Title of invention: Overlaid blank for hot stamping, method for producing overlaid hot stamping molded article, and overlaid hot stamping article
Technical field
[0001]
　TECHNICAL FIELD The present invention relates to a superposed blank for hot stamping, a method for producing a superposed hot stamped compact, and a superposed hot stamped compact.
Background technology
[0002]
　In recent years, in applications of steel sheets for automobiles, a steel sheet having both high strength and high formability has been desired, and as one of the steel sheets having both high strength and high formability, martensite of retained austenite There is TRIP (Transformation Induced Plasticity) steel that utilizes transformation. With this TRIP steel, it is possible to manufacture a high-strength steel sheet having excellent formability and a strength of the order of 1000 MPa. However, using the technology of TRIP steel, it is difficult to secure formability with ultra-high-strength steel having even higher strength (for example, 1500 MPa or more). There is a problem of poor accuracy.
[0003]
　In contrast to the above-described method of forming at around room temperature (so-called cold press method), a method that has recently attracted attention is also called hot stamping (hot press, hot press, die quench, press quench, etc.). ). This hot stamping secures formability by hot pressing immediately after heating a steel plate to an Ac of 3 points or more (for example, 800° C. or more) and austenitizing the steel sheet, and holds Ms point in the mold while maintaining the bottom dead center. This is a method of manufacturing a component in which a desired high-strength material is obtained after pressing by martensiticizing the material by quenching to the following (for example, 400° C. or less) and quenching. According to this method, it is possible to obtain an automobile part that is also excellent in shape fixability after molding.
[0004]
　On the other hand, various press-molded products used for parts constituting automobile bodies have various performances and characteristics from various viewpoints such as static strength, dynamic strength, collision safety, and weight reduction. Improvement is required. For example, for automobile parts such as A-pillar reinforcement, B-pillar reinforcement, bumper reinforcement, tunnel reinforcement, side sill reinforcement, roof reinforcement or floor cross member, only specific parts of the respective automobile parts can be identified. It is required to have more collision resistance properties than general parts excluding parts.
[0005]
　Therefore, a method of manufacturing a superposed hot stamped body by hot-stamping the obtained steel sheets after superposing and welding a plurality of steel sheets only on a portion corresponding to a specific portion requiring reinforcement in an automobile part. However, it has been actually adopted since around 2007 (see Patent Documents 1 and 2). According to this construction method, it is possible to partially strengthen only a specific part of the superposed hot stamped product while reducing the number of press dies, and the part thickness is not unnecessarily increased. It can also contribute to weight reduction. In addition, the blank produced by superposing and welding in this way is called an overlay blank (also called a patchwork blank). In addition, a blank is a metal plate such as a steel plate that is a material for forming including a press.
[0006]
　When the steel plates to be superposed are non-plated steel plates, oxide scale is generated on the surface of the superposed hot press member to be produced by high temperature heating accompanying hot press forming. Therefore, there is a problem that after hot press molding, for example, it is necessary to remove the oxide scale generated by shot blasting, or the corrosion resistance of the manufactured lap hot press member is likely to decrease. Furthermore, as a peculiar problem when using an unplated steel sheet as a material for a laminated blank, a portion that is not laminated (hereinafter, also referred to as “one piece portion”) can be shot blasted, but it is laminated. The oxide scale formed between the steel plates of the part (hereinafter, also referred to as “overlapping part”) is difficult to remove by shot blasting, and there is a problem that corrosion resistance is particularly likely to decrease.
[0007]
　If the steel sheets to be superposed are plated steel sheets, the need for performing shot blasting on the superposed hot pressing members after hot press forming is eliminated. Examples of the plated steel sheet used for hot pressing generally include Zn-based plated steel sheet and Al-based plated steel sheet. For both Zn-based plating and Al-based plating, Zn-based plating becomes Zn-Fe-based plating and Al-based plating becomes Al-Fe-based plating after hot stamping due to an alloying reaction in which Fe diffuses during plating. Become.
[0008]
　As shown in Patent Document 2 and Patent Document 3, a Zn-based plated steel sheet (that is, a plated steel sheet containing 50% by mass or more of Zn (Zn plating, Zn—Fe alloy, Zn—Ni alloy, Zn—Fe—Al) Zn-based alloy plating) such as alloys) suppresses the formation of oxide scale and solves the problem that shot blasting is required. However, when a Zn-plated steel sheet is used as the overlay blank material and bending is applied to the overlay portion during hot stamping, cracks may occur in the base metal, causing a problem in collision resistance. This is because when zinc having a relatively low melting point remains, Zn becomes a liquid metal and penetrates into the base metal from the plating surface, and is due to a problem called so-called liquid metal embrittlement. Bending is a means of ensuring collision resistance from the aspect of shape, and bending at a superposed portion is an extremely important method of using a superposed body.
[0009]
　As shown in Patent Document 2 and Patent Document 3, as a measure against liquid metal embrittlement that is adopted when a Zn-based plated steel sheet is used as a hot stamp, generally, a Zn—Fe alloying reaction is advanced during hot stamp heating. There is a measure for increasing the melting point of the plating, and a measure for lowering the molding temperature during bending of the hot stamp to wait for zinc to solidify. However, as a peculiar problem when using zinc-based plated steel sheets as the material of the laminated blank, both the heating rate and the cooling rate are slow because the plate thickness of the overlapping part is thicker than one sheet, and hot stamping At times, there is a problem that it is difficult to progress the Zn-Fe alloying reaction. Further, with respect to the forming temperature during hot stamping, when waiting for the overlapping portion to cool down, one sheet portion will cool down quickly, and there is a problem that the martensite structure cannot be secured. Further, in the single-sheet portion, Zn forms a zinc oxide film and suppresses evaporation of Zn. However, in the atmosphere between the steel plates of the overlapping portion, Zn is evaporated due to oxygen deficiency, and the corrosion resistance of the overlapping portion is reduced. The problem of deterioration and embrittlement of liquid metal becomes more serious.
[0010]
　In an Al-based plated steel sheet as shown in Patent Document 4 (that is, a plated steel sheet containing 50% by mass or more of Al (Al plating or Al-based alloy plating such as Al-Si alloy or Al-Fe-Si alloy)) , Zn, which suppresses the formation of oxide scale and eliminates the need for shot blasting. Furthermore, since it does not cause the problem of liquid metal embrittlement, it can be used as a material for a laminated blank. It is suitable.
Prior art documents
Patent literature
[0011]
Patent Document 1: Japanese Patent Laid-Open No. 2011-88484
Patent Document 2
: Japanese Patent No. 6178301 Patent Document 3: Japanese Patent Laid-Open No. 2016-124029
Patent Document 4: International Publication No. 2002/103073
Summary of the invention
Problems to be Solved by the Invention
[0012]
　However, when an Al-based plated steel sheet as disclosed in Patent Document 4 is used as a material of the overlay blank, there is a problem that the heating rate of the overlay portion is slow during heating during hot stamping. .. As described in Patent Document 3, the Al—Fe alloying reaction of the plating that progresses by heating during hot stamping is important for improving the corrosion resistance of the plating. When the rate of temperature rise is slow, the alloying reaction does not proceed sufficiently to the surface of the plating, so there is a problem that the corrosion resistance of the molded product after hot stamping decreases. As a measure against such a problem, it is conceivable that the alloying reaction proceeds by prolonging the heating time during hot stamping, but such a measure reduces the productivity of hot stamping and In the part, the alloying reaction proceeds excessively to form a plating having a high Fe concentration, and in this case also, there is a problem that the corrosion resistance of the plating decreases.
[0013]
　Therefore, as described above, an aluminum-based plated steel sheet that is suitable for use as a blank for a hot stamping laminated blank because it suppresses the oxide scale of the base metal and does not cause the problem of liquid metal embrittlement. With respect to the above, it is desired to solve the problem of the difference in temperature rising rate between the superposed portion and the single sheet portion to improve the corrosion resistance of the plating after hot stamping.
[0014]
　Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to use an aluminum-based plated steel sheet as a raw material, and to raise the temperature rise rate of the overlapping portion and the one-sheet portion. And a method for producing a superposed hot-stamp molded article, and a superposed hot-stamp molded article capable of further improving the corrosion resistance of plating after hot stamping To provide.
Means for solving the problem
[0015]
　The present inventors have conducted extensive studies to solve the above problems, and as a result of focusing on the relationship between the coating amount of aluminum-based plated steel sheet and the heating rate, the smaller the coating amount is, the higher the heating rate is. I found it. This is a characteristic of the rate of temperature rise during hot stamping of an aluminum-based plated steel sheet, regarding the appearance of the aluminum-based plated steel sheet, the emissivity of the silver-white surface where the alloying reaction in which Fe diffuses during plating has not progressed Is low, the surface becomes blackish after the alloying reaction proceeds to the surface, resulting in a high emissivity of the surface. Therefore, it is considered that the surface emissivity increases faster when the deposition amount of the plating, which accelerates the alloying to the surface, is smaller, and thus the temperature rising rate is increased.
[0016]
　Based on the above knowledge, as a result of studying the optimum amount of plating adhered to the problem of the heating rate difference between the superposed portion and the single sheet portion of the superposed blank for hot stamping, the result is that the steel plate thickness is large and the heating rate is high. It is important to reduce the amount of plating adhered in the overlapping part where the temperature is slow, and conversely, it is important to increase the amount of adhered plating and decrease the temperature increase in one sheet part where the heating rate is fast. I found out that. More specifically, in the superimposing blank for hot stamping, a steel sheet having a large area (first steel sheet) serving as a base of the molded body after hot stamping is added to a steel sheet having a small area corresponding to the superimposing portion (first steel sheet). Second steel plate) is spot welded, for example, and the first steel plate is an aluminum-plated steel plate with a large plating adhesion amount, and the second steel plate is an aluminum-plated steel plate with a small plating adhesion amount. It has been found that the problem of difference in temperature rising rate at the joining part can be solved.
　The gist of the present invention completed based on the above findings is as follows.
[0017]
[1] A first steel plate and at least one second steel plate having an area smaller than that of the first steel plate, the second steel plate being connected to the surface of the first steel plate via a welding point, One steel sheet is a plated steel sheet having an aluminum-based plating layer on both sides of the first steel sheet, and the second steel sheet is a plated steel sheet having an aluminum-based plating layer on both sides of the second steel sheet. Yes, the adhesion amount of the aluminum-based plating layer on the first steel plate is W1 (g/m 2 ) in terms of the average adhesion amount on both surfaces, and does not contact the first steel plate in the second steel plate. The adhesion amount of the aluminum-based plating layer on the side surface is W2 (g/m 2 ), and both W1 and W2 are in the range of 20 g/m 2 or more and 120 g/m 2 or less, and , A superimposing blank for hot stamping, which satisfies the following expressions (1) and (2).
　　30≦(W1−W2)≦100 Equation (1)
　　(W1/W2) 2 ×(t1/t2)≧1.5 Equation (2)
　However, in the above Equation (2), t1 (mm) is the plate thickness of the first steel plate, and t2 (mm) is the plate thickness of the second steel plate.
[2] The overlay blank for hot stamping according to [1], wherein the welding is spot welding, and the spot density of the spot welding is 1 point/200 cm 2 or more.
[3] The first steel sheet has a portion that becomes a flange portion made of only the first steel sheet after being subjected to hot stamping, and the first steel sheet and the second steel sheet are superposed on each other. At least a part of the portion has a portion which becomes a bent portion after being subjected to hot stamping, and at least one spot of the spot welding exists in a portion which becomes a bent portion after hot stamping, [2] Superimposed blank for hot stamping described in.
[4] The plate thickness t1 (mm) of the first steel plate and the plate thickness t2 (mm) of the second steel plate satisfy the relationship of the following expression (3), [1] to [3] The superposed blank for hot stamping according to any one of 1.
　　(T2/t1)≦2.0 Equation (3)
[5] The aluminum-based plating layer of each of the first steel plate and the second steel plate faces the base metal plate from the surface. In order, it has a two-layer structure of an aluminum layer and an aluminum-iron alloy layer, and has a thickness d1 (μm) of the aluminum-iron alloy layer of the first steel plate and the thickness of the second steel plate. The laminated blank for hot stamping according to any one of [1] to [4], wherein the thickness d2 (μm) of the aluminum-iron alloy layer satisfies the relationship of the following expression (4).
　　2≦(d2−d1)≦10 Equation (4)
[6] In the second steel sheet, the surface of the aluminum-based plating layer that is not in contact with the first steel sheet has an emissivity of 0. The hot stamp superimposing blank according to any one of [1] to [5], further including a carbon-based coating of 7 or more.
[7] ZnO or TiO 2 is formed on the surface of the aluminum-based plating layer located on the surface of the second steel plate. The superposed blank for hot stamping according to any one of [1] to [6], which further comprises a coating film comprising at least one of the above and having an adhesion amount per one surface of 0.2 g/m 2 or more.
[8] A first steel plate and at least one second steel plate, which has an area smaller than that of the first steel plate and is connected to the surface of the first steel plate via a welding point, One steel sheet is a plated steel sheet having an aluminum-based plating layer on both sides of the first steel sheet, and the second steel sheet is a plated steel sheet having an aluminum-based plating layer on both sides of the second steel sheet. Yes, the adhesion amount of the aluminum-based plating layer on the first steel plate is W1 (g/m 2 ) in terms of the average adhesion amount on both surfaces, and does not contact the first steel plate in the second steel plate. The adhesion amount of the aluminum-based plating layer on the side surface is W2 (g/m 2 ), and both W1 and W2 are in the range of 20 g/m 2 or more and 120 g/m 2 or less, and In the hot stamp forming in which the superposed blank for hot stamp satisfying the relationships of the following formulas (1) and (2) is heated and is formed after the heating, the first steel plate and the second steel plate are A method for producing a superposed hot-stamp molded article, wherein a bent portion subjected to a bending process is provided on at least a part of the superposed portion.
　　30≦(W1−W2)≦100 Equation (1)
　　(W1/W2) 2 ×(t1/t2)≧1.5 Equation (2)
　However, in the above formula (2), t1 (mm) is the plate thickness of the first steel plate, and t2 (mm) is the plate thickness of the second steel plate.
[9] The method for producing a superposed hot stamped article according to [8], wherein the welding is spot welding, and the spot density of the spot welding is 1 point/200 cm 2 or more.
[10] The method for producing a superposed hot stamped article according to [9], wherein at least one spot of the spot welding is present in a portion that becomes the bent portion after hot stamping.
[11] The plate thickness t1 (mm) of the first steel plate and the plate thickness t2 (mm) of the second steel plate satisfy the relationship of the following expression (3), [8] to [10] 5. The method for manufacturing a superposed hot stamp molded body according to any one of 1.
　　(T2/t1)≦2.0 Equation (3)
[12] The aluminum-based plating layer of each of the first steel plate and the second steel plate faces the base metal plate from the surface. In order, it has a two-layer structure of an aluminum layer and an aluminum-iron alloy layer, and has a thickness d1 (μm) of the aluminum-iron alloy layer of the first steel sheet and the above-mentioned second steel sheet. The method for producing a superposed hot stamped article according to any one of [8] to [11], wherein the thickness d2 (μm) of the aluminum-iron based alloy layer satisfies the relationship of the following expression (4): ..
　　2≦(d2-d1)≦10 Equation (4)
[13] In the second steel plate, the emissivity of 0..0 is formed on the surface of the aluminum-based plating layer on the side not in contact with the first steel plate. The method for producing a superposed hot stamped article according to any one of [8] to [12], further having a carbon-based coating of 7 or more.
[14] A film made of at least one of ZnO and TiO 2 on the surface of the aluminum-based plating layer located on the surface of the second steel plate, and having an adhesion amount per surface of 0.2 g/m 2 or more. The method for producing a superposed hot stamped article according to any one of [8] to [13], further comprising:
[15] A first steel plate having a plate thickness of T1 (mm), which is connected to the surface of the first steel plate via a welding point, has an area smaller than that of the first steel plate, and has a plate thickness Is at least one second steel plate having a thickness of T2 (mm), and the first steel plate has aluminum having an average plating thickness of K1 (μm) on both surfaces of the first steel plate. The second steel sheet is a steel sheet having an aluminum-based plating layer having a plating thickness of K2 (μm) on the surface not in contact with the first steel sheet. A superposed hot-stamp molded body that satisfies the relationships of formula (11) and formula (12).
　10≦(K1-K2)≦33 ··· Equation (11)
　(K1/K2) 2 ×(T1/T2)≧1.5 ··· Equation (12)
Effect of the invention
[0018]
　As described above, according to the present invention, when an aluminum-plated steel sheet is used as a material, the problem regarding the difference in temperature rising rate between the overlapping portion and the single sheet portion is solved, and the plating after hot stamping is performed. It becomes possible to further improve the corrosion resistance.
Brief description of the drawings
[0019]
FIG. 1 is an explanatory view schematically showing an example of a superposed blank for hot stamp, a method for manufacturing a superposed hot stamp molded body, and an example of a superposed hot stamp molded body according to an embodiment of the present invention.
FIG. 2 is an explanatory view schematically showing the structure of an aluminum-based plating layer having an aluminum layer and an aluminum-iron-based alloy layer in the hot-stamp overlay blank according to the same embodiment.
FIG. 3 shows the structure of an aluminum layer, an aluminum plating layer having an aluminum-iron alloy layer, and a carbon-based coating, or ZnO, TiO 2 on the surface of the laminated blank for hot stamping according to the embodiment. It is explanatory drawing which shows typically the structure which has the film which contains.
[FIG. 4] Having a spot welding spot in a bent portion after forming by increasing spot density of spot welding, a hot stamp overlay blank according to the embodiment, and a method for producing an overlay hot stamp molded product, It is explanatory drawing which shows an example of an overlap molded article typically.
[Fig. 5] Fig. 5 is an explanatory view schematically showing a mounting position of a thermocouple as a method of measuring a temperature rising rate of a superposed section and a single sheet section of an example.
FIG. 6 is an explanatory view schematically showing the shape of a molded product by a mold used for evaluating the corrosion resistance of the molded product of the example.
[FIG. 7] A hot stamp overlay blank according to an example of the present invention, which has a higher spot density of spot welding than that of FIG. 5 and has spot welding spots in a bent portion after molding. FIG. 3 is an explanatory view schematically showing an example of a method of manufacturing a superposed hot stamped product and an overlapped molded product.
8] A hot stamp overlay blank according to an example of the present invention, in which the spot density of spot welding of the embodiment is reduced as compared with FIG. 7, and the spot of spot welding is formed in a portion which becomes a bent portion after forming, FIG. 3 is an explanatory view schematically showing an example of a method of manufacturing a superposed hot stamped product and an overlapped molded product.
MODE FOR CARRYING OUT THE INVENTION
[0020]
　Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, constituent elements having substantially the same functional configuration are designated by the same reference numerals, and a duplicate description will be omitted.
[0021]
　FIG. 1 is an explanatory view schematically showing an example of a hot stamp superimposition blank according to an embodiment of the present invention, a method of manufacturing a superposition hot stamp compact, and an example of the superposition hot stamp compact.
[0022]
　The superposed blank for hot stamping according to the present embodiment is used as a material for a superposed hot stamped body.
[0023]
　As schematically shown in FIG. 1, a hot stamp superposed blank 4 according to the present embodiment welds a first steel plate 1 and a second steel plate 2 having an area smaller than that of the first steel plate (3). ) Is configured by. At this time, in the hot stamp superposition blank 4, the part where the second steel plates 2 are superposed is referred to as a superposition part 4a, and the part which is not superposed is referred to as a single sheet part 4b. In addition, in the superimposition blank 4 for hot stamping according to the present embodiment, the second steel plate 2 has the first steel plate 1 so that there is no portion protruding from the first steel plate 1 as schematically shown in FIG. It is preferably arranged inside the one steel plate 1.
[0024]
　On the surface of the first steel plate 1, aluminum-based plating (not shown) is applied to both the surface 1a on the side that contacts the second steel plate 2 and the surface 1b on the side that does not contact the second steel plate 2. ) Is similarly applied to the second steel plate 2, and both surfaces 2a on the side contacting the first steel plate 1 and 2b on the side not contacting the first steel plate 1 are plated with aluminum. (Not shown).
[0025]
　The superimposing blank 4 for hot stamping is a method for manufacturing a superimposing hot stamping compact according to this embodiment, in which the steel plate is austenitized by being heated up to Ac 3 points or more in the heating furnace 5, and immediately after being taken out from the furnace. The steel sheet undergoes martensitic transformation by being press-formed and rapidly cooled by the die 6. As a result, the hot-stamp superposed blank 4 becomes the superposed hot-stamp molded body 12 according to the present embodiment having excellent collision resistance. At this time, at least a part of the overlapping portion 4a has a portion that becomes the bent portion 8 when the overlapping hot stamp molded body 12 is formed.
[0026]
　In FIG. 1, a molded product using a hat-shaped mold is shown as an example of the superposed hot stamp molded body 12, and the names of the parts of the hot stamp molded body 12 are referred to as the crown portion 7 and the bending of the crown portion. The portion 8, the vertical wall portion 10, the flange portion 11, and the bent portion 9 of the flange portion.
[0027]
　In addition, in FIG. 1, the second steel plate 2 according to the present embodiment is arranged on the outer side on the crown 7 side, but by disposing the second steel plate 2 on the inner side of the crown 7, The object of the invention is achieved.
[0028]
(1. Hot Stamp Superimposing Blank) The
　hot stamp superimposing blank 4 according to the present embodiment will be described in detail below.
　As described above, the hot stamp superposed blank 4 according to the present embodiment is connected to the first steel plate 1 and the surface of the first steel plate 1 via welding points (that is, the first steel plate 1). And a second steel plate 2 having a smaller area than the first steel plate 1, and both surfaces of the first steel plate 1 and the second steel plate 2 are plated with aluminum. Has been done. That is, the 1st steel plate 1 and the 2nd steel plate 2 which concern on this embodiment are the aluminum plating steel plates which have an aluminum type plating layer on both surfaces of the steel plate used as a base material.
[0029]
In the
　hot-stamp overlapping blank 4 according to the present embodiment, the chemical composition of the base material in each of the first steel plate 1 and the second steel plate 2 is not particularly limited. However, for example, in order to obtain a tensile strength of 1500 MPa or more (about 400 HV or more in Vickers hardness when the load is 9.81 N), in mass%, C: 0.19% or more and 0.5% or less, Si : 0.01% to 1.5%, Mn: 0.4% to 2%, Cr: 0.01% to 1.0%, Ti: 0.001% to 0.1%, B : 0.0005% or more and 0.005% or less, Nb: 0.1% or less, Mo, Ni, Cu, Co, W, Sn, V, Sb: 0.5% or less each, Mg, Ca, Zr, REM : It is preferable to use a base material having a chemical composition of 0.005% or less and the balance Fe and impurities. Further, within the range of the above chemical composition, the chemical composition of the base material of the first steel plate 1 and the chemical composition of the base material of the second steel plate 2 may be the same or different. Good.
[0030]
　The method for producing an aluminum-plated steel sheet having the above-described chemical composition as a base material is not particularly limited, and for example, a conventional ironmaking step, and a steelmaking step, hot rolling, pickling, cold rolling What was manufactured in the process of Sendzimir type hot dip aluminum plating can be used.
[0031]
　In the present embodiment, optionally, the ratio (t2/t1) between the plate thickness t1 (mm) of the first steel plate 1 and the plate thickness t2 (mm) of the second steel plate 2 is expressed by the following formula (3). ), it is preferably 2.0 or less.
[0032]

　　(T2/t1)≦2.0 Equation (3)
[0033]
　The reason why it is preferable to satisfy the above (3) will be described below.
　The characteristics required for the aluminum-plated steel sheet in the present embodiment include a superposed portion (the temperature rising rate is slow) and a single sheet portion (the temperature rising rate is fast), which are problems when used as a superposed blank. It is important to further suppress the difference in the temperature rising rate of 1. Therefore, it is important that the plate thickness t2 of the second steel plate 2 is suppressed to some extent with respect to the plate thickness t1 of the first steel plate 1. it is conceivable that. When the value of the ratio (t2/t1) exceeds 2.0, the plate thickness t2 of the second steel plate 2 becomes too large, and the temperature rising rate of the overlapping portion may become too large than that of the single sheet portion. Will be more likely. The value of the ratio (t2/t1) is more preferably 0.9 or less. On the other hand, the lower limit value of the ratio (t2/t1) is not particularly specified, but if the value of the ratio (t2/t1) is less than 0.3, there is a problem in suppressing the difference in temperature rising rate. However, there is a possibility that it will be insufficient from the viewpoint of improving the collision resistance property for use as an automobile part by the overlapping portion. Therefore, the value of the ratio (t2/t1) is preferably 0.3 or more.
[0034]
　The plate thickness t1 of the first steel plate 1 and the plate thickness t2 of the second steel plate 2 can be measured using a micrometer. Further, the plate thicknesses t1 and t2 described above are plate thicknesses including the plate thickness of the base material and the thicknesses of the aluminum-based plating layers provided on both surfaces.
[0035]

　Adhesion amount W1 (g/m 2 ) of the aluminum plating layer applied to both surfaces of the first steel plate 1 and adhesion of the aluminum plating layer applied to both surfaces of the second steel plate 2. The amount W2 (g/m 2 ) is 20 g/m 2 or more and 120 g/m 2 or less in both W1 and W2 , and satisfies the relationships of the following formulas (1) and (2). Here, the adhesion amount W1 of the aluminum-based plating layer on the first steel plate 1 represents the average adhesion amount on both surfaces of the first steel plate 1. That is, when the adhesion amounts of the aluminum-based plating layers on one surface of the first steel plate 1 are W1a and W1b (g/m 2 ), respectively , W1=0.5×(W1a+W1b). Further, the adhesion amount W2 of the aluminum plating layer on the second steel plate 2 represents the adhesion amount of the aluminum plating layer on the surface that is not in contact with the first steel plate 1. In the second steel plate 2, the surface on the side not in contact with the first steel plate 1 is a surface exposed to a heat source for heating when the manufactured laminated blank is heated during hot stamping.
[0036]

　　30≦(W1−W2)≦100 Equation (1)
　　(W1/W2) 2 ×(t1/t2)≧1.5 Equation (2)
[0037]
　The properties required for the aluminum-based plating layer according to the present embodiment include (a) suppressing the generation of Fe scale during hot stamping, and (b) slipping off of plating during hot stamping (also referred to as powdering). (3) Suppressing plating chipping and flaws caused by Powdering occurs due to compressive stress applied to the plating on the inner surface of the bent portion during molding, shear stress applied to plating due to sliding from the mold during molding, and the like. When the adhered amounts W1 and W2 of the aluminum-based plating layer on each steel sheet are less than 20 g/m 2 , the thickness of the plating becomes thin, and the problem of insufficient Fe scale control occurs. Therefore, the adhesion amounts W1 and W2 of the aluminum-based plating layer on each steel sheet are independently set to 20 g/m 2 or more. The adhesion amounts W1 and W2 of the aluminum-based plating layer on each steel sheet are preferably independently 30 g/m 2 or more, and more preferably 35 g/m 2 or more. On the other hand, in the case where the adhered amounts W1 and W2 of plating on one surface of each steel sheet exceed 120 g/m 2 , there is a problem that the suppression of powdering is insufficient. Therefore, in the present embodiment, the adhesion amounts W1 and W2 of the plating per one surface of each steel sheet are independently set to 120 g/m 2 or less. Adhesion amount W1, W2 of the plating per side in each steel sheet are each independently preferably 115 g / m 2 or less, more preferably 100 g / m 2It is the following.
[0038]
　The thickness (μm) of the aluminum-based plating layer in each steel sheet can be roughly estimated from the coating adhesion amount (g/m 2 ). It can be determined by 5).
[0039]

　　(Plating thickness)=(Amount of coating)/3... Formula (5)
[0040]
　Further, the characteristics required for the aluminum-based plating layer according to the present embodiment include (c) a problem when using as an overlay blank, that is, an overlay part (a slow heating rate) and a single sheet part (a heating rate). The difference in the temperature rising rate between the above and the above is suppressed. As a measure for suppressing the difference in temperature rising rate between the overlapped portion and the single sheet portion, the adhesion amount W2 of the aluminum-based plating layer on the second steel plate 2 is determined by the adhesion amount W2 of the aluminum-based plating layer on the first steel plate 1. The amount of adhesion is smaller than the amount W1, and specifically, as shown in the above formula (1), the difference (W1-W2) in the amount of plating adhesion is set to 30 g/m 2 or more and 100 g/m 2 or less. By satisfying the relationship represented by the above formula (1), the alloying reaction of plating that increases the emissivity when the hot stamp is heated can be rapidly advanced to the surface. If the difference (W1−W2) in the amount of plating adhered is less than 30 g/m 2 , it is not possible to sufficiently obtain the above-mentioned improvement in the difference in temperature rising rate. The difference (W1−W2) in the coating weight is preferably 35 g/m 2 or more, more preferably 40 g/m 2 or more. On the other hand, the upper limit of the difference (W1-W2) in the amount of plating adhered is not particularly limited from the viewpoint of suppressing the difference in the temperature rising rate as described above. lower limit and upper limit, respectively 20 g / m 2 , 120 g / m 2 because it is computationally 100 g / m 2Is the upper limit. Further, when the difference (W1−W2) in the amount of plating adhered exceeds 100 g/m 2 , the corrosion resistance of the plating decreases, which is not preferable. The difference (W1−W2) in the coating weight is preferably 90 g/m 2 or less, more preferably 80 g/m 2 or less. In consideration of satisfying the relationship shown in the equation (1), the upper limit of adhesion amount W2 of the aluminum-based plating layer in the second steel plate 2, 90 g / m is substantially 2 is the upper limit ..
[0041]
　Further, the aluminum-based plating layer according to the present embodiment satisfies the relationship shown in the above (2) together with the above expression (1). By satisfying the relationship shown in the above (2), it becomes possible to promptly advance the alloying reaction of plating for improving the emissivity to the surface when the hot stamp is heated. In the above formula (2), the exponent of the plate thickness ratio (t1/t2) is 1, while the exponent of the plating adhesion ratio (W1/W2) is 2. From this, in the present invention, it is understood that the ratio (W1/W2) of the amount of plating adhered is more important than the ratio (t1/t2) of the plate thickness.
[0042]
　If the value of (W1/W2) 2 ×(t1/t2) is less than 1.5, it is not possible to sufficiently obtain the difference in temperature rising rate. The value of (W1/W2) 2 ×(t1/t2) is preferably 2 or more, and more preferably 2.5 or more. On the other hand, the upper limit of (W1/W2) 2 ×(t1/t2) is not particularly specified. However, an excessive increase in the value of (W1/W2) 2 ×(t1/t2), that is, an increase in (W1/W2) or (t1/t2) causes an increase in the material cost due to an increase in W1 or t1, W2. Causes a decrease in corrosion resistance and a decrease in t2 results in a decrease in collision resistance. Therefore, the value of (W1/W2) 2 ×(t1/t2) is preferably 80 or less. The value of (W1/W2) 2 ×(t1/t2) is more preferably 60 or less.
[0043]
　FIG. 2 schematically shows the layer structure on one side of the plated steel sheet 13 provided with the aluminum-based plating layer according to the present embodiment. A more preferable layer structure of the aluminum-based plating layer according to the present embodiment, which is selectively realized, will be described below with reference to FIG. 2.
[0044]
　Regarding the plating structure in which one side of the plated steel sheet 13 treated with the aluminum plated layer is schematically shown, the aluminum plated layer applied to the first steel sheet 1 and the second steel sheet 2 is It is preferable to have a two-layer structure of an aluminum layer 14 and an aluminum-iron based alloy layer 15 in the order toward the base material 16. Here, the thickness d1 (μm) of the aluminum-iron based alloy layer 15 of the first steel plate 1 is preferably 1 μm or more, and more preferably 2 μm or more. Further, the thickness d2 (μm) of the aluminum-iron alloy layer 15 of the second steel plate 2 is preferably 2 μm or more, and more preferably 3 μm or more. On the other hand, the thickness d1 of the aluminum-iron alloy layer 15 of the first steel sheet 1 is preferably 9 μm or less, more preferably 8 μm or less. Further, the thickness d2 of the aluminum-iron alloy layer 15 of the second steel plate 2 is preferably 10 μm or less, more preferably 9 μm or less.
[0045]
　In addition to the aluminum-based plating layer applied to the first steel plate 1 and the second steel plate 2 having a two-layer structure, the aluminum-iron alloy layer 15 of the first steel plate 1 has a thickness d1. The difference (d2-d1) between (μm) and the thickness d2 (μm) of the aluminum-iron alloy layer 15 of the second steel plate 2 is 2 μm or more and 10 μm or less as shown in the following formula (4). Is more preferable.
[0046]

　　2≦(d2-d1)≦10 Equation (4)
[0047]
　This is a characteristic required for the aluminum-based plating according to the present embodiment to suppress the difference in the heating rate between the overlapping portion (the heating rate is slow) and the one-sheet portion (the heating rate is fast). Can be mentioned. At this time, in the superposed portion, in order to promptly promote the alloying reaction of the plating, which increases the emissivity when the hot stamp is heated, to the surface, the aluminum-iron system of the second steel plate 2 before the hot stamp is heated. While it is preferable to increase the thickness d2 of the alloy layer 15, the thickness d1 of the aluminum-iron alloy layer 15 of the first steel sheet 1 may be decreased because the alloying reaction is delayed in one sheet. This is because it is preferable. If the difference in thickness (d2-d1) of the aluminum-iron based alloy layer 15 is less than 2 μm, the above difference in temperature rising rate cannot be sufficiently improved. The difference in thickness (d2-d1) of the aluminum-iron alloy layer 15 is more preferably 3 μm or more. On the other hand, the upper limit of the difference (d2-d1) in the thickness of the aluminum-iron based alloy layer 15 is not particularly limited in terms of the difference in the temperature rising rate, but the value of the thickness d2 of the aluminum-iron based alloy layer 15 is If it exceeds 10 μm, alloying will proceed excessively and powdering in the molding portion at the time of hot stamping will become severe, so that 10 μm is the upper limit as described above. The difference in thickness (d2-d1) of the aluminum-iron alloy layer 15 is more preferably 8 μm or less.
[0048]
　In addition, according to a general hot dip plating method as a method for treating an aluminum-based plating on a steel sheet, an aluminum-based material whose adhesion amount is adjusted by dipping the steel sheet in a hot dip aluminum bath and gas wiping with nitrogen or the atmosphere A plated steel sheet can be manufactured. As a result, the aluminum-iron alloy layer 15 is inevitably formed at the interface between the plating layer and the base steel sheet (base material 16 in this embodiment) due to the elution of Fe during hot dipping. The thickness of the formed aluminum-iron alloy layer 15 can be increased by extending the immersion time in the hot dip coating.
[0049]
　The chemical composition of the molten aluminum plating bath for forming the above aluminum-based plating layer is not particularly limited. However, the content of the molten aluminum plating bath Al for forming the heat-resistant aluminum is preferably 80% by mass or more, and it is easy to control the thickness of the aluminum-iron alloy layer 15, The content of Si in the plating bath is preferably 2% by mass or more. If the Si content is less than 2% by mass, the aluminum-iron alloy layer 15 becomes too thick and the formability deteriorates. On the other hand, if the content of Si in the molten aluminum plating bath exceeds 15% by mass, alloying during heating of the hot stamp is delayed and the hot stamp productivity is reduced. Therefore, the content of Si in the molten aluminum plating bath is preferably 15% by mass or less.
[0050]
　When Si is contained in an amount of 2% by mass or more and 15% by mass or less, a eutectic structure of Al and Si is formed in the aluminum layer 14 based on the phase diagram. In the case of the hot dip coating method, Fe may inevitably be contained in an amount of 1 mass% or more as an elution component from the steel sheet. Other unavoidable impurities include elements such as Cr, Mn, V, Ti, Sn, Ni, Cu, W, Bi, Mg, and Ca, which are caused by elution components of the hot dip plating equipment and impurities of the ingot of the hot dip aluminum plating bath. And may contain less than 1 mass% of these elements.
[0051]
　As the chemical composition of the aluminum-iron alloy layer 15, a binary alloy of Al and Fe, a θ phase (FeAl 3 ), an η phase (Fe 2 Al 5 ), a ζ phase (FeAl 2 ), Fe 3 Al, Examples include Fe-based BCC phases (α2, α), and the combination of these plating phases forms the aluminum-iron-based alloy layer 15. The chemical composition of the aluminum-iron alloy layer 15 containing Si includes τ1-Al 2 Fe 3 Si 3 , τ2-Al 3 FeSi, τ3-Al 2 FeSi, τ4-Al 3 FeSi 2 , τ5-Al. 8 Fe 2 Si, τ6-Al 9 Fe 2 Si 2 , τ 7-Al 3 Fe 2Si 3 , τ8-Al 2 Fe 3 Si 4 , τ10-Al 4 Fe 1.7 Si, τ 11 -Al 5 Fe 2 Si and the like are mentioned, and they are mainly composed of τ 5 .
[0052]
　As a method for specifying the amount of the aluminum-based plating layer attached, for example, a sodium hydroxide-hexamethylenetetramine/hydrochloric acid stripping weight method can be mentioned. Specifically, according to JIS G 3314:2011, a test piece having a predetermined area S (m 2 ) (for example, 50×50 mm) is prepared and the weight w1 (g) is measured. After that, it is successively dipped in an aqueous solution of sodium hydroxide and an aqueous solution of hydrochloric acid added with hexamethylenetetramine, dipped until the bubbling caused by the dissolution of the plating is subsided, immediately washed with water, and the weight w2 (g) is measured again. At this time, the adhesion amount Wp (g/m 2 ) of the aluminum-based plating layer can be obtained from the following equation (6).
[0053]

　　Wp=(w1-w2)/S... Formula (6)
[0054]
　In addition, when the size of the test piece is small, the cross section of the plating is observed with an optical microscope (area: 100 μm×100 μm), and the plating thickness is measured in the same manner in three visual fields. It can be obtained by converting the average value of the above into the attached amount using the equation (5). The plating thickness measured at this time is the total thickness of the aluminum layer 14 and the aluminum-iron alloy layer 15 shown in FIG.
[0055]
　Similarly, the thickness of the aluminum-iron based alloy layer 15 means that the thickness of the aluminum-iron based alloy layer 15 is measured by observing the cross section of the plating with an optical microscope (area: 100 μm×100 μm) without etching. It is possible to obtain the average value of the thicknesses measured in three visual fields by performing the same operation in the visual fields.
[0056]

　FIG. 3 shows the aluminum-based plating layer according to the present embodiment, and the layered structure on one side of the plated steel sheet 18 further provided with a carbon-based coating on the surface thereof, or a film containing ZnO and TiO 2. 3 schematically shows the layered structure on one side of the plated steel sheet 18' provided with. A more preferable layer structure of the aluminum-based plating layer according to the present embodiment, which is selectively realized, and the carbon-based coating or the coating containing ZnO or TiO 2 on the surface thereof is shown in FIG. 3 below. Explanations will be given with reference.
[0057]
[Coating layer (carbon-based)] In
　the second steel plate 2, a carbon-based coating layer 17 having an emissivity of 0.7 or more is formed on the surface of the aluminum-based plating layer located on the surface not in contact with the first steel plate 1. It is preferable to further provide. At this time, the aluminum-based plating layer has the carbon-based coating layer 17, the aluminum layer 14, and the aluminum-iron-based alloy layer 15 on the base material 16 in this order from the surface to the base material 16, as described above. In order to suppress the difference in the heating rate between the superposed portion (the heating rate is slow) and the one-sheet portion (the heating rate is fast), which is a problem when using it as a superposed blank, the carbon-based coating layer 17 The emissivity of is preferably 0.7 or more. If the emissivity is less than 0.7, the improvement effect is insufficient. In principle, the emissivity is set to 1 as the upper limit. Examples of the component having a high emissivity include metal oxides and metal nitrides, and a carbon-based coating containing carbon black is preferable. By using a carbon-based coating containing carbon as a main component, the coating is burned and discharged as CO 2 etc. when the hot stamp is heated, which makes it difficult to remain after hot stamping and the corrosion resistance of the molded product after hot stamping. This is because it is possible to prevent a decrease in
[0058]
　As a method for specifying the emissivity, for example, when the radiant temperature of the sample is measured by using infrared thermography (G100EX manufactured by Nippon Avionics Co., Ltd.) and at the same time the temperature of the sample is measured by a K-type thermocouple, the radiant temperature is the thermoelectric value. It can be specified by determining the emissivity at the temperature that most closely matches the temperature measured by the pair. As a method for identifying the carbon-based coating layer 17, a high-frequency glow discharge emission surface analyzer (GDS, manufactured by Horiba Ltd.) was used to analyze the coating in the depth direction. A method of identifying the presence of the carbon-based coating layer 17 when the carbon element (C) is detected can be mentioned. The thickness of the carbon-based coating layer 17 is not particularly limited as long as the emissivity is 0.7 or more, but it is preferably 0.2 μm or more, and 0.5 μm, from the viewpoint of easy industrial treatment of the coating treatment. The above is more preferable. On the other hand, the thickness of the carbon-based coating layer 17 is not more than 5 μm because the effect of improving the emissivity is saturated and it is not economical even if it is excessively thick, and the adhesion of the coating to the steel sheet is reduced. It is preferably 3 μm or less, and more preferably 3 μm or less. The thickness of the carbon-based coating layer 17 can be measured by the depth direction analysis by GDS described above.
[0059]
[Film layer (ZnO, TiO 2 )] Further
　, the aluminum-based plating layer applied to the surface of the second steel sheet 2 further comprises at least one of ZnO and TiO 2 with respect to the surface , and one side It is preferable to have a coating layer 17′ having an attached amount of 0.2 g/m 2 or more. The amount of adhesion here means the amount of metal Zn or metal Ti deposited per unit area. ZnO and TiO 2 are oxides having good infrared absorption in addition to improving emissivity. Therefore, by providing such a coating layer 17 ′, the difference in the heating rate between the overlapping portion (the temperature rising rate is slow) and the one-sheet portion (the temperature rising rate is high), which is a problem when using as a laminated blank. Can be suppressed. In particular, as compared with the case where the carbon-based coating layer 17 is burned during hot stamping heating, the oxides ZnO and TiO 2 remain during heating. Therefore, the coating layer 17' can further contribute to the improvement of the emissivity at high temperature. If the amount of the coating layer 17' deposited is less than 0.2 g/m 2 , the effect of suppressing the difference in temperature rising rate may not be sufficiently expected. The coating amount of the coating layer 17′ is more preferably 0.3 g/m 2 or more. On the other hand, the upper limit of the coating amount of the coating layer 17 ′ is not particularly defined, but if the coating amount is too large, the effect is saturated and the coating cost becomes high, which is not practical, and ZnO and TiO even after hot stamping are heated. Since No. 2 remains, corrosion resistance and the like may decrease. Therefore, it is more preferable that the amount of the coating layer 17′ attached is 3 g/m 2 or less. The amount of ZnO and TiO 2 deposited can be determined by performing elemental analysis on the surface using a fluorescent X-ray analyzer (ZSX Primus manufactured by RIGAKU) and quantifying metallic Zn and metallic Ti.
[0060]
The treatment method of 　the carbon-based coating layer 17 and the coating layer 17′ having ZnO or TiO 2 described above is not particularly limited, but for example, water-dispersed carbon black (for example, RCF#52 manufactured by Mitsubishi Chemical Corporation), ZnO (For example, Nano Tek manufactured by CI Kasei Co., Ltd.) or TiO 2 (for example, Nano Tek manufactured by CI Kasei Co., Ltd.) is prepared in water to prepare a water-based coating liquid, and after performing the hot dip aluminum plating treatment, a roll coater. It can be manufactured by coating with the above and performing a dry baking treatment.
[0061]
　The aluminum-based plating layer according to the present embodiment may include both the carbon-based coating layer 17 and the coating layer 17′ containing ZnO or TiO 2 . In this case, the carbon-based coating layer 17, ZnO or TiO 2 coating layer 17 having a 'is not particularly limited either arrangement order of the carbon-based coating layer 17 is ZnO or TiO 2 coating layer 17 having a' The coating layer 17 ′ having ZnO or TiO 2 may be located above the carbon-based coating layer 17.
[0062]
　Further, the carbon-based film 17 and the film layer 17′ containing ZnO and TiO 2 may be provided on both sides of the steel plate that is the base material, but in the steel plate that is the base material, when the hot stamp is heated. More preferably, it is provided only on the surface exposed to the heat source.
[0063]
In
　the superimposition blank for hot stamping in which the first steel plate 1 and the second steel plate 2 are overlapped and welded, the welding is spot welding, and the spot density of the spot welding is 1 point/200 cm 2. The above is preferable. The reason will be described below.
[0064]
　In the overlapping portion, heat transfer is improved by making good contact between the first steel plate 1 and the second steel plate 2, and there is a problem in the case of using the first steel plate 1 and the second steel plate 2 as an overlapping blank (the temperature rising rate is slow. .) and one sheet portion (the temperature rising rate is high) can be suppressed.
[0065]
　As the type of welding, spot welding, seam welding, brazing welding, laser welding, plasma welding, arc welding, etc. can be selected, but from the point of good contact of the overlapping part, there are multiple parts up to the inside of the overlapping part. It is preferable to use spot welding, which allows the two steel sheets to be in contact with each other at the above point and to directly join the steel sheets by applying pressure between the steel sheets.
[0066]
　As described above, the spot density of spot welding is preferably 1 point/200 cm 2 or more. If the dot density is less than 1 point/200 cm 2 , the contact between the steel sheets will be insufficient, and the improvement of the temperature rise in the overlapping portion will be insufficient. The spot density of spot welding is more preferably 1 point/40 cm 2 or more. On the other hand, the upper limit of the spot density of spot welding is not particularly defined, but if the density is too high, welding current is shunted, which makes welding difficult . Therefore, it is preferably 1 point/1 cm 2 or less.
[0067]
　The spot density (dots/cm 2 ) of the spot welding is obtained by dividing the number of spot welding spots in the blank-treated second steel plate 2 by the area of ​​the second steel plate 2.
[0068]
　Further, it is preferable that at least one spot of the spot welding is present at a portion which becomes a bent portion after hot stamping. In order to suppress the difference in the heating rate between the overlapping part (the temperature rising rate is slow) and the one-sheet part (the temperature rising rate is high), which is a problem when using it as the overlapping blank, It is important to bring the first steel plate 1 and the second steel plate 2 into good contact with each other. Here, as shown in FIG. 4, hot stamping superimposition blank 22 is used for hot stamping to manufacture hot stamp superposition molded body 26. At this time, in the bent portion, since stress is relatively more likely to be applied than the top portion or the vertical wall portion during hot stamping, voids are likely to occur, a sufficient cooling rate cannot be obtained during cooling of the mold, and the hardness decreases. Collision resistance is deteriorated. Therefore, by disposing the spot welding spot (welding portion 24) at the bent portion of the hot stamped body 26, it is possible to suppress the void of the bent portion. Therefore, in the superposed blank 22 for hot stamping, as shown in FIG. 4, it is preferable to provide spot welding spots (welding portion 20) on the portion that becomes the bent portion after hot stamping. In the present embodiment, after hot stamping, spot welding spots (welding portion 19) are applied to the crown portion and spot welding spots (welding portion 21) are applied to the vertical wall portion. Good. As a result, after spot welding, spot welding spots (welding portions 23) are arranged on the crown of the hot stamping compact 26, and spot welding spots (welding spots 25) are formed on the vertical wall portion of the hot stamping compact 26. Will be placed.
[0069]
(2. Superposed Hot Stamp Molded Body and Manufacturing Method Thereof) In the
　method for manufacturing a hot stamp molded body according to the present embodiment, as shown in FIG. At the time of molding immediately after heating, at least a part of the overlapped portion is provided with a bent portion, so that the overlapped hot stamp molded body 12 of the present embodiment is manufactured.
[0070]
　Although the heating temperature is not particularly limited, it is generally within a temperature range of Ac3 point (for example, 800° C.) or higher and 1000° C. or lower, and cooling is performed using a cooling medium such as a mold or water at the time of molding immediately after heating. As a result, it is possible to obtain the superposed hot-stamp molded body 12 having excellent collision resistance. In addition, the temperature of the heating means the highest temperature reached of the steel sheets in the overlapped portion, and the heating method includes heating by an electric furnace, a gas furnace, a far infrared furnace, a near infrared furnace, etc. , High frequency heating, induction heating and the like can be exemplified.
[0071]
　The superposed hot stamped compact 12 according to the present embodiment manufactured as described above is superposed on the first steel plate having a plate thickness of T1 (mm) and welded to the first steel plate. , And at least one second steel plate having an area smaller than that of the first steel plate and a plate thickness of T2 (mm). Here, the first steel sheet in the superposed hot stamped body 12 is a plated steel sheet having an aluminum-based plating layer having an average plating thickness of K1 (μm) on both surfaces of the first steel sheet. Further, the second steel plate of the superposed hot stamped body 12 is a plated steel plate having an aluminum-based plating layer having a plating thickness of K2 (μm) on the surface not in contact with the first steel plate. In addition, in the second steel plate, the plating thickness of the aluminum-based plating layer on the surface in contact with the first steel plate is not particularly specified.
[0072]
　Here, the average plating thickness K1 of the aluminum-based plating layer in the first steel sheet is preferably 20 μm or more, and more preferably 25 μm or more. The plating thickness K2 on the side of the aluminum-based plating layer of the second steel sheet that is not in contact with the first steel sheet is preferably 10 μm or more, and more preferably 15 μm or more. On the other hand, the average plating thickness K1 of the aluminum-based plating layer in the first steel sheet is preferably 55 μm or less, and more preferably 50 μm or less. Further, the plating thickness K2 on the side of the aluminum-based plating layer in the second steel sheet that is not in contact with the first steel sheet is preferably 45 μm or less, more preferably 40 μm or less. By setting the average plating thicknesses K1 and K2 within the above ranges, respectively, it becomes possible to maintain the corrosion resistance of the superposed hot stamp molding 12 in a good state.
[0073]
　Furthermore, the superposed hot stamped body 12 according to the present embodiment satisfies the relationships of the following formulas (11) and (12).
[0074]

　10≦(K1-K2)≦33 ··· Equation (11)
　(K1/K2) 2 ×(T1/T2)≧1.5 ··· Equation (12)
[0075]
　When the difference (K1−K2) in plating thickness is less than 10 in the superposed hot stamping compact 12 according to the present embodiment, the superpositioning hot stamped compact 12 can be kept in good corrosion resistance. It will be difficult. The difference in plating thickness (K1-K2) is preferably 12 μm or more, and more preferably 14 μm or more. On the other hand, when the difference in plating thickness (K1-K2) exceeds 33, the corrosion resistance of the plating decreases, which is not preferable. The difference in plating thickness (K1-K2) is preferably 30 μm or less, and more preferably 27 μm or less.
[0076]
　In addition, the superposed hot stamp molded body 12 according to the present embodiment satisfies the relationship shown in the above (12) together with the above expression (11). By satisfying the relationship shown in (12) above, the alloy reaction of plating that improves the emissivity during heating of the hot stamp rapidly progresses to the surface, and as a result, the superposed hot stamp molded body 12 has good corrosion resistance. As shown.
[0077]
　When the value of (K1/K2) 2 ×(T1/T2) is less than 1.5, it is difficult to sufficiently improve the difference in temperature rising rate, and it is difficult to maintain good corrosion resistance. Becomes The value of (K1/K2) 2 ×(T1/T2) is preferably 2 or more, and more preferably 2.5 or more. On the other hand, the upper limit of (K1/K2) 2 ×(T1/T2) is not particularly specified. However, an excessive increase in the value of (K1/K2) 2 ×(T1/T2), that is, an increase in (K1/K2) or (T1/T2), results in an increase in material cost due to an increase in K1 or T1, K2. Lowers the corrosion resistance and lowers the T2, resulting in lower collision resistance. Therefore, the value of (K1/K2) 2 ×(T1/T2) is preferably 80 or less. The value of (K1/K2) 2 ×(T1/T2) is more preferably 60 or less.
[0078]
　Here, the plating thicknesses K1 and K2 described above are obtained by observing the cross section of the plating with an optical microscope (area: 100 μm×100 μm) after nital etching and measuring the plating thickness in three visual fields. It can be obtained as an average value of the measured plating thickness. Incidentally, the plating thickness of the first steel sheet has a position of one sheet portion and a position of two sheet portions in contact with the second steel sheet, but the heating rate is fast and the heating time in the hot stamp is the longest and the corrosion resistance deteriorates. The plating thickness of the first steel plate is measured from one sheet part because it is easy to perform.
[0079]
　When the superposed hot stamp molding 12 of the present embodiment is used as an automobile part, it is generally used after being subjected to welding, phosphoric acid-based chemical conversion treatment, electrodeposition coating and the like. Therefore, for example, a zinc phosphate film and a phosphoric acid film formed by phosphoric acid-based chemical conversion treatment, and an organic film of 5 μm or more and 50 μm or less formed by electrodeposition coating on the surface thereof may be formed on the surface of the hot stamp molding 12. is there. In order to improve the appearance quality and corrosion resistance after the electrodeposition coating, intermediate coating, top coating, etc. may be further applied.
Example
[0080]
　Hereinafter, the present invention will be described more specifically with reference to examples.
[0081]
(Example 1) As
　shown in Table 1, chemical components (% by mass, C: 0.21%, Si: 0.2%, Mn: 1.1% ) that have undergone the normal hot rolling process and cold rolling process. , P: 0.01%, S: 0.008%, Cr: 0.3%, Ti: 0.02%, B: 0.002%, balance: Fe and impurities) As a test material, the both sides were subjected to aluminum plating treatment on a Sendzimir type hot dip aluminum coating line. After plating, the coating amount was adjusted by the gas wiping method and then cooled. The composition of the plating bath at this time was 89% Al-9% Si-2% Fe. The plate thickness is 2 mm, the coating amount is manufactured as shown in Table 1, and as shown in FIG. 5, the first steel plate 27a is 300×240 mm, and the second steel plate 27b is 250×120 mm. Spot-welding was performed as shown by the welding point 30 (welded portion 30) to prepare a hot stamping overlay blank 27. This blank was heated by hot stamping at 910° C. to examine the temperature rising rate, and immediately cooled by the die to obtain a superposed hot stamped body 31. Table 1 shows the invention examples (hereinafter, simply referred to as “invention examples”) of the present application as A1 to A12 and the comparative examples as A13 to A17. The mold is a mold from which a hat molded part having the shape and size shown in FIG. 6 is obtained. In addition, in Table 1 shown below, the coating adhesion amount W1 of the first steel plate indicates the average adhesion amount on both sides, and the plating adhesion amount W2 of the second steel plate is used as a heat source during hot stamp heating. The amount of adhesion on the exposed surface (one surface) is shown.
[0082]
[table 1]

[0083]
　The plate thickness of the steel plate and the amount of plating adhered were measured by the method described in Micro Gauge and JIS G 3314:2011, respectively, as described above.
[0084]
　In order to investigate the difference in temperature rising rate between the superposed portion of the blank and the one-sheet portion, a K-type thermocouple was attached to the center 29 and the one-sheet portion 28 of the superposed blank 27 for hot stamping shown in FIG. Each heating time was obtained by welding and evaluated. The temperature rising time was obtained from the time when the temperature reached 900° C., and the evaluation was performed based on the difference between the temperature rising times of the overlapped portion and one sheet portion. The evaluation criteria are as follows. The evaluations A to E were judged to be good, and the evaluation F was judged to be bad.
　A: 130 seconds or less
　B: 130 seconds or more and 140 seconds or less
　C: 140 seconds or more and 150 seconds or less
　D: 150 seconds or more and 160 seconds or less
　E: 160 seconds or more and 170 seconds or less
　F: 170 seconds or more
[0085]
　Table 1 summarizes the results of the investigation on the difference in the heating rate between the blank overlapping portion and the blank portion.
[0086]
　In the invention examples A1 to A12, the coating amount W1 of the first steel sheet and the coating amount W2 of the second steel sheet are both 20 g/m 2 or more and 120 g/m 2 or less, and the difference in the coating amount ( W1-W2) is 30 g / m 2 or more 100 g / m 2 satisfying the heating rate difference between the overlapping portions and one portion was good. However, Comparative Examples A13 to A17 were defective.
[0087]
　Furthermore, among the invention examples, the evaluation of A1 to A6, A8, A9, and A11 is D, and the difference between the plating adhesion amount W1 of the first steel plate and the plating adhesion amount W2 of the second steel plate is more preferable as described above. Since it is within the range of 35 g/m 2 or more, it is considered that the difference in temperature rising rate between the overlapped portion and the single sheet portion was better than the evaluation E of A7, A10, and A12.
[0088]
　Separately from the above A1 to A17, a product having a difference in the amount of adhered plating (W1-W2) of more than 100 g/m 2 was prepared, but sufficient results could not be obtained in the separately performed corrosion resistance evaluation. ..
[0089]
(Example 2)
　The effect of spot welding was investigated under the same manufacturing conditions as the level A9 of Example 1. The spot density of spot welding is obtained from (number of spot welding spots/area of ​​second steel plate). The spot density of A9 is 6 points/300 cm 2 (=1 point/50 cm 2 ) as shown in FIG. 5, and there is no spot welding spot in the bent portion after hot stamping in the overlapping portion. .. The level of the hot stamped body using the first blank and the second steel plate similar to the level A9 and using a lapped blank in which spot welding was performed at one point in the center of the lapped portion is set to A18. In this level A18, the spot density is 1 point/300 cm 2 , and similarly, in the overlapped portion, there is no spot welding spot in the bent portion after hot stamping. In addition, the level of the hot stamped body using the first blank and the second blank similar to A9 and using the lapped blank on which spot welding was performed as shown in FIG. 7 is A19. In this level A19, the spot density is 10 points/300 cm 2 (=1 point/30 cm 2 ), and spot welding spots are present in the overlapping portion at the bent portion after hot stamping. Similarly, the level of the hot stamped body using the first blank and the second blank similar to A9 and using the lapped blank subjected to spot welding as shown in FIG. 8 is A20. In this level A20, the dot density is 5 points/300 cm 2 (=1 point/60 cm 2), and a spot welding spot exists in a portion which becomes a bent portion after hot stamping in the overlapping portion.
[0090]
　The difference in temperature rising rate between the overlapped portion of A9 and A18 to A20 and one sheet portion was evaluated in the same manner as in Example 1. As a result, A9 was D as described above, A18 was E, A19 was C, and A20 was C. RBI density of spot welding point / 200 cm 2 is less than A18, the RBI density of spot welding point / 200 cm 2 slightly inferior than A9 is at least, part RBI spot welding is bent portion after the hot stamping It can be seen that A19 and A20 existing in A are superior to A9.
[0091]
[Table 2]

[0092]
(Example 3) As
　shown in Table 3, a hot stamp superposition blank 27 was produced in the same manner as in Example 1. At this time, a blank in which the plate thicknesses of the first steel plate and the second steel plate were changed as shown in Table 3 was produced, and the temperature rising rate was investigated by hot stamping the blank at 910°C. At this time, the difference in temperature rising rate between the overlapping portion and the one sheet portion was evaluated in the same manner as in Example 1. Table 2 shows the levels of the invention examples B1 to B4 and the comparative example B5.
[0093]
[Table 3]

[0094]
　Regarding the plate thickness ratio (t2/t1) of the first steel plate and the second steel plate, B4 satisfying (t2/t1)≦0.9 is higher in the overlapping portion and one sheet portion than B1, B2, and B3. It can be seen that the temperature difference is better. Further, in B5 in which the value of (W1/W2) 2 ×(t1/t2) was less than 1.5, the difference in temperature rising rate between the overlapping portion and the single sheet portion was poor.
[0095]
(Example 4) As
　shown in Table 4, chemical components (in mass%, C: 0.31%, Si: 0.2%) that have undergone the usual hot rolling step and cold rolling step as in Example 1 Mn: 1.1%, P: 0.01%, S: 0.008%, Cr: 0.3%, Ti: 0.02%, B: 0.002%, balance: Fe and impurities) A cold-rolled steel sheet of steel component was used as a test material, and both sides were subjected to aluminization treatment in a Sendzimir type hot dip aluminization treatment line. At this time, the thickness of the aluminum-iron alloy layer was changed by adjusting the immersion time in the hot dip aluminum plating bath. After plating, the coating amount was adjusted by the gas wiping method and then cooled. The plating bath composition at this time was 93% Al-5% Si-2% Fe. The plate thickness and the deposition amount of plating are manufactured as shown in Table 3, and as shown in FIG. 5, the first steel plate 27a is cut to 300×240 mm, and the second steel plate 27b is cut to 250×120 mm to prepare it. Spot-welding was performed as shown at the spots (welded portion 30) to produce a hot stamp superposition blank 27. This blank was heated by hot stamping at 910° C. to examine the temperature rising rate, and immediately cooled by the die to obtain a superposed hot stamped body 31. The respective levels are shown in Table 3 as invention examples C1 to C4. The mold is a mold from which a hat molded part having the shape and size shown in FIG. 6 is obtained.
[0096]
[Table 4]

[0097]
　Table 4 summarizes the results of the investigation on the difference in the heating rate between the blank superposed portion and the single sheet portion. The evaluation criteria for the difference in temperature rising rate between the overlapping portion and the single sheet portion are the same as in Example 1.
[0098]
　The difference (d2-d1) between the thickness d1 of the aluminum-iron alloy layer of the first steel sheet and the thickness d2 of the aluminum-iron alloy layer of the second steel sheet is 2≤(d2-d1)≤10. It can be seen that the invention examples C2 to C4 satisfying the above condition are inferior to the temperature rising speed difference between the overlapped portion and the one sheet portion as compared with C1 not satisfying the above relation.
[0099]
(Example 5) As
　shown in Table 5, chemical components (in mass%, C: 0.35%, Si: 0.2%) that have undergone the usual hot rolling step and cold rolling step as in Example 1 Mn: 0.6%, P: 0.01%, S: 0.008%, Cr: 0.3%, Ti: 0.02%, B: 0.002%, balance: Fe and impurities) A cold-rolled steel sheet of steel component was used as a test material, and both sides were subjected to aluminization treatment in a Sendzimir type hot dip aluminization treatment line. After plating, the coating amount was adjusted by the gas wiping method and then cooled. Then, an aqueous coating liquid containing a predetermined amount of carbon black, ZnO or TiO 2 was applied using a roll coater. The film thickness was obtained by observing the film from the cross section with an optical microscope. The film thickness of the carbon-based film containing carbon black was 0.5 to 3 μm as shown in Table 5, and the single film of ZnO and TiO 2 adhered. The amount was 0.5 or 1.0 g/m 2 . The plating bath composition was 86% Al-12% Si-2% Fe. The plate thickness and the deposition amount of plating are manufactured as shown in Table 5, and as shown in FIG. Spot-welding was performed as shown at the spots (welded portion 30) to produce a hot stamp superposed blank 27. This blank was heated by hot stamping at 910° C. to examine the temperature rising rate, and immediately cooled by the die to obtain a superposed hot stamped body 31. The respective levels are shown in Table 5 as invention examples D1 to D10. The mold is a mold from which a hat molded part having the shape and size shown in FIG. 6 is obtained.
[0100]
[Table 5]

[0101]
　Table 5 summarizes the results of investigations on the difference in temperature rising rate between the blank overlapping portion and the blank portion. The evaluation criteria for the difference in temperature rising rate between the overlapping portion and the single sheet portion are the same as in Example 1.
[0102]
　In the second steel sheet, D2 to D4, which are invention examples having a carbon-based coating having an emissivity of 0.7 or more, on the surface of the aluminum-based plating layer applied to the surface not in contact with the first steel sheet are carbon. It can be seen that the difference in the heating rate between the superposed portion and the single sheet portion is superior to that of D1 having no system coating. Furthermore, it is an invention example in which the surface of the aluminum-based plating layer applied to the surface of the second steel sheet has a film made of at least one of ZnO and TiO 2 and having an adhesion amount of 0.2 g/m 2 or more. It can be seen that D5, D6, and D9 are similarly excellent in the difference in the heating rate between the overlapping portion and the single sheet portion as compared with D1 which is not satisfied. It can be seen that D7, D8, and D10 having both the above carbon-based coating and the coating made of at least one of ZnO and TiO 2 are superior to D1 to D6 and D9.
[0103]
(Example 6)
　The superposed hot stamped articles of A8, A9 and A13 (heating conditions: 910°C x 7 minutes) obtained in Example 1 were examined for corrosion resistance regarding corrosion thinning. More specifically, the galvannealed steel sheet GA (1.2t) having a coating adhesion amount of 45 g/m 2 on one surface of both the flange portions of the A8, A9, and A13 superposed hot stamped compacts Each sample was prepared by spot welding three points on one side, a total of six points. Then, each test material was corroded for 60 days in accordance with CCT-JASO610 defined in JASO610 of the Japan Automobile Technology Association. Then, the corrosion thinning on the A8, A9, A13 side of the welded joint after corrosion was measured. As a result, the degree of corrosion reduction of A8 and A9 (plate reduction) was better (pass) than the GA material of the welding partner, but the degree of corrosion reduction of A13 (plate reduction) of the welding partner was The board reduction was inferior (failed) to GA. The average plating thickness (K1) of the first steel plate, the plating thickness (K2) of the second steel plate, and the plate thickness (T1, T2) of the molded products of A8, A9, and A13 before corrosion are as follows. It is as shown in Table 6. The reason why the corrosion resistance evaluation confirmed the reduction of the welded part of the flange part is that the electrodeposition coating liquid, which is generally processed when hot stamped products are used in automobiles, is difficult to enter in the welded part. This is because it is positioned as a corrosive point. For the purpose of simulating that it is difficult to enter, no electrodeposition coating was applied in the evaluation of corrosion resistance in Example 6.
[0104]
[Table 6]

[0105]
　The preferred embodiments of the present invention have been described above in detail with reference to the accompanying drawings, but the present invention is not limited to these examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.
Explanation of symbols
[0106]
　　1 1st steel plate
　　1a Surface
　　1b which contacts the 2nd steel plate in the 1st steel plate 1 Surface which does not contact the 2nd steel plate in the 1st steel
　　plate
　　2 2nd steel plate 2a In the 2nd steel plate Surface
　　2b of the second steel plate that is not in contact with the second steel plate
　　3 that is not in contact with the second steel plate 3 Welding portion
　　4 Hot stamp superimposing blank
　　4a Superimposing portion of the hot stamp superimposing blank
　　4b One piece in the superposed blank for hot stamping
　　5 Heating furnace for
　　hot stamping 6 Press die for hot stamping
　　7 Top part
　　8 Bend part on top part
　　9 Bend part on flange side
　10 Vertical wall Part
　11 Flange part
　12 Superposed hot stamped body
　13 One surface
　14 of aluminum-based plated steel sheet Aluminum layer
　15 Aluminum-iron alloy layer
　16 Base material
　17 carbon coating
　17 'ZnO and TiO 2 coating layer containing at least one of
　the surface of one side of the plated steel sheet having 18 carbon coating further surface of the aluminum-based plating layer
　18' ZnO and TiO 2 at least one of One side surface of a plated steel sheet having a coating layer containing one on the surface of the aluminum-based plating layer
　19 Welded portion at the top (dots)
　20 Welded portion at the bent portion (dots)
　21 Welded portion at the vertical wall (dots)
　22 Superimposed blank for hot stamping
　23 Welded portion (dots) at the top after forming
　24 Welded portion (dots) at the bent portion
　after forming 25 Welded portion (dots) at the vertical wall portion after forming
　26 Overlapping hot stamping Body
　27 Hot stamp superposition blank
　27a First steel plate of
　hot stamp superposition blank 27b Second steel plate of hot stamp superposition blank
　28 Thermocouple installation position of one sheet
　29 Thermocouple installation position of superposition part
　30 Welded part
　31 Overlapping hot stamped body

The scope of the claims
[Claim 1]
　A first steel plate,
　said connected via the welding point on the first surface of the steel sheet, and a small least one of the second steel plate area than the first steel plate
provided with,
　the first steel plate is plated steel sheet on both sides of the first steel sheet having an aluminum-based plating layer, and said second steel plate is a plated steel sheet having an aluminum-based plating layer on both surfaces of the second steel sheet,
　it said The adhesion amount of the aluminum-based plating layer on the first steel sheet is W1 (g/m 2 ) as an average adhesion amount on both surfaces, and the surface of
　the second steel sheet on the side not in contact with the first steel sheet The adhesion amount of the aluminum-based plating layer in is W2 (g/m 2 )
　, both W1 and W2 are in the range of 20 g/m 2 or more and 120 g/m 2 or less, and A superimposing blank for hot stamping, which satisfies the relationships of formula (1) and formula (2).
　　30≦(W1−W2)≦100 Equation (1)
　　(W1/W2) 2 ×(t1/t2)≧1.5 Equation (2)
　However, in the above Equation (2), t1 (mm) is the plate thickness of the first steel plate, and t2 (mm) is the plate thickness of the second steel plate.
[Claim 2]
　The overlay blank for hot stamping according to claim 1, wherein the welding is spot welding, and the
　spot density of the spot welding is 1 point/200 cm 2 or more.
[Claim 3]
　The first steel sheet has a portion that becomes a flange portion made of only the first steel sheet after being subjected to hot stamping
　, and at least the overlapping portion of the first steel sheet and the second steel sheet. The part has a part which becomes a bending part after being subjected to hot stamping
　, and at least one spot of the spot welding exists in a part which becomes a bending part after hot stamping. Stacked blank for hot stamping.
[Claim 4]
　4. The plate thickness t1 (mm) of the first steel plate and the plate thickness t2 (mm) of the second steel plate satisfy the relationship of the following expression (3). Superimposed blank for hot stamping described in.
　　(T2/t1)≦2.0 Equation (3)
[Claim 5]
　The aluminum-based plating layer of each of the first steel sheet and the second steel sheet has a two-layer structure of an aluminum layer and an aluminum-iron alloy layer in the order from the surface to the base steel sheet. The thickness d1 (μm) of the aluminum-iron alloy layer of the first steel plate and the thickness d2 (μm) of the aluminum-iron alloy layer of the second steel plate are expressed by the following formula (4) The hot stamp superposed blank according to any one of claims 1 to 4, which satisfies the relationship (1).
　　2≦(d2-d1)≦10 Equation (4)
[Claim 6]
　6. The second steel sheet according to claim 1, further comprising a carbon-based coating having an emissivity of 0.7 or more on a surface of the aluminum-based plating layer which is not in contact with the first steel sheet. Superimposed blank for hot stamping described in.
[Claim 7]
　On the surface of the aluminum-based plating layer located on the surface of the second steel plate , there is further provided a film made of at least one of ZnO and TiO 2 and having an adhesion amount of 0.2 g/m 2 or more per one surface. The overlay blank for hot stamping according to any one of claims 1 to 6.
[Claim 8]
　A first steel plate,
　said connected via the welding point on the first surface of the steel sheet, and a small least one of the second steel plate area than the first steel plate
provided with,
　the first steel plate is plated steel sheet on both sides of the first steel sheet having an aluminum-based plating layer, and said second steel plate is a plated steel sheet having an aluminum-based plating layer on both surfaces of the second steel sheet,
　it said The adhesion amount of the aluminum-based plating layer on the first steel sheet is W1 (g/m 2 ) as an average adhesion amount on both surfaces, and the surface of
　the second steel sheet on the side not in contact with the first steel sheet The adhesion amount of the aluminum-based plating layer in is W2 (g/m 2 )
　, both W1 and W2 are in the range of 20 g/m 2 or more and 120 g/m 2 or less, and At the time of hot stamping, in which the superimposing blank for hot stamping that satisfies the relations of the formulas (1) and (2) is heated and is molded after the heating,
　the superposed part of the first steel plate and the second steel plate. A method for manufacturing a superposed hot-stamp molded article, wherein a bent portion subjected to a bending process is provided on at least a part of the above.
　　30≦(W1−W2)≦100 Equation (1)
　　(W1/W2) 2×(t1/t2)≧1.5 Equation (2)
　However, in the above Equation (2), t1 (mm) is the plate thickness of the first steel plate, and t2 (mm) is It is the plate thickness of the second steel plate.
[Claim 9]
　The method for producing a superposed hot stamped body according to claim 8, wherein the welding is spot welding, and the
　spot density of the spot welding is 1 point/200 cm 2 or more.
[Claim 10]
　The method for manufacturing a superposed hot stamp compact according to claim 9, wherein at least one spot of the spot welding is present in a portion which becomes the bent portion after hot stamp molding.
[Claim 11]
　The plate thickness t1 (mm) of the first steel plate and the plate thickness t2 (mm) of the second steel plate satisfy the relationship of the following formula (3): The method for producing the superposed hot stamped article according to 1.
　　(T2/t1)≦2.0 Equation (3)
[Claim 12]
　The aluminum-based plating layer of each of the first steel plate and the second steel plate has a two-layer structure of an aluminum layer and an aluminum-iron-based alloy layer in the order from the surface to the base steel plate. The thickness d1 (μm) of the aluminum-iron alloy layer of the first steel plate and the thickness d2 (μm) of the aluminum-iron alloy layer of the second steel plate are expressed by the following formula (4) The method for producing a superposed hot stamped article according to any one of claims 8 to 11, which satisfies the relationship (4).
　　2≦(d2-d1)≦10 Equation (4)
[Claim 13]
　13. The second steel plate according to claim 8, further comprising a carbon-based coating having an emissivity of 0.7 or more on a surface of the aluminum-based plating layer which is not in contact with the first steel plate. The method for producing the superposed hot stamped article according to item 1.
[Claim 14]
　On the surface of the aluminum-based plating layer located on the surface of the second steel plate , there is further provided a film made of at least one of ZnO and TiO 2 and having an adhesion amount of 0.2 g/m 2 or more per one surface. The method for producing a superposed hot stamped article according to any one of claims 8 to 13.
[Claim 15]
　A first steel plate having a plate thickness of T1 (mm) is
　connected to the surface of the first steel plate via a welding point, has an area smaller than that of the first steel plate, and has a plate thickness of T2( mm) and at least one second steel plate
,
　wherein the first steel plate is an aluminum-based plating layer having an average plating thickness of K1 (μm) on both surfaces of the first steel plate. a plated steel sheet having,
　the second steel plate is a plated steel sheet plating thickness on the surface of said first steel plate not in contact with the side having an aluminum-based plating layer is K2 ([mu] m),
　the following equation (11 ) And the formula (12) are satisfied.
　10≦(K1-K2)≦33 ··· Equation (11)
　(K1/K2) 2 ×(T1/T2)≧1.5 ··· Equation (12)