the surface of the softened layer, laminated steel plates of Table B-1-1 ~ Table B-1-4 No. steel and for mid-thickness of 1-52 was comparable to the components of the surface layer steel plate.
[0107]
　The metal structure of the steel sheet after the hot stamping, as measured by the foregoing method, the hardness of the plate thickness center portion for steel plates constituting the plate thickness center part, the thickness of the softened layer from the surface of the surface layer steel plate constituting the softened layer in the metal structure up to half the the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries than 1 ° of the crystal grains, the total of the crystal grains the crystal orientation differences is 8 ° ~ 15 ° to calculate the area ratio of. The calculated value of the area ratio of Table B-3-1 ~ Table B-3-2 item "and the maximum crystal orientation difference 1 ° or less of the crystal grains large angle in the grain boundaries, the largest misorientation 8 ° ~ 15 ° shown in the total area ratio of crystal grains (%) ".
[0108]
　A tensile test was carried out of the hot stamping body. The results are shown in Table B-3-1 ~ Table B-3-2. Tensile test, to prepare a No. 5 test piece described in JIS Z 2201, was carried out according to the test method described in JIS Z 2241.
[0109]
　Hydrogen embrittlement resistance of a hot stamping molded article, as with Production Example A, were evaluated using a test piece cut out from the molded body. That is, from the shaped body, cut out a test specimen having a thickness of 1.2 mm × width 6 mm × length 68mm, after applying the distortion of considerable yield stress at four-point bending test, and 100h immersed in pH3 hydrochloric acid, cracks It was to evaluate the resistance to hydrogen embrittlement in the occurrence or non-occurrence. Pass the case without a break (○), in the case of rupture there was judged as failure (×).
[0110]
　To evaluate the anti-collision properties of a hot stamping molded article, based on the VDA standard defined by the German Automobile Industry Association (VDA238-100), it was evaluated in the same measurement conditions as in Production Example A. The displacement at maximum load obtained in the bending test in the present invention is converted into an angle in VDA standard, by determining the maximum bending angle, were evaluated crashworthiness properties of hot stamping molding.
[0111]
　Hardness variation of the molding was evaluated by measurement of hardness in a cross section perpendicular to the longitudinal direction of the molded body. Through the thickness center of the total cross-sectional area, on a straight line parallel to the surface of the molded body, using a Vickers hardness tester, to measure the Vickers hardness load 1 kgf, at 1mm pitch. For each of the hot stamping body No.1B ~ 52B, the average value of the measured hardness and minimum hardness Table B-3-1, "average cross-sectional hardness" in Table B-3-2 and "minimum hardness" It is shown in the item. The "average cross-sectional hardness - Minimum hardness" is the difference between the average cross-sectional hardness and minimum hardness. Also, for each of the hot stamping body No.1B ~ 52B, harder than 100HV from the average value was regarded as passed if there is no area to be reduced.
[0112]
　Tensile strength is at least 1500 MPa, yet, the maximum bending angle (°) is not less 90 (°) or more, yet, a case where hydrogen embrittlement resistance becomes accepted as excellent crashworthiness properties and hydrogen embrittlement resistance , it was the invention example. Of the above three performances, if not satisfied with any one sample of Comparative Example.
[0113]
　Both hot stamping molded article of the present invention embodiment, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries than 1 ° and the crystal grains, the total area ratio of the crystal orientation differences 8 ° ~ a 15 ° crystal grains was less than 20% or more 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0114]
　In contrast, hot stamping of No.5B the hardness of the plate thickness center portion is insufficient for the carbon content of the steel plate for plate thickness central portion was small, the tensile strength was insufficient. Hot stamping of No.9B, since the carbon content of the steel plate for plate thickness center part was excessive, the hardness of the plate thickness central portion becomes excessive, bending resistance of the target is not obtained. Also, the hot stamping of No.11B is hardness variation of the molding section to the Mn content of the steel sheet for plate thickness center portion is poor is increased.
[0115]
　Hot stamping of No.25B ~ 27B are comparative examples manufactured by using the laminated steel sheet for hot stamping molded preferred heat treatment before hot stamping process was not applied. Hot stamping of No.25B because the heat treatment temperature before hot stamp process is too low, the growth of soft tissue and intermediate hardness of the metal structure is insufficient, the influence of surface properties of a hot stamping molded article, can not eliminate the influence of the transition portion leading to the softened layer from a thickness center part, it was not possible to obtain excellent bendability.
[0116]
　Also, the hot stamping of No.26B because the heat treatment temperature before hot stamping process was excessively high, the growth of soft tissue and intermediate hardness of the metal structure becomes excessive, the hardness of the softened layer and mid-thickness portion the difference becomes too large, the effect of reducing an abrupt hardness gradient of the thickness direction generated during bending deformation could not be obtained. Therefore, hot stamping of No.26B could not obtain excellent bendability.
[0117]
　Hot stamping of No.27B because the heat treatment time before the hot stamping process is too short, the metal structure of the softened layer to a thickness of 1/2 from the surface of the softened layer, soft tissues and intermediate hardness growth of the metal structure becomes insufficient, bendability of the target is not obtained.
[0118]
　No. Hot stamping of 49B is rolling temperature of the rough rolling was low. In addition, No. Hot stamping of 50B is sheet thickness reduction rate of the rough rolling was low. In addition, No. Hot stamping of 51B, the path between the time a small rolling times under conditions of more than 3 seconds. These hot stamping body, because it is not manufactured in a suitable rough rolling conditions, the growth of soft tissue and intermediate hardness of the metal structure is insufficient, it is impossible to relieve the strain caused by bending deformation , it was not possible to obtain a bending of a target.
[0119]
　Hot stamping of No52B is a steel plate with a controlled speed casting in a continuous casting process of surface layer steel plates than 6 ton / min, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, 15 maximum crystal orientation difference of the inner area surrounded by ° or more grain boundaries and is 1 ° or less of crystal grains, it is possible to crystal orientation differences increase the total area ratio of crystal grains is 8 ° ~ 15 °, bending It is excellent in sex.
[0120]
[Table B-1-1]

[0121]
[Table B-1-2]

[0122]
[Table B-1-3]

[0123]
[Table B-1-4]

[0124]
[Table B-2-1]

[0125]
[Table B-2-2]

[0126]
[Table B-3-1]

[0127]
[Table B-3-2]

[0128]
Production Example C]
　to remove the Table C-1-1 by grinding the surface of the plate thickness center portion for steel plates having the chemical compositions shown in through Table C-1-2 surface oxide. Thereafter, both sides or one side in Table C-1-3 of the respective plate thickness central steel plate, and the surface layer steel sheet having the chemical compositions shown in Table C-1-4 was laminated in arc welding, hot stamping member a laminated steel sheet No.1 ~ 59 of use was produced. In the table, the column of component composition 0 indicates that the corresponding component is not intentionally added.
[0129]
　Incidentally, the thickness of the sum of the surface steel plate and the plate thickness center part for the steel sheet after arc welding and 200 mm ~ 300 mm, the thickness of the surface layer for steel sheet, about 1/3 of the thickness of the steel sheet mid-thickness portion ( in the case of one side was about 1/4). Laminated steel plate No. 38 is a steel with a welded surface steel plate only on one side. No. The laminated steel plate other than 38, the surface layer steel plate on both sides of each of the plate thickness center portion for steel plates are welded. Of Table C-1-1 ~ Table C-1-4 of the laminated steel sheet No.1 ~ 59, for a steel sheet thickness center portion satisfy the composition requirements of the mid-thickness portion of the hot stamping molded body according to the present invention nothing is indicated as "comparative steel" remarks.
[0130]
　For each of the laminated steel sheets No.1 ~ 59, in Table C-2-1 ~ Table C-2-2 are shown production conditions No.1 ~ 59 conditions, hot rolling before the heat treatment, rough rolling and heat during rolling, and the steel sheet is subjected to cold rolling. Then, Table C-2-1 against the steel plate, (in the table, "heat treatment of a hot stamping molded article") heat treatment shown in Table C-2-2 performs hot stamping by applying hot stamping body ( Table C-3-1 and Table C-3-2 of the item "molded article") the No.1C ~ 59C were prepared, respectively. Incidentally, Nanba36C, the hot stamping of 37C, at the molten plating line, the steel sheet base metal surface, the adhesion amount 120 ~ 160 g / m 2 was aluminum plating. Note that each item of Table C-2-1 ~ Table C-2-2 correspond respectively to the items shown in Table A-2-1 ~ Table A-2-2. Further, in the table, symbol "-" is attached column indicates that has not been appropriate treatment.
[0131]
　Table C-3-1, Table C-3-2, showing a metal structure and characteristics of the hot stamping body No.1C ~ 59C. Position of the sheet thickness 1/2 of the samples taken from the hot stamping material (plate thickness center) and the component of the analysis of the position of 20μm from the surface of the softened layer, Table C-1-1 ~ Table C-1- for mid-thickness portion of the fourth laminated steel No.1 ~ 59 steel sheet and was comparable to the components of the surface layer steel plate.
[0132]
　The metal structure of the steel sheet after the hot stamping, as measured by the foregoing method, the hardness of the plate thickness center portion for steel plates constituting the plate thickness center part, the thickness of the softened layer from the surface of the surface layer steel plate constituting the softened layer in the metal structure up to half the the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries than 1 ° of the crystal grains, the total of the crystal grains the crystal orientation differences is 8 ° ~ 15 ° to calculate the area ratio of. The calculated value of the area ratio of Table C-3-1 ~ Table C-3-2 item "and the maximum crystal orientation difference 1 ° or less of the crystal grains large angle in the grain boundaries, the largest misorientation 8 ° ~ 15 ° shown in the total area ratio of crystal grains (%) ".
[0133]
　A tensile test was carried out of the hot stamping body. The results in Table C-3. Tensile test, to prepare a No. 5 test piece described in JIS Z 2201, was carried out according to the test method described in JIS Z 2241.
[0134]
　Hydrogen embrittlement resistance of a hot stamping molded article, as with Production Example A, were evaluated using a test piece cut out from the molded body. That is, from the shaped body, cut out a test specimen having a thickness of 1.2 mm × width 6 mm × length 68mm, after applying the distortion of considerable yield stress at four-point bending test, and 100h immersed in pH3 hydrochloric acid, cracks It was to evaluate the resistance to hydrogen embrittlement in the occurrence or non-occurrence. Pass the case without a break (○), in the case of rupture there was judged as failure (×).
[0135]
　To evaluate the anti-collision properties of a hot stamping molded article, based on the VDA standard defined by the German Automobile Industry Association (VDA238-100), it was evaluated in the same measurement conditions as in Production Example A. The displacement at maximum load obtained in the bending test in the present invention is converted into an angle in VDA standard, by determining the maximum bending angle, were evaluated crashworthiness properties of hot stamping molding.
[0136]
　Tensile strength is at least 1500 MPa, yet, the maximum bending angle (°) is not less 90 (°) or more, yet, a case where hydrogen embrittlement resistance becomes accepted as excellent crashworthiness properties and hydrogen embrittlement resistance , it was the invention example. Of the above three performances, if not satisfied with any one sample of Comparative Example.
[0137]
　Both hot stamping molded article of the present invention embodiment, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries than 1 ° and the crystal grains, the total area ratio of the crystal orientation differences 8 ° ~ a 15 ° crystal grains was less than 20% or more 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0138]
　In contrast, hot stamping of No.5C the hardness of the plate thickness center portion is insufficient for the carbon content of the steel plate for plate thickness central portion was small, the tensile strength was insufficient. Hot stamping of No.9C, since the carbon content of the steel plate for plate thickness center part was excessive, the hardness of the plate thickness central portion becomes excessive, bending resistance of the target is not obtained. Also, the hot stamping of No.11C, since the Si content of steel sheet thickness center portion is poor, the area fraction of retained austenite is less than 1%, the uniform elongation was insufficient.
[0139]
　Table C-1-3, "component ratio of the plate thickness center portion for steel plates and surface steel plate" is in Table C-1-4, C content, Si content, and for the Mn content, the mid-thickness portion the ratio of the content in the surface layer steel plate with respect to the content in use steel. Nanba30C, hot stamping molded article. 37C, C content, Si content, and none of the Mn content is 0.6 times greater than the corresponding element content of mid-thickness portion.
[0140]
　Hot stamping of No.30C ~ 32C are comparative examples manufactured by using the laminated steel sheet for hot stamping molded preferred heat treatment before hot stamping process was not applied. Hot stamping of No.30C because the heat treatment temperature before hot stamp process is too low, the metal structure of the softened layer to a thickness of 1/2 from the surface of the softened layer, soft tissues and intermediate hardness growth of the metal structure becomes insufficient, bendability of the target is not obtained. Also, the hot stamping of No.31C because the heat treatment temperature before hot stamping process was excessively high, the growth of soft tissue and intermediate hardness of the metal structure becomes excessive, the hardness of the softened layer and mid-thickness portion the difference becomes too large, the effect of reducing an abrupt hardness gradient of the thickness direction generated during bending deformation could not be obtained. Therefore, hot stamping of No.31C could not obtain excellent bendability. Hot stamping of No.32C because the heat treatment time before the hot stamping process is too short, the metal structure of the softened layer to a thickness of 1/2 from the surface of the softened layer, soft tissues and intermediate hardness growth of the metal structure becomes insufficient, bendability of the target is not obtained.
[0141]
　No. Hot stamping of 56C, the rolling temperature of the rough rolling was low. In addition, No. Hot stamping of 57C is sheet thickness reduction rate of the rough rolling was low. In addition, No. Hot stamping of 58C, the path between the time a small rolling times under conditions of more than 3 seconds. These hot stamping body, because it is not manufactured in a suitable rough rolling conditions, the growth of soft tissue and intermediate hardness of the metal structure is insufficient, it is impossible to relieve the strain caused by bending deformation , it was not possible to obtain a bending of a target.
[0142]
　No. Hot stamping of 59C is a steel plate with a controlled speed casting in a continuous casting process of surface layer steel plates than 6 ton / min, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, 15 maximum crystal orientation difference of the inner area surrounded by ° or more grain boundaries and is 1 ° or less of crystal grains, it is possible to crystal orientation differences increase the total area ratio of crystal grains is 8 ° ~ 15 °, bending It is excellent in sex.
[0143]
[Table C-1-1]

[0144]
[Table C-1-2]

[0145]
[Table C-1-3]

[0146]
[Table C-1-4]

[0147]
[Table C-2-1]

[0148]
[Table C-2-2]

[0149]
[Table C-3-1]

[0150]
[Table C-3-2]

[0151]
Production Example D]
　Table D-1-1, the surface of the plate thickness center portion for steel No.1 ~ 38 with the chemical compositions shown in Table D-1-2 ( "steels No.1 ~ 38" in the table) to remove surface oxides by grinding. Then, by laminating a surface layer for steel sheet having the chemical compositions shown in Table D-1-3 ~ Table D-1-4 on both or one side of the respective plate thickness central portion for steel plates in arc welding, hot stamping member a laminated steel sheet No.1 ~ 60 of use was produced. Incidentally, the thickness of the sum of the surface steel plate and the plate thickness center part for the steel sheet after arc welding and 200 mm ~ 300 mm, the thickness of the surface layer for steel sheet, about 1/3 of the thickness of the steel sheet mid-thickness portion ( in the case of one side was about 1/4). Laminated steel plate No. 38 is a steel with a welded surface steel plate only on one side. No. The laminated steel plate other than 38, the surface layer steel plate on both sides of each of the plate thickness center portion for steel plates are welded. Of Table D-1-1 ~ Table D-1-3 No.1 ~ 60 of the laminated steel sheet, steel sheet for plate thickness center portion satisfy the composition requirements of the mid-thickness portion of the hot stamping molded body according to the present invention nothing is indicated as "comparative steel" remarks.
[0152]
　For each of the laminated steel sheets No.1 ~ 60, in Table D-2-1 ~ Table D-2-3 are shown production conditions No.1 ~ 60 conditions, hot rolling before the heat treatment, rough rolling and heat during rolling, and the steel sheet is subjected to cold rolling. Then, heat treatment (in the table, "heat treatment of a hot stamping molded article") shown in Table D-2-1 ~ Table D-2-3 against the steel plate subjected to hot stamp by applying hot stamping body ( Table D-3-1 ~ D-3-3 item "molded body") No.1D ~ 60D were prepared, respectively. Note that the hot stamping of Nanba38,39, in hot-dip plating line, the steel sheet base metal surface, the adhesion amount 120 ~ 160 g / m 2 was aluminum plating. Note that each item of Table D-2-1 ~ Table D-2-3 correspond respectively to the items shown in Table A-2-1 ~ Table A-2-2. Further, in the table, symbol "-" is attached column indicates that has not been appropriate treatment.
[0153]
　Table D-3-1 ~ D-3-3, showing a metal structure and characteristics of the hot stamping body No.1D ~ 60D. Position of the sheet thickness 1/2 of the samples taken from the hot stamping material (plate thickness center) and the component of the analysis of the position of 20μm from the surface of the softened layer is Table D-1-1 ~ Table D-1- for mid-thickness portion of the fourth laminated steel No.1 ~ 60 steel sheet and was comparable to the components of the surface layer steel plate.
[0154]
　The metal structure of the steel sheet after the hot stamping, as measured by the foregoing method, the hardness of the plate thickness center portion for steel plates constituting the plate thickness center part, the thickness of the softened layer from the surface of the surface layer steel plate constituting the softened layer in the metal structure up to half the the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries than 1 ° of the crystal grains, the total of the crystal grains the crystal orientation differences is 8 ° ~ 15 ° to calculate the area ratio of. A maximum crystal orientation difference 1 ° or less of the crystal grains in the item "high angle grain boundary of the area ratio of the calculated value in Table D-3-1 ~ D-3-3, the maximum crystal orientation difference of 8 ° ~ 15 ° crystals shown in the total area ratio of the particle (%) ".
[0155]
　A tensile test was carried out of the hot stamping body. The results are shown in Table D-3-1 ~ D-3-3. Tensile test, to prepare a No. 5 test piece described in JIS Z 2201, was carried out according to the test method described in JIS Z 2241.
[0156]
　Hydrogen embrittlement resistance of a hot stamping molded article, as with Production Example A, were evaluated using a test piece cut out from the molded body. That is, from the shaped body, cut out a test specimen having a thickness of 1.2 mm × width 6 mm × length 68mm, after applying the distortion of considerable yield stress at four-point bending test, and 100h immersed in pH3 hydrochloric acid, cracks It was to evaluate the resistance to hydrogen embrittlement in the occurrence or non-occurrence. Pass the case without a break (○), in the case of rupture there was judged as failure (×).
[0157]
　To evaluate the anti-collision properties of a hot stamping molded article, based on the VDA standard defined by the German Automobile Industry Association (VDA238-100), it was evaluated in the same measurement conditions as in Production Example A. The displacement at maximum load obtained in the bending test in the present invention is converted into an angle in VDA standard, by determining the maximum bending angle, were evaluated crashworthiness properties of hot stamping molding.
[0158]
　Crash-resisting properties of the hot stamping member was evaluated in terms of ductility. Specifically, to evaluate the crashworthiness characteristics seeking uniform elongation of the steel sheet by a tensile test of the steel sheet after the hot stamping. Tensile test, to prepare a No. 5 test piece described in JIS Z 2201, was performed according to the test method described in JIS Z 2241, and the uniform elongation of the elongation maximum tensile load was obtained.
[0159]
　Local softening unit deformation is concentrated at the time of a collision, to become a factor of cracking, variation in the hardness in the molding body is small, that is, to secure stable strength to ensure the anti-collision properties in is important. Therefore, the anti-collision properties of a hot stamping molded article was evaluated in terms of hardness variation. The cross section perpendicular to the longitudinal direction of the elongated hot stamping molded article, taken at an arbitrary position in the longitudinal direction, to measure the hardness of the plate thickness center position of the entire cross-section area including the vertical wall. Using Vickers tester for measuring, measuring load is 1 kgf, the number of measurement points is 10 points, the measurement interval was set to 1 mm. The difference between the average cross-sectional hardness and the minimum hardness shown in Table D-3-1 ~ Table D-3-3. All hardness variation where there is no measurement point from the mean value falls below 100Hv of measurement points is small, that is excellent in strength stability, and pass as excellent crashworthiness characteristics as a result, when there are measurement points below 100Hv not It was passed.
[0160]
　Tensile strength is at least 1500 MPa, yet, the maximum bending angle (°) is not less 90 (°) or more, yet, a case where hydrogen embrittlement resistance becomes accepted as excellent crashworthiness properties and hydrogen embrittlement resistance , it was the invention example. Of the above three performances, if not satisfied with any one sample of Comparative Example.
[0161]
　Both hot stamping molded article of the present invention embodiment, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries than 1 ° and the crystal grains, the total area ratio of the crystal orientation differences 8 ° ~ a 15 ° crystal grains was less than 20% or more 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0162]
　In contrast, hot stamping of No.5D the hardness of the plate thickness center portion is insufficient for the carbon content of the steel plate for plate thickness central portion was small, the tensile strength was insufficient. Hot stamping of No.9D, since the carbon content of the steel plate for plate thickness center part was excessive, the hardness of the plate thickness central portion becomes excessive, bending resistance of the target is not obtained. Further, Nanba10D, hot stamping molded article 11D, since the Si content of the steel sheet mid-thickness portion is poor, the area fraction of retained austenite is less than 1%, the uniform elongation was insufficient. Further, Nanba12D, hot stamping molded body 13D in order Mn content is insufficient, the hardness of the plate thickness center portion is insufficient, the tensile strength was insufficient. No.14D and No.15D hot stamping molded article, since Si content and Mn content is poor, the area fraction of retained austenite is less than 1.0%, the uniform elongation was insufficient.
[0163]
　Hot stamping of No.33D ~ 35D are comparative examples manufactured by using the laminated steel sheet for hot stamping molded preferred heat treatment before hot stamping process was not applied. Hot stamping of No. 33D, since the heat treatment temperature before hot stamp process is too low, the metal structure of the softened layer to a thickness of 1/2 from the surface of the softened layer, soft tissues and intermediate hardness growth of the metal structure becomes insufficient, bendability of the target is not obtained. Also, the hot stamping of No.34D because the heat treatment temperature before hot stamping process was excessively high, the growth of soft tissue and intermediate hardness of the metal structure becomes excessive, the hardness of the softened layer and mid-thickness portion the difference becomes too large, the effect of reducing an abrupt hardness gradient of the thickness direction generated during bending deformation could not be obtained. Therefore, hot stamping of No.34D could not obtain excellent bendability. Hot stamping of No.35D because the heat treatment time before the hot stamping process is too short, the metal structure of the softened layer to a thickness of 1/2 from the surface of the softened layer, soft tissues and intermediate hardness growth of the metal structure becomes insufficient, bendability of the target is not obtained.
[0164]
　Hot stamping of No.40D in order Si content was excessive, the residual austenite is excessively generated until more than 5% by area fraction. Therefore, hot stamping of No.40D is inferior in bendability. Hot stamping of No.41D, since Mn content was excessive, bending property is deteriorated. Since the hot stamping of No.42D has poor content of aluminum of acid-soluble, bendability is deteriorated. Also, hot stamping molding of No.45D is to include an excess of the aluminum content of acid-soluble, bendability is deteriorated.
[0165]
　No. Hot stamping of 57D are rolling temperature of the rough rolling was low. In addition, No. Hot stamping of 58D is sheet thickness reduction rate of the rough rolling was low. In addition, No. Hot stamping of 59D, the path between the time a small rolling times under conditions of more than 3 seconds. These hot stamping body, because it is not manufactured in a suitable rough rolling conditions, the growth of soft tissue and intermediate hardness of the metal structure is insufficient, it is impossible to relieve the strain caused by bending deformation , it was not possible to obtain a bending of a target.
[0166]
　Hot stamping of No60D is a steel plate with a controlled speed casting in a continuous casting process of surface layer steel plates than 6 ton / min, the metal structure of the surface of the surface layer steel plate to a thickness of 1/2, 15 maximum crystal orientation difference of the inner area surrounded by ° or more grain boundaries and is 1 ° or less of crystal grains, it is possible to crystal orientation differences increase the total area ratio of crystal grains is 8 ° ~ 15 °, bending It is excellent in sex.
[0167]
[Table D-1-1]

[0168]
[Table D-1-2]

[0169]
[Table D-1-3]

[0170]
[Table D-1-4]

[0171]
[Table D-2-1]

[0172]
[Table D-2-2]

[0173]
[Table D-2-3]

[0174]
[Table D-3-1]

[0175]
[Table D-3-2]

[0176]
[Table D-3-3]

Industrial Applicability
[0177]
　Hot stamping molding of the present invention, bendability, ductility, crashworthiness properties and excellent hydrogen embrittlement resistance, and since the hardness variation is small, the structural member and reinforcing member of intensity automobiles and structures required it can be suitably used.

The scope of the claims
[Requested item 1]
　And the plate thickness center part, a hot stamping member and a softening layers disposed on both sides or one side of the plate thickness center part,
　the plate thickness central portion,
　by mass%,
C: 0.20% or more , less than 0.70%
Si: less than
3.00%, Mn: 0.20% to less than 3.00%
P: 0.10% or
less, S: 0.10% or
less, Sol.Al:0.0002 %, more 3.0000% or
less, N: contains 0.01% or less,
　the balance being Fe and unavoidable impurities, having the following hardness above 500 Hv 800 Hv,
　the depth of 20μm below the surface of the softened layer metal structure to a thickness half the depth of the softening layer from being, in a cross section parallel to the thickness direction, a region surrounded by the grain boundaries having a misorientation of 15 ° or more when defining the crystal grain in a grain maximum crystal misorientation inside than 1 ° of the crystal grains, the maximum crystal grain inside the Hot stamping molded article total area ratio of the crystal orientation difference is 15 ° or less 8 ° or more crystal grains is equal to or less than 20% to 50%.
[Requested item 2]
　Si content is not more than 0.50% Mn content is 0.20% or more, and less than 1.50%, hot stamping molded article according to claim 1.
[Requested item 3]
　Si content is not more than 0.50% Mn content is 1.50% or more, and less than 3.00%, hot stamping molded article according to claim 1.
[Requested item 4]
　Si content of 0.50 percent, less than 3.00% Mn content is 0.20% or more and less than 1.50%, the plate thickness central portion, an area fraction, 1. 0% or more, characterized in that it comprises a residual austenite of less than 5.0%, hot stamping molded article according to claim 1.
[Requested item 5]
　Si content of 0.50 percent, less than 3.00% Mn content is 1.50% or more and less than 3.0%, the plate thickness central portion, an area fraction, 1. 0% or more, characterized in that it comprises a residual austenite of less than 5.0%, hot stamping molded article according to claim 1.
[Requested item 6]
　Mid-thickness portion further contains, by mass%, Ni: hot stamping molded article according to any one of claims 1 to 5, characterized in that it contains 0.01% or more 3.00% or less.
[Requested item 7]
　Mid-thickness portion further contains, by mass%, Nb: 0.010% or more 0.150% or less, Ti: 0.010% or more 0.150% or less, Mo: 0.005% or more 1.000% or less , B: 1 or of 0.0005% or more 0.0100% or less, or hot stamping molded article according to any one of claims 1 to 6, characterized by containing two or more.
[Requested item 8]
　Hot stamping molded article according to any one of claims 1 to 7, wherein the plating layer is formed on the softened layer.