TWI513829B - A hot-pressed steel sheet member, a method for manufacturing the same, and a steel sheet for hot pressing - Google Patents

Description

Hot-pressed steel sheet member, method for producing the same, and steel sheet for hot pressing Field of invention

The present invention relates to a hot-pressed steel sheet member used for a mechanical structural part or the like, a method for producing the same, and a steel sheet for hot pressing.

Background of the invention

In order to reduce the weight of the car, it is moving in the direction of increasing the strength of the steel used in the car body and reducing the weight of the steel. Steel sheets widely used in automobiles generally have a decrease in press formability as strength increases, resulting in difficulty in manufacturing complicated-shaped parts. For example, as the ductility is lowered, there is a break in a portion having a high degree of workability, or a large rebound causes deterioration in dimensional accuracy. Therefore, for high-strength steel sheets (especially those having a tensile strength of 980 MPa or more), it is difficult to manufacture parts by press forming. If the press forming is not performed by roll forming, the high-strength steel sheet is easier to machine, but the object to be applied is limited to parts having the same cross section in the longitudinal direction.

Among the high-strength steel sheets, a method of obtaining hot pressing for the purpose of obtaining high moldability is as described in Patent Documents 1 and 2. According to the hot pressing, the high-strength steel sheet can be formed with high precision, and a high-strength hot-pressed steel sheet member can be obtained.

On the other hand, ductility is also required for hot-pressed steel sheet members. However, the steel structure of the steel sheet obtained by the methods described in Patent Documents 1 and 2 is a substantial single phase of the Ma Tian loose iron, and it is difficult to improve the ductility.

Further, in Patent Documents 3 and 4, high-strength hot-pressed steel sheet members for the purpose of improving ductility are described. However, such conventional hot-pressed steel sheet members have other problems in that toughness is lowered. The reduction in toughness is not only used in the case of automobiles, but also in the case of mechanical structural parts. Although Patent Documents 5 and 6 describe techniques for improving fatigue characteristics, it is difficult to obtain sufficient ductility and toughness even in accordance with these.

Advanced technical literature Patent literature

Patent Document 1: British Patent Gazette No. 1490535

Patent Document 2: Japanese Patent Laid-Open No. Hei 10-96031

Patent Document 3: Japanese Patent Laid-Open Publication No. 2010-65292

Patent Document 4: Japanese Patent Laid-Open Publication No. 2007-16296

Patent Document 5: Japanese Patent Laid-Open Publication No. 2007-247001

Patent Document 6: Japanese Patent Laid-Open Publication No. 2005-298957

Summary of invention

An object of the present invention is to provide a hot-pressed steel sheet member having high strength and excellent ductility and toughness, a method for producing the same, and a steel sheet for hot pressing.

The inventor of this case is highly aware of the purpose of improving the scalability The strength of the hot-pressed steel sheet member is reviewed for the cause of the decrease in toughness. As a result, it is found that when the steel structure of the hot-pressed steel sheet member is set to a multiphase structure containing the ferrite iron and the granulated iron for the purpose of ductility improvement, the hot pressing of the hot-pressed steel sheet member can be obtained during heating and Decarburization is easier in air cooling, and toughness is reduced due to decarburization. That is, as a result of the decarburization, it is found that in the depth region from the surface of the hot-pressed steel sheet member to about 15 μm, the ratio of the ferrite-grained iron is increased, and a layered structure composed of, for example, a single phase of the ferrite-rich iron is also present (hereinafter Called the "fertilizer iron layer", the fragility of the ferrite grain boundary in this area will induce significant deterioration of toughness. This decarburization is particularly noticeable when obtaining a multiphase structure, and this phenomenon has not been found in the prior art.

The inventors of the present invention conducted intensive studies based on such findings, and found that the steel sheet for hot pressing having a predetermined steel structure and containing a predetermined amount of C and Mn, and having a predetermined steel structure, utilizes heat under appropriate conditions. By pressing and the like, it is possible to obtain a hot-pressed steel sheet member in which the steel structure is a multiphase structure containing the ferrite iron and the granulated iron, and the decarburization of the surface portion is suppressed. The inventors of the present invention have further found that the hot-pressed steel sheet member has a high tensile strength of 980 MPa or more, and also has excellent ductility and toughness. The inventors of the present invention have also found that the hot-pressed steel sheet member unexpectedly also has excellent fatigue characteristics. Therefore, the inventors of the present invention conceived the following aspects of the invention.

(1) A hot-pressed steel sheet member having the chemical composition shown below: C: 0.10% to 0.34%, Si: 0.5% to 2.0%, in terms of mass%, Mn: 1.0% to 3.0%, sol. Al: 0.001% to 1.0%, P: 0.05% or less, S: 0.01% or less, N: 0.01% or less, Ti: 0% to 0.20%, Nb: 0% to 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 remainder: Fe and impurities; from surface to The area ratio of the ferrite iron in the surface layer portion having a depth of 15 μm is 1.20 times or less of the area ratio of the ferrite iron in the inner layer portion, and the inner layer portion is a portion other than the surface layer portion; the inner layer portion has an area percentage For ferrite iron: 10%~70%, Ma Tian loose iron: 30%~90%, ferrite iron and 麻田散铁 total area ratio: 90%~100% steel structure; In the inner layer portion, the Mn concentration in the granulated iron is 1.20 times or more of the Mn concentration in the ferrite iron, and the tensile strength is 980 MPa or more.

(2) The hot-pressed steel sheet member according to the above aspect, wherein the chemical composition is one or more selected from the group consisting of: Ti: 0.003% to 0.20, by mass%. %, Nb: 0.003% to 0.20%, V: 0.003% to 0.20%, Cr: 0.005% to 1.0%, Mo: 0.005% to 1.0%, Cu: 0.005% to 1.0%, and Ni: 0.005% to 1.0% .

(3) The hot-pressed steel sheet member according to the above aspect, wherein the chemical composition is one or more selected from the group consisting of: Ca: 0.0003%~0.01%, Mg: 0.0003%~0.01%, REM: 0.0003%~0.01%, and Zr: 0.0003%~0.01%.

(4) The hot-pressed steel sheet member according to any one of (1) to (3), wherein the chemical composition contains B: 0.0003% to 0.01% by mass%.

(5) The hot-pressed steel sheet member according to any one of (1) to (4), wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%.

(6) A steel sheet for hot pressing having the chemical composition shown below: C: 0.10% to 0.34%, Si: 0.5% to 2.0%, Mn: 1.0% to 3.0%, sol. Al: by mass% 0.001%~1.0% or less, P: 0.05% or less, S: 0.01% or less, N: 0.01% or less, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 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 remainder: Fe and impurities; and has the following steel structure: containing ferrite and ferrem Carbon iron and toughened iron The total area ratio of the granulated iron is 0% to 10%, the area ratio of ferritic carbon iron is more than 1%, and the Mn concentration in swarf carbon iron is 5% or more.

(7) The steel sheet for hot press according to the above aspect, wherein the chemical composition is one or more selected from the group consisting of: Ti: 0.003% to 0.20, by mass%. %, Nb: 0.003% to 0.20%, V: 0.003% to 0.20%, Cr: 0.005% to 1.0%, Mo: 0.005% to 1.0%, Cu: 0.005% to 1.0%, and Ni: 0.005% to 1.0% .

(8) The steel sheet for hot press according to the above aspect, wherein the chemical composition is one or more selected from the group consisting of: Ca: 0.0003%~0.01%, Mg: 0.0003%~0.01%, REM: 0.0003%~0.01%, and Zr: 0.0003%~0.01%.

The steel sheet for hot press according to any one of (6), wherein the chemical composition contains B: 0.0003% to 0.01% by mass%.

The steel sheet for hot press according to any one of the above aspects, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%.

(11) A method for producing a hot-pressed steel sheet member, comprising: heating the steel sheet for hot pressing according to any one of (6) to (10) to a temperature range of 720 ° C or higher and Ac ₃ or lower, and The Mn concentration in the Worthite iron is set to 1.20 times or more of the Mn concentration in the ferrite iron; and the hot pressing is performed after the heating, and is cooled to the Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec. In the period from the end of the heating to the start of the hot pressing, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%.

(12) The method of producing a hot-pressed steel sheet member according to the above aspect, wherein the time period from the end of the heating to the start of the hot pressing is that the time for exposing the hot-pressed steel sheet to the atmosphere is less than 15 Seconds.

According to the present invention, high tensile strength can be obtained, and excellent ductility and toughness can be obtained.

Form for implementing the invention

Hereinafter, embodiments of the present invention will be described. The embodiment of the present invention relates to a hot-pressed steel sheet member having a tensile strength of 980 MPa or more.

First, the chemical composition of the hot-pressed steel sheet member (hereinafter also referred to as "steel sheet member") of the embodiment of the present invention and the steel sheet for hot pressing used in the production thereof will be described. In the following description, the "%" of the content of each element contained in the steel sheet member or the hot-pressed steel sheet is not specifically stated. Refers to "% by mass".

The chemical composition of the steel sheet member of the present embodiment and the steel sheet for hot pressing used in the production thereof is C: 0.10% to 0.34%, Si: 0.5% to 2.0%, and Mn: 1.0% by mass%. 3.0%, sol.Al: 0.001% to 1.0%, P: 0.05% or less, S: 0.01% or less, N: 0.01% or less, Ti: 0% to 0.20%, Nb: 0% to 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% to 0.01%, Zr: 0% to 0.01%, B: 0% to 0.01%, Bi: 0% to 0.01%, and the remainder: Fe and impurities. The impurities may be, for example, those contained in raw materials such as ore and scrap, and included in the production steps.

(C: 0.10%~0.34%)

The C system is a very important element for improving the hardenability of the steel sheet for hot pressing and mainly determining the strength of the steel sheet member. If the C content of the steel sheet member is less than 0.10%, it is difficult to ensure a tensile strength of 980 MPa or more. Therefore, the C content of the steel sheet member is set to be 0.10% or more. The C content of the steel sheet member is preferably 0.12% or more. When the C content of the steel sheet member exceeds 0.34%, the granulated iron in the steel sheet member becomes hard and the toughness is remarkably deteriorated. Therefore, the C content of the steel sheet member is set to 0.34% or less. From the viewpoint of weldability, the C content of the steel sheet member is preferably 0.30% or less, more preferably 0.25% or less. As will be described later, decarburization occurs in the production of the hot-pressed steel sheet member. However, since the amount is as small as negligible, the C content of the hot-pressed steel sheet substantially matches the C content of the steel sheet member.

(Si: 0.5%~2.0%)

The Si system is a very effective element for improving the ductility of the steel sheet member and ensuring the strength stability of the steel sheet member. If the Si content is less than 0.5%, it is difficult to obtain the above effect. Therefore, the Si content is set to 0.5% or more. If the Si content exceeds 2.0%, the effect caused by the above action is saturated, which is not economical, and causes the plating wettability to be remarkably lowered, resulting in multiple electroless plating. Therefore, the Si content is set to be 2.0% or less. From the viewpoint of improving the weldability, the Si content is preferably 0.7% or more, more preferably 1.1% or more. From the viewpoint of suppressing surface defects of the steel sheet member, the Si content is preferably 1.8% or less, more preferably 1.35% or less.

(Mn: 1.0% to 3.0%)

Mn is a very effective element for improving the hardenability of the steel sheet for hot press and for ensuring the strength of the steel sheet member. When the Mn content is less than 1.0%, it is extremely difficult to secure the tensile strength of the steel sheet member to 980 MPa or more. Therefore, the Mn content is set to 1.0% or more. In order to more reliably obtain the above effects, the Mn content is preferably 1.1% or more, more preferably 1.15% or more. When the Mn content exceeds 3.0%, the steel structure of the steel sheet member becomes a distinct band shape, resulting in a decrease in bendability and a remarkable deterioration in impact resistance. Therefore, the Mn content is set to 3.0% or less. The Mn content is preferably 2.5% or less, more preferably 2.45% or less, from the viewpoint of productivity in obtaining hot-rolling and cold-rolling of the hot-pressed steel sheet.

(sol.Al (acid soluble Al): 0.001% to 1.0%)

The Al system has an element that deoxidizes steel to improve the steel material. If the sol. Al content is less than 0.001%, it is difficult to obtain the above effects. Therefore, the sol. Al content is set to 0.001% or more. In order to obtain the above effects more reliably, the sol. Al content is preferably 0.015% or more. If the sol.Al content exceeds 1.0%, the weldability tends to decrease, and the oxide medium increases, and the surface properties deteriorate. Obvious. Therefore, the sol. Al content is set to 1.0% or less. In order to obtain a better surface property, the sol. Al content is preferably set to 0.080% or less.

(P: 0.05% or less)

P is not an essential element, but is, for example, an impurity contained in steel. From the viewpoint of weldability, the lower the P content, the better. In particular, if the P content exceeds 0.05%, the weldability is remarkably lowered. Therefore, the P content is set to be 0.05% or less. In order to ensure better weldability, the P content is preferably 0.018% or less. On the other hand, P has an effect of increasing the strength of steel by solid solution strengthening. In order to obtain this effect, it may also contain 0.003% or more of P.

(S: 0.01% or less)

S is not an essential element, but is, for example, an impurity contained in steel. From the viewpoint of weldability, the lower the S content, the better. In particular, if the S content exceeds 0.01%, the weldability is significantly lowered. Therefore, the S content is set to be 0.01% or less. In order to ensure better weldability, the S content is preferably 0.003% or less, more preferably 0.0015% or less.

(N: 0.01% or less)

N is not an essential element, but is, for example, an impurity contained in steel. From the viewpoint of weldability, the lower the N content, the better. In particular, if the N content exceeds 0.01%, the weldability is remarkably lowered. Therefore, the N content is set to 0.01% or less. In order to ensure better weldability, the N content is preferably 0.006% or less.

Ti, Nb, V, Cr, Mo, Cu, Ni, Ca, Mg, REM, Zr, B, and Bi are not essential elements, and any of a predetermined amount of an element may be contained in the steel sheet member and the hot-pressed steel sheet as appropriate.

(Ti: 0%~0.20%, Nb: 0%~0.20%, V: 0%~0.20%, Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%)

Ti, Nb, V, Cr, Mo, Cu, and Ni are all effective elements for ensuring the strength and stability of steel sheet members. Therefore, one or two or more types selected from the group consisting of these elements may be included. However, if the content of any of Ti, Nb, and V is more than 0.20%, it is difficult to obtain hot rolling and cold rolling of the hot-pressed steel sheet, and it is difficult to secure the stability. Therefore, the Ti content, the Nb content, and the V content are all set to 0.20% or less. Correlated Cr, if it exceeds 1.0%, leads to difficulty in ensuring stability. Therefore, the Cr content is set to 1.0% or less. When the content of Mo is more than 1.0%, it is difficult to obtain hot rolling and cold rolling of the steel sheet for hot pressing. Therefore, the Mo content is set to 1.0% or less. When the content of any of Cu and Ni is 1.0%, the effect by the above action is saturated, which is not economical, and it is difficult to obtain hot rolling and cold rolling of the steel sheet for hot pressing. Therefore, both the Cu content and the Ni content are set to 1.0% or less. In order to ensure the stability of the steel plate member, the Ti content, the Nb content, and the V content are preferably 0.003% or more, and the Cr content, the Mo content, the Cu content, and the Ni content are preferably 0.005% or more. That is, it is preferable that "Ti: 0.003% to 0.20%", "Nb: 0.003% to 0.20%", "V: 0.003% to 0.20%", "Cr: 0.005% to 1.0%", and "Mo: 0.005%" At least one of 1.0%", "Cu: 0.005% to 1.0%", and "Ni: 0.005% to 1.0%".

(Ca: 0%~0.01%, Mg: 0%~0.01%, REM: 0%~0.01%, Zr: 0%~0.01%)

Ca, Mg, REM, and Zr are all controlled by the medium (especially Finely dispersed, an element that contributes to the improvement of toughness. Therefore, one or two or more types selected from the group consisting of these elements may be included. However, if any content exceeds 0.01%, the deterioration of the surface properties may be apparent. Therefore, the Ca content, the Mg content, the REM content, and the Zr content are all set to 0.01% or less. In order to improve the toughness, the Ca content, the Mg content, the REM content, and the Zr content are preferably 0.0003% or more. That is, it is preferable to satisfy at least one of "Ca: 0.0003% to 0.01%", "Mg: 0.0003% to 0.01%", "REM: 0.0003% to 0.01%", and "Zr: 0.0003% to 0.01%". .

REM (rare earth metal) means a total of 17 elements such as Sc, Y, and lanthanoid elements, and "REM content" means the total content of the 17 elements. The lanthanoid element is industrially added, for example, in the form of a misch metal (rare earth metal alloy).

(B: 0%~0.01%)

The B system belongs to an element having an effect of improving the toughness of the steel sheet. Therefore, it can also contain B. However, when the B content exceeds 0.01%, the hot workability is deteriorated, and it is difficult to obtain hot rolling of the steel sheet for hot pressing. Therefore, the B content is set to be 0.01% or less. In order to improve the toughness, the B content is preferably 0.0003% or more. That is, the B content is preferably 0.0003% to 0.01%.

(Bi: 0%~0.01%)

The Bi system is an element having a function of making the steel structure uniform and improving the impact resistance. Therefore, Bi may also be contained. However, when the Bi content exceeds 0.01%, the hot workability is deteriorated, and it is difficult to obtain hot rolling of the steel sheet for hot pressing. Therefore, the Bi content is set to 0.01% or less. To improve impact resistance, Bi content Preferably, it is 0.0003% or more. That is, the Bi content is preferably 0.0003% to 0.01%.

Next, the steel structure of the steel sheet member of the present embodiment will be described. In the steel sheet member, the area ratio of the ferrite iron in the surface layer portion from the surface to the depth of 15 μm is 1.20 times or less of the area ratio of the inner layer portion of the outer layer portion except the surface layer portion, and the inner layer portion is based on the area %. It has ferrite iron: 10%~70%, Ma Tian loose iron: 30%~90%, and the combined area ratio of fertilized iron and granulated iron: 90%~100% steel structure. Further, in the inner layer portion, the Mn concentration in the granulated iron is 1.20 times or more the Mn concentration in the granulated iron in the inner layer portion. The "surface layer portion of the steel sheet member" means a surface portion from the surface to a depth of 15 μm; the "inner layer portion" means a portion other than the surface layer portion. That is, the inner layer portion is a portion other than the surface layer portion of the steel sheet member. The value of the steel structure in the inner layer portion is, for example, the average value of the entire thickness direction of the inner layer portion, and the depth from the surface of the steel sheet member is 1/4 of the thickness of the steel sheet member (hereinafter, the point is referred to as "1/4 depth". The steel structure related values of position ") are representative. For example, if the thickness of the steel sheet member is 2.0 mm, it can be represented by a numerical value at a depth of 0.50 mm from the surface. The reason is that the steel structure at the 1/4 depth position indicates the average steel structure in the thickness direction of the steel sheet member. Here, in the present invention, the area ratio of the ferrite iron and the area ratio of the granulated iron in the 1/4 depth position are set as the area ratio of the ferrite iron in the inner layer portion and the area ratio of the granulated iron in the inner layer. In addition, the surface layer portion is defined as a surface portion from the surface to a depth of 15 μm, and is limited to a maximum depth of degaking in the range of about 15 μm due to the review by the inventors of the present invention.

(The area ratio of the fertilized iron in the surface layer: 1.20 times or less of the area ratio of the fertilized iron in the inner layer)

If the area ratio of the fertilized iron in the surface layer exceeds 1.20 times the area ratio of the ferrite in the inner layer, the ferrite grain boundary in the surface layer is weak and the toughness is significantly reduced. Therefore, the area ratio of the ferrite iron in the surface layer portion is set to 1.20 times or less of the area ratio of the ferrite iron in the inner layer portion. The area ratio of the fertilized iron in the surface layer portion is preferably 1.18 or less of the area ratio of the fertilized iron in the inner layer portion. In addition, when the hot-pressed steel sheet according to the embodiment of the present invention is subjected to hot pressing under the conditions described later, since the decarburization is less likely to occur, the area ratio of the ferrite iron in the surface layer portion of the steel sheet member is more likely to become the fat of the inner layer portion. The iron area ratio is 1.16 or less.

Further, when heating by ordinary hot pressing, the treatment for increasing the C concentration in the vicinity of the surface of the steel sheet is not performed as in the carburizing treatment. Therefore, in general, the area ratio of the fertilized iron in the surface layer portion is not less than the area ratio of the fertilized iron in the inner layer portion, and the area ratio of the fertilized iron in the surface layer portion is 1.0 times or more than the area ratio of the fertilized iron in the inner layer portion.

(fertilizer iron area ratio of inner layer: 10%~70%)

Good ductility can be obtained by having an appropriate amount of ferrite in the inner layer. If the area ratio of the fertilized iron in the inner layer is less than 10%, most of the fertilized iron is isolated and cannot obtain good ductility. Therefore, the area ratio of the ferrite iron in the inner layer portion is set to 10% or more. If the area ratio of the ferrite iron in the inner layer portion exceeds 70%, the granulated iron which belongs to the strengthening phase cannot be sufficiently ensured, and it is difficult to ensure the tensile strength of 980 MPa or more. Therefore, the area ratio of the ferrite iron in the inner layer is set to be 70% or less. In order to ensure better ductility, the area ratio of the ferrite iron in the inner layer is preferably 30% or more.

(The area of the Ma Tian loose iron in the inner layer: 30%~90%)

High strength can be obtained by having an appropriate amount of granulated iron in the inner layer. If the area ratio of the Ma Tian loose iron in the inner layer is less than 30%, it is difficult to ensure Tensile strength of 980 MPa or more. Therefore, the area ratio of the granulated iron in the inner layer is set to 30% or more. If the area ratio of the granulated iron in the inner layer is more than 90%, the area ratio of the ferrite iron is less than 10%, and as described above, good ductility cannot be obtained. Therefore, the area ratio of the granulated iron in the inner layer is set to be less than 90%. In order to ensure better ductility, the area ratio of the granulated iron in the inner layer is preferably 70% or less.

(The total area ratio of the ferrite iron and the granulated iron in the inner layer: 90%~100%)

The inner layer portion of the hot-pressed steel sheet member of the present embodiment is preferably composed of ferrite iron and 麻田散铁, that is, the total area ratio of the ferrite iron and the granulated iron is 100%. However, depending on the manufacturing conditions, it is possible to contain phases or structures other than fertilized iron and granulated iron, for example, from the group consisting of toughened iron, residual Worth iron, swarf carbon iron, and ferritic iron. Kind or more than two. In this case, if the area ratio of the phase or the structure other than the ferrite iron and the granulated iron exceeds 10%, the target characteristics may not be obtained due to the influence of the phase or the structure. Therefore, the ratio of the phase or tissue area other than the ferrite iron and the granulated iron in the inner layer is set to be 10% or less. In other words, the total area ratio of the ferrite iron and the granulated iron in the inner layer portion is set to 90% or more.

The method for measuring the area ratio of each phase of the above steel structure may be a method well known to those skilled in the art. The area ratios can be obtained, for example, from the values measured by the orthogonal cross sections in the rolling direction and the average values of the measured values in the cross section of the sheet width direction (orthogonal direction of the rolling direction). That is, for example, the average of the area ratios measured by the two cross sections can be obtained.

(The concentration of Mn in the granulated iron in the inner layer: the fat in the inner layer 1.20 times or more of the Mn concentration in iron)

If the Mn concentration in the granulated iron in the inner layer is less than 1.20 times the Mn concentration in the ferrite iron in the inner layer, the area ratio of the ferrite iron in the surface layer is inevitably increased, and good toughness cannot be obtained. Therefore, the Mn concentration in the granulated iron in the inner layer portion is set to 1.20 times or more of the Mn concentration in the ferrite iron in the inner layer portion. There is no special limit on the upper limit of the ratio, but it should not exceed 3.0.

Such a steel sheet member can be produced by subjecting a predetermined steel sheet for hot pressing to a predetermined condition.

Here, the steel structure and the like of the steel sheet for hot pressing used in the production of the steel sheet member of the present embodiment will be described. The hot-pressed steel sheet contains ferrite iron and ferritic carbon iron, and has a steel structure in which the total area ratio of the toughened iron and the granulated iron is 0% to 10%, and the area ratio of the stellite carbon iron is 1% or more. Further, the Mn concentration in the smectite carbon iron is 5% or more.

(Fat grain iron and Xueming carbon iron)

Fertilizer iron and ferritic carbon iron may also be present in the Borne iron or may be independent of the Borne iron. Examples of the steel structure of the steel sheet for hot pressing may be, for example, a multiphase structure of ferrite iron and a ferritic iron, and a multiphase structure of ferrite iron, ferritic iron, and spheroidized stellite. The steel structure of the steel sheet for hot pressing may further contain 麻田散铁. If the total area ratio of ferrite iron and ferritic carbon iron is less than 90%, decarburization is more likely to occur in hot pressing. Therefore, the total area ratio of ferrite iron and ferritic carbon iron also includes more than 90% of the portion contained in the Borne iron.

(Xueming carbon iron area ratio: 1% or more)

If the area ratio of Xueming carbon iron is less than 1%, decarburization is likely to occur during hot pressing. The hot-pressed steel sheet member obtained from the hot-pressed steel sheet is less likely to have good toughness. Therefore, the area ratio of Xueming carbon iron is set to be 1% or more.

(Total area ratio of toughened iron and 麻田散铁: 0%~10%)

When the total area ratio of the toughened iron and the granulated iron is more than 10%, decarburization is extremely likely to occur during hot pressing, and the hot-pressed steel sheet member obtained from the hot-pressed steel sheet cannot obtain good toughness. Therefore, the total area ratio of the toughened iron and the granulated iron is set to be 10% or less. It may also not contain toughened iron and 麻田散铁. On the other hand, when the total area ratio of the toughened iron and the granulated iron is 10% or less, if the ferrite iron and the swarf carbon iron are contained, the hot-pressed steel sheet member can obtain good toughness.

(Mn concentration in Xueming carbon iron: 5% or more)

When the Mn concentration in the smectite carbon iron is less than 5%, decarburization is more likely to occur in hot pressing, and the hot-pressed steel sheet member obtained from the hot-pressed steel sheet cannot obtain good toughness. Therefore, the Mn concentration in Xueming carbon iron is set to 5% or more.

Next, a method of manufacturing the steel sheet member according to the present embodiment, that is, a method of performing treatment on the hot-pressed steel sheet will be described. In the treatment of the hot-pressed steel sheet, the hot-pressed steel sheet is heated to a temperature range of 720° C. or more and Ac ₃ point or less, and the Mn concentration in the Worth iron is set to 1.20 times or more of the Mn concentration in the ferrite iron. After the heating, hot pressing is performed, and then cooled to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec. In addition, during the period from the end of the heating to the start of the hot pressing, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005%.

(heating temperature of steel sheet for hot pressing: 720 ° C or higher and temperature range of Ac ₃ or less)

The heating of the steel sheet for hot pressing (that is, the steel sheet for hot pressing) is performed in a temperature range of 720 ° C or higher and Ac ₃ or lower. The Ac ₃ point is the temperature (unit: ° C) of the single phase of the Worthite iron as defined by the following experimental formula (i).

Ac ₃ = 910-203 × (C ^0.5 ) - 15.2 × Ni + 44.7 × Si + 104 × V + 31.5 × Mo-30 × Mn-11 × Cr - 20 × Cu + 700 × P + 400 × Al + 50 × Ti. . . (i)

Here, the element symbol in the above formula represents the content (unit: mass %) of each element of the chemical composition of the steel sheet.

When the heating temperature is less than 720 ° C, the formation of Worthite iron derived from the solid solution of smectite carbon iron is difficult or insufficient, and it is difficult to set the tensile strength of the steel sheet member to 980 MPa or more. Therefore, the heating temperature is set to 720 ° C or higher. If the heating temperature exceeds the Ac ₃ point, the steel structure of the steel sheet member becomes a single phase of the granulated iron, and the ductility deterioration tends to be conspicuous. Therefore, the heating temperature is set to be equal to or less than Ac ₃ points.

The heating rate in the temperature range of 720 ° C or more and Ac ₃ or less and the heating time held in the above temperature range are not particularly limited, and it is preferable to set the following range.

In the heating in the temperature range of 720 ° C or more and Ac ₃ or less, the average heating rate is preferably set to 0.2 ° C / sec or more and 100 ° C / sec or less. By setting the average heating rate to 0.2 ° C / sec or more, higher productivity can be ensured. Further, by setting the above average heating rate to 100 ° C / sec or less, it is possible to control the heating temperature by heating in a normal furnace.

Especially in the temperature range of 600 ° C or more and 720 ° C or less The average heating rate is preferably set to 0.2 ° C / sec or more and 10 ° C / sec or less. The reason is that by promoting the distribution of Mn between the ferrite iron and the Worthite iron, the Mn concentration of the Worthite iron is further promoted, and decarburization can be more reliably suppressed.

The heating time in the temperature range of 720 ° C or more and Ac ₃ or less is preferably set to 3 minutes or more and 10 minutes or less. Here, the "heating time" means the time from when the steel sheet temperature reaches 720 ° C until the end of heating. The term "end of heating" means that when the furnace is heated, it means that the steel sheet is taken out from the heating furnace, and when the electric heating or the induction heating is performed, it means that the electric current is ended. By setting the heating time to 3 minutes or longer, the distribution of Mn between the ferrite iron and the Worthite iron can be promoted, and the Mn concentration of the Worthite iron can be further promoted, so that decarburization can be more reliably suppressed. Therefore, the area ratio of the ferrite iron in the surface layer portion of the steel sheet member is likely to be 1.20 times or less the area ratio of the ferrite iron in the inner layer portion. By setting the heating time to 10 minutes or less, the steel structure of the steel sheet member can be made finer, so that the impact resistance of the steel sheet member can be further improved.

(Mn concentration in Worthite iron: 1.20 times or more of Mn concentration in fertilized iron)

The Mn concentration in the Vostian iron was set to 1.2 times or more of the Mn concentration in the ferrite iron until the end of the heating. By setting the Mn concentration in the Worthite iron to 1.2 times or more the Mn concentration in the ferrite iron, the Worthite iron can be made more stable, and decarburization is less likely to occur when hot pressing is performed. When the Mn concentration in the Worthite iron is not 1.2 times or more the Mn concentration in the ferrite iron, that is, at the end of the heating, the Mn concentration in the Worth iron is less than 1.2 times the Mn concentration in the ferrite iron, which is insufficient. By promoting the distribution of Mn between the ferrite iron and the Worthite iron, the Worth iron is more easily decomposed, and it is easier to decarburize during the period from the end of heating to the start of hot pressing when the steel sheet is exposed to the atmosphere. Therefore, the Mn concentration in the Worthite iron was set to 1.2 times or more of the Mn concentration in the ferrite iron until the end of the heating. The upper limit of the ratio is not specified, but it should not exceed 3.0. Further, the Mn concentration in the Worthite iron and the Mn concentration in the ferrite iron can be adjusted by using the chemical composition of the hot-pressed steel sheet, the steel structure, and the heating conditions. For example, in the above, by heating the heating time in the temperature range of 720 ° C or more and Ac ₃ or less, the Mn concentration of the Worthite iron can be promoted.

(In the period from the end of heating to the start of hot pressing, the amount of C reduction on the surface of the steel sheet for hot pressing: less than 0.0005%)

If the amount of C reduction on the surface of the hot-pressed steel sheet during this period is 0.0005% or more, the area ratio of the surface of the steel sheet member to the surface of the steel sheet member may not be the area of the ferrite iron in the inner layer due to the effect of decarburization. The rate is 1.20 times or less. Therefore, the steel sheet member cannot obtain sufficient toughness. Therefore, the C reduction amount is set to less than 0.0005%. The amount of C reduction can be measured, for example, by using a glow discharge spectroscope (GDS) or an electron probe micro analyzer (EPMA). That is, when the surface analysis of the hot-pressed steel sheet is performed at the end of the heating and at the start of the hot pressing, and the result is compared, the amount of C reduction can be obtained.

The method of adjusting the amount of C reduction is not particularly limited. For example, during the period from the extraction of the heating device such as the heating furnace used for heating to the introduction of the hot pressing device, it is exposed to the atmosphere, and the time is preferably as short as possible, and the longest is preferably less than 15 seconds. More preferably, it is less than 10 seconds. The reason is that if the time is more than 15 seconds, decarburization will occur, resulting in the surface layer of the steel plate member. The area of the fertilized iron area increased.

This time adjustment series can be carried out, for example, by adjusting the conveyance time from the extraction of the heating device to the transfer of the press die of the heated press device.

(average cooling rate up to the Ms point: 10 ° C / sec or more and 500 ° C / sec or less)

After heating, hot pressing is performed, and cooling is performed to an Ms point at an average cooling rate of 10 ° C /sec or more and 500 ° C / sec or less. When the average cooling rate is less than 10 ° C / sec, the diffusion-type metamorphosis such as the toughening iron metamorphosis is excessively performed, and the area ratio of the granulated iron in the reinforced phase cannot be ensured, and it is difficult to set the tensile strength of the steel sheet member to 980 MPa or more. Therefore, the average cooling rate is set to be 10 ° C / sec or more. If the average cooling rate exceeds 500 ° C / sec, it is extremely difficult to maintain the soaking of the member, resulting in unstable strength. Therefore, the average cooling rate is set to be 500 ° C / sec or less.

Further, in this cooling, after the temperature reaches 400 ° C, the heat generation due to the phase change state tends to become extremely large. Therefore, when the cooling in the low temperature range of less than 400 ° C is carried out in the same manner as the cooling in the temperature range of 400 ° C or higher, a sufficient average cooling rate cannot be ensured. Therefore, cooling from 400 ° C to the Ms point is preferably carried out more strongly than cooling up to 400 ° C. For example, the following method is preferred.

In general, the hot-pressing cooling system is formed by previously forming a steel mold used for forming a heated steel sheet at a normal temperature or a temperature of about 10 ° C, and bringing the steel sheet into contact with the mold. Therefore, the average cooling rate can be controlled by, for example, a change in heat capacity derived from a change in the size of the mold. By Changing the material of the mold to a dissimilar metal (such as Cu) can also control the average cooling rate. The average cooling rate can also be controlled by using a water-cooled mold and varying the amount of cooling water flowing through the mold. A plurality of grooves are formed in the mold in advance, and the average cooling rate can be controlled by circulating water in the grooves during hot pressing. The hot press is pulled up during the hot pressing, and the average cooling rate can also be controlled by circulating water during this period. The average cooling rate can also be controlled by adjusting the mold gap to change the contact area between the mold and the steel sheet.

The method of increasing the cooling rate from thereafter on at about 400 ° C can be, for example, the following three types.

(a) Immediately after reaching 400 ° C, the steel sheet was moved to a mold having a different heat capacity or a mold at room temperature.

(b) Using a water-cooled mold, the amount of water flowing in the mold is increased just after reaching 400 °C.

(c) Immediately after reaching 400 ° C, water was passed between the mold and the steel sheet. The method can also increase the amount of water by mixing the temperature, and increase the cooling rate.

The form of hot pressing of the present embodiment is not particularly limited. The forming form can be, for example, bending, deep drawing, stretch forming, reaming, and flange forming. The molding form may be appropriately selected in accordance with the type of the target steel sheet member. Representative examples of the steel sheet member include, for example, a door guard bar and a bumper reinforcement which are reinforcing parts for automobiles. Further, it is lifted before the steel sheet can be cooled at the same time as or immediately after the completion of the forming, and the thermoforming is not limited to hot pressing. For example, hot forming can also be performed by roll forming.

By performing such a series of the above-mentioned predetermined hot-pressed steel sheets The steel sheet member of the present embodiment can be produced by the treatment. That is, a hot-pressed steel sheet member having a desired steel structure, a tensile strength of 980 MPa, and excellent ductility and toughness can be obtained.

For example, the ductility can be evaluated by the total elongation (EL) of the tensile test. In the present embodiment, the total elongation of the tensile test is preferably 12% or more. The total elongation is better than 14%.

Bead blasting can also be carried out after hot pressing and cooling. The scale can be removed by bead blasting. Since the bead blasting treatment also has an effect of introducing compressive stress on the surface of the steel sheet member, the effect of suppressing delayed fracture and improving fatigue strength can be obtained.

In the method of producing the steel sheet member, when the hot-pressing system is not subjected to the pre-forming, the hot-pressed steel sheet is heated to a temperature range of 720 ° C or more and Ac ₃ or less, and is generated to a certain extent. Only after metamorphosis is implemented. Therefore, the mechanical properties of the steel sheet for hot pressing at room temperature before heating are not important. Therefore, for the steel sheet for hot pressing, for example, a hot-rolled steel sheet, a cold-rolled steel sheet, a plated steel sheet, or the like can be used. The hot-rolled steel sheet may be, for example, a multiphase structure having ferrite iron and a ferritic iron, and a spheroidizing annealing at a temperature of 650 ° C or higher and 700 ° C or lower, and containing spheroidized swarovski carbon iron. The cold rolled steel sheet can be, for example, a fully hard material and an annealed material. The plated steel sheet may be, for example, an aluminum-based plated steel sheet or a zinc-based plated steel sheet. These manufacturing methods are not particularly limited. Further, in the case of using a hot-rolled steel sheet or a full-hard material, if the steel structure is a multiphase structure of ferrite iron and ferrite, it is easier to further promote the distribution of Mn in the heating by hot pressing. Further, when an annealing material is used, if the annealing temperature is set to the two-phase temperature range of the ferrite iron and the Worth iron, it is easier to further promote the distribution of Mn in the heating of the hot press.

The steel sheet member of the present embodiment can also be produced by hot pressing accompanying preforming. For example, in a range of conditions for satisfying the above-described heating, decarburization treatment, and cooling, the hot-pressed steel sheet is pre-formed by press working using a predetermined-shaped mold, and then placed in a mold of the same shape, and pressed and pressed to perform rapid cooling. It is also possible to manufacture a hot-pressed steel sheet member. In this case, the type and steel structure of the steel sheet for hot pressing are not limited. However, in order to facilitate preforming, it is preferable to use a steel sheet having as low a strength as possible and ductility. For example, the tensile strength is preferably 700 MPa or less. The coiling temperature of the hot-rolled steel sheet after hot rolling is preferably set to 450 ° C or more in order to obtain a soft steel sheet, and it is preferably set to 700 ° C or less in order to reduce the scale loss. In order to obtain a soft steel sheet, it is preferable to anneal the cold-rolled steel sheet, and the annealing temperature is preferably at a temperature of Ac ₁ point or more and an Ac ₃ point or lower. Further, the average cooling rate up to room temperature after annealing is preferably below the upper critical cooling rate.

It is to be noted that the above-described embodiments are merely examples of the specific embodiments of the present invention, and the technical scope of the present invention is not limited by the above. That is, the present invention can be implemented in various forms without departing from the technical idea or main features of the escape.

[Examples]

Next, an experiment performed by the inventor of the present invention will be described. In this experiment, first, seven types of steel materials having the chemical compositions shown in Table 1 were used, and 24 kinds of steel sheets for hot pressing having the steel structure shown in Table 2 (steel sheets provided for heat treatment) were produced. In addition, the remainder of each steel material is Fe and impurities. In addition, the combined area ratio of ferrite iron and ferritic carbon iron in Table 2 is also included in the Bora iron. Area ratio of fertilized iron and ferritic carbon iron. In the production of a steel sheet for heat treatment, the steel stock melted in the laboratory is first heated at 1250 ° C for 30 minutes, and then hot rolled at a temperature of 900 ° C or higher until the thickness becomes 2.6 mm. Next, it was cooled to 600 ° C by spraying with water, placed in a furnace, and kept at 600 ° C for 30 minutes. Then, gradually cool to room temperature at 20 ° C / hour. This cooling process simulates the coiling step of hot rolling. The steel structure of the hot-rolled steel sheet obtained according to this is a multiphase structure of ferrite iron and Borne iron.

Next, except for the sample material No. 21, the remaining portion was removed from the hot-rolled steel sheet by pickling, and then the hot-rolled steel sheet was cold-rolled until the thickness became 1.2 mm. On the other hand, the sample material No. 6 was subjected to cold rolling, and the cold-rolled steel sheet obtained by cold rolling was subjected to annealing in the single phase of the Iwostian iron. Further, after the cold rolling, the sample material No. 19 was subjected to annealing in a duplex phase of the cold-rolled steel sheet obtained by cold rolling and the ferrite iron and the Vostian iron, and the plating amount per one-side plating was 60 g/ Melt galvanizing of m ² .

The sample material No. 21 was subjected to pickling to remove scale from the hot-rolled steel sheet, and then subjected to spheroidizing annealing. This spheroidizing annealing system held the hot rolled steel sheet at 650 ° C for 5 hours.

After the steel sheet subjected to the heat treatment was produced, the steel sheet was heated in a gas heating furnace having an air-fuel ratio of 0.85 in accordance with the conditions shown in Table 2. The "heating time" in Table 2 indicates the time from when the steel sheet temperature is reached to 720 ° C after the steel sheet is placed in the gas heating furnace to when the steel sheet is taken out from the gas heating furnace. In addition, the "heating temperature" in Table 2 does not mean the temperature of the steel sheet, but the temperature in the gas heating furnace. Next, the steel sheet was taken out from the gas heating furnace, air-cooled was performed for various times, and hot pressing of the steel sheet was performed, and the steel sheet was cooled. A flat steel mold is used for hot pressing. That is, no shaping is performed. When the steel sheet was cooled, the steel sheet was cooled to an Ms point at an average cooling rate shown in Table 2 in a state where the steel sheet was brought into contact with the mold, and further cooled to 150 ° C, and then taken out from the mold and allowed to cool. When cooling to 150 ° C, the periphery of the mold was cooled by cooling water until the steel sheet temperature became 150 ° C, or a room temperature mold was prepared in advance, and the steel sheet was held in the mold until the steel sheet temperature became 150 ° C. The average cooling rate was measured up to 150 ° C, and a thermocouple was attached to the steel plate in advance, and the temperature history was analyzed. According to this, 24 kinds of test materials (plates for test bodies) were produced. Hereinafter, the sample material (the steel sheet for the test piece) is referred to as a "hot pressed steel sheet".

[Table 1]

[Table 2]

After obtaining the hot-pressed steel sheet, the area ratio of the ferrite grain in the surface layer portion, the area ratio of the ferrite grain in the inner layer portion, and the area ratio of the granulated iron in the inner layer portion were obtained for the steel sheets. These area ratios are calculated by performing an optical microscope observation image or an image observation of an electron microscope observation image by an orthogonal cross section in the rolling direction and an orthogonal cross section in the sheet width direction (orthogonal direction of the rolling direction). The average value of the value. The steel structure observation of the surface layer portion was observed from the surface of the steel sheet to a depth of 15 μm. The steel structure observation of the inner layer was observed at a position of 1/4 depth. Table 3 shows the ratio of the area ratio of the fertilized iron in the surface layer to the ratio of the area of the ferrite iron in the inner layer, the area ratio of the ferrite in the inner layer, and the area ratio of the granulated iron in the field.

Furthermore, the mechanical properties of the hot-pressed steel sheets were also investigated. The survey was conducted to measure tensile strength (TS), total elongation (EL), and toughness evaluation. The tensile strength and the total elongation were measured by taking a JIS No. 5 tensile test piece from the vertical direction of each of the steel sheets in the rolling direction, and performing a tensile test. The toughness evaluation was carried out at 0 ° C and the Charpy impact test was carried out, and the brittle fracture rate was measured. The Charpy impact test sample was prepared by taking four V-notch test pieces from each steel sheet, and the layers were laminated and screwed. The results of these surveys are also shown in Table 3. Further, although the hot-pressed steel sheet was subjected to hot pressing using a flat steel mold, it was not formed at the time of hot pressing. However, the mechanical properties of the hot-pressed steel sheet reflect the mechanical properties of the hot-pressed steel sheet member when subjected to the same thermal experience as the experimental hot press during forming. That is, regardless of whether or not the forming is performed at the time of hot pressing, as long as the heat history is substantially the same, the mechanical properties thereafter are substantially the same.

Further, an electron beam microanalyzer (EPMA) was used to measure the Mn concentration in the ferrite iron immediately after heating and the Mn concentration in the Worthite iron. this The measurement was carried out by maintaining the steel structure immediately after heating, and heating was carried out in a gas heating furnace under the conditions shown in Table 2, and immediately after being taken out from the gas heating furnace, it was cooled by water. With this water cooling, the Worthfield iron will be metamorphosed into a granulated iron without diffusion, while the ferrite iron remains intact. Therefore, the Mn concentration in the ferrite iron after water cooling is consistent with the Mn concentration in the ferrite iron immediately after heating, and the Mn concentration in the granulated iron after the water cooling is in the Worthite iron immediately after heating. The Mn concentration was consistent. Then, the Mn concentration ratio (Mn ratio) in the ferrite iron was calculated for the Mn concentration in the Worth iron. The results are also shown in Table 3.

[table 3]

As shown in Table 3, sample materials No. 1, No. 3, No. 5, No. 8 to No. 10, No. 12, No. 13, No. 15, No. 17 to No. 19, No. .21 and No. 22 are examples of the present invention and exhibit excellent ductility and toughness. That is, a tensile strength (TS) of 980 MPa or more, a total elongation (EL) of 12% or more, and a brittle fracture rate of 10% or less can be obtained.

On the other hand, in the sample material No. 2, since the chemical composition exceeded the range of the present invention, the tensile strength of 980 MPa or more could not be obtained after cooling (after quenching). The test materials No. 4 and No. 7 are manufactured outside the scope of the present invention, and the hot-rolled steel structure also exceeds the scope of the present invention, so that the required steel structure cannot be obtained, and after cooling (after quenching) A tensile strength of 980 MPa or more was obtained. The sample material No. 6 is because the steel structure of the steel sheet which is subjected to the heat treatment exceeds the range of the present invention, so that excessive decarburization occurs. That is, the manufacturing conditions are beyond the scope of the present invention. Moreover, the hot pressed steel structure also exceeds the scope of the present invention. Therefore, the required steel structure cannot be obtained, and the brittle fracture rate exceeds 10%. The sample material No. 11 had a total elongation of less than 12% because the chemical composition exceeded the range of the present invention. The sample material No. 14 exceeded the scope of the present invention because the manufacturing conditions exceeded, and the steel structure after the hot pressing exceeded the range of the present invention, so that the total elongation was less than 12%. The sample material No. 16 exceeded the scope of the present invention because the manufacturing conditions exceeded, and the steel structure after the hot pressing exceeded the range of the present invention, so that the desired steel structure could not be obtained, and the brittle fracture rate exceeded 10%. Since the chemical composition No. 20 exceeded the range of the present invention, the tensile strength of 980 MPa or more could not be obtained after cooling (after quenching). Further, since the steel structure of the steel sheet which is subjected to the heat treatment exceeds the range of the present invention, excessive decarburization occurs. That is, the manufacturing conditions are over the present Outside the scope of the invention. Therefore, the required steel structure cannot be obtained, and the brittle fracture rate exceeds 10%. The sample material No. 23 caused excessive decarburization because the steel structure of the steel sheet for which heat treatment was provided exceeded the range of the present invention. That is, the manufacturing conditions are beyond the scope of the present invention. Therefore, the required steel structure cannot be obtained, and the brittle fracture rate exceeds 10%. In the sample material No. 24, since the steel sheet subjected to the heat treatment was provided, the Mn concentration in the swarf carbon iron exceeded the range of the present invention, so that excessive decarburization occurred. That is, the manufacturing conditions are beyond the scope of the present invention. Therefore, the required steel structure cannot be obtained, and the brittle fracture rate exceeds 10%.

Industrial availability

The present invention can be utilized, for example, in the manufacturing industry and related industries such as automobile body structure parts that emphasize excellent ductility and toughness. The present invention can also be utilized in the manufacturing industry of other mechanical structural parts, related industries, and the like.

Claims (34)

A hot-pressed steel sheet member having the chemical composition shown below: C: 0.10% to 0.34%, Si: 0.5% to 2.0%, Mn: 1.0% to 3.0%, sol. Al: 0.001% by mass% 1.0%, P: 0.05% or less, S: 0.01% or less, N: 0.01% or less, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 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 remaining portion: Fe and impurities; and the area ratio of the ferrite iron in the surface layer portion from the surface to the depth of 15 μm is 1.20 times or less of the area ratio of the ferrite iron in the inner layer portion, and the inner layer portion is other than the surface layer portion. The inner layer portion has a ratio of % by area: ferrite iron: 10% to 70%, 麻田散铁: 30% to 90%, ferrite iron and 麻田散铁 total area ratio: 90% to 100% steel In the inner layer portion, the Mn concentration in the granulated iron is 1.20 times or more of the Mn concentration in the ferrite iron; and the tensile strength is 980 MPa or more. The hot-pressed steel sheet member according to claim 1, wherein the chemical composition is one or more selected from the group consisting of: Ti: 0.003% to 0.20%, Nb: 0.003, by mass%. %~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%. The hot-pressed steel sheet member according to claim 1 or 2, wherein the chemical composition is one or more selected from the group consisting of: Ca: 0.0003% to 0.01%, Mg, by mass% :0.0003%~0.01%, REM: 0.0003% to 0.01%, and Zr: 0.0003% to 0.01%. The hot-pressed steel sheet member according to claim 1 or 2, wherein the chemical composition is B: 0.0003% to 0.01% by mass%. The hot-pressed steel sheet member according to claim 3, wherein the chemical composition is B: 0.0003% to 0.01% by mass%. The hot-pressed steel sheet member according to claim 1 or 2, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. The hot-pressed steel sheet member according to claim 3, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. The hot-pressed steel sheet member according to claim 4, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. The hot-pressed steel sheet member according to claim 5, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. A steel sheet for hot pressing has the chemical composition shown below: C: 0.10% to 0.34%, Si: 0.5% to 2.0%, Mn: 1.0% to 3.0%, sol. Al: 0.001% by mass% 1.0% or less, P: 0.05% or less, S: 0.01% or less, N: 0.01% or less, Ti: 0% to 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%, remaining part: Fe And impurities; and having the following steel structure: containing ferrite iron and ferritic carbon iron, and the total area ratio of the toughened iron and the granulated iron is 0% to 10%, and the area ratio of the ferritic carbon iron is 1% or more. The Mn concentration in Xueming carbon iron is 5% or more. The hot-pressing steel sheet according to claim 10, wherein the chemical composition is one or more selected from the group consisting of Ti: 0.003% to 0.20%, and Nb: 0.003. %~0.20%, V: 0.003%~0.20%, Cr: 0.005%~1.0%, Mo: 0.005%~1.0%, Cu: 0.005% to 1.0%, and Ni: 0.005% to 1.0%. The hot-pressing steel sheet according to claim 10, wherein the chemical composition is one or more selected from the group consisting of: Ca: 0.0003% to 0.01%, Mg, by mass% : 0.0003% to 0.01%, REM: 0.0003% to 0.01%, and Zr: 0.0003% to 0.01%. The hot-pressed steel sheet according to claim 10 or 11, wherein the chemical composition contains B: 0.0003% to 0.01% by mass%. The steel sheet for hot pressing according to claim 12, wherein the chemical composition is B: 0.0003% to 0.01% by mass%. The steel sheet for hot pressing according to claim 10 or 11, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. The steel sheet for hot pressing according to claim 12, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. The hot-pressing steel sheet according to claim 13, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. The steel sheet for hot pressing according to claim 14, wherein the chemical composition contains Bi: 0.0003% to 0.01% by mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a hot-pressed steel sheet according to claim 10 or 11 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worthite iron as a ferrite iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the heat In the period in which the pressure is started, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a hot-pressed steel sheet according to claim 12 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worth iron as fat iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the start of the hot pressing In the period of time, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a steel sheet for hot pressing according to claim 13 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worth iron as fat iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the start of the hot pressing In the period of time, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a steel sheet for hot pressing according to claim 14 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worth iron as fat iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the start of the hot pressing In the period of time, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a hot-pressed steel sheet according to claim 15 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worth iron as fat iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the start of the hot pressing In the period of time, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a steel sheet for hot pressing according to claim 16 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worth iron as fat iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the start of the hot pressing In the period of time, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a hot-pressed steel sheet according to claim 17 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worth iron as fat iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the start of the hot pressing In the period of time, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. A method for producing a hot-pressed steel sheet member, comprising: heating a hot-pressed steel sheet according to claim 18 to a temperature range of 720 ° C or more and Ac ₃ or less, and setting the Mn concentration in the Worth iron as fat iron a step of 1.20 times or more of the Mn concentration; and a step of performing hot pressing after the heating and cooling to an Ms point at an average cooling rate of 10 ° C / sec to 500 ° C / sec; from the end of the heating to the start of the hot pressing In the period of time, the amount of C reduction on the surface of the hot-pressed steel sheet is set to less than 0.0005 mass%. The method for producing a hot-pressed steel sheet member according to claim 19, wherein the time period from the end of the heating to the start of the hot pressing is that the hot-pressed steel sheet is exposed to the atmosphere for less than 15 seconds. In the method of producing a hot-pressed steel sheet member according to claim 20, the time during which the hot-pressed steel sheet is exposed to the atmosphere is set to be less than 15 seconds from the end of the heating to the start of the hot pressing. The method for producing a hot-pressed steel sheet member according to claim 21, wherein the time during which the hot-pressed steel sheet is exposed to the atmosphere is less than 15 seconds from the end of the heating to the start of the hot pressing. The method for producing a hot-pressed steel sheet member according to claim 22, wherein the hot-pressed steel sheet is used from the end of the heating to the start of the hot pressing The time of exposure to the atmosphere is set to less than 15 seconds. The method for producing a hot-pressed steel sheet member according to claim 23, wherein the time during which the hot-pressed steel sheet is exposed to the atmosphere is less than 15 seconds from the end of the heating to the start of the hot pressing. The method for producing a hot-pressed steel sheet member according to claim 24, wherein the time period from the end of the heating to the start of the hot pressing is that the hot-pressed steel sheet is exposed to the atmosphere for less than 15 seconds. The method for producing a hot-pressed steel sheet member according to claim 25, wherein the time during which the hot-pressed steel sheet is exposed to the atmosphere is less than 15 seconds from the end of the heating to the start of the hot pressing. The method for producing a hot-pressed steel sheet member according to claim 26, wherein the time during which the hot-pressed steel sheet is exposed to the atmosphere is less than 15 seconds from the end of the heating to the start of the hot pressing.