Hot-dip plated steel material

Abstract

A hot-dip plated steel material having a plated layer on a surface of a steel material, the plated layer being Al: more than 22.5% and 50.0% or less, Mg: more than 3.0% and 15.0% or less, Ca: 0.03 to 0.6%, Si: 0.03 to 1.0%, Fe: 2 to 25%, and the remainder including Zn and impurities, wherein, in an X-ray diffraction pattern of the surface of the plated layer measured using Cu-Kα rays under conditions of an X-ray output of 50 kV and 300 mA, I1 calculated from X-ray diffraction peaks of Al 0.5 Fe 1.5 is 1.1 or more, and I2 calculated from X-ray diffraction peaks of Zn, Al, and MgZn2 is 0.25 or less.

Description

TECHNICAL FIELD

[0001] The present application relates to hot-dip plated steel materials.

[0002] This application claims priority based on Japanese Patent Application No. 2022-024940 filed on February 21, 2022, and the contents thereof are hereby incorporated by reference. BACKGROUND

[0003] For plated steel materials, depending on the manufacturing method, they are classified into post-plated products and pre-plated products. The post-plated products are manufactured by a method in which a steel sheet is processed to make a steel material into a prescribed shape, and then the steel material is immersed in a hot-dip zinc plating bath (dip plating method). On the other hand, the pre-plated products are manufactured by a method in which a steel sheet is continuously immersed in a hot-dip plating bath to make a hot-dip plated steel sheet, and then the hot-dip plated steel sheet is processed into a prescribed shape. In JIS H 8641:2007, for the post-plated products, the kind, the symbol, the plating quality, the appearance, and the attached amount are prescribed. For example, the attached amount of plating of the symbol HDZ35 is set to 350 g / m 2 For the symbol HDZ55, the attached amount is set to 550 g / m 2 or more.

[0004] Such plated steel materials are used in various fields, but particularly, as a condition in which the corrosion environment is severe, there is a use in water. As a use of such plated steel materials, for example, a steel waterway / catch basin or the like is assumed. According to the homepage of the general incorporated association, Japan Hot-Dip Galvanizing Association, "About Galvanizing", the corrosion speed of zinc in water reaches 30 to 100 g / m 2 This means that even the post-plated products corresponding to the symbols HDZ35 to 55, which are relatively thick in plating thickness, end the life of the plating layer in 3 to 5 years at the fastest.

[0005] Therefore, in the use in the environment in water, the use which can cause water wetting (wetted by water), the thickness of the plating needs to be rather thick, and for such use, a post-plating product manufactured by a dip coating method is mostly used. However, in the water immersion environment, Zn in the Zn plating layer is ionized and slowly eluted into water. If the Zn phase (η phase) on the surface of the Zn plating layer disappears, the interface alloy layer (Zn-Fe alloy layer) at the interface of the plating and the steel material corrodes. If the interface alloy layer further continues to corrode, the corrosion of the base metal progresses. Therefore, hitherto, the life of the plating layer has been studied by improving the corrosion resistance of the Zn phase in the surface layer of the plating and the interface alloy layer. For example, Patent Literature 1 is an example in which a Zn-Al-Mg plating layer is applied instead of the Zn phase of the plating surface layer, and Patent Literature 2 is an example in which an alloy element is further added to the Zn phase so that the corrosion resistance is improved. However, if the corrosion resistance in the environment in water or wetted by water can be further improved, it can be expected that the post-plating product will be more widely adopted as a plated steel material used in a pool / river / coast, etc.

[0006] Prior Art Documents

[0007] Patent Literature

[0008] Patent Literature 1: Japanese Patent Application Laid-Open No. 2010-070810

[0009] Patent Literature 2: Japanese Patent Application Laid-Open No. 2021-004403 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] The present application has been made in view of the above circumstances, and a problem to be solved is to provide a hot-dip plated steel material which can exhibit high corrosion resistance in water or in a constant water wetting environment which can cause water wetting.

[0012] MEANS FOR SOLVING THE PROBLEMS

[0013] In order to solve the above problems, the present application adopts the following configuration.

[0014] [1] A hot-dip plated steel material which is a plated steel material having a plating layer on the surface of a steel material,

[0015] The average chemical composition of the above plating layer is, in mass%:

[0016] Al: more than 22.5% and 50.0% or less,

[0017] Mg: more than 3.0% and 15.0% or less,

[0018] Sn: 0% to 0.7%,

[0019] Bi: 0% to 0.3%,

[0020] In: 0% to 0.3%,

[0021] Ca: 0.03% to 0.6%,

[0022] Y: 0% to 0.30%,

[0023] La: 0% to 0.30%,

[0024] Ce: 0% to 0.30%,

[0025] Si: 0.03% to 1.0%,

[0026] Cr: 0% to 0.25%,

[0027] Ti: 0% to 0.25%,

[0028] Ni: 0% to 0.25%,

[0029] Co: 0% to 0.25%,

[0030] V: 0% to 0.25%,

[0031] Nb: 0% to 0.25%,

[0032] Cu: 0% to 0.25%,

[0033] Mn: 0% to 0.25%,

[0034] Fe: 2.0% to 25%,

[0035] Sr: 0% to 0.50%,

[0036] Sb: 0% to 0.50%,

[0037] Pb: 0% to 0.50%,

[0038] B: 0% to 0.50%,

[0039] Li: 0% to 0.50%,

[0040] Zr: 0% to 0.50%,

[0041] Mo: 0% to 0.50%,

[0042] W: 0% to 0.50%,

[0043] Ag: 0% to 0.50%,

[0044] P: 0% to 0.50%,

[0045] the remainder comprising Zn and impurities,

[0046] the total amount of Sn, Bi and In, ΣA, is 0% to 0.7%,

[0047] the total amount of Ca, Y, La and Ce, ΣB, is 0.03% to 0.60%, the total amount of Cr, Ti, Ni, Co, V, Nb, Cu and Mn, ΣC, is 0% to 0.25%,

[0048] the total amount of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P, ΣD, is 0% to 0.50%,

[0049] the following formulae (1) to (3) are satisfied,

[0050] in the X-ray diffraction pattern of the above plating layer surface measured using Cu-Ka rays under conditions of an X-ray output of 50 kV and 300 mA, I1 is obtained by defining the X-ray diffraction peak of Al 0.5 Fe 1.5 satisfies formula (A-2) in the case where I1 is obtained by defining the X-ray diffraction peak of Al

[0051] satisfies formula (B-2) in the case where I2 is obtained by defining the X-ray diffraction peak of Zn, Al and MgZn2 by formula (B-1).

[0052] Sn ≤ Si (1)

[0053] 15 ≤ Mg / Si (2)

[0054] 1.0 ≤ Si / Ca ≤ 5.0 (3)

[0055] [Mathematical Formula 1]

[0056]

[0057] 1.10 ≤ I1 (A-2)

[0058]

[0059] I2 ≤ 0.25 (B-2)

[0060] where, in formulae (1) to (3), Sn, Si, Mg and Ca are the contents (mass %) of each element in the above plating layer, Imax (k to m°) in formula (A-1) and formula (B-1) is the maximum value of the X-ray diffraction intensity between diffraction angles k to m°, Imax (n°) in formula (A-1) is the X-ray diffraction intensity at diffraction angle n°, and k, m and n are the diffraction angles shown in formula (A-1) and formula (B-1).

[0061] [2] The hot-dip plated steel product according to [1], wherein, in an X-ray diffraction pattern of the plated layer surface measured using Cu-Ka rays with an X-ray output of 50 kV and 300 mA, I3 calculated from an X-ray diffraction peak of MgZn2 defined by Formula (C-1) satisfies Formula (C-2).

[0062]

[0063] I3≤ 0.03 (C-2)

[0064] wherein Imax(k~m°) in Formula (C-1) is a maximum value of X-ray diffraction intensity between diffraction angles k~m°, and k, m are diffraction angles shown in Formula (C-1), respectively.

[0065] [3] The hot-dip plated steel product according to [1] or [2], wherein, in an X-ray diffraction pattern of the plated layer surface measured using Cu-Ka rays with an X-ray output of 50 kV and 300 mA, I4 calculated from an X-ray diffraction peak of Ca(Al2Si2)O8 defined by Formula (D-1) satisfies Formula (D-2).

[0066]

[0067] 1.1≤ I4 (D-2)

[0068] wherein Imax(k~m°) in Formula (D-1) is a maximum value of X-ray diffraction intensity between diffraction angles k~m°, Imax(n°) is X-ray diffraction intensity at diffraction angle n°, and k, m, n are diffraction angles shown in Formula (D-1), respectively.

[0069] Effects of the Invention

[0070] According to the present application, it is possible to provide a hot-dip plated steel product capable of exhibiting high corrosion resistance in water (in simulated acid rain or in salt water like sea water) or in a constant water-wet environment that can cause water wetting. Note that in the following description, "in simulated acid rain" is sometimes referred to as water having a relatively low salt concentration, and "sea water (salt water)" is sometimes referred to as water having a relatively high salt concentration. BRIEF DESCRIPTION OF DRAWINGS

[0071] Figure 1 is a schematic diagram for explaining Formula (A-1).

[0072] Figure 2 is a schematic diagram for explaining Formula (D-1). DETAILED DESCRIPTION

[0073] The inventors of the present invention have conducted intensive studies on hot-dip plated steel manufactured by a hot-dip galvanizing method of the dip-coating type, having a plated layer containing Al, Mg, and Zn, in order to improve corrosion resistance in a constant water-wet environment.

[0074] The inventors of the present invention have conducted intensive studies in order to optimize corrosion resistance in water / water-wet applications, and as a result, have found a post-plating plated structure and a contained substance that are least likely to corrode when wetted with water. In the present invention, corrosion resistance in water-wet applications of the plated layer can be sufficiently improved, and the reduction of the life cycle cost of the hot-dip plated steel can contribute to the development of industry.

[0075] If Zn is contained in the plated layer, it is possible that a Zn phase is formed in the structure of the plated layer. The Zn phase is easily corroded in water, and corrosion proceeds until the Zn phase disappears, so it cannot be used as the main phase of the plated layer. In the plated layer containing Al, Mg, and Zn, various intermetallic compound phases are confirmed, but in the present invention, in order to limit the amount of the Zn phase, the chemical composition is adjusted, and in particular, the amount of Al is increased.

[0076] If the amount of Al is increased, a large amount of Al phase is formed in the structure of the plated layer. In soft water / hard water / acid rain, etc., in which the salt concentration of the water is relatively low, the corrosion resistance of the Al phase is excellent, so Al can also be contained in the plated layer. The reason why the water resistance of the Al phase is excellent is believed to be because an aluminum oxide film such as Al2O3 is formed on the surface of Al.

[0077] Furthermore, it has been found that, in the case of a method in which a two-stage plating method and a dip-coating plating method are combined (hereinafter referred to as a dip-coating two-stage plating method), that is, a method in which a plated base sheet made of a Zn-based plated steel is immersed in a hot-dip plating bath and then taken out, a relatively thick plated layer can be obtained compared to the case in which a steel sheet having no plated layer is used as a plated base sheet to perform dip-coating plating. For example, if an alloyed Zn-based plated steel sheet having an interfacial alloy layer between the plated layer and the base metal is used as a plated base sheet to perform dip-coating plating, a new hot-dip plated layer can be formed on the interfacial alloy layer of the plated base sheet, and the thickness of the entire plated layer including the interfacial alloy layer can be increased. Thus, in order to improve corrosion resistance in a constant water-wet environment, the inventors of the present invention have studied the structure of the interfacial alloy layer that is least likely to be dissolved into water, and as a result, have found that (AlFe3) 0.5 (hereinafter referred to as Al 0.5 Fe 1.5 ) has a structure in which the potential difference between the surrounding plated layer and the base metal is small, and it is least likely to be dissolved, and exhibits high corrosion resistance.

[0078] On the other hand, in seawater or the like containing salt, since Al is easily corroded, it is necessary to limit the content of Al. In order to improve the corrosion resistance to seawater or the like in a state where the amount of Al is increased, it is preferable to increase the proportion of those having a complex crystal structure such as intermetallic compounds, for example, it is preferable to make the plating layer contain a large amount of MgZn2 phase. However, in the case where a large amount of MgZn2 phase is contained, it is necessary to reduce the MgZn2 phase of a specific plane orientation contained in the ternary eutectic structure, and make the coarse grains (for example, MgZn2 phase having a particle diameter of more than 3 μm) of the MgZn2 phase grow greatly. This is because: the majority of the MgZn2 phase existing in the ternary eutectic structure together with the Zn phase, Al phase, or the like is easily corroded. It is considered that the reason is: the coupling reaction caused by the surrounding structure is vigorous; and the specific orientation of the MgZn2 phase exists in the ternary eutectic structure. By limiting the MgZn2 phase of a specific plane orientation contained in the ternary eutectic structure, it is possible to exhibit extremely high corrosion resistance even in seawater.

[0079] Further, in order to improve the corrosion resistance of the plating layer, it is more preferable to form an oxide film having high barrier properties on the surface of the plating layer. The inventors of the present application have found that an oxide suitable for the barrier properties is Ca(Al2Si2)O8, and by making it form on the surface, it is possible to greatly improve the water-wet corrosion resistance.

[0080] Furthermore, when, in the dip coating two-stage plating method, a plating original plate having an interface alloy layer is used, and a Zn-Al-Mg-based plating bath containing a large amount of Al is used as the hot dip plating bath of the second stage, iron contained in the interface alloy layer of the plating original plate reacts with Al in the plating bath to generate a Fe-Al-based compound, and a new interface alloy layer containing the Fe-Al-based compound is formed between the steel material and the new plating layer. At this time, the newly formed Fe-Al-based compound needs to be Al 0.5 Fe 1.5 The inventors of the present application have conducted intensive research, and as a result, have found that, in order to form an interface alloy layer containing Al 0.5 Fe 1.5 , it is necessary to optimize the interface alloy layer contained in the plating original plate, and at the same time, optimize the dipping conditions in the plating bath.

[0081] The present application is based on the above-described knowledge. Hereinafter, a plated steel sheet according to an embodiment of the present application will be described.

[0082] The hot-dip plated steel sheet of the embodiment of the present application is a plated steel sheet having a plated layer on the surface of the steel sheet, the average chemical composition of the plated layer, in terms of mass%, being Al: more than 22.5% and 50.0% or less, Mg: more than 3.0% and 15.0% or less, Sn: 0% to 0.7%, Bi: 0% to 0.3%, In: 0% to 0.3%, Ca: 0.03% to 0.6%, Y: 0% to 0.30%, La: 0% to 0.30%, Ce: 0% to 0.30%, Si: 0.03% to 1.0%, Cr: 0% to 0.25%, Ti: 0% to 0.25%, Ni: 0% to 0.25%, Co: 0% to 0.25%, V: 0% to 0.25%, Nb: 0% to 0.25%, Cu: 0% to 0.25%, Mn: 0% to 0.25%, Fe: 2.0% to 25%, Sr: 0% to 0.50%, Sb: 0% to 0.50%, Pb: 0% to 0.50%, B: 0% to 0.50%, Li: 0% to 0.50%, Zr: 0% to 0.50%, Mo: 0% to 0.50%, W: 0% to 0.50%, Ag: 0% to 0.50%, P: 0% to 0.50%, the remainder including Zn and impurities, the total amount ΣA of Sn, Bi and In being 0% to 0.7%, the total amount ΣB of Ca, Y, La and Ce being 0.03% to 0.60%, the total amount ΣC of Cr, Ti, Ni, Co, V, Nb, Cu and Mn being 0% to 0.25%, the total amount ΣD of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P being 0% to 0.50%, satisfying the following formulas (1) to (3), and in the X-ray diffraction pattern of the surface of the plated layer measured using Cu-Kα rays under the conditions of an X-ray output of 50 kV and 300 mA, in the case where I1 is obtained by defining the X-ray diffraction peak of Al 0.5 Fe 1.5 satisfies formula (A-2), and in the case where I2 is obtained by defining the X-ray diffraction peak of Zn, Al and MgZn2 by formula (B-1), formula (B-2) is satisfied.

[0083] Sn≤Si (1)

[0084] 15≤Mg / Si (2)

[0085] 1.0≤Si / Ca≤5.0 (3)

[0086]

[0087] 1.10≤I1 (A-2))

[0088]

[0089] Ⅰ2≤0.25 (B-2)

[0090] wherein, in formula (1) to (3), Sn, Si, Mg, Ca is the content of each element in the plating layer (mass %), Imax (k~m°) in formula (A-1) and formula (B-1) is the maximum value of the X-ray diffraction intensity between diffraction angles k~m°, Imax (n°) in formula (A-1) is the X-ray diffraction intensity at diffraction angle n°, k, m, n are the diffraction angles shown in formula (A-1) and formula (B-1), respectively.

[0091] In the following description, "%" of the content of each element of the chemical composition means "mass %". In addition, the numerical range indicated using "~" means the range including the lower limit value and the upper limit value of the numerals written before and after "~". In addition, the numerical range in the case where "more than" or "less than" is indicated for the numerals written before and after "~" means the range excluding these numerals as the lower limit value or the upper limit value.

[0092] In addition, "corrosion resistance" means the property that the plating layer itself is not easily corroded. Since the Zn-based plating layer has a sacrificial corrosion prevention effect on the steel material, the plating layer is corroded before the steel material is corroded, and the plating layer is white-rusted, and after the white-rusted plating layer disappears, the steel material is corroded to produce red rust, which is the corrosion process of the plated steel sheet.

[0093] The steel material to be plated is described.

[0094] The raw material of the steel material is a steel sheet. The size of the steel sheet is not particularly limited. As long as it is a steel sheet used as a plating base sheet for a general hot-dip galvanizing process, and a steel sheet in which a plating layer can be solidified on the surface by immersion in a molten metal by a continuous hot-dip galvanizing line (CGL) or a batch-type immersion plating galvanizing process, etc. By performing various processes (including welding) on such a steel sheet alone or in combination with a plurality of steel sheets, a steel material of various shapes can be obtained. The shape of the steel material is not particularly limited in terms of the characteristics of the immersion plating method applied in the present embodiment, and can also be a steel material processed from a steel sheet, a steel material joined by welding and joining a steel sheet.

[0095] The material of the steel sheet, which is the raw material of the steel material, is not particularly limited. For example, various steel sheets such as general steel, Al-killed steel, extra-low carbon steel, high carbon steel, various high-tension steels, and a part of high-alloy steels (steel containing Ni, Cr, etc. corrosion resistance strengthening elements, etc.) can be applied. In addition, with respect to the steel sheet, the manufacturing method of the steel sheet (blast furnace material, electric furnace material), the manufacturing method of the steel sheet (hot rolling method, pickling method, cold rolling method, etc.), and the like are also not particularly limited.

[0096] Note that, as described below, as the plated base sheet of the present embodiment, as one example, a plated steel sheet (for example, JIS H 8641:2007) or the like in which a hot-dip plated Zn layer is formed on the surface of the above-described steel material is preferably used. In order to form the plated layer possessed in the hot-dip plated steel sheet of the present embodiment, it is necessary to use a plated steel sheet as a plated base sheet, and it is necessary to cause the plated layer of the plated steel sheet to contain a Zn-Fe alloy layer (interface alloy layer) having a thickness in a specific range.

[0097] Next, the plated layer possessed in the hot-dip plated steel sheet of the present embodiment will be described. The main body of the plated layer of the present embodiment is divided into a Zn-Al-Mg alloy layer on the surface layer side and an Al-Fe alloy layer (interface alloy layer) present at the interface with the base metal. Further, in the plated layer, it is also possible to contain an oxygen-containing thick irregular-shaped oxide film formed on the Zn-Al-Mg alloy layer.

[0098] The Zn-Al-Mg alloy layer is formed of a Zn-Al-Mg alloy. The Zn-Al-Mg alloy refers to a ternary alloy containing Zn, Al, and Mg. The Zn-Al-Mg alloy layer is located away from the base metal (steel material). The Zn-Al-Mg alloy layer is formed by being replaced with the molten metal of the plating bath after being dissolved in the plating bath at the time of dip plating of the portion of the plated base sheet that is a Zn layer or a Zn alloy layer. Therefore, the Zn-Al-Mg alloy layer is an alloy layer of substantially the same composition as the plating bath, is excellent in corrosion resistance, and is also rich in patination corrosion resistance because it contains a large amount of Zn and Mg components.

[0099] The Al-Fe alloy layer is an interface alloy layer located between the steel material and the Zn-Al-Mg alloy layer. The Al-Fe alloy layer is present on the base metal side, and therefore Fe diffuses from the base metal side at the time of dip plating of the plated base sheet. Therefore, the Al-Fe alloy layer is set as a layer containing both Al in the plating bath and Fe diffused from the base metal at the time of plating. In fact, if the cross section of the Al-Fe alloy layer is enlarged, there are a collection of AlFe-based intermetallic compounds existing in a rod shape and a mixed phase of the constituent phases contained in the Zn-Al-Mg alloy layer of the surface layer.

[0100] Further, the Al-Fe alloy layer is also a layer formed by the reaction of the portion of the interface alloy layer (the above-described Zn-Fe alloy layer) formed of a Zn-Fe alloy possessed in the plated base sheet and Al in the plating bath at the time of dip plating of the plated base sheet, and exhibits extremely high corrosion resistance in a water environment (simulated acid rain and seawater (salt water)).

[0101] The Al-Fe alloy layer of the hot-dip plated steel material is formed on the surface of the steel material (specifically, between the steel material and the Zn-Al-Mg alloy layer), and is formed by atomic diffusion between the base metal (steel material) and the plating bath. In the case of using a hot-dip plating method as the production method, an Al-Fe alloy layer is easily formed in a plated layer containing Al element. The Al-Fe alloy layer of the present embodiment contains Al 0.5 Fe 1.5 Regarding Al 0.5 Fe 1.5 will be described below.

[0102] Si is contained in the plated layer of the present embodiment. Si is particularly easily taken into the Al-Fe alloy layer, and can become an Al-Fe-Si intermetallic compound phase. This intermetallic compound is an intermetallic compound formed between the base metal (steel material) and the Al-Fe alloy layer at a thickness of less than 1 μm at the time of dip plating of the original plate. As the identified intermetallic compound phase, there are AlFeSi phases, and as isomers, there are α, β, q1, q2-AlFeSi phases, etc. Therefore, the Al-Fe alloy layer sometimes detects these AlFeSi phases, etc.

[0103] Generally, on the surface of the plated layer, an oxide film containing oxides of the constituent elements of the plated layer can be formed. In the present embodiment, an oxide film having a thickness of 10 μm or less or less than 1 μm can be partially formed. Generally, the elements contained in the plated layer bond with oxygen on the surface of the plated layer. In the case where the plated layer of the present embodiment has an oxide film, by surface analysis such as XPS (X-ray spectroscopy), Zn-O, Mg-O, Al-O, Si-O, Ca-O, etc. bonds, or Mg-Al-O, Al-Si-O, Ca-Al-Si-O, etc. bonds can be confirmed. Such an oxide film is a useful film for ensuring high corrosion resistance in water (simulated acid rain and seawater (salt water)).

[0104] The thickness of the entire plated layer is influenced by the plating conditions, shape, and the like, and thus the upper limit and lower limit of the thickness of the entire plated layer are not particularly limited. For example, as the thickness of each single surface, the thickness of the entire plated layer can be about 50 to 120 μm. The thickness of the Al-Fe alloy layer and the Zn-Al-Mg alloy layer is not particularly limited, but for example, the thickness of the Al-Fe alloy layer can be 10 to 100 μm, and can account for 20 to 80% of the thickness of the entire plated layer. Furthermore, the Zn-Al-Mg alloy layer on the interface alloy layer accounts for at least 20% or more of the entire thickness, and this thickness can be, for example, 15 to 100 μm. However, this thickness is the thickness at the flat portion of the general plated steel sheet, and for example, the thickness at portions having complex shapes such as end surface portions, corner portions, and the like can reach about 1 mm due to the formation of plated run-off and accumulation.

[0105] Next, the average chemical composition of the plated layer will be described. The average chemical composition of the plated layer as a whole is the average chemical composition of the Al-Fe alloy layer and the Zn-Al-Mg alloy layer taken together.

[0106] In the case where the Zn-based plated steel material is used as the plated base sheet to perform dip plating, the chemical composition of the Zn-Al-Mg alloy layer finally adhering to the surface of the steel material becomes approximately the same as that of the plating bath. This is due to the fact that the Zn-based plated layer of the plated base sheet has substantially no residue other than the interface alloy layer, and the amount of the plating bath for dip plating is overwhelmingly larger than the adhering amount of the Zn-based plated layer of the plated base sheet.

[0107] On the other hand, the Al-Fe alloy layer is changed into the Al-Fe alloy layer from the interface alloy layer including the Zn-Fe alloy phase provided in the plated base sheet by the reaction at the time of dip plating, and thus the Al concentration and the Fe concentration of the Al-Fe alloy layer have a tendency to be higher than the plating bath composition for dip plating. On the other hand, the Zn concentration of the Al-Fe alloy layer can be slightly higher than the plating bath composition for dip plating because the Zn in the Zn-Fe alloy phase provided in the plated base sheet can remain. The other components can be lower than the plating bath composition for dip plating.

[0108] On the other hand, in view of the alloy layer portion of the present application, the concentration of the component ratio between the elements after removing Fe becomes approximately the same as the plating bath composition.

[0109] Next, the elements contained in the plated layer will be described. These components are prerequisites for exerting the prescribed plated structure and properties of the present application, and it is difficult to produce the plated layer of the present embodiment outside the range.

[0110] Al: more than 22.5% and 50.0% or less

[0111] Al is an element that constitutes the main body of the plated layer. In Zn-Al-Mg plating, Al forms an Al phase in the plated layer. If the Al content is 22.5% or less, during solidification of the plated layer, a Zn phase and a ternary eutectic structure containing the Zn phase (a Zn / Al / MgZn2 ternary eutectic structure containing a Zn phase, an Al phase, and a MgZn2 phase) are formed. The Zn phase has low corrosion resistance in water (simulated acid rain and seawater (salt water)), and the Zn phase contained in the ternary eutectic structure also has the same. Thus, in order to make the Zn phase and the ternary eutectic structure crystallize as little as possible, the Al content is set to be more than 22.5%. On the other hand, if the Al content is more than 50.0%, the melting point of the plating bath rises, and thus the growth of the Al-Fe alloy layer becomes active, the generation reaction of the Al-Fe alloy layer becomes unstable, and a large amount of Fe is contained in the plated layer, resulting in that the Al-Fe alloy layer desired is not obtained, and the performance of the plated layer is impaired. Therefore, the Al content is set to be 50.0% or less.

[0112] In addition, the Al content greatly affects the structure of the Al-Fe alloy layer. Details will be described later, but if the Al content becomes more than 35.0%, the amount of the Zn phase in the plated layer decreases, and the corrosion resistance in water (in simulated acid rain / salt water) can be further improved. Therefore, the Al content is preferably more than 35.0%.

[0113] Mg: more than 3.0% and 15.0% or less

[0114] Mg is an element that constitutes the main body of the plated layer, like Al and Zn. If Mg is insufficient, there is a tendency that the corrosion resistance in water containing salt decreases, and thus the Mg content is set to be more than 3.0%. On the other hand, if the Mg content is more than 15.0%, there is a problem in the soundness of the plated layer, and it is difficult to ensure the corrosion resistance in water (in simulated acid rain and seawater (salt water)). Thus, the Mg content is set to be 15.0% or less.

[0115] In addition, since Mg is not easily reacted with Fe, there is a tendency that the distribution of Mg in the thickness direction of the plated layer is low in the vicinity of the interface with the base metal and in the vicinity of the Al-Fe alloy layer, and the concentration of Mg becomes high in the surface layer of the plated layer. If the Mg content in the plated layer becomes more than 5.0%, the amount of the Zn phase in the plated layer decreases, and the corrosion resistance in water (in simulated acid rain / salt water) can be further improved. Therefore, the Mg content is preferably more than 5.0%.

[0116] Element group A

[0117] Sn: 0% to 0.7%

[0118] Bi: 0% to 0.3%

[0119] In: 0% to 0.3%

[0120] Total amount of Sn, Bi and In: 0% to 0.7%

[0121] Each element of the element group A (Sn, Bi, In) is an optional element, and thus the content of each is set to 0% or more. If Sn is contained, there is a tendency to form Mg9Sn5 in the plated layer. Bi also forms Mg3Bi2, and In also forms Mg3In, etc. Thus, the corrosion resistance in brine is improved.

[0122] The effect on the corrosion resistance in water (simulated acid rain and seawater (brine)) is small if these elements are contained in small amounts, but if they are contained in excess, the corrosion resistance in simulated acid rain / brine deteriorates extremely, and thus the upper limit of the content needs to be limited. Since each element shows the same effect, the total amount of the element group A needs to be managed. The total amount of the element group A needs to be set to 0.7% or less.

[0123] Note that these elements have no effect on the reaction of the interfacial alloy layer, but since there is a tendency to bond with Mg, there is a tendency for the concentration to be slightly higher in the surface layer, showing a similar composition distribution to Mg.

[0124] Element group B

[0125] Ca: 0.03 to 0.6%

[0126] Y: 0 to 0.30%

[0127] La: 0 to 0.30%

[0128] Ce: 0 to 0.30%

[0129] Total amount of Ca, Y, La and Ce: 0.03% to 0.60%

[0130] These elements are required to control the reaction rate of the plated layer together with Si in dip plating for the original plating panel, and are also required to control the diffusion of Fe in the plating bath. Furthermore, in order to ensure the adhesion of the base metal to the Al-Fe alloy layer, the formation reaction of intermetallic compounds containing these elements between the base metal and the interfacial alloy layer becomes necessary. If the elements of the element group B (particularly Ca) are not contained, the plating adhesion and the distribution of the plated composition cannot be controlled.

[0131] In the case where Ca is contained in the plated layer, needle-shaped Al-Ca-Si-based compounds are likely to be formed in the vicinity of the base metal. This produces an anchoring effect of the base metal and the Al-Fe alloy layer, and becomes a plated layer with excellent adhesion. The Al-Ca-Si-based compounds are formed only when Si and Ca are within a specific composition range. Therefore, in order to ensure corrosion resistance in water (simulated acid rain and seawater (salt water)), it is necessary to form Al-Ca-Si-based compounds in the vicinity of the interface between the base metal and the Al-Fe alloy layer. In particular, Ca has a tendency to bond with Si, and Al-Ca-Si-based compounds have a tendency to be formed when the composition range satisfies 1.0 < Si / Ca < 5.0.

[0132] In the case where the Ca content is relatively high, in addition to the formation of Al-Ca-Si-based compounds, Al 2.15 Zn 1.85 Ca, etc. These compounds have high corrosion resistance in simulated acid rain / salt water. It is presumed that since these compounds are formed in the vicinity of the interface alloy layer of the base metal in particular, bonding with Si, they contribute to the corrosion resistance of the base metal in the vicinity of the interface in water (simulated acid rain and seawater (salt water)) while ensuring plating adhesion. Note that in order to adjust the formation of these compounds in the vicinity of the interface, there is a close relationship with the method of manufacturing the hot-dip plated steel sheet of the present embodiment. In order to ensure corrosion resistance in water (simulated acid rain and seawater (salt water)), it is necessary to strictly manage the composition ratio of Ca and Si. In light of the above, the Ca content is set to 0.03% to 0.6%.

[0133] Further, in the case where Ca is contained in the plated layer, a Ca-Al-Si-O oxide film containing Ca can be formed on the plated surface.

[0134] As elements that exhibit the same effect as Ca, there are Y, La, and Ce. These elements are arbitrary additive elements, and when contained, there is a tendency to substitute for Ca elements. However, even if Y, La, and Ce are contained, they do not exhibit sufficient performance in the absence of Ca. Y, La, and Ce are contained in a range of 0.30% or less, respectively, so as to form a mutual substitution body with each other, and exhibit the same effect as Ca in water (simulated acid rain and seawater (salt water)). However, if Y, La, and Ce exceed 0.30% each, the corrosion resistance in water (simulated acid rain and seawater (salt water)) deteriorates extremely. Thus, the content of Y, La, and Ce is set to 0.30% or less each.

[0135] Further, even if the total amount of the elements of element group B becomes excessive, the corrosion resistance in water (simulated acid rain and seawater (salt water)) deteriorates, and thus the total amount of Ca, Y, La, and Ce, ΣB, is set to 0.03% to 0.60%.

[0136] Si: 0.03%~1.0%

[0137] Si is an element required for the formation of necessary intermetallic compounds in the coating. In this embodiment, the plating bath temperature generally exceeds 500°C. If the steel sheet is immersed in a plating bath at this temperature range, the Al-Fe alloying reaction proceeds excessively, the Fe concentration in the coating becomes high, and the corrosion resistance in water (simulating acid rain and seawater (saltwater)) tends to deteriorate. Therefore, it is necessary to contain more than 0.03% Si in the coating. If Si is present in the coating, there is a tendency to form Al-Ca-Si compounds, which can suppress excessive Al-Fe reaction. It should be noted that the formation of Al-Ca-Si compounds, as described above, is closely related to the preparation method disclosed in this embodiment. These compounds concentrate near the interface, thus suppressing Fe diffusion, and the microstructure of the coating forms a suitable microstructure according to the solidification process.

[0138] Furthermore, Si is an element that readily bonds with Ca, easily forming various Al-Ca-Si compounds such as CaAlSi, Al2CaSi2, Ca2Al4Si3, and Ca2Al3Si4, all exhibiting needle-like shapes. However, excessive Si can impair the corrosion resistance of the coating in water (simulating acid rain and seawater (saltwater)).

[0139] Furthermore, by including Si in the coating, a Si-containing Ca-Al-Si-O oxide film can also be formed on the coated surface. Based on the above, the Si content is set to 0.03% to 1.0%.

[0140] Element group C

[0141] Cr: 0%–0.25%

[0142] Ti: 0%~0.25%

[0143] Ni: 0%–0.25%

[0144] Co: 0%–0.25%

[0145] V: 0%~0.25%

[0146] Nb: 0%–0.25%

[0147] Cu: 0%–0.25%

[0148] Mn: 0%~0.25%

[0149] The total amount of Cr, Ti, Ni, Co, V, Nb, Cu, and Mn, ΣC: 0%–0.25%

[0150] The elements of the element group C are metal elements that can be contained in the plated layer, and can also be contained. These metal elements have a tendency to exist in the plated layer to displace Al, Zn, and the like, thereby moving the potential of the plated layer to a high potential, and have a tendency to improve corrosion resistance in water (particularly in simulated acid rain) by being contained within the concentration range. However, excessive containing of these elements forms intermetallic compounds containing these elements, and thus deteriorates corrosion resistance in water. Therefore, the content of Cr, Ti, Co, V, Nb, Cu, and Mn is set to 0.25% or less, respectively. Furthermore, even if the total amount of the elements of the element group C becomes excessive, corrosion resistance in water deteriorates, and thus the total amount of the elements of the element group C is set to 0.25% or less.

[0151] Fe: 2.0% to 25%

[0152] The hot-dip plated steel sheet of the present embodiment is manufactured by dip plating the plated base sheet, and thus there is a possibility that Fe diffuses from the steel sheet and the interface alloy layer (Fe-Zn-based alloy layer) provided in the plated base sheet to the Zn-Al-Mg alloy layer at the time of dip plating. Therefore, Fe can be contained up to 25% in the entire plated layer, but no change in corrosion resistance due to the containing of this element has been confirmed. Thus, the content of Fe in the plated layer is set to 2.0 to 25%. Note that the concentration of Fe in the Zn-Al-Mg alloy layer on the surface side of the plated layer becomes substantially lower than 2.0%, and this Fe concentration becomes close to the plating bath composition. Furthermore, the chemical composition of the plated layer other than Fe is substantially identical to the plating bath composition.

[0153] Element group D

[0154] Sr: 0% to 0.50%

[0155] Sb: 0% to 0.50%

[0156] Pb: 0% to 0.50%

[0157] B: 0% to 0.50%

[0158] Li: 0% to 0.50%

[0159] Zr: 0% to 0.50%

[0160] Mo: 0% to 0.50%

[0161] W: 0% to 0.50%

[0162] Ag: 0% to 0.50%

[0163] P: 0% to 0.50%

[0164] The total amount of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag, and P: 0% to 0.50%

[0165] Elements of element group D can also be contained in the plated layer. These elements are elements that have the same effects as the elements of element group C explained above and are more easily contained than the elements of element group C. Thus, the content of each element of element group D is set to 0 to 0.50% respectively. Furthermore, if the total amount of the elements of element group D becomes excessive, the corrosion resistance in water (simulated acid rain and seawater (salt water)) deteriorates, and thus the total amount of the elements of element group D is set to 0 to 0.50%.

[0166] Remaining portion: Zn and impurities

[0167] It is preferable to contain Zn in the remaining portion. The hot-dip plated steel sheet of the present embodiment is a Zn-based plated steel sheet that is high in versatility, and by containing Zn in an amount or more for the purpose of securing sacrificial corrosion resistance, it is possible to impart appropriate sacrificial corrosion resistance and the like to the steel sheet. With respect to corrosion resistance in water that is low in salt concentration, the content of Al is preferably more, but in water that contains a relatively large amount of salt such as seawater, it is necessary to secure corrosion resistance by containing Zn-Mg-based intermetallic compounds such as MgZn2 in order to secure corrosion resistance. Thus, in order to secure the necessary amount of Zn-Mg-based intermetallic compounds, the remaining portion is set to Zn.

[0168] Impurities refer to components contained in raw materials or components mixed in during the manufacturing process, and are components that are not intentionally contained. For example, in the plated layer, by atomic diffusion of the steel sheet (base metal) and the plating bath with each other, it is possible that components other than Fe are also mixed in a trace amount as impurities.

[0169] Furthermore, the plated layer of the present embodiment needs to satisfy the following equations (1) to (3). Sn, Si, Mg, and Ca in equations (1) to (3) are the content (mass%) of each element in the plated layer.

[0170] Sn ≤ Si (1)

[0171] 15 ≤ Mg / Si (2)

[0172] 1.0 ≤ Si / Ca ≤ 5.0 (3)

[0173] Sn ≤ Si

[0174] The Si content needs to be set to be the Sn content or more. If the Si content becomes lower than the Sn content, excessive Fe diffuses from the steel sheet into the plated layer, and it becomes difficult to form the intermetallic compound that is the target.

[0175] 15 ≤ Mg / Si

[0176] Further, with respect to the Si content, it is necessary to satisfy 15 ≤ Mg / Si. Thereby, the corrosion resistance in water (simulated acid rain and sea water (salt water)) is improved. If the Si content becomes high with respect to the Mg content, Mg / Si becomes lower than 15, resulting in a large amount of Mg2Si being formed in the plated layer, and the corrosion resistance in water (simulated acid rain and sea water (salt water)) becomes unable to be sufficiently exerted. It is preferable to satisfy 20 ≤ Mg / Si. By Mg / Si becoming 20 or more, the corrosion resistance in salt water is further improved.

[0177] 1.0 ≤ Si / Ca ≤ 5.0

[0178] Si and Ca easily bond to each other and easily form a compound. Further, Y, La, or Ce also easily bond to Si in the same manner. When Si / Ca is lower than 1.0, a large amount of Ca-Al-Zn-based compounds are formed, and Al-Ca-Si-based compounds become difficult to be formed in the vicinity of the interface between the plated layer and the steel material, the plated layer becomes easy to be peeled in water, and the corrosion resistance in water is significantly impaired. Further, if Si / Ca exceeds 5.0, the effect of Ca contained in the plated layer becomes small, a large amount of Mg2Si is formed, and Al-Ca-Si-based compounds become not to be formed, and the corrosion resistance in water is significantly impaired. Therefore, this index is introduced as a management index. In the case where 1.0 ≤ Si / Ca ≤ 5.0 is satisfied, the corrosion resistance in salt water is improved. It is more preferable to satisfy 1.0 ≤ Si / Ca ≤ 3.0. Thereby, the corrosion resistance in salt water is further improved.

[0179] For the identification of the average chemical composition of the plated layer, the plated layer is peeled and dissolved with an acid containing an inhibitor that inhibits corrosion of the base metal (steel material) to obtain an acid solution. Next, by measuring the obtained acid solution by ICP emission spectrometry or ICP-MS method, the chemical composition can be obtained. The kind of acid is not particularly limited as long as it is an acid that can dissolve the plated layer. If the area and the weight before and after peeling are measured, the plating adhesion amount (g / m 2 ) can also be obtained at the same time.

[0180] Next, the intermetallic compound contained in the plated layer is described. First, the intermetallic compound contained in the Zn-Al-Mg-based alloy layer is described. Note that the intermetallic compound described below can also be contained in the Al-Fe alloy layer.

[0181] Zn phase

[0182] The Zn phase exists in the plating layer, and exists mainly as a ternary eutectic structure (Zn / Al / MgZn2 ternary eutectic structure). There are also Zn phases that are not included in the ternary eutectic structure. The Zn phase and the ternary eutectic structure including the Zn phase have low corrosion resistance in water, and if immersed in water (simulated acid rain and seawater (salt water)), they disappear in a short period of time, and thus it is necessary to reduce these Zn phases as much as possible. In the present embodiment, the content of the Zn phase is strictly limited, and the Zn contained in the plating layer is solid-solved in the Al phase, or made into an Al-Zn phase, or made into an intermetallic compound as a MgZn2 phase. Thereby, it is possible to ensure the corrosion resistance of the plating layer in water (simulated acid rain and seawater (salt water)).

[0183] Al phase

[0184] The Al phase exists in the plating layer as Al primary crystals in a bulk shape. In the plating layer of the present embodiment, a certain amount of Zn is contained, but the Al phase existing in a bulk shape contains at most about 35% of Zn. Therefore, the bulk Al primary crystals are strictly Al-Zn phases. The Al-Zn phase is a collection of extremely fine grains, and if the crystal size is confirmed, it is a structure in which fine grains of several nm to about 3 μm are collected. By X-ray diffraction, TEM, etc., it is sometimes confirmed as a collection of structures including fine Al phases and Zn phases, and in the present invention, such fine structures are also referred to as Al phases.

[0185] The Al phase that can contain at most about 35% of Zn forms a stable oxide film of Al2O3 or the like on the surface, and in particular, has high corrosion resistance in water (simulated acid rain). It is presumed that the Al concentration needs to exceed 35% in this oxide film. On the other hand, in water containing salt or the like, Al2O3 cannot stably exist, and the corrosion resistance deteriorates extremely.

[0186] Note that, during solidification of the plating layer, a phase in which the Al concentration is 30% or less and the remaining portion is Zn is also formed, but since the corrosion resistance in water is poor, it is treated as a Zn phase in the present embodiment.

[0187] MgZn2 phase

[0188] The MgZn2 phase exists in the plated layer, and in addition to existing as a bulk of MgZn2 phase, a certain amount of MgZn2 phase is contained as fine grains in dendritic structures or ternary eutectic structures (Zn / Al / MgZn2 ternary eutectic structures) formed when solidified together with the Al phase on the Al-MgZn2 eutectic line. The MgZn2 phase has good corrosion resistance in water (simulated acid rain and seawater (salt water)), and has high corrosion resistance in both of simulated rain / salt water. On the other hand, the corrosion resistance of the MgZn2 phase has a dependence on the particle size, and the MgZn2 and the like contained in the ternary eutectic structures have a tendency to be easily corroded by coupling reactions and the like. The MgZn2 contained in the ternary eutectic structures shows a diffraction peak of the (102) plane in X-ray diffraction measurement. Therefore, by reducing the MgZn2 phase showing the (102) orientation, there is a tendency for the corrosion resistance in water (simulated acid rain and seawater (salt water)) to improve.

[0189] Next, the intermetallic compounds contained in the Al-Fe alloy layer will be described.

[0190] As described above, since a certain concentration or more of Al is contained in the plating bath, when the plating original plate is subjected to dip plating, the Zn-Fe alloy layer possessed by the plating original plate is replaced with the Al-Fe alloy layer. As the intermetallic compounds that can be contained in the Al-Fe alloy layer, AlFe phase, Al 0.5 Fe 1.5 (AlFe3) phase, Al5Fe2 phase, Al 13 Fe4, and the like can be listed. Further, since a certain concentration of Zn is contained in the plating bath, the crystal morphology of the Al-Fe alloy layer is not changed, but there are intermetallic compounds in which a part of Al is replaced with Zn. Further, it is also possible that intermetallic compounds containing Si are also contained.

[0191] Generally, among the above-described intermetallic compounds, Al5Fe2 is easily generated. Al5Fe2 is formed in the Al-Fe alloy layer. Further, it is also possible that Al5Fe2 is formed at the interface between the Al-Fe alloy layer and the steel material.

[0192] However, in the present embodiment, by applying the dip two-stage plating method using a plating bath containing the plating component of the present application, the diffusion of Fe is suppressed, and an Al-Fe alloy layer in which the Al ratio is relatively high, Al 13 Fe4, Al 0.5 Fe 1.5 is formed. Due to this, the corrosion resistance in water (simulated acid rain and seawater (salt water)) of the entire plated layer is greatly improved. In the case where the diffusion of Fe is not appropriately controlled, an Al-Fe alloy layer in which the AlFe phase is the main body, an Al-Fe alloy layer containing the Al5Fe2 phase, the corrosion resistance in water (simulated acid rain and seawater (salt water)) is reduced.

[0193] In the case where the two-stage plating method of immersion plating is applied to form a relatively thick plated layer of, for example, 50 μm or more, the thickness of the Al-Fe alloy layer becomes about 30 μm, and the thickness of the Zn-Al-Mg alloy layer becomes about 20 μm. In terms of corrosion in water, if the potential difference between the Al-Fe alloy layer and the Zn-Al-Mg alloy layer is large, there is a tendency that the corrosion of one of the layers proceeds extremely. The natural potential of each layer has a tendency to become lower if the content of the Fe component is large, and to become higher if the content of the Fe component is small. In the case where the amount of Fe in the Al-Fe alloy layer is large and the natural potential is low, there is a tendency that the corrosion of the Al-Fe alloy layer proceeds rapidly and the plated layer falls off. On the other hand, in the case where the amount of Fe in the Al-Fe alloy layer is small and the natural potential is high, there is a tendency that the corrosion becomes easy to proceed at the interface between the Zn-Al-Mg alloy layer and the Al-Fe layer, and the Zn-Al-Mg alloy layer falls off. By setting the phase of the main body of the Al-Fe alloy layer to Al 13 Fe4, Al 0.5 Fe 1.5 and thus the falling off of the plated layer can be prevented, the corrosion resistance can be ensured in a relatively thick plated layer of, for example, 50 μm, and the corrosion resistance in water (simulated acid rain and seawater (salt water)) can be ensured.

[0194] As described above, the inventors of the present application have sought improvement of the plated layer with the aim of ensuring the corrosion resistance in water (simulated acid rain and seawater (salt water)), and as a result, it has been found that the corrosion resistance in water can be ensured by forming a specific intermetallic compound. In order to determine the presence of the specific intermetallic compound in the plated layer, it is preferable to use the X-ray diffraction method. This detection method gives average information of the plated layer, and is less selective in the measurement site (field of view) and excellent in quantification, as compared with SEM observation, TEM observation, and the like. Further, if the measurement conditions are specified, in the case where the specific intermetallic compound is present, the diffraction peak intensity is obtained at the same angle (2θ) in a specific ratio, and thus the internal structure of the plated layer can be simply inferred.

[0195] The conditions for obtaining the X-ray diffraction pattern are set as follows.

[0196] As the X-ray source, the X-ray diffraction method using Cu as the target is the most convenient because it gives average information of the constituent phase in the plated layer. As one example of the measurement conditions, the conditions of X-ray are set to a voltage of 50 kV and a current of 300 mA. As the X-ray diffraction apparatus, there is no particular limitation, but for example, the sample horizontal type powerful X-ray diffraction apparatus RINT-TTR III manufactured by Rigaku Corporation can be used.

[0197] The following describes the substance that becomes the measurement target in the X-ray diffraction measurement. The substance that becomes the measurement target is Al 0.5 Fe 1.5 , Zn, Al, MgZn2, Ca(Al2Si2)O8.

[0198] Al 0.5 Fe 1.5

[0199] Al 0.5 Fe 1.5 The corrosion resistance in simulated acid rain and seawater (salt water) can be ensured in the Al-Fe alloy layer. Al 0.5 Fe 1.5 is a substance represented by database number (ICDD-JCPDS powder diffraction database) 01-077-6757. As for the index, the substance indexed as (AlFe3) 0.5 is the same as Al 0.5 Fe 1.5 . The diffraction angle at which the intermetallic compound is conveniently detected is 43.95° ((110) plane) in terms of 2θ.

[0200] Zn

[0201] Zn is a substance represented by database number (ICDD-JCPDS powder diffraction database) 00-004-0831. Within the plating composition range of the present embodiment, there is one angle at which Zn is conveniently detected. That is, 36.30° ((002) plane) in terms of diffraction angle 2θ.

[0202] Al

[0203] Within the plating composition range of the present embodiment, there is one angle at which Al is conveniently detected. That is, 38.47° ((111) plane) in terms of diffraction angle 2θ.

[0204] MgZn2

[0205] Within the plating composition range of the present embodiment, there is one angle at which the intermetallic compound is conveniently detected. That is, 19.67° ((100) plane) in terms of diffraction angle 2θ.

[0206] Ca(Al2Si2)O8

[0207] An oxide film that can be formed on the surface of the plated layer contains Ca(Al2Si2)O8. Ca(Al2Si2)O8 is a substance represented by database number (ICDD-JCPDS powder diffraction database) 00-051-0064. In the composition range of the plated layer of the present embodiment, the diffraction angle at which the intermetallic compound is conveniently detected is 23.41° ((102) plane) in terms of 2θ.

[0208] The diffraction peaks at the above-mentioned diffraction angles do not overlap with the diffraction peaks of the main crystal structure of the plated layer, and thus are convenient for quantification and determination of the content. That is, if a diffraction peak having a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target substance is certainly contained.

[0209] In the X-ray diffraction pattern of the surface of the plated layer measured using Cu-Kα rays under the conditions of an X-ray output of 50 kV and 300 mA, I1 is defined by formula (A-1) as the X-ray diffraction intensity of Al 0.5 Fe 1.5 at the (110) plane. In this case, in order to ensure the corrosion resistance of the hot-dip plated steel material in water (simulated acid rain and seawater (salt water)), formula (A-2) needs to be satisfied.

[0210]

[0211] 1.10 ≤ I1 (A-2)

[0212] In formula (A-1), Imax(k~m°) is the maximum value of the X-ray diffraction intensity between diffraction angles k~m°, Imax(n°) is the X-ray diffraction intensity at diffraction angle n°, and k, m, and n are the diffraction angles shown in formula (A-1).

[0213] That is, Imax(43.45~44.45°) is the maximum value of the X-ray diffraction intensity between diffraction angles 43.45~44.45°, and corresponds to the diffraction intensity of the (110) plane of Al 0.5 Fe 1.5 . I(43.45°) and I(44.45°) are the X-ray diffraction intensities at diffraction angles 43.45° and 44.45°, respectively, and correspond to the background intensities of the diffraction peaks of the (110) plane of Al 0.5 Fe 1.5 .

[0214] The molecule (Imax(43.45~44.45°)) of formula (A-1) corresponds to the diffraction intensity of the (110) plane of Al 0.5 Fe 1.5The intensity of the diffraction peak at 2θ = 43.95° ((110) plane) is the maximum diffraction intensity of the diffraction peak including the background intensity. Due to the measurement error of X-ray diffraction, the diffraction angle of the (110) plane may deviate from 43.95°, so the maximum value between 43.45° and 44.45° is obtained.

[0215] The denominator of equation (A-1) is obtained by calculating the background intensity at a diffraction angle of 43.95° from the diffraction intensities at 43.45° and 44.45°. That is, as... Figure 1 As shown, draw a straight line connecting the diffraction line at 43.45° and the diffraction line at 44.45°. This straight line becomes the baseline of the diffraction peak. Next, calculate I(43.45°) - I(44.45°). Furthermore, calculate the ratio (0.50 / 1.00 = 0.50) of the difference between diffraction angles 43.45° and 43.95° (0.50°) to the difference between diffraction angles 43.45° and 44.45° (1.00°). Then, calculate the background intensity at diffraction angle 43.95° using the mathematical expression described in the denominator of the above equation (A-1).

[0216] By setting formula (A-1) as described above, Al can be measured with good accuracy even if measurement errors or background changes occur due to different measurement conditions. 0.5 Fe 1.5 The intensity of the diffraction peak at 2θ = 43.95° ((110) plane).

[0217] As shown in formula (A-2), by having I1 greater than or equal to 1.10, a sufficient amount of Al is contained in the Al-Fe alloy layer of the coating. 0.5 Fe 1.5 This ensures corrosion resistance in water. Specifically, it improves corrosion resistance in simulated rainwater and salt water. I1 is preferably a large value, more preferably 2.0 or higher. If I1 is 2.0 or higher, then most of the Al-Fe alloy layer becomes Al. 0.5 Fe 1.5 Other Al-Fe compounds become unobservable. At I1 values ​​of 1.10–2.00, it is possible that, besides Al... 0.5 Fe 1.5 In addition, Al was also confirmed 13 Fe4. When I1 is below 1.10, Al is present. 0.5 Fe 1.5 Al 13 AlFe compounds other than Fe4. In dip coating, by setting the immersion time to less than 20 seconds, formula (A-2) is satisfied. The upper limit of I1 does not need to be specifically limited, but it can also be below 2.50.

[0218] Further, in order to ensure the corrosion resistance of the hot-dip plated steel sheet in water (simulated acid rain and seawater (salt water)), in the X-ray diffraction pattern of the plated layer surface measured using Cu-Ka rays with an X-ray output of 50 kV and 300 mA, in the case where I2defined by formula (B-1) from the X-ray diffraction peaks of Zn, Al, and MgZn2is I2≤ 0.25 (B-2) needs to be satisfied.

[0219]

[0220] I2≤ 0.25 (B-2)

[0221] wherein Imax(k~m°) in formula (B-1) is the maximum value of the X-ray diffraction intensity between diffraction angles k~m°.

[0222] That is, Imax(36.00~36.60°) in formula (B-1) is the maximum value of the X-ray diffraction intensity between diffraction angles 36.00~36.60°, which corresponds to the diffraction intensity of the (002) plane of Zn.

[0223] Imax(38.00~39.00°) is the maximum value of the X-ray diffraction intensity between diffraction angles 38.00~39.00°, which corresponds to the diffraction intensity of the (111) plane of Al.

[0224] Imax(19.20~20.00°) is the maximum value of the X-ray diffraction intensity between diffraction angles 19.20~20.00°, which corresponds to the diffraction intensity of the (100) plane of MgZn2.

[0225] Thus, I2defined by formula (B-1) represents the ratio of the diffraction intensity of Zn with respect to the total of the diffraction intensities of Zn, Al, and MgZn2, and the smaller I2is, the less Zn phase there is in the plated layer. In the present embodiment, I2is set to 0.25 or less. Thereby, the corrosion resistance in water (simulated acid rain and seawater (salt water)) can be ensured. That is, the ratio of the Zn phase is low in the plated layer, which leads to the improvement of the corrosion resistance in water, the improvement of the corrosion resistance in simulated rainwater / salt water, and the maintenance of the plated layer in water. By setting the Al content in the plated layer to more than 30% and the Mg content to more than 5.0%, the Zn phase can be reduced. Further, the amount of the Zn phase is affected by the formation behavior of the Al-Fe alloy layer, and in the case where AlFe, Al5Fe2are formed in large amounts, there is a tendency that the Zn phase becomes more, and thus both of formula (A-2) and (B-2) need to be satisfied. I2is preferably 0.10 or less. The lower limit of I2is not particularly limited, but can also be 0 or more.

[0226] Second, in the composition range of the plated layer of the present embodiment, the MgZn2 phase crystallizes. The MgZn2 phase originally has high corrosion resistance in water (simulated acid rain and seawater (salt water)), but if surrounded by fine Al phase and Zn phase, corrosion is promoted by coupling reactions between these phases. In addition, the MgZn2 phase has a lower corrosion potential than the Zn phase. Therefore, the MgZn2 phase surrounded by the Al phase and the Zn phase dissolves early in water (simulated acid rain and seawater (salt water)). As such MgZn2 phase, the MgZn2 phase contained in the ternary eutectic structure in the plated layer can be cited. Therefore, in the present embodiment, it is preferable to reduce the MgZn2 phase contained in the ternary eutectic structure, and further preferably to reduce the ternary eutectic structure.

[0227] As the diffraction angle at which the MgZn2 phase contained in the ternary eutectic structure is conveniently detected by X-ray diffraction, there is one angle. The diffraction intensity of the (102) plane of the MgZn2 phase contained in the ternary eutectic structure is strong. That is, the diffraction peak appearing at the diffraction intensity in the (102) plane at a diffraction angle 2θ of 28.73° does not overlap with the diffraction peak of the main crystal structure of the plated layer, and thus is convenient for quantification and determination of the content. That is, if a diffraction peak having a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target phase is certainly contained.

[0228] The MgZn2 phase showing a crystal orientation other than the (102) plane is a coarse MgZn2 phase that covers the Al phase by peritectic reaction, or a coarse MgZn2 phase that is precipitated by a reaction other than the ternary eutectic reaction, and has high corrosion resistance in water (simulated acid rain and seawater (salt water)). These MgZn2 phases having excellent corrosion resistance in water show diffraction intensities of 20.78° ((002) plane), 22.26° ((101) plane) in addition to 19.67° ((100) plane) in the above-described diffraction angle 2θ. The diffraction peaks appearing at these diffraction angles do not overlap with the diffraction peak of the main crystal structure of the plated layer, and thus are convenient for quantification and determination of the content.

[0229] Most of the MgZn2 phase contained in the plated layer shows one of the above-described four diffraction peaks. Thus, in the hot-dip plated steel sheet of the present embodiment, in the X-ray diffraction pattern of the plated layer surface measured using Cu-Kα rays and under conditions of 50 kV and 300 mA of X-ray output, when I3 calculated from the X-ray diffraction peak of MgZn2 is defined by formula (C-1), it is preferable to satisfy formula (C-2).

[0230]

[0231] I3≤0.03 (C-2)

[0232] In Equation (C-1), Imax(k~m°) is the maximum value of X-ray diffraction intensity between diffraction angles k and m°, where k and m are the diffraction angles shown in Equation (C-1).

[0233] That is, Imax (28.52~28.92°) in equation (C-1) is the maximum value of X-ray diffraction intensity between diffraction angles of 28.52~28.92°, corresponding to the diffraction intensity of the (102) plane of MgZn2. This MgZn2 is equivalent to the MgZn2 phase contained in the ternary eutectic structure.

[0234] Imax (19.20~20.00°) is the maximum value of X-ray diffraction intensity between diffraction angles of 19.20~20.00°, corresponding to the diffraction intensity of the (100) plane of MgZn2.

[0235] Imax (20.58~20.98°) is the maximum value of X-ray diffraction intensity between diffraction angles of 20.58~20.98°, corresponding to the diffraction intensity of the (002) plane of MgZn2.

[0236] Imax (22.06~22.45°) is the maximum value of X-ray diffraction intensity between diffraction angles of 22.06~22.45°, corresponding to the diffraction intensity of the (101) plane of MgZn2.

[0237] Therefore, I3, as defined by equation (C-1), represents the ratio of the diffraction intensity of the MgZn2 phase contained in the ternary eutectic structure to the total diffraction intensity of the MgZn2 phase contained in the coating. A smaller I3 indicates a lower amount of MgZn2 phase, or even less ternary eutectic structure, in the ternary eutectic structure. In this embodiment, I3 is set to 0.03 or less. As a result, the MgZn2 phase present as a ternary eutectic structure essentially disappears, further improving corrosion resistance in simulated acid rain / salt water. The lower limit of I3 does not need to be specifically limited, but it can also be above 0. To control I3, it is advisable to control the immersion time in the plating bath in the two-stage dip-coating method.

[0238] Secondly, on the surface of the coating of the hot-dip galvanized steel in this embodiment, it is possible to form an oxide film containing Ca(Al2Si2)O8. Since Ca(Al2Si2)O8 improves the corrosion resistance of the coating in simulated rainwater / salt water, it is preferable to form an oxide film containing Ca(Al2Si2)O8. Therefore, in the hot-dip galvanized steel of this embodiment, in the X-ray diffraction pattern of the coating surface measured using Cu-Kα rays under conditions of 50kV and 300mA X-ray output, when I4 is defined by formula (D-1) from the X-ray diffraction peak of Ca(Al2Si2)O8, it is preferable to satisfy formula (D-2).

[0239]

[0240] 1.1≤I4 (D-2)

[0241] In Equation (D-1), Imax(k~m°) is the maximum value of X-ray diffraction intensity between diffraction angles k~m°, Imax(n°) is the X-ray diffraction intensity at diffraction angle n°, and k, m, and n are the diffraction angles shown in Equation (D-1).

[0242] That is, Imax (22.91°~23.91°) in equation (D-1) is the maximum value of X-ray diffraction intensity between diffraction angles of 22.91° and 23.91°, corresponding to the diffraction intensity of the (102) plane of Ca(Al2Si2)O8. I(22.91°) and I(23.91°) are the X-ray diffraction intensities at diffraction angles of 22.91° and 23.91°, respectively, corresponding to the background intensity of the diffraction peak of the (102) plane of Ca(Al2Si2)O8.

[0243] The molecule (Imax (22.91~23.91°)) of formula (D-1) is the intensity of the diffraction peak at 2θ=23.41° ((102) plane) of Ca(Al2Si2)O8, which is the maximum diffraction intensity of the diffraction peak including the background intensity. Due to the measurement error of X-ray diffraction, the diffraction angle of the (102) plane may deviate from 23.41°, so the maximum value between 22.91° and 23.91° is obtained.

[0244] The denominator of equation (D-1) is obtained by calculating the background intensity at a diffraction angle of 23.41° from the diffraction intensities at 22.91° and 23.91°. That is, as... Figure 2 As shown, draw a straight line connecting the diffraction ray at 22.91° and the diffraction ray at 23.91°. This straight line becomes the baseline of the diffraction peak. Next, calculate I(22.91°) - I(23.91°). Furthermore, calculate the ratio (0.50 / 1.00 = 0.50) of the difference between diffraction angles 22.91° and 23.41° (0.50°) to the difference between diffraction angles 22.91° and 23.91° (1.00°). Then, calculate the background intensity at diffraction angle 23.41° using the mathematical expression described in the denominator of the above equation (D-1).

[0245] By setting formula (D-1) as described above, the intensity of the diffraction peak of Ca(Al2Si2)O8 at 2θ = 23.41° (102 plane) can be measured with good accuracy, even if measurement errors or background changes occur due to different measurement conditions.

[0246] As shown in formula (D-2), by I4 being 1.1 or greater, corrosion resistance in simulated rain / salt water can be ensured. The greater the value of I4, the thicker the oxide film formed, which is preferable from the aspect of ensuring corrosion resistance. The upper limit of I4 is not particularly limited, but for example, can be 1.5 or less. Furthermore, in order to satisfy formula (D-2), the chemical composition of the plated layer needs to satisfy the range of the present application, and appropriate plating manufacturing methods, heat treatment, and atmosphere control are performed in the manufacturing method. Specifically, it is necessary to form an oxide film in advance on the surface of the plating bath.

[0247] Next, the manufacturing method of the hot-dip plated steel material of the present embodiment will be described.

[0248] The hot-dip plated steel material of the present embodiment can be manufactured by a dip coating two-stage plating method. In the case of a dip coating plating method in which the surface of the steel material is treated with a flux and then immersed in a plating bath, the residue of the flux after reacting with Mg in the plating bath tends to remain, and it is not possible to form the desired Al-Fe alloy layer, so a dip coating two-stage plating method is appropriate.

[0249] The hot-dip plated steel material of the present embodiment is manufactured by immersing a plated steel material having an interface alloy layer in a hot-dip plating bath, and after a prescribed immersion time, the plated steel material is lifted and then cooled. In addition, the plating bath is bubbled as necessary. The manufacturing conditions will be described in detail below.

[0250] As one example, the plated steel material used as the plated steel material is a plated steel material (for example, JIS H 8641:2007) in which a hot-dip plated Zn layer is formed in advance on the surface of the steel material, or the like. In the plated layer of the plated steel material, it is necessary to include a Zn-Fe alloy layer (interface alloy layer) having a thickness in a specific range. The plated steel material that becomes the plated steel material is preferably manufactured by a dip coating plating method. In general, a hot-dip plated steel sheet or the like manufactured by a continuous hot-dip galvanizing production line does not have these interface alloy layers or even if they are present, they are not sufficiently thick, so a continuous hot-dip plating method is not suitable for manufacturing the plated steel material that becomes the plated steel material.

[0251] The hot-dip Zn layer included in the plated steel material as a plated base sheet preferably has a thickness of more than 30 μm. The hot-dip Zn layer includes a Zn layer (η phase) and a Zn-Fe alloy layer. The Zn-Fe alloy layer is an interfacial alloy layer formed between the Zn layer and the steel material, and includes a ζ phase, a δ phase, a Γ phase, and a Γ1 phase. These phases are stacked in the order of the Γ phase / Γ1 phase, the δ phase, and the ζ phase from the steel material side, and the Zn layer as the η phase is present on the ζ phase. The Zn-Fe alloy layer is replaced with an Al-Fe alloy layer by immersing the plated base sheet in a plating bath for dip plating. Therefore, in order to obtain a desired Al-Fe alloy layer, it is important to make the microstructure of the interfacial alloy layer (Zn-Fe alloy layer) included in the plated base sheet (plated steel material) appropriate. Note that the Zn layer is dissolved and replaced with a Zn-Al-Mg alloy layer when immersed in the plating bath for dip plating.

[0252] The inventors of the present application have studied the preferred Zn-Fe alloy layer, and as a result, have found that it is necessary to control the thickness of each phase included in the Zn-Fe alloy layer. By using a plated base sheet including the preferred Zn-Fe alloy layer, it is possible to include Al 0.5 Fe 1.5 in the Al-Fe alloy layer of the hot-dip plated steel material 13 Fe4. If an alloy layer outside this range is used, an AlFe phase is formed.

[0253] In most cases, the ζ phase included in the Zn-Fe alloy layer is FeZn 13 with a Fe concentration of 2 to 6%, the δ phase is FeZn7 with a Fe concentration of 7 to 12%, the Γ phase is Fe3Zn 10 with a Fe concentration of 21 to 27%, and the Γ1 phase is Fe5Zn 21 The longer the immersion time in the plating bath when the plated steel material (plated base sheet) is manufactured by dip plating (plating in the first stage), the more the proportion of the Γ phase and the δ phase becomes, and if the immersion time is shortened, the ζ phase is formed. Among these, when dip plating is performed on the plated base sheet (when plating is performed in the second stage), the ζ phase is changed to Al 0.5 Fe 1.5 , the δ phase is changed to Al 13 Fe4. On the other hand, the Γ phase and the Γ1 phase are changed to AlFe, etc. Therefore, among the phases constituting the Zn-Fe alloy layer in the plated steel material (plated base sheet), it is preferable to include a relatively large amount of the ζ phase. In the case where the δ phase, the Γ phase, and the Γ1 phase are relatively large, a hot-dip plated layer having excellent corrosion resistance in an aqueous environment (simulated acid rain and seawater (salt water)) cannot be formed.

[0254] Specifically, the ratio of the average thickness of the thickness of the ζ phase to the average thickness of the Zn-Fe alloy layer (average thickness of the thickness of the ζ phase / average thickness of the Zn-Fe alloy layer) is set to 0.75 or more. This index means that the δ phase is actually thinned as much as possible in the plated base sheet, and the Γ phase and Γ1 phase are not substantially formed. Note that it was ascertained that the Γ phase is formed if the δ phase grows in a prescribed ratio, and the Γ phase is gradually formed if the average thickness of the thickness of the δ phase / average thickness of the Zn-Fe alloy layer exceeds 0.20. If the Γ phase increases, the adhesion of the hot-dip plated layer of the present embodiment decreases, and thus is not preferable. Therefore, the average thickness of the thickness of the δ phase / average thickness of the Zn-Fe alloy layer is preferably set to 0.20 or less. The average thickness of the Zn-Fe alloy layer is set to 30 μm or more.

[0255] In order to set the ratio of the average thickness of the thickness of the ζ phase to the average thickness of the Zn-Fe alloy layer (average thickness of the thickness of the ζ phase / average thickness of the Zn-Fe alloy layer) to 0.75 or more, the immersion time in the immersion plating method is set to 60 to 600 seconds, and preferably 120 to 300 seconds. Further, the temperature of the plating bath is set to 420 to 520°C, and preferably 430 to 470°C. After being taken out of the plating bath, water cooling is performed from a temperature of 300°C or more, and preferably 350°C or more of the steel sheet.

[0256] The thickness of the Zn-Fe alloy layer and each phase can be easily confirmed by polishing the plated layer, etching it with nitric acid ethanol or the like, and then observing the cross section using an optical microscope.

[0257] Note that, with respect to the hot-dip plated Zn layer according to JIS H 8641, there are cases where the above conditions are satisfied and cases where they are not satisfied, and it is not possible to use an arbitrary Zn-plated steel sheet for the plated base sheet as a matter of course. It is desirable that the thickness of the Zn layer (η phase) of the surface layer of the hot-dip plated Zn layer be 30 μm or more while strictly adhering to the above conditions. The plating adhesion amount (including the Zn-Fe alloy layer) of the plated base sheet is 300 g / m 2 The above is desirable.

[0258] Next, the conditions of the immersion plating are described.

[0259] In the manufacturing method of the present embodiment, the plated base sheet described above is immersed in a hot-dip plating bath and then taken out. The composition of the plated layer can be controlled by the composition of the plating bath in which the bath is prepared. The preparation of the bath of the plating bath is performed by mixing pure metals in prescribed amounts, and for example, an alloy of the composition of the plating bath is prepared by a dissolution method in an inert atmosphere.

[0260] It is not necessary to heat the plating original plate before immersion. This is because if the plating original plate is heated, the Al-Fe reaction becomes excessively active at the time of immersion in the plating bath, and the desired Al-Fe alloy layer cannot be obtained.

[0261] The temperature of the plating bath is set to 530°C to 600°C in the case where the Al concentration is 35% or less, and is set to 570°C to 630°C in the case where the Al concentration exceeds 35%.

[0262] Further, in order to obtain the desired Al-Fe alloy layer, it is necessary to control the immersion time of the plating original plate in the plating bath. The immersion time in the plating bath is set to a range of 2 seconds or more and less than 20 seconds. It is preferably set to a range of 3 to 10 seconds. If the immersion time exceeds 10 seconds, Al 0.5 Fe 1.5 Al5Fe2and AlFe are formed in the Al-Fe alloy layer, Al 13 Fe4. If the immersion time exceeds 20 seconds, a large amount of Al5Fe2and AlFe are formed in the Al-Fe alloy layer, Al 0.5 Fe 1.5 decreases, and it becomes impossible to satisfy the above formula (A-2). Further, in order to reduce the Zn phase for controlling the orientation of the crystal of MgZn2, it is necessary to set the immersion time to 2 seconds or more. Thus, the immersion time in the plating bath is set to 2 seconds or more and less than 20 seconds.

[0263] After being lifted from the plating bath, cooling is performed in such a manner that the required time from the time of lifting from the plating bath until the surface temperature of the attached molten metal (plating layer) reaches 450°C becomes 5 seconds or less. This is in order to suppress the diffusion of Fe from the base metal as much as possible. If the temperature of the plating layer becomes lower than 450°C, the diffusion of Fe substantially converges, and thus the required time until 450°C is controlled.

[0264] Further, in the case where an oxide film is formed on the surface of the plating layer, it is preferable to circulate the plating bath by air bubbling or the like. By performing air bubbling, an oxide film is formed on the surface of the plating bath. This oxide film is carried up at the time of lifting of the plating original plate and is attached to the surface of the molten metal (plating bath). If the immersion / lifting speed of the plating original plate at the time of immersion and at the time of lifting in the plating bath is excessively fast, there is a possibility that the oxide film is broken and becomes unable to form an oxide film on the entire surface of the plating layer, and thus the immersion / lifting speed of the plating original plate is preferably adjusted to 10 cm / second or less. However, the immersion / lifting speed can also depend on the shape of the plating original plate, and thus the above condition is only a general standard.

[0265] In the case where the oxide film is formed without performing the atmospheric bubbling, the plating bath can be kept in a state of rest for a long time to form an oxide film on the surface of the plating bath, and then the plating original plate can be immersed. However, in order to form the oxide film on the surface of the plating bath without bubbling, a long time is required, and thus it is not suitable in the case where a plurality of plating original plates are continuously immersed.

[0266] If the plated steel material having the Zn-Fe alloy layer as the interface alloy layer is subjected to the dip plating as the plating original plate, in the plating bath, the Zn layer of the surface layer of the plating original plate is dissolved and replaced with the Zn-Al-Mg alloy layer. Further, the iron contained in the Zn-Fe alloy layer of the plating original plate reacts with Al in the plating bath to generate the Fe-Al compound, and a new Al-Fe alloy layer containing the Fe-Al compound is formed between the steel material and the Zn-Al-Mg alloy layer. In the Al-Fe alloy layer, a large amount of Al is contained 0.5 Fe 1.5 .

[0267] After the dip plating, various chemical conversion treatments, painting treatments can be performed. The pattern of the concavo-convex shape of the plated surface can be utilized to further impart a plated layer of Cr, Ni, Au, or the like, and a pattern design can be imparted by further painting. Further, in order to further improve the corrosion resistance, a repair paint, a spray treatment, or the like can be applied to the welded portion, the processed portion, or the like.

[0268] For the plated steel material of the present embodiment, a film can be formed on the plated layer. One layer or two or more layers of the film can be formed. As the type of the film on the top of the plated layer, for example, a chromate film, a phosphate film, a non-chromate film can be exemplified. The chromate treatment, the phosphate treatment, the non-chromate treatment for forming these films can be performed by a known method.

[0269] For the chromate treatment, there are an electrolytic chromate treatment in which a chromate film is formed by electrolysis, a reaction type chromate treatment in which a film is formed by a reaction with a raw material and then the excess treatment liquid is rinsed off, and a coating type chromate treatment in which a film is formed by coating a treatment liquid on a coated object and drying without water washing. Any one of the treatments can be adopted.

[0270] As the electrolytic chromate treatment, an electrolytic chromate treatment using chromic acid, silica sol, a resin (phosphoric acid, acrylic resin, vinyl ester resin, vinyl acetate-acrylic emulsion, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resin, and the like), and hard silica can be exemplified.

[0271] As the phosphate treatment, for example, a zinc phosphate treatment, a calcium zinc phosphate treatment, a manganese phosphate treatment can be exemplified.

[0272] A chromium-free treatment is particularly desirable because it does not load the environment. For chromium-free treatment, there are the following chromium-free treatments: an electrolytic chromium-free treatment in which a chromium-free coating film is formed by electrolysis; a reaction-type chromium-free treatment in which a coating film is formed by reaction with a raw material and then the excess treatment liquid is rinsed off; and a coating-type chromium-free treatment in which a coating film is formed by applying the treatment liquid to the coated object and drying without water washing. Any of these treatments can be used.

[0273] Further, on the coating film directly above the plating layer, one or two or more organic resin coating films can be provided. The organic resin is not limited to a particular type, and examples include polyester resins, polyurethane resins, epoxy resins, acrylic resins, polyolefin resins, and modified versions of these resins. The modified versions are resins obtained by reacting a reactive functional group contained in the structure of these resins with another compound (monomer, crosslinking agent, etc.) that contains a functional group that can react with the functional group.

[0274] One or two or more types of organic resin (unmodified resin) can be used in combination as such an organic resin, or one or two or more types of organic resin obtained by modifying at least one other organic resin in the presence of at least one type of organic resin can be used in combination. In addition, any coloring pigment or rust-preventive pigment can be included in the organic resin coating film. These organic resins can also be resins that have been water-based by being dissolved or dispersed in water.

[0275] Note that in the present embodiment, the corrosion resistance in acid rain and the corrosion resistance in salt water were measured and evaluated by the following operations. Cases in which the corrosion resistance in acid rain and the corrosion resistance in salt water were both rated "E" were set as failures, and all other cases were set as passes.

[0276] (Corrosion resistance in acid rain)

[0277] The corrosion resistance in acid rain was evaluated by a simulated acid rain corrosion resistance test. This test is a test that simulates the conditions in which acid rain in the atmosphere flows in. As the simulated acid rain, a test water was prepared by adding NaCl, HNO3, and H2SO4 to ion exchange water and adjusting the pH with NaOH so as to adjust Cl - : 10 ppm, NO 3- : 20 ppm, SO4 2-: 40 ppm, pH 5.0 ± 0.2. 60 L of test water was charged into a container of a cubic shape with one side of 50 cm. A plated steel test piece was attached to the front end of a stainless steel shaft (φ 25 mm) by a clamp and a bolt. The test piece was set as a circular plate of 130 mm in diameter. A hole was provided in the center of the circular plate, and the front end of the stainless steel shaft was inserted into the hole to fix it. The test piece was immersed in the test water, and rotated at a high speed in such a manner that the peripheral speed of the test piece became 2.2 m / s. The portion of the test piece in contact with the clamp was insulated by taping, etc. The pH was monitored constantly, and in the case where the range of pH 5.0 ± 0.2 was departed from, diluted hydrochloric acid or NaOH aqueous solution was used to restore the pH to 5.0. The water temperature was maintained in the range of 23 to 25°C. The test liquid was replaced every 250 hours. After 1000 hours, the test piece was taken out, immersed in 30% chromium (VI) aqueous solution for 15 minutes, and the weight difference before and after the immersion was measured to obtain the corrosion loss (g / m 2 ). For the test piece, the end face portion was set as an open state, and the central hole portion was set as an evaluation outside. The evaluation criteria were set as described below.

[0278] Corrosion loss less than 5 g / m 2 : Corrosion resistance in simulated acid rain is "S"

[0279] Corrosion loss 5 g / m 2 or more and less than 15 g / m 2 : Corrosion resistance in simulated acid rain is "A"

[0280] Corrosion loss 15 g / m 2 or more and less than 30 g / m 2 : Corrosion resistance in simulated acid rain is "B"

[0281] Corrosion loss 30 g / m 2 or more and less than 50 g / m 2 : Corrosion resistance in simulated acid rain is "C"

[0282] Corrosion loss 50 g / m 2 or more and less than 75 g / m 2 : Corrosion resistance in simulated acid rain is "D"

[0283] Corrosion loss 75 g / m 2 or more: Corrosion resistance in simulated acid rain is "E"

[0284] (Corrosion resistance in salt water)

[0285] The corrosion resistance in salt water was evaluated by a corrosion resistance test in a salt water solution. This test was conducted in the same manner as the simulated acid rain corrosion resistance test, except that the test water was set to a 5% NaCl aqueous solution. After 1000 hours, the immersion in a 30% aqueous chromium (VI) solution for 15 minutes was performed, and the corrosion loss before and after the immersion was determined. The evaluation criteria were set as described below.

[0286] Corrosion loss less than 30 g / m 2 Corrosion resistance in salt water: "S"

[0287] Corrosion loss 30 g / m 2 and less than 40 g / m 2 Corrosion resistance in salt water: "A"

[0288] Corrosion loss 40 g / m 2 and less than 60 g / m 2 Corrosion resistance in salt water: "B"

[0289] Corrosion loss 60 g / m 2 and less than 80 g / m 2 Corrosion resistance in salt water: "C"

[0290] Corrosion loss 80 g / m 2 and less than 100 g / m 2 Corrosion resistance in salt water: "D"

[0291] Corrosion loss 100 g / m 2 and more: Corrosion resistance in salt water: "E"

[0292] Examples

[0293] The plated steel materials shown in Tables 1A to 4C were produced, and performance evaluations were performed. For the blending of the various plating baths, the pure metals were blended to make the baths. The plating bath temperature was set to 550°C in the case where the Al concentration was 35% or less, and to 600°C in the case where the Al concentration exceeded 35%. The heating of the plated original plate was not performed. The plated original plate was set to Al to C3 shown in Table 5 below, the conditions for the dip plating were set to Dl to E6 of Table 6 below, and the presence or absence of the atmospheric bubbling was set as shown in Table 7 below. The thickness of the plated layer of the plated original plate was all more than 30 μm, and the thickness of the η phase was 30 μm or more. The thickness of the ZnFe alloy layer of Table 5 was the average thickness. Regarding the comparative example conditions, the original plate was set to A3, B3, C3, and the conditions for the dip plating were set to D6, El to E6.

[0294] The intensity of the X-rays was measured as follows.

[0295] The plated hot-dip steel material was cut into 20 mm squares, and a high-angle X-ray diffractometer (Rigaku Co., Ltd. (Model RINT-TTR III)) was used, with the X-ray output set to 50 kV, 300 mA, a copper (Cu) target, a goniometer TTR (horizontal goniometer), a slit width of 0.05 mm for the Kβ filter, a length limit slit width of 2 mm, a light receiving slit width of 8 mm, and the light receiving slit 2 open, as the measurement conditions, with the scanning speed set to 5 deg. / min, the step width set to 0.01 deg, and the scanning axis 2θ (5 to 90°) to perform the measurement, and the cps intensity at each angle was obtained.

[0296] The corrosion resistance in simulated acid rain and in salt water was measured and evaluated as follows. The results are shown in Tables 4A to 4C. The case where the corrosion resistance in acid rain and the corrosion resistance in salt water were both evaluated as "E" was set as unqualified, and the other cases were set as qualified.

[0297] (Corrosion resistance in acid rain)

[0298] The corrosion resistance in acid rain was evaluated by a simulated acid rain corrosion resistance test. This test is a test that assumes the condition of the inflow of acid rain in the atmosphere. As the simulated acid rain, a test water was prepared by adding NaCl, HNO3, H2SO4 to ion exchange water and adjusting the pH with NaOH, so as to adjust Cl": 10 ppm, NO 3- : 20 ppm, SO4 2- : 40 ppm, pH 5.0 ± 0.2. 60 L of the test water was added to a container of a cubic shape with one side of 50 cm. A plated steel test piece was attached to the tip of a stainless steel shaft (φ 25 mm) by a jig and a bolt. The test piece was set as a circular plate of 130 mm in diameter. A hole was provided in the center of the circular plate, and the tip of the stainless steel shaft was inserted in the hole to fix it. The test piece was immersed in the test water, and rotated at a high speed in such a manner that the peripheral speed of the test piece became 2.2 m / s. The portion of the test piece in contact with the jig was insulated by taping, etc. The pH was monitored at all times, and in the case where the range of pH 5.0 ± 0.2 was deviated, it was restored to pH 5.0 with dilute hydrochloric acid or NaOH aqueous solution. The water temperature was maintained in the range of 23 to 25°C. The test liquid was replaced every 250 hours. After 1000 hours, the test piece was taken out, immersed in 30% chromium (VI) aqueous solution for 15 minutes, and the weight difference before and after the immersion was measured to obtain the corrosion loss (g / m 2 ). For the test piece, the end face portion was set as an open state, and the central hole portion was set as the evaluation outside. The evaluation criteria were set as described below.

[0299] The corrosion loss of less than 5 g / m 2: corrosion resistance in simulated acid rain is "S"

[0300] corrosion loss is 5 g / m 2 or more and less than 15 g / m 2 : corrosion resistance in simulated acid rain is "A"

[0301] corrosion loss is 15 g / m 2 or more and less than 30 g / m 2 : corrosion resistance in simulated acid rain is "B"

[0302] corrosion loss is 30 g / m 2 or more and less than 50 g / m 2 : corrosion resistance in simulated acid rain is "C"

[0303] corrosion loss is 50 g / m 2 or more and less than 75 g / m 2 : corrosion resistance in simulated acid rain is "D"

[0304] corrosion loss is 75 g / m 2 or more: corrosion resistance in simulated acid rain is "E"

[0305] (corrosion resistance in salt water)

[0306] Corrosion resistance in salt water is evaluated by a corrosion resistance test in an aqueous salt solution. This test is operated in the same manner as the corrosion resistance test in simulated acid rain, except that the test water is set to be an aqueous 5% NaCl solution. After 1000 hours, the corrosion loss before and after immersion in an aqueous 30% chromium (VI) solution for 15 minutes is found. The evaluation criteria are set as described below.

[0307] corrosion loss is less than 30 g / m 2 : corrosion resistance in salt water is "S"

[0308] corrosion loss is 30 g / m 2 or more and less than 40 g / m 2 : corrosion resistance in salt water is "A"

[0309] corrosion loss is 40 g / m 2 or more and less than 60 g / m 2 : corrosion resistance in salt water is "B"

[0310] corrosion loss is 60 g / m 2 or more and less than 80 g / m 2 : corrosion resistance in salt water is "C"

[0311] corrosion loss is 80 g / m 2 or more and less than 100 g / m 2: Corrosion resistance in salt water was "D"

[0312] Corrosion reduction was 100 g / m 2 : Corrosion resistance in salt water was "E"

[0313] As shown in Tables 1A to 4C, No. 1 and 8 deviated from the range of the present application in terms of Al content, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0314] No. 9 and 14 deviated from the range of the present application in terms of Mg content, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0315] No. 17, 19, 21, 24 deviated from the range of the present application in terms of the elements of Group A, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0316] No. 25, 32, 33, 49, 51, 53, 54 deviated from the range of the present application in terms of the elements of Group B, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0317] No. 35 to 47 and 96 to 108 deviated from the preferred range of the manufacturing conditions, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0318] No. 55, 61 deviated from the range of the present application in terms of Si content, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0319] No. 57 deviated from the range of the present application in terms of Mg / Si ratio, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0320] No. 63, 65, 67, 69, 71, 73, 75, 77, 79, 80 deviated from the range of the present application in terms of the elements of Group C, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0321] No. 78 deviated from the range of the present application in terms of Fe, and I1 and I2 deviated from the range of the present application, so that the corrosion resistance in water was reduced. No. 115 deviated from the range of the present application in terms of Fe, and I1 deviated from the range of the present application, so that the corrosion resistance in water was reduced. No. 116 deviated from the range of the present application in terms of Fe, and Formula (1) deviated from the range of the present application, so that I1 deviated from the range of the present application, so that the corrosion resistance in water was reduced.

[0322] No. 82, 84, 86, 88, 90, 92, 94, 110, 112, 114 are out of the scope of the present application because the elements of the element group D are out of the scope of the present application, and thus, I1and I2are out of the scope of the present application, and thus, the corrosion resistance in water is reduced.

[0323] On the other hand, as shown in Tables 1A to 4C, the chemical composition of the plated layer of the hot-dip plated steel material other than the above, I1and I2satisfy the scope of the present application, and the corrosion resistance in water is excellent. The thickness of the plated layer of these hot-dip plated steel materials is in the range of 70 to 90 μm in terms of the thickness per single face, the thickness of the Al-Fe alloy layer is in the range of 50 to 60 μm, and the thickness of the Zn-Al-Mg alloy layer is in the range of 20 to 30 μm.

[0324] [Table 1A]

[0325]

[0326] The underlined part indicates that it is out of the scope of the present application.

[0327] [Table 1B]

[0328]

[0329] The underlined part indicates that it is out of the scope of the present application.

[0330] [Table 1C]

[0331]

[0332] The underlined part indicates that it is out of the scope of the present application.[Table 2A]

[0333]

[0334] The underlined part indicates that it is out of the scope of the present application.

[0335] [Table 2B]

[0336]

[0337] The underlined part indicates that it is out of the scope of the present application.

[0338] [Table 2C]

[0339]

[0340] The underlined part indicates that it is out of the scope of the present application.[Table 3A]

[0341]

[0342] The underlined part indicates that it is out of the scope of the present application.

[0343] [Table 3B]

[0344]

[0345] The underlined portion is outside the scope of the present application.

[0346] [Table 3C]

[0347]

[0348] The underlined portion is outside the scope of the present application.

[0349] [Table 4A]

[0350]

[0351] The underlined portion is outside the scope of the present application.

[0352] [Table 4B]

[0353]

[0354] The underlined portion is outside the scope of the present application.

[0355] [Table 4C]

[0356]

[0357] The underlined portion is outside the scope of the present application.

[0358] [Table 5]

[0359]

[0360] (*) The proportion of the Zn-Fe alloy layer is the proportion of each phase when the total thickness of Z is set to 1

[0361] [Table 6]

[0362]

[0363] [Table 7]

[0364]

[0365] Industrial applicability

[0366] According to the present application, a hot-dip plated steel material capable of exhibiting high corrosion resistance in water (in simulated acid rain or salt water like seawater) or in a constant water-wet environment that can cause water wetting can be provided, and thus the present application has high industrial applicability.

Claims

1. A hot-dip galvanized steel product, comprising a coating on the surface of a steel product, wherein the average chemical composition of the coating, expressed as a percentage by mass, is: A1: More than 22.5% but less than 50.0% Mg: More than 3.0% but less than 15.0% Sn: 0%–0.7% Bi: 0%~0.3% In: 0%~0.3% Ca: 0.03%–0.6% Y: 0%~0.30% La: 0%~0.30% Ce: 0%–0.30% Si: 0.03%~1.0% Cr: 0%–0.25% Ti: 0%~0.25% Ni: 0%~0.25% Co: 0%–0.25% V: 0%~0.25% Nb: 0%–0.25% Cu: 0%–0.25% Mn: 0%~0.25% Fe: 2.0%–25% Sr: 0%~0.50% Sb: 0%~0.50% Pb: 0%–0.50% B: 0%~0.50% Li: 0%~0.50% Zr: 0%~0.50% Mo: 0%–0.50% W: 0%–0.50% Ag: 0%~0.50% P: 0%–0.50%, The remaining portion contains Zn and impurities. The total amount of Sn, Bi, and In, ΣA, is 0%–0.7%. The combined stoichiometry ΣB of Ca, Y, La, and Ce is 0.03%–0.60%, while the combined stoichiometry ΣC of Cr, Ti, Ni, Co, V, Nb, Cu, and Mn is 0%–0.25%. The total amount of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P, ΣD, is 0% to 0.50%, satisfying the following equations (1) to (3). In the X-ray diffraction pattern of the plated layer surface measured using Cu-Ka rays under conditions of an X-ray output of 50 kV and 300 mA, in the case where I1 is obtained by defining the X-ray diffraction peak of Al 0.5 Fe 1.5 satisfies formula (A-2) in the case where I2 is obtained by defining the X-ray diffraction peak of Zn, Al, and MgZn2 by formula (B-1), satisfies formula (B-2) in the case where I2 is obtained by defining the X-ray diffraction peak of Zn, Al, and MgZn2 by formula (B-1), Sn≤ Si (1) 15≤ Mg / Si (2) 1.0≤ Si / Ca≤ 5.0 (3) 1.10≤Ⅰ1 (A-2) Ⅰ2≤0.25 (B-2) wherein, In formulae (1) to (3), Sn, Si, Mg, Ca are contents of each element in the plating layer in mass%, Imax(k~m°) in formula (A-1) and formula (B-1) is a maximum value of X-ray diffraction intensity between diffraction angles k~m°, I(n°) in formula (A-1) is X-ray diffraction intensity at diffraction angle n°, k, m, n are diffraction angles shown in formula (A-1) and formula (B-1), respectively.

2. The hot-dip plated steel product according to claim 1, wherein, in an X-ray diffraction pattern of the plating layer surface measured using Cu-Ka rays with an X-ray output of 50 kV and 300 mA, I3 calculated from an X-ray diffraction peak of MgZn2 defined by formula (C-1) satisfies formula (C-2), I3≤ 0.03 (C-2) Imax(k~m°) in formula (C-1) is a maximum value of X-ray diffraction intensity between diffraction angles k~m°, k, m are diffraction angles shown in formula (C-1). wherein 3. The hot-dip plated steel product according to claim 1 or claim 2, wherein, in an X-ray diffraction pattern of the plating layer surface measured using Cu-Ka rays with an X-ray output of 50 kV and 300 mA, I4 calculated from an X-ray diffraction peak of Ca(Al2Si2)O8 defined by formula (D-1) satisfies formula (D-2), 1.1≤ I4 (D-2) Imax(k~m°) in formula (D-1) is a maximum value of X-ray diffraction intensity between diffraction angles k~m°, Imax(n°) is X-ray diffraction intensity at diffraction angle n°, k, m, n are diffraction angles shown in formula (D-1). ​ wherein ​

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