Al-BASED PLATED STEEL SHEET, METHOD FOR MANUFACTURING Al-BASED PLATED STEEL SHEET, AND METHOD FOR MANUFACTURING TAILORED BLANK

Abstract

To provide an Al-based plated steel sheet that can be manufactured with heat cutting and can be used as a material for a tailored blank having a weld metal excellent in mechanical strength and corrosion resistance, and to provide a method for manufacturing the same and a method for manufacturing a tailored blank having a weld metal excellent in mechanical strength and corrosion resistance.SOLUTION: An Al-based plated steel sheet according to one embodiment of the present disclosure includes: a base steel sheet; and a plating layer including Al as the principal component. A plating layer removal part where the base steel sheet is exposed is provided in at least one of the surfaces plated with the plating layer. The plating layer removal part comes into contact with at least part of an end surface of the Al-based plated steel sheet and extends along the end surface. At least part of the end surface of the Al-based plated steel sheet has a streak that is formed in a thickness direction of the Al-based plated steel sheet. The Al-based plated steel sheet has an Al adhesion part in at least part of the end surface having the streak, where the Al adhesion part comes into contact with the plating layer removal part.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an Al-based plated steel sheet, a method for manufacturing an Al-based plated steel sheet, and a method for manufacturing a tailored blank. [Background technology]

[0002] Hot stamping is a manufacturing technique in which steel sheets are heated to high temperatures and press-formed at temperatures above the Ar3 transformation temperature. Welded steel sheets known as tailored blanks are sometimes used as steel sheets for hot stamping. Tailored blanks are obtained by butting the end faces of multiple steel sheets together and welding them. Tailored blanks are a type of butt-welded joint.

[0003] A tailored blank comprises multiple steel plates and butt welds joining them. The multiple steel plates typically have different properties, such as thickness, strength, and surface treatment. This allows the tailored blank to enhance the functionality of formed parts manufactured by hot stamping. For example, by placing thick steel plates in areas where strength is required and thin steel plates in other areas, the formed part can be made lighter and stronger. Furthermore, tailored blanks make it easy to manufacture such highly functional formed parts.

[0004] The steel sheet used as the material for tailored blanks is often Al-plated steel sheet. Al-plated steel sheet is a plated steel sheet with a plating layer made primarily of Al on one or both sides. Because Al-plated steel has a high melting point, it prevents surface oxidation of the base steel sheet during hot stamping of tailored blanks.

[0005] For example, Patent Document 1 discloses a method for producing a precoated steel sheet, the method comprising the following successive steps: providing a precoated steel strip including a steel substrate having a precoating on at least one main surface, the precoating including an intermetallic compound alloy layer and a metal alloy layer extending on the intermetallic compound alloy layer, the metal alloy layer being an aluminum layer, an aluminum alloy layer, or an aluminum-based alloy layer; and laser-cutting the precoated steel strip to obtain at least one precoated steel sheet, the precoated steel sheet having a cut edge surface resulting from the cutting operation, the cut edge surface including a substrate region and a precoating portion, and a thickness of the precoated steel sheet being between 1 mm and 5 mm, the laser-cutting step directly producing an aluminum-reduced zone on the cut edge surface extending over the entire height of the cut edge surface and over a length that is equal to or less than the length of the cut edge surface, the surface percentage of aluminum on the substrate region of the aluminum-reduced zone on the cut edge surface directly resulting from the laser-cutting operation being between 0.3% and 6%.

[0006] Patent Document 2 discloses a method for producing a precoated steel sheet, which comprises the following successive steps: a step of providing a precoated steel strip including a steel substrate having a precoating on at least one main surface thereof, the precoating including an intermetallic compound alloy layer and a metal alloy layer extending on the intermetallic compound alloy layer, the metal alloy layer being an aluminum layer, an aluminum alloy layer or an aluminum-based alloy layer; a step of laser-cutting the precoated steel strip to obtain at least one precoated steel sheet, the precoated steel sheet including a cut edge surface resulting from the cutting operation, the cut edge surface including a substrate region and a precoating region, and and a thickness of the pre-coated steel sheet is comprised between 0.8 mm and 5 mm, and the laser cutting step is carried out in a manner that directly results in a corrosion-improved zone of the cut edge surface extending over the entire height of the cut edge surface and over a length that is less than or equal to the length of the cut edge surface, the surface percentage of aluminum over the substrate area of ​​the corrosion-improved zone of the cut edge surface resulting directly from the laser cutting operation being 9% or greater, and the surface percentage of aluminum in the lower half of the substrate area of ​​the corrosion-improved zone of the cut edge surface resulting directly from the laser cutting operation being 0.5% or greater.

[0007] Patent Document 3 discloses a method for producing precoated steel blanks, the method including the steps of providing a continuous precoated steel strip comprising a steel substrate having a precoat on at least one of its main surfaces, the precoat comprising an intermetallic alloy layer and a metal layer extending over the intermetallic alloy layer, the metal layer being a layer of aluminum, an aluminum alloy, or an aluminum-based alloy; and laser-cutting the precoated steel strip to obtain at least one precoated steel blank, the precoated steel blank comprising a laser-cut edge surface resulting from the laser cutting operation, the laser-cut edge surface comprising a substrate portion and a precoat portion, the laser-cutting being carried out such that the substrate portion of the laser-cut edge directly resulting from the cutting operation has an oxygen content of 15% by weight or more.

[0008] Patent Document 4 discloses a steel sheet comprising: a first plating portion in which an intermetallic compound layer and an aluminum plating layer are provided on a surface of a base steel sheet in this order from the base steel sheet side; a first plating layer removed portion in which the base steel sheet is exposed; and a second plating portion in which the intermetallic compound layer and the aluminum plating layer are provided on the surface of the base steel sheet in this order from the base steel sheet side; in which the first plating portion, the first plating layer removed portion, the second plating portion, and the edge of the steel sheet are arranged in this order on at least one surface of the base steel sheet in a first direction that is perpendicular to the thickness direction of the steel sheet and extends from the first plating portion toward one edge of the steel sheet; and in which at least the first plating portion, the first plating layer removed portion, and the edge of the steel sheet are arranged in this order on the other surface of the base steel sheet in the first direction. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6961815 [Patent Document 2] Patent No. 6961816 [Patent Document 3] International Publication No. 2021 / 123891 [Patent Document 4] International Publication No. 2019 / 093440 Summary of the Invention [Problem to be solved by the invention]

[0010] Patent Documents 1 to 3 explain that aluminum may reduce the mechanical strength of the weld metal. In the techniques of Patent Documents 1 to 3, a removal zone is formed by removing the aluminum-containing precoat, and this removal zone is welded to prevent a reduction in the mechanical strength of the weld metal. On the other hand, Patent Documents 1 to 3 do not take into consideration the corrosion resistance of the weld metal.

[0011] Furthermore, in the techniques of Patent Documents 1 to 3, it is considered preferable to leave the intermetallic compound alloy layer in the removal zone. When such steel plates are butt-welded, a brittle intermetallic compound alloy layer remains at the boundary between the weld metal and the heat-affected zone. The boundary between the weld metal and the heat-affected zone is a stress concentration area. Furthermore, the brittle intermetallic compound alloy layer is likely to become the starting point for fatigue cracks. Therefore, it is expected that the fatigue strength of the weld will be low in the techniques of Patent Documents 1 to 3.

[0012] Patent Document 4 discloses that the corrosion resistance of the weld metal after painting is improved by providing a second plating portion having a small width at the edge of the steel sheet and mixing an appropriate amount of Al into the weld metal.

[0013] However, the technology of Patent Document 4 tends to complicate the process for providing the second plated portion. The technology of Patent Document 4 states that it is most preferable to form the plated steel sheet by shearing, such as shearing, and then remove the aluminum plating layer at the edge of the plated steel sheet by cutting using an end mill or the like. When a plated steel sheet is manufactured by shearing, sagging occurs at the edge of the plated steel sheet. It is believed that by cutting the surface of the edge of the plated steel sheet where sagging has occurred, the aluminum plating layer can be left in the area where sagging has occurred and the aluminum plating layer can be removed from other areas. However, in manufacturing methods that utilize sagging, it is difficult to control the sagging, and specific molds and equipment may be required. To manufacture plated steel sheets for tailored blanks without requiring specific molds and equipment, it is preferable to thermally cut the steel strip. However, in such cases, a means for optimizing the amount of the plating layer mixed into the weld metal is needed.

[0014] In view of the above circumstances, an object of the present disclosure is to provide an Al-based plated steel sheet that can be produced by thermal cutting and that can be used as a material for tailored blanks having weld metal with excellent mechanical strength and corrosion resistance, a method for producing the same, and a method for producing tailored blanks having weld metal with excellent mechanical strength and corrosion resistance. [Means for solving the problem]

[0015] The gist of the present disclosure is as follows.

[0016] (1) An Al-based plated steel sheet according to one embodiment of the present disclosure is an Al-based plated steel sheet including a base steel sheet and a plating layer containing Al as a main component, disposed on one or both surfaces of the base steel sheet, wherein a plating layer-removed portion exposing the base steel sheet is provided on at least one of the surfaces on which the plating layer is disposed, the plating layer-removed portion being in contact with and extending along at least a part of an end surface of the Al-based plated steel sheet, at least a part of the end surface of the Al-based plated steel sheet having a streak formed in the thickness direction of the Al-based plated steel sheet, and the Al-based plated steel sheet has an Al-deposited portion in at least a part of the end surface having the streak, and the Al-deposited portion is in contact with the plating layer-removed portion. (2) Preferably, in the Al-based plated steel sheet according to (1) above, the ratio of the area of ​​the Al-deposited portion to the area of ​​the end face on which the Al-deposited portion is disposed is more than 6%. (3) Preferably, in the Al-based plated steel sheet according to (1) or (2) above, the width of the plated layer removed portion is 0.5 mm or more. (4) Preferably, in the Al-based plated steel sheet according to any one of (1) to (3) above, the plating layer is disposed on both surfaces of the base steel sheet, and the plating layer removal portion is disposed on both surfaces of the Al-based plated steel sheet. (5) Preferably, in the Al-based plated steel sheet according to any one of (1) to (4) above, at the end face with which the plating layer removal portion contacts, the ratio of the length of the plating layer removal portion to the length of the end face with which the plating layer removal portion contacts is 80% or more, and the maximum length of the plating layer remaining portion in which the plating layer remains is 7.0 mm or less.

[0017] (6) A method for producing an Al-based plated steel sheet according to another aspect of the present disclosure includes the steps of: cutting out an Al-based plated steel sheet from a raw material having a base steel sheet and a plating layer containing Al as a main component, the plating layer being disposed on one or both surfaces of the base steel sheet; and removing the plating layer in the vicinity of an end face of the Al-based plated steel sheet to expose the base steel sheet, wherein the means for cutting out the Al-based plated steel sheet from the raw material is thermal cutting, which involves locally heating the raw material and blowing gas onto the heated portion, and the cutting speed in the thermal cutting is 2 to 100 m / min. (7) Preferably, in the method for producing an Al-based plated steel sheet as described in (6) above, the heating means in the thermal cutting is a laser.

[0018] (8) A method for manufacturing a tailored blank according to another aspect of the present disclosure includes a step of butt-welding the end face of the Al-based plated steel sheet according to any one of (1) to (5) above, the end face having the Al-adhesion portion in at least a portion thereof in contact with the plating layer removal portion, to the end face of another steel sheet. [Effects of the Invention]

[0019] According to the present disclosure, it is possible to provide an Al-based plated steel sheet that can be produced by thermal cutting and that can be used as a material for tailored blanks having weld metal with excellent mechanical strength and corrosion resistance, a method for manufacturing the same, and a method for manufacturing tailored blanks having weld metal with excellent mechanical strength and corrosion resistance. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view of an Al-based plated steel sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of an end face having streaks and an Al-deposited portion of an Al-based plated steel sheet. [Figure 3] These are electron microscope photographs of the edge surface with streaks and the Al adhesion area of ​​an Al-based plated steel sheet. The left side is a BSE image, and the right side is an image of the Al concentration distribution taken using an EPMA. [Figure 4]FIG. 2 is a cross-sectional schematic diagram of an Al-based plated steel sheet immediately before butt welding. [Figure 5] FIG. 1 is a perspective view of an Al-based plated steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] (1. Al-plated steel sheet 1) An Al-based plated steel sheet 1 according to one embodiment of the present disclosure comprises a base steel sheet 11 and a plating layer 12 containing Al as a main component, which is disposed on one or both surfaces of the base steel sheet 11. At least one of the surfaces on which the plating layer 12 is disposed has a plating layer-removed portion 13 where the base steel sheet 11 is exposed. The plating layer-removed portion 13 is in contact with and extends along at least a part of an end surface of the Al-based plated steel sheet 1. At least a part of the end surface of the Al-based plated steel sheet 1 has a striation 15 formed in the thickness direction of the Al-based plated steel sheet 1. The Al-based plated steel sheet 1 has an Al-adhesion portion 14 in at least a part of the end surface having the striation 15, and the Al-adhesion portion 14 and the plating layer-removed portion 13 are in contact with each other.

[0022] (Al-based plated steel sheet 1 and base steel sheet 11) The Al-based plated steel sheet 1 according to this embodiment has a base steel sheet 11 and a plating layer 12. The Al-based plated steel sheet 1 is a steel sheet that serves as a material for a tailored blank. The Al-based plated steel sheet 1 is cut out from a raw material such as a steel strip.

[0023] In this embodiment, the two largest surfaces of the base steel sheet 11 are referred to as the surfaces of the base steel sheet 11. Furthermore, the side surfaces connecting the two surfaces of the base steel sheet 11 are referred to as the end surfaces of the base steel sheet 11. Similarly, the two largest surfaces of the Al-based plated steel sheet 1 are referred to as the surfaces of the Al-based plated steel sheet 1. Furthermore, the side surfaces connecting the two surfaces of the Al-based plated steel sheet 1 are referred to as the end surfaces of the Al-based plated steel sheet 1. The surfaces of the base steel sheet 11 are the same as the rolled surfaces of a steel strip. The end surfaces of the base steel sheet 11 are cut surfaces formed when the base steel sheet 11 is cut out from a raw material such as a steel strip.

[0024] (Plating layer 12) The Al-based plated steel sheet 1 according to this embodiment has a plating layer 12 disposed on one or both surfaces of a base steel sheet 11. The plating layer 12 is a plating layer containing Al as its main component, i.e., an Al-based plating layer. The plating layer 12 containing Al as its main component is a plating layer 12 in which Al accounts for the highest proportion of the chemical composition of the plating layer 12, or a plating layer 12 in which the concentration of Al in the chemical composition of the plating layer 12 is 50 mass % or more. Therefore, the plating layer 12 containing Al as its main component (hereinafter simply referred to as "plating layer 12") can contain alloy elements other than Al.

[0025] The plating layer 12 may have an intermetallic compound layer. The intermetallic compound layer is a layer formed at the interface between the Al-based plating and the base steel sheet 11, and is made of an intermetallic compound between the Al-based plating and steel.

[0026] (Plating layer removal section 13) In the Al-based plated steel sheet 1 according to this embodiment, the base steel sheet 11 is exposed in a portion of the surface on which the plating layer 12 is provided. The region where the base steel sheet 11 is exposed on the surface on which the plating layer 12 is provided is referred to as the plating layer removal portion 13. If the plating layer 12 has an intermetallic compound layer, the intermetallic compound layer is also removed in the plating layer removal portion 13. If the plating layer 12 is provided on one surface of the base steel sheet 11, the plating layer removal portion 13 is provided on that surface. If the plating layer 12 is provided on both surfaces of the base steel sheet 11, the plating layer removal portion 13 is provided on at least one surface.

[0027] The coating layer removal portion 13 is a welding target when the Al-based plated steel sheet 1 is butt-welded to produce a tailored blank. Therefore, as shown in Fig. 1 , the coating layer removal portion 13 is disposed so as to contact at least a portion of an end surface of the Al-based plated steel sheet 1 and extend along the end surface. When the end surface provided with the coating layer removal portion 13 is butt-welded to another steel sheet, at least a portion of the coating layer removal portion 13 is incorporated into the weld metal WM, as shown in Fig. 4 . Fig. 4 is a schematic cross-sectional view of the Al-based plated steel sheet 1 according to this embodiment immediately before the start of butt welding. The region WM surrounded by a dashed line in Fig. 4 indicates the region where the weld metal WM will be formed after butt welding.

[0028] The plating layer removal portion 13 may be provided over the entire length of the surface on which the plating layer 12 is provided, so as to contact the entire length of the end face to be welded. Alternatively, as illustrated in Fig. 1, the plating layer removal portion 13 may be provided on a part of the surface on which the plating layer 12 is provided, so as to contact only a part of the end face to be welded. On the surface on which the plating layer 12 is provided, a portion where the plating layer remains so as to contact the end face to be welded and where the base steel sheet 11 is not exposed is referred to as a remaining plating layer portion 16. As illustrated in Fig. 5, the plating layer removal portion 13 may be divided by the remaining plating layer portion 16.

[0029] (Edge scratches 15) As shown schematically in FIG. 2 , at least a portion of the end surface of the Al-based plated steel sheet 1 has scratches 15 formed in the thickness direction of the Al-based plated steel sheet 1. The scratches 15 are formed by thermal cutting, such as laser cutting, gas cutting, and arc cutting. On the other hand, when the end surface is formed by shearing, such scratches 15 are not formed. Also, when the end surface is formed by cutting, such as by an end mill, scratches 15 may be formed, but when the end surface is formed by cutting, the Al deposition portion described below does not exist. In other words, in the Al-based plated steel sheet 1 according to this embodiment, the end surface having scratches 15 and where the Al deposition portion exists is a thermal cut surface formed by thermal cutting. Note that in JIS Z 3001-1:2008, scratches 15 formed by thermal cutting are defined as "draglines." Note that when the end surface is formed by shearing, such as shearing, sagging is formed on the end surface and its vicinity. On the other hand, no sagging is formed on the end surface on which the scratches 15 are formed of the Al-based plated steel sheet 1 according to this embodiment. Therefore, the surface of the Al-based plated steel sheet 1 is flat near the end face where the streaks 15 are formed.

[0030] (Al adhesion part 14 on the end surface) Al is deposited on at least a portion of the thermal cut surface of the Al-based plated steel sheet 1, i.e., the end surface having the scratches 15. In this embodiment, the portion of the end surface to which Al is deposited is referred to as an Al deposition portion 14. The Al deposition portion 14 can be confirmed by observing the end surface with an electron microscope. FIG. 3 shows an example of an Al deposition portion 14. The image on the left side of FIG. 3 is a BSE image of the end surface, and the image on the right side of FIG. 3 is an area analysis image of the Al concentration taken using an EPMA at the same location as the image on the left. In the area analysis image, the brighter region on the upper side of the end surface is the Al deposition portion 14.

[0031] 1, Al adhesion portion 14 is in contact with plating layer removal portion 13. Specifically, Al adhesion portion 14 is provided on the end face in contact with plating layer removal portion 13, is in contact with the surface on which plating layer removal portion 13 is provided, and is adjacent to plating layer removal portion 13.

[0032] As described above, the plating layer removal portion 13 is a portion to be welded. Therefore, the Al adhesion portion 14 is also a welding target. When the Al-based plated steel sheet 1 is butt-welded to produce a tailored blank, the Al adhesion portion 14 is incorporated into the weld metal WM of the tailored blank.

[0033] One example of a method for producing the Al adhesion portion 14 is to allow the plating layer 12 on the surface of the base steel sheet 11 to flow onto the end face of the base steel sheet 11 when cutting the Al-plated steel sheet from the raw material. This makes it possible to easily form the Al adhesion portion 14. The plating layer removal portion 13 may be formed after the Al adhesion portion 14 is formed. Suitable examples of thermal cutting methods capable of forming the Al adhesion portion 14 will be described later.

[0034] (Action and effect) The coating layer removed portion 13 of the Al-based plated steel sheet 1 according to this embodiment can increase the joint strength of the weld metal WM of a tailored blank obtained by butt-welding the Al-based plated steel sheet 1. Furthermore, the Al-adhesion portion 14 of the Al-based plated steel sheet 1 according to this embodiment can increase the post-painting corrosion resistance of the weld metal WM of the tailored blank. Furthermore, the Al-based plated steel sheet 1 according to this embodiment can be manufactured by thermal cutting. These effects will be described below with reference to FIG. 4. FIG. 4 is a schematic cross-sectional view of the Al-based plated steel sheet 1 according to this embodiment immediately before the start of butt welding. The region WM surrounded by a dashed line in FIG. 4 indicates the region where the weld metal WM will be formed after butt welding.

[0035] (Function and effect of plating layer removal section 13) The toe T of the weld metal WM of a tailored blank, i.e., the point where the surface of the weld base metal and the surface of the weld metal WM intersect, is a location where stress is likely to concentrate. Furthermore, when Al-based plated steel sheets 1 are butt-welded, Al from the plating layer 12 is incorporated into the weld metal WM and concentrates in the vicinity of the toe T of the weld metal WM. This impairs the mechanical properties of the weld metal WM in the vicinity of the toe T, and reduces the joint strength of the weld.

[0036] The coating layer removal portion 13 of the Al-based plated steel sheet 1 according to this embodiment exhibits the effect of suppressing Al concentration in the vicinity of the toe T of the weld metal WM. The coating layer 12, which is primarily composed of Al, is removed in the coating layer removal portion 13. When the end faces of the Al-based plated steel sheet 1 provided with the coating layer removal portion 13 are butt-welded, the amount of coating layer 12 incorporated into the weld metal WM can be reduced. In particular, when the coating layer removal portion 13 is provided so that the toe T of the weld metal WM is located inside the coating layer removal portion 13, the amount of coating layer 12 incorporated into the weld metal WM can be made substantially zero. This increases the joint strength of the weld in a tailored blank obtained from the Al-based plated steel sheet 1 according to this embodiment.

[0037] The coating layer 12, which is primarily composed of Al, may have a brittle intermetallic compound layer at the interface with the base steel sheet 11. The intermetallic compound layer present on the surface of the base steel sheet 11 near the toe T may become the starting point for fracture in the heat-affected zone, potentially impairing the fatigue strength of the weld. However, in the coating layer-removed portion 13 of the Al-based coated steel sheet 1 according to this embodiment, the intermetallic compound layer has been removed, exposing the base steel sheet 11. The coating layer-removed portion 13 also has the effect of ensuring the fatigue strength of the weld.

[0038] (Action and effect of Al adhesion portion 14) Furthermore, the Al-based plated steel sheet 1 according to this embodiment has an Al adhesion portion 14 in at least a part of the end face having the striations 15. The Al adhesion portion 14 is in contact with the coating layer removal portion 13. Therefore, when the end faces provided with the coating layer removal portion 13 are butt-welded, the Al adhesion portion 14 is incorporated into the weld metal WM.

[0039] While Al contained in the weld metal WM may impair the mechanical properties of the weld metal WM, it also functions to improve the corrosion resistance of the weld metal WM after painting. It is thought that Al suppresses the formation of scale on the surface of the weld metal WM, improves the chemical conversion treatability of the weld metal WM, and improves the adhesion of paint.

[0040] The Al adhesion portion 14 is incorporated into the weld metal WM, improving the corrosion resistance after painting. Furthermore, the Al adhesion portion 14 present on the end surface is incorporated into a location away from the toe T of the weld metal WM. Therefore, the Al adhesion portion 14 optimizes the amount of Al mixed into the weld metal WM and can suppress Al concentration in stress-concentrated areas of the weld metal WM. Therefore, the Al adhesion portion 14 does not impair the mechanical properties of the weld.

[0041] (Effects of Streak 15) Furthermore, the Al-based plated steel sheet 1 according to this embodiment has, on at least a portion of the end surface, streaks 15 that are traces of thermal cutting. Therefore, the Al-based plated steel sheet 1 according to this embodiment can be produced by thermal cutting.

[0042] The above has described the most basic aspect of the Al-based plated steel sheet 1 according to this embodiment. A more preferred aspect will now be described.

[0043] (Coverage of Al-deposited portion 14 and its measurement method) In the Al-based plated steel sheet 1 according to this embodiment, the coverage of the Al adhesion portion 14, i.e., the ratio of the area of ​​the Al adhesion portion 14 to the area of ​​the end face on which the Al adhesion portion 14 is disposed, is preferably greater than 6%. This further improves the post-painting corrosion resistance of the weld metal WM formed after welding the end face. The coverage of the Al adhesion portion 14 may be 7% or more, 8% or more, 10% or more, or 15% or more. There is no particular upper limit to the coverage of the Al adhesion portion 14. For example, the coverage of the Al adhesion portion 14 may be 100%. That is, the Al adhesion portion 14 may extend from the upper end to the lower end of the end face. On the other hand, the coverage of the Al adhesion portion 14 may be 50% or less, 30% or less, 10% or less, less than 9%, or 8% or less.

[0044] The method for measuring the coverage of the Al adhesion portion 14 is as follows. The distribution of Al concentration on the end face having the scratches 15 is quantitatively analyzed using an EPMA. The acceleration voltage during the quantitative analysis is 15 kV. In the quantitative analysis, the location where the Al concentration is 1.0 mass % or more is defined as the Al adhesion portion 14. The observation range for measuring the distribution of Al concentration includes from one surface to the other surface of the end face. The coverage of the Al adhesion portion 14 is determined by dividing the total area of ​​the Al adhesion portion 14 in the observation range by the area of ​​the end face in the observation range.

[0045] (Width of plating layer removal portion 13 and its measurement method) In the Al-based plated steel sheet 1 according to this embodiment, the width of the plating layer removal portion 13, i.e., the size of the plating layer removal portion 13 measured in a direction perpendicular to the end surface with which the plating layer removal portion 13 contacts, is preferably 0.5 mm or more. This more reliably prevents Al from concentrating near the toe T of the weld metal WM. The width of the plating layer removal portion 13 may be 1.0 mm or more, 1.5 mm or more, or 2.0 mm or more. There is no particular upper limit to the width of the plating layer removal portion 13, but from the viewpoint of paintability, the width may be, for example, 10.0 mm or less, 8.0 mm or less, 6.0 mm or less, or 3.0 mm or less.

[0046] The shape of plating layer removal portion 13 can be easily identified visually. The width of plating layer removal portion 13 is identified by measuring the size of plating layer removal portion 13 identified visually along a direction perpendicular to the end face.

[0047] (Position of plating layer removal portion 13) When the plating layer 12 is disposed on both surfaces of the Al-based plated steel sheet 1, the plating layer removal portion 13 may be provided on at least one surface of the Al-based plated steel sheet 1. Preferably, the plating layer removal portion 13 is provided on both surfaces of the Al-based plated steel sheet 1. This further improves the mechanical properties of the weld. Note that when the plating layer removal portion 13 is provided on both surfaces of the Al-based plated steel sheet 1, the Al adhesion portion 14 may be in contact with either one of the plating layer removal portions 13.

[0048] (Coverage of Al-deposited portion 14 on end surface not in contact with plating layer removed portion 13, and method for measuring same) As described above, the plating layer removal portion 13 may be provided so as to contact at least a portion of the end surface of the Al-based plated steel sheet 1. Therefore, the Al-based plated steel sheet 1 may have an end surface that is not provided with the plating layer removal portion 13 and does not contact the plating layer removal portion 13. For example, the plating layer removal portion 13 is not provided near an end surface that is not intended to be welded. When the plating layer 12 is provided on one surface of the base steel sheet 11, the plating layer 12 contacts the surface on which the plating layer 12 is provided over the entire length of the end surface at the end surface that is not intended to be welded. When the plating layer 12 is provided on both surfaces of the base steel sheet 11, the plating layer 12 contacts both surfaces over the entire length of the end surface at the end surface that is not intended to be welded. Furthermore, the end surface that is not contacted by the plating layer removal portion 13 may be an end surface that has a streak 15 formed by thermal cutting. An Al-adhesion portion 14 may be provided on such an end surface that does not have the plating layer removal portion 13.

[0049] The longer the length of the plating layer removal portion 13, the more preferable the proportion of the length of the end face to which welding is to be performed. For example, at the end face where the plating layer removal portion 13 contacts, the proportion of the length of the plating layer removal portion 13 to the length of the end face where the plating layer removal portion 13 contacts is preferably 80% or more, 85% or more, or 90% or more. Furthermore, at the end face where the plating layer removal portion 13 contacts, the maximum length of the plating layer remaining portion 16 where the plating layer remains is preferably 7.0 mm or less, 6.5 mm or less, or 6.0 mm or less. The maximum length of the plating layer remaining portion 16 refers to the length of the plating layer remaining portion 16 that is longest in the direction along the end face. For example, in the Al-based plated steel sheet illustrated in FIG. 5, there are three plating layer remaining portions 16 that contact the end face. Of the three plating layer remaining portions 16, the longest in the direction along the end face is the plating layer remaining portion 16 at the center of the drawing. The length of the remaining plating layer portion 16 at the center of the paper along the end face is the maximum length of the remaining plating layer portion 16. The remaining plating layer portion 16 may be present so as to contact multiple points on the end face that is in contact with the plating layer removed portion 13. Note that the remaining plating layer portion 16 is a concept that includes the remaining intermetallic compound layer portion described below.

[0050] (2. Method for manufacturing Al-based plated steel sheet 1) Although the method for manufacturing the Al-based plated steel sheet 1 according to this embodiment is not particularly limited, a suitable example will be described below. According to the manufacturing method described below, the Al-based plated steel sheet 1 according to this embodiment can be easily manufactured. Below, a method for manufacturing the Al-based plated steel sheet 1 according to another aspect of the present invention will be described in detail.

[0051] First, an Al-based plated steel sheet 1 is cut out from a raw material such as a steel strip. Like the Al-based plated steel sheet 1 according to this embodiment, the raw material has a base steel sheet and a plating layer containing Al as its main component arranged on one or both surfaces of the base steel sheet.

[0052] The Al-based plated steel sheet 1 is cut from the raw material by thermal cutting. Thermal cutting is a general term for methods that use heat to locally melt or burn a material to cut it. Examples of thermal cutting include gas cutting, arc cutting, and laser cutting. The most preferred cutting method is laser cutting. In thermal cutting, the Al-based plated steel sheet 1 is locally heated using a heating means such as a gas flame, arc, or laser, while gas is sprayed onto the heated area. The heated and molten metal is removed by the gas.

[0053] During thermal cutting, the molten coating layer 12 flows into the end surface of the Al-based coated steel sheet 1. As a result, the Al contained in the coating layer 12 forms an Al-adhered portion 14 on the end surface.

[0054] When performing thermal cutting, it is preferable to increase the cutting speed. According to the results of experiments conducted by the present inventors, there was a tendency for the faster the cutting speed, the higher the coverage rate of the Al adhesion portion 14. The reason for this is unclear, but it is presumed as follows: The faster the cutting speed, the lower the temperature of the molten metal at the cut portion, and the higher the viscosity of the molten metal. As a result, it is thought that molten Al is more likely to remain on the end surface when gas is blown. For example, when the thermal cutting is laser cutting, it is preferable for the cutting speed to be within the range of 2 to 100 m / min. More preferably, the cutting speed is within the range of 5 to 50 m / min.

[0055] By performing thermal cutting under the above conditions, it is possible to simultaneously cut out the Al-based plated steel sheet 1 and form the Al-adhered portion 14. This allows the Al-based plated steel sheet 1 to be produced quickly and easily. Note that it is sufficient that the above conditions are satisfied at least at the end face to be welded.

[0056] Although the thermal cutting conditions other than the cutting speed are not particularly limited, the following are examples of suitable conditions for thermal cutting using a laser. Laser oscillator types: solid-state lasers (e.g., fiber lasers, disk lasers, diode lasers, YAG lasers, etc.), CO2 lasers, etc. Laser beam focal position: +2.0mm to -5.0mm Nozzle gap: 0.1~1.0mm Assist gas type: Nitrogen gas, Ar gas, or a mixture of 5% or less oxygen gas and nitrogen gas or Ar gas Assist gas pressure: 0.5 to 1.5 MPa Nozzle diameter: 0.5~5.0mm The focal position of the laser light is described by defining the top surface of the workpiece as the origin (0), with the upper side of the workpiece defined as a positive number and the lower side defined as a negative number.

[0057] Next, the plating layer 12 is removed near the end face to be welded to expose the base steel sheet 11. Specifically, the plating layer 12 is removed in a region that contacts and extends along the end face where the Al adhesion portion 14 is formed. This forms a plating layer-removed portion 13 that contacts the Al adhesion portion 14. The plating layer 12 is removed by, for example, cutting using a machining tool such as a turning tool, end mill, or metal saw, or by laser processing such as laser gouging.

[0058] (3. Tailored Blank Manufacturing Method) A method for manufacturing a tailored blank according to another aspect of the present disclosure includes a step of butt-welding an end face of an Al-based plated steel sheet 1 according to the present embodiment, at least a portion of which has an Al adhesion portion 14 in contact with the coating layer removed portion, to an end face of another steel sheet. As a result, the Al adhesion portion 14 is incorporated into the weld metal WM, improving the post-painting corrosion resistance of the weld metal WM. Furthermore, as described above, a coating layer removed portion 13 is provided near the end face having the Al adhesion portion 14 in contact with the coating layer removed portion. This prevents the coating layer 12 provided on the surface of the base steel sheet 11 from being incorporated into the vicinity of the toe T of the weld metal WM and prevents fatigue fracture originating from the surface of the base steel sheet 11 in the vicinity of the toe T, improving the mechanical properties of the weld.

[0059] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited thereto and can be modified as appropriate without departing from the technical spirit thereof. More preferred examples of the Al-based plated steel sheet 1 and the method for manufacturing a tailored blank according to the present embodiments will be described below. Unless otherwise specified, the examples described below are applicable to both the Al-based plated steel sheet 1 and the method for manufacturing a tailored blank.

[0060] (Components, thickness, and mechanical properties of base steel sheet 11) The configuration of the base steel sheet 11 is not particularly limited, but a preferred example of the configuration of the base steel sheet 11 will be described below.

[0061] The base steel sheet 11 is obtained by a normal manufacturing method including, for example, hot rolling, cold rolling, heat treatment, etc. The base steel sheet 11 may be a hot-rolled steel sheet or a cold-rolled steel sheet.

[0062] The thickness of the base steel sheet 11 can be appropriately selected depending on the application of the Al-based plated steel sheet 1. When the application of the Al-based plated steel sheet 1 is the production of tailored blanks, the thickness of the base steel sheet 11 is preferably, for example, 0.8 mm or more, 1.0 mm or more, or 1.2 mm or more. In this case, the thickness of the base steel sheet 11 is preferably, for example, 4.0 mm or less, 3.0 mm or less, or 2.0 mm or less.

[0063] Suitable examples of the chemical composition of the base steel sheet 11 are, in mass %, C: 0.02% to 0.58%, Mn: 0.20% to 3.00%, Al: 0.005% to 0.20%, 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 The aluminum-plated steel sheet 11 contains 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%, Bi: 0% to 0.05%, Si: 0% to 2.00%, P: 0.03% or less, S: 0.010% or less, N: 0.010% or less, and the balance: Fe and impurities. The impurities refer to components that are mixed in with raw materials such as ore or scrap during industrial steel production, or due to various factors in the manufacturing process, and are acceptable within a range that does not adversely affect the aluminum-plated steel sheet 1 according to this embodiment. The chemical components of the base steel sheet 11 can be measured in accordance with JIS G 0321:2017, "Methods for analyzing steel products and their allowable variations."

[0064] The tensile strength of the base steel sheet 11 can be selected appropriately depending on the application of the Al-based plated steel sheet 1. For example, if the application of the Al-based plated steel sheet 1 is to ensure the strength of a press-molded product, the tensile strength of the base steel sheet 11 after quenching is preferably 1300 MPa or more, 1500 MPa or more, or 1800 MPa or more. On the other hand, if the application of the Al-based plated steel sheet 1 is to manufacture an exterior material to ensure the design of a press-molded product, the tensile strength of the base steel sheet 11 after quenching is preferably 300 MPa or more, 400 MPa or more, or 500 MPa or more. The tensile strength of the base steel sheet 11 can be measured in accordance with JIS Z 2241:2011 "Methods for tensile testing of metallic materials."

[0065] The Vickers hardness of the base steel sheet 11 can be appropriately selected depending on the application of the Al-based plated steel sheet 1. For example, if the application of the Al-based plated steel sheet 1 is to ensure the strength of a press-molded product, the Vickers hardness of the base steel sheet 11 after quenching is preferably 400 Hv or more, 450 Hv or more, or 500 Hv or more. On the other hand, if the application of the Al-based plated steel sheet 1 is to manufacture an exterior material to ensure the design of a press-molded product, the Vickers hardness of the base steel sheet 11 after quenching is preferably 90 Hv or more, 120 Hv or more, or 150 Hv or more. The hardness of the base steel sheet 11 can be measured in accordance with JIS Z 2244:2009 "Vickers Hardness Test - Test Method." The test force for measuring the Vickers hardness of the base steel sheet 11 is 500 g.

[0066] (Components, Thickness, and Coating Weight of Plating Layer 12) Examples of alloy elements other than Al contained in the plating layer 12 include Si and Fe. Si and Fe have the function of improving the corrosion resistance of the plating layer 12. One suitable example of the plating layer 12 has a chemical composition containing, by mass %, 5% to 12% Si, with the balance containing aluminum and impurities. Another suitable example of the plating layer 12 has a chemical composition containing, by mass %, 5% to 12% Si and 2% to 4% Fe, with the balance containing aluminum and impurities.

[0067] The thickness and coating weight of the plating layer 12 are not particularly limited. A preferred example of the thickness of the plating layer 12 is 8 μm to 50 μm. A preferred example of the coating weight of the plating layer 12 per side is 30 g / m 2 ~120g / m 2 is.

[0068] (Intermetallic compound layer) As described above, the plating layer 12 may have an intermetallic compound layer. The intermetallic compound layer is formed along the interface between the plating layer 12 and the base steel sheet 11. The intermetallic compound layer is mainly composed of Fe x Al y (x and y are numbers equal to or greater than 1). When the plating layer 12 contains Si, the intermetallic compound layer is preferably formed of a plurality of compounds represented by the formula Fe x Aly and Fe x Al y Si z It is preferable that the insulating layer is formed from a plurality of compounds represented by the formula (x, y, and z each represent a number of 1 or more).

[0069] The thickness of the intermetallic compound layer is not particularly limited, but may be, for example, an average thickness of 3 μm or more, preferably 4 μm or more. The thickness of the intermetallic compound layer may be, for example, an average thickness of 10 μm or less, preferably 8 μm or less. The thickness of the intermetallic compound layer can be controlled by the temperature and immersion time of the molten metal bath containing aluminum as the main component.

[0070] (Remaining part of intermetallic compound layer) The Al-based plated steel sheet 1 according to this embodiment may have a remaining intermetallic compound layer portion. The remaining intermetallic compound layer portion refers to a portion where the surface of the plating layer 12 has been removed but the intermetallic compound layer remains, and the base steel sheet 11 is not exposed. For example, a part of the plating layer removed portion 13 may be replaced with a remaining intermetallic compound layer portion. This is because the intermetallic compound layer has the function of improving the corrosion resistance of the base steel sheet 11. For example, the remaining intermetallic compound layer portion may be disposed in a location where high fatigue strength is not required.

[0071] (Welding method) The welding method for producing the tailored blank is not particularly limited. Suitable examples of the welding method include laser welding and arc welding. The chemical composition of the weld bead may be adjusted by adding a filler material such as a filler wire to the molten pool. The welding conditions are also not particularly limited. The welding conditions can be appropriately selected depending on the thickness, chemical composition, etc. of the Al-based plated steel sheet 1. [Example]

[0072] The effects of one embodiment of the present disclosure will be explained in more detail using examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the present disclosure and the object of the present disclosure is achieved.

[0073] Al-based plated steel sheets were cut out from various test materials having a base steel sheet and an Al-based plated layer. The test materials were 1500 MPa class Al-plated hot stamp steel sheets with a thickness of 1.6 mm. The plated layers were provided on both sides of the test materials. The coating weight (per side) of the plated layer of the test materials was 40 g / m 2 , and 80 g / m 2 The cutting method was laser cutting. In Example No. 1, the end surface formed by laser cutting was ground, thereby simulating mechanical cutting. In the other examples, no additional processing was performed on the end surface formed by laser cutting. The cutting speed in laser cutting was as shown in Table 1.

[0074] After laser cutting at various cutting speeds to cut out aluminum-based plated steel sheets from the test materials, the aluminum plating layers on the top and bottom surfaces near the edge of the aluminum-based plated steel sheet were removed by cutting to form plating layer-removed areas. The ratio of the length of the plating layer-removed area to the length of the edge where it contacts was set to 100% in all examples. The width of the plating layer-removed area is shown in Table 1. Table 1 also shows whether or not the base steel sheet was exposed in the plating layer-removed area.

[0075] The test pieces were then laser welded together with the end faces in contact with the removed plating layer facing each other. Filler was added to the weld during the laser welding. The blank obtained by butt welding was then heated to a furnace temperature of 900°C for a dwell time of 4 minutes, and then quenched using a mold.

[0076] The laser cutting conditions other than the cutting speed are as follows: Laser type: Fiber laser Laser beam focal position: -0.75mm Nozzle gap: 1.0mm Nozzle diameter: Φ2.0mm Assist gas type: 100% nitrogen gas Assist gas pressure: 0.8MPa

[0077] After quenching, the blank was subjected to chemical conversion treatment and electrodeposition coating to prepare test specimens. The chemical conversion treatment solution was PB-SX35T manufactured by Nihon Parkerizing Co., Ltd. The electrodeposition paint was Powernics 110, a cationic electrodeposition paint manufactured by Nippon Paint Co., Ltd. The target thickness of the electrodeposition film was approximately 15 μm. The test specimen was prepared by heating at 170°C for 20 minutes to bake the coating. The test specimen measured 65 mm in length and 100 mm in width. The weld was positioned in the center of the width direction.

[0078] The test pieces were subjected to a corrosion test in accordance with JASO M610-92, an automotive parts external corrosion test. The corrosion resistance after painting was evaluated based on the corrosion state after 360 cycles (120 days).

[0079] The evaluation procedure was as follows. First, after the corrosion test, photographs of the weld were taken. The shape of the weld bead was visible without removing the electrodeposition coating. The area of ​​red rust that had developed on the weld bead in the photograph of the weld was measured by analyzing the photograph using commercially available image analysis software. The red rust area was then used as the evaluation criterion. The pass / fail judgment for the corrosion test was based on the red rust area of ​​a test piece (reference test piece) whose weld metal did not contain Al. The reference test piece was prepared by removing the Al-based plating layer on the surface of the test piece and the Al-adhered portion on the end face using an end mill. The test piece was then butt-welded using an Al-free filler wire. The test piece was then subjected to chemical conversion treatment and electrodeposition coating according to the procedure described above. Specimens with red rust development covering more than 3 / 4 of the red rust area were rated as "× (fail)," specimens with red rust development covering 3 / 4 or less or more than 1 / 2 were rated as "△ (pass)," and specimens with red rust development covering 1 / 2 or less were rated as "○ (pass)."

[0080] After quenching the welded blank under the above conditions, No. 5 tensile test specimens were taken so that the weld line was perpendicular to the tensile direction, and static tensile tests were performed. Test specimens that fractured at the weld metal were judged to be "× (fail)" in terms of mechanical strength, and test specimens that fractured at the base metal were judged to be "○ (pass)."

[0081] [Table 1]

[0082] The Al-plated steel sheet of Example 1 had no Al-adhered portion on its end face. In Example 1, the Al concentration in the weld metal was insufficient, and the corrosion resistance of the weld metal after painting was unacceptable.

[0083] The Al-based plated steel sheet of Example 2 did not have a portion where the plated layer was removed, exposing the base steel sheet. In the portion where the plated layer was removed in Example 2, the intermetallic compound layer remained, and the base steel sheet was not exposed. In Example 2, the Al concentration in the weld metal was excessive, and the mechanical strength of the weld metal was unacceptable.

[0084] On the other hand, in the Al-based plated steel sheets of Examples 3 to 9, plated layer-removed portions were provided on both surfaces where the plated layer was disposed, exposing the base steel sheet, and Al-deposited portions were present on at least a portion of the end faces, with the Al-deposited portions and the plated layer-removed portions being in contact with each other. The test specimens obtained from Examples 3 to 9 had excellent weld metal corrosion resistance after painting and excellent mechanical strength. [Explanation of symbols]

[0085] 1. Al-plated steel sheet 11 Base steel sheet 12 plating layer 13 Plating layer removal section 14 Al adhesion area 15 marks 16 Remaining plating layer WM weld metal T Toe

Claims

1. A base steel sheet, a plating layer containing Al as a main component, which is disposed on one or both surfaces of the base steel sheet; An Al-based plated steel sheet comprising: a plating layer removed portion in which the base steel sheet is exposed is provided on at least one of the surfaces on which the plating layer is disposed, the plating layer removal portion is in contact with at least a part of an end surface of the Al-based plated steel sheet and extends along the end surface, at least a part of the end surface of the Al-based plated steel sheet has a streak formed in the thickness direction of the Al-based plated steel sheet, the Al-based plated steel sheet has an Al-deposited portion in at least a part of the end surface having the striations, The Al-adhered portion and the plating layer-removed portion are in contact with each other. Aluminum-plated steel sheet.

2. The ratio of the area of ​​the Al adhering portion to the area of ​​the end face on which the Al adhering portion is disposed is more than 6%. The Al-based plated steel sheet according to claim 1.

3. 2. The aluminum-based plated steel sheet according to claim 1, wherein the width of the plated layer removed portion is 0.5 mm or more.

4. the plating layer is disposed on both surfaces of the base steel sheet, The plating layer removal portions are arranged on both surfaces of the Al-based plated steel sheet. The Al-based plated steel sheet according to claim 1.

5. At the end surface with which the plating layer removal portion is in contact, the ratio of the length of the plating layer removal portion to the length of the end surface with which the plating layer removal portion is in contact is 80% or more, and the maximum length of the plating layer remaining portion in which the plating layer remains is 7.0 mm or less. The Al-based plated steel sheet according to claim 1.

6. a step of cutting out an Al-based plated steel sheet from a raw material having a base steel sheet and a plating layer containing Al as a main component arranged on one or both surfaces of the base steel sheet; removing the plating layer in the vicinity of the end face of the Al-based plated steel sheet to expose the base steel sheet; Equipped with a means for cutting out the Al-based plated steel sheet from the raw material is thermal cutting in which the raw material is locally heated and gas is blown onto the heated portion; The cutting speed in the thermal cutting is set to 2 to 100 m / min. Manufacturing method of aluminum-plated steel sheet.

7. The heating means in the thermal cutting is a laser. The method for producing an Al-based plated steel sheet according to claim 6.

8. 6. A method for manufacturing a tailored blank, comprising: butt-welding the end face of the Al-based plated steel sheet according to claim 1, at least a portion of which is provided with the Al-adhesion portion that contacts the plating layer removed portion, to an end face of another steel sheet.

Images