Title of the invention: Steel plate, tailored blank, hot press molded product, steel pipe, hollow hardened molded product, and method for manufacturing steel plate.
Technical field
[0001]
　The present disclosure relates to steel sheets, tailored blanks, hot press molded products, steel pipes, hollow hardened molded products, and methods for manufacturing steel sheets.
　This application claims priority based on Japanese Patent Application No. 2018-119189 filed in Japan on June 22, 2018 and Japanese Patent Application No. 2018-119190 filed in Japan on June 22, 2018. Is used here.
Background technology
[0002]
　In recent years, in order to reduce CO 2 gas emissions from the viewpoint of protecting the global environment, weight reduction of automobile bodies has become an urgent issue in the automobile field. On the other hand, the application of high-strength steel sheets is being actively studied, and the strength of the steel sheets is increasing more and more.
[0003]
　Hot stamping (hereinafter, may be referred to as "hot stamping") is attracting attention as one of the techniques for molding automobile members. In hot stamping, a steel sheet is heated to a high temperature, press-formed in a temperature range equal to or higher than the Ar3 transformation temperature, rapidly cooled by heat removal by a die, and transformed at the same time as molding under a press pressure. Thereby, it is a technique capable of producing a hot press molded product (hereinafter, may be referred to as "hot stamp molded product") having high strength and excellent shape freezing property.
[0004]
　Further, in order to improve the yield and functionality of press-formed products of automobile members, butt-welded members (hereinafter, "tailored blanks") in which the end faces of at least two steel plates are butted and joined by laser welding, plasma welding, or the like. ”) Is applied as a material for pressing. Since the tailored blank joins a plurality of steel plates according to the purpose, the plate thickness and strength can be freely changed in one component. As a result, the tailored blank can improve the functionality of the automobile member and reduce the number of automobile members. Further, by hot stamping using a tailored blank, it is possible to manufacture a high-strength press-molded product in which the plate thickness, strength, etc. are freely changed.
[0005]
　When a tailored blank is used as a press material and a member for an automobile is molded by hot stamping, the tailored blank is heated to, for example, a temperature range of 800 ° C. to 1000 ° C. For this reason, a steel plate plated with aluminum such as Al—Si, which has a high plating boiling point, is often used as a tailored blank for hot stamping.
[0006]
　So far, as a steel plate for forming a tailored blank, for example, a steel plate having a plating layer has been variously studied (see, for example, Patent Documents 1 to 7).
Prior art literature
Patent documents
[0007]
Patent Document 1: Japanese Special Table 2009-534529
Patent Document 2: Japanese Special Table 2015-525677
Patent Document 3: Japanese Special Table 2015-523210
Patent Document 4: Japanese Special Table 2015-536246 JP
Patent Document 5: Japanese Patent 2013-220445 JP
Patent Document 6: Chinese Patent application Publication No. 106 334 875 No.
Patent Document 7: Japanese Patent 2016-073989 JP
Outline of the invention
Problems to be solved by the invention
[0008]
　However, with the conventional steel sheet, the fatigue strength of the joint and the corrosion resistance of the welded portion after painting are not sufficient.
　The subject of the present disclosure is a steel plate, a tailored blank, and a hot press, which have excellent fatigue strength of a joint and excellent corrosion resistance after painting of the welded portion even after the welded portion formed during butt welding is coated. It provides a method for manufacturing a molded product, a steel pipe, a hollow hardened molded product, and a steel plate.
Means to solve problems
[0009]
　The means for solving the above problems include the following aspects.
[0010]
<1> A
　base steel plate, a plated portion in which an intermetallic compound layer and an aluminum plating layer are provided in this order from the base steel plate side on the surface of the base steel plate, and an exposed portion where the base steel plate is exposed. A steel sheet having, which is perpendicular to the thickness direction of the steel sheet and at least on both surfaces of the base steel sheet in a first direction from the plated portion toward one edge of the steel sheet. The portion, the exposed portion, and the edge of the steel sheet are arranged in this order, and when viewed from a cross section parallel to the first direction and the thickness direction of the steel sheet, the edge side of the steel sheet and the edge of the steel sheet are The shape of the end portion of the plated portion on the outer side from the inside of the base material steel plate toward the surface of the base material steel plate is a curve convex toward the first direction represented by the radius of curvature R1. A steel sheet in which R1 satisfies the following formula (1).
　Equation (1) 5 μm ≦ R1
<2> In the
　cross section, the shape of the end portion of the exposed portion on the plating portion side is a concave curve represented by the radius of curvature R2, and the R2 is the following equation (2). The steel plate according to <1> that satisfies the above conditions.
　Equation (2) 260 μm ≦ R2
<3> In the
　cross section, the depth in the thickness direction from the virtual line extending the surface of the aluminum plating layer of the plating portion in the first direction to the surface of the base steel sheet. The steel sheet according to <2>, wherein the relationship between D, R1 and R2 satisfies the following formula (3), where D is the depth of the exposed portion.
　Equation (3) D ≤ (R1 + R2)
<4>
　The base steel plate is C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 0.06%, P: 0. 03% or less, S: 0.010% or less, N: 0.010% or less, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%, Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100%, Mg: 0% to 0.05%, Ca: 0% to 0.05%, REM: 0% to 0.05%, Sn: 0% to 0.5%, The steel plate according to any one of <1> to <3>, which has a chemical composition of Bi: 0% to 0.05%, Si: 0% to 2.00%, and the balance: Fe and impurities.
<5>
　The steel sheet according to any one of <1> to <4>, wherein the aluminum plating layer has an average thickness of 8 μm to 35 μm, and the intermetallic compound layer has an average thickness of 3 μm to 10 μm.
<6>
　A tailored blank having a weld metal portion adjacent to the exposed portion of the steel sheet according to any one of <1> to <5>.
<7>
　A tailored blank having at least two steel plates according to any one of <1> to <5> and having a welded metal portion adjacent to the exposed portion, and the at least two steel plates. Of the steel sheet A, which has a smaller product of the thickness of the steel sheet and the tensile strength of the steel sheet after hot press forming, the steel
　sheet A is directed from the plated portion to the welded metal portion in the second direction and the steel plate. When viewed from a cross section parallel to the thickness direction of
　When the length in the thickness direction from the virtual line extending the surface of the aluminum plating layer in the plating portion in the second direction to the surface of the base steel plate is defined as the depth of the exposed portion,
　the first of the steel plate A. The depth D1 (μm) of the exposed portion formed on the surface of the surface 1 and
　the depth D2 (μm) of the exposed portion formed on the surface of the second surface of the
　steel plate A, and the plate of the steel plate A. A tailored blank having a thickness t (μm) that satisfies the following formula (4).
　Formula (4) ((D1 + D2) / t) × 100 ≦ 20
<8>
　A hot press-molded product using the tailored blank according to <6> or <7>.
<9>
　A steel pipe having a weld metal portion adjacent to the exposed portion of the steel plate according to any one of <1> to <5>.
<10>
　A hollow hardened molded product using the steel pipe according to <9>.
<11> The
　method for manufacturing a steel sheet according to any one of <1> to <5>,
　which comprises a step of forming the exposed portion by cutting with an end mill.
Effect of the invention
[0011]
　According to the present disclosure, a steel plate, a tailored blank, and a hot press, which have excellent fatigue strength of a joint and excellent corrosion resistance after painting of the welded portion even after the welded portion formed during butt welding is coated. A method for producing a molded product, a steel pipe, a hollow hardened molded product, and a steel plate is provided.
A brief description of the drawing
[0012]
FIG. 1 is a schematic cross-sectional view showing an example of an end portion of the steel plate of the present disclosure.
FIG. 2 is an enlarged cross-sectional view showing an example of an end portion of the steel plate of the present disclosure.
FIG. 3 is an enlarged cross-sectional view showing another example of the end portion of the steel plate of the present disclosure.
FIG. 4 is a cross-sectional view showing an example of the tailored blank of the present disclosure.
FIG. 5 is a schematic cross-sectional view showing another example of the end portion of the steel plate of the present disclosure.
FIG. 6 is an enlarged cross-sectional view showing another example of the end portion of the steel plate of the present disclosure.
FIG. 7 is an enlarged cross-sectional view showing another example of the end portion of the steel plate of the present disclosure.
FIG. 8 is a cross-sectional view showing another example of the tailored blank of the present disclosure.
FIG. 9 is an enlarged cross-sectional view showing another example of the end portion of the steel plate of the present disclosure.
FIG. 10 is an enlarged cross-sectional view showing an end portion of Comparative Example 18.
Mode for carrying out the invention
[0013]
　Hereinafter, an example of a preferred embodiment of the present disclosure will be described in detail.
　In addition, in this specification, the numerical range represented by using "-" means the range including the numerical values ​​before and after "-" as the lower limit value and the upper limit value.
　In the present specification, the content of the component (element) may be referred to as "C amount" in the case of the content of C (carbon), for example. In addition, the content of other elements may be described in the same manner.
　In the present specification, the term "process" is used not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. included.
[0014]
　In the present disclosure, the terms "base steel sheet", "intermetallic compound layer", and "aluminum plating layer" will be described later in "Definition of the range of the base steel sheet, the intermetallic compound layer, and the aluminum plating layer". ..
　In the present disclosure, the term "thickness direction" means a direction for measuring the plate thickness at the center of the plate width of the steel plate.
　In the present disclosure, the term "end face of steel sheet" means a surface of a steel sheet that is exposed in a direction orthogonal to the thickness direction.
　In the present disclosure, the term "edge of steel sheet" means a portion adjacent to the end face of the steel sheet.
　In the present specification, the term "end of steel plate" is located around the steel plate, and the entire width from the end face of the steel plate (that is, the length from the edge to the edge of the opposing steel plate). ) Represents an area within 20%. That is, the "edge" occupies a region (40% in total) of 20% at both ends of the entire plate width.
　In the present specification, the term "central portion of the steel plate" is used in the range of 20% or less of the entire width of the plate (that is, the length from the edge to the edge of the opposing steel plate) from the region end face. Represents a region excluding the region. That is, the "central portion" of the steel sheet is a region other than the end portion of the steel plate and occupies 60% of the entire plate width. In the
　present specification, the "end portion of the plating portion". Is located around the plated part and is within 20% of the entire width of the plated part from the end face of the plated part (that is, the length from the edge to the edge of the opposite plated part). Representing an area. In the
　present specification, the “edge portion of the exposed portion” refers to an region in a range from the edge of the exposed portion to within 20% of the width of the exposed portion.
　In the present specification, the term "cross section" of a steel sheet refers to a cross section cut in the plate thickness direction. Specifically, in FIGS. 1 and 5, the thickness direction of the steel plate 100 is Z, and the longitudinal direction of the exposed portion 22 (direction orthogonal to the display plane of FIGS. 1 and 5) is X. Then, the direction orthogonal to the direction Z and the direction X is defined as Y. At this time, the cross section means a cross section cut by the YZ plane.
　In the present specification, the term "welded portion" refers to a region including a weld metal portion, an exposed portion of a steel plate located around the weld metal portion, and a periphery of the plated portion on the weld metal side.
[0015]

　The steel plate of the present disclosure includes a base steel plate, aluminum plating layers provided on both sides of the base steel plate, and an intermetallic compound layer formed between the base steel plate and the aluminum plating layer. ..
　Further, in the steel plate of the present disclosure, an exposed portion where the base steel plate is exposed and a remaining portion formed on the center side of the exposed portion (hereinafter, may also be referred to as a plating portion) on both sides of the end portion of the steel plate. ), And has a plated portion in which an aluminum plating layer and an intermetallic compound layer remain in a region other than the exposed portion. That is, in the steel plate of the present disclosure, at least a plated portion, an exposed portion, and an edge of the steel plate are arranged in this order on both surfaces of the base steel plate in the first direction.
　Further, when the boundary between the exposed portion and the plated portion is viewed from the cross section, a plated portion formed by a convex curve represented by a radius of curvature R1 is formed on the outer surface side of the steel sheet at the boundary between the exposed portion and the plated portion. Have. Then, R1 satisfies the following equation (1). That is, the steel plate of the present disclosure is on the edge side of the steel plate and on the outer side from the inside of the base steel plate toward the surface of the base steel plate when viewed from a cross section parallel to the first direction and the thickness direction of the steel plate. The shape of the end portion of the plated portion of the above is a curved line convex in the first direction represented by the radius of curvature R1, and the R1 satisfies the following formula (1). Further, the steel plate of the present disclosure may have a concave curve in which the shape of the end portion of the exposed portion on the plated portion side is represented by the radius of curvature R2. Further, when the end portion of the exposed portion is a concave curve represented by the radius of curvature R2, R2 satisfies the following equation (2).
Equation (1) 5 μm ≦ R1
Equation (2) 260 μm ≦ R2
　The shape of the steel sheet is not particularly limited.
[0016]
　FIG. 1 is a schematic cross-sectional view showing an example of an end portion of the steel plate of the present disclosure. Further, FIG. 2 is an enlarged cross-sectional view showing an example of an end portion of the steel plate of the present disclosure. FIG. 5 is a schematic cross-sectional view showing another example of the end portion of the steel plate of the present disclosure. FIG. 6 is an enlarged cross-sectional view showing another example of the end portion of the steel plate of the present disclosure.
　In FIGS. 1, 2, 5, and 6, 100 is a steel plate, 12 is a base steel plate, 14 is an aluminum plating layer, 16 is an intermetallic compound layer, 22 is an exposed portion, and 26 is a plating portion.
　Further, 100A indicates the end face of the steel sheet 100, and 100B indicates the boundary between the exposed portion 22 and the plated portion 26. D is a vertical direction (thickness of the steel plate) from the virtual line extending the surface of the aluminum plating layer 14 (the surface on the outer surface side of the steel plate 100) in the direction of the exposed portion 22 (first direction) to the surface of the base steel plate 12. The depth of the direction) (hereinafter, may be referred to as “removal depth”) is shown. W indicates the width of the exposed portion 22. Here, F1 indicates a first direction (first direction) which is perpendicular to the thickness direction of the steel sheet and is a direction (Y direction) from the plated portion toward one edge of the steel sheet.
[0017]
　As shown in FIGS. 1 and 5, in the steel plate 100 of the present disclosure, aluminum-plated layers 14 are formed on both surfaces of the base steel plate 12, and between the base steel plate 12 and the aluminum-plated layer 14 between metals. The compound layer 16 is formed.
　Further, as shown in FIGS. 1, 2, 5, and 6, an exposed portion 22 in which the base steel plate 12 is exposed is formed on both sides of the end portion of the steel plate 100, and is centered on the exposed portion 22. The plating portion 26 is formed on the side, in a region other than the exposed portion 22. That is, the exposed portion 22 is formed in a region between the edge of the end face 100A of the steel plate 100 and the boundary 100B between the exposed portion 22 and the plating portion 26.
[0018]
　Further, as shown in FIGS. 2 and 6, the steel plate 100 of the present disclosure has a cross section of the boundary 100B between the exposed portion 22 and the plated portion 26 (a cut surface in the direction along the plate thickness direction of the steel plate 100, that is, the first direction). The aluminum plating layer 14 of the plating portion 26 is provided on the outer surface side (aluminum plating layer 14 side) of the steel plate 100 at the boundary 100B when viewed from F1 and the cross section parallel to the thickness direction of the steel plate 100. .. An exposed portion 22 is provided on the base steel plate 12 side of the boundary 100B. Further, the central portion of the boundary 100B and the end portion on the base steel plate 12 side extend in the direction along the thickness direction. The aluminum plating layer 14 of the plating portion 26 on the outer surface side of the steel plate 100 at the boundary 100B has a convex curve formed toward the outside of the aluminum plating layer 14, and the radius of curvature is indicated by R1. In the steel sheet 100 of the present disclosure, R1 is 5 μm or more. That is, R1 satisfies the relationship of the formula (1) 5 μm ≦ R1. On the other hand, as shown in FIG. 6, the exposed portion 22 on the other end side of the boundary 100B has a concave curve formed toward the inside of the base steel plate 12, and the radius of curvature is indicated by R2. That is, the shape of the plated portion 26 side end portion of the exposed portion 22 is a concave curve. R2 satisfies the relationship of the formula (2) 260 μm ≦ R2.
　Although the steel plate 100 of the present disclosure has been described with reference to FIGS. 1, 2, 5, and 6, the steel plate 100 of the present disclosure is not limited thereto.
[0019]
　Conventionally, a tailored blank is known in which a steel plate plated with a metal mainly containing aluminum is butt-welded by a welding method such as laser welding or plasma welding. In this tailored blank, a large amount of aluminum due to aluminum plating may be mixed in the weld metal part. When the tailored blank thus obtained is hot stamped, the weld metal portion of the butt weld may be softened. For example, in a tailored blank after this hot stamping, as a result of a tensile strength test of a portion including a weld metal portion, it has been reported that a fracture occurs in the weld metal portion.
[0020]
　In order to avoid breakage of the weld metal portion, for example, in Patent Document 1, the aluminum plating layer 14 of the welded portion to be welded is removed to obtain a steel plate in which the intermetal compound layer 16 remains, and the steel plate is scheduled to be welded. A tailored blank in which the portions are butt welded is disclosed.
[0021]
　However, the fatigue strength of the joint is reduced in the tailored blank in which the aluminum plating layer 14 is removed to form a steel sheet in which the intermetallic compound layer 16 is left, and the end faces of the regions in which the intermetallic compound layer 16 is left are abutted and welded by butt welding. To do.
　In the case of a steel plate in which the intermetallic compound layer 16 remains in the planned welding portion, since the hard and brittle intermetallic compound layer 16 remains, the weld metal portion and the region where the aluminum plating layer 14 is not removed (stress concentration). Part) is affected by the intermetallic compound layer 16 remaining. As a result, a tailored blank is formed from the steel plate disclosed in Patent Document 1, and the hot stamped product using the tailored blank loses the fatigue strength of the joint when repeatedly subjected to a load. Therefore, the steel sheet in which only the aluminum-plated layer 14 of the planned welding portion is removed and the intermetallic compound layer 16 is left is insufficiently applied to a portion where fatigue characteristics are important.
[0022]
　Further, Patent Documents 2 to 6 disclose a tailored blank in which the aluminum plating layer 14 and the intermetallic compound layer 16 of the planned welding portion are removed from the steel plate, and the planned welding portion of the steel plate is butt-welded. There is.
[0023]
　However, in the steel sheets disclosed in Patent Documents 2 to 6, at the boundary between the exposed portion 22 and the plated portion 26, the thickness of the coating film after painting varies depending on the cross-sectional shape of the boundary. Corrosion resistance decreases after painting. Further, when the intermetallic compound layer and the aluminum plating layer are removed, a part of the base steel sheet may be removed together with the intermetallic compound layer and the aluminum plating layer. Then, depending on the state in which the base steel plate is removed, the fatigue strength and static strength of the joint are reduced.
[0024]
　On the other hand, Patent Document 7 discloses that the side surface of the cut hole is processed into a convex curved surface from the viewpoint of ensuring the corrosion resistance after painting of the hole-drilled surface.
　However, in the technique disclosed in Patent Document 7, drilling is performed by laser cutting. Since this technique is a technique for obtaining a shape by melt cutting depending on the irradiation direction of the laser beam, it is not a technique suitable for removing both the intermetallic compound layer 16 and the aluminum plating layer 14.
[0025]
　On the other hand, in the steel plate 100 of the present disclosure, at least a part of the end portion of the steel plate 100, the aluminum plating layer 14 and the intermetallic compound layer 16 on both sides are removed, and the exposed portion 22 where the base steel plate 12 is exposed is provided. Have. Further, it has a plating portion 26 that does not remove the aluminum plating layer 14 and the intermetallic compound layer 16. Further, on the cross-sectional portion of the boundary between the exposed portion 22 and the plating portion 26, an aluminum plating layer which is a plating portion 26 formed in a convex shape having a radius of curvature represented by R1 on the outer surface side of the steel plate 100 at this boundary. Has 14. And R1 is 5 μm or more.
[0026]
　The steel plate 100 of the present disclosure has an aluminum plating layer 14 of the plating portion 26 having a radius of curvature represented by R1 on the outer surface side of the steel plate 100 at the boundary between the exposed portion 22 and the plating portion 26. Even when the surroundings are coated, the occurrence of variation in the thickness of the coated coating film is suppressed. Therefore, corrosion resistance is ensured after welding. However, if R1 is too small, the thickness of the coating film varies widely. Therefore, by setting R1 to 5 μm or more, corrosion resistance after painting is ensured.
[0027]
　By having the exposed portion 22 whose radius of curvature is represented by R2 on the other end side of the boundary 100B (the end side of the exposed portion 22 on the plated portion 26 side), the fatigue strength of the joint obtained by using the steel plate 100 can be determined. The decrease is suppressed. That is, since the shape of the end portion of the exposed portion 22 on the plated portion 26 side is a concave curve represented by the radius of curvature R2, the stress concentration is suppressed and the steel plate 100 obtained by exposing the base steel plate 12 is used. The decrease in fatigue strength of the joint is suppressed.
　However, if R2 is too small, the stress concentration becomes high when a stress load is applied to the joint. Therefore, the fatigue strength of the joint is ensured by setting R2 to 260 μm or more. Since the steel plate 100 of the present disclosure has the above configuration, the static strength of the joint of the butt welded member using the steel plate 100 of the present disclosure is also excellent.
　When R1 is 5 μm or more and R2 is 260 μm or more, the corrosion resistance after painting is further improved as compared with the case where only the condition of R1 is satisfied, which is preferable.
[0028]
　Therefore, the tailored blank (butt-welded member) obtained by butt-welding the end faces of the ends having the exposed portions 22 using the steel plate 100 of the present disclosure is hard between the weld metal portion and the plated portion 26. It does not have a brittle intermetallic compound layer 16. Further, the outer surface side of the steel plate 100 at the boundary between the exposed portion 22 and the plated portion 26 satisfies the above condition. Therefore, even when the tailored blank made of the steel plate 100 of the present disclosure is used as a hot stamped product, it is considered that the decrease in fatigue strength of the joint is suppressed. Further, since the variation in the thickness of the coating film after coating is suppressed, it is considered that the welded portion is excellent in corrosion resistance after coating even after coating on the hot stamp molded product.
[0029]
　Hereinafter, the steel sheet of the present disclosure will be described.
[0030]
[Base steel plate] The
　base steel plate 12 is a steel plate before the aluminum plating layer 14 is provided. The base steel sheet 12 may be obtained by a usual method and is not particularly limited. The base steel plate 12 may be either a hot-rolled steel plate or a cold-rolled steel plate. Further, the thickness of the base steel plate 12 may be set according to the purpose, and is not particularly limited. For example, as for the plate thickness of the base steel plate 12, the plate thickness of the entire steel plate after the aluminum plating layer 14 is provided may be 0.8 mm to 4 mm, and further to be 1 mm to 3 mm. The thickness of the plate can be mentioned.
[0031]
　The base steel sheet 12 means, for example, various properties related to mechanical deformation and fracture such as high mechanical strength (for example, tensile strength, yield point, elongation, drawing, hardness, impact value, fatigue strength, etc.). It is preferable to use a steel plate formed so as to have.). Specifically, a steel plate having a tensile strength of 400 to 2700 MPa can be used. The plate thickness is 0.7 mm to 3.2 mm. As the base steel plate 12, a steel plate having low mechanical strength may be used. Specifically, they are 1300 MPa class, 1200 MPa class, 1000 MPa class, 600 MPa class, and 500 MPa class. For example, in the case of a B-pillar of an automobile, a steel plate having a tensile strength of 1500 to 2000 MPa is used from the upper part to the central part where deformation is desired to be prevented, and a steel plate having a tensile strength of 500 MPa to 1500 MPa is used for the lower part which is an energy absorbing part. Is desirable. More preferably, the lower part is a steel plate of 600 MPa class to 1300 MPa class. The thickness of the steel plate of the B-pillar is preferably 1.4 mm to 2.6 mm at the upper part and 1.0 mm to 1.6 mm at the lower part.
[0032]
　As an example of the base steel sheet 12, various properties related to mechanical deformation and fracture such as high mechanical strength (for example, tensile strength, yield point, elongation, drawing, hardness, impact value, fatigue strength, etc.) It is preferable to use a steel plate formed so as to have (meaning).
[0033]
　As an example of the preferable chemical composition of the base steel sheet 12, the following chemical composition can be mentioned, for example.
　By mass%, C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 0.06%, P: 0.03% or less, S: 0.010% or less, N: 0.010% or less, Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1 .0%, Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0 .0100%, Mg: 0% to 0.05%, Ca: 0% to 0.05%, REM: 0% to 0.05%, Sn: 0% to 0.5%, Bi: 0% to 0 It has a chemical composition of 0.05%, Si: 0% to 2.00%, and the balance: Fe and impurities.
　Hereinafter, "%" indicating the content of the component (element) means "mass%".
[0034]
(C: 0.02% to 0.58%)
　C is an important element that enhances the hardenability of the base steel sheet 12 and mainly determines the strength after quenching. Further, C is an element that lowers the A3 point and promotes lowering of the quenching treatment temperature. If the amount of C is less than 0.02%, the effect may not be sufficient. Therefore, the amount of C is preferably 0.02% or more. On the other hand, when the amount of C exceeds 0.58%, the toughness of the hardened portion is significantly deteriorated. Therefore, the amount of C is preferably 0.58% or less. Preferably, the amount of C is 0.45% or less.
[0035]
(Mn: 0.20% to 3.00%)
　Mn is a very effective element for enhancing the hardenability of the base steel sheet 12 and stably securing the strength after quenching. If the amount of Mn is less than 0.20%, the effect may not be sufficient. Therefore, the amount of Mn is preferably 0.20% or more. Preferably, the amount of Mn is 0.80% or more. On the other hand, if the amount of Mn exceeds 3.00%, not only the effect is saturated, but also it may be difficult to secure stable strength after quenching. Therefore, the amount of Mn is preferably 3.00% or less. Preferably, the amount of Mn is 2.40% or less.
[0036]
(Al: 0.005% to 0.06%)
　Al functions as a deoxidizing element and has an action of making the base steel sheet 12 sound. If the amount of Al is less than 0.005%, it may be difficult to obtain the effect of the above action. Therefore, the amount of Al is preferably 0.005% or more. On the other hand, if the amount of Al exceeds 0.06%, the effect of the above action is saturated, which is disadvantageous in terms of cost. Therefore, the amount of Al is preferably 0.06% or less. Preferably, the amount of Al is 0.05% or less. The amount of Al is preferably 0.01% or more.
[0037]
　(P: 0.03% or less)
　P is an element contained as an impurity. If P is contained in excess, the toughness of the base steel sheet 12 tends to decrease. Therefore, the amount of P is preferably 0.03% or less. Preferably, the amount of P is 0.01% or less. The lower limit of the amount of P does not need to be specified, but from the viewpoint of cost, the lower limit is preferably 0.0002%.
[0038]
　(S: 0.010% or less)
　S is an element contained as an impurity. S has an action of forming MnS and embrittlement of the base steel sheet 12. Therefore, the amount of S is preferably 0.010% or less. A more desirable amount of S is 0.004% or less. The lower limit of the amount of S does not need to be specified, but from the viewpoint of cost, the lower limit is preferably 0.0002%.
[0039]
　(N: 0.010% or less)
　N is an element contained as an impurity in the base steel sheet 12. Further, N is an element that forms inclusions in the base steel sheet 12 and deteriorates the toughness after hot press forming. Therefore, the amount of N is preferably 0.010% or less. The amount of N is preferably 0.008% or less, more preferably 0.005% or less. The lower limit of the amount of N does not need to be specified, but from the viewpoint of cost, the lower limit is preferably 0.0002%.
[0040]
(Ti: 0% to 0.20%, Nb: 0% to 0.20%, V: 0% to 1.0%, W: 0% to 1.0%)
　Ti, Nb, V, and W are , An element that promotes mutual diffusion of Fe and Al in the aluminum plating layer 14 and the base steel plate 12. Therefore, at least one or more of Ti, Nb, V, and W may be contained in the base steel sheet 12. However, if 1) the amount of Ti and Nb exceeds 0.20%, or 2) the amount of V and W exceeds 1.0%, the effect of the above action is saturated, which is disadvantageous in terms of cost. Therefore, the Ti amount and the Nb amount are often 0.20% or less, and the V amount and the W amount are preferably 1.0% or less. The Ti amount and Nb amount are preferably 0.15% or less, and the V amount and W amount are preferably 0.5% or less. In order to obtain the effect of the above action more reliably, it is preferable that the lower limit values ​​of the Ti amount and the Nb amount are 0.01% and the lower limit values ​​of the V amount and the W amount are 0.1%.
[0041]
(Cr: 0% to 1.0%, Mo: 0% to 1.0%, Cu: 0% to 1.0%, Ni: 0% to 1.0%, B: 0% to 0.0100% )
　Cr, Mo, Cu, Ni, and B are elements that are effective in enhancing the hardenability of the base steel plate 12 and stably ensuring the strength after quenching. Therefore, one or more of these elements may be contained in the base steel sheet 12. However, even if the contents of Cr, Mo, Cu, and Ni are more than 1.0% and the amount of B is more than 0.0100%, the above effect is saturated and it is disadvantageous in terms of cost. Therefore, the content of Cr, Mo, Cu, and Ni is preferably 1.0% or less. The amount of B is preferably 0.0100% or less, preferably 0.0080% or less. In order to obtain the above effect more reliably, it is preferable to satisfy either the content of Cr, Mo, Cu, and Ni of 0.1% or more and the content of B of 0.0010% or more.
[0042]
(Ca: 0% to 0.05%, Mg: 0% to 0.05%, REM: 0% to 0.05%)
　Ca, Mg, and REM refine the morphology of inclusions in steel. It has the effect of preventing the occurrence of cracks during hot press molding due to inclusions. Therefore, one or more of these elements may be contained in the base steel sheet 12. However, if it is added in an excessive amount, the effect of miniaturizing the morphology of the inclusions in the base steel sheet 12 is saturated, and only the cost increases. Therefore, the Ca amount is 0.05% or less, the Mg amount is 0.05% or less, and the REM amount is 0.05% or less. In order to obtain the effect of the above action more reliably, it is preferable to satisfy any one of Ca amount of 0.0005% or more, Mg amount of 0.0005% or more, and REM amount of 0.0005% or more.
[0043]
　Here, REM refers to 17 elements of Sc, Y and lanthanoid, and the content of REM refers to the total content of these elements. In the case of lanthanoids, they are industrially added to the base steel sheet 12 in the form of misch metal.
[0044]
(Sn: 0% to 0.5%)
Sn is an element that improves the corrosion resistance of the exposed portion 22. Therefore, Sn may be contained in the base steel plate 12. However, if Sn is contained in the base steel sheet 12 in excess of 0.5%, the base steel sheet 12 becomes embrittled. Therefore, the Sn amount is set to 0.5% or less. Preferably, the Sn amount is 0.3% or less. In order to obtain the effect of the above action more reliably, the Sn amount is preferably 0.02% or more. More preferably, the Sn amount is 0.04% or more.
[0045]
(Bi: 0% to 0.05%)
　Bi becomes a solidified nucleus in the solidification process of molten steel, and by reducing the secondary arm spacing of dendrites, segregation of Mn and the like segregated within the secondary arm spacing of dendrites. It is an element that has an inhibitory effect. Therefore, Bi may be contained in the base steel sheet 12. In particular, for steel sheets that often contain a large amount of Mn, such as steel sheets for hot pressing, Bi is effective in suppressing deterioration of toughness due to segregation of Mn. Therefore, it is preferable that such a steel grade contains Bi. However, even if Bi is contained in the base steel sheet 12 in excess of 0.05%, the effect of the above action is saturated, resulting in an increase in cost. Therefore, the amount of Bi is set to 0.05% or less. The amount of Bi is preferably 0.02% or less. In order to obtain the effect of the above action more reliably, the Bi amount is preferably 0.0002% or more. More preferably, the amount of Bi is 0.0005% or more.
[0046]
(Si: 0% to 2.00%)
　Si is a solid solution strengthening element and can be effectively utilized when it is contained in the base steel sheet 12 up to 2.00%. However, if Si is contained in the base steel sheet 12 in an amount of more than 2.00%, there is a concern that the plating property may be defective. Therefore, when the base steel sheet 12 contains Si, the amount of Si is preferably 2.00% or less. The preferred upper limit is 1.40% or less, more preferably 1.00% or less. The lower limit is not particularly limited, but the lower limit is preferably 0.01% in order to obtain the effect of the above action more reliably.
[0047]
(Remaining) The
　remaining is Fe and impurities. Here, the impurities include components contained in raw materials such as ore and scrap, or components mixed in the base steel sheet 12 in the manufacturing process. Impurities mean components that are not intentionally contained in the steel sheet.
[0048]
[Aluminum plating layer] The
　aluminum plating layer 14 is formed on both surfaces of the base steel plate 12. The method for forming the aluminum plating layer 14 is not particularly limited. For example, the aluminum plating layer 14 is formed on both sides of the base steel plate 12 by a hot-dip galvanizing method (a method of immersing the base steel plate 12 in a molten metal bath containing mainly aluminum to form the aluminum plating layer 14). May be good.
[0049]
　Here, the aluminum plating layer 14 is a plating layer containing aluminum as a main component, and may contain 50% by mass or more of aluminum. Depending on the purpose, the aluminum plating layer 14 may contain an element other than aluminum (for example, Si), or may contain impurities that are mixed in during the manufacturing process. Specifically, the aluminum-plated layer 14 may contain, for example, 5% to 12% of Si (silicon) in mass%, and the balance may have a chemical composition of aluminum and impurities. Further, the aluminum plating layer 14 contains 5% to 12% of Si (silicon) and 2% to 4% of Fe (iron) in mass%, and the balance has a chemical composition consisting of aluminum and impurities. May be good.
　When Si is contained in the aluminum plating layer 14 in the above range, deterioration of workability and corrosion resistance can be suppressed. Further, the thickness of the intermetallic compound layer 16 can be reduced.
[0050]
　The thickness of the aluminum plating layer 14 provided in the region other than the end portion of the steel sheet 100 is not particularly limited, and for example, the average thickness is often 8 μm (micrometer) or more, preferably 15 μm or more. The thickness of the aluminum plating layer 14 in the plating portion 26 is, for example, preferably 50 μm or less, preferably 40 μm or less, more preferably 35 μm or less, and 30 μm or less in average thickness. Is even more preferable. The thickness of the aluminum plating layer 14 represents the average thickness in the region other than the end portion of the steel plate 100.
[0051]
　The aluminum plating layer 14 prevents corrosion of the base steel plate 12. Further, the aluminum plating layer 14 has a scale (iron compound) due to oxidation of the surface of the base steel plate 12 even if the base steel plate 12 is heated to a high temperature when the steel plate is processed by hot press forming. Prevent the occurrence. Further, the aluminum plating layer 14 has a higher boiling point and melting point than a plating coating made of an organic material or a plating coating made of another metal material (for example, a zinc material). Therefore, when the hot press molded product is molded, the coating does not evaporate, so that the surface protection effect is high.
[0052]
　The aluminum plating layer 14 can be alloyed with iron (Fe) in the base steel sheet 12 by heating during hot dip galvanizing and hot press forming.
[0053]
[Intermetallic compound layer] The
　intermetallic compound layer 16 is a layer formed at a boundary between the base steel plate 12 and the aluminum plating layer 14 when aluminum plating is provided on the base steel plate 12. Specifically, the intermetallic compound layer 16 is formed by the reaction of iron (Fe) and a metal containing aluminum (Al) of the base steel sheet 12 in a molten metal bath containing mainly aluminum. The intermetallic compound layer 16 is mainly formed of a plurality of types of compounds represented by FixAly (x and y represent 1 or more). When the aluminum-plated layer 14 contains Si (silicon), the intermetallic compound layer 16 is formed of a plurality of types of compounds represented by FixAly and FixAlySiz (x, y, z represent 1 or more).
[0054]
　The thickness of the intermetallic compound layer 16 formed in the region other than the end portion of the steel sheet 100 is not particularly limited, and for example, the average thickness is preferably 1 μm or more, preferably 3 μm or more, and 4 μm or more. Is more preferable. Further, the thickness of the intermetallic compound layer 16 formed in the region other than the end portion of the steel sheet 100 is preferably, for example, 10 μm or less in average, and preferably 8 μm or less. The thickness of the intermetallic compound layer 16 represents the average thickness in the region other than the end portion.
　The thickness of the intermetallic compound layer 16 can be controlled by the temperature and immersion time of the molten metal bath containing mainly aluminum.
[0055]
　Here, the confirmation of the base steel plate 12, the intermetallic compound layer 16 and the aluminum plating layer 14, and the measurement of the thickness of the intermetallic compound layer 16 and the aluminum plating layer 14 are carried out by the following methods.
[0056]
　Cutting is performed so that the cross section of the steel plate 100 is exposed, and the cross section of the steel plate 100 is polished. The orientation of the cross section of the exposed steel sheet 100 is not particularly limited. However, the cross section of the steel sheet 100 is preferably a cross section orthogonal to the longitudinal direction of the exposed portion 22. The cross section of the polished steel sheet 100 is line-analyzed from the surface of the steel sheet 100 to the base steel sheet 12 by an electron probe microanalyzer (FE-EPMA), and the aluminum concentration and the iron concentration are measured. The aluminum concentration and the iron concentration are preferably average values ​​measured three times. The measurement conditions are an acceleration voltage of 15 kV, a beam diameter of about 100 nm, an irradiation time of 1000 ms per point, and a measurement pitch of 60 nm. The measurement distance may be such that the thickness of the plating layer can be measured. For example, the measurement distance is about 30 μm to 80 μm in the plate thickness direction (thickness direction) from the surface of the steel plate 100 to the base steel plate 12. The plate thickness (thickness) of the base steel plate 12 is preferably measured using a scale with an optical microscope.
[0057]
As
　a measured value of the aluminum concentration in the cross section of the steel plate 100, the region where the aluminum (Al) concentration is less than 0.06% by mass is the base steel plate. 12. The region where the aluminum concentration is 0.06% by mass or more is determined to be the intermetallic compound layer 16 or the aluminum plating layer 14. Further, among the intermetallic compound layer 16 and the aluminum plating layer 14, the region where the iron (Fe) concentration is more than 4% by mass is the intermetallic compound layer 16, and the region where the iron concentration is 4% by mass or less is the aluminum plating layer 14. Judge.
　The thickness of the intermetallic compound layer 16 is defined as the distance from the boundary between the base steel plate 12 and the intermetallic compound layer 16 to the boundary between the intermetallic compound layer 16 and the aluminum plating layer 14. Further, the distance from the boundary between the intermetallic compound layer 16 and the aluminum plating layer 14 to the surface of the steel plate 100 on which the aluminum plating layer 14 is formed is defined as the thickness of the aluminum plating layer 14.
[0058]
　The thickness of the aluminum plating layer 14 and the thickness of the intermetallic compound layer 16 are linearly analyzed from the surface of the steel plate 100 to the surface of the base steel plate 12 (the boundary between the base steel plate 12 and the intermetallic compound layer 16), and the following Measure in this way.
　The thickness of the aluminum plating layer 14 is obtained by dividing the thickness from the surface of the steel plate 100 having the aluminum plating layer 14 to the intermetallic compound layer 16 into five equal parts in the region other than the end portion according to the above-mentioned criteria. The thickness of the aluminum plating layer 14 is defined as the average value of the obtained values ​​obtained at the position of.
　For example, when measuring the thickness of the plated portion 26, taking the plated portion 26 of FIGS. 1 and 5 as an example, the longitudinal direction of the exposed portion 22 (the X direction in FIGS. 1 and 5, hereinafter referred to as the third direction). The thickness of the aluminum plating layer 14 at five positions obtained by dividing the total length of the plated portion 26 in the third direction (the same applies to the specification of the total length below) into five equal parts was obtained, and the obtained values ​​were averaged. The value may be the thickness of the aluminum plating layer 14. Here, the thickness measurement position in the first direction F1 is performed at a position halved of the width of the plating portion 26 in each of the five cross-sectional views (hereinafter, the thickness measurement is performed in the same manner). The width of the plating portion 26 indicates the distance between the edges of the plating portion 26 in the first direction F1, and is also simply referred to as the width of the plating portion 26.
　The distinction between the aluminum plating layer 14, the intermetallic compound layer 16, and the base steel plate 12 at the time of thickness measurement is determined according to the above-mentioned determination criteria. When the exposed portion 22 is extended on the curve, the thickness may be obtained at a portion where the total length along the curve is divided into five equal parts.
　Similarly, when measuring the thickness of the intermetallic compound layer 16, the intermetallic compound layer 16 is divided into five equal parts in the third direction, and the total length of the intermetallic compound layer 16 is divided into five equal parts. The thickness of the compound layer 16 is obtained, and the value obtained by averaging the obtained values ​​is taken as the thickness of the intermetallic compound layer 16. When measuring the thickness of the intermetallic compound layer 16 of the plating portion 26, the thickness is measured at a position halved of the width of the plating portion 26, as in the case of measuring the thickness of the aluminum plating layer 14. Further, the distinction between the aluminum plating layer 14, the intermetallic compound layer 16 and the base steel plate 12 at the time of thickness measurement is determined according to the above-mentioned determination criteria.
[0059]
[End
　of Steel Sheet ] The steel plate 100 of the present disclosure has exposed portions 22 on both sides of the end portion of the steel plate 100 in which the base steel plate 12 is exposed. The exposed portion 22 is present in at least a part of the end portion. Further, the plating portion 26 is provided on the central portion side of the steel plate 100 with respect to the exposed portion 22. The plated portion 26 has a structure similar to that in the region other than the end portion.
[0060]
(Exposed portion) The
　exposed portion 22 is formed on both sides of the end portion of the steel plate 100 to be welded, and is formed along the edge of the steel plate 100. That is, the exposed portion 22 is formed in a range from the edge of the steel plate 100 to the boundary between the exposed portion 22 and the plated portion 26 at the end portion to be welded. Here, taking FIGS. 2 and 6 as examples, the exposed portion 22 is formed in a range from the end face 100A of the steel sheet 100 to the boundary 100B. In the case of FIGS. 2 and 6, the width of the exposed portion 22 is W.
[0061]
　The exposed portions 22 formed on at least both sides of the end portion of the steel plate 100 are formed at the boundary between the weld metal portion formed on the joint and the steel plate 100 after the end portions of the steel plate 100 to be welded are butt-welded. It suffices that the aluminum plating layer 14 and the intermetallic compound layer 16 are formed so as not to remain. The exposed portion 22 is provided on both sides of at least a part of the end portion of the steel plate 100 along the edge of the steel plate 100 so as to be in this state.
[0062]
　The width of the exposed portion 22 is (maximum width of weld metal portion × 1.2) / 2 to (welded metal) in terms of fatigue strength of the joint when it is a butt welded member and a hot press molded product, and corrosion resistance after painting. It is preferable to satisfy the relationship of maximum width of part × 4) / 2. The fatigue strength of the joint and the corrosion resistance after painting depend on the maximum width of the molten metal. As the maximum width of the weld metal portion, the larger width of the front surface (first surface) and the back surface (second surface) may be adopted. The maximum width of each weld metal portion on the front surface and the back surface may satisfy the above relation.
[0063]
　By setting the upper limit of the width of the exposed portion 22 to the above range, it becomes easy to suppress a decrease in fatigue strength of the joint when the butt welded member and the hot press molded product are used. Further, when a hot press molded product is used, a decrease in corrosion resistance after painting of the welded portion is likely to be suppressed. Further, when the hot press molded product is used, the range in which the scale is formed does not become too wide, so that damage to the press mold is easily suppressed. On the other hand, by setting the lower limit of the width of the exposed portion 22 to the above range, it is possible to prevent the aluminum plating layer 14 and the intermetallic compound layer 16 from being melted by the laser for butt welding during butt welding. Therefore, the mixing of the aluminum component into the weld metal portion is suppressed, so that the fracture of the molten metal is easily suppressed.
[0064]
　In the same respect, the width of the exposed portion 22 in the first direction F1 is preferably 0.1 mm or more on average. More preferably, the width of the exposed portion 22 is 0.2 mm or more. By setting the width of the exposed portion 22 to 0.1 mm or more, it is possible to prevent aluminum from remaining at the end portion of the weld metal portion during welding of the tailored blank. The width of the exposed portion 22 is preferably 5.0 mm or less. By setting the width of the exposed portion 22 to 5.0 mm or less, deterioration of corrosion resistance after painting can be suppressed. When the butt welding is laser welding, the width of the exposed portion 22 is preferably 0.5 mm or more, and the width of the exposed portion 22 is 1.5 mm or less. When the butt welding is plasma welding, the width of the exposed portion 22 is preferably 1.0 mm or more, and the width of the exposed portion 22 is preferably 4.0 mm or less.
　Here, referring to FIG. 2, the width of the exposed portion 22 is the distance from the edge of the end face 100A of the steel plate 100 to the boundary 100B between the exposed portion 22 and the plating portion 26, and is represented by W. The width of the exposed portion 22 is, for example, the width of the exposed portion 22 measured from five cross sections obtained by dividing the total length of the exposed portion 22 in the third direction (X direction) into five equal parts using a microscope, and the average value thereof. And.
[0065]
　The range of the depth D is not particularly limited as long as the aluminum plating layer 14 and the intermetallic compound layer 16 can be removed and the base steel plate 12 can be exposed. That is, the range of the depth D may be equal to or larger than the total thickness of the aluminum plating layer 14 and the intermetallic compound layer 16. However, from the viewpoint of static strength (joint static strength) and fatigue strength, the range of depth D is preferably as small as possible within the range of the total thickness of the aluminum plating layer 14 and the intermetallic compound layer 16. .. The depth D may be equal to the total thickness of the aluminum plating layer 14 and the intermetallic compound layer 16. In this case, the shape of the end portion of the plated portion 26 on the edge side of the steel plate 100 and the inner side of the base steel plate 12 may be a concave curve represented by the radius of curvature R2.
[0066]
　Further, in the exposed portions 22 provided on both sides of the end portion of the steel plate 100, as shown in FIG. 9, the relationship between the depth D and the above-mentioned radii of curvature R1 and R2 has the relationship of the following equation (3). It is good to meet. By satisfying this relationship, the fatigue strength of the joint becomes more excellent. Also, the static strength will be better. The relationship D ≦ (R1 + R2) between the depth D (μm) and the radius of curvature R1 (μm) and the radius of curvature R2 (μm) represents the relationship per one side of the exposed portion, and both sides have this relationship. You should be satisfied.
　Equation (3) D ≦ (R1 + R2)
[0067]
　Specifically, the depth D is often set to (thickness of base steel plate 12 × 0.15) / 2 or less in consideration of the static strength and fatigue strength of the joint, and (thickness of base steel plate 12). It is preferably x0.1) / 2 or less.
[0068]
　Here, as a method of measuring the depth D and the width (removal width W) of the exposed portion 22 from the tailored blank and the hot stamped product, the following method can be mentioned.
[0069]
　The depth D is determined by, for example, cutting a steel plate 100 having an exposed portion 22 adjacent to a weld metal portion in the plate thickness direction in a tailored blank and a hot stamped product, and observing the cut cross section with an optical microscope. Can be done. In the cut cross section, the thickness of the base steel plate 12 at the exposed portion 22 adjacent to the weld metal portion, and the total thickness of the aluminum plating layer 14, the intermetallic compound layer 16, and the region other than the end portion of the base steel plate 12. Should be measured.
[0070]
　Specifically, first, in the region other than the end portion, the thickness of the base steel plate 12 and the total thickness (thickness A) of the aluminum plating layer 14 and the intermetallic compound layer 16 formed on the base steel plate 12 Ask for. The thickness A is an average value of values ​​obtained at five positions obtained by dividing the plate width into five equal parts in a region other than the end portion.
　Next, the thickness (thickness B) of the base steel sheet 12 in the portion excluding the exposed portion 22 located at the boundary between the exposed portion 22 and the plating portion 26 is determined. The thickness B is a range from the end point on the base steel plate 12 side at the boundary between the exposed portion 22 and the plated portion 26 (the end on the plated portion 26 side of the exposed portion 22) to the end point of the exposed portion 22 on the edge side of the steel plate 100. Is the measured average value. However, with respect to the total width of this range, the range of 10% from the end point of the exposed portion 22 on the edge side of the steel plate 100 toward the central portion, and the base steel plate 12 side at the boundary between the exposed portion 22 and the plated portion 26. The range of 10% from the end point toward the edge side of the steel sheet 100 is excluded from the measurement. In this excluded range, measurements are taken at five positions divided into five equal parts, and the average value is defined as the thickness B.
　Then, the depth D is obtained by subtracting the thickness B from the thickness A obtained above (that is, the depth D is obtained by the following formula: depth D = thickness A-thickness B).
　The depths D1 and D2 described later may be measured in the same manner.
[0071]
　Further, the width of the exposed portion 22 may be measured by observing the exposed portion 22 with an optical microscope. The specific method for measuring the width of the exposed portion 22 is as follows.
　First, five measurement samples including a cross section in which the entire width of the exposed portion 22 at the end of the steel plate 100 can be observed are collected. Next, the steel sheet 100 is cut so that the cross section is exposed, embedded in resin, polished, and the cross section is enlarged with an optical microscope. The distance (width of the exposed portion 22) from the edge of the steel plate 100 to the plated portion 26 is measured with reference to the edge of the steel plate 100. The average value measured at five points is defined as the width of the exposed portion 22.
[0072]
(Boundary between exposed portion and plated portion)
　The cross-sectional shape of the boundary between the exposed portion 22 and the plated portion 26 is such that the outer surface side of the steel plate 100 at the boundary is curved when the boundary between the exposed portion 22 and the plated portion 26 is viewed from the cross section. It has a plated portion 26 formed by a convex curve represented by a radius R1. That is, the shape of the end portion of the plated portion 26 on the end face 100A side of the steel plate 100 and on the outer side from the inside of the base steel plate 12 toward the surface of the base steel plate 12 is represented by the radius of curvature R1 in the first direction F1. It is a curved curve that is convex to the side. Further, an exposed portion formed by a concave curve represented by a radius of curvature R2 may be provided on the other end side of the boundary. That is, the shape of the end portion of the exposed portion 22 on the plating portion 26 side may be a concave curve represented by the radius of curvature R2. The plating portion 26 formed by the convex curve is an aluminum plating layer 14. The radius of curvature R1 satisfies the relationship of 5 μm ≦ R1. Further, the radius of curvature R2 satisfies the relationship of 260 ≦ R2.
[0073]
　In terms of corrosion resistance after coating, the larger R1 is, the better the adhesion of the coating film is. Therefore, R1 may satisfy 10 μm ≦ R1, may satisfy 15 μm ≦ R1, or may satisfy 20 μm ≦ R1. The upper limit of R1 is not particularly limited. From the viewpoint of coating corrosion resistance, the removal width (exposed width) of the aluminum plating layer 14 and the intermetallic compound layer 16 is preferably small, and therefore R1 is preferably 500 μm or less (R1 ≦ 500 μm).
　Further, in terms of the fatigue strength of the joint, the larger R2 is, the more the stress concentration when a stress load is applied is relaxed. Therefore, R2 may satisfy 260 μm ≦ R2, 400 μm ≦ R2, or 1000 μm ≦ R2. The upper limit of R2 is not particularly limited, and examples thereof include R2 ≦ 100,000 μm.
[0074]
　Here, the method of measuring R1 and R2 at the boundary between the exposed portion 22 and the plated portion 26 from a steel plate, a tailored blank, a hot stamped product, or the like is the same as the method for measuring the width of the exposed portion 22 described above. Depending on the method, it may be measured with an optical microscope. R1 measured from the cross-sectional photograph is set to the smallest value (excluding 0) in the radius of curvature measured in the swell curve at the end of the plated portion 26. R2 measured from the cross-sectional photograph is set to the smallest value (excluding 0) in the radius of curvature measured in the swell curve at the end of the exposed portion 22. R1 and R2 are the average values ​​of the values ​​of R1 and the values ​​of R2 obtained from the five cross sections obtained by dividing the total length of the exposed portion 22 in the longitudinal direction into five equal parts.
[0075]
　At the boundary between the exposed portion 22 and the plated portion 26, the central portion of the boundary and the end portion on the base steel plate 12 side may extend in the direction along the plate thickness direction (FIGS. 1, FIG. 2, FIG. 5). , See FIG. 6). Further, the central portion of the boundary and the end portion on the base steel plate 12 side are inclined with respect to the plate thickness direction if R1 satisfies the above conditions (for example, the base steel plate 12 side of the boundary is more than the outer surface side of the steel plate 100). It may be inclined toward the edge side of the steel plate 100 (see FIGS. 3 and 7). When it is inclined, R2 may satisfy the condition of the equation (2).
[0076]
　The width W of the exposed portion 22 when the central portion of the boundary is inclined will be described with reference to FIGS. 3 and 7. 3 and 7 are enlarged cross-sectional views showing another example of the end portion of the steel plate 100 of the present disclosure. As shown in FIGS. 3 and 7, the boundary 100B between the exposed portion 22 and the plated portion 26 is inclined toward the edge side of the steel plate 100. Then, as shown in FIGS. 3 and 7, the width W of the exposed portion 22 is from the edge of the end surface 100A of the steel sheet 100 to the intermetallic compound layer 16 side at the boundary 100B between the exposed portion 22 and the plating portion 26. It is represented by the distance to the base steel plate 12.
[0077]
　Here, in the steel plate 100 of the present disclosure, an exposed portion 22 of the base steel plate 12 is formed at an end portion of a planned welding portion. An unexposed portion in which at least the intermetallic compound layer 16 remains is formed in the region including the edge of the steel sheet 100 as long as the weld metal portion does not break when made into a tailored blank or a hot stamped product. It may have been done.
[0078]
　For example, when the steel plate 100 is punched to obtain a punched member, sagging may occur in a region including the edge of the steel plate 100 in the end portion of the steel plate 100 by a cutting means such as a shear. When the intermetallic compound layer 16 and the aluminum plating layer 14 are removed from the steel sheet 100 in which the sagging has occurred, for example, by cutting or the like at the end of the steel sheet 100, at least the intermetallic compound layer 16 is formed in the portion where the sagging occurs. May remain. The portion where at least the intermetallic compound layer 16 remains is the unexposed portion. The presence of this unexposed portion is permissible as long as the weld metal portion does not break when it is made into a tailored blank or a hot stamped product.
[0079]
　The concentration (Al concentration) of aluminum contained in the weld metal portion of the tailored blank and the hot stamped molded product is 0.065% by mass to 1% by mass or less (preferably 0.8% by mass or less). That is good. Within this range, breakage of the weld metal portion in the tailored blank and the hot stamped product is likely to be suppressed.
[0080]
　The aluminum concentration in the weld metal part is the average concentration. The aluminum concentration in the weld metal part is measured as follows.
　It is cut in a direction orthogonal to the laser welding line, embedded in a resin, polished, and mapped and analyzed from the surface of the steel sheet 100 to the base steel sheet 12 by an electron probe microanalyzer (FE-EPMA) to measure the aluminum concentration. The measurement conditions are an acceleration voltage of 15 kV, a beam diameter of about 100 nm, an irradiation time of 1000 ms, and a measurement pitch of 5 μm in a grid pattern. The measured value of the aluminum concentration of the weld metal part is averaged to obtain the average concentration.
[0081]
　Next, an example of a preferable manufacturing method of the steel sheet 100 of the present disclosure will be described. The formation of the exposed portion 22 is not particularly limited, and either laser processing or machining may be used. An example of a preferred manufacturing method for the steel sheet 100 of the present disclosure includes a step of forming the exposed portion 22 by cutting. As an example of a more preferable manufacturing method, there is a step of forming the exposed portion 22 by cutting by machining. As an example of a more preferable manufacturing method, there is a step of forming the exposed portion 22 by cutting with an end mill. The end mill facilitates the manufacture of the shape of the steel plate 100 of the present disclosure by making the R shape of the end portion of the tool appropriate.
　Hereinafter, an example of a preferable method for forming the exposed portion 22 will be specifically described.
[0082]
　As an example of a preferable method for forming the exposed portion 22 on both sides of at least a part of the end portion of the steel sheet 100, for example, the following method can be mentioned.
　At least a part of the end portion of the steel plate 100, the intermetallic compound layer 16 and the aluminum plating layer 14 formed on both surfaces of the base steel plate 12 are removed by cutting on both sides to expose the base steel plate 12 in the exposed portion 22. May have a step of forming (formation method A).
[0083]
　The forming method A is a method of forming the exposed portion 22 at the end portion of the steel plate 100, for example, as follows. First, as a steel plate before forming a tailored blank, a steel plate cut to a desired size is prepared. Next, the aluminum plating layer 14 and the intermetallic compound layer 16 formed on both surfaces of the base steel sheet 12 are removed by cutting at least a part of the end portion of the steel sheet after cutting. Then, an exposed portion 22 on which the base steel plate 12 is exposed is formed at the end portion of the steel plate 100.
[0084]
　The method of removing by cutting to form the exposed portion 22 is not particularly limited. For example, a method of cutting by polishing, cutting, cutting machine, slicing machine, end mill, metal saw or the like can be mentioned. Further, these methods may be combined to form the exposed portion 22 by removing the intermetallic compound layer 16 and the aluminum plating layer 14.
[0085]
　As another method other than machining, removal by laser machining such as laser gouging can be mentioned. However, when the exposed portion 22 is formed by laser processing such as laser gouging, hydrogen is generated on the base steel plate 12 of the portion where the exposed portion 22 is formed due to water vapor in the atmosphere due to heat being applied. May be mixed. Further, since the base steel plate 12 in the portion where the exposed portion 22 is formed is rapidly cooled after the laser processing, martensite is generated in the metal structure of the base steel plate 12 in this portion. This may cause delayed fracture at the end face of the steel sheet before welding.
　On the other hand, when the exposed portion 22 is formed by machining, the temperature rise of the base steel plate 12 of the portion where the exposed portion 22 is formed is suppressed and martensite is not generated. In addition, since hydrogen does not enter, the occurrence of delayed fracture is suppressed. In this respect, it is preferable to employ machining by machining as a method for forming the exposed portion 22.
　Further, when the exposed portion 22 is formed by machining, it is not necessary to take measures against light shielding against the laser beam when performing laser machining such as laser gouging, which is advantageous in terms of cost and the like.
[0086]
　Further, as a method of forming R1 and R2 at the boundary between the exposed portion 22 and the plating portion 26, it is preferable to form them by the above machining. When it is formed by machining, it may be formed by using, for example, an end mill (the tip blade of the end mill, the side blade of the end mill), a metal saw, or the like.
　Among the machining, the exposed portion 22 is preferably formed by cutting with an end mill. Cutting by an end mill is cutting by rotary motion. Therefore, the exposed portion 22 formed by the end mill has a fine uneven shape on the cutting surface (exposed surface of the base steel plate 12 in the exposed portion 22 and the cross section of the plated portion 26 at the boundary between the exposed portion 22 and the plated portion 26). There are cutting marks.
[0087]
　As long as the exposed portions 22 are formed on both sides of at least a part of the end portions of the steel sheet 100, the order of forming the exposed portions 22 at the end portions is not limited to the above-mentioned forming method A. The exposed portion 22 may be provided at the end portion where welding is planned.
　As an example of another preferable method of forming the exposed portion 22 on both sides of at least a part of the end portion of the steel sheet 100, for example, the following method can be mentioned.
[0088]
　In at least a part of the region other than the end of the steel plate 100, the aluminum plating layer 14 and the intermetallic compound layer 16 formed on both sides of the base steel plate 12 are removed on both sides by cutting to expose the base steel plate 12. The step of forming the exposed exposed portion 22 and the cutting of the steel plate 100 so that the exposed portion of the base steel plate 12 is held at the end of the steel plate 100, and the base steel plate 12 at least a part of the end of the steel plate 100. It may have a step of forming the exposed portion 22 exposed on both sides of the steel sheet 100 (referred to as the forming method B).
[0089]
　Specifically, the forming method B is, for example, the following method. First, a steel plate 100 that has been punched and cut to a desired size is prepared. Next, with respect to the cut steel plate 100, the aluminum plating layer 14 and the intermetallic compound layer 16 formed on the base steel plate 12 are removed by cutting, and the exposed portion 22 in which the base steel plate 12 is exposed is provided. Form. The exposed portion 22 is formed in a region other than the end portion of the steel plate 100 so as to extend in one direction, for example. Then, in the cut steel plate 100, the exposed portion of the base steel plate 12 is cut so that the exposed portion 22 follows the edge of the steel plate 100. The steel sheet 100 obtained by cutting is the steel sheet 100 before forming the tailored blank.
[0090]
　In the case of the forming method B, the width of the exposed portion 22 formed by removing the aluminum plating layer 14 and the intermetallic compound layer 16 is preferably 0.4 mm to 30 mm, preferably 0.4 mm to 10 mm. .. The position where the exposed portion 22 is cut may be a position near the center line of the exposed portion 22 so as to have a desired width.
[0091]
　The width of the exposed portion 22 of the base steel plate 12 formed by the above forming method A may be 10% to 50% larger than half the width of the molten region (welded metal portion) after the steel plates 100 are butt-welded. Good.
　The width of the exposed portion 22 of the base steel plate 12 before cutting the steel plate 100 formed as in the above forming method B is 10 from half the width of the molten region (welded metal portion) after the steel plates 100 are butt-welded. It should be% to 50% larger.
　Within these ranges, aluminum is suppressed from being mixed into the weld metal portion after the steel sheet 100 is butt-welded, so that the welded portion has excellent corrosion resistance after painting and a decrease in tensile strength is also suppressed. .. Further, since the hard and brittle intermetallic compound layer 16 is not provided between the weld metal portion and the plating portion 26, a decrease in fatigue strength of the steel sheet 100 after hot stamping is suppressed.
[0092]

　Next, a butt welding member (tailored blank) will be described.
　The butt-welded member (tailored blank) is a tailored blank in which at least two steel plates 100 are butt-welded through an end having at least one steel plate 100 of the present disclosure and having an exposed portion 22 of the steel plate 100 of the present disclosure. is there. If at least one steel plate 100 of the present disclosure is provided, the end faces of the two steel plates may be welded in a butt state, or the end faces of the three steel plates may be welded in a butt state. .. For example, the tailored blank may be a welded member welded in a state where the end face of the end portion of the steel plate 100 of the present disclosure having the exposed portion 22 and the end face of the end portion of the planned welding portion of another steel plate are butted against each other. The other steel sheet to be butt-welded may be a zinc-based plated steel sheet (zinc, zinc-iron, zinc-nickel, zinc-magnesium) having a tensile strength of 400 to 2700 MPa after hot pressing. It is desirable that the galvanized steel sheet is welded without forming the exposed portion 22.
　Further, the tailored blank may be welded, for example, in a state where the end faces of the ends having the exposed portions 22 of the two steel plates 100 of the present disclosure are butted against each other, and the exposed portions 22 of the three steel plates 100 of the present disclosure. Welding may be performed in a state where the end faces of the ends having the Further, the end faces of the exposed portions 22 of the three or more steel plates 100 of the present disclosure may be welded in a state of being butted against each other.
[0093]
　That is, the tailored blank is a weld metal portion that includes at least one steel plate 100 of the present disclosure and joins the ends of at least two steel plates to a steel plate in which the ends of at least two steel plates are arranged so as to face each other. It has a weld metal portion provided adjacent to the exposed portion 22 where the base steel plate 12 of the steel plate 100 of the present disclosure is exposed. For example, specifically, the exposed portion 22 is provided on both sides of the two steel plates joined by the weld metal portion, which are located around the weld metal portion.
[0094]
　Two or more steel plates for obtaining a tailored blank may be used in combination according to the purpose. As the two or more steel plates for obtaining the tailored blank, for example, steel plates of the same strength class may be used, or steel plates of different strength classes may be used. Further, as the two or more steel plates, steel plates having the same thickness may be used, or steel plates having different thicknesses may be used.
　Further, the two or more steel plates for obtaining the tailored blank may be steel plates having the same width of the exposed portion 22 at the end of the steel plate or different steel plates. Further, the steel plate may have the same boundary mode between the exposed portion 22 and the plated portion 26 of the steel plate, or may be different.
　For example, as a combination in which the boundary between the exposed portion 22 and the plated portion 26 of the steel sheet is different, a combination in which R1 on the outer surface side of the steel plate at the boundary between the exposed portion 22 and the plated portion 26 is different can be mentioned. Further, the combination of the steel plate 100 having R1 and R2 is, for example, 1) a combination in which R1 is different and R2 is the same, 2) a combination in which R1 is the same and R2 is different, and 3) R1 is different. R2 also includes a combination of different aspects.
[0095]
　Further, the tailored blank is a welded member in which at least two steel plates 100 of the present disclosure are butt-welded through an end having an exposed portion 22 in terms of fatigue strength of the joint and corrosion resistance of the welded portion after painting. Is good. In this case, it is preferable to satisfy the following conditions.
　Of the at least two steel sheets 100 of the present disclosure, the steel sheet 100 having the smaller product between the thickness of the steel sheet 100 and the tensile strength of the steel sheet 100 after hot press forming (hereinafter, may be referred to as steel sheet A). Let the plate thickness be t (μm). Further, when the steel plate A is viewed from the second direction F2 from the plating portion 26 toward the weld metal portion and the cross section parallel to the thickness direction of the steel plate, the surface of the aluminum plating layer 14 in the plating portion 26 is in the second direction F2. The length of the steel plate 100 from the extended virtual line to the surface of the base steel plate 12 in the thickness direction is defined as the depth of the exposed portion. Of the exposed portions 22 formed on both sides of the end portion of the steel plate A, the depth of the exposed portion 22 formed on one surface (first surface) in the vertical direction is defined as D1 (hereinafter, "" The depth of the vertically exposed portion in the exposed portion 22 formed on the other surface (second surface) is D2 (hereinafter, “removal depth D2”). It may be referred to as). At this time, the relationship of t (μm), D1 (μm), and D2 (μm) may satisfy the relationship of the following formula (4). When the following formula (4) is satisfied, the fatigue strength is improved. Normally, the unit of plate thickness is mm, but the numerical value to be substituted for t is substituted as a value converted to μm.
　Equation (4) ((D1 + D2) / t) × 100 ≦ 20
[0096]
　Note that D1 and D2 are of the above-mentioned depth D (that is, the depth in the vertical direction from the virtual line in which the surface of the aluminum plating layer 14 is extended in the direction of the exposed portion 22 to the surface of the base steel plate 12). It is obtained by the same measurement method as the depth to the portion excluding the exposed portion 22 at the boundary between the exposed portion 22 and the plated portion 26).
　Further, in "the product of the plate thickness of the steel plate and the tensile strength of the steel plate after hot press forming", the plate thickness is the plate thickness of the steel plate after hot press forming, and the tensile strength is the tensile strength after hot press forming. Tensile strength is used respectively.
[0097]
　Here, the plate thickness t, the depth D1, and the depth D2 in the tailored blank will be described with reference to FIGS. 4 and 8. FIG. 4 is a cross-sectional view showing an example of the tailored blank of the present disclosure. The tailored blank 200 shown in FIG. 4 is formed by butt-welding the ends of the steel plate 110 and the planned welding portion of the steel plate 120. In the tailored blank 200, the steel plate 110 and the steel plate 120 are joined by the weld metal portion 30, the exposed portion 22 is adjacent to the weld metal portion 30, and the exposed portion 22 is separated from the weld metal portion 30. It has a plating portion 26 adjacent to the.
[0098]
　As shown in FIGS. 4 and 8, the thickness of the steel plate 120 is smaller than that of the steel plate 110. The steel plate 110 and the steel plate 120 have the same tensile strength of the steel plate after hot press forming. Therefore, in the tailored blank 200 shown in FIGS. 4 and 8, the product of the tensile strength and the thickness of the steel sheet after hot press forming is smaller in the steel plate 120 than in the steel plate 110. Therefore, in FIGS. 4 and 8, the plate thickness t, the depth D1, and the depth D2 are the values ​​of the steel plate 120. The plate thickness t is the plate thickness of the steel plate 120. The depth D1 is the distance between the surface of the base steel plate 12 and the virtual line in which the surface of the aluminum-plated layer 14 on one surface is extended in the direction of the exposed portion 22 (second direction F2). The depth D2 is the distance between the surface of the base steel plate 12 and the virtual line in which the surface of the aluminum-plated layer 14 on the other surface is extended in the direction of the exposed portion 22 (second direction F2).
[0099]
　If the depth D is too large, the durable load of the joint tends to decrease. The durable load is represented by the product of the thickness and strength of the base steel sheet 12 before the aluminum plating treatment. Therefore, the durable load of the joint depends on the steel plate having the smaller durable load among the two steel plates when forming the tailored blank 200. Therefore, it is preferable that the relationship of t, D1, and D2 satisfies the above relationship. The relationship between t, D1 and D2 may be ((D1 + D2) / t) × 100 ≦ 10 or ((D1 + D2) / t) × 100 ≦ 7.
[0100]
　The welding method for performing butt welding is not particularly limited, and examples thereof include welding methods such as laser welding (laser beam welding), arc welding, and electron beam welding. Further, examples of arc welding include plasma welding, TIG (Tungsten Inert Gas) welding, MIG (Metal Inert Gas) welding, MAG (Metal Active Gas) welding, and the like, and examples of suitable arc welding include plasma welding. .. Welding conditions may be selected according to the desired conditions such as the thickness of the steel sheet to be used.
　Further, welding may be performed while supplying a filler wire, if necessary.
[0101]
　As described above, the tailored blank 200 is butt-welded in a state where the end faces of the ends having the exposed portions 22 are abutted. Therefore, the weld metal portion 30 has a small amount of aluminum mixed due to the intermetallic compound layer 16 and the aluminum plating layer 14. Further, since the exposed portion 22 in which the intermetallic compound layer 16 does not exist is adjacent to the weld metal portion 30, the decrease in fatigue strength of the tailored blank 200 and the joint after hot stamping is suppressed. In addition, a decrease in the tensile strength of the joint is suppressed.
[0102]

　Next, the hot press molded product will be described.
　The hot press molded product (hot stamp molded product) is a molded product obtained by hot press molding a tailored blank 200 having at least one steel plate 100 of the present disclosure. That is, the hot press-formed product obtained by hot press molding contains at least one steel plate 100 of the present disclosure, and at least two steel plates are arranged so that the ends of the two steel plates face each other. It is a weld metal portion 30 for joining the end portions of the steel plates of the above, and has a weld metal portion 30 provided adjacent to the exposed portion 22 where the base steel plate 12 of the steel plate 100 of the present disclosure is exposed. For example, specifically, the exposed portion 22 is provided on both sides of the two steel plates joined by the weld metal portion 30 and which are located around the weld metal portion 30.
　The hot stamped product is a welded member in which at least two steel plates of the present disclosure are butt-welded through an end having an exposed portion 22 in terms of fatigue strength of the joint and corrosion resistance after painting of the welded portion. It is preferably a molded product obtained by molding.
[0103]
　The hot stamped product can be manufactured as follows.
　First, the tailored blank 200 is heated to a high temperature to soften the tailored blank 200. Then, using a mold, the softened tailored blank 200 is molded and cooled by hot stamping and then quenched to obtain a hot stamped product having a desired shape. The hot stamped molded product is hardened by heating and cooling to obtain, for example, a molded product having a high tensile strength of about 1500 MPa or more.
[0104]
　As a heating method for hot stamping, in addition to a normal electric furnace and a radiant tube furnace, a heating method by infrared heating, energization heating, induction heating or the like can be adopted.
[0105]
　In the hot stamped article, the aluminum-plated layer 14 of the steel sheet 100 is transformed into an intermetallic compound that imparts protection against oxidation of the steel sheet 100 when heated. For example, when the aluminum plating layer 14 contains silicon (Si), when the aluminum plating layer 14 is heated, the Al phase becomes an intermetallic compound, that is, Al—Fe due to mutual diffusion with Fe. It changes to an alloy phase and an Al—Fe—Si alloy phase. The melting points of the Al—Fe alloy phase and the Al—Fe—Si alloy phase are high, 1000 ° C. or higher. There are a plurality of types of Al—Fe phase and Al—Fe—Si phase, and when heated at a high temperature or for a long time, the phase changes to an alloy phase having a higher Fe concentration. These intermetallic compounds prevent oxidation of the steel sheet 100.
[0106]
　The maximum temperature reached during hot stamping is not particularly limited, but is preferably 850 ° C to 1000 ° C, for example. In hot stamping, the maximum temperature reached is usually about 900 ° C. to 950 ° C. because it is heated in the austenite region.
[0107]
　In hot stamping, a tailored blank 200 heated to a high temperature is press-molded with a die cooled by water cooling or the like, and at the same time, quenched by cooling with the die. Further, if necessary, water may be sprayed directly onto the blank material through the gap of the mold to cool the blank material. Then, a hot stamped product having a desired shape can be obtained. The hot stamped product may be used as it is as a part, or may be used after descaling the welded portion by shot blasting, brushing, laser cleaning or the like, if necessary.
[0108]
　When the tailored blank 200 is heated to a high temperature, the metal structure of the base steel sheet 12 becomes at least a part, preferably the whole, austenite single-phase structure. Then, when press-molded in a die, austenite is transformed into at least one of martensite and bainite by cooling under the desired cooling conditions. Then, in the obtained hot stamped product, the metal structure of the base steel sheet 12 becomes any one of martensite, bainite, or martensite-bainite.
[0109]
　Here, an example of the process from the production of the steel sheet 100 to the production of the hot stamped molded product is as follows.
　First, an aluminum plating layer 14 is formed on both sides of the base steel sheet 12 to obtain a steel sheet. At this time, the intermetallic compound layer 16 is formed between the base steel plate 12 and the aluminum plating layer 14.
[0110]
　Next, the steel plate having aluminum plating on both sides of the base steel plate 12 is wound into a coil. Next, the steel plate wound in a coil shape is pulled out and punched to obtain a punched member.
[0111]
　Next, at least a part of the end portion of the steel plate, the aluminum plating layer 14 and the intermetallic compound layer 16 on both sides of the steel plate 100 are removed to form the exposed portion 22 of the base steel plate 12, and the steel plate of the present disclosure Get 100.
　Here, the exposed portion 22 formed at the end of the steel plate 100 may be formed in a state where the steel plate is wound into a coil and then the steel plate wound into the coil is pulled out. In this case, after forming the exposed portion 22, punching is performed so that the exposed portion 22 is held at the end of the steel sheet 100 to obtain a punched member.
　Further, the exposed portion 22 formed at the end of the steel plate 100 may be formed after the steel plate wound in a coil shape is pulled out and the pulled out steel plate is punched to form a punched member. In this case, the exposed portion 22 may be formed at the end of the punching member. Further, after forming an exposed region in a portion other than the end portion of the punching member so as to extend in one direction, for example, the exposed region of the punching member is cut so that the exposed portion 22 is formed at the end portion of the steel plate 100. You may.
[0112]
　Next, at least one punched member having an exposed portion 22 formed on the end portion of the steel plate 100 is prepared. For example, one punched member or two punched members on which the exposed portion 22 is formed may be prepared.
　Next, butt welding is performed with the ends of the punched members abutted to obtain a tailored blank. Specifically, when two punching members on which the exposed portion 22 is formed are prepared, butt welding is performed with the ends having the exposed portions 22 abutted to obtain a tailored blank 200.
[0113]
　Next, the tailored blank 200 is heated in a heating furnace.
　Next, the heated tailored blank 200 is pressed, molded and hardened by a pair of upper and lower dies.
　Then, by removing it from the mold, the desired hot stamped product can be obtained.
[0114]
　The hot stamp molded product is useful, for example, for application to various automobile members such as automobile bodies as well as various members of industrial machines.
[0115]

　Next, the steel pipe will be described.
　The steel pipe is welded through the end of the open pipe made of the steel plate 100 of the present disclosure. That is, the steel pipe is a steel pipe obtained by welding the steel plate 100 of the present disclosure as an open pipe in a state where the end faces of the ends having the exposed portions 22 are butted against each other. That is, the steel pipe has at least one weld metal portion (that is, a weld metal portion that joins the ends of the open pipes of the steel plate), and both sides of the tubular body made of the steel plate 100 of the present disclosure adjacent to the weld metal portion. It has an exposed portion 22 in which the base metal steel plate 12 is exposed.
[0116]
　Examples of the steel pipe include those obtained as follows.
　1) A steel plate 100 having a first exposed portion 22 provided at the first end portion and a second exposed portion 22 provided at the second end portion is prepared. This single steel plate 100 is formed into a tubular shape to form an open pipe. After that, in the obtained open pipe, a steel pipe obtained by welding in a state where the end face of the end portion having the first exposed portion 22 and the end face of the end portion having the second exposed portion 22 are butted may be used. ..
　2) Two or more steel plates 100 are prepared with the first exposed portion 22 provided at the first end portion and the steel plate 100 provided with the second exposed portion 22 at the second end portion. When the number of the steel plates 100 is two, the end face of the end portion of the first steel plate 100 including the first exposed portion 22 and the end face of the second steel plate 100 of the end portion including the second exposed portion 22. Is welded in a butt state to obtain a tailored blank 200. Then, the tailored blank 200 is formed into a tubular shape to form an open tube. After that, in the obtained open pipe, the end face of the end portion of the first steel plate 100 portion including the second exposed portion 22 which has not been welded and the first exposed portion 22 which has not been welded are provided. A steel pipe obtained by welding in a state where the end face of the end portion of the 100 portion of the steel plate of No. 2 is butted against each other may be used. The open pipe may be formed in a direction parallel to the welding line in the tailored blank 200 before the open pipe is formed, or may be formed in a direction intersecting the weld line.
[0117]
　When a steel pipe is formed from the tailored blank 200, the two or more steel plates forming the tailored blank 200 for forming the steel pipe are not limited to the above, and may be used in combination depending on the purpose. Examples of the combination of two or more steel plates include the same combination as the steel plate described in the steel plate for forming the tailored blank 200 described above.
[0118]
　The method of forming into a tubular shape is not particularly limited, and for example, any method such as a UOE method or a bending roll method may be used.
　Further, the welding after forming into a tubular shape is not particularly limited, and examples thereof include laser welding; plasma welding; electric resistance welding, and electric sewing welding in which welding is performed by high frequency induction heating welding.
[0119]

　Next, the hollow quenching molded product will be described.
　The hollow hardened molded product (hereinafter, may be referred to as “hollow hot stamp molded product”) is formed from the steel plate 100 of the present disclosure or the tailored blank 200 obtained by butt welding the steel plate 100 of the present disclosure. It is a hollow molded product obtained by quenching a steel pipe.
　That is, the hollow hardened molded product obtained by hot stamping the steel pipe has at least one weld metal portion (that is, a weld metal portion that joins the end portions of the steel sheet 100) and is adjacent to the weld metal portion. Both sides of the hollow molded body made of the steel plate 100 of the present disclosure have exposed portions 22 in which the base steel plate 12 is exposed.
[0120]
　The hollow hardened molded product is obtained, for example, as follows.
　A steel pipe obtained by using the steel plate 100 of the present disclosure is formed by a bender. Next, it is heated by a heating furnace, energization heating, or high frequency induction heating. Since the temperature for heating the steel pipe needs to be in the austenite region, it is often set to, for example, 850 ° C to 1100 ° C, and preferably 900 ° C to 1000 ° C. Next, the heated steel pipe is cooled by water cooling or the like and quenched.
　In addition, molding and quenching may be performed at the same time. This is called three-dimensional hot bending quenching (3DQ). For example, a steel pipe is hardened by heating it, deforming it by applying a load, and immediately cooling it by water cooling or the like. By going through these processes, the desired hollow hardened molded product can be obtained. The hollow hardened molded product may be used as it is as a part. Further, if necessary, the welded portion may be descaled (for example, shot blasting, brushing, laser cleaning, etc.) before use.
[0121]
　The use of the hollow hardened molded product of the present disclosure is not particularly limited, and examples thereof include various automobile members such as automobile bodies and various members of industrial machines. Specific examples of automobile members include various pillars; reinforcements such as stabilizers, door beams, roof rails and bumpers; frames; and various parts such as arms.
Example
[0122]
　Hereinafter, examples of the present disclosure will be illustrated, but the present disclosure is not limited to the following examples.
　It is clear that a person skilled in the art can come up with various modifications or amendments within the scope of the ideas described in the claims, and of course, these are also the technical scope of the present disclosure. It is understood that it belongs to.
[0123]

　First, a base steel sheet (strength class 1300 to 1800 MPa after hot stamping) and a low strength steel sheet (strength class 590 to 980 MPa after hot stamping) having the chemical compositions shown in Table 1 are used in Table 2. A steel plate plated with aluminum was prepared so as to have the indicated thickness. Then, this steel plate was cut out to obtain a square steel plate having a side of 10 cm. Next, exposed portions were formed by cutting with an end mill on both sides of the end portion of the prepared base steel plate.
　For some steel sheets, the aluminum plating layer and the intermetallic compound layer 16 were not removed. Further, in some steel sheets, only the aluminum plating layer was removed, and the intermetallic compound layer 16 was not removed. The steel sheet used in No. 18 had the aluminum plating layer and the intermetallic compound layer removed so as to have a shape as shown in FIG.
[0124]
　For the exposed portion, the aluminum plating layer or the aluminum plating layer and the intermetallic compound layer formed on both sides were removed according to the removal portion types shown in Tables 4 and 5, respectively. The exposed portion was formed so that the width of the exposed portion (removal width W) was 2 mm, which was an average value measured at five points as described above. Further, the exposed portion was formed so as to have a depth D shown in Tables 4 and 5. Further, when the exposed portion is formed, the radius of curvature R1 on the aluminum plating layer side and the radius of curvature R2 on the base steel plate side are the values ​​shown in Tables 4 and 5 as the cross-sectional shape of the boundary between the exposed portion and the plated portion. It was formed so as to be. The exposed portion was formed on both sides of the end portion of the steel plate so that only one of the four sides of the steel plate had a total length of 10 cm.
[0125]
　Next, as shown in Table 3, two of the above steel plates (steel plate 1 and steel plate 2) are prepared, and the end faces of the ends of the planned welding portions are abutted by the combination of the steel plates 1 and 2 and laser welded. Butt welding was performed to prepare a tailored blank. Welding was adjusted so as to perform penetration welding under the conditions of a laser output of 3.0 kW to 5.0 kW and a welding speed of 4.0 m / min to 7.0 m / min. Welding was performed so that the width of the weld metal portion was 2.0 mm.
　The prepared tailored blank was held in a furnace heated to 920 ° C. for 4 minutes, then molded with a water-cooled mold and quenched to prepare a flat plate hot stamped product.
　The Vickers hardness of the weld metal portion was HV500 or higher. Further, in Tables 1 to 3, the strength class after HS (hot stamping) represents the strength class after hot stamping.
[0126]
[Evaluation]
(Fatigue strength test and joint static strength) From the
　obtained hot stamped molded product, a dumbbell-shaped test piece with a welded part as a test piece for tensile strength test and a test piece for fatigue strength test. Was collected.
　The test piece had a parallel portion distance of 20 mm and a width of the parallel portion of 15 mm, and was collected so as to have a welding line at the center portion of the parallel portion over the entire width so as to be orthogonal to the longitudinal direction. A fatigue strength test and a joint static strength test were performed using this test piece.
　The joint static strength (denoted as static strength) was calculated by dividing the breaking load by the tensile strength x the cross-sectional area on the side with the smaller plate thickness. The static strength ratio in Table 6 is 100, which is obtained by dividing the joint static strength obtained in the joint static strength test by the static strength of the steel plate 2 having the lower strength among the steel plates 1 and 2 in Table 3. It is the value multiplied by. The static strength ratio was evaluated according to the following criteria, and A and B were passed, and C was rejected.
-Judgment criteria-
A: Static strength ratio is 100% or more
B: Static strength ratio is 90% or more and less than 100%
C: Static strength ratio is less than 90%
　Fatigue strength test (denoted as fatigue limit) is an electromagnetic resonance Using a type fatigue strength tester, the test conditions were carried out in the air at room temperature under the test conditions of complete swing tension of load control axial force, stress ratio 0.1, number of stress repetitions 107 times, and repetition rate of about 80 Hz. These results are shown in Table 6. The fatigue limit ratio in Table 6 is the fatigue limit ratio in Table 6. The fatigue limit obtained in the fatigue strength test is divided by the fatigue limit of the steel sheet 2 having the lower strength among the steel plates 1 and 2 in Table 3. It is a value obtained by multiplying the value by 100. The fatigue limit ratio was evaluated according to the following criteria, and A and B were passed and C was rejected.
-Judgment criteria-
A: Fatigue limit ratio is 100% or more
B: Fatigue limit ratio is 90% or more and less than 100%
C: Fatigue limit ratio is less than 90%
[0127]
(Corrosion resistance test after painting)
　The hot stamped molded product obtained above was subjected to chemical conversion treatment, electrodeposited coating was performed, and a corrosion resistance test after coating was performed. The chemical conversion treatment was carried out with a chemical conversion treatment liquid PB-SX35T manufactured by Nihon Parkerizing Co., Ltd. Then, as the electrodeposition paint, Nippon Paint Co., Ltd.'s cationic electrodeposition paint Powernics 110 was used, and the electrodeposition coating was performed with a target of an electrodeposition film thickness of about 15 μm. After washing with water, it was heated at 170 ° C. for 20 minutes and baked to prepare a test plate. The size of the test plate was 65 mm in length and 100 mm in width (the welded portion is in the center of the width).
　Using this test plate, the automobile parts appearance corrosion test JASO M610-92 was used to evaluate the corrosion resistance after painting under the corrosion condition after 360 cycles (120 days).
[0128]
　The evaluation of corrosion resistance after painting was performed with the maximum corrosion depth as the maximum corrosion depth, and the welded part was evaluated by the following criteria using a point micrometer. A and B were passed, and C was rejected.
- criteria -
A: less than the maximum corrosion depth is 0.1mm
B: less than the maximum corrosion depth is 0.1mm 0.2mm or more
C: the maximum corrosion depth is more than 0.2mm
[0129]
　The steel plates in Tables 2 and 3 show steel plates in which both sides of the base steel plate are plated with aluminum.
[0130]
　Further, in Tables 4 and 5, the notations of "A", "B", and "C" in the removal unit type column are as follows.
"A": Removes aluminum plating layer and intermetallic compound layer
"B": Removes aluminum plating layer (remains intermetallic compound layer)
"C": Remains aluminum plating layer and intermetallic compound layer (does not remove)
[0131]
[table 1]

[0132]
[Table 2]

[0133]
[Table 3]

[0134]
[Table 4]

[0135]
[Table 5]

[0136]
[Table 6]

[0137]
　In Tables 4 and 5, R1 of the steel plate 1 and the steel plate 2 of No. 2 indicates the radius of curvature of the aluminum plating layer, and R2 indicates the radius of curvature of the end portion of the exposed portion on the plating portion side.
　In Table 6, "((D1 + D2) / t) x 100" in the butt welding member column indicates that the product of the thickness of the steel plate and the strength of the steel plate after hot stamping is small among the two steel plates to be butt welded. This is the value obtained for the steel sheet that becomes. t represents the plate thickness (converted to μm), D1 represents the depth formed on the first surface (μm), and D2 represents the depth formed on the second surface (μm).
[0138]
　As shown in Tables 3 to 6, No. 1 using a steel plate in which neither the aluminum plating layer nor the intermetallic compound layer is removed has inferior fatigue strength.
　No. 2, which uses a steel plate in which the aluminum plating layer is removed, the intermetallic compound layer remains, and the base steel plate does not have an exposed portion, has an R1 of 5 μm or more, and therefore has excellent corrosion resistance after painting. However, since the intermetallic compound layer remains, the fatigue strength is inferior.
　No. 3 using a steel plate from which both the aluminum plating layer and the intermetallic compound layer have been removed has excellent fatigue strength. However, since R1 is less than 5 μm, the corrosion resistance after painting is inferior.
　In No. 18, which uses a steel plate having the shape shown in FIG. 10, the end portion on the plated portion side is not a curved line but a straight line, and R2 on the exposed portion side is more than 100,000. Therefore, the base steel plate and the intermetallic compound layer Stress concentration occurs due to the difference in hardness, and the fatigue strength is inferior. Moreover, since R1 is less than 5 μm, the corrosion resistance after painting is also inferior.
　On the other hand, as shown in Tables 3 to 6, Nos. 4 to 17 and Nos. 19 to 23 using steel plates in which both the aluminum plating layer and the intermetallic compound layer are removed and the R1 satisfies 5 μm or more are used. Has excellent fatigue strength and corrosion resistance after painting.
Description of the sign
[0139]
　12 Base steel plate
　14 Aluminum plating layer
　16 Intermetallic compound layer
　22 Exposed part
　26 Plating part
　100 Steel plate
　F1 First direction
The scope of the claims
[Claim 1]
　A base steel sheet,
　on the surface of the base material steel plate, the intermetallic compound layer in this order from the base material steel plate side, and a plating part which aluminum layer is provided,
　and the exposed portion of the base steel sheet is exposed
　with a A steel sheet, which
　is perpendicular to the thickness direction of the steel sheet, and in a first direction from the plated portion toward one edge of the steel sheet, at least the plated portion, said to be on both surfaces of the base steel sheet. The exposed portion and the edge of the steel sheet are arranged in this order
　, and when viewed from a cross section parallel to the first direction and the thickness direction of the steel sheet, the edge side of the steel sheet and the base material The shape of the end portion of the plated portion on the outer side from the inside of the steel plate toward the surface of the base steel plate is a curve convex toward the first direction represented by the radius of curvature R1, and R1 is described below. A steel sheet satisfying the formula (1).
　Equation (1) 5 μm ≤ R1
[Claim 2]
　The steel sheet according to claim 1, wherein in the cross section, the shape of the end portion of the exposed portion on the plating portion side is a concave curve represented by a radius of curvature R2, and the R2 satisfies the following formula (2).
　Equation (2) 260 μm ≦ R2
[Claim 3]
　In the cross section, the depth of the exposed portion is defined as the depth in the thickness direction from the virtual line extending the surface of the aluminum plating layer of the plating portion in the first direction to the surface of the base steel plate. The steel sheet according to claim 2, wherein the relationship between D, R1 and R2 satisfies the following formula (3).
　Equation (3) D ≤ (R1 + R2)
[Claim 4]
　The base steel sheet is
C: 0.02% to 0.58%,
Mn: 0.20% to 3.00%,
Al: 0.005% to 0.06%,
P: 0. 03% or less,
S: 0.010% or less,
N: 0.010% or less,
Ti: 0% to 0.20%,
Nb: 0% to 0.20%,
V: 0% to 1.0%,
W: 0% to 1.0%,
Cr: 0% to 1.0%,
Mo: 0% to 1.0%,
Cu: 0% to 1.0%,
Ni: 0% to 1.0%,
B: 0% to 0.0100%,
Mg: 0% to 0.05%,
Ca: 0% to 0.05%,
REM: 0% to 0.05%,
Sn: 0% to 0.5%, The steel plate according to any one of claims 1 to 3, which has a chemical composition consisting of
Bi: 0% to 0.05%,
Si: 0% to 2.00%, and the
balance: Fe and impurities.
[Claim 5]
　The steel sheet according to any one of claims 1 to 4, wherein the aluminum plating layer has an average thickness of 8 μm to 35 μm, and the intermetallic compound layer has an average thickness of 3 μm to 10 μm.
[Claim 6]
　A tailored blank having a weld metal portion adjacent to the exposed portion of the steel sheet according to any one of claims 1 to 5.
[Claim 7]
　A tailored blank having at least two steel plates according to any one of claims 1 to 5 and having a welded metal portion adjacent to the exposed portion, and among the at least two steel plates. In the steel sheet A in which the product of the thickness of the steel sheet and the tensile strength of the steel sheet after hot press forming is smaller, the steel sheet A
　is directed from the plated portion to the welded metal portion in the second direction and the thickness direction of the steel plate. When viewed from a cross section parallel to each
　of the exposed portions, the length in the thickness direction from the imaginary line obtained by extending the surface of the aluminum plating layer in the plating portion in the second direction to the surface of the base steel sheet is the length of the exposed portion. When defined as
　the depth, the depth D1 (μm) of the exposed portion formed on the surface of the first surface of the
　steel sheet A and the depth of the exposed portion formed on the surface of the second surface of the steel sheet A.
　A tailored blank in which D2 (μm) and the thickness t (μm) of the steel plate A satisfy the following formula (4).
　Equation (4) ((D1 + D2) / t) × 100 ≦ 20
[Claim 8]
　A hot press molded product using the tailored blank according to claim 6 or 7.
[Claim 9]
　A steel pipe having a weld metal portion adjacent to the exposed portion of the steel plate according to any one of claims 1 to 5.
[Claim 10]
　A hollow hardened molded product using the steel pipe according to claim 9.
[Claim 11]
　The method for manufacturing a steel sheet according to any one of claims 1 to 5
　, wherein the method for manufacturing a steel sheet includes a step of forming the exposed portion by cutting with an end mill.