Plated steel sheet

Abstract

This plated steel sheet has a plating layer on at least a portion of the surface of a steel sheet, the plating layer having a chemical composition containing, in mass%, 0.50-4.50% of Al, 0.50-less than 3.00% of Mg, 0.01-15.00% of Fe, and the balance of Fe and unavoidable impurities. The plating layer selectively contains one or more elements selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, element group F, and element group G, with the remainder being 5.00 mass% or more of Zn and impurities, and the plating layer has an average particle size of 1-5 [mu] m in a measurement result obtained by measuring the plating layer by X-ray diffraction. The peak intensity ratio I100 / I002 of the intensity I100 of the peak corresponding to the (100) plane and the intensity I002 of the peak corresponding to the (002) plane of the MgZn2 phase is 2.50 or more.

Description

Technical Field

[0001] The present invention relates to a plated steel sheet. Background Art

[0002] Galvanized steel sheets are blanks widely used in the fields of construction, automobiles, etc. from the viewpoint of improving the corrosion resistance of structural members. At this time, the following method is used: various structural members are manufactured by welding a previously galvanized steel sheet by arc welding, laser welding, etc.

[0003] Here, in the case of manufacturing a structural member by welding a galvanized steel sheet, there are the following specific problems. In the heat-affected zone of the welded metal and the base material, there are liquid metal embrittlement cracks (Liquid Metal Embrittlement: LME) caused by hot-dip plating, and porosity formation due to Zn combustion during welding, and as a result, the corrosion resistance around the welded part (weld heat-affected zone) is reduced.

[0004] In order to solve the problems of LME and porosity formation as described above, various solutions have been proposed in the past. For example, Patent Document 1 below proposes a plated steel material having: a steel sheet, and a plating layer disposed on the surface of the steel sheet and containing a Zn-Al-Mg alloy layer. In the cross section of the Zn-Al-Mg alloy layer, the area fraction of the MnZn2 phase is 45 to 75%, the total area fraction of the MgZn2 phase and the Al phase is 70% or more, and the area fraction of the Zn-Al-MnZn2 ternary eutectic structure is 0 to 5%, and the plating layer has a specified chemical composition.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: International Publication No. 2018 / 139620 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Here, by using the plated steel material proposed in Patent Document 1 above, the problems of LME or porosity formation can be solved. However, as a result of in-depth research by the present inventors, the technology proposed in Patent Document 1 above still has room for improvement, and for the problems related to LME and the problems related to film blistering after welding, it is desired to be further improved by adopting a technical method different from that of Patent Document 1 above.

[0010] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a plated steel sheet that can further suppress the generation of LME during welding and film blistering after welding.

[0011] Solutions for Solving the Problems

[0012] In order to solve the above problems, the inventors of the present invention have conducted in-depth research on film blistering during welding. As a result, it has been found that by controlling the orientation of a specific metallographic structure in the surface structure of the plating layer, LME during welding can be suppressed and film blistering during welding can be inhibited, thereby completing the present invention.

[0013] The gist of the present invention completed based on this insight is as follows.

[0014] (1) A plated steel sheet having a plating layer on at least a part of the surface of the steel sheet,

[0015] The plating layer has the following chemical composition:

[0016] Containing, by mass%,

[0017] Al: 0.50 or more and 4.50 or less,

[0018] Mg: 0.50% or more and less than 3.00%,

[0019] Fe: 0.01 to 15.00%,

[0020] Optionally containing one or more selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, element group F, and element group G, with the balance being Zn and impurities of 5.0000% by mass or more,

[0021] In the measurement result obtained by measuring the aforementioned plating layer by X-ray diffraction method, the intensity I of the peak corresponding to the (100) plane of the MgZn2 phase 100 and the intensity I of the peak corresponding to the (002) plane 002 The peak intensity ratio I of 100 / I 002 Is 2.50 or more.

[0022] [Element group A]: One or two selected from the group consisting of Si: greater than 0% and 2.00% or less and Ca: greater than 0% and 2.00% or less

[0023] [Element group B]: One or more selected from the group consisting of Sb: greater than 0% and 0.5000% or less, Pb: greater than 0% and 0.5000% or less, and Sr: greater than 0% and 0.5000% or less

[0024] [Element group C]: selected from one or more of the group consisting of Co: greater than 0% and 1.0000% or less, V: greater than 0% and 1.0000% or less, Cu: greater than 0% and 1.0000% or less, Ti: greater than 0% and 1.0000% or less, Cr: greater than 0% and 1.0000% or less, Nb: greater than 0% and 1.0000% or less, Ni: greater than 0% and 1.0000% or less, Mn: greater than 0% and 1.0000% or less, and Mo: greater than 0% and 1.0000% or less

[0025] [Element group D]: selected from one or more of the group consisting of In: greater than 0% and 1.0000% or less, Bi: greater than 0% and 1.0000% or less, and Sn: greater than 0% and 1.0000% or less

[0026] [Element group E]: selected from one or more of the group consisting of Zr: greater than 0% and 1.0000% or less, Ag: greater than 0% and 1.0000% or less, and Li: greater than 0% and 1.0000% or less

[0027] [Element group F]: selected from one or more of the group consisting of La: greater than 0% and 0.5000% or less, Ce: greater than 0% and 0.5000% or less, and Y: greater than 0% and 0.5000% or less

[0028] [Element group G]: B: greater than 0% and 0.5000% or less

[0029] (2) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group A.

[0030] (3) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group B.

[0031] (4) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group C.

[0032] (5) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group D.

[0033] (6) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group E.

[0034] (7) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group F.

[0035] (8) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group G.

[0036] (9) The plated steel sheet according to any one of (1) to (8) above, wherein the tensile strength of the steel sheet is 780 MPa or more.

[0037] (10) The plated steel sheet according to any one of (1) to (8) above, wherein the peak intensity ratio I 100 / I 002 is 5.00 or more.

[0038] (11) The plated steel sheet according to (9) above, wherein the peak intensity ratio I 100 / I 002 is 5.00 or more.

[0039] (12) The plated steel sheet according to (10) above, wherein the peak intensity ratio I 100 / I 002 is 10.00 or more.

[0040] (13) The plated steel sheet according to (11) above, wherein the peak intensity ratio I 100 / I 002 is 10.00 or more.

[0041] (14) The plated steel sheet according to any one of (1) to (8) above, wherein in the measurement result obtained by glow discharge emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

[0042] (15) The plated steel sheet according to (9) above, wherein in the measurement result obtained by glow discharge emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

[0043] (16) The plated steel sheet according to (10) above, wherein in the measurement result obtained by glow discharge emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

[0044] (17) The plated steel sheet according to (11) above, wherein in the measurement result obtained by glow discharge emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

[0045] (18) The coated steel sheet according to (12) above, wherein in the measurement result obtained by glow discharge emission spectrometry in the depth direction of the coated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

[0046] (19) The coated steel sheet according to (13) above, wherein in the measurement result obtained by glow discharge emission spectrometry in the depth direction of the coated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

[0047] Effects of the Invention

[0048] As described above, according to the present invention, it is possible to provide a coated steel sheet that can further suppress the occurrence of LME during welding and film blistering after welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1A It is an explanatory view schematically showing the configuration of the coated steel sheet of the embodiment of the present invention.

[0050] Figure 1B It is an explanatory view schematically showing the configuration of the coated steel sheet of the same embodiment.

[0051] Figure 2 It is a schematic view for explaining the MgZn2 phase in the coating layer of the coated steel sheet of the same embodiment.

[0052] Figure 3 It is an explanatory view for explaining the peak intensity in the XRD measurement result. DETAILED DESCRIPTION OF THE INVENTION

[0053] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that in this specification and the drawings, for components having substantially the same functional structure, repeated description is omitted by assigning the same reference numerals.

[0054] (For the coated steel sheet)

[0055] First, with reference to Figure 1A and Figure 1B , the overall structure of the coated steel sheet of the embodiment of the present invention will be described. Figure 1A and Figure 1B are explanatory views schematically showing an example of the coated steel sheet of the present embodiment.

[0056] As Figure 1ASchematically shown, the plated steel sheet 1 of the present embodiment has: a steel sheet 10 as a base material, and a plating layer 20 located on at least a part of the surface of the steel sheet 10. In addition, the plating layer 20 does not exist only on Figure 1A one surface of the steel sheet 10 shown, and may also be as shown in Figure 1B schematically shown, and exist on both surfaces of the steel sheet 10.

[0057] <Regarding the steel sheet 10>

[0058] According to a certain mode, the size, composition, structure, and mechanical properties of the steel sheet 10 used as the base material of the plated steel sheet 1 of the present embodiment are not particularly limited. For example, various steel sheets can be used according to the mechanical strength (such as tensile strength) required for the plated steel sheet 1. As such a steel sheet 10, for example, various Al-killed steels can be cited; extra-low carbon steels containing Ti, Nb, etc.; high-strength steels in which extra-low carbon steels further contain strengthening elements such as P, Si, and Mn; various steel sheets containing various other components (Cr, N, Cu, B, Ni, Mg, Ca, V, Co, Zn, As, Y, Zr, Mo, Sn, Sb, Ta, W, Pb, Bi, REM, etc.), etc.

[0059] In addition, the thickness of the steel sheet 10 is not particularly limited, and can be appropriately set according to the mechanical strength required for the plated steel sheet 1, etc.

[0060] According to another mode, as the steel sheet 10, a steel sheet with a tensile strength of 780 MPa or more is used. Such a steel sheet 10 is preferably used as the base material steel sheet for forming the plating layer 20 of the present embodiment. As the steel sheet 10, it is more preferable to use a steel sheet with a tensile strength of 980 MPa or more.

[0061] <Regarding the plating layer 20>

[0062] As schematically shown in Figure 1A and Figure 1B , the plating layer 20 is provided on the surface of the steel sheet 10, and more preferably provided on the entire surface of the steel sheet 10. Hereinafter, the chemical composition of the plating layer 20 will be described in detail first.

[0063] ◇Regarding the chemical composition of the plating layer 20

[0064] According to a certain method, the chemical composition of the coating layer 20 in this embodiment has the following chemical composition: containing Al: 0.50% or more and 4.50% or less, Mg: 0.50% or more and less than 3.00%, Fe: 0.01 to 15.00, and the balance being Zn and impurities of 5.0000% by mass or more. That is, in the chemical composition of the coating layer 20 in this embodiment, the contents of Al, Mg, and Fe are within the above ranges, and the total of these contents is less than 95.0000% by mass, and the balance is Zn and impurities of 5.0000% by mass or more.

[0065] In addition, according to another method, the chemical composition of the coating layer 20 in this embodiment has the following chemical composition: containing Al: 0.50% or more and 4.50% or less, Mg: 0.50% or more and less than 3.00%, Fe: 0.01 to 15.00%, and further containing one or more selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, element group F, and element group G, and the balance being Zn and impurities of 5.0000% by mass or more. That is, in the chemical composition of the coating layer 20 in this embodiment, the contents of Al, Mg, and Fe are within the above ranges, and the total of the contents of these Al, Mg, Fe, and element groups A to G is less than 95.0000% by mass, and the balance is Zn and impurities of 5.0000% by mass or more.

[0066] [Element group A]: One or two selected from the group consisting of Si: greater than 0% and 2.00% or less and Ca: greater than 0% and 2.00% or less

[0067] [Element group B]: One or more selected from the group consisting of Sb: greater than 0% and 0.5000% or less, Pb: greater than 0% and 0.5000% or less, and Sr: greater than 0% and 0.5000% or less

[0068] [Element group C]: One or more selected from the group consisting of Cu: greater than 0% and 1.0000% or less, Ti: greater than 0% and 1.0000% or less, Cr: greater than 0% and 1.0000% or less, Nb: greater than 0% and 1.0000% or less, Ni: greater than 0% and 1.0000% or less, Mn: greater than 0% and 1.0000% or less, and Mo: greater than 0% and 1.0000% or less

[0069] [Element group D]: One or more selected from the group consisting of In: greater than 0% and 1.0000% or less, Bi: greater than 0% and 1.0000% or less, and Sn: greater than 0% and 1.0000% or less

[0070] [Element group E]: Select one or more than one selected from the group consisting of Zr: greater than 0% and 1.0000% or less, Ag: greater than 0% and 1.0000% or less, and Li: greater than 0% and 1.0000% or less

[0071] [Element group F]: Select one or more than one selected from the group consisting of La: greater than 0% and 0.5000% or less, Ce: greater than 0% and 0.5000% or less, and Y: greater than 0% and 0.5000% or less

[0072] [Element group G]: B: greater than 0% and 0.5000% or less

[0073] Thus, the coating layer 20 of the present embodiment is a coating layer having the following chemical composition: containing Al: 0.50% or more and 4.50% or less, Mg: 0.50% or more and less than 3.00%, Fe: 0.01 to 15.00% by mass, selectively containing one or more than one selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, element group F, and element group G, and the balance being Zn and impurities of 5.0000% by mass or more.

[0074] [Al: 0.50% by mass or more and 4.50% by mass or less]

[0075] Al is an element necessary for the main metallographic structure (Zn - Al - Mg based metallographic structure) of the coating layer 20 of the present embodiment. The plated steel sheet contains a certain amount or more of this element to ensure the corrosion resistance of the part that becomes the heat - affected zone of welding and the part that becomes the non - welded part. When the Al content in the coating layer 20 is less than 0.50% by mass, the corrosion resistance of the parts that become the above - mentioned heat - affected zone of welding and non - welded part cannot be guaranteed. Therefore, in the coating layer 20 of the present embodiment, the Al content is 0.50% by mass or more. The Al content is preferably 1.00% by mass or more, more preferably 1.50% by mass or more. By the Al content reaching the above range, the corrosion resistance of the plated steel sheet 1 can be guaranteed.

[0076] On the other hand, when the Al content in the coating layer 20 is greater than 4.50% by mass, during welding, the formation of the Zn - Fe alloy phase is hindered, resulting in the liquid - phase Zn - Mg contacting the steel base, and LME cannot be sufficiently inhibited. In addition, during welding, α primary crystals precipitate in the coating layer of the non - heat - affected zone, resulting in the hindrance of the columnar orientation of the subsequent MgZn2 phase, and the film blistering after welding cannot be sufficiently inhibited. Therefore, in the coating layer 20 of the present embodiment, the Al content is 4.50% by mass or less. The Al content is preferably 4.00% by mass or less, more preferably 3.00% by mass or less.

[0077] [Mg: 0.50 mass% or more and less than 3.00 mass%]

[0078] Mg is an element necessary for the main metallographic structure (Zn-Al-Mg-based metallographic structure) of the coating layer 20 of the present embodiment, and is particularly necessary for forming the MgZn2 phase described later. That is, the coated steel sheet contains Mg in a certain amount or more to ensure the corrosion resistance of the part that becomes the heat-affected zone of welding and the part that becomes the non-welded part. Therefore, in the coating layer 20 of the present embodiment, the Mg content is 0.50 mass% or more. The Mg content is preferably 1.00 mass% or more, and more preferably 1.50 mass% or more. When the Mg in the coating layer 20 is less than 0.50 mass%, the corrosion resistance of the part that becomes the non-welded part may be insufficient, and the columnar orientation of the MgZn2 phase described later may be insufficient. By making the Mg content reach the above range, the corrosion resistance of the coated steel sheet 1 can be ensured and the MgZn2 phase described later can be formed.

[0079] On the other hand, when the Mg content in the coating layer 20 reaches 3.00 mass% or more, the alloying reaction between Zn in the coating layer during welding and the steel base is hindered, resulting in the contact of the liquid-phase Zn-Mg with the steel base, and LME cannot be sufficiently suppressed. In addition, the nucleation sites of the MgZn2 phase in the coating layer increase excessively, and the orientation control of the MgZn2 phase becomes difficult. Therefore, in the coating layer 20 of the present embodiment, the Mg content is less than 3.00 mass%. The Mg content is preferably 2.50 mass% or less, and more preferably 2.00 mass% or less. By making the Mg content reach the above range, LME during welding of the coated steel sheet 1 can be sufficiently suppressed and the MgZn2 phase described later can be formed.

[0080] [Fe: 0.01 - 15.00 mass%]

[0081] Sometimes, the elements constituting the steel sheet may be mixed into the coating layer 20 from the steel sheet 10 as the base material. Especially in the hot-dip plating method, due to the mutual diffusion of elements caused by the solid-liquid reaction between the steel sheet 10 and the coating layer 20, the elements constituting the steel sheet 10 are likely to be mixed into the coating layer 20. Such element mixing causes the coating layer 20 to contain a certain amount of Fe, and its content can usually reach 0.01 mass% or more. If the above mutual diffusion is promoted, the adhesion between the steel sheet 10 and the coating layer 20 is improved. From the viewpoint of improving the adhesion between the steel sheet 10 and the coating layer 20, the Fe content in the coating layer 20 is preferably 0.20 mass% or more.

[0082] In addition, within the range not impairing the effects of the present invention, Fe may also be intentionally added to the plating bath used for manufacturing the plating layer 20. However, if the Fe content in the plating bath increases, high-melting-point intermetallic compounds of Fe and Al will be formed in the plating bath, and there is a tendency for the high-melting-point intermetallic compounds to adhere to the plating layer 20 as scum, resulting in a significant reduction in the appearance quality. Therefore, it is not preferred. From this perspective, by adjusting the Fe content in the plating bath, the Fe content in the plating layer 20 is made 15.00 mass% or less. The Fe content in the plating layer 20 is more preferably 10.00 mass% or less.

[0083] In the plating layer 20, the balance of the above-mentioned Al, Mg, and Fe is Zn and impurities of 5.0000 mass% or more. Zn is an essential element for the main metallographic structure (Zn-Al-Mg-based metallographic structure) constituting the plating layer 20 of the present embodiment and is an important element for improving the corrosion resistance of the plated steel sheet. In addition, the plating layer 20 contains the above-mentioned Al, Mg, and Fe within the above range and further contains 5.0000 mass% or more of Zn, thereby being able to suppress LME during welding.

[0084] Next, the element groups A to E that the chemical composition of the plating layer 20 of another mode of the present embodiment may selectively have will be described in detail.

[0085] It should be noted that when the plating layer 20 of the present embodiment contains at least any one element belonging to the following element groups B to E, it is preferably contained in the following content range and the total content is 5.0000 mass% or less in a manner of containing at least any one element belonging to the following element groups B to E.

[0086] By making the total content of the elements belonging to element groups B to E 5.0000 mass% or less, the effects exhibited by adding each element described in detail below can be enjoyed without mutual impairment. The total content of the elements belonging to element groups B to E is preferably 1.0000 mass% or less, and more preferably 0.2000 mass% or less.

[0087] ◇ Element group A

[0088] The element group A that the plating layer 20 of another mode of the present embodiment may contain will be described. At least any one of the following element group A is an element that can be contained in the plating layer 20 in place of a part of the balance of Zn.

[0089] [Element group A]: One or two selected from the group consisting of Si: greater than 0% and 2.00% or less and Ca: greater than 0% and 2.00% or less

[0090] [Si: 0 - 2.00 mass%]

[0091] Since the coating layer 20 of this embodiment may also contain no Si, the lower limit of its content is 0% by mass. On the other hand, Si is an element that can inhibit the excessive growth of the Fe-Al-based intermetallic compound phase formed at the interface between the coating layer and the steel sheet and further improve the adhesion between the coating layer and the steel sheet. When the coating layer 20 contains Si, in order to inhibit the excessive growth of the Fe-Al-based intermetallic compound phase, the content of Si is preferably 0.05% by mass or more, more preferably 0.20% by mass or more.

[0092] On the other hand, when the content of Si is greater than 2.00% by mass, a high-melting-point intermetallic compound phase with Mg is excessively formed, and the columnar orientation of the MgZn2 phase described later is hindered, and film blistering cannot be sufficiently inhibited. Therefore, when the coating layer 20 contains Si, the content of Si is made 2.00% by mass or less. From other viewpoints, by setting the content of Si to 2.00% by mass or less, the viscosity of the plating bath can be made appropriate and the operability can be improved. The content of Si in the coating layer 20 is preferably 0.50% by mass or less, more preferably 0.20% by mass or less.

[0093] [Ca: 0 to 2.00% by mass]

[0094] Since the coating layer 20 of this embodiment may also contain no Ca, the lower limit of its content is 0% by mass. On the other hand, when the coating layer 20 contains Ca, it forms an intermetallic compound phase with Al and Zn. Furthermore, when Si is contained together with Ca in the coating layer 20, Ca forms an intermetallic compound with Si. These intermetallic compounds have a high melting point and a stable structure, so that the LME of the plated steel sheet during welding can be further inhibited. When the coating layer 20 contains Ca, the effect of inhibiting LME during welding is manifested by making the Ca content 0.01% by mass or more. The Ca content in the coating layer 20 is more preferably 0.10% by mass or more.

[0095] On the other hand, when the Ca content in the coating layer 20 is greater than 2.00% by mass, the corrosion resistance of the plated steel sheet may be reduced. From this viewpoint, the Ca content in the coating layer 20 is 2.00% by mass or less. The Ca content in the coating layer 20 is preferably 1.50% by mass or less, more preferably 0.50% by mass or less.

[0096] ◇Element group B

[0097] Next, an element group B that the coating layer 20 of this embodiment may contain in another mode will be described. At least any one of the elements in the following element group B is an element that can be contained in the coating layer 20 in place of a part of the balance of Zn.

[0098] [Element group B]: Select one or more from the group consisting of Sb: greater than 0% and 0.5000% or less, Pb: greater than 0% and 0.5000% or less, and Sr: greater than 0% and 0.5000% or less

[0099] [Sb: 0 to 0.5000 mass%]

[0100] [Pb: 0 to 0.5000 mass%]

[0101] [Sr: 0 to 0.5000 mass%]

[0102] Since the coating layer 20 of the present embodiment may also contain no Sb, Pb, or Sr, the lower limit of the content of these elements is 0 mass%. On the other hand, when the coating layer 20 contains at least any one of Sb, Pb, and Sr, spangles will form on the surface of the coating layer 20, and an improvement in metallic luster can be achieved. Therefore, from the viewpoint of further improving the designability of the coated steel sheet, it is preferable that the coating layer 20 contains at least any one of Sb, Pb, and Sr. This effect of improving the appearance is manifested when the content of at least any one of Sb, Pb, and Sr reaches 0.0500 mass% or more. Therefore, when the coating layer 20 contains at least any one of Sb, Pb, and Sr, it is preferable that the contents of these elements are each independently 0.0500 mass% or more.

[0103] When forming a coating layer 20 in which any one of the contents of Sb, Pb, and Sr is greater than 0.5000 mass%, the amount of scum generated in the plating bath for forming the coating layer 20 increases, and a coated steel sheet with good coating properties cannot be manufactured. Therefore, the contents of Sb, Pb, and Sr in the coating layer 20 are each independently 0.5000 mass% or less. The contents of Sb, Pb, and Sr are preferably each independently 0.2000 mass% or less.

[0104] ◇Element group C

[0105] Next, an element group C that the coating layer 20 of the present embodiment may contain in another mode will be described. At least any one of the following element group C is an element that can be contained in the coating layer 20 in place of a part of the balance of Zn.

[0106] [Element group C]: Select one or more than two selected from the group consisting of Co: greater than 0% and 1.0000% or less, V: greater than 0% and 1.0000% or less, Cu: greater than 0% and 1.0000% or less, Ti: greater than 0% and 1.0000% or less, Cr: greater than 0% and 1.0000% or less, Nb: greater than 0% and 1.0000% or less, Ni: greater than 0% and 1.0000% or less, Mn: greater than 0% and 1.0000% or less, and Mo: greater than 0% and 1.0000% or less

[0107] [Co: 0 to 1.0000 mass%]

[0108] [V: 0 to 1.0000 mass%]

[0109] [Cu: 0 to 1.0000 mass%]

[0110] [Ti: 0 to 1.0000 mass%]

[0111] [Cr: 0 to 1.0000 mass%]

[0112] [Nb: 0 to 1.0000 mass%]

[0113] [Ni: 0 to 1.0000 mass%]

[0114] [Mn: 0 to 1.0000 mass%]

[0115] Since it is possible that the coating layer 20 in the present embodiment does not contain Co, V, Cu, Ti, Cr, Nb, Ni, and Mn, the lower limit of the content of these elements is 0 mass%. On the other hand, when the coating layer 20 contains at least any one of Co, V, Cu, Ti, Cr, Nb, Ni, and Mn, when welding the plated steel sheet, these elements are introduced into the Fe-Al-based metallographic structure formed by welding, and the corrosion resistance of the formed welded portion can be further improved. This effect of improving the corrosion resistance of the welded portion is manifested when the content of at least any one of Co, V, Cu, Ti, Cr, Nb, Ni, and Mn in the coating layer 20 reaches 0.0050 mass% or more. Therefore, when the coating layer 20 contains at least any one of Co, V, Cu, Ti, Cr, Nb, Ni, and Mn, it is preferable that the content of these elements is independently 0.0050 mass% or more respectively.

[0116] On the other hand, when forming the coating layer 20 in which any one of the contents of Co, V, Cu, Ti, Cr, Nb, Ni, and Mn is greater than 1.0000% by mass, in the plating bath used to form the coating layer 20, these elements form various intermetallic compounds, resulting in an increase in the viscosity of the plating bath and making it impossible to manufacture a plated steel sheet with good plating properties. Therefore, the contents of Co, V, Cu, Ti, Cr, Nb, Ni, and Mn in the coating layer 20 are each independently 1.0000% by mass or less. Preferably, the contents of Co, V, Cu, Ti, Cr, Nb, Ni, and Mn are each independently 0.2000% by mass or less.

[0117] [Mo: 0 to 1.0000% by mass]

[0118] Since the coating layer 20 of the present embodiment may also not contain Mo, the lower limit of its content is 0% by mass. On the other hand, when the coating layer 20 contains Mo, the corrosion resistance can be further improved. This effect of improving the corrosion resistance is manifested when the content of Mo reaches 0.0100% by mass or more. Therefore, when containing Mo, it is preferably made to have a content of 0.0100% by mass or more.

[0119] On the other hand, when forming the coating layer 20 with a Mo content greater than 1.00% by mass, it causes a large amount of scum to be generated in the used plating bath, so it is not preferred. Therefore, the content of Mo is 1.0000% by mass or less. The content of Mo is preferably 0.0500% by mass or less.

[0120] ◇Element group D

[0121] Next, an element group D that the coating layer 20 in another aspect of the coating layer 20 of the present embodiment may contain will be described. The elements of the element group D shown below are elements that can be included in the coating layer 20 in place of a part of the balance of Zn.

[0122] [Element group D]: One or more selected from the group consisting of In: greater than 0% and 1.0000% or less, Bi: greater than 0% and 1.0000% or less, and Sn: greater than 0% and 1.0000% or less

[0123] [In: 0 to 1.0000% by mass]

[0124] [Bi: 0 to 1.0000% by mass]

[0125] [Sn: 0 to 1.0000% by mass]

[0126] Since the coating layer 20 of the present embodiment may also contain no In, Bi, and Sn, the lower limit of their content is 0% by mass. When the coating layer 20 containing In, Bi, and Sn is placed in a corrosive environment, these are elements that increase the dissolution rate of Mg. If the dissolution rate of Mg increases, Mg ions are supplied to the exposed part of the steel sheet 10, and the corrosion resistance is further improved. From this viewpoint, when containing In, Bi, and Sn, it is preferable that their content is 0.00500% by mass or more.

[0127] On the other hand, excessive addition of In, Bi, and Sn will excessively promote the Mg dissolution rate, and the corrosion resistance of the plated steel sheet may be reduced. This increase in the Mg dissolution rate is significant when any one of the contents of In, Bi, and Sn is greater than 1.0000% by mass. Therefore, the content of In, Bi, and Sn is 1.0000% by mass or less. The content of In, Bi, and Sn is preferably 0.2000% by mass or less.

[0128] ◇Element group E

[0129] Next, an element group E that the coating layer 20 in another mode of the present embodiment may contain will be described. At least any one of the elements in the element group E shown below is an element that can be contained in the coating layer 20 in place of a part of the balance of Zn.

[0130] [Element group E]: One or more selected from the group consisting of Zr: greater than 0% and 1.0000% or less, Ag: greater than 0% and 1.0000% or less, and Li: greater than 0% and 1.0000% or less

[0131] [Zr: 0 - 1.0000% by mass]

[0132] [Ag: 0 - 1.0000% by mass]

[0133] [Li: 0 - 1.0000% by mass]

[0134] Since the coating layer 20 of the present embodiment may also contain no Zr, Ag, and Li, the lower limit of the content of these elements is 0% by mass. On the other hand, when the coating layer 20 contains at least any one of Zr, Ag, and Li, the plating operability can be further improved. This effect of improving the plating operability is manifested when the content of at least any one of Zr, Ag, and Li in the coating layer 20 reaches 0.0100% by mass or more. Therefore, when containing at least any one of Zr, Ag, and Li, it is preferable that the content of these elements is independently 0.0100% by mass or more.

[0135] On the other hand, when forming the coating layer 20 in which any one of the contents of Zr, Ag, and Li is greater than 1.0000% by mass, a large amount of scum is likely to be generated in the plating bath for forming the coating layer 20. Therefore, the content of at least any one of Zr, Ag, and Li is independently 1.0000% by mass or less. The content of at least any one of Zr, Ag, and Li is independently 0.1000% by mass or less.

[0136] ◇Element group F

[0137] Next, an element group F that the coating layer 20 in another mode of the coating layer 20 of the present embodiment may contain will be described. At least any one element in the element group F shown below is an element that can be contained in the coating layer 20 in place of a part of the balance of Zn.

[0138] [Element group F]: One or more selected from the group consisting of La: greater than 0% and 0.5000% or less, Ce: greater than 0% and 0.5000% or less, and Y: greater than 0% and 0.5000% or less

[0139] [La: 0 to 0.5000% by mass]

[0140] [Ce: 0 to 0.5000% by mass]

[0141] [Y: 0 to 0.5000% by mass]

[0142] Since the coating layer 20 of the present embodiment may not contain La, Ce, and Y, the lower limit of the content of these elements is 0% by mass. On the other hand, La, Ce, and Y are elements that exhibit an effect approximately equivalent to that of Ca and further suppress the formation of pores during welding. This is because the atomic radius of each element is close to the atomic radius of Ca. When these elements are contained in the coating layer 20, they will be substituted at the Ca position. Therefore, in EDS (Energy Dispersive X-ray Spectroscopy), these elements will be detected at the same position as Ca. In addition, when oxides of these elements are formed after welding of the plated steel sheet, oxides of these elements will also be detected at the same position as CaO.

[0143] The effect of suppressing the formation of pores during welding is manifested by making the content of these elements independently 0.0100% by mass or more. Therefore, when containing at least any one of Zr, Ag, and Li, it is preferable to make the content of these elements independently 0.0100% by mass or more. More preferably, the contents of La, Ce, and Y in the coating layer 20 are independently 0.0500% by mass or more.

[0144] On the other hand, when the contents of La, Ce, and Y in the plating bath used for manufacturing the plating layer 20 are excessive, the viscosity of the plating bath increases above the required level, and the plating operability may decrease. Therefore, from the viewpoint of plating operability, by adjusting the contents of La, Ce, and Y in the plating bath, the contents of La, Ce, and Y are each independently 0.5000 mass% or less. Preferably, the contents of La, Ce, and Y are each independently 0.1000 mass% or less.

[0145] ◇Element group G

[0146] Next, an element group G that the plating layer 20 in another mode of the plating layer 20 of the present embodiment may contain will be described. The elements of the element group G shown below are elements that can be contained in the plating layer 20 in place of a part of the balance of Zn.

[0147] [Element group G]: B: greater than 0% and 0.5000% or less

[0148] [B: 0 to 0.5000 mass%]

[0149] Since the plating layer 20 of the present embodiment may not contain B, the lower limit of its content is 0 mass%. On the other hand, when the plating layer 20 contains B, it has an effect of further suppressing LME. It is speculated that the reason is that when the plating layer 20 contains B, it combines with at least one of Zn, Al, Mg, and Ca to form various intermetallic compounds. In addition, it can be considered that since B exists in the plating layer 20, B diffuses from the plating layer 20 to the steel sheet 10, and has an effect of further suppressing the LME of the steel sheet 10 by grain boundary strengthening. And since the melting points of the various intermetallic compounds formed by B are extremely high, it is speculated that it also plays a role in suppressing Zn combustion during welding. This improvement effect is manifested by containing 0.05 mass% or more of B. Therefore, when containing B, the content of B is preferably 0.0500 mass% or more.

[0150] On the other hand, since the plating layer 20 contains B, when the plating bath contains an excessive amount of B, it will cause a sharp rise in the plating melting point, reduce the plating operability, and it is impossible to manufacture a plating steel sheet with excellent plating properties. This reduction in plating operability is significant when the content of B is greater than 0.5000 mass%, so the content of B is 0.5000 mass% or less. The content of B is preferably 0.1000 mass% or less.

[0151] [Method for measuring chemical composition]

[0152] The chemical composition of the above-mentioned coating layer 20 can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). It should be noted that ICP-AES is used for the analysis of chemical composition in units of 0.1 mass%, while ICP-MS is used for the analysis of trace chemical components less than 0.1 mass%. The coated steel sheet is immersed in a 10% HCl aqueous solution added with an inhibitor for about 1 minute, and the coating layer part is peeled off to prepare a solution in which the coating layer is dissolved. The obtained solution is analyzed using ICP-AES or ICP-MS, thereby enabling the average chemical composition of the entire coating layer to be obtained.

[0153] ◇Regarding the coating amount of the coating layer 20

[0154] There is no special regulation for the coating amount of the coating layer 20 described above. For example, it is preferably 15 to 250 g / m on each side of the steel sheet. 2 or so. By making the coating amount of the coating layer 20 within the above range, the coated steel sheet 1 of the present embodiment can exhibit sufficient corrosion resistance. The thickness of the coating layer 20 having this coating amount can generally reach about 5 to 40 μm.

[0155] It should be noted that the coating amount of the coating layer 20 is measured in the following manner. First, a sample with a size of 30 mm × 30 mm is cut out from the coated steel sheet in a plan view, and the mass of this sample is measured in advance. It should be noted that when cutting out the sample, it is cut out in the entire thickness direction. A tape is pasted on one side of this sample so that the coating layer on this side will not dissolve in the next process. On this basis, the sample is immersed in a 10% HCl aqueous solution added with an inhibitor, and the coating layer is pickled and peeled off, and the mass of the pickled sample is measured. Based on the mass change of the sample before and after pickling, the coating amount of each side of the coating layer 20 can be determined.

[0156] ◇Regarding the metallographic structure of the coating layer 20

[0157] Next, the metallographic structure of the coating layer 20 having the chemical composition described above will be described.

[0158] The coating layer 20 of the present embodiment has the chemical composition as described above and is formed by the manufacturing method described in detail below, and thus contains metal phases or intermetallic compound phases (metallographic structures) such as ηZn phase, α phase, τ phase, MgZn2 phase, Mg2Zn3 phase, and MgZn phase. In addition to the above metallographic structure, depending on the elements that the coating layer 20 may further contain, it may also contain metallographic structures such as Al-Si-Ca phase, Al-Si-Ca-Fe phase, Mg2Si phase, and Mg2Sn phase. The coating layer 20 of the present embodiment exhibits the properties of suppressing the occurrence of LME and having excellent corrosion resistance by having the above-described metallographic structure.

[0159] Here, in order to determine what kind of metallographic structure the coating layer 20 of the present embodiment has, the surface of the coating layer 20 can be observed using a scanning electron microscope (SEM). That is, the solidification structure of the coating layer 20 is observed using SEM, and in the observation field of view, based on the point analysis results using SEM-EPMA (Electron Probe MicroAnalyzer) and the crystal phase morphology in the backscattered electron image, it is possible to determine what kind of metallographic structure it has. At this time, pretreatment such as polishing may not be performed before SEM observation, but in the case where a chemical conversion treatment film or the like is applied, in order to remove the chemical conversion treatment film or the like, polishing or the like may be performed. When polishing is performed, polishing is carried out in such a way that 80% or more of the thickness of the coating layer remains, and after the surface is in a mirror finish state, SEM observation is performed, and this is used as the surface structure.

[0160] More specifically, for example, JXA-8500 manufactured by JEOL Ltd. is used as the analysis device, the observation positions are set at any 5 places, and the size of the observation area for each place is set to 40 μm × 40 μm. The acceleration voltage is set to 15.0 kV, the irradiation current is set to 5.0×10 -7 A, the irradiation time is set to 50 milliseconds, and this range is observed at a magnification of 4000 times. Under these conditions, a backscattered electron image of the range of interest is obtained, and then point analysis of each metallographic structure is performed using the contrast of the backscattered electron image.

[0161] When the present inventors studied the film blistering at the welded part generated during welding, they focused on the MgZn2 phase in the above-described metallographic structure.

[0162] The MgZn2 phase is a phase of an intermetallic compound of Mg and Zn formed in the coating layer 20 of the present embodiment. The MgZn2 phase is contained as a phase for improving corrosion resistance and weldability. That is, compared with the Zn phase, the MgZn2 phase has high insulation and high corrosion resistance. In addition, compared with the Zn phase, it has a lower corrosion potential, excellent sacrificial corrosion protection, and improves the corrosion resistance around the welded part. In addition, it densifies the corrosion products after welding and inhibits red rust. In addition, it inhibits the combustion of the coating layer 20 during welding. The coating layer 20 of the present embodiment further controls the crystal orientation of the MgZn2 phase and forms a columnar orientation to inhibit film blistering.

[0163] Use Figure 2 The columnar orientation of the MgZn2 phase of the coating layer 20 of the present embodiment will be described. Figure 2 It is a schematic diagram showing an outline of the columnar orientation of the MgZn2 phase of the present embodiment and an outline of film blistering that may occur on the coated steel sheet 1.

[0164] First, the crystal structure of the MgZn2 phase in the coating layer 20 of the present embodiment will be described. The MgZn2 phase has a hexagonal crystal structure, and three unit cells of a quadrangular prism structure aggregate to form Figure 2 the hexagonal prism structure shown. In Figure 2 the hexagonal prism structure shown, the plane represented by the hexagon is the (002) plane of the MgZn2 phase, and one of the columnar planes orthogonal to the (002) plane of the MgZn2 phase is the (100) plane of the MgZn2 phase. It should be noted that Figure 2 the size of the MgZn2 phase shown is only for convenience and does not represent the formation of a single crystal of this size.

[0165] Next, the columnar orientation of the MgZn2 phase in the coating layer 20 of the present embodiment will be described. In the coating layer 20 of the present embodiment, when pole measurement is performed by X-ray diffraction (XRD), in the material coordinate system defined by the RD (Rolling Direction) axis and the TD (Transversal Direction, width direction) axis, the (100) plane of the MgZn2 phase is oriented in such a way as to form a plane perpendicular to the ND (Normal Direction) axis, which is the normal direction of the RD-TD plane (that is, to form a plane parallel to the RD-TD plane).

[0166] Here, the (100) plane of the MgZn2 phase is a crystal plane perpendicular to the (002) plane of the MgZn2 phase. Therefore, by orienting the (100) plane of the MgZn2 phase to form a plane perpendicular to the ND axis, the (002) plane of the MgZn2 phase can be oriented to form a plane parallel to the ND axis (i.e., a plane perpendicular to the RD-TD plane). It should be noted that the (002) plane of the MgZn2 phase only needs to be parallel to the ND axis, and the orientation on the RD-TD plane (orientation relative to the RD axis or TD axis) is not particularly limited.

[0167] Next, the film blistering will be described. For the plated steel sheet 1 of the present embodiment, coating is applied on the coating layer 20 after welding to form a coating film 30. Under the coating film 30 in the heat affected zone, corrosion of the coating layer 20 (i.e., under-film corrosion) sometimes occurs. As Figure 2 shown by the thick arrow (corrosion), the under-film corrosion progresses along a direction perpendicular to the ND axis. Due to the progress of this under-film corrosion, the thickness of the coating layer 20 changes, and the thickness of the coating film 30 formed on the coating layer 20 changes, thereby causing film blistering.

[0168] The inventors of the present invention verified the under-film corrosion, and as a result, newly found that when the under-film corrosion progresses in the MgZn2 phase, the progress of the under-film corrosion can be suppressed in the direction perpendicular to the (002) plane of the MgZn2 phase compared to the direction perpendicular to other crystal planes of the MgZn2 phase. It is considered that this is because the (002) plane is a dense plane of the crystal of MgZn2.

[0169] Based on the above insights, the inventors of the present invention obtained the following concept: by orienting the (002) plane of the MgZn2 phase perpendicular to the progress direction of the under-film corrosion, it may be possible to suppress the progress of the under-film corrosion and suppress film blistering. It should be noted that although the under-film corrosion progresses in an arbitrary direction within the RD-TD plane, the orientation of the (002) plane of the MgZn2 phase on the RD-TD plane is randomly oriented. Therefore, the coating layer 20 contains MgZn2 phases in which the (002) plane is perpendicular to any progress direction of the under-film corrosion. Thus, in this specification, orienting the MgZn2 phase such that the (002) plane of the MgZn2 phase is perpendicular to the progress direction of the under-film corrosion is referred to as columnar orientation.

[0170] In the coating layer 20 of the present embodiment, for whether the MgZn2 phase forms columnar orientation, XRD can be used and judged based on whether the following conditions are satisfied. That is, when measuring the surface of the coating layer 20 of the present embodiment using a commercially available wide-angle X-ray diffractometer, when in the obtained measurement result, the intensity I of the peak corresponding to the (100) plane of the MgZn2 phase 100The intensity I of the peak corresponding to the (002) plane of the MgZn2 phase 002 The peak intensity ratio I 100 / I 002 When it is 2.50 or more, it can be determined that the columnar orientation of the (002) plane shown in Figure 2 has been achieved.

[0171] ◇Commercially available wide-angle X-ray diffractometers (e.g., RINT1500 manufactured by Rigaku Corporation, etc.)

[0172] ·X-ray source: Cu tube target

[0173] ·Voltage: 40 kV

[0174] ·Current: 150 mA

[0175] ·Accessories: Sample changer specimen stage

[0176] ·Filter: None

[0177] ·Monochromator: Used

[0178] More specifically, for the surface of the coating 20 of interest, instead of performing pretreatment such as polishing, it is observed using the above XRD. At this time, any position on the surface of the coating 20 is observed, and the above peak intensity ratio I 100 / I 002 is calculated. Such measurement / calculation processing is performed at any 5 positions on the surface of the coating 20, and the average value of the obtained 5 peak intensity ratios I 100 / I 002 is taken as the peak intensity ratio I 100 / I 002 of the coating 20 in this embodiment.

[0179] It should be noted that in the XRD spectrum obtained by measuring under the measurement conditions as described above, the peak corresponding to the (100) plane is the peak observed at 2θ = 19.67 ± 0.4°, and the peak corresponding to the (002) plane is the peak observed at 2θ = 20.79 ± 0.4°. In addition, when two or more peaks are observed within this range, the peak existing at a position closer to the reference position is used as the corresponding peak.

[0180] In addition, considering the baseline of the peak of interest in the XRD spectrum schematically shown in Figure 3 , the intensity of the peak attributed to each plane direction is set to the intensity obtained by subtracting the intensity I p of the baseline from the intensity I b of the peak of interest (i.e., "I p -I b ").

[0181] When the peak intensity ratio I 100 / I 002 is less than 2.50, the orientation state of the MgZn2 phase does not become Figure 2 the columnar orientation state shown, and it is impossible to sufficiently suppress the film blistering caused by the progress of the under-film corrosion in the heat-affected part. The peak intensity ratio I 100 / I 002 is preferably 5.00 or more, more preferably 10.00 or more.

[0182] On the other hand, the upper limit of the peak intensity ratio I 100 / I 002 is not particularly limited, and it can be understood that the higher it is, the more preferable the orientation state is formed. However, the upper limit is substantially about 30.

[0183] It should be noted that, in the case where the MgZn2 phase randomly exists in the parent phase without controlling the orientation of the MgZn2 phase, theoretically, the above-mentioned peak intensity ratio I 100 / I 002 shows a value of 1.75 ± 0.02.

[0184] ◇Regarding the tensile strength of the plated steel sheet

[0185] The tensile strength of the plated steel sheet 1 of the present embodiment depends on the tensile strength of the steel sheet 10 used as the base material. Therefore, according to one method, the tensile strength of the plated steel sheet 1 of the present embodiment is 780 MPa or more, and according to another method, it is 980 MPa or more. The tensile strength of the plated steel sheet 1 can be measured by a well-known method. As an example, a test piece having the size that can be collected from the component is made from the plated steel sheet 1 for which the tensile strength is to be measured, and the tensile strength of the test piece is measured by the method specified in JIS Z 2241 (2011).

[0186] ◇Regarding the carbon (C) concentration on the surface of the plated steel sheet

[0187] In the plated steel sheet 1 of the present embodiment, starting from the surface of the plating layer 20, measurement is performed in the depth direction by glow discharge optical emission spectrometry (GDS: Glow Discharge Optical Emission Spectrometry), and depth curves are measured for the distributions of Zn, Fe, and C.

[0188] It should be noted that this measurement using GDS can be carried out using a commercially available glow discharge optical emission analyzer under the following conditions.

[0189] ◇Commercially available glow discharge optical emission analyzer (for example, manufactured by LECO Japan Co., Ltd. (model GDS850A), etc.)

[0190] Ar gas pressure: 0.27 MPa

[0191] Anode diameter: 4 mm Φ

[0192] RF (high frequency) output power: 30 W

[0193] In the obtained measurement results, first, the position of the interface between the coating 20 and the steel sheet 10 is defined. More specifically, in the depth curve obtained for the distribution of Zn and Fe, the depth at which the curve representing the intensity of Zn intersects the curve representing the intensity of Fe is taken as the interface between the coating 20 and the steel sheet 10. Then, in the depth curve for the C distribution, starting from the above interface, the change in the C concentration is confirmed. That is, the C concentration of concern below can be said to be the C concentration of the part of the steel sheet 10 adjacent to the interface between the coating 20 and the steel sheet 10.

[0194] For the plated steel sheet 1 of the present embodiment, according to a certain method, starting from the above interface, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more. By making the depth at which the C concentration is 0.05% or less by mass 10 μm or more, the LME during welding of the plated steel sheet 1 can be further suppressed. C in the steel is an element that promotes LME and thus becomes the starting point for the generation of LME cracks. Therefore, by reducing the C concentration on the surface layer of the steel, the LME during welding can be further suppressed and the LME resistance can be improved. The depth at which the C concentration is 0.05% or less by mass is preferably 15 μm or more. On the other hand, the upper limit of the depth at which the C concentration is 0.05% or less by mass is not particularly limited.

[0195] Here, by controlling the conditions of the decarburizing annealing applied to the steel sheet 10, the C concentration of the surface layer part of the steel sheet 10 can be made to reach a desired value. In the manufacture of the plated steel sheet, this decarburizing annealing is carried out as required.

[0196] Above, while referring to Figures 1A to 3 , the plated steel sheet 1 of the present embodiment has been described in detail. As described above, the plated steel sheet 1 of the present embodiment can be preferably used, for example, as a blank for a chassis component of an automobile.

[0197] It should be noted that the plated steel sheet 1 of the present embodiment may further have one or two or more layers of various films on the above coating 20. Examples of such films include: chromate film, phosphate film, chromium-free chromate film, organic resin film, etc.

[0198] (Regarding the manufacturing method of the plated steel sheet)

[0199] Next, an example of the manufacturing method of the coated steel sheet 1 described above will be described. The coated steel sheet 1 of the present embodiment is manufactured by the following method: using the above-mentioned steel sheet 10 as the base material, applying strain to the surface of the steel sheet 10 through a heavy grinding process, and then forming a coating layer 20 on the strained surface.

[0200] In the heavy grinding process, the surface of the steel sheet 10 is ground with a heavy grinding brush to apply strain to the surface, thereby forming nucleation sites on the surface of the steel sheet 10 for the growth of the MgZn2 phase in a columnar orientation. Then, a specific heat treatment is performed on the coating layer 20 formed on the surface of the steel sheet 10, so that the MgZn2 phase grows in a columnar orientation. In addition, by applying strain to the surface, Zn-Fe alloying can be promoted during welding of the coated steel sheet 1, and LME can be further suppressed.

[0201] In the formation of the coating layer 20, in addition to the hot-dip plating method, spraying methods, cold spraying methods, sputtering methods, evaporation plating methods, electroplating methods, etc. can also be applied. However, in terms of cost, the hot-dip plating method is the most preferable for forming a coating layer with a thickness commonly used in automobiles and the like.

[0202] Then, the obtained coated steel sheet (steel sheet 10 with the coating layer 20) is subjected to the specific heat treatment process described below, thereby enabling the manufacture of the coated steel sheet 1 of the present embodiment.

[0203] Hereinafter, an example of the manufacturing method of the coated steel sheet 1 of the present embodiment obtained by the hot-dip plating method will be described in detail.

[0204] In the manufacturing process of the coated steel sheet 1, first, the steel sheet 10 used as the base material is rolled by the Sendzimir method to form a desired plate thickness, then wound into a coil shape, and set on a hot-dip plating production line.

[0205] On the hot-dip plating production line, the steel sheet 10 is continuously passed while being unwound from the coil. During the passing of the sheet, strain is applied to the surface of the steel sheet using a heavy grinding brush provided at a specified position. Then, using an annealing device provided on the production line, in an environment where oxidation hardly occurs, such as an oxygen concentration of 20 ppm or less, in an atmosphere of N2-(1 to 10)% H2 gas with a dew point of -60 to 10°C, the steel sheet is heated and reduced at 700 to 900°C for more than 0 seconds and 300 seconds or less, and then air-cooled to about the bath temperature of the subsequent plating bath + 20°C with N2 gas and immersed in the plating bath. It should be noted that strain was applied to the steel sheet before annealing in the above process, but even in the case where at least a part of the applied strain is released by annealing, recrystallization generated in the steel surface layer during annealing is promoted to refine the Fe particle size, so that it functions as a nucleation site when the coating layer solidifies in the subsequent plating process.

[0206] In the heating reduction treatment step, decarburization of the surface of the steel sheet 10 can be carried out. When decarburization is carried out, the dew point in the N2-(1 to 10)% H2 atmosphere gas in the heating reduction treatment step is set to -10 to 10°C. According to the manufacturing method including this decarburization, in the measurement results obtained by GDS in the depth direction of the manufactured plated steel sheet 1, the depth at which the C concentration is 0.05% or less by mass can reach 10 μm or more. When decarburization is not carried out, the dew point in the N2-(1 to 10)% H2 atmosphere gas in the heating reduction treatment step can also be -30 to -70°C.

[0207] Here, in the plating bath, a plating alloy having the above-described chemical composition and in a molten state is prepared. The bath temperature of the plating bath is set to be above the melting point of the plating alloy (for example, about 460 to 660°C). At this time, it is preferable to focus on the melting point of the above-described plating alloy and, based on the "theoretical temperature for MgZn2 phase nucleation" (hereinafter also referred to as the theoretical temperature) described below, determine the bath temperature of the plating bath to be a value above this theoretical temperature (for example, about the theoretical temperature + 40°C).

[0208] When producing the material of the plating alloy, it is preferable to use pure metals (purity 99% or more) as alloy materials for blending. First, a prescribed amount of alloy metals are mixed to form the above-described coating composition, and it is completely melted using a high-frequency induction furnace, an electric arc furnace, etc. in a vacuum or an inert gas replacement state to produce an alloy. Further, in the atmosphere, the alloy mixed with the prescribed composition (the above-described coating composition) is melted, and the obtained melt is used as the plating bath.

[0209] It should be noted that in the production of the above-described plating alloy, there is no particular limitation on the use of pure metals, and existing Zn alloys, Mg alloys, Al alloys can also be melted and used. At this time, there is no problem as long as a prescribed composition alloy with fewer impurities is used.

[0210] After the steel sheet is immersed in the above-described plating bath, it is lifted at a prescribed lifting speed. At this time, for example, N2 purge gas is used to control the plating adhesion amount so that the formed coating layer 20 reaches the desired thickness. Here, for conditions other than the bath temperature, conventional plating operation conditions can be applied, and no special equipment or conditions are required.

[0211] Next, the following first cooling step and second cooling step are carried out on the plating alloy in a molten state located on the steel sheet whose surface has been strained by a heavy abrasive brush, so that the molten plating alloy forms the coating layer 20 and the MgZn2 phase grows in a columnar orientation. Hereinafter, the first cooling step and the second cooling step will be described in detail.

[0212] The first cooling process is a cooling process carried out when the temperature of the plated alloy is within the range of the bath temperature to the "theoretical temperature for MgZn2 phase nucleation" (theoretical temperature). In this first cooling process, in an atmosphere with a dew point of -20°C or lower, a cooling medium is sprayed onto the plated steel sheet within the above-mentioned temperature range at a flow rate of 3000 L / m 2 / min or less, so as to perform rapid cooling at an average cooling rate of 15°C / second or more. It should be noted that when the hot-dip plating method is used in the plating process, this first cooling process is immediately carried out after the steel sheet comes out of the plating bath. Thereby, nucleation occurs at the nucleation sites where the MgZn2 phase forms on the steel sheet surface. The bath temperature to the theoretical temperature in the first cooling process is likely to cause the formation of coarse oxides on the coating surface. In order to prevent oxidation in this high-temperature region, the dew point is set to -20°C or lower and cooling is performed at a relatively large cooling rate. In addition, at this cooling rate, when the flow rate of the cooling medium is excessive, the nucleation sites are on the surface of the coating rather than at the interface between the coating and the steel substrate. In this case, even if the subsequent second cooling process is carried out, it will be difficult to control the orientation of the MgZn2 phase. Therefore, the flow rate of the cooling medium is made 3000 L / m 2 / min or less.

[0213] Here, the above-mentioned "theoretical temperature for MgZn2 phase nucleation" (theoretical temperature) can be determined based on the calculated phase diagram obtained by the CALPHAD method for the Mg-Al-Zn ternary system.

[0214] The flow rate of the cooling medium in the first cooling process is preferably 1500 L / m 2 / min or less, more preferably 1000 L / m 2 / min or less. In addition, the average cooling rate is preferably 25°C / second or more. It should be noted that the lower limit value of the flow rate of the cooling medium is not particularly specified, but for example, about 5 L / m 2 / min can be the substantial lower limit. In addition, for the upper limit value of the average cooling rate, there is also no particular specification, but for example, about 90°C / second can be the substantial upper limit.

[0215] Then, when the temperature of the plated alloy (coating) is within the range of the "theoretical temperature for MgZn2 phase nucleation" (theoretical temperature) to 300°C, the second cooling process is carried out in an atmosphere with a dew point of 0°C or higher. In this second cooling process, at 5000 L / m 2Cool the plated steel sheet within the above-mentioned temperature range with a flow rate of 3000 L / min or less of the cooling medium to perform slow cooling at an average cooling rate of 5°C / second or less. As a result, the nucleated MgZn2 phase grows in a columnar orientation. Below the theoretical temperature of the second cooling step, from the viewpoint of forming a dense oxide in the low-temperature region, the dew point is set to 0°C or higher, and slow cooling is performed at a relatively small cooling rate.

[0216] The flow rate of the cooling medium in the second cooling step is preferably 3000 L / m 2 / min or less, more preferably 2000 L / m 2 / min or less. In addition, the average cooling rate is preferably 3°C / second or less, more preferably 1°C / second or less. It should be noted that the lower limit value of the flow rate of the cooling medium is not particularly specified, but for example, around 500 L / m 2 / min can be the substantial lower limit.

[0217] It should be noted that regarding the switching of the average cooling rate and the dew point from the first cooling step to the second cooling step, in order to control the dew point, by pre-setting two or more pipeline systems for spraying the atmosphere gas, the switching can be smoothly performed, so it is preferred. In addition, when it is difficult to switch both the average cooling rate and the dew point at the boundary of the theoretical temperature, the average cooling rate can also be switched at the boundary of the theoretical temperature, and the atmosphere gas for controlling the dew point can be switched within the range of (the theoretical temperature ± 10)°C.

[0218] As described above, by forming a coating layer in a state where strain is applied to the surface of the steel sheet using a heavy grinding brush, and then supplying the coating layer to two-stage cooling steps, that is, while controlling the flow rate and dew point of the cooling medium, performing rapid cooling in the temperature range from the bath temperature to the theoretical temperature, and performing slow cooling in the temperature range from the theoretical temperature to 300°C, the MgZn2 phase in the coating layer 20 can grow in a columnar orientation.

[0219] It should be noted that for the cooling state from 300°C to room temperature, there is no particular specification, and it can be cooled to room temperature by various methods.

[0220] Here, the interval from the end of the first cooling step to the start of the second cooling step is preferably set within 3 seconds, and it is preferably to start the second cooling step immediately after the end of the first cooling step. When the interval from the end of the first cooling step to the start of the second cooling step is greater than 3 seconds, an unintended cooling process will occur, and the desired orientation control cannot be achieved.

[0221] It should be noted that even if strain is appropriately applied to the surface of the steel sheet, the desired orientation control cannot be achieved without implementing either the first cooling process or the second cooling process as described above. On the basis of appropriately applying strain to the surface of the steel sheet, further implementing both the first cooling process and the second cooling process as described above enables the plating layer 20 of the present embodiment in which the orientation direction is controlled as exemplified in Figure 2 to be obtained.

[0222] In addition, after the above-described second cooling process, if an alloying heat treatment process (for example, a heat treatment process accompanied by heating to a plate temperature of about 480 to 550°C), which is usually implemented in the manufacture of alloyed hot-dip galvanized steel sheets, is implemented, the columnar orientation of the MgZn2 phase controlled by the first cooling process and the second cooling process will be destroyed. As a result, the effect of suppressing film blistering, which is the focus of the present embodiment, cannot be obtained. From this perspective, it is important not to implement the heat treatment process after the second cooling process.

[0223] Here, in the cooling treatment as described above, for example, a generally known method such as N2 gas cooling can be applied. In addition to N2 gas, cooling gases such as He gas and hydrogen gas, which have a high heat dissipation effect, can also be used.

[0224] It should be noted that as a method for actually measuring the plating layer temperature, for example, a contact thermocouple (K type) can be used. By installing the contact thermocouple on the steel sheet as the base material, the average temperature of the entire plating layer can be continuously monitored. In addition, if various speeds and thicknesses are mechanically controlled and various operating conditions such as the preheating temperature of the steel sheet and the plating bath temperature are unified, the temperature of the entire plating layer at that moment under these manufacturing conditions can be monitored approximately accurately. Thereby, the cooling treatment in the first cooling process and the second cooling process can be precisely controlled. It should be noted that although not as accurate as the contact type, the surface temperature of the plating layer can also be measured using a non-contact radiation thermometer.

[0225] In addition, the relationship between the surface temperature of the plating layer and the average temperature of the entire plating layer can also be obtained in advance by performing a simulation of heat conduction analysis. Specifically, based on various manufacturing conditions such as the preheating temperature of the steel sheet, the plating bath temperature, the speed at which the steel sheet is lifted from the plating bath, the thickness of the steel sheet, the thickness of the plating layer, the heat exchange amount between the plating layer and the manufacturing equipment, and the heat dissipation amount of the plating layer, the surface temperature and the average temperature of the entire plating layer of the plating layer are obtained. Then, using the obtained results, the relationship between the surface temperature of the plating layer and the average temperature of the entire plating layer can be obtained. Thereby, by actually measuring the surface temperature of the plating layer when manufacturing the plated steel sheet, the average temperature of the entire plating layer at that moment under these manufacturing conditions can be inferred. As a result, the cooling treatment in the first cooling process and the second cooling process can be precisely controlled.

[0226] Above, an example of the method for manufacturing the plated steel sheet according to this embodiment has been specifically described.

[0227] It should be noted that in the method for manufacturing the plated steel sheet according to this embodiment, after the above-mentioned second cooling step, a treatment for forming one or two or more kinds of various films may be further performed. Examples of such treatment include: chromate treatment, phosphate treatment, chromium-free treatment, organic resin film formation treatment, etc.

[0228] Chromate treatment includes: electrolytic chromate treatment for forming a chromate film by electrolysis; reactive chromate treatment for forming a film by reacting with the blank and then rinsing the excess treatment liquid; coating type chromate treatment for coating the treatment liquid and drying without water washing to form a film, etc. Any chromate treatment can be adopted.

[0229] As an example of electrolytic chromate treatment, for example, electrolytic chromate treatment using chromic acid, silica sol, resin (phosphate resin, acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene butadiene latex, diisopropanolamine modified epoxy resin, etc.) and hard silica can be exemplified.

[0230] As an example of phosphate treatment, for example, zinc phosphate treatment, zinc calcium phosphate treatment, manganese phosphate treatment, etc. can be exemplified.

[0231] Chromium-free treatment does not impose a burden on the environment, and thus is particularly preferred. Such chromium-free treatment includes: electrolytic chromium-free treatment for forming a chromium-free film by electrolysis; reactive chromium-free treatment for forming a film by reacting with the blank and then rinsing the excess treatment liquid; coating type chromium-free treatment for coating the treatment liquid and drying without water washing to form a film, etc. Any chromium-free treatment can be adopted.

[0232] In addition, the organic resin used in the organic resin film formation treatment is not limited to a specific resin. For example, various resins such as polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, and modified products of these resins can be used. Here, the modified product refers to a resin formed by reacting other compounds (such as monomers, crosslinking agents, etc.) containing functional groups capable of reacting with the reactive functional groups contained in the structure of these resins with the reactive functional groups in the structure of these resins.

[0233] As the organic resin, one kind as described above can be used alone, or two or more kinds of unmodified organic resins can be used in combination. Additionally, one kind or two or more kinds of organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin can be used. Further, an organic resin solubilized or dispersed in water to form an aqueous system can be used. Moreover, various coloring pigments and rust-preventive pigments may be contained in the organic resin film.

[0234] Examples

[0235] Hereinafter, the plated steel sheets of the present invention will be specifically described while showing examples and comparative examples. It should be noted that the examples shown below are merely examples of the plated steel sheets of the present invention, and the plated steel sheets of the present invention are not limited to the examples shown below.

[0236] In the examples and comparative examples shown below, as the base steel sheets, three kinds of steel sheets used as chassis steel sheets were used. The three kinds of steel sheets are: any one of a steel sheet having a composition of mild steel with a tensile strength of 440 MPa grade, a steel sheet having a composition of high-strength material with a tensile strength of 780 MPa grade, and a steel sheet having a composition of high-strength material with a tensile strength of 980 MPa grade (all manufactured by Nippon Steel & Sumitomo Metal Corporation). The plate thickness of the hot-rolled steel sheets was all set to 3.2 mm. Using these hot-rolled steel sheets, a plurality of test pieces were fabricated for each hot-rolled steel sheet.

[0237] For the prepared test pieces, the following two kinds of heavy-duty grinding brushes were used to apply strain to the surfaces of the test pieces. It should be noted that when grinding, a 1.0 - 5.0% aqueous NaOH solution was previously coated on the steel sheet surface. The brush pressing amount was appropriately adjusted within the range of 0.5 - 10.0 mm, and the brush rotation speed was appropriately adjusted within the range of 100 - 1000 rpm, thereby controlling the amount of strain applied to the surface. It should be noted that among the following two kinds of heavy-duty grinding brushes, the A-type brush is a brush with stronger grinding force. It should be noted that for comparison, test pieces without such heavy-duty grinding were also prepared.

[0238] A-type brush: D-100 manufactured by Hodani Co., Ltd.

[0239] B-type brush: M-33 manufactured by Hodani Co., Ltd.

[0240] Prepare plating baths for achieving the coatings having the compositions shown in Table 1 below, respectively, and set them in the batch-type hot-dip plating test apparatus manufactured by our company, and perform plating on the above test pieces. Here, use a thermocouple spot-welded to the center of the test piece to measure the temperature of the test piece. In addition, for the test piece immersed in the plating bath, before immersing in the plating bath, in a furnace with an oxygen concentration of 20 ppm or less, heat and reduce the surface of the plating base plate in an N2-4% H2 gas atmosphere at 840 °C. After the heat reduction treatment, air-cool the test piece with N2 gas. After the temperature of the test piece reaches the bath temperature +20 °C, immerse the test piece in the plating bath of the hot-dip plating test apparatus for about 3 seconds.

[0241] During the heat reduction treatment, set the dew point in the N2-4% H2 atmosphere gas to 0 °C for decarburization. In addition, for comparison, test pieces with the dew point in the N2-4% H2 atmosphere gas set to -40 °C and without decarburization were also prepared. In the measurement results obtained by GDS in the depth direction of the manufactured plated steel sheet 1 of the test piece that has undergone decarburization, the depth at which the C concentration is 0.05% or less by mass reaches 10 μm or more. In the test piece without decarburization, the depth at which the C concentration is 0.05% or less by mass is 0 μm, that is, the C concentration on the surface of the test piece is greater than 0.05%. The depth (C0.05% or less depth) at which the C concentration in each test piece is 0.05% or less by mass is shown in Table 1 below.

[0242] After immersing in the plating solution, lift the test piece at a lifting speed of 20 to 200 mm / second. When lifting, use N2 purge gas for control to achieve the desired plating adhesion amount. In the following examples and comparative examples, control the plating adhesion amount so that the adhesion amount of the plating on each side of the test piece after drying reaches 40 to 120 g / m 2 . After lifting the test piece from the plating bath, cool the test piece from the plating bath temperature to room temperature under the conditions shown in Table 1 below. In the examples and comparative examples shown below, immediately start the second cooling process after the end of the first cooling process (that is, the interval from the end of the first cooling process to the start of the second cooling process is 0.2 seconds or less). In the examples and comparative examples other than Comparative Examples 31 and 32, the switching temperature for switching between the first cooling process and the second cooling process is set to their respective theoretical temperatures. In addition, for Comparative Examples 31 and 32, a temperature different from the theoretical temperature is used as the switching temperature.

[0243] Here, cut out a 30 mm × 30 mm sized plated steel sheet from the test piece that has been plated in the above manner, immerse the plated steel sheet in a 10% HCl aqueous solution added with an inhibitor, perform pickling and peeling of the coating, and then measure the composition of the coating by ICP analysis of the elements dissolved in the aqueous solution.

[0244] In addition, for the obtained coating, the peak intensity ratio I was calculated by XRD measurement according to the method described previously. 100 / I 002 。

[0245] <Evaluation of Film Blistering during Welding>

[0246] A test piece with a size of 150 mm × 50 mm was cut from the obtained test piece as the first steel plate, and a test piece with a size of 150 mm × 30 mm was cut and used as the second steel plate. The long sides of these steel plates were overlapped and welded by arc welding or laser welding (lap fillet welding).

[0247] Here, the welding conditions for arc welding are as follows.

[0248] Welding current: 250 A, welding voltage: 26.4 V, welding speed: 100 cm / min

[0249] Welding gas: 20% CO2 + Ar, gas flow rate: 20 L / min

[0250] Welding wire: YGW16 manufactured by Nippon Welding Industries Co., Ltd., φ1.2 mm

[0251] (C: 0.1 mass%, Si: 0.80 mass%, Mn: 1.5 mass%, P: 0.015 mass%, S: 0.008 mass%, Cu: 0.36 mass%)

[0252] Torch inclination angle: 45°

[0253] Overlap amount: 10 mm

[0254] Steel plate size: upper plate side (first steel plate) 150 × 50 mm, lower plate side (second steel plate) 150 × 30 mm

[0255] Plate gap: 0 mm

[0256] In addition, the welding conditions for laser welding are as follows.

[0257] Output power: 7 kW, welding speed: 400 cm / min, forward / backward angle: 0°

[0258] Steel plate size: upper plate side (first steel plate) 150 × 50 mm, lower plate side (second steel plate) 150 × 30 mm

[0259] Overlap amount: 50 mm

[0260] Plate gap: 0 mm

[0261] For the welded joints obtained as above, automotive phosphoric acid chemical conversion treatment (phosphoric acid Zn treatment, SD5350 system: specifications prepared by Nipponpaint Industrial Coatings Co., LTD) and electrodeposition coating (PN110 PowerNix Gray: specifications prepared by Nipponpaint Industrial Coatings Co., LTD) are carried out. At this time, the electrodeposition film thickness is set to 20 μm. The samples after electrodeposition coating are subjected to a composite cyclic corrosion test (240 cycles) based on JASO (M609-91), and the film blistering width at the weld toe of the weld bead is evaluated. The evaluation criteria are as follows.

[0262] "Evaluation Criteria"

[0263] Score "AAA": The film blistering width is 1.8 mm or less

[0264] "AA": The film blistering width is greater than 1.8 mm and 3.0 mm or less

[0265] "A": The film blistering width is greater than 3.0 mm and 4.0 mm or less

[0266] "B": The film blistering width is greater than 5.0 mm

[0267] It should be noted that the above "weld toe" refers to the position specified in JIS Z3001 (2018), which corresponds to the point where the surface of the base material intersects the surface of the weld bead. In this example, the point where the surface of the coating layer of the coated steel plate intersects the surface of the weld bead portion corresponds to this "weld toe".

[0268] In addition, if the above film blistering width is 4.0 mm or less, it can be evaluated that the test piece of interest has good post - coating corrosion resistance.

[0269] <Evaluation of Liquid Metal Embrittlement Resistance>

[0270] For the liquid metal embrittlement resistance of the obtained test pieces, it is evaluated by a hot tensile test. More specifically, for both the obtained test pieces and the steel plate without coating, the temperature is raised to 900 °C at a heating rate of 100 °C / second, held at 900 °C for 1 second, then cooled to 750 °C, and a tensile test is carried out at 750 °C with a stroke speed of 10 mm / second. Thus, the stress - stroke curves of both the steel plate without coating and the test pieces are obtained. Then, based on the obtained stress - stroke curves, the stress × stroke values (the area of the stress - stroke curve) are calculated respectively, and based on the following evaluation criteria, the evaluation value (%) = {(stress × stroke value of the test piece) / (stress × stroke value of the steel plate without coating) × 100} is evaluated.

[0271] "Evaluation Criteria"

[0272] Rating “AA”: The evaluation value is above 95%.

[0273] “A”: The evaluation value is above 85% and less than 95%.

[0274] “B”: The evaluation value is less than 85%.

[0275] The obtained results are summarized in Table 1 below.

[0276] [Table 1]

[0277]

[0278] As can be seen from Table 1 above, in the examples belonging to the embodiments of the present invention, LME and film blistering can be suppressed. In contrast, in the examples belonging to the comparative examples of the present invention, sufficient performance cannot be demonstrated in at least any one aspect of LME or film blistering.

[0279] For example, in No. 28 where the Al content in the plating layer is outside the scope of the present invention, due to the excessive Al content, the alloying reaction between Zn in the plating layer and the steel substrate during welding is hindered, and the liquid-phase Zn-Mg contacts the steel substrate, making it impossible to suppress LME. In addition, due to the excessive Al content, primary α crystals precipitate in the plating layer in the non-heat-affected zone, and the columnar orientation of the MgZn2 phase is hindered, making it impossible to suppress film blistering.

[0280] In No. 29 where the Mg content in the plating layer is outside the scope of the present invention, due to the insufficient Mg content, the corrosion resistance of the plating layer is insufficient, and the columnar orientation of the MgZn2 phase is insufficient, making it impossible to suppress film blistering.

[0281] In No. 30 where the Mg content in the plating layer is outside the scope of the present invention, due to the excessive Mg content, the alloying reaction between Zn in the plating layer and the steel substrate during welding is hindered, and the liquid-phase Zn-Mg contacts the steel substrate, making it impossible to suppress LME. In addition, due to the excessive Mg content, the nucleation sites of the MgZn2 phase in the plating layer increase excessively, and the columnar orientation of the MgZn2 phase is insufficient, making it impossible to suppress film blistering.

[0282] In addition, regarding the manufacturing conditions of the plated steel sheet, in No. 31 where the switching temperature is different from the theoretical temperature and the cooling rate in the first cooling process is outside the scope of the manufacturing conditions disclosed in the present application, due to the insufficient columnar orientation of the MgZn2 phase, it is impossible to suppress the burning of the plating layer during welding and impossible to suppress film blistering.

[0283] In No. 32 where the switching temperature is different from the theoretical temperature and the cooling rate in the second cooling process is outside the range of the manufacturing conditions of the present disclosure, due to insufficient columnar orientation of the MgZn2 phase, it is impossible to suppress the burning of the coating during welding and to suppress the formation of coating blisters.

[0284] In No. 33 where the flow rate of the refrigerant in the first cooling process is outside the range of the manufacturing conditions of the present disclosure, the columnar orientation of the MgZn2 phase is insufficient, resulting in the inability to suppress the burning of the coating during welding and to suppress the formation of coating blisters.

[0285] In No. 34 where the cooling rate in the second cooling process is outside the range of the manufacturing conditions of the present disclosure, the columnar orientation of the MgZn2 phase is insufficient, resulting in the inability to suppress the burning of the coating during welding and to suppress the formation of coating blisters.

[0286] In No. 35 where the flow rate of the refrigerant in the second cooling process is outside the range of the manufacturing conditions of the present disclosure, the columnar orientation of the MgZn2 phase is insufficient, resulting in the inability to suppress the burning of the coating during welding and to suppress the formation of coating blisters.

[0287] In No. 36 where the heavy grinding of the present disclosure is not carried out, the alloying behavior in the coating cannot be controlled and the η phase is formed. Therefore, the columnar orientation of the MgZn2 phase is insufficient, resulting in the inability to suppress the burning of the coating during welding and to suppress the formation of coating blisters.

[0288] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, the present invention is not limited to this example. Those skilled in the art can clearly conceive of various modification examples or correction examples within the scope of the technical idea described in the claims. Of course, these are also understood to belong to the technical scope of the present invention.

[0289] The embodiments disclosed this time are exemplary in all aspects and not restrictive. Without departing from the appended claims, the constitution and gist of the technical scope of the present invention described hereinafter, the above embodiments can be omitted, replaced, and changed in various forms. For example, within the range not impairing the effects, the constituent elements of the above embodiments can be arbitrarily combined. In addition, based on this arbitrary combination, the functions and effects of the constituent elements involved in the combination can of course be obtained, and other functions and other effects that can be clearly understood by those skilled in the art based on the description of this specification can also be obtained.

[0290] In addition, the effects described in this specification are merely illustrative or exemplary and not restrictive. That is, the technology of the present invention can achieve the above effects, or can achieve other effects that can be clearly understood by those skilled in the art based on the description of this specification in place of the above effects.

[0291] It should be noted that the following configurations also fall within the technical scope of the present invention.

[0292] (1) A plated steel sheet having a plating layer on at least a part of the surface of the steel sheet,

[0293] The plating layer has the following chemical composition:

[0294] Containing, by mass%,

[0295] Al: 0.50 or more and 4.50 or less,

[0296] Mg: 0.50% or more and less than 3.00%,

[0297] Fe: 0.01 - 15.00%,

[0298] Optionally containing one or more selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, element group F, and element group G, with the balance being Zn and impurities of 5.0000 mass% or more,

[0299] In the measurement result obtained by measuring the aforementioned plating layer by X-ray diffraction method, the intensity I of the peak corresponding to the (100) plane of the MgZn2 phase 100 and the intensity I of the peak corresponding to the (002) plane 002 The peak intensity ratio I of the 100 / I 002 is 2.50 or more.

[0300] [Element group A]: One or two selected from the group consisting of Si: greater than 0% and 2.00% or less and Ca: greater than 0% and 2.00% or less;

[0301] [Element group B]: One or more selected from the group consisting of Sb: greater than 0% and 0.5000% or less, Pb: greater than 0% and 0.5000% or less, and Sr: greater than 0% and 0.5000% or less;

[0302] [Element group C]: One or more selected from the group consisting of Co: greater than 0% and 1.0000% or less, V: greater than 0% and 1.0000% or less, Cu: greater than 0% and 1.0000% or less, Ti: greater than 0% and 1.0000% or less, Cr: greater than 0% and 1.0000% or less, Nb: greater than 0% and 1.0000% or less, Ni: greater than 0% and 1.0000% or less, Mn: greater than 0% and 1.0000% or less, and Mo: greater than 0% and 1.0000% or less;

[0303] [Element group D]: Select one or more from the group consisting of In: greater than 0% and 1.0000% or less, Bi: greater than 0% and 1.0000% or less, and Sn: greater than 0% and 1.0000% or less;

[0304] [Element group E]: Select one or more from the group consisting of Zr: greater than 0% and 1.0000% or less, Ag: greater than 0% and 1.0000% or less, and Li: greater than 0% and 1.0000% or less;

[0305] [Element group F]: Select one or more from the group consisting of La: greater than 0% and 0.5000% or less, Ce: greater than 0% and 0.5000% or less, and Y: greater than 0% and 0.5000% or less;

[0306] [Element group G]: B: greater than 0% and 0.5000% or less

[0307] (2) The plated steel sheet according to (1) above has a chemical composition containing the aforementioned element group A.

[0308] (3) The plated steel sheet according to (1) or (2) above has a chemical composition containing the aforementioned element group B.

[0309] (4) The plated steel sheet according to any one of (1) to (3) above has a chemical composition containing the aforementioned element group C.

[0310] (5) The plated steel sheet according to any one of (1) to (4) above has a chemical composition containing the aforementioned element group D.

[0311] (6) The plated steel sheet according to any one of (1) to (5) above has a chemical composition containing the aforementioned element group E.

[0312] (7) The plated steel sheet according to any one of (1) to (6) above has a chemical composition containing the aforementioned element group F.

[0313] (8) The plated steel sheet according to any one of (1) to (7) above has a chemical composition containing the aforementioned element group G.

[0314] (9) The plated steel sheet according to any one of (1) to (8) above, wherein the tensile strength of the aforementioned steel sheet is 780 MPa or more.

[0315] (10) The plated steel sheet according to any one of (1) to (9) above, wherein the aforementioned peak intensity ratio I 100 / I 002 is 5.00 or more.

[0316] (11) The plated steel sheet according to (10) above, wherein the peak intensity ratio I 100 / I 002 is 10.00 or more.

[0317] (12) The plated steel sheet according to any one of (1) to (11) above, wherein, in the measurement result obtained by glow discharge emission spectroscopic analysis in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

[0318] Description of reference numerals

[0319] 1 Plated steel sheet

[0320] 10 Steel sheet

[0321] 20 Coating

Claims

1. A coated steel sheet having a coating on at least a part of the surface of the steel sheet, wherein the coating has the following chemical composition: by mass percentage containing Al: 0.50 or more and 4.50 or less, Mg: 0.50% or more and less than 3.00%, Fe: 0.01 - 15.00%, optionally containing one or more selected from the group consisting of the following element group A, element group B, element group C, element group D, element group E, element group F and element group G, with the balance being Zn and impurities of 5.0000 mass% or more, In the measurement result obtained by measuring the coating by X-ray diffraction method, the intensity I of the peak corresponding to the (100) plane of the MgZn2 phase 100 and the intensity I of the peak corresponding to the (002) plane 002 The peak intensity ratio I 100 / I 002 is 2.50 or more, [Element group A]: one or two selected from the group consisting of Si: more than 0% and 2.00% or less and Ca: more than 0% and 2.00% or less; [Element group B]: one or more selected from the group consisting of Sb: more than 0% and 0.5000% or less, Pb: more than 0% and 0.5000% or less, and Sr: more than 0% and 0.5000% or less; [Element group C]: one or more selected from the group consisting of Co: more than 0% and 1.0000% or less, V: more than 0% and 1.0000% or less, Cu: more than 0% and 1.0000% or less, Ti: more than 0% and 1.0000% or less, Cr: more than 0% and 1.0000% or less, Nb: more than 0% and 1.0000% or less, Ni: more than 0% and 1.0000% or less, Mn: more than 0% and 1.0000% or less, and Mo: more than 0% and 1.0000% or less; [Element group D]: one or more selected from the group consisting of In: more than 0% and 1.0000% or less, Bi: more than 0% and 1.0000% or less, and Sn: more than 0% and 1.0000% or less; [Element group E]: one or more selected from the group consisting of Zr: more than 0% and 1.0000% or less, Ag: more than 0% and 1.0000% or less, and Li: more than 0% and 1.0000% or less; [Element group F]: one or more selected from the group consisting of La: more than 0% and 0.5000% or less, Ce: more than 0% and 0.5000% or less, and Y: more than 0% and 0.5000% or less; [Element group G]: B: more than 0% and 0.5000% or less.

2. The coated steel sheet according to claim 1, having a chemical composition containing the element group A.

3. The coated steel sheet according to claim 1, having a chemical composition containing the element group B.

4. The coated steel sheet according to claim 1, having a chemical composition containing the element group C.

5. The coated steel sheet according to claim 1, having a chemical composition containing the element group D.

6. The coated steel sheet according to claim 1, having a chemical composition containing the element group E.

7. The coated steel sheet according to claim 1, having a chemical composition containing the element group F.

8. The plated steel sheet according to claim 1, which has a chemical composition containing the element group G.

9. The plated steel sheet according to any one of claims 1 to 8, wherein, The tensile strength of the steel sheet is 780 MPa or more.

10. The plated steel sheet according to any one of claims 1 to 8, wherein, The peak intensity ratio I 100 / I 002 is 5.00 or more.

11. The plated steel sheet according to claim 9, wherein, The peak intensity ratio I 100 / I 002 is 5.00 or more.

12. The plated steel sheet according to claim 10, wherein, The peak intensity ratio I 100 / I 002 is 10.00 or more.

13. The plated steel sheet according to claim 11, wherein, The peak intensity ratio I 100 / I 002 is 10.00 or more.

14. The plated steel sheet according to any one of claims 1 to 8, wherein, In the measurement result obtained by glow discharge optical emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

15. The coated steel sheet according to claim 9, wherein, In the measurement result obtained by glow discharge optical emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

16. The plated steel sheet according to claim 10, wherein, In the measurement result obtained by glow discharge optical emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

17. The plated steel sheet according to claim 11, wherein, In the measurement result obtained by glow discharge optical emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

18. The plated steel sheet according to claim 12, wherein, In the measurement result obtained by glow discharge optical emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

19. The plated steel sheet according to claim 13, wherein, In the measurement result obtained by glow discharge optical emission spectrometry in the depth direction of the plated steel sheet, the depth at which the C concentration is 0.05% or less by mass is 10 μm or more.

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