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, good strength after hot stamping, crashworthiness properties, ductility, hydrogen embrittlement resistance, and hardness variations in related small hot stamping molding.
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]For example, hot stamping parts, such as a conventional hat member manufactured by press hardening, the bending during vehicle collision deformation, localized deformation by hat member buckles, reduced load capacity of the hat member to. That is, the maximum load of the member as a hot stamp component not only members strength also affected the likelihood of buckling. When the ductility of the steel sheet is high, the deformation area is hardly localized in a state formed into a predetermined shape as a member. That is, the member is less likely to buckle.
[0006]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. May be locally hardness lower region is formed in the order steel. 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.
[0007]Therefore it is important ductility in hot stamp component generally ductility of martensite is low. Also, penetration of hydrogen due to the high density of the surface layer of the lattice defects of the steel sheet is promoted, it is a problem that becomes poor hydrogen embrittlement resistance. For this reason, hot pressed parts manufactured by press hardening, application site in automotive parts has been limited.
[0008]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.
[0009]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
[0010]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
[0011]In view of the problems of the prior art, to provide a by both high bending resistance and high ductility and hydrogen embrittlement resistance to achieve the anti-collision properties and reduce the hardness variation hot stamping member for the purpose.
Means for Solving the Problems
[0012]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, in the case where the central portion of the sheet thickness of a hard tissue, reduce 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.
[0013]Therefore, we, the surface layer of the tissue control a soft tissue examined good bendability metal structure of the obtained steel sheets were intensive studies. As a result, the metal structure constituting the surface layer, in the 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 a 1 ° or less crystal grains, the maximum crystal orientation difference of the inside of the crystal grains was found to be to have been configured with the crystal grains of 8 ° ~ 15 °. These measurements were made in the region of 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). Such metal structure, 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.
[0014]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 excellent bendability, ductility, more strength stability particular success, it was possible to obtain excellent hot stamping body crashworthiness properties and hydrogen embrittlement resistance.
[0015]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,
　the softened layer metal structure from the depth of 20μm below the surface to a thickness of 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 when defining the crystal grains, and the grain up to the crystal orientation difference of inside than 1 ° of the crystal grains, the formation Hot stamping molded article Akiratsubu internal maximum crystal orientation differences 8 ° or more and 15 ° or less grain total area ratio of the is equal to or less than 85% than 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, hot stamping molded article according to and less than 3.00% (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) the thickness center portion, further, by mass%, Ni: characterized by containing 0.01% or more 3.00% or less (1) to according to any one of (5) hot stamping body.
(7) The plate thickness central 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 according to any one of - (6) body.
(8) the 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
[0016]
　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
[0017]
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
[0018]
(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.
[0019]
(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%.
[0020]
(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%.
[0021]
(Si: less than
　3.00%) Si is an element contributing to improving the strength in the solid solution strengthening. Si addition amount for obtaining the effect of improving the strength of the steel sheet by solid solution of Si to metal structure is preferably 0.30% or more, even with the addition of Si exceeding 0.5% the effect is saturated.
[0022]
　Si also has the effect of increasing the ductility to produce a residual austenite. To obtain the effect it is necessary to at least 0.50% super added. On the other hand, the effect even if added over 3.00% is to saturate, the addition amount of Si is an upper limit of less than 3.00%. Preferably less than 2.0%.
[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 3.0% 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: 0.010% 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 can be obtained with less than 0.010%, the addition of 0.010% 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%.
[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, 1.0% 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 0.0100% 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 JIS 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, if the area fraction of retained austenite is 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 can be measured by the following method. From member after hot stamping molding, the samples were harvested, scalped from the rolling surface normal direction to 1/2 depth of 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 the 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.
[0040]
(Metal structure of the softened layer)
　As a result of investigating the inventors have good bending properties resulting steel sheet metal structure, the metal structure that constitutes the softened layer is in a thickness cross section, having a misorientation of 15 ° or more when defining the region surrounded by the grain boundaries and crystal grains, wherein the grains up to the crystal orientation difference of inside than 1 ° of the crystal grains, the crystal grains maximum crystal misorientation interior of 8 ° ~ 15 ° it may be constituted by crystal grains were found. These measurements were made 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., that 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 It has been found. Such metal structure, the influence of the surface properties of the hot stamping material, it is possible to eliminate the influence of transition portion leading to the softened layer from a thickness center portion.
[0041]
　In the metal structure of the softened layer, and the crystal grain maximum crystal misorientation inside than 1 ° of the crystal grains, the crystal grains inside the maximum crystal orientation differences 8 ° ~ 15 ° of the crystal grains total area ratio of of is 50% or more, more preferably may is 55% or more. On the other hand, in the metal structure the total area ratio of the softening layer is 85% or more, the gradient of the softened layer and difference in hardness between the mid-thickness portion becomes too large, the bending plate thickness direction of the abrupt stiffness generated during deformation to reduce the effect can not be obtained, and less than 85%. More preferably, 80% 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 surface to be measured of the hot stamping material, subjected to the hardness test. Process for the preparation of the measurement surface may be carried out according to JIS 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 JIS 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 material to a thickness of the center portion (1/2 position in the plate thickness), the 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 sides, 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 decide.
[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 (crystal grains at the end of the measurement region is not included), and carrying out the analysis, the maximum crystal orientation difference of the inner area surrounded by 15 ° or more grain boundaries 1 ° and less 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%, 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%, the content of the preferred Si softening layer is less than 0.30%, more 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: 0.12% or more, 1.80 less than
　%%) Mn are the elements contributing to the improvement of strength in the solid solution strengthening, it may be added 0.12% or more in order to increase 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.
[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 less 0.70% is there. 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 than 1.80%, preferably not more than 1.40% it is.
[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. 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%.
[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%, it is preferable to add 0.01% or more. 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%.
[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%, it is preferable to add 0.010% or more. 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%, preferably 0.010% or more. 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%, preferably 0.005% or more. 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, 0.0100% 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 effect of addition is less than 0.0005% is not sufficiently obtained, it is preferable to add 0.0005% or more. More preferably 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]
(Hot sectional hardness distribution of the stamp formed body)
　in a cross section perpendicular to the surface of the hot stamping material, it is preferable hardness in the sheet thickness central distribution is variation without 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 taken, at the thickness center position of the entire cross-section area including the vertical wall, in 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 invention may take the form of a multi-layer steel sheet described below but it is not limited to.
[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 softened layer formed steel plate on the side (hereinafter, referred to as. "surface steel plate") laminated. Fixing method of the steel sheet for the surface layer steel plate and the plate thickness central portion is not particularly limited, may be performed by adhering with arc welding. Incidentally, the laminated C content, Si content, and any one or two or more surface steel plate is less than 0.6 times the corresponding element content of steel sheet mid-thickness portion of the Mn content it is preferable to.
[0068]
　Further, by controlling the speed casting in a continuous casting process of surface layer steel plates above ton / min, it is suppressed microscopic segregation of Mn in the surface layer steel sheet, a uniform concentration distribution of Mn in the surface layer for steel sheet be able to. 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, it may control the speed casting in a continuous casting process of surface layer steel plates than 6 ton / min.
[0069]
　Also, a multi-layer steel sheet produced by the above method, further 1100 ° C. or higher, it is preferable to hold less than 60 minutes over 20 minutes at 1350 ° C. or lower. Those retained, it is preferable to use as the steel sheet for hot stamping molded article according to the present invention. Results inventors studied, 1100 ° C. or higher, by performing a heat treatment for holding less than 1350 ° C. 60 minutes or more and 20 minutes or less, the metal structure of the region up to the softening layer center from a depth position of the surface under 20μm softening layer , when a region surrounded by the grain boundaries having a misorientation of 15 ° or more was defined as crystal grains, and grain maximum crystal misorientation inside than 1 ° of the crystal grains, the crystal grains inside the maximum crystal orientation differences 8 ° ~ 15 ° of the total area ratio of crystal grains of 50% or more, and less than 85%, good bending properties and hydrogen embrittlement resistance could be obtained.
[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 mid-thickness portion, the hot rolling after the heat treatment of the multilayer steel plate, includes a rough rolling and finish rolling, at the rough rolling is 1100 ° C. or more temperature 1 sheet thickness reduction rate is less than 5% to 50% of the per pass, 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. Meanwhile, the curve 2 is the change of the dislocation density when the sheet thickness reduction rate large, the amount of strain introduced by rolling is increased, the recovery is likely to be promoted, the dislocation density is rapidly lowered. 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 Is required.
[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]
　Further, for the purpose of adjustment of the intensity it 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]
　Table surface oxide surface by grinding the mid-thickness portion for steel No.1 ~ 18 having chemical compositions shown in A-1-1 ( "Steel No.1 ~ 18" in the table) It was removed. Then, by laminating a surface layer for steel sheet having the chemical compositions shown in Table A-1-2 to both surfaces or one side surface of each of the plate thickness center portion for steel plates in arc welding, laminated steel No.1 for hot stamping member We were prepared to 43. 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. 37 is a steel with a welded surface steel plate only on one side. TABLE A-1-1 ~ TABLE A-1-2 of the laminated steel No.1 ~ 43, the steel sheet thickness center part does not meet the composition requirement of the mid-thickness portion of the hot stamping molded body according to the present invention what it is shown as "comparative steel" remarks.
[0083]
　For each of the laminated steel sheets No.1 ~ 43, in Table A-2-1 ~ Table A-2-2 are shown production conditions No.1 ~ 43 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 ~ 43A were prepared, respectively. Incidentally, Nanba35A, the hot stamping of 36A, in hot-dip plating line, on its surface, the adhesion amount 120 ~ 160 g / m 2 was aluminum plating.
[0084]
　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.
[0085]
　Table A-3, showing the metal structure and characteristics of the hot stamping material No. 1A ~ 43A. 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 1-43 was comparable to the components of the surface layer steel plate.
[0086]
　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 to a crystal grain up to misorientation of the internal region surrounded is 1 ° or less 15 ° or more of the grain boundary, the total area ratio of crystal grains the crystal orientation differences is 8 ° ~ 15 ° It was 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 ".
[0087]
　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.
[0088]
　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 (×).
[0089]
　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.
[0090]
　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
[0091]
　Tensile strength is at least 1500 MPa, yet, the maximum bending angle (°) is not less 70 (°) 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.
[0092]
　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 85% to 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0093]
　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.
[0094]
　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 is lower heat treatment temperature before hot stamping process, hot stamp molding of No.31A a hot stamping for the heat treatment time of the previous step was short, thick from the surface of the softened layer of 1 / in the metal structure of the softened layer to 2, the growth of soft tissue and intermediate hardness of the metal structure becomes insufficient, bendability of the target is not obtained. Also, the hot stamping of No.32A because the heat treatment temperature before hot stamping process was excessively high, the effect of reducing the gradient of the sudden stiffness in the thickness direction generated during bending deformation could not be obtained.
[0095]
　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.
[0096]
　Production No. Hot stamping of 44 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 1 ° or less crystal grains and the crystal orientation differences increase the total area ratio of crystal grains is 8 ° ~ 15 ° (percent) It is excellent in bendability.
[0097]
[TABLE A-1-1]

[0098]
[TABLE A-1-2]

[0099]
[A-2-1 Table]

[0100]
[TABLE A-2-2]

[0101]
[Table A-3]

[0102]
[Production Example B]
　grinding the surface of the table B-1-1 are shown mid-thickness portion for steel No.1 ~ 18 having the chemical composition (in Table B-1-1 of the "steel No.1 ~ 18") to remove the surface oxide and. Then, by laminating a surface layer for steel sheet having the chemical compositions shown in Table B-1-2 on both or one side of the respective plate thickness central portion for steel plates in arc welding, laminated steel No.1 for hot stamping member We were prepared to 41. 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. 37 is a steel with a welded surface steel plate only on one side. No. The laminated steel plate other than 37, the surface layer steel plate on both sides of each of the plate thickness center portion for steel plates are welded. Of laminated steel No.1 ~ 41 in Table B-1-3, which steel sheet mid-thickness portion does not satisfy the composition requirements of the mid-thickness portion of the hot stamping molded body according to the present invention, the remarks " It has been shown as compared to steel. "
[0103]
　For each of the laminated steel sheets No.1 ~ 41, in Table B-2-1 ~ Table B-2-2 are shown production conditions No.1 ~ 41 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 ~ 41B were prepared, respectively. Incidentally, Nanba35B, the hot stamping of 36B, in hot-dip plating line, on its 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.
[0104]
　Table B-3-1 and Table B-3-2, showing a metal structure and characteristics of the hot stamping body No.1B ~ 41B. 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 B-1-1 ~ Table B-1- for mid-thickness portion of the laminated steel No.1 ~ 41 3 steel plate and was comparable to the components of the surface layer steel plate.
[0105]
　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 maximum misorientation of the internal region surrounded by 15 ° or more grain boundaries of 1 ° or less and the crystal grains, the crystal grains of the crystal orientation difference is 8 ° ~ 15 ° calculated total 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 (%) ".
[0106]
　Also, for each of the hot stamping body No.1B ~ 41B, the average hardness in the sheet thickness center (thickness 1/2 position) (HV) and the minimum hardness of (HV), it was measured by previously described the method . As the measurement results shown in Table B-3-1 ~ Table B-3-2. For each of the hot stamping body No.1B ~ 41B, the average hardness (HV) and minimum hardness the difference between (HV) Table B-3-1 ~ Table B-3-2 "hardness variation in the cross section" to show. Incidentally, the hardness variation in cross section is rejected more than a 100 HV.
[0107]
　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.
[0108]
　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 (×).
[0109]
　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.
[0110]
　Tensile strength is at least 1500 MPa, yet, the maximum bending angle (°) is not less 70 (°) 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.
[0111]
　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 ° ~ 15 ° a crystal grain (%) was less than 85% than 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0112]
　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 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.
[0113]
　Hot stamping of No.30B ~ 32B 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.30B is lower heat treatment temperature before hot stamping process, hot stamp molding of No.31B a hot stamping for the heat treatment time of the previous step was short, thick from the surface of the softened layer of 1 / in the metal structure of the softened layer to 2, the growth of soft tissue and intermediate hardness of the metal structure becomes insufficient, bendability of the target is not obtained. Also, the hot stamping of No.32B because the heat treatment temperature before hot stamping process was excessively high, the effect of reducing the gradient of the sudden stiffness in the thickness direction generated during bending deformation could not be obtained.
[0114]
　No. Hot stamping of 38B is rolling temperature of the rough rolling was low. In addition, No. Hot stamping of 39B is sheet thickness reduction rate of the rough rolling was low. In addition, No. Hot stamping of 40B, 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.
[0115]
　Hot stamping of No41B 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.
[0116]
[Table B-1-1]

[0117]
[Table B-1-2]

[0118]
[Table B-1-3]

[0119]
[Table B-2-1]

[0120]
[Table B-2-2]

[0121]
[Table B-3-1]

[0122]
[Table B-3-2]

[0123]
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. Then, by laminating a surface layer for steel sheet having the chemical compositions shown in Table C-1-3 ~ Table C-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 ~ 49 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. 31 is a steel with a welded surface steel plate only on one side. Of Table C-1-1 ~ Table C-1-4 of laminated steel No.1 ~ 53, for a steel sheet thickness center part does not meet the composition requirement of the mid-thickness portion of the hot stamping molded body according to the present invention what it is shown as "comparative steel" remarks.
[0124]
　Table C-1-3 ~ Table C-1-4 "C the surface layer steel plate to the steel sheet for mid-thickness portion, Si, the ratio of Mn content" laminated steel sheets No.1 ~ for hot stamping member relates 53 each show C of steel sheet mid-thickness portion, Si, the surface layer steel plate to Mn content C, Si, the ratio of Mn content.
[0125]
　For each of the laminated steel sheets No.1 ~ 53, in Table C-2-1 ~ Table C-2-2 are shown production conditions No.1 ~ 53 conditions, hot rolling before the heat treatment, rough rolling and heat during rolling, and the steel sheet is subjected to cold rolling. Then, with respect to the steel plate, (in the table, "heat treatment of a hot stamping molded article") heat treatment shown in Table C-2-1 ~ Table C-2-2 performs hot stamping by applying hot stamping member (item Table C-3-1 ~ Table C-3-2 "molded body") the No.1C ~ 53C were prepared, respectively. Note that the hot stamping of Nanba30C, in hot-dip plating line, on its 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.
[0126]
　Table C-3-1 ~ Table C-3-2, showing a metal structure and characteristics of the hot stamping body No.1C ~ 53C. 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 laminated steel No.1 ~ 53 4 sheet and was comparable to the components of the surface layer steel plate.
[0127]
　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 maximum misorientation of the internal region surrounded by 15 ° or more grain boundaries of 1 ° or less and the crystal grains, the crystal grains of the crystal orientation difference is 8 ° ~ 15 ° to calculate the total 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 (%) ".
[0128]
　A tensile test was carried out of the hot stamping body. The results are shown in Table C-3-1 ~ Table C-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.
[0129]
　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 (×).
[0130]
　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.
[0131]
　Tensile strength is at least 1500 MPa, yet, the maximum bending angle (°) is not less 70 (°) or more, a uniform elongation of 5% or more and yet, a case where hydrogen embrittlement resistance characteristics becomes accepted, crashworthiness characteristics and as excellent hydrogen embrittlement resistance and ductility, and the invention example. Of the above three performances, if not satisfied with any one sample of Comparative Example.
[0132]
　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 1/2 of the surface layer steel sheet, the maximum crystal orientation of the inner region surrounded by 15 ° or more grain boundaries and the difference is 1 ° or less of crystal grains, the total area ratio of the crystal orientation differences 8 ° ~ a 15 ° crystal grains was less than 85% to 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0133]
　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 has a low Si content in steel sheet mid-thickness portion, area fraction of retained austenite of the metal structure of the mid-thickness portion (gamma) is located less than 1.0% , uniform elongation was low.
[0134]
　No.25C ~ 27C, 49C of the hot stamping body is a comparative example prepared by using the laminated steel sheet for hot stamping molded preferred heat treatment before hot stamping process was not applied. Hot stamping of No.25C, since 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.
[0135]
　Also, the hot stamping of No.26C because the heat treatment time before the 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 manufacturing No.26C is bendability a target is not obtained.
[0136]
　Further, Nanba27C, hot stamping of 49C, to heat treatment time before the hot stamping process is too long, the hardness difference between the softened layer and mid-thickness portion is too large, since the heat treatment temperature was excessively high , the effect of reducing the gradient of the sudden stiffness in the thickness direction generated during bending deformation could not be obtained. Therefore, preparation Nanba27C, 49C hot stamping molded article, it was not possible to obtain a good bending property.
[0137]
　No. Hot stamping of 50C, the rolling temperature of the rough rolling was low. In addition, No. Hot stamping of 51C is sheet thickness reduction rate of the rough rolling was low. In addition, No. Hot stamping of 52C, 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.
[0138]
　No. Hot stamping of 53C 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.
[0139]
[Table C-1-1]

[0140]
[Table C-1-2]

[0141]
[Table C-1-3]

[0142]
[Table C-1-4]

[0143]
[Table C-2-1]

[0144]
[Table C-2-2]

[0145]
[Table C-3-1]

[0146]
[Table C-3-2]

[0147]
Production Example D]
　Table D-1-1, the surface of the plate thickness center portion for steel No.1 ~ 37 with the chemical compositions shown in Table D-1-2 ( "steels No.1 ~ 37" in the table) to remove surface oxides by grinding. Thereafter, both sides or one side in Table D-1-3 of the respective plate thickness central steel plate, and the surface layer steel sheet having the chemical compositions shown in Table D-1-4 was laminated 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. 37 is a steel with a welded surface steel plate only on one side. No. The laminated steel plate other than 37, 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 laminated steel No.1 ~ 60 in D-1-4, for a steel sheet thickness center part does not meet the composition requirement of the mid-thickness portion of the hot stamping molded body according to the present invention what it is shown as "comparative steel" remarks.
[0148]
　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 ~ Table D-3-3 of the item "molded body") No.1D ~ 60D were prepared, respectively. Incidentally, Nanba38D, the hot stamping of 39D, in hot-dip plating line, on its 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.
[0149]
　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 third laminated steel No.1 ~ 60 steel sheet and was comparable to the components of the surface layer steel plate.
[0150]
　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 maximum misorientation of the internal region surrounded by 15 ° or more grain boundaries of 1 ° or less and the crystal grains, the crystal grains of the crystal orientation difference is 8 ° ~ 15 ° to calculate the total 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 (%) ".
[0151]
　A tensile test was carried out of the hot stamping body No.1D ~ 60D. The results are shown in Table D-3-1 ~ Table 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.
[0152]
　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 (×).
[0153]
　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.
[0154]
　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.
[0155]
　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.
[0156]
　A tensile strength of not less than 1500 MPa, and a uniform elongation of 5% or more, and pass the hardness variation, the maximum bending angle (°) is not less 70.0 (°) or more, pass the hydrogen embrittlement resistance the case where, was evaluated as an excellent hot stamping body crashworthiness properties and hydrogen embrittlement resistance (invention examples in Table D-3-1 ~ Table D-3-3). On the other hand, among the five performance, if that does not satisfy one or a sample of Comparative Example.
[0157]
　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 85% to 50%. Moreover, both hot stamp molding of the present invention embodiment is excellent tensile strength, bending resistance and hydrogen embrittlement resistance.
[0158]
　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 and No.11D hot stamping body is uniform elongation because Si content in steel sheet mid-thickness portion poor was insufficient. Also, the hot stamping of No.12D 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. Incidentally, hot stamping molding of No.12D ~ No.15D are all hardness variation is large, have failed.
[0159]
　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 because the heat treatment temperature before hot stamping process is 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 of the metal tissue growth becomes insufficient, bendability of the target is not obtained. Hot stamping of No.34D because the heat treatment temperature before hot stamping process was excessively high, the fractions of the structures to a depth position in the thickness 1/2 of the softened layer from the position from the surface of 20μm softening layer It has been developed to more than 85 percent. Therefore, in the hot stamping of Nanba34D, softened layer and hardness difference between the mid-thickness portion becomes too large, the effect of reducing the gradient of the sudden stiffness in the thickness direction that occurs when bending deformation is obtained There was no. Also, the hot stamping of No.35D because the heat treatment time before the hot stamping process is short, the metal structure of the softened layer to a thickness of 1/2 from the surface of the softened layer, soft tissues and hardness of the intermediate the growth of the metal structure becomes insufficient, bendability of the target is not obtained.
[0160]
　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, the tensile strength becomes maximum in the hot stamping body No.1D ~ 56D, bending property is deteriorated. Hot stamping of No.42D the inclusion containing oxygen is excessively generated for poor content of aluminum of acid-soluble, bendability is deteriorated. Also, hot stamping molding of No.45D is to include an excess of aluminum, aluminum metallic oxide is excessively formed that the bending property is deteriorated.
[0161]
　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.
[0162]
　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.
[0163]
[Table D-1-1]

[0164]
[Table D-1-2]

[0165]
[Table D-1-3]

[0166]
[Table D-1-4]

[0167]
[Table D-2-1]

[0168]
[Table D-2-2]

[0169]
[Table D-2-3]

[0170]
[Table D-3-1]

[0171]
[Table D-3-2]

[0172]
[Table D-3-3]

Industrial Applicability
[0173]
　Hot stamping molding of the present invention, the strength, ductility, bendability, excellent crashworthiness properties and hydrogen embrittlement resistance, and because a small hardness variation, 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: it 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 and the maximum crystal misorientation inside than 1 ° of the crystal grains, the crystal grains 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 85% than 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 3.00%, 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]
　The thickness central portion further contains, by mass%, Ni: as claimed in any one of claims 1 to 5, characterized in that it contains 0.01% or more 3.00% or less hot stamping body.
[Requested item 7]
　The thickness central 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% hereinafter, B: hot stamping molded article according to any one of claims 1 to 6, characterized in that it contains one or more kinds of not less than 0.0005% 0.0100% or less.
[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.