JP6947335B1 - Steel plate for hot stamping and hot stamping molded product - Google Patents

Abstract

The steel plate for hot stamping and the hot stamped body have Ti: 0.005 to 0.100%, Nb: 0.015 to 0.100%, V: 0.005 to 0.100%, and Zr: 0. It has a predetermined chemical composition containing one or more of the group consisting of .005 to 0.100%, and the Sn concentration in the surface layer region is at the position of 1/4 of the plate thickness in the plate thickness direction from the surface. It is 0.99 to 1.10 times the Sn concentration.

Description

The present invention relates to a hot stamping steel sheet and a hot stamping molded product. Specifically, the present invention relates to a hot stamping steel plate and a hot stamping molded body having excellent deformation characteristics and corrosion resistance at the time of a collision, which contribute to weight reduction of a vehicle body and improvement of collision safety.
The present application claims priority based on Japanese Patent Application No. 2019-205439 filed in Japan on November 13, 2019, the contents of which are incorporated herein by reference.

In recent years, the application of high-strength steel plates to vehicle body parts used in automobiles has been expanding due to the demand for weight reduction of vehicle bodies and improvement of collision safety. Since the vehicle body parts are molded by press molding, improvement of press moldability, particularly improvement of shape freezing property is an issue. Therefore, the hot stamping method is attracting attention as a method for manufacturing high-strength vehicle body parts having excellent shape accuracy.

Further, in recent years, a technique for applying a tailored blank to a hot stamping method has been studied. The tailored blank is made by joining steel plates having different plate thicknesses, chemical compositions, metal structures, etc. by welding, and the characteristics in one joined blank can be partially changed. For example, the impact can be absorbed by increasing the strength of one portion to suppress deformation and reducing the strength of another portion to deform.

As a technique for applying a tailored blank to the hot stamping method, a tailored blank in which a steel plate having low strength after hot stamping (low strength material) and a steel plate having high strength after hot stamping (high strength material) are joined by welding is used. There is a technique to use. As the steel sheet having high strength after hot stamping, for example, a steel sheet as shown in Patent Document 1 can be used. For a steel sheet having low strength after hot stamping, the chemical composition of the steel may be adjusted so that the strength becomes low after cooling the mold by hot stamping.

Parts with low-strength parts manufactured by hot stamping tailored blanks are often used in the lower part of the center pillar. Corrosion resistance is required for the parts used in the lower part of the center pillar. In the prior art, in order to obtain corrosion resistance in the above-mentioned parts, auxiliary materials such as wax and sealer are used to cover the end face which is easily corroded to ensure the corrosion resistance. However, there are restrictions on the shape of parts in order to apply auxiliary materials. In addition, depending on the shape of the parts, it may not be possible to introduce auxiliary materials, and a part of the vehicle body may be corroded.

In general, it is known that it is effective to include Sn in a steel sheet in order to improve corrosion resistance. However, as described in Patent Documents 2 and 3, it is known that since Sn is an easily oxidizing element, it is concentrated on the surface layer of the steel sheet. When Sn is concentrated on the surface layer of the steel sheet, the corrosion resistance of the surface layer of the steel sheet is improved. However, when the corrosion pits are formed deeper than the Sn-concentrated layer on the surface layer, the effect of suppressing corrosion by Sn may not be obtained. Further, when exposed to a corrosive environment for a long time, the corroded pits may develop to the deep part of the steel sheet, and a portion where the plate thickness is greatly reduced may occur.

Japanese Patent Application Laid-Open No. 2004-197213 Japanese Patent Application Laid-Open No. 2012-255184 Japanese Patent Application Laid-Open No. 2002-206139

In view of the above problems, the present invention provides a hot stamped body capable of obtaining excellent corrosion resistance even when exposed to a corrosive environment for a long time, and a hot stamping steel sheet capable of obtaining the hot stamped body. The purpose is to do. The present invention also provides a hot stamped product having the strength and ductility desired as a low-strength material for a tailored blank to be hot stamped, and a steel plate for hot stamping capable of obtaining the hot stamped product. The purpose.

As described above, even if Sn is contained in the steel sheet in order to improve the corrosion resistance, Sn is concentrated on the surface layer of the steel sheet, and the corrosion pits are more than the Sn-concentrated layer on the surface layer due to exposure to a corrosive environment for a long time. When it is deeply formed, the effect of suppressing corrosion by Sn may not be obtained. The reason is not clear, but when a Sn-enriched layer is formed, there is a possibility that a Sn-deficient layer is formed in the range from the depth position directly under the Sn-enriched layer to the depth position of about 20 μm from the surface layer. Therefore, it is considered that the progress of corrosion is promoted when the corrosion pit reaches the Sn-deficient layer.

In order to uniformly disperse Sn in a steel sheet and obtain the effect of suppressing corrosion by Sn even when exposed to a corrosive environment for a long time, the present inventors have a predetermined temperature range during hot rolling. It was found that it is effective to suppress the oxidation time in. Specifically, the present inventors have found that it is effective to suppress the oxidation time in the temperature range of 1050 to 1150 ° C., which corresponds to the temperature range of rough rolling during hot rolling.

Since Sn is incorporated into the scale during oxidation at a high temperature of 1200 ° C. or higher, it is unlikely that the surface of the steel sheet will be thickened. On the other hand, Sn is concentrated on the ground iron side of the interface between the scale and the base iron during oxidation in the temperature range of 105 to 1150 ° C. Therefore, in order not to concentrate Sn on the surface layer of the steel sheet, it is effective not to oxidize for a long time in the above temperature range.

Descaling is performed before each hot rolling pass. Therefore, in order to control the oxidation time, the present inventors can control the time between rolling (time between passes) in the temperature range of 105 to 1150 ° C. for hot rolling to oxidize. It was found to be effective for controlling time. Then, the present inventors have found that in hot rolling, the surface layer concentration of Sn can be suppressed by setting the maximum pass-to-pass time in the temperature range of 1050 to 1150 ° C. to 120 seconds or less. At the same time, the present inventors have also found that descaling is effective in the temperature range of 1050-1150 ° C.

The gist of the present invention made based on the above findings is as follows.
(1) The steel sheet for hot stamping according to one aspect of the present invention has a chemical composition of% by mass.
C: 0.035 to 0.100%,
Si: 0.005 to 0.500%,
Mn: 0.10 to 2.00%,
Al: 0.010 to 0.080%,
Sn: 0.005 to 0.200%,
P: 0.030% or less,
S: 0.0100% or less,
N: 0.0100% or less,
Cr: 0-1.00%,
Mo: 0-1.00%, and B: 0-0.0050%
Containing and
Ti: 0.005 to 0.100%,
Nb: 0.015-0.100%,
V: 0.005 to 0.100%, and Zr: 0.005 to 0.100%
Containing one or more of the group consisting of
Balance comprising a steel ing Fe and impurities,
The Sn concentration in the surface layer region, which is a region 5 μm in the plate thickness direction from the surface of the steel plate to 30 μm in the plate thickness direction from the surface, is centered on a position 1/4 of the plate thickness from the surface. It is 0.99 to 1.10 times the Sn concentration in the region of 20 μm in the thickness direction (the region of 40 μm in the plate thickness direction when the front and back surfaces are combined).
(2) The hot stamping steel sheet according to (1) above has a chemical composition of% by mass.
One or two of Cr: 0.005 to 1.00% and Mo: 0.005 to 1.00% may be contained.
(3) The hot stamping steel sheet according to the above (1) or (2) may contain B: 0.0002 to 0.0050% in terms of the chemical composition in mass%.
(4) The hot stamping steel sheet according to any one of (1) to (3) above may have a plating layer on the surface.
(5) In the hot stamping steel sheet according to (4) above, the plating layer may be an Al-based plating layer.
Hot stamping molded body according to another aspect of the (6) The present invention (1) to comprise a steel sheet to have a chemical composition according to any one of (3), the plate thickness direction from the surface of the steel sheet The Sn concentration in the surface layer region, which is the region from the 5 μm position to the 30 μm position in the plate thickness direction from the surface, is 20 μm in the plate thickness direction (front and back) centered on the position of 1/4 of the plate thickness from the surface. In total, it may be 0.99 to 1.10 times the Sn concentration in the region of 40 μm in the plate thickness direction).
(7) The hot stamped molded article according to (6) above may have a plating layer on the surface.
(8) In the hot stamp molded product according to (7) above, the plating layer is an Al-based plating layer, and the Sn concentration in the diffusion layer existing in the Al-based plating layer is in the surface layer region of the steel sheet. It may be 1.05 times or more the Sn concentration.

According to the above aspect of the present invention, it has the strength and ductility desired as a low-strength material for hot stamped tailored blanks, and excellent corrosion resistance can be obtained even when exposed to a corrosive environment for a long time. It is possible to provide a hot stamped molded product, and a hot stamping steel plate from which the hot stamped molded product can be obtained.

According to the above aspect of the present invention, a hot stamped molded product having excellent deformation characteristics and corrosion resistance at the time of a collision can be obtained, which contributes to weight reduction of an automobile body and improvement of collision safety.

Hereinafter, the hot stamping steel plate and the hot stamping compact according to the present embodiment will be described in detail. First, the reason for limiting the chemical composition of the hot stamping steel sheet according to the present embodiment will be described.

In addition, the lower limit value and the upper limit value are included in the numerical limitation range described below with "~" in between. Numerical values indicated as "less than" and "greater than" do not include the values in the numerical range. All% of the chemical composition indicates mass%.

[Steel plate for hot stamping]
The steel plate for hot stamping according to the present embodiment has a chemical composition of mass%, C: 0.035 to 0.100%, Si: 0.005 to 0.500%, Mn: 0.10 to 2.00. %, Al: 0.010 to 0.080%, Sn: 0.005 to 0.200%, P: 0.030% or less, S: 0.0100% or less, N: 0.0100% or less, Cr: It contains 0 to 1.00%, Mo: 0 to 1.00% and B: 0 to 0.0050%, and Ti: 0.005 to 0.100%, Nb: 0.015 to 0.100. %, V: 0.005 to 0.100% and Zr: 0.005 to 0.100%, and one or more of the group is contained, and the balance is composed of Fe and impurities.
Hereinafter, each element will be described in detail.

C: 0.035 to 0.100%
C is an element that greatly affects the strength of the hot stamping steel sheet (hot stamp molded product) after hot stamping. When the C content is low, the strength of the hot stamped molded product is low, and the amount of energy absorbed at the time of collision is low. Therefore, the C content is set to 0.035% or more. Preferably, it is 0.040% or more and 0.045% or more.
On the other hand, if the C content is high, the strength of the hot stamped molded product becomes too high, and cracks may occur during deformation at the time of collision. Therefore, the C content is set to 0.100% or less. Preferably, it is 0.090% or less and 0.085% or less.

Si: 0.005 to 0.500%
Si is a solid solution strengthened alloy element and is an element necessary for ensuring the strength of a hot stamped molded product. When the Si content is extremely low, this effect cannot be obtained, so the Si content is set to 0.005% or more. Preferably, it is 0.010% or more and 0.015% or more.
On the other hand, if the Si content exceeds 0.500%, a surface scale problem arises. That is, after pickling the scale generated during hot rolling, a pattern due to surface unevenness is generated, and the surface appearance becomes inferior. Further, when the surface of the steel sheet is plated, the plating property deteriorates when the Si content is high. Therefore, the Si content is set to 0.500% or less. Preferably, it is 0.480% or less, 0.450% or less, and 0.400% or less.

Mn: 0.10 to 2.00%
Mn is an element that improves the strength of the hot stamped compact and the hardenability of steel. If the Mn content is less than 0.10%, sufficient strength cannot be obtained in the hot stamped molded product. Therefore, the Mn content is set to 0.10% or more. Preferably, it is 0.20% or more, 0.40% or more, 0.70% or more, and 1.00% or more.
On the other hand, even if Mn is contained in excess of 2.00%, the above effect is saturated, so the Mn content is set to 2.00% or less. Preferably, it is 1.80% or less and 1.60% or less.

Al: 0.010 to 0.080%
Al is an element used as a deoxidizing material for molten steel. The Al content is 0.010% or more in order to sufficiently deoxidize the molten steel. Preferably, it is 0.020% or more and 0.030% or more.
On the other hand, when the Al content exceeds 0.080%, a large amount of non-metal inclusions are formed, and surface defects are likely to occur in the product. Therefore, the Al content is set to 0.080% or less. Preferably, it is 0.070% or less and 0.060% or less.

Sn: 0.005 to 0.200%
Sn is an element necessary for improving the corrosion resistance of the hot stamped molded product. In order to obtain this effect, the Sn content is set to 0.005% or more. Preferably, it is 0.015% or more, 0.030% or more, 0.045% or more, and 0.060% or more.
On the other hand, even if Sn of more than 0.200% is contained, the above effect is saturated, so the Sn content is set to 0.200% or less. Preferably, it is 0.180% or less and 0.160% or less.

P: 0.030% or less P is a solid solution strengthened alloy element, which is a useful element for improving the strength of a hot stamped article. However, if the P content exceeds 0.030%, the weld crackability and toughness are adversely affected. Therefore, the P content is limited to 0.030% or less. Preferably, it is 0.020% or less.
The lower limit of the P content is not particularly specified, but the P content may be 0.001% or more because the refining cost increases if the P content is excessively reduced.

S: 0.0100% or less S affects non-metal inclusions in the steel and deteriorates the ductility of the hot stamped compact. Therefore, the S content is limited to 0.0100% or less. Preferably, it is 0.0080% or less and 0.0050% or less.
The lower limit of the S content is not particularly specified, but the S content may be 0.0001% or more because the production cost of the desulfurization step increases if the S content is excessively reduced.

N: 0.0100% or less N is an element contained in steel as an impurity, and if the N content exceeds 0.0100%, the ductility of the hot stamped molded product may deteriorate due to the coarsening of the nitride. be. Therefore, the N content is limited to 0.100% or less. Preferably, it is 0.0080% or less and 0.0060% or less.
The lower limit of the N content is not particularly specified, but the N content may be 0.0010% or more because the manufacturing cost of the steelmaking process increases if the N content is excessively reduced.

One of the groups consisting of Ti: 0.005 to 0.100%, Nb: 0.015 to 0.100%, V: 0.005 to 0.100%, and Zr: 0.005 to 0.100%. Species or two or more species Ti, Nb, V and Zr have the effect of forming carbonitrides in steel and improving the strength of the hot stamped compact by precipitation strengthening. In order to exert this effect, one or more kinds of Ti: 0.005% or more, Nb: 0.015% or more, V: 0.005% or more and Zr: 0.005% or more are contained. Preferably, one or more of Ti: 0.010% or more, Nb: 0.020% or more, V: 0.010% or more, and Zr: 0.010% or more.
On the other hand, when the content of even one of these elements is more than 0.100%, a large amount of carbonitride is generated and the ductility of the hot stamped molded product is lowered. Therefore, the contents of Ti, Nb, V and Zr are set to 0.100% or less, respectively. Preferably, each is 0.080% or less.

The balance of the chemical composition of the hot stamping steel sheet according to the present embodiment may be Fe and impurities. Examples of impurities include elements that are unavoidably mixed from steel raw materials or scrap and / or in the steelmaking process and are allowed as long as they do not impair the characteristics of the hot stamping steel sheet according to the present embodiment.

The hot stamping steel sheet according to the present embodiment may contain the following elements as optional elements instead of a part of Fe. When the following optional elements are not contained, the content is 0%.

Cr: 0.005 to 1.00% and Mo: 0.005 to 1.00%
Cr and Mo are elements that improve the hardenability of steel and have the effect of improving the strength of the hot stamped compact, so they may be contained as necessary. In order to ensure that this effect is exhibited, it is preferable that the content of either Cr or Mn is 0.005% or more. However, if the content of either Cr or Mn exceeds 1.00%, the carbides present after hot rolling, cold rolling or annealing (including after plating) are stabilized and hot. Hardenability may be reduced by delaying the dissolution of carbides by heating during stamping. Therefore, the contents of Cr and Mo are set to 1.00% or less, respectively.

B: 0.0002 to 0.0050%
Since B has the effect of improving the hardenability during press molding (hot stamping) or cooling during press molding to improve the strength of the hot stamped product, it may be contained as necessary. In order to ensure that this effect is exhibited, the B content is preferably 0.0002% or more. However, if B is excessively contained, cracks may occur during hot rolling and the above effects may be saturated. Therefore, the B content is set to 0.0050% or less.

In addition to the elements described above, the hot stamping steel sheet according to the present embodiment may contain Ni, Cu, W, Sb, As, Ca, REM and Y. The contents of Ni, Cu and W are not particularly regulated, but the content of each of these elements is preferably 1.00% or less because the castability may be deteriorated if these elements are excessively contained. .. Elements that may be unavoidably contained, such as Sb and As, may deteriorate the ductility of the hot stamped molded product if they are excessively contained. Therefore, the total content of these elements is 0.100% or less. It is preferable to do so. Further, Ca, REM and Y may be contained for controlling the morphology of the sulfide. If these elements are excessively contained, the ductility of the hot stamping steel sheet may deteriorate. Therefore, the total content of these elements is preferably 0.01% or less.

The chemical composition of the above-mentioned hot stamping steel sheet may be measured by a general analytical method. For example, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) may be used for measurement. C and S may be measured by using the combustion-infrared absorption method, and N may be measured by using the inert gas melting-thermal conductivity method. When the hot stamping steel sheet has a plating layer on the surface, the plating layer on the surface may be removed by mechanical grinding, and then the chemical composition may be analyzed.

Sn concentration in the surface layer region: 0.99 to 1.10 times the Sn concentration at the 1/4 position of the plate thickness in the plate thickness direction from the surface When Sn is concentrated in the surface layer region of the hot stamping steel plate, the surface layer region in the initial stage of corrosion However, when the corrosion pits are formed in a region deeper than the surface layer region where Sn is concentrated due to exposure to a corrosive environment for a long time, it is difficult to obtain the effect of suppressing corrosion by Sn. Become. Therefore, the Sn concentration in the surface layer region of the steel sheet for hot stamping is the Sn concentration at the position of 1/4 of the plate thickness in the plate thickness direction from the surface of the steel plate (hereinafter, may be referred to as the Sn concentration at the position of 1/4 of the plate thickness). 0.99 to 1.10 times. The surface layer region refers to a region 5 μm in the plate thickness direction from the surface of the hot stamping steel plate to 30 μm in the plate thickness direction from the surface.

When the Sn concentration in the surface layer region is more than 1.10 times the Sn concentration at the plate thickness 1/4 position, the Sn concentration is concentrated in the surface layer region, and excellent corrosion resistance is obtained when exposed to a corrosive environment for a long time. I can't get it. Therefore, the Sn concentration in the surface layer region is 1.10 times or less the Sn concentration at the position where the plate thickness is 1/4. It is preferably 1.05 times or less.
On the other hand, if the Sn concentration in the surface layer region is less than 0.90 times the Sn concentration at the plate thickness 1/4 position, the corrosion resistance at the initial stage of corrosion is lowered, and many starting points of corrosion pits are formed, resulting in swelling of the coating film. Is not preferable because it becomes large. Therefore, the Sn concentration in the surface layer region is 0.90 times or more the Sn concentration at the position where the plate thickness is 1/4. Preferably, it is 0.95 times or more.

Method for measuring Sn concentration An electron probe microanalyzer (EPMA) is used to measure the Sn concentration.
The Sn concentration in the surface layer region is 5 μm in the thickness direction from the surface to the plate from the surface at an arbitrary position 50 mm or more away from the end face of the hot stamping steel plate (a position avoiding the end if this position cannot be measured). The Sn concentration in the region at the position of 30 μm in the thickness direction is measured.
The Sn concentration at the plate thickness 1/4 position is the Sn concentration in the region of 20 μm in the plate thickness direction (the region of 40 μm in the plate thickness direction with the front and back combined) centered on the position of 1/4 thickness from the surface. taking measurement.

As the measuring method, mapping is used, and the above-mentioned measurement is performed with a width of 50 μm in the plate surface direction to obtain the average value of the Sn concentration in the width direction in the surface layer region and the plate thickness 1/4 position. As a result, the Sn concentration in the surface layer region and the Sn concentration at the plate thickness 1/4 position are obtained. By dividing the Sn concentration of the obtained surface layer region by the Sn concentration of the plate thickness 1/4 position, it is obtained how many times the Sn concentration of the surface layer region is the Sn concentration of the plate thickness 1/4 position.

Plating layer The steel sheet for hot stamping according to the present embodiment may have a plating layer on the surface of the steel sheet for the purpose of further improving the corrosion resistance. The plating layer is, for example, an Al-based plating layer such as a hot-dip aluminum plating layer and an aluminum-zinc plating layer, a hot-dip zinc plating layer, an alloyed hot-dip zinc plating layer, an electrozinc plating layer, and a Zn-based plating layer such as a zinc nickel plating layer. Can be considered.

The plating layer may be arranged on the surface of either one of the hot stamping steel sheets, or may be arranged on both sides. The amount of adhesion is not particularly limited, but Al-based plating layer: 15 to 120 g / m ^{2 on} one side, hot-dip galvanized layer: 30 to 120 g / m ^{2 on} one side, alloyed hot-dip galvanized layer: 30 to 120 g / m ^{2 on} one side, electricity. Zinc-plated layer and zinc-nickel-plated layer: preferably 5 to ^{100 g / m 2 on one side.}

When a hot stamping steel sheet having an Al-based plating layer is hot-stamped, Fe diffuses from the steel sheet to the Al-based plating layer when the hot stamp is heated, and an Fe—Al alloy layer is formed. Of these Fe-Al alloy layers, the surface side (opposite to the steel plate) of the Al-based plating layer is a Fe-Al compound layer (Fe-Al alloy layer including a part of Fe-Al-Si alloy layer). Is generated, and a layer called a diffusion layer is formed on the steel plate side of the Al-based plating layer. By optimizing the heating conditions during hot stamping, Sn can be concentrated in the diffusion layer. This is because when Fe in the steel sheet and Al in the Al-based plating layer are alloyed, Fe in the steel sheet is diffused into the Al-based plating layer, and Sn in the steel sheet is also Fe in the Al-based plating layer at the same time. This is to spread inside.

When Sn is concentrated in the diffusion layer in the Al plating layer, the corrosion resistance of the hot stamp molded product is further improved. Therefore, the hot stamping steel sheet according to the present embodiment preferably has an Al-based plating layer on the surface of the steel sheet. The amount of the plating layer adhered may be ^{10 to 150 g / m 2 per side.}

In the present embodiment, the Al-based plating layer means a plating layer containing 50% by mass or more of Al. Elements other than Al include Si: 0.1 to 20% by mass, Fe: 0.1 to 10% by mass and Zn: 0.1 to 45% by mass, and the balance (Cu, Na, K, Co, Ni, Mg). Etc.): It may be contained in an amount of less than 0.5% by mass.

Further, when a hot stamping steel sheet having a Zn-based plating layer is hot-stamped, Fe diffuses from the steel sheet to the Zn-based plating layer to form an Fe—Zn alloy layer when the hot stamp is heated. As the Fe—Zn alloy layer, a Zn solid solution phase, a capital gamma (Γ) phase, and the like are generated.

In the present embodiment, the Zn-based plating layer means a plating layer containing 50% by mass or more of Zn. Elements other than Zn include Si: 0.01 to 20% by mass, Fe: 0.1 to 10% by mass, Al: 0.01 to 45% by mass, and the balance (Cu, Na, K, Co, Ni, Mg). Etc.): It may be contained in an amount of less than 0.5% by mass.

The component analysis of the plating layer is performed by the following method.
A sample is cut out so that a cross section perpendicular to the surface (thick cross section) can be observed from an arbitrary position 50 mm or more away from the end face of the hot stamping steel plate (a position avoiding the end when sampling cannot be performed from this position). The size of the sample depends on the measuring device, but is set to a size that can be observed by about 10 mm in the rolling direction.

After embedding the sample in a resin and polishing it, the layer structure of the plate thickness cross section is observed with a scanning electron microscope (SEM). Specifically, the observation is performed by SEM at a magnification at which the steel plate and the plating layer are included in the observation field of view. For example, by observing with a backscattered electron composition image (COMPO image), it is possible to infer how many layers the cross-sectional structure is composed of.

Next, using an electron probe microanalyzer (EPMA), the range of 50 μm in the plate surface direction and the plating layer thickness + 30 μm in the plate thickness direction is analyzed by mapping. When the plating layer is an Al-based plating layer, the average values of the Fe concentration and the Al concentration in the plate surface direction are obtained. Next, the relationship between the plate thickness position and the Al concentration and the relationship between the plate thickness position and the Fe concentration are obtained. The plate thickness position where the Al concentration and Fe concentration are the same as the Al concentration and Fe concentration of the steel sheet may be determined as the interface between the steel sheet and the Al-based plating layer. The Al concentration and Fe concentration of the steel sheet referred to here are obtained by measurement by EPMA.

When the plating layer is a Zn-based plating layer, the average values of the Fe concentration and the Zn concentration in the plate surface direction are obtained. Next, the relationship between the plate thickness position and the Zn concentration and the relationship between the plate thickness position and the Fe concentration are obtained. The plate thickness position where the Zn concentration and the Fe concentration are the same as the Zn concentration and the Fe concentration of the steel sheet may be determined as the interface between the steel sheet and the Zn-based plating layer. The Zn concentration and Fe concentration of the steel sheet referred to here are obtained by measurement by EPMA.

In the present embodiment, even when the hot stamping steel sheet has a plating layer, the Sn distribution state in the hot stamping steel sheet is the same as when it does not have a plating layer. That is, even when the hot stamping steel sheet has a plating layer, the Sn concentration in the surface layer region of the steel sheet is 0.99 to 1. It is 10 times.

In the measurement of Sn concentration when the hot stamping steel sheet has an Al-based plating layer, the position where the Fe concentration and Al concentration are the same as those of the steel sheet is the position where the Fe concentration and Al concentration are the same as those of the steel sheet and the Al-based plating layer, as in the case of component analysis of the plating layer. The Sn concentration may be measured by judging that it is an interface with. Further, in the measurement of Sn concentration when the steel sheet for hot stamping has a Zn-based plating layer, the position where the Fe concentration and the Zn concentration are the same as those of the steel sheet is determined to be the interface between the steel sheet and the Zn-based plating layer. The Sn concentration may be measured.

[Hot stamp molded product]
Next, a hot stamping molded body manufactured by using the above-mentioned hot stamping steel sheet will be described. The hot stamped compact according to the present embodiment has the same chemical composition as the above-mentioned chemical composition of the hot stamping steel sheet. The chemical composition of the hot stamped product may be measured by the same method as for the hot stamping steel sheet.

The Sn concentration in the surface layer region of the hot stamped compact is 0.99 to 1.10 times the Sn concentration at the position of 1/4 of the plate thickness in the plate thickness direction from the surface of the steel plate. This is the same as the Sn concentration in the surface layer region of the hot stamping steel sheet. The surface layer region of the hot stamped molded product means a region 5 μm in the plate thickness direction from the surface of the hot stamped molded product to 30 μm in the plate thickness direction from the surface.

When the Sn concentration in the surface layer region is more than 1.10 times the Sn concentration at the plate thickness 1/4 position, the Sn concentration is concentrated in the surface layer region, and excellent corrosion resistance is obtained when exposed to a corrosive environment for a long time. I can't get it. Therefore, the Sn concentration in the surface layer region is 1.10 times or less the Sn concentration at the position where the plate thickness is 1/4. It is preferably 1.05 times or less.

On the other hand, if the Sn concentration in the surface layer region is less than 0.90 times the Sn concentration at the plate thickness 1/4 position, the corrosion resistance at the initial stage of corrosion is lowered, and many starting points of corrosion pits are formed, resulting in a coating film. It is not preferable because the swelling becomes large. Therefore, the Sn concentration in the surface layer region is 0.90 times or more the Sn concentration at the position where the plate thickness is 1/4. Preferably, it is 0.95 times or more.

Similar to the hot stamping steel plate, the hot stamping molded product may have a plating layer on the surface for the purpose of further improving the corrosion resistance. The plating layer is, for example, an Al-based plating layer such as a hot-dip aluminum plating layer and an aluminum-zinc plating layer, a hot-dip zinc plating layer, an alloyed hot-dip zinc plating layer, an electrozinc plating layer, and a Zn-based plating layer such as a zinc nickel plating layer. Can be considered.

The plating layer may be arranged on the surface of either one of the hot stamping compacts, or may be arranged on both sides. Since Fe in the steel sheet diffuses into the plating layer at the time of heating the hot stamp, these plating layers become an alloy of the plating metal and Fe.

The chemical composition of the hot stamped product, the measurement of the Sn concentration, and the analysis of the plating layer may be performed by the same method as that of the hot stamping steel sheet.

When a hot stamping steel sheet having an Al-based plating layer on the surface is hot-stamped, the Al-based plating layer becomes a Fe-Al alloy layer, and a part of the hot-stamping steel sheet becomes a Fe-Al-Si alloy layer. In the Al-based plating layer, a layer called a diffusion layer in which Al is solid-solved in Fe having a crystal structure of bcc is formed in the vicinity of the interface between the Al-based plating layer and the steel sheet. That is, the Al-based plating layer is specifically composed of a Fe—Al alloy layer (partly a Fe—Al—Si alloy layer) and a diffusion layer. The layer structure of the hot stamped molded product having an Al-based plating layer on the surface is, in order from the surface, an Fe-Al alloy layer including a Fe-Al-Si alloy layer in part, a diffusion layer, and a base iron (steel plate).

When the Sn concentration in the diffusion layer existing in the Al-based plating layer is made higher than the Sn concentration in the surface layer region of the steel sheet, the corrosion resistance of the hot stamped molded product can be further improved. Specifically, by setting the Sn concentration in the diffusion layer existing in the Al-based plating layer to 1.05 times or more the Sn concentration in the surface layer region of the steel sheet, the corrosion resistance of the hot stamped molded product is further improved. be able to. The Sn concentration in the diffusion layer is preferably 1.10 times or more and 1.20 times or more the Sn concentration in the surface layer region of the steel sheet.
The upper limit of the Sn concentration in the diffusion layer is not particularly limited, but may be 1.70 times or less and 1.50 times or less the Sn concentration in the surface layer region of the steel sheet.

The Sn concentration in the diffusion layer and the Sn concentration in the surface layer region of the steel sheet are measured using EPMA from the outermost surface of the plating to a depth of plating thickness (μm) + 30 μm. Other conditions are the same as the above-mentioned method for measuring Sn concentration.
The diffusion layer means a region of the Al-based plating layer from the plate thickness position where the Al concentration is 30% by mass or less to the interface between the Al-based plating layer and the steel sheet.

Plate thickness, tensile strength and total elongation The plate thickness of the hot stamping steel plate and the hot stamping compact according to the present embodiment is not particularly specified, but may be 0.5 to 3.5 mm from the viewpoint of reducing the weight of the vehicle body.

Further, the hot stamped molded product according to the present embodiment preferably has the tensile (maximum) strength desired as a low-strength material for a tailored blank to be hot stamped. Specifically, the tensile strength of the hot stamped molded product is preferably 450 to 1200 MPa.

The total elongation is 10% or more when the tensile strength is 450 to 700 MPa, 7% or more when the tensile strength is more than 700 MPa and 800 MPa or less, 6% or more when the tensile strength is more than 800 MPa and 1000 MPa or less, more than 1000 MPa and 1200 MPa. In the following cases, it is preferably 5% or more.

Tensile strength and total elongation may be obtained by performing a tensile test in accordance with JIS Z 2241: 2011.

[Production method]
Next, a method for manufacturing a hot stamping steel sheet according to the present embodiment will be described.
In the present embodiment, it is important to control the Sn concentration in the surface layer region of the steel sheet by suppressing the oxidation of Sn, which is a factor that causes Sn to be concentrated in the surface layer region of the steel sheet.

The steel piece (steel material) to be subjected to hot rolling may be a steel piece manufactured by a conventional method, and may be, for example, a steel piece manufactured by a general method such as a continuously cast slab or a thin slab caster. Steel pieces having the above-mentioned chemical composition are subjected to hot rolling. In order to uniformly disperse Sn in the steel sheet, during hot rolling, the oxidation time in the temperature range of 1050 to 1150 ° C., which corresponds to the temperature range of rough rolling, is suppressed.

At a high temperature of 1200 ° C. or higher, Sn is incorporated into the scale during oxidation, so that the concentration on the surface of the steel sheet is unlikely to occur. On the other hand, in the temperature range of 1050 to 1150 ° C., Sn is concentrated on the ground iron side at the interface between the scale and the base iron during oxidation, so it is necessary to prevent oxidation for a long time in this temperature range. By suppressing the concentration of Sn, which is an easily oxidizing element, in the surface layer region due to oxidation, a uniform dispersion state of Sn can be maintained.

The steel piece (steel material) to be subjected to hot rolling may be heated to a temperature range of 1200 to 1400 ° C. and then subjected to hot rolling.

The suppression of oxidation time can be controlled by the maximum inter-pass time and descaling in the temperature range of 1050-1150 ° C. In the method for manufacturing a hot stamping steel sheet according to the present embodiment, descaling is performed before each pass in hot rolling. In order to control the oxidation time, the maximum value of the time between rolling and rolling (maximum pass-to-pass time) is controlled in the temperature range of 1050 to 1150 ° C. of hot rolling, and descaling is performed before each pass. It is effective to do it. In hot rolling, by setting the maximum pass-to-pass time in the temperature range of 1050 to 1150 ° C. to 120 seconds or less, the surface layer concentration of Sn can be suppressed. If there is even one pass-to-pass time of more than 120 seconds, Sn will be concentrated in the surface layer region.

As the descaling conditions, for example, it is preferable that the amount of jet water per nozzle is 10 to 100 L / min, the discharge pressure is 6 MPa or more, and the nozzle interval in the width direction is 150 to 350 mm. The discharge pressure is more preferably 12 MPa or more.

In the temperature range of 1050 to 1150 ° C., descaling is performed before each pass and the time between passes is controlled, so that the scale that becomes the oxygen supply source to Sn can be removed. As a result, the Sn concentration in the surface layer region of the steel sheet can be reduced. Descaling also has the significance of controlling the temperature of the steel sheet. Descaling may be performed not only before the rolling pass but also after the rolling pass so that the time of staying in the temperature range of 1050 to 1150 ° C. is not unnecessarily prolonged due to the temperature rise due to the processing heat generation.

When the temperature of the steel sheet is less than 1050 ° C., the surface layer concentration of Sn due to the oxidation reaction is unlikely to occur. It is presumed that this is because the temperature of the steel sheet is lowered and the diffusion of Sn is less likely to occur. Therefore, it is not necessary to control the maximum inter-pass time and descaling in the temperature range below 1050 ° C.

The finish rolling completion temperature may be in a temperature range that does not impair productivity, and may be 800 to 1000 ° C. From the same viewpoint, the winding temperature may be 400 to 800 ° C. As a result, a hot-rolled steel sheet is obtained.
In this embodiment, from the viewpoint of suppressing the production cost, it is desirable that the coil is not slowly cooled by using a heat insulating cover, a heat insulating chamber, or the like after winding.

The obtained hot-rolled steel sheet is cold-rolled. The cumulative rolling reduction rate during cold rolling may be within a range that does not impair productivity, and may be 30 to 80%. As a result, a cold-rolled steel sheet is obtained.

The obtained cold-rolled steel sheet may be annealed to soften it. After annealing, it is preferable to perform temper rolling. The rolling reduction of the steel sheet in temper rolling may be 2% or less as long as it does not hinder the productivity. A tension leveler may be used for shape correction.

If necessary, the cold-rolled steel sheet may be subjected to Al-based plating such as aluminum plating and aluminum-zinc plating, or Zn-based plating. Although aluminum and zinc are the main components of the plating composition, elements such as Ni may be added to improve corrosion resistance. Further, the plating may contain an element such as iron as an impurity.

There is no problem in the method of applying plating by a conventional method. For aluminum plating, the Si concentration in the bath is 5 to 12% by mass, and the balance is suitable for aluminum and impurities of less than 0.5%. For aluminum-zinc plating, a Zn concentration in the bath is 40 to 50% by mass, and the balance is suitable for aluminum and impurities of less than 0.5%. Further, there is no particular problem whether Mg or Zn is mixed in the aluminum plating or Mg is mixed in the aluminum-zinc plating. The atmosphere at the time of applying plating may be the normal plating conditions regardless of whether it is a continuous plating facility having a non-oxidizing furnace or a continuous plating facility not having a non-oxidizing furnace. In the zinc plating, a method such as hot-dip galvanizing, electrogalvanizing, or alloyed hot-dip galvanizing may be adopted.

The surface of the steel sheet may be pre-plated with metal before plating. Examples of the metal pre-plating include Ni pre-plating, Fe pre-plating, and other metal pre-plating for improving the plating property. Further, there is no particular problem even if a different kind of metal plating or a film of an inorganic or organic compound is applied to the surface of the plating layer.
By the above method, a steel plate for hot stamping according to this embodiment is obtained.

Next, a method for producing the hot stamped molded article according to the present embodiment will be described. The hot stamped molded product according to the present embodiment can be obtained by applying, for example, the following hot stamping conditions to the hot stamping steel sheet obtained by the above method.

First, the steel sheet for hot stamping _{is heated to a temperature range of Ac 3} transformation point to 1000 ° C., held in the temperature range for 0.1 to 30.0 minutes, and then immediately conveyed onto a mold for press molding. Perform (hot stamping). After that, the steel sheet is pressurized, and the steel sheet after press forming is cooled in the mold to a temperature range of 250 ° C. or lower by heat transfer between the steel sheet and the mold.

The average heating rate from the Ac ₃ transformation point to the temperature range of 1000 ° C. may be 0.1 to 200 ° C./s. The average cooling rate in the mold should be equal to or higher than the critical cooling rate at which martensitic transformation occurs when a metal structure containing martensite as the main phase (the area ratio of martensite is 80% or more) is obtained after hot stamping. is required. Since the critical cooling rate changes depending on the chemical composition of the steel sheet, the average cooling rate in the mold may be, for example, 1.0 to 200 ° C./s. If the metal structure containing martensite as the main phase is not required after hot stamping, it is not necessary to limit the cooling rate in the mold. However, when using a tailored blank bonded to a high-strength material containing martensite as the main phase after hot stamping, it may be necessary to cool the bonded high-strength material at a cooling rate higher than the critical cooling rate at which martensitic transformation occurs. Conceivable. Alternatively, the surface pressure may be increased by adjusting the mold only for the portion of the high-strength material to improve the cooling rate.

Further, in _{the temperature range from the Ac 3} transformation point to 1000 ° C., the temperature of the steel sheet may be changed or kept constant.
The Ac ₃ transformation point can be calculated by the following formula.

Ac ₃ transformation point (° C.) = exp (X) + 31.5 × Mo-28
X = 6.8165-0.47132 x C-0.057321 x Mn + 0.0660261 x Si-0.050211 x Cr + 0.10593 x Ti + 2.0272 x N + 1.0536 x S-0.12024 x Si x C + 0.11629 x Cr x C +0.29225 x C ² +0.01566 xMn ² +0.017315 x Cr ²
The element symbol in the above formula is the content of the element in mass%, and if it is not contained, 0 is substituted.

Regarding the transport time from the heating furnace to the mold, ferrite-pearlite transformation and bainite transformation start when a metal structure containing martensite as the main phase (martensite area ratio is 80% or more) is obtained after hot stamping. It is necessary to carry it onto the mold and perform press molding faster than this. For ferrite-pearlite transformation and bainite transformation, the time at which the transformation occurs can be investigated by attaching a thermocouple to a blank (steel plate for hot stamping) and measuring the temperature, and observing the transformation heat generation. However, when the metal structure containing martensite as the main phase is not required after hot stamping, it is not necessary to perform press molding earlier than the ferrite-pearlite transformation and the bainite transformation start. When the temperature at the time of press molding becomes low, the moldability deteriorates and molding defects such as cracks and wrinkles occur. Therefore, it is desirable to start the press molding at 600 ° C. or higher, preferably 700 ° C. or higher.

When the hot stamping steel sheet has a Zn-based plating layer on the surface, blisters and the like may occur if the heating temperature is high and the heating time is long, so it is necessary to make appropriate adjustments within the above hot stamping conditions. ..

When the hot stamping steel sheet has an Al-based plating layer, the heating temperature is such that the following formula (1) is satisfied in order to concentrate Sn in the diffusion layer in the Al-based plating layer during heating during hot stamping. And it is preferable to control the holding time. When the heating conditions at the time of hot stamping satisfy the following formula (1), the Sn concentration in the diffusion layer existing in the Al-based plating layer can be set to 1.05 times or more the Sn concentration in the surface layer region of the steel sheet. can.

t <Sn ^1.7 x 2600000 / T ... (1)
In the above (1), T is the heating temperature (° C.), t is the holding time (min), and Sn is the Sn content (mass%) in the steel sheet constituting the hot stamped product. The heating temperature T is the surface temperature of the hot stamping steel plate, and the holding time t is from the heating furnace from the time when the steel plate temperature rises and reaches a temperature 10 ° C. lower than the target heating temperature during heating during hot stamping. It is the time to take it out. If the holding time exceeds 20 minutes, the manufacturing cost increases, which is economically unfavorable. Therefore, the holding time is preferably 20 minutes or less.

If the holding time is long and the diffusion layer in the Al-based plating layer grows too much, the Sn concentration in the diffusion layer will decrease. Therefore, the heating time and heating temperature may be set according to the Sn content in the steel sheet. is important. It is desirable to measure the surface temperature of the hot stamping steel sheet by installing a thermocouple on the blank (hot stamping steel sheet).

The steel plate for hot stamping according to the present embodiment is suitably used as a vehicle body part in which a tailored blank is created by joining with a steel plate having high strength after hot stamping and the strength in the part is changed by hot stamping. NS. Various methods such as laser welding, seam welding, arc welding, and plasma welding can be considered as the welding method for the tailored blank, but the welding method is not particularly limited. Further, the steel plate (high-strength material) having high strength after hot stamping is not particularly limited. It may be appropriately selected for each part to be manufactured. Further, a part (hot stamp molded product) may be manufactured by using only the hot stamping steel plate according to the present embodiment without using it as a tailored blank. Further, a patchwork blank may be created by joining and stacking hot stamping steel plates according to the present embodiment by spot welding, and then hot stamping the patchwork blank.

Next, an example of the present invention will be described. The conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is described in this one condition example. It is not limited. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Using steel pieces having the chemical compositions shown in Tables 1 and 2, hot rolling, pickling, cold rolling, continuous annealing or continuous hot-dip plating line, and if necessary, continuous annealing and then electroplating to plate. Cold-rolled steel sheets and plated steel sheets having a thickness of 0.5 to 3.5 mm were manufactured. The maximum inter-pass time in the temperature range of 1050 to 1150 ° C. during hot rolling was as shown in Tables 3 and 4. The finish rolling completion temperature was 800 to 1000 ° C., and the cumulative rolling reduction in cold rolling was 30 to 80%.

Descaling in the temperature range of 1050 to 1150 ° C. during hot rolling was performed under the following conditions. The amount of jet water per nozzle was 10 to 100 L / min, the discharge pressure was 6 MPa or more, and the nozzle interval in the width direction was 150 to 350 mm. Descaling was performed before each pass of hot rolling.

The "types of plating layer" shown in Tables 3 and 4 are as follows, respectively.
CR: No plating layer GI: Hot-dip galvanizing layer (target weight 60 g / m ^{2 on} one side, double-sided plating)
GA: Alloyed hot-dip galvanized layer (target weight 45 g / m ^{2 on} one side, double-sided plating)
EG: Electrogalvanized layer (target weight 20 g / m ^{2 on} one side, double-sided plating)
AL: Al-based plating layer (target weight 80 g / m ^{2 on} one side, double-sided plating)

Using the produced cold-rolled steel sheet and plated steel sheet, hot stamping was performed under the conditions shown in Tables 3 and 4. For hot stamping, a flat steel plate was sandwiched between water-cooled dies and pressed so that a test piece for performing a tensile test and metal structure observation could be easily prepared. Under all experimental conditions, the molding temperature was 600 ° C. or higher. The cooling end temperatures in the mold are as shown in Tables 3 and 4.

By collecting JIS No. 5 test pieces from the hot stamped steel sheet (hot stamp molded product) and conducting a tensile test in accordance with JIS Z 2241: 2011, the tensile (maximum) strength (MPa) and total elongation (%) were obtained. ) Was asked.

When the obtained tensile strength was 450 to 1200 MPa, it was judged to be acceptable as having the tensile strength desired as a low-strength material for a tailored blank to be hot stamped. On the other hand, when the obtained tensile strength was less than 450 MPa or more than 1200 MPa, it was judged to be unacceptable because it did not have the tensile strength desired as a low-strength material for a tailored blank to be hot stamped.

Further, the obtained total elongation is 10% or more when the tensile strength is 450 to 700 MPa, 7% or more when the tensile strength is more than 700 MPa and 800 MPa or less, and 6% or more when the tensile strength is more than 800 MPa and 1000 MPa or less. If it is more than 1000 MPa and less than 1200 MPa, and if it is 5% or more, it is judged to be acceptable because it has excellent ductility. In cases other than the above, it was judged to be unacceptable because it was inferior in ductility.

Corrosion resistance after painting was evaluated by the method specified in JASO M609 established by the Society of Automotive Engineers of Japan. Specifically, it was evaluated by the following method.

A 70 mm long flaw was made with a cutter on the flat surface of the sample having a thickness of 15 μm and an electrodeposition coating film was applied, and the sample was subjected to a cycle corrosion test. The sample after 120 cycles was taken out, immersed in a commercially available coating film remover for 30 minutes, and then the coating film was peeled off with a brush. Then, the sample was immersed in a 5% aqueous solution of ammonium citrate containing an inhibitor for a steel sheet, and the rust formed on the corroded portion was removed with a brush. Using a KEYENCE digital microscope VHX-7000, the maximum value of the plate thickness reduction from the reference plane was measured for each 35 mm length of the flaw, with the central portion of the 70 mm flaw as the boundary. The reference surface was the surface of the non-corroded part after the coating film was peeled off, regardless of the presence or absence of plating. The average value of the maximum values of the two obtained plate thickness reductions was calculated.

The average value of the maximum value of the obtained plate thickness reduction was evaluated according to the following criteria. When the evaluations were E, V, and G, it was judged to be acceptable because excellent corrosion resistance was obtained even when exposed to a corrosive environment for a long time. On the other hand, when the evaluation was B, it was judged to be unacceptable because excellent corrosion resistance could not be obtained when exposed to a corrosive environment for a long time. Even in the case where the evaluation was B, there was a difference in the degree of plate thickness reduction.

E (Excellent): Less than 0.05 mm V (Very Good): 0.05 mm or more, less than 0.10 mm G (Good): 0.10 mm or more, less than 0.15 mm B (Bad): 0.15 mm or more

The above results are shown in Tables 3 and 4. Looking at Tables 3 and 4, the examples of the present invention have the strength and ductility desired as a low-strength material for hot stamped tailored blanks, and are excellent even when exposed to a corrosive environment for a long time. It can be seen that corrosion resistance was obtained. Among them, the example of the present invention having an Al-based plating layer on the surface and having a Sn concentration in the diffusion layer existing in the Al plating layer is 1.05 times or more the Sn concentration in the surface layer region of the steel sheet for a long time. It can be seen that better corrosion resistance was obtained even when exposed to a corrosive environment.

On the other hand, in the comparative example, it can be seen that one or more of tensile strength, ductility and corrosion resistance did not satisfy the acceptance criteria.

According to the above aspect of the present invention, it has the strength and ductility desired as a low-strength material for hot stamped tailored blanks, and excellent corrosion resistance can be obtained even when exposed to a corrosive environment for a long time. It is possible to provide a hot stamped molded product, and a hot stamping steel plate from which the hot stamped molded product can be obtained. According to the above aspect of the present invention, a hot stamped molded product having excellent deformation characteristics and corrosion resistance at the time of a collision can be obtained, which contributes to weight reduction of an automobile body and improvement of collision safety.

Claims (8)

The chemical composition is mass%,
C: 0.035 to 0.100%,
Si: 0.005 to 0.500%,
Mn: 0.10 to 2.00%,
Al: 0.010 to 0.080%,
Sn: 0.005 to 0.200%,
P: 0.030% or less,
S: 0.0100% or less,
N: 0.0100% or less,
Cr: 0-1.00%,
Mo: 0-1.00%, and B: 0-0.0050%
Containing and
Ti: 0.005 to 0.100%,
Nb: 0.015-0.100%,
V: 0.005 to 0.100%, and Zr: 0.005 to 0.100%
Containing one or more of the group consisting of
Balance comprising a steel ing Fe and impurities,
The Sn concentration in the surface layer region, which is a region 5 μm in the plate thickness direction from the surface of the steel plate to 30 μm in the plate thickness direction from the surface, is centered on a position 1/4 of the plate thickness from the surface. A steel sheet for hot stamping, which is 0.99 to 1.10 times the Sn concentration in a region of 20 μm in the thickness direction (a region of 40 μm in the plate thickness direction when the front and back surfaces are combined). When the chemical composition is mass%,
The hot stamping steel sheet according to claim 1, wherein one or two of Cr: 0.005 to 1.00% and Mo: 0.005 to 1.00% are contained. When the chemical composition is mass%,
B: The steel sheet for hot stamping according to claim 1 or 2, which contains 0.0002 to 0.0050%. The hot stamping steel sheet according to any one of claims 1 to 3, further comprising a plating layer on the surface. The hot stamping steel sheet according to claim 4, wherein the plating layer is an Al-based plating layer. Comprising a steel sheet to have a chemical composition according to any one of claims 1 to 3,
The Sn concentration in the surface layer region, which is a region 5 μm in the plate thickness direction from the surface of the steel plate to 30 μm in the plate thickness direction from the surface, is centered on a position 1/4 of the plate thickness from the surface. A hot stamp molded product characterized in that the Sn concentration is 0.99 to 1.10 times the Sn concentration in a region of 20 μm in the thickness direction (a region of 40 μm in the plate thickness direction when the front and back surfaces are combined). The hot stamp molded article according to claim 6, further comprising a plating layer on the surface. The plating layer is an Al-based plating layer.
The hot stamped body according to claim 7, wherein the Sn concentration in the diffusion layer existing in the Al-based plating layer is 1.05 times or more the Sn concentration in the surface layer region of the steel sheet.