The name of the invention: hot press steel plate member, its production method and hot press for steel plate
Technical field
[0001]
　The present invention, hot press steel sheet member used for the machine structural parts and the like, a production method thereof and a hot-press steel sheet.
Background technique
[0002]
　For weight reduction of the automobile, achieving high strength of the steel material to be used on the vehicle body, efforts to reduce the use weight of the steel has been promoted. In the steel sheets are widely used in motor vehicles, in general, with an increase in strength, decrease the press formability, it becomes difficult to produce a complex shaped parts. For example, lowering processing a high degree of site or rupture with the ductility, dimensional accuracy is deteriorated by spring back increases. Therefore, high-strength steel sheet, in particular, it is difficult to manufacture the parts by pressing a steel sheet having the above tensile strength 980 MPa. Rather than press forming, according to the roll forming, easily but processed steel sheet of a high strength, its application target is limited to parts having a uniform cross section in the longitudinal direction.
[0003]
　Method called hot pressing for the purpose of obtaining a high moldability in high-strength steel sheet is disclosed in Patent Documents 1 and 2. According to the hot pressing, it can be a high-strength steel sheet was molded with high accuracy to obtain a hot press-parts of high strength.
[0004]
　On the other hand, the hot press-parts are becoming also required improvement in collision characteristics when used in an automobile. Collision characteristics can be improved to some extent by improving the ductility. However, the steel structure of the steel sheet obtained by the method described in Patent Documents 1 and 2 are substantially martensite single phase, it is difficult to improve the ductility.
[0005]
　Although hot press-parts of high strength for the purpose of improving the ductility in Patent Documents 3 to 5 are described, it is difficult to obtain sufficient collision characteristics with these conventional hot press-parts is there. The technology relating to hot pressing in Patent Documents 6-8 have been described, it is difficult to obtain sufficient collision characteristics thereby.
CITATION
Patent literature
[0006]
Patent Document 1: United Kingdom Patent Publication No. 1490535
Patent Document 2: Laid-Open Publication No. 10-96031
Patent Document 3: Unexamined Publication No. 2010-65292
Patent Document 4: Unexamined Publication No. 2007-16296
Patent Document 5: JP 2005- Publication No. 329,449
Patent Document 6: JP Publication No. 2006-104546
Patent Document 7: JP Publication No. 2006-265568
Patent Document 8: JP Publication No. 2007-154258
Summary of the invention
Problems that the Invention is to Solve
[0007]
　The present invention, while having high strength, hot press-parts that can be obtained excellent collision characteristics, and to provide its production method and hot press steel sheet.
Means for Solving the Problems
[0008]
　The inventors have studied hard reason is possible to obtain excellent impact performance by conventional high-strength hot press-parts for the purpose of improving ductility. As a result, the improvement of crash performance, it became clear improvement only Not bending improvement of ductility is also important. Of the bending is a concern, hot and cause extreme plastic deformation to press the steel plate member, is because the surface portion of the hot press steel plate member is to be subject to severe bending deformation in the event of a collision. Bending of importance, tensile strength was also revealed to be manifested in the case of more than 980MPa.
[0009]
　The present inventors, as a result of extensive study based on this finding, comprises a predetermined amount of C and Mn, further comprising a chemical composition comprising Si relatively larger amount, with a predetermined steel structure heat between press steel plates, by treatment with decarburization processing of appropriate conditions, a double-phase structure steel structure comprises ferrite and martensite, the area ratio of the ferrite in the surface portion than in the inner layer portion hot press steel plate member which is elevated it was found that the resulting. The present inventor has further the hot press steel sheet member has a high tensile strength of over 980 MPa, it was also found to have also an excellent ductility and bendability. Then, the present inventor has conceived to aspects of the invention described below.
[0010]
　（１）
　質量％で、
　Ｃ　：０．１０％～０．３４％、
　Ｓｉ：０．５％～２．０％、
　Ｍｎ：１．０％～３．０％、
　ｓｏｌ．Ａｌ：０．００１％～１．０％、
　Ｐ　：０．０５％以下、
　Ｓ　：０．０１％以下、
　Ｎ　：０．０１％以下、
　Ｔｉ：０％～０．２０％、
　Ｎｂ：０％～０．２０％、
　Ｖ　：０％～０．２０％、
　Ｃｒ：０％～１．０％、
　Ｍｏ：０％～１．０％、
　Ｃｕ：０％～１．０％、
　Ｎｉ：０％～１．０％、
　Ｃａ：０％～０．０１％、
　Ｍｇ：０％～０．０１％、
　ＲＥＭ：０％～０．０１％、
　Ｚｒ：０％～０．０１％、
　Ｂ　：０％～０．０１％、
　Ｂｉ：０％～０．０１％、
　残部：Ｆｅ及び不純物
で表される化学組成を有し、
　表面から深さ１５μｍまでの表層部におけるフェライトの面積率が、前記表層部を除いた部位である内層部におけるフェライトの面積率の１．２０倍超であり、前記内層部が、面積％で、フェライト：１０％～７０％、マルテンサイト：３０％～９０％、フェライト及びマルテンサイトの合計面積率：９０％～１００％である鋼組織を有し、
　引張強度が９８０ＭＰａ以上であることを特徴とする熱間プレス鋼板部材。
[0011]
　(2)
　the chemical composition, by
　mass%,
　Ti: 0.003% ~
　0.20%, Nb: 0.003% ~ 0.20%, V: 0.003% ~
　0.20%, Cr:
　Pasento ～ 1.0 0.005 Pasento,
　Mo: 0.005 Pasento ～ 1.0 Pasento, Cu: 0.005 Pasento ～ 1.0 Pasento, and
　Ni: 0.005% ~ 1.0%
from the group consisting of hot press-parts according to (1) that contain one or more selected.
[0012]
　(3)
　the chemical composition, in
　mass%,
　Ca: 0.0003% ~
　0.01%, Mg: 0.0003% ~ 0.01%, REM: 0.0003% ~ 0.01%, and
　Zr : 0.0003% - 0.01%
hot press-parts according to one or more selected from the group consisting of characterized by containing (1) or (2).
[0013]
　(4)
　the chemical composition, by mass%, B: 0.0003% ~ characterized by containing 0.01% (1) hot pressing the steel plate member according to any one of (3).
[0014]
　(5)
　the chemical composition, in mass%, Bi: 0.0003% ~ characterized by containing 0.01% (1) hot pressing the steel plate member according to any one of (4).
[0015]
　（６）
　質量％で、
　Ｃ　：０．１１％～０．３５％、
　Ｓｉ：０．５％～２．０％、
　Ｍｎ：１．０％～３．０％、
　ｓｏｌ．Ａｌ：０．００１％～１．０％、
　Ｐ　：０．０５％以下、
　Ｓ　：０．０１％以下、
　Ｎ　：０．０１％以下、
　Ｔｉ：０％～０．２０％、
　Ｎｂ：０％～０．２０％、
　Ｖ　：０％～０．２０％、
　Ｃｒ：０％～１．０％、
　Ｍｏ：０％～１．０％、
　Ｃｕ：０％～１．０％、
　Ｎｉ：０％～１．０％、
　Ｃａ：０％～０．０１％、
　Ｍｇ：０％～０．０１％、
　ＲＥＭ：０％～０．０１％、
　Ｚｒ：０％～０．０１％、
　Ｂ　：０％～０．０１％、
　Ｂｉ：０％～０．０１％、
　残部：Ｆｅ及び不純物
で表される化学組成を有し、
　厚さが３０μｍ以下の内部酸化層を有し、
　表面から深さ１００μｍまでの領域におけるフェライトの面積率が３０％～９０％、表面から深さ１００μｍまでの領域を除く領域における平均粒径が５μｍ以上のパーライトの面積率が１０％～７０％の鋼組織を有することを特徴とする熱間プレス用鋼板。
[0016]
　(7)
　the chemical composition, by
　mass%,
　Ti: 0.003% ~
　0.20%, Nb: 0.003% ~ 0.20%, V: 0.003% ~
　0.20%, Cr:
　Pasento ～ 1.0 0.005 Pasento,
　Mo: 0.005 Pasento ～ 1.0 Pasento, Cu: 0.005 Pasento ～ 1.0 Pasento, and
　Ni: 0.005% ~ 1.0%
from the group consisting of hot press steel sheet according to, characterized by containing one or more selected (6).
[0017]
　(8)
　the chemical composition, in
　mass%,
　Ca: 0.0003% ~
　0.01%, Mg: 0.0003% ~ 0.01%, REM: 0.0003% ~ 0.01%, and
　Zr : 0.0003% - 0.01%
for hot pressing steel sheet according to one or more selected from the group consisting of characterized by containing (6) or (7).
[0018]
　(9)
　the chemical composition, in mass%, Bs: hot-press steel sheet according to any one of the characterized by containing 0.0003% 0.01% (6) to (8).
[0019]
　(10)
　the chemical composition, in mass%, Bi: hot-press steel sheet according to any one 0.0003%, characterized by containing 0.01% (6) to (9).
[0020]
　(11) (6)
　to the hot-press steel sheet according to any one of (10), Ac 720 ° C. or higher 3 and heating to a temperature range of less points,
　after the heating, the hot-press steel sheet the steps of the C content make the decarburization processing to reduce 0.0005% to 0.015% by weight at the surface of,
　said after the decarburization processing, it performs a hot press, of 10 ℃ / sec ~ 500 ℃ / sec. a step of cooling to the Ms point at an average cooling rate
　method for producing a hot press steel sheet member characterized by having a.
[0021]
　(12)
　the step of performing decarburization treatment method for manufacturing a hot press-parts according to, characterized by comprising a step of performing air cooling of 5 seconds to 50 seconds (11).
Effect of the invention
[0022]
　According to the present invention, it is possible to obtain excellent crashworthiness while obtaining high tensile strength. In particular, when the hot press-parts according to the present invention is used in the body structural part of the motor vehicle, even collisions extreme plastic deformation occurs is caused to absorb the impact with the bending deformation of the surface layer portion be able to.
DESCRIPTION OF THE INVENTION
[0023]
　Hereinafter, embodiments of the present invention will be described. Embodiments of the present invention, tensile strength about hot press-parts above 980 MPa.
[0024]
　First, hot press steel sheet member according to an embodiment of the present invention (hereinafter sometimes referred to as "steel plate member") and the chemical composition of the hot-press steel sheet used in its manufacture is described. In the following description, a unit of content of each element contained in the steel plate member or the hot press steel sheet "%" it is especially meant to "mass%" unless otherwise specified.
[0025]
　The chemical composition of the steel plate member according to the present embodiment includes, by mass%, C: 0.10% ~ 0.34%, Si: 0.5% ~ 2.0%, Mn: 1.0% ~ 3.0 %, sol. Al: 0.001% ~ 1.0%, P: 0.05% or less, S: 0.01% or less, N: 0.01% or less, Ti: 0% ~ 0.20%, Nb: 0% ~ 0.20%, V: 0% ~ 0.20%, Cr: 0% ~ 1.0%, Mo: 0% ~ 1.0%, Cu: 0% ~ 1.0%, Ni: 0% ~ 1.0%, Ca: 0% ~ 0.01%, Mg: 0% ~ 0.01%, REM: 0% ~ 0.01%, Zr: 0% ~ 0.01%, B: 0% ~ 0.01%, Bi: 0% ~ 0.01%, the balance being represented by Fe and impurities. The chemical composition of the hot-press steel sheet used in the manufacture of the steel plate member according to the present embodiment includes, by mass%, C: 0.11% ~ 0.35%, Si: 0.5% ~ 2.0%, Mn: 1.0% ~ 3.0%, sol. Al: 0.001% ~ 1.0%, P: 0.05% or less, S: 0.01% or less, N: 0.01% or less, Ti: 0% ~ 0.20%, Nb: 0% ~ 0.20%, V: 0% ~ 0.20%, Cr: 0% ~ 1.0%, Mo: 0% ~ 1.0%, Cu: 0% ~ 1.0%, Ni: 0% ~ 1.0%, Ca: 0% ~ 0.01%, Mg: 0% ~ 0.01%, REM: 0% ~ 0.01%, Zr: 0% ~ 0.01%, B: 0% ~ 0.01%, Bi: 0% ~ 0.01%, the balance being represented by Fe and impurities. As an impurity, those included in raw materials such as ores and scrap, intended to be included in the manufacturing process, is exemplified.
[0026]
　(Of hot press for steel plate member C: 0.10% ~ 0.34%, of the hot press for steel plate C: 0.11 Pasento ～ 0.35 Pasento)
　C is, the hardening of the hot press for steel plate enhanced, and is a very important element that primarily determine the strength of the steel plate member. The C content of the steel plate member is less than 0.10%, it is difficult to secure a tensile strength of at least 980 MPa. Therefore, C content in the steel plate member is set to 0.10% or more. The C content 0.34% of the steel member, decrease in bendability and weldability is significant. Therefore, C content of the steel plate member is equal to or less than 0.34%. From the viewpoint of productivity in hot rolling and cold rolling to obtain a hot-press steel sheet, C content of the hot-press steel sheet is preferably 0.30% or less, more preferably 0.25% less. As described later, since the decarburization of the hot-press steel sheet in the production of hot press-parts is carried out, the hot-press steel sheet thereof more by C is contained, the C content is 0.11% or more of 0.35% or less.
[0027]
　(Si: 0.5 Pasento ～ 2.0
　Pasento) Si is a very some effective elements to ensure that the stability of the strength of the improvement and the steel plate member of the ductility of the steel plate member. The Si content is less than 0.5%, it is difficult to obtain the above effect. Therefore, Si content is 0.5% or more. The Si content of 2.0 percent, the effect of the above action in terms of the economic disadvantage saturated, decrease in plating wettability is remarkably non-coating often occurs. Therefore, Si content is 2.0% or less. From the viewpoint of improving the weldability, Si content is preferably 0.7% or more. From the viewpoint of suppressing the surface defects of the steel plate member, Si content is preferably not more than 1.8%.
[0028]
　(Mn: 1.0 Pasento ～ 3.0 Pasento) Mn
　is a very a effective element to ensure the strength of the hardening of the improvement and the steel plate member of the hot press for steel plate. The Mn content is less than 1.0%, it is very difficult to secure a tensile strength of at least 980MPa to the steel plate member. Therefore, Mn content is 1.0% or more. To obtain the effects more reliably, Mn content is preferably 1.1% or more. The Mn content of 3.0 percent, the steel structure of the steel plate member becomes prominent band shape, the bending of the deterioration becomes remarkable. Therefore, Mn content is less than 3.0%. From the viewpoint of productivity in hot rolling and cold rolling to obtain a hot-press steel sheet, Mn content is preferably 2.5% or less.
[0029]
　(Sol.Al (acid-soluble Al): 0.001 Pasento ～ 1.0
　Pasento) Al is an element that has the effect of consolidation of the steel was deoxidized steel. sol. Al content is less than 0.001%, it is difficult to obtain the above effect. Therefore, sol. Al content is 0.001% or more. In order to obtain the above action more reliably, sol. Al content is preferably 0.015% or more. sol. The Al content of 1.0 percent, with decreasing weldability becomes significant, oxide inclusion is increased, the deterioration of the surface property becomes remarkable. Therefore, sol. Al content is 1.0% or less. To obtain a better surface properties, sol. Al content is preferably less 0.080%.
[0030]
　(P: 0.05% or less)
　P is not an essential element, is contained as an impurity for example in steel. From the point of view of weldability, P content is better as low as possible. Particularly P content is 0.05 percent, a significant decrease in weldability. Therefore, P content is less than 0.05%. In order to ensure a better weldability, P content is preferably not more than 0.018%. Meanwhile, P is, it has the effect of increasing the strength of steel by solid solution strengthening. To obtain this effect, 0.003% or more P may be contained.
[0031]
　(S: 0.01% or less)
　S is not an essential element, is contained as an impurity for example in steel. From the point of view of weldability, S content is preferably as low as possible. In particular the S content is 0.01 percent, a significant decrease in weldability. Therefore, S content is 0.01% or less. In order to ensure a better weldability, S content is at preferably 0.003% or less, more preferably 0.0015% or less.
[0032]
　(N: 0.01% or less)
　N is not an essential element, is contained as an impurity, for example, in the steel. From the point of view of weldability, N content, the better the lower the. Particularly N content is 0.01 percent, a significant decrease in weldability. Therefore, N content is 0.01% or less. In order to ensure a better weldability, N content is preferably 0.006% or less.
[0033]
　Ｔｉ、Ｎｂ、Ｖ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉ、Ｃａ、Ｍｇ、ＲＥＭ、Ｚｒ、Ｂ、及びＢｉは、必須元素ではなく、鋼板部材及び熱間プレス用鋼板に所定量を限度に適宜含有されていてもよい任意元素である。
[0034]
　（Ｔｉ：０％～０．２０％、Ｎｂ：０％～０．２０％、Ｖ：０％～０．２０％、Ｃｒ：０％～１．０％、Ｍｏ：０％～１．０％、Ｃｕ：０％～１．０％、Ｎｉ：０％～１．０％）
　Ｔｉ、Ｎｂ、Ｖ、Ｃｒ、Ｍｏ、Ｃｕ、及びＮｉは、いずれも鋼板部材の強度の安定した確保に効果のある元素である。従って、これらの元素からなる群から選択された１種又は２種以上が含有されていてもよい。しかし、Ｔｉ、Ｎｂ及びＶについては、いずれかの含有量が０．２０％超であると、熱間プレス用鋼板を得るための熱間圧延及び冷間圧延が困難になるだけでなく、逆に、強度を安定して確保することが困難になる。従って、Ｔｉ含有量、Ｎｂ含有量、及びＶ含有量は、いずれも０．２０％以下とする。Ｃｒ及びＭｏについては、いずれかの含有量が１．０％超であると、熱間プレス用鋼板を得るための熱間圧延及び冷間圧延が困難になる。従って、Ｃｒ含有量及びＭｏ含有量は、いずれも１．０％以下とする。Ｃｕ及びＮｉについては、いずれかの含有量が１．０％であると、上記作用による効果は飽和して経済的に不利となるうえに、熱間プレス用鋼板を得るための熱間圧延及び冷間圧延が困難になる。従って、Ｃｕ含有量及びＮｉ含有量は、いずれも１．０％以下とする。鋼板部材の強度の安定した確保のために、Ｔｉ含有量、Ｎｂ含有量、及びＶ含有量は、いずれも好ましくは０．００３％以上であり、Ｃｒ含有量、Ｍｏ含有量、Ｃｕ含有量、及びＮｉ含有量は、いずれも好ましくは０．００５％以上である。つまり、「Ｔｉ：０．００３％～０．２０％」、「Ｎｂ：０．００３％～０．２０％」、「Ｖ：０．００３％～０．２０％」、「Ｃｒ：０．００５％～１．０％」、「Ｍｏ：０．００５％～１．０％」、「Ｃｕ：０．００５％～１．０％」、及び「Ｎｉ：０．００５％～１．０％」のうちの少なくとも一つが満たされることが好ましい。
[0035]
　（Ｃａ：０％～０．０１％、Ｍｇ：０％～０．０１％、ＲＥＭ：０％～０．０１％、Ｚｒ：０％～０．０１％）
　Ｃａ、Ｍｇ、ＲＥＭ、及びＺｒは、いずれも介在物の制御、特に、介在物の微細分散化に寄与し、低温靭性を高める作用を有する元素である。従って、これらの元素からなる群から選択された１種又は２種以上が含有されていてもよい。しかし、いずれかの含有量が０．０１％超であると、表面性状の劣化が顕在化する場合がある。従って、Ｃａ含有量、Ｍｇ含有量、ＲＥＭ含有量、及びＺｒ含有量は、いずれも０．０１％以下とする。低温靭性の向上のために、Ｃａ含有量、Ｍｇ含有量、ＲＥＭ含有量、及びＺｒ含有量は、いずれも好ましくは０．０００３％以上である。つまり、「Ｃａ：０．０００３％～０．０１％」、「Ｍｇ：０．０００３％～０．０１％」、「ＲＥＭ：０．０００３％～０．０１％」、及び「Ｚｒ：０．０００３％～０．０１％」のうちの少なくとも一つが満たされることが好ましい。
[0036]
　REM (rare earth metals) refers Sc, Y, and total 17 kinds of elements of the lanthanide, "REM content" means the total content of these 17 kinds of elements. Lanthanoids, Industrially, are added for example in the form of misch metal.
[0037]
　(Bs: 0% ~ 0.01%)
　Bs is an element having an effect of enhancing the low temperature toughness of the steel plate. Thus, B may be contained. However, when the B content is 0.01 percent, hot workability is deteriorated, hot rolled to obtain a hot-press steel sheet becomes difficult. Therefore, B content is less than 0.01%. In order to improve the low temperature toughness, B content is preferably 0.0003% or more. That, B content is preferably 0.0003% 0.01%.
[0038]
　(Bi: 0% ~
　0.01%) Bi is an element having an effect of a uniform steel structure, improve the low temperature toughness of the steel plate. Accordingly, Bi may be contained. However, when the Bi content is 0.01 percent, hot workability is deteriorated, hot rolled to obtain a hot-press steel sheet becomes difficult. Therefore, Bi content is less than 0.01%. In order to improve the low-temperature toughness, Bi content is preferably 0.0003% or more. That, Bi content is preferably 0.0003% 0.01%.
[0039]
　Next, a description will be given of the steel structure of the steel plate member according to an embodiment of the present invention. The steel sheet member, the area ratio of the ferrite in the surface layer to a depth of 15μm from the surface, is 1.20 times greater than the area ratio of the ferrite in the inner layer portion is a portion excluding the surface layer portion, the inner layer portion, the area %, the ferrite: 10% to 70%, martensite: 30% to 90%, the total area ratio of ferrite and martensite: has a steel structure is 90% to 100%. The surface layer portion of the steel plate member, means a surface portion to a depth of 15μm from the surface, and the inner layer portion means a portion excluding the surface layer portion. That is, the inner layer portion is a portion other than the surface layer portion of the steel plate member. Figures for the steel structure of the inner layer portion is, for example, a thickness direction Overall Average value of the inner layer portion, a point depth from the surface of the steel plate member is 1/4 of the thickness of the steel plate member (hereinafter, this point it is possible to represent in the figures for steel structure in is referred to as "1/4 depth position"). For example, the thickness of the steel plate member if 2.0 mm, it is possible to depth from the surface is represented by a numerical value at the point of 0.50 mm. This steel structure with 1/4 depth positions and show average steel structure in the thickness direction of the steel plate member. Therefore, in the present invention, the area ratio of the measured area ratio of ferrite and martensite in the 1/4 depth position, the area ratio of the area ratio and martensite of ferrite in each of the inner layer portion.
[0040]
　: (Area ratio of ferrite in the surface layer 1.20 times greater than the area ratio of the ferrite in the inner layer portion)
　by increasing the area ratio of the ferrite in the surface layer than the area ratio of ferrite in the inner layer portion, wealth surface layer portion in ductility becomes useless, even when having a high tensile strength of over 980 MPa, it is possible to obtain excellent ductility and bendability. In the following 1.20 times the area ratio of ferrite in the area ratio of the ferrite in the surface layer is the inner layer portion, fine cracks are likely to occur in the surface layer portion, it is impossible to obtain sufficient bending resistance. Therefore, the area ratio of the ferrite in the surface layer is 1.20 times greater than the area ratio of the ferrite in the inner layer portion.
[0041]
　(Area ratio of the ferrite in the inner layer section 10% to 70%)
　by the presence of an appropriate amount of ferrite in the inner layer portion, it is possible to obtain good ductility. The area ratio of ferrite is less than 10% in the inner layer portion, most of ferrite isolated, it is impossible to obtain good ductility. Therefore, the area ratio of ferrite in the inner layer portion is 10% or more. In more than 70% area ratio of the ferrite in the inner layer portion, it becomes impossible to secure a sufficient martensite is strengthening phase, it is difficult to secure a tensile strength of at least 980 MPa. Therefore, the area ratio of ferrite in the inner layer portion is 70% or less.
[0042]
　(Area ratio of martensite in the inner layer portion of 30% to 90%)
　by the presence of an appropriate amount of martensite in the inner layer portion, it is possible to obtain high strength. The area ratio of martensite is less than 30% in the inner layer portion, it is difficult to secure a tensile strength of at least 980 MPa. Therefore, the area ratio of the martensite in the inner layer portion is 30% or more. The area ratio of 90% martensite in the inner layer portion, the area ratio of ferrite is less than 10%, as described above, it is impossible to obtain good ductility. Therefore, the area ratio of the martensite in the inner layer portion is 90% or less.
[0043]
　(Total area ratio of the ferrite and martensite in the inner layer portion of 90% to 100%)
　the inner portion of the hot press-parts according to this embodiment, be comprised of ferrite and martensite, that is, the total of ferrite and martensite it is preferable that the area ratio is 100%. However, depending on the manufacturing conditions, as the phase or tissue other than ferrite and martensite, bainite, residual austenite, cementite, and also contain one or two or more selected from the group consisting of perlite. In this case, when the area ratio of the phase or tissues other than ferrite and martensite is 10 percent, due to the influence of these phases or tissue, may not be obtained characteristics of interest. Therefore, the area ratio of the phase or organization other than the ferrite and martensite in the inner layer portion is 10% or less. In other words, the total area ratio of ferrite and martensite in the inner layer portion is 90% or more.
[0044]
　As a measuring method for each phase area ratio in the above steel structure, it can be employed methods well known to those skilled in the art. These area ratio, for example, is determined as an average value of measured values ​​in a cross section perpendicular to the measured in a cross section perpendicular to the rolling direction value and the sheet width direction (direction perpendicular to the rolling direction). Thus, for example, it is determined as an average value of the measured area ratio in two cross-section.
[0045]
　Such steel sheet member can be prepared by treating the pressed steel plate between predetermined heat under predetermined conditions.
[0046]
　It will now be described steel structure or the like of the hot-press steel sheet used for the production of the steel plate member according to the present embodiment. The hot-press steel sheet has an internal oxide layer is less 30μm thick, 30% to 90% area ratio of the ferrite in the region to a depth of 100μm from the surface, the area to a depth of 100μm from the surface the average particle diameter in the region excluding the area ratio of 5μm or more pearlite has a 10% to 70% of the steel structure.
[0047]
　(The thickness of the internal oxide layer: 30μm or less)
　bending property is lowered in the steel plate member about internal oxide layer is thick, the thickness of the internal oxide layer is a decrease in the bending resistance at 30μm than is remarkable. Therefore, the thickness of the internal oxide layer and 30μm or less. For example, the internal oxide layer can be observed with an electron microscope, the thickness of the inner oxide layer can be measured by electron microscope.
[0048]
　(Area ratio of the ferrite in the region to a depth of 100μm from the surface: 30% to 90%)
　ferrite in the region to a depth of 100μm from the surface contributes to securing of the ferrite in the surface layer of the steel plate member. The area ratio of the ferrite in the region of less than 30%, it is difficult to 1.20 times greater than the area ratio of the inner layer portion the area ratio of the ferrite in the surface layer of the steel plate member. Therefore, the area ratio of the ferrite in the region to a depth of 100μm from the surface is 30% or more. The area ratio of the ferrite in the region of 90 percent, it is difficult to the area ratio of the ferrite in the inner layer portion of the steel plate member 70% or less. Therefore, the area ratio of the ferrite in the region to a depth of 100μm from the surface is 90% or less.
[0049]
　(Average particle size area ratio of 5μm or more pearlite in the region except for the region to a depth of 100μm from the surface: 10% to 70%)
　average particle size in the region except the region to a depth of 100μm from the surface is not less than 5μm perlite contributes to the generation of martensite in the inner layer portion of the steel plate member. The average particle size of area ratio of 5μm or more pearlite in this region is less than 10%, it is difficult to the area ratio of martensite in the inner layer portion of the steel plate member at least 30%. Therefore, the area ratio of pearlite is 10% or more. The average particle size of area ratio of 5μm or more pearlite in this region than 70%, it is difficult to the area ratio of martensite in the inner layer portion of the steel plate member 90% or less. Therefore, the area ratio of the pearlite is 70% or less. The area ratio of pearlite is sensitive to the C content of the hot-press steel sheet, if the area ratio of pearlite is 70 percent, the C content of the hot-press steel sheet used in the manufacture 0 often it has a .35 percent. Therefore, in order to average particle size in the region except the region to a depth of 100μm from the surface to the area ratio of 5μm or more pearlite and 70% or less, for example C content for press between 0.35% or less of the heat it is effective to use a steel sheet. Here, the average particle diameter of the perlite means the average value of the diameter of the rolling direction diameter and the plate width direction of the pearlite grains (the direction perpendicular to the rolling direction).
[0050]
　The hot-press steel sheet, for example, can be used hot rolled steel sheet, cold rolled steel, hot-dip galvanizing cold-rolled steel or the like. For example, hot-rolled steel sheet having the above-mentioned steel organization, to complete the finish rolling at 850 ℃ or more, after holding for 10 seconds or more in the range of 650 ℃ from 720 ℃, hot wound in a temperature range of more than 600 ℃ rolling it can be produced by. For example, cold-rolled steel and hot-dip galvanized cold-rolled steel sheet having the above-mentioned steel structure, after cold rolling, in nitrogen and in an atmosphere of mixed gas of hydrogen to the dew point -10 ℃ or higher, 850 ℃ of below 720 ℃ or more it can be manufactured through the annealing heating to a temperature range.
[0051]
　Next, a manufacturing method of the steel plate member according to the present embodiment, that is, how to handle hot-press steel sheet will be described. In the process of hot press steel sheet, the hot-press steel sheet Ac 720 ° C. or higher 3 heated to a temperature range of less points, after this heating, the C content in the surface of the hot-press steel sheet 0. which resulted in the removal of coal processing to reduce 0005 mass% to 0.015% by weight, after this decarburization processing, performs a hot press, cooled to Ms point at an average cooling rate of 10 ℃ / sec ~ 500 ℃ / sec.
[0052]
　(Heating temperature of the hot press for steel plate 720 ℃ or more Ac 3 temperature range following points of)
　steel plate to be subjected to the hot press, that the heating of the hot press for steel sheet, 720 ℃ or more Ac 3 is carried out in the temperature range of the following points . Ac 3 points, the temperature at which the austenite single phase defined by the following empirical formula (i) (Unit: ° C.) is.
[0053]
　Ac3=910-203×(C0.5)-15.2×Ni+44.7×Si+104×V+31.5×Mo-30×Mn
　　　-11×Cr-20×Cu+700×P+400×Al+50×Ti　　・・・　　（ｉ）
　ここで、上記式中における元素記号は、鋼板の化学組成における各元素の含有量（単位：質量％）を示す。
[0054]
　The heating temperature is lower than 720 ° C., the generation of the austenite due to the solid solution of cementite difficult or insufficient, it is difficult to tensile strength of the steel plate member 980MPa or more. Therefore, the heating temperature is set to 720 ℃ or more. Heating temperature Ac 3 When it is point greater than the steel structure of the steel plate member is a martensitic single phase deterioration of ductility becomes significant. Therefore, the heating temperature is Ac 3 or less points.
[0055]
　720 ° C. or higher Ac 3 The heating rate and heating time to be held in the temperature range up following temperature range point is not particularly limited, it is preferably in the range of less, respectively.
[0056]
　720 ° C. or higher Ac 3 average heating rate in the heating to a temperature range below the point is preferably set to 0.2 ° C. / sec or more 0.89 ° C. / sec or less. By the average heating rate and 0.2 ° C. / sec or more, it is possible to ensure a higher productivity. Further, by the average heating rate and 0.89 ° C. / sec or less, in case of heating using conventional furnace, it is easy to control the heating temperature.
[0057]
　720 ℃ or more Ac 3 heating time in the points following the temperature range is preferably less than 10 minutes for one minute or more. Here, the heating time is the time until the completion of the heating since the temperature of the steel sheet has reached 720 ° C.. At completion of heating and, specifically, in the case of furnace heating is the time when the steel sheet is removed from the furnace, in the case of conduction heating or induction heating is when you exit the energization or the like. By heating time is more than 1 minute, the decarburization during heating, tends ferrite is formed in the surface layer portion, the area ratio of the ferrite in the surface layer portion is 1.20 times greater than the area ratio of the ferrite in the inner layer portion It tends to be. To obtain the effects more reliably, it is more preferable that the heating time more than 4 minutes. By the heating time more than 10 minutes, it is possible to more finely steel structure of the steel plate member, the low temperature toughness of the steel plate member is further improved.
[0058]
　(The amount of decarburization at the decarburization 0.0005 wt% to 0.015 wt%)
　by decarburization, easily ferrite is formed than portions serving as the inner layer portion in a portion that becomes the surface layer portion of the steel plate member. If it is less than amount of 0.0005% by weight of the decarburization, can not be sufficiently obtained the above action, it is difficult to the area ratio of ferrite in the surface layer and 1.20 times more than the area ratio of the ferrite in the inner layer portion it is. Therefore, the amount of decarburization is 0.0005% by weight or more. If the amount is greater than 0.015% by weight of the decarburization, to ensure a sufficient amount of martensite in the steel plate member bainite transformation occurs during the decarburization process, in other words, it is difficult to obtain or more of tensile strength 980MPa is there. Therefore, the amount of decarburization to 0.015% by mass or less. The amount of decarburization is, for example, glow discharge emission spectroscopic analysis apparatus (GDS: glow discharge spectroscope) or an electron beam micro-analyzer (EPMA: electron probe micro analyzer) can be measured using a. That is, it analyzed the surface of the hot-press steel sheet before and after decarburization, it is possible to determine the amount of decarburization by comparing the results.
[0059]
　The method of decarburization is not particularly limited, for example, can be performed by air cooling. For example, during the period from extraction from the heating device of a heating furnace used in the heating of the to introduction into the hot press device, decarburizing treatment atmosphere, temperature, and by performing the appropriate control the air-cooling time, etc. it can be performed. More specifically, air cooling, for example, can be carried out during the extraction from the heating device, during transport from the heating device to the hot pressing device, and when turned to the hot press device.
[0060]
　When performing such air cooling, air cooling time from the end of heating to the start of the hot pressing is preferably not more than 50 seconds or 5 seconds. By air cooling time than 5 seconds, it is possible to perform a sufficient decarburization, easily, make the area ratio of the ferrite in the surface layer and 1.20 times greater than the area ratio of the ferrite in the inner layer portion it can. The air-cooling time by less 50 seconds, to suppress the progress of the bainite transformation, it is easy to secure the area fraction of martensite is strengthening phase, the tensile strength of the hot press-parts easily be at least 980MPa become. To obtain the effects more reliably, air cooling time is preferably not more than 30 seconds, more preferably up to 20 seconds.
[0061]
　Adjustment of the air cooling time is, for example, can be performed by adjusting the transport time from extraction from the heating device to the press mold of the heating press.
[0062]
　(Average cooling rate of up to Ms point: 10 ℃ / sec or more 500 ℃ / sec or less)
　After air cooling, do the hot press, cooled at an average cooling rate of 10 ℃ / sec or more 500 ℃ / sec or less until Ms point . The average cooling rate is less than 10 ℃ / sec, diffusion type transformation of bainite transformation, etc. will progress too, will not be able to secure the area ratio of martensite is a strengthening phase, the tensile strength of the steel plate member and more than 980MPa it is difficult. Therefore, this average cooling rate is set to 10 ℃ / sec or more. The average cooling rate is 500 ° C. / sec greater, it becomes extremely difficult to keep the soaking member, strength can not be stabilized. Therefore, this average cooling rate is set to 500 ℃ / sec or less.
[0063]
　It should be noted that, in this cooling, since the temperature reached 400 ℃, the heat generated by phase transformation is very easy to become large. Thus, the cooling in the low temperature range of less than 400 ° C., in the case of performing in the same manner as the cooling in the temperature range above 400 ° C. may not have enough average cooling rate. Thus, the cooling of up to Ms point from 400 ℃ than the cooling of up to 400 ℃, it is preferable to perform more strongly. For example, it is preferable to adopt the following method.
[0064]
　Generally, cooling in hot pressing, a steel of a mold for molding the heated steel sheet leave advance room temperature or the number 10 of about ℃ temperature, the steel sheet is performed by contacting the mold . Therefore, the average cooling rate may be controlled for example by a change in heat capacity due to a change of the mold dimensions. The mold of the material it is possible to control the average cooling rate also by changing the dissimilar metals (eg, Cu, etc.). Using a mold of water cooling type, it is possible to control the average cooling rate by varying the amount of cooling water flowing in the mold. In advance in the mold previously formed a plurality of grooves, you can also control the average cooling rate by passing water into the groove during hot pressing. Raised hot press in the course of hot pressing, it is possible to control the average cooling speed by flowing water therebetween. Adjust the mold clearance, it is possible to control the average cooling rate by changing the contact area between the steel plate of the mold.
[0065]
　As a method of enhancing the subsequent cooling rate at 400 ° C. before and after, for example, the following three types.
　(A) immediately after reaching 400 ℃, to move the steel sheet to a different mold or mold of the room temperature state of the heat capacity.
　(B) using a water-cooled mold, to increase the water flow in the mold immediately after 400 ℃ reach.
　(C) immediately after reaching 400 ℃, flow of water between the mold and the steel plate. In this method, it may be increased more cooling speed by increasing the amount of water depending on the temperature.
[0066]
　Form of shaped in hot press in this embodiment is not particularly limited. As a form of molding, for example, bending, stop molding, stretch forming, hole expansion molding, and include a flange molding. Molding of the embodiment may be selected appropriately depending on the kind of the steel plate member of interest. As a typical example of the steel plate member, door guard bar and bumper reinforcement such as a reinforcement parts for automobiles and the like. Further, if it is possible to cool the steel plate to the molded simultaneously with or immediately after, hot forming is not limited to hot pressing. For example, it may be carried out roll-forming as hot forming.
[0067]
　By performing such a series of processes in a predetermined hot press steel sheet described above, it is possible to produce a steel member according to the present embodiment. That is, a desired steel structure, the tensile strength is 980 MPa, it is possible to obtain a hot press steel plate member having a superior ductility and bendability.
[0068]
　For example, the ductility can be evaluated by the total elongation of the tensile test (EL), in the present embodiment, it is preferable that the total elongation of the tensile test is 12% or more. Total elongation is more preferably not less than 14%. For example, the bending property can be evaluated by a radius bending limit of V bending test of the tip angle of 90 °, in the present embodiment, when the thickness of the hot press-parts represented by t, is the critical bending radius it is preferably 5 or less × t.
[0069]
　After hot pressing and cooling may be carried out shot blasting. The shot blast treatment can remove scale. Shot blasting, because also has the effect of introducing compressive stresses in the surface of the steel sheet member, the delayed fracture is suppressed, the effect is also obtained that the fatigue strength is improved.
[0070]
　Incidentally, in the manufacturing method of the above-parts, hot pressing without preforming, hot-press steel sheet Ac 720 ° C. or higher 3 after causing the austenite transformation to some extent by heating to a temperature range of below points molding is carried out. Therefore, the mechanical properties of the hot-press steel sheet at room temperature before heating is not critical.
[0071]
　Steel member according to the present embodiment can also be produced through hot pressing with preformed. For example, in a range where the above heating, decarburization, the conditions of cooling is satisfied, the hot-press steel plate by pressing a mold having a predetermined shape preformed and placed into a mold of the same type, presser pressure was added, by quenching, may be produced hot press-parts. Again, the type and the steel structure of the hot-press steel sheet are not limited, to facilitate preformed, it is preferable to use a steel plate with a ductile lowest possible intensity. For example, it is preferred that tensile strength is not more than 700 MPa.
[0072]
　The above embodiments are all only show examples of concrete for carrying out the present invention, in which technical scope of the present invention should not be limitedly interpreted. That is, the present invention is its technical idea or without departing from its essential characteristics, can be implemented in various forms.
Example
[0073]
　Next, a description will be given experiment by the present inventors went. In this experiment, first, using the 19 types of steel having the chemical compositions shown in Table 1, were prepared 28 kinds of the hot-press steel sheet having a steel structure shown in Table 2 (steel sheet subjected to heat treatment). Incidentally, the remainder of each steel is Fe and impurities. Any thickness of the steel sheet subjected to heat treatment was set to 2.0 mm. Table 2 in "full hard" indicates a full hard steel plate, "plated steel sheet" is coating weight is 60g / m per single-sided 2 shows the hot-dip galvanized cold-rolled steel sheet. Full hard steel sheet used in this experiment, the thickness is steel sheet obtained by cold rolling a hot-rolled steel sheets of 3.6 mm, not subjected to annealing after cold rolling. In Table 2 of the column of "ferrite area ratio of" number (unit:%) indicates the area ratio of the ferrite in a region from the surface of the steel sheet to 100 .mu.m. Further, the column of figures "area ratio of pearlite" in Table 2 (unit:%), the average particle size in the region except the region to a depth of 100μm from the surface indicating the area ratio of 5μm or more perlite. These area ratio is the average value of the cross section and the plate width direction value calculated by performing an image analysis of electron microscopy images of two cross-section of the cross section perpendicular to (a direction perpendicular to the rolling direction) perpendicular to the rolling direction .
[0074]
　After fabrication of the steel sheet subjected to heat treatment, heating the steel sheet under the conditions shown in Table 2 in the air-fuel ratio in a gas heating furnace was set to 0.9. Table 2 "heating time" during indicates the time from when the temperature of the steel sheet instrumentation after turning of the steel sheet to a gas heating furnace reached 720 ° C., until taken out steel from a gas furnace. Furthermore, "heating temperature" in Table 2 is not the temperature of the steel sheet, showing the temperature in the gas heating furnace. Then removed steel from a gas heating furnace, subjected to decarburization of the steel sheet by air cooling, subjected to hot pressing of a steel plate was cooled steel plate. The hot pressing was used steel mold plates. In other words, the molding was not carried out. In decarburization process, the steel plate subjected to air cooling until placed in a mold is removed from the gas heating furnace, it was adjusted for this air cooling time. Upon cooling of the steel sheet while contacting the steel with the mold, and cooled to 0.99 ° C. or less Ms point at an average cooling rate shown in Table 2, it was allowed to cool then removed from the mold. In the cooling of up to 150 ℃, or the periphery of the mold until the temperature of the steel sheet is 150 ℃ and cooled by the cooling water, or in advance to prepare the mold that is at room temperature, until the temperature of the steel sheet is 150 ℃ It was maintained steel sheet into the mold. In the measurement of the average cooling rate of up to 150 ℃, it leaves stuck in advance thermocouple in steel plate, were analyzed the temperature history. In this way, it was produced 28 kinds of test materials (test trial steel plate). Or less, the test material (the test trial steel plate) is sometimes referred to as "hot-pressed steel plate."
0077]
　After obtaining hot-pressed steel sheet, for each of these steel sheets, the area ratio of the ferrite in the surface layer, the area ratio of the ferrite in the inner layer portion, and determine the area ratio of martensite in the inner layer portion. These area ratio is the average value of the cross section and the plate width direction value calculated by performing an image analysis of electron microscopy images of two cross-section of the cross section perpendicular to (a direction perpendicular to the rolling direction) perpendicular to the rolling direction . The surface layer of the steel structure of observation, were observed in the region up to a depth 15μm from the surface of the steel sheet. The inner layer portion of the steel structure of observation, were observed in 1/4 depth positions. Table 3 shows the ratio of the area ratio of the ferrite in the surface layer to the area ratio of the ferrite in the inner layer portion, and the area ratio and the area ratio of martensite of ferrite in the inner layer portion.
[0078]
　Moreover, the mechanical properties of the hot-pressed steel sheet were investigated. In this study, the measurement of tensile strength (TS) and total elongation (EL), was subjected to bending of the evaluation as well. The tensile strength and measurement of total elongation, were subjected to a tensile was collected tested JIS5 No. tensile test piece in a direction perpendicular to the rolling direction from each steel sheet. The bendability of the evaluation, ridge bend from each steel plate test piece such that the rolling direction (30mm × 60mm) was taken, the tip angle of 90 °, the tip radius was V bending test of 10 mm. Then, visually observed the surface of the bending portion after the test, the case where cracking is not observed well, and the case where cracks were observed as defective. These survey results are also shown in Table 3. Incidentally, the hot press steel sheet, while hot pressing using a steel die of a flat plate is applied, forming during hot pressing is not performed. However, the mechanical properties of the hot press steel sheet reflects the mechanical properties of the same thermal history and heat-pressing of the experiment made by receiving at the time of molding the hot press-parts. That is, with or without molded during hot pressing, heat history is equal substantially the same, even substantially be the same subsequent mechanical properties.
0080]
　As shown in Table 3, an invention example test material No. 2, No. 6, No. 8 ~ No. 10, No. 12 ~ No. 14, No. 16, No. 18, No. 22, No. 23, No. 26, and No. 27, showed excellent ductility and bending resistance. Therefore, the hot-press steel sheet full hard steel, cold rolled steel, hot-rolled steel sheet, be either galvanized cold rolled steel sheet, it is found to exhibit excellent effects by the present invention.
[0081]
　On the other hand, the test material No. 1, since the chemical composition is out of the scope the present invention, the ductility was bad. Test specimen No. 3, No. 17, and No. 20, production conditions are outside the scope the present invention, since the steel structure after hot pressing were also outside the scope the present invention, 980 MPa or more tensile strength is not obtained after cooling (after hardening). Test specimen No. 4, the manufacturing conditions are outside the scope the present invention, since the steel structure after hot pressing were also outside the scope the present invention, bending property was poor. Test specimen No. 5 and the test material No. 7, the steel structure of the steel sheet subjected to the heat treatment is outside the range present invention, since the steel structure after hot pressing were also outside the scope the present invention, 980 MPa or more in tensile strength after cooling can not be obtained. Test specimen No. 11, since the steel structure of the steel sheet subjected to heat treatment were outside the scope the present invention, bending property was poor. No. 19, the steel structure of the steel sheet subjected to the heat treatment is outside the range present invention, since the steel structure after hot pressing were also outside the scope the present invention, bending property was poor. Test specimen No. 15 and No. 21, since the chemical composition is out of the scope the present invention, 980 MPa or more tensile strength is not obtained after cooling (after hardening). Test specimen No. 24, production conditions are outside the scope the present invention, since the steel structure after hot pressing were also outside the scope the present invention, the ductility was bad. Test specimen No. 25, because the chemical composition is out of the scope the present invention, bending was poor. Test specimen No. 28, the chemical composition is outside the range present invention, since the steel structure after hot pressing were also outside the scope the present invention, the ductility was bad.
[0082]
　It should be noted that the sample material is a comparative example No. In 17, but even though the bending resistance ratio of the area ratio of ferrite is less than 1.20 in the surface layer to the area ratio of the ferrite in the inner layer portion was good, this is the tensile strength (TS) and a 591MPa This is because very low.
Industrial applicability
[0083]
　The present invention is, for example, can be utilized in manufacturing industry and use industrial body structural components of automobiles that are important excellent collision characteristics view. The present invention can also be utilized in the manufacturing industry and utilization industries of other mechanical structural parts.
The scope of the claims
[Claim 1]
　By
　mass%, C:
　0.10% ~
　0.34%, Si: 0.5% ~ 2.0%, Mn: 1.0% ~
　3.0%, sol. Al: 0.001 Pasento ～
　1.0 Pasento, P: 0.05 Pasento or
　less, S: 0.01 Pasento or
　less, N: 0.01 Pasento or
　less, Ti: 0 Pasento ～ 0.20
　Pasento, Nb: 0 Pasento 0.20
　Pasento ～,
　V:
　0 Pasento ～ 0.20 Pasento, Cr: 0 Pasento ～ 1.0 Pasento,
　Mo: 0 Pasento ～ 1.0 Pasento, Cu: 0 Pasento ～ 1.0
　Pasento, Ni: 0 Pasento
　1.0
　Pasento ～,
　Ca: 0 Pasento ～ 0.01 Pasento, Mg: 0 Pasento ～ 0.01 Pasento,
　REM: 0 Pasento ～ 0.01 Pasento, Zr: 0 Pasento ～ 0.01
　Pasento, B: 0 Pasento
　0.01% ~, Bi: 0% ~ 0.01%,
　balance: Fe and impurities
having a chemical composition represented by,
　the area ratio of the ferrite in the surface layer to a depth of 15μm from the surface, the surface layer portion 1.20 times greater than the area ratio of the ferrite in the inner layer portion is a portion excluding the inner section, in area%, ferrite: 10% to 70%, martensite: 30% to 90%, ferrite and the total area fraction of martensite: having a steel structure which is 90% to 100%,
　a tensile hot press-parts which intensity is equal to or more than 980 MPa.
[Claim 2]
　The chemical composition, by
　mass%,
　Ti:
　0.003% ~ 0.20%, Nb: 0.003% ~ 0.20%, V:
　0.003% ~ 0.20%, Cr: 0.005
　~ 1.0%%,
　Mo: 0.005% ~ 1.0%, Cu: 0.005% ~ 1.0%, and
　Ni: 0.005% ~ 1.0%
is selected from the group consisting of one or hot press-parts according to claim 1, characterized by containing two or more.
[Claim 3]
　The chemical composition, in
　mass%,
　Ca: 0.0003% ~
　0.01%, Mg: 0.0003% ~ 0.01%, REM: 0.0003% ~ 0.01%, and
　Zr: 0. 0003% ~ 0.01%
hot press steel sheet member according to claim 1 or 2, characterized by containing one or more selected from the group consisting of.
[Claim 4]
　The chemical composition, by mass%, B: 0.0003% ~ hot press-parts according to any one of claims 1 to 3, characterized by containing 0.01%.
[Claim 5]
　The chemical composition, in mass%, Bi: 0.0003% ~ hot press steel sheet member according to any one of claims 1 to 4, characterized in that it contains 0.01%.
[6.]
　By
　mass%, C:
　0.11% ~
　0.35%, Si: 0.5% ~ 2.0%, Mn: 1.0% ~
　3.0%, sol. Al: 0.001 Pasento ～
　1.0 Pasento, P: 0.05 Pasento or
　less, S: 0.01 Pasento or
　less, N: 0.01 Pasento or
　less, Ti: 0 Pasento ～ 0.20
　Pasento, Nb: 0 Pasento 0.20
　Pasento ～,
　V:
　0 Pasento ～ 0.20 Pasento, Cr: 0 Pasento ～ 1.0 Pasento,
　Mo: 0 Pasento ～ 1.0 Pasento, Cu: 0 Pasento ～ 1.0
　Pasento, Ni: 0 Pasento
　1.0
　Pasento ～,
　Ca: 0 Pasento ～ 0.01 Pasento, Mg: 0 Pasento ～ 0.01 Pasento,
　REM: 0 Pasento ～ 0.01 Pasento, Zr: 0 Pasento ～ 0.01
　Pasento, B: 0 Pasento
　0.01% ~, Bi: 0% ~ 0.01%,
　balance: Fe and impurities
having a chemical composition represented by,
　has an inner oxide layer of 30μm or less in thickness,
　to a depth of 100μm from the surface 30% to 90% area ratio of the ferrite in the region, that the average particle size in the region except the region to a depth of 100μm from the surface area ratio of the above perlite 5μm has a 10% to 70% of the steel structure hot pressing for a steel plate which is characterized.
[7.]
　The chemical composition, by
　mass%,
　Ti:
　0.003% ~ 0.20%, Nb: 0.003% ~ 0.20%, V:
　0.003% ~ 0.20%, Cr: 0.005
　~ 1.0%%,
　Mo: 0.005% ~ 1.0%, Cu: 0.005% ~ 1.0%, and
　Ni: 0.005% ~ 1.0%
is selected from the group consisting of hot press steel sheet according to claim 6, characterized by containing one or two or more species.
[8.]
　The chemical composition, in
　mass%,
　Ca: 0.0003% ~
　0.01%, Mg: 0.0003% ~ 0.01%, REM: 0.0003% ~ 0.01%, and
　Zr: 0. 0003% - 0.01%
for hot pressing steel sheet according to claim 6 or 7, characterized by containing one or more selected from the group consisting of.
[9.]
　The chemical composition, by mass%, B: 0.0003% ~ hot press steel sheet according to any one of claims 6 to 8, characterized in that it contains 0.01%.
[10.]
　The chemical composition, in mass%, Bi: 0.0003% ~ hot press steel sheet according to any one of claims 6 to 9, characterized in that it contains 0.01%.
[11.]
　The hot-press steel sheet according to any one of claims 6 to 10, Ac 720 ° C. or higher 3 and heating to a temperature range of less points,
　after the heating, the surface of the hot-press steel sheet and performing decarburization to reduce the C content 0.0005% to 0.015% by weight,
　after the decarburization treatment, carried out hot pressing, the average cooling rate of 10 ° C. / sec - 500 ° C. / sec in a step of cooling to the Ms point
　method for producing a hot press steel sheet member characterized by having a.
[12.]
　Wherein the step of performing decarburization treatment method for manufacturing a hot press-parts according to claim 11, comprising a step of performing air cooling of 5 seconds to 50 seconds.