Hot-dip galvanized steel sheet

Abstract

A hot-dip galvanized steel sheet, wherein the coating layer contains Al: more than 30.0% and 50.0% or less, Mg: more than 5.0% and 15.0% or less, Si: more than 0.5% and 1.0% or less when Al is more than 30.0% and less than 35.0%, 0.03% - 1.0% when Al is 35.0% - 50%, Fe: 0% - 5.0%, and the balance contains Zn and impurities. In the X-ray diffraction pattern of the coating surface, I1 obtained from the X-ray diffraction peaks of Zn, Al, and MgZn2 is 0.10 or less, and I2 obtained from the X-ray diffraction peak of Al2O5Si is 1.05 or more.

Description

Technical Field

[0001] The present invention relates to hot-dip coated steel sheets.

[0002] This application claims priority based on Japanese Patent Application No. 2022-024939 filed in Japan on February 21, 2022, and the contents are incorporated herein by reference. Background Art

[0003] Plated steel products are classified into post-plated products and pre-plated products according to the different manufacturing methods. Post-plated products are manufactured by processing a steel sheet into a steel material of a specified shape, and then immersing the steel material in a hot-dip galvanizing bath (dip coating method; Japanese: どぶ漬けめっき法). On the other hand, pre-plated products are manufactured by continuously immersing a steel sheet in a hot-dip galvanizing bath to form a hot-dip plated steel sheet, and then processing the hot-dip plated steel sheet into a specified shape. JIS H 8641:2007 specifies the type, symbol, plating quality, appearance, and adhesion amount for post-plated products. For example, the adhesion amount of the plating with the symbol HDZ35 is set to 350g / m 2 As for the plating of symbol HDZ55, the adhesion amount is set to 550g / m 2 above.

[0004] Such plated steel is used in various applications, but in particular, it is used in water under severe corrosive conditions. As an example of the use of such plated steel, steel waterways / water collection tanks are envisioned. According to the homepage of the Japan Hot Dip Galvanizing Association, "About Galvanizing", the corrosion rate of zinc in water is 30 to 100 g / m 2 This means that even for post-plated products with relatively thick plating thickness, equivalent to the symbol HDZ35 to 55, the life of the plating layer will end in 3 to 5 years at the earliest.

[0005] Therefore, in the use in the water environment or the use that may cause water wetting (getting wet by water), the thickness of the plating needs to be quite thick, and for such use, post-plated products manufactured by the dip coating method are often used. On the other hand, the pre-plated products use hot-dip galvanized steel sheets or zinc alloy plated steel sheets manufactured by various steel manufacturers as raw materials, but the plating thickness of these plated steel sheets is less than about 1 / 3 of the plating thickness of the post-plated products, so in the water environment or the environment that causes water wetting, it is extremely disadvantageous in terms of the durability.

[0006] The inventors of the present invention have studied the application of pre-coated products as coated steel materials used in an underwater environment or an environment that causes water wetting. For example, Zn-based coated steel sheets as shown in Patent Documents 1 to 3 have been developed. As a result, although corrosion resistance can be ensured even in underwater / water-wetting applications, there is still room for further improvement. If the corrosion resistance in an underwater or water-wetted environment can be further enhanced, it is expected that pre-coated products will be more widely adopted as coated steel materials used in water tanks / rivers / coasts, etc.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: International Publication No. 2018 / 139619

[0010] Patent Document 2: International Publication No. 2018 / 139620

[0011] Patent Document 3: International Publication No. 2019 / 221193 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] In view of the above circumstances, the present invention has been made, and the problem is to provide a hot-dip galvanized steel sheet that can exhibit high corrosion resistance in an underwater or constantly water-wetted environment that can cause water wetting.

[0014] Means for Solving the Problems

[0015] To solve the above problems, the present invention adopts the following configuration.

[0016] [1] A hot-dip galvanized steel sheet having a coating layer on the surface of the steel sheet,

[0017] The average chemical composition of the above coating layer is by mass%:

[0018] Al: More than 30.0% and 50.0% or less,

[0019] Mg: More than 5.0% and 15.0% or less,

[0020] Sn: 0% to 0.70%,

[0021] Bi: 0% to 0.30%,

[0022] In: 0% to 0.30%,

[0023] Ca: 0.03% to 0.60%,

[0024] Y: 0% to 0.30%,

[0025] La: 0% to 0.30%,

[0026] Ce: 0% to 0.30%,

[0027] Si: More than 0.5% and 1.0% or less when Al exceeds 30.0% and is less than 35.0%, 0.03% to 1.0% when Al is 35.0% - 50.0%,

[0028] Cr: 0% to 0.25%,

[0029] Ti: 0% to 0.25%,

[0030] Ni: 0% to 1.0%,

[0031] Co: 0% to 0.25%,

[0032] V: 0% to 0.25%,

[0033] Nb: 0% to 0.25%,

[0034] Cu: 0% to 0.25%,

[0035] Mn: 0% to 0.25%,

[0036] Fe: 0% to 5.0%,

[0037] Sr: 0% to 0.5%,

[0038] Sb: 0% to 0.5%,

[0039] Pb: 0% to 0.5%,

[0040] B: 0% to 0.5%,

[0041] Li: 0% to 0.5%,

[0042] Zr: 0% to 0.5%,

[0043] Mo: 0% to 0.5%,

[0044] W: 0% to 0.5%,

[0045] Ag: 0% to 0.5%,

[0046] P: 0% to 0.5%,

[0047] The balance contains Zn and impurities,

[0048] The total amount ΣA of Sn, Bi and In is 0% to 0.70%,

[0049] The total content ΣB of Ca, Y, La and Ce is 0.03% to 0.60%, and the total content ΣC of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is 0% to 1.00%.

[0050] The total content ΣD of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P is 0% to 0.5%.

[0051] The following formulas (1) to (3) are satisfied.

[0052] In the X-ray diffraction pattern of the above-mentioned coating surface measured under the conditions of using Cu-Kα rays and an X-ray output of 50 kV and 300 mA, when I1 is defined by formula (A-1) from the X-ray diffraction peaks of Zn, Al and MgZn2, formula (A-2) is satisfied.

[0053] When I2 is defined by formula (B-1) from the X-ray diffraction peak of Al2O5Si, formula (B-2) is satisfied.

[0054] Sn ≤ Si (1)

[0055] 15 ≤ Mg / Si (2)

[0056] 1.0 ≤ Si / Ca ≤ 5.0 (3)

[0057]

[0058] I1 ≤ 0.10 (A-2)

[0059]

[0060] 1.05 ≤ I2 (B-2)

[0061] Among them, in formulas (1) to (3), Sn, Si, Mg, and Ca are the contents (mass %) of the respective elements in the above-mentioned coating. In formulas (A-1) and (B-1), Imax(k to m°) is the maximum value of the X-ray diffraction intensity between diffraction angles k to m°, Imax(n°) is the X-ray diffraction intensity at diffraction angle n°, and k, m, and n are the diffraction angles shown in formulas (A-1) and (B-1), respectively.

[0062] [2] For the hot-dip galvanized steel sheet according to [1], in the X-ray diffraction pattern of the above-mentioned coating surface measured under the conditions of using Cu-Kα rays and an X-ray output of 50 kV and 300 mA, when I3 is defined by formula (C-1) from the X-ray diffraction peak of MgZn2, formula (C-2) is satisfied.

[0063]

[0064] I3 ≤ 0.03 (C - 2)

[0065] Among them, Imax(k~m°) in formula (C - 1) is the maximum value of the X - ray diffraction intensity between diffraction angles k~m°, and k and m are the diffraction angles shown in formula (C - 1) respectively.

[0066] Advantages of the Invention

[0067] According to the present invention, it is possible to provide a hot - dip galvanized steel sheet that can exhibit high corrosion resistance in water (simulated acid rain or salt water such as seawater) or a constantly water - wetted environment that can cause water wetting. It should be noted that in the following description, "simulated acid rain" is sometimes referred to as water with a relatively low salt concentration, and "seawater (salt water)" is sometimes referred to as water with a relatively high salt concentration. Brief Description of the Drawings

[0068] Figure 1 It is a schematic diagram for explaining formula (B - 1). Detailed Description of the Invention

[0069] The inventors of the present invention have conducted in - depth research on a hot - dip galvanized steel sheet having a coating containing Al, Mg, and Zn and manufactured by a continuous hot - dip galvanizing method in order to improve the corrosion resistance in a constantly water - wetted environment.

[0070] If Zn is contained in the coating, it is possible to form a Zn phase in the structure of the coating. Since the Zn phase is easily corroded in water and the corrosion proceeds until the Zn phase disappears, it cannot be used as the main phase of the coating. In a coating containing Al, Mg, and Zn, various intermetallic compound phases are confirmed. However, in the present invention, in order to limit the phase amount of the Zn phase, its chemical composition is adjusted, especially the amount of Al is increased.

[0071] If the amount of Al is increased, a large amount of Al phase is formed in the structure of the coating. In water with a relatively low salt concentration such as soft water / hard water / acid rain, the Al phase has excellent corrosion resistance, so Al can also be contained. It is considered that the reason for the excellent water resistance of the Al phase is that an alumina film such as Al2O3 is formed on the surface of Al. However, when the amount of Al is low, since the effect of this film is insufficient, the surface needs to be covered with an oxide that is stable in water. Adding Si, which is also stable as an oxide, to the coating is useful, and the corrosion resistance in water can be ensured by containing an Al - Si - O - based compound.

[0072] On the other hand, in seawater containing salt, since Al is easily corroded, the Al content has to be limited. In order to improve the corrosion resistance to salt water while increasing the amount of Al, it is preferred to increase the proportion of those with complex crystal structures such as intermetallic compounds, for example, preferably contain a large amount of MgZn2 phase. However, in the case of containing a large amount of MgZn2 phase, it is necessary to reduce the specific plane-oriented MgZn2 phase contained in the ternary eutectic structure so that the coarse-grained MgZn2 phase grows greatly. This is because: most of the MgZn2 phases present in the ternary eutectic together with the Zn phase, Al phase, etc. are easily corroded. It is believed that the reason is: the coupling reaction caused by the surrounding organization is vigorous; and there is a specific orientation of the MgZn2 phase in the ternary eutectic structure. By limiting the specific plane-oriented MgZn2 phase contained in the ternary eutectic structure, extremely high corrosion resistance can be exerted even in salt water.

[0073] On the other hand, if a large amount of Al is contained in the plating bath containing Al, Mg and Zn, when the steel sheet is immersed, the iron contained in the steel sheet reacts with the Al in the plating bath to generate Fe-Al compounds, which become an interface alloy layer and are formed between the plating layer and the steel sheet. If the interface alloy layer is formed thickly, the plating layer becomes relatively thinner and sufficient corrosion resistance cannot be obtained. In addition, the adhesion of the plating layer is reduced. Therefore, in order to manufacture the hot-dip plated steel sheet of the present invention, it becomes necessary to make an effort to prevent the formation of the interface alloy layer as much as possible.

[0074] Hereinafter, a plated steel sheet according to an embodiment of the present invention will be described.

[0075] The hot-dip galvanized steel sheet according to an embodiment of the present invention is a hot-dip galvanized steel sheet having a coating on the surface of the steel sheet. The average chemical composition of the coating is, by mass%, Al: more than 30.0% and 50.0% or less, Mg: more than 5.0% and 15.0% or less, Sn: 0% to 0.70%, Bi: 0% to 0.3%, In: 0% to 0.3%, Ca: 0.03% to 0.60%, Y: 0% to 0.3%, La: 0% to 0.3%, Ce: 0% to 0.3%, Si: more than 0.5% and 1.0% or less when Al is more than 30.0% and less than 35.0%, 0.03% to 1.0% when Al is 35.0% or more and less than 50.0%, Cr: 0% to 0.25%, Ti: 0% to 0.25%, Ni: 0% to 1.0%, 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: 0% to 5.0%, Sr: 0% to 0.5%, Sb: 0% to 0.5%, Pb: 0% to 0.5%, B: 0% to 0.5%, Li: 0% to 0.5%, Zr: 0% to 0.5%, Mo: 0% to 0.5%, W: 0% to 0.5%, Ag: 0% to 0.5%, P: 0% to 0.5%, and the balance contains Zn and impurities. The total amount ΣA of Sn, Bi, and In is 0% to 0.70%, the total amount ΣB of Ca, Y, La, and Ce is 0.03% to 0.60%, the total amount ΣC of Cr, Ti, Ni, Co, V, Nb, Cu, and Mn is 0% to 1.00%, and the total amount ΣD of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag, and P is 0% to 0.5%. The following formulas (1) to (3) are satisfied. In the X-ray diffraction pattern of the coating surface measured under the conditions of using Cu-Kα rays and an X-ray output of 50 kV and 300 mA, when I1 is defined by formula (A-1) from the X-ray diffraction peaks of Zn, Al, and MgZn2, formula (A-2) is satisfied. When I2 is defined by formula (B-1) from the X-ray diffraction peak of Al2O5Si, formula (B-2) is satisfied.

[0076] Sn ≤ Si (1)

[0077] 15 ≤ Mg / Si (2)

[0078] 1 ≤ Si / Ca ≤ 5.0 (3)

[0079]

[0080] I1 ≤ 0.10 (A-2)

[0081]

[0082] 1.05 ≤ I2 (B - 2)

[0083] Among them, in formulas (1) to (3), Sn, Si, Mg, and Ca are the contents (mass %) of each element in the coating. In formulas (A - 1) and (B - 1), Imax(k~m°) is the maximum value of the X - ray diffraction intensity between diffraction angles k and m°, Imax(n°) is the X - ray diffraction intensity at diffraction angle n°, and k, m, and n are the diffraction angles shown in formulas (A - 1) and (B - 1), respectively.

[0084] It should be noted that in the following description, "%" of the content of each element in the chemical composition refers to "mass %". In addition, the numerical range represented by "~" means a range that includes the numerical values recorded before and after "~" as the lower limit value and the upper limit value. In addition, when numerical values recorded before and after "~" are marked with "exceeding" or "lower than", the numerical range means a range that does not include these numerical values as the lower limit value or the upper limit value.

[0085] In addition, "corrosion resistance" represents the property of the coating itself being not easily corroded. Since the Zn - based coating has a substitutional anticorrosion effect on steel, before the steel corrodes, the coating corrodes and turns white - rusted. After the white - rusted coating disappears, the steel corrodes and red - rust is generated. This is the corrosion process of the coated steel sheet.

[0086] The steel sheet to be coated will be described.

[0087] The shape of the steel sheet is mainly a sheet, but there is no particular limitation on its size. It is a sheet manufactured through the usual hot - dip galvanizing process. The coated steel sheet manufactured through a process of dipping in molten metal and solidifying it, such as a continuous hot - dip galvanizing line (CGL), conforms to this sheet. If these sheets are processed (including welding) and combined, various products can be processed, and steel structure members (pre - coated products) with excellent corrosion resistance can be manufactured.

[0088] There is no particular limitation on the base material of the steel sheet. For example, various steel sheets such as general steel, pre - coated steel thinly coated with various metals, Al - killed steel, extra - low - carbon steel, high - carbon steel, various high - tensile steels, and some high - alloy steels (steels containing corrosion - resistance strengthening elements such as Ni and Cr) can be used. In addition, regarding the steel sheet, there are no particular limitations on conditions such as the manufacturing method of the steel sheet (blast - furnace material, electric - furnace material) and the manufacturing method of the steel sheet (hot - rolling method, pickling method, cold - rolling method, etc.).

[0089] Next, the coating layer will be described. The coating layer of this embodiment contains a Zn-Al-Mg alloy layer. When alloying elements such as Al and Mg are added to Zn, the corrosion resistance is improved. Therefore, it has the same corrosion resistance as that of a thin film, for example, about half of the normal Zn coating layer. Thus, the present invention also ensures corrosion resistance equal to or higher than that of the Zn coating layer with a thin film. In addition, an Al-Fe alloy layer may also be included in the coating layer.

[0090] 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.

[0091] The Al-Fe alloy layer is an interfacial alloy layer located between the steel material and the Zn-Al-Mg alloy layer.

[0092] That is, the coating layer may have a single-layer structure of a Zn-Al-Mg alloy layer, or may have a laminated structure including a Zn-Al-Mg alloy layer and an Al-Fe alloy layer. In the case of the laminated structure, it is preferable that the Zn-Al-Mg alloy layer is set as the layer constituting the surface of the coating layer.

[0093] It should be noted that, as described below, when a hot-dip galvanized steel sheet or a hot-dip galvanized alloy steel sheet manufactured by CGL is used as the plating base plate, traces of the interfacial alloy layer formed when the steel sheet is immersed remain. On the other hand, when an electrogalvanized steel sheet or the like is used as the base plate, traces of the interfacial alloy layer and the like basically disappear, and it may be basically impossible to confirm an Al-Fe alloy layer or the like. In addition, when a Ni pre-coated steel sheet is used as the plating base plate, or when Sn, Cr, etc. are used for the plated steel sheet in advance, these metals may be mixed into the interfacial alloy layer.

[0094] Through the Al-Fe alloy layer, the steel material and the Zn-Al-Mg alloy layer are bonded. Regarding the thickness of the interfacial alloy layer, it can be arbitrarily controlled by controlling the plating bath temperature, plating bath immersion time, production line speed, and wiping pressure during the manufacture of the plated steel material. Generally, for the manufacturing method of hot-dip galvanized steel sheets represented by the Sendzimir method, since the Zn-Al-Mg alloy layer becomes the main body of the coating layer and the thickness of the Al-Fe alloy layer is sufficiently small, the influence on the corrosion resistance of the coating layer is small. In addition, since it is formed near the interface, it basically does not affect the corrosion resistance in the initial stage of corrosion and the appearance of the coating layer. Therefore, when a steel sheet that has been plated once by CGL or the like is immersed again in the plating bath of the present invention, the thickness of the interfacial alloy layer is also mostly sufficiently small, and in most cases, it is difficult to confirm the traces of the interfacial alloy layer.

[0095] The Al-Fe alloy layer is formed on the surface of the steel sheet (specifically, between the steel sheet and the Zn-Al-Mg alloy layer), and the main phase of the structure is the Al5Fe2 phase. The Al-Fe alloy layer is formed by the mutual atomic diffusion of the base metal (steel sheet) and the plating bath. When using the continuous hot-dip plating method as the manufacturing method, in the plating layer containing the Al element, the Al-Fe alloy layer is easily formed. In the present invention, since the plating bath contains Al above a certain concentration, the Al5Fe2 phase is formed the most. However, atomic diffusion takes time, and in the part close to the base metal, there is also a part where the Fe concentration becomes high. Therefore, the Al-Fe alloy layer may also contain a small amount of AlFe phase, Al3Fe phase, Al5Fe2 phase, etc. partially. In addition, since the plating bath also contains a certain concentration of Zn, in the Al-Fe alloy layer, Zn is also contained in a small amount or Si that is likely to concentrate at the interface.

[0096] In the present invention, Si is contained in the plating layer. Si is particularly likely to be incorporated into the Al-Fe alloy layer and may become an Al-Fe-Si intermetallic compound phase. As the identified intermetallic compound phase, there is the AlFeSi phase, and as isomers, there are α, β, q1, q2-AlFeSi phases, etc. Therefore, these AlFeSi phases, etc. may be detected in the Al-Fe alloy layer. The Al-Fe alloy layer containing these AlFeSi phases, etc. is also referred to as the Al-Fe-Si alloy layer.

[0097] In addition, when using a steel sheet with a pre-plating layer as the plating base plate, Ni, Sn, Cr, etc. constituting the pre-plating layer may remain in the interface alloy layer in a layered form. In particular, elements with a high melting point tend to remain in the interface alloy layer in a layered form, and may be mixed into the Al-Fe alloy layer or exist as intermetallic compounds containing these elements. Low-melting metals such as Sn are not likely to leave traces and may not be confirmed.

[0098] The thickness of the entire plating layer is affected by the plating conditions, so there is no particular limitation on the upper and lower limits of the thickness of the entire plating layer. In addition, for example, in the usual hot-dip plating method, the thickness of the entire plating layer is related to the viscosity and specific gravity of the plating bath. Furthermore, the plating amount per unit area is adjusted by the lifting speed of the steel sheet (plating base plate) and the strength of wiping. The maximum value of the thickness of the plating layer formed by the usual hot-dip plating method is mostly 100 μm or less in continuous hot-dip plating and 200 μm or less in batch plating.

[0099] On the outermost surface of the coating, an oxide film of the constituent elements of the coating is preferably formed to a thickness of less than about 1 μm. Generally, since the elements contained in the coating bond with oxygen on the coating surface, an oxide film such as Zn-O, Mg-O, Al-O, Si-O, Ca-O bonds or a thin film of Mg-Al-O, Al-Si-O, etc. can be confirmed by surface analysis such as XPS (X-ray photoelectron spectroscopy). The more easily oxidizable the element is, the more likely it is to be present on the plating surface. These oxides are films useful for ensuring high corrosion resistance in water, but since they are extremely thin, less than 1 μm, it is difficult to confirm their exact function by an electron microscope or the like. In the present invention, as described below, its presence is confirmed by X-ray diffraction measurement.

[0100] Next, the average chemical composition of the coating will be described. When the coating is a single-layer structure of a Zn-Al-Mg alloy layer, the average chemical composition of the coating is the average chemical composition of the Zn-Al-Mg alloy layer. In addition, when the coating is a laminated structure of an Al-Fe alloy layer and a Zn-Al-Mg alloy layer, it is the combined average chemical composition of the Al-Fe alloy layer and the Zn-Al-Mg alloy layer.

[0101] Generally, in a continuous hot-dip plating method, since the formation reaction of the Zn-Al-Mg alloy layer is basically completed in the plating bath, the chemical composition of the Zn-Al-Mg alloy layer becomes substantially the same as that of the plating bath. In addition, in a continuous hot-dip plating method, the Al-Fe alloy layer is instantaneously formed and grows immediately after immersion in the plating bath. Moreover, the formation reaction of the Al-Fe alloy layer is completed in the plating bath, and its thickness is mostly sufficiently small compared to the Zn-Al-Mg alloy layer. Therefore, as long as no special heat treatment such as heat alloying treatment is performed after plating, the average chemical composition of the entire coating is substantially the same as the chemical composition of the Zn-Al-Mg alloy layer, and components such as the Al-Fe alloy layer can be ignored.

[0102] Al: more than 30.0% and 50.0% or less,

[0103] Al is an element that constitutes the main body of the coating. In Zn-Al-Mg system plating, Al phase is mainly formed in the coating. If the Al content is 30.0% or less, Zn phase and ternary eutectic structure (Zn / Al / MgZn2 ternary eutectic structure containing Zn phase, Al phase, and MgZn2 phase) are formed during the solidification of the coating. The MgZn2 phase contained in the Zn phase and ternary eutectic structure has insufficient corrosion resistance in water. Therefore, in order not to form Zn phase and ternary eutectic structure, the Al content is set to exceed 30.0%. On the other hand, if the Al content exceeds 50.0%, the melting point of the plating bath rises, and thus the growth of the Al-Fe alloy layer becomes active, and a large amount of Fe is contained in the coating, which impairs the performance of the coating. Therefore, the Al content is set to 50.0% or less.

[0104] Mg: More than 5.0% and 15.0% or less

[0105] Mg, like Zn, is an element that constitutes the main body of the coating. If Mg is insufficient, the corrosion resistance in water containing salt tends to be low. Therefore, the Mg content is set to exceed 5.0%. On the other hand, when the Mg content exceeds 15.0%, there are problems with the soundness of the coating, and it is difficult to ensure corrosion resistance in water (simulated acid rain and seawater (brine)). Therefore, the Mg content is set to 15.0% or less.

[0106] Element group A

[0107] Sn: 0% to 0.70%

[0108] Bi: 0% to 0.30%

[0109] In: 0% to 0.30%

[0110] Total amount ΣA of Sn, Bi and In: 0% to 0.70%

[0111] Since each element of element group A (Sn, Bi, In) is an optionally contained element, their respective contents are set to 0% or more. If Sn is contained, there is a tendency to form Mg9Sn5 in the coating. Bi also forms Mg3Bi2, and In also forms Mg3In, etc. Thus, there is a tendency to improve the corrosion resistance in brine. If the content of these elements is small, the influence on the corrosion resistance in water (simulated acid rain and seawater (brine)) is small, but if they are contained in excess, the corrosion resistance in simulated acid rain / brine deteriorates extremely. Therefore, it is necessary to limit the upper limit of their content. Since any element shows the same effect, element group A needs to be managed by its total amount. The total amount of element group A needs to be set to 0.70% or less.

[0112] Element group B

[0113] Ca: 0.03% to 0.60%

[0114] Y: 0% to 0.30%

[0115] La: 0% to 0.30%

[0116] Ce: 0% to 0.30%

[0117] Total content ΣB of Ca, Y, La and Ce: 0.03% to 0.60%

[0118] To ensure corrosion resistance in water (simulated acid rain and seawater (brine)), it is necessary to form Al-Ca-Si based compounds near the interface between the coating and the steel sheet. In particular, Ca has a tendency to bond with Si, and Al-Ca-Si based compounds are easily formed when the composition range satisfies 1 ≤ Si / ΣB ≤ 5. If the Ca content is high, in addition to forming Al-Ca-Si based compounds, Al 2.15 Zn 1.85 Ca, etc. are also formed. It is speculated that these compounds have high corrosion resistance in simulated acid rain / brine, especially around the interfacial alloy layer formed by bonding with Si near the base metal, thus ensuring plating adhesion and contributing to the corrosion prevention of the base metal near the interface in water. It should be noted that in order to adjust the formation of these compounds near the interface, it is closely related to the manufacturing method disclosed in the present invention. Based on the above situation, the Ca content is set to 0.03% to 0.60%.

[0119] Elements such as Y, La, and Ce play the same role as Ca. These elements are optional addition elements and tend to replace Ca when present. However, in the case of no Ca, even if Y, La, and Ce are contained, sufficient performance may not be achieved. Y, La, and Ce form mutual substitution bodies with each other by being contained within the range of 0.30% or less respectively, and play the same role as Ca in water (simulated acid rain and seawater (brine)). However, if Y, La, and Ce exceed 0.30% respectively, the corrosion resistance in water (simulated acid rain and seawater (brine)) deteriorates extremely. Therefore, the content of Y, La, and Ce is set to 0.30% or less respectively.

[0120] In addition, even if the total content of the elements in element group B becomes excessive, the corrosion resistance in water (simulated acid rain and seawater (brine)) deteriorates. Therefore, the total content ΣB of Ca, Y, La, and Ce is set to 0.03% to 0.60%.

[0121] Si:

[0122] When Al is more than 30.0% and less than 35.0%, Si is more than 0.5% and 1.0% or less

[0123] When Al is 35.0% to 50.0%, Si is 0.03% to 1.0%

[0124] Si is an element required to form intermetallic compounds in the coating. In a plating bath with Al of 35.0% to 50.0%, usually in most cases, the bath temperature exceeds 500°C. If the steel sheet is immersed in the plating bath in this temperature range, the Al-Fe alloying reaction proceeds excessively, the Fe concentration in the coating becomes high, and the corrosion resistance in water tends to deteriorate. Therefore, when Al is 35.0% or more, the Si content needs to be set at 0.03% or more. By containing Si in the coating to form Al-Ca-Si compounds, the excessive Al-Fe reaction can be suppressed. It should be noted that the formation of compounds such as Al-Ca-Si is closely related to the manufacturing method disclosed in the present invention. These compounds and the like concentrate near the interface between the coating and the steel sheet, becoming able to suppress Fe diffusion, and the structure in the coating forms a suitable structure according to the solidification process.

[0125] On the other hand, when Al is in the range of more than 30.0% and less than 35.0%, the Al content is relatively small, and the corrosion resistance in water is likely to be insufficient. In this case, if the Si content is set to more than 0.5%, Al-Si-O oxides are formed on the coating surface, and the corrosion resistance in water can be ensured. Therefore, when Al is in the range of more than 30.0% and less than 35.0%, the Si content is set to more than 0.5%. It should be noted that for the formation of Al-Si-O oxides, the coating needs to be formed in an atmosphere with an oxygen concentration above a certain concentration.

[0126] In addition, Si is an element that easily bonds with Ca. For example, it easily forms various Al-Ca-Si compounds such as CaAlSi, Al2CaSi2, Ca2Al4Si3, and Ca2Al3Si4. However, excessive Si impairs the corrosion resistance of the coating in water. Thus, the Si content is set to 1.0% or less.

[0127] Element group C

[0128] Cr: 0% to 0.25%

[0129] Ti: 0% to 0.25%

[0130] Ni: 0% to 1.0%

[0131] Co: 0% to 0.25%

[0132] V: 0% to 0.25%

[0133] Nb: 0% to 0.25%

[0134] Cu: 0% to 0.25%

[0135] Mn: 0% to 0.25%

[0136] Total amount ΣC of Cr, Ti, Ni, Co, V, Nb, Cu and Mn: 0% to 1.00%

[0137] The elements of element group C are metal elements that can be contained in the coating layer and may also be contained. The presence of these metal elements in the coating layer has a tendency to displace with Al, Zn, etc. and the potential of the coating layer moves towards a higher potential. By containing within this concentration range, there is a tendency to improve the corrosion resistance in water (especially simulated acid rain). Excessive containment of these elements will form intermetallic compounds containing these elements, thus deteriorating the corrosion resistance in water. Therefore, the contents of Cr, Ti, Co, V, Nb, Cu, and Mn are each set to 0.25% or less. The content of Ni is set to 1.0% or less. The total amount of the elements of element group C is set to 0 to 1.00%.

[0138] Fe: 0% to 5.0%

[0139] Since the hot-dip galvanized steel sheet of this embodiment is manufactured by a continuous hot-dip coating method, it is possible for Fe to diffuse from the coating base plate to the coating layer during manufacturing. In the coating layer, Fe may contain up to 5.0% at most, but no change in corrosion resistance due to the containment of this element has been confirmed. Therefore, the Fe content is set to 0 to 5.0%.

[0140] Element group D

[0141] Sr: 0% to 0.5%

[0142] Sb: 0% to 0.5%

[0143] Pb: 0% to 0.5%

[0144] B: 0% to 0.5%

[0145] Li: 0% to 0.5%

[0146] Zr: 0% to 0.5%

[0147] Mo: 0% to 0.5%

[0148] W: 0% to 0.5%

[0149] Ag: 0% to 0.5%

[0150] P: 0% to 0.5%

[0151] Total amount ΣD of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P is 0% to 0.5%

[0152] The elements of element group D may also be contained in the coating layer. These elements have the same effects as the elements of element group C described above and are elements that are relatively easy to contain compared to element group C. Therefore, the content of each element of element group D is set to 0 to 0.5%, respectively. In addition, the total content of the elements of element group D is set to 0 to 0.5%.

[0153] Remainder: Zn and impurities

[0154] It is preferable to contain Zn in the remainder. The hot-dip galvanized steel sheet of the present embodiment is a Zn-based coated steel sheet with high versatility. By containing a certain amount or more of Zn for the purpose of ensuring substitutional corrosion resistance, it is possible to impart appropriate substitutional corrosion resistance, etc. to the steel sheet. Regarding the corrosion resistance in water with a low salt concentration, it is preferable that the content of Al is relatively large. However, in water containing a relatively large amount of salt such as seawater, in order to ensure corrosion resistance, it is necessary to ensure corrosion resistance by containing intermetallic compounds such as MgZn2 of the Zn-Mg system. In order to ensure the necessary amount of the Zn-Mg-based intermetallic compound, the remainder is set to Zn.

[0155] Impurities refer to components contained in the raw materials or components mixed in during the manufacturing process, and are components that are not intentionally contained. For example, in the coating layer, due to the mutual atomic diffusion between the steel material (base metal) and the plating bath, it is possible that components other than Fe are also slightly mixed in as impurities.

[0156] In addition, the coating layer of the present embodiment needs to satisfy the following formulas (1) to (3). Sn, Si, Mg, and Ca in formulas (1) to (3) are the contents (mass%) of the respective elements in the coating layer.

[0157] Sn ≤ Si (1)

[0158] 15 ≤ Mg / Si (2)

[0159] 1.0 ≤ Si / Ca ≤ 5.0 (3)

[0160] Sn ≤ Si

[0161] The Si content needs to be set to be equal to or higher than the Sn content. If the Si content becomes lower than the Sn content, excessive Fe diffuses from the steel sheet into the coating layer, and it becomes difficult to form the target intermetallic compound.

[0162] 15 ≤ Mg / Si

[0163] Furthermore, regarding the Si content, it is necessary to satisfy 15 ≤ Mg / Si. Thereby, the corrosion resistance in water (simulating acid rain and seawater (brine)) is improved. If the Si content becomes higher relative to the Mg content and Mg / Si becomes lower than 15, a large amount of Mg2Si is formed in the coating, and the corrosion resistance in water (simulating acid rain and seawater (brine)) cannot be fully exerted. It is preferably satisfied that 20 ≤ Mg / Si. By making Mg / Si 20 or more, the corrosion resistance in brine is further improved.

[0164] 1.0 ≤ Si / Ca ≤ 5.0

[0165] Si and Ca are likely to bond with each other and easily form compounds. In addition, Y, La, or Ce also easily bond with Si. When Si / Ca is lower than 1.0, a large amount of Ca-Al-Zn-based compounds are formed, and it becomes difficult to form Al-Ca-Si-based compounds near the interface between the coating and the steel sheet, and the corrosion resistance in water is significantly impaired. In addition, if Si / Ca exceeds 5.0, the effect of containing Ca in the coating becomes small, a large amount of Mg2Si is formed, and Al-Ca-Si-based compounds are not formed, and the corrosion resistance in water is significantly impaired. Therefore, this index is introduced as a management index. When 1.0 ≤ Si / Ca ≤ 5.0 is satisfied, the corrosion resistance in brine is improved. More preferably, it is satisfied that 1.0 ≤ Si / Ca ≤ 4.0. Thereby, the amount of Mg2Si can be suppressed, and a sufficient amount of Al-X-Si is formed to sufficiently ensure the corrosion resistance in water. Further preferably, it is satisfied that 1.0 ≤ Si / Ca ≤ 3.0. Thereby, the corrosion resistance in brine is further improved.

[0166] For the identification of the average chemical composition of the coating, the coating is peeled and dissolved with an acid containing an inhibitor that inhibits the corrosion of the base metal (steel) to obtain an acid solution. Then, by measuring the obtained acid solution by ICP emission spectrometry or ICP-MS method, the chemical composition can be obtained. The acid type is not particularly limited as long as it can dissolve the coating. If the area and weight before and after peeling are measured, the plating adhesion amount (g / m 2 ) can also be obtained simultaneously.

[0167] Next, the intermetallic compounds contained in the coating will be described. Since the coating of this embodiment is a Zn-Al-Mg-based alloy coating, a Zn phase, an Al phase, and an MgZn2 phase are contained in the coating. The corrosion resistance changes depending on the content of each phase, but by controlling the coating structure containing intermetallic compounds, etc., the corrosion resistance in water (simulating acid rain and seawater (brine)) environment can be ensured.

[0168] Zn phase

[0169] The Zn phase exists in the coating and mainly exists as a ternary eutectic structure (Zn / Al / MgZn2 ternary eutectic structure). There is also a Zn phase that is not included in the ternary eutectic structure. The Zn phase and the ternary eutectic structure containing the Zn phase have low corrosion resistance in water (simulating acid rain and seawater (brine)). If immersed in water, they will disappear within a short period. Therefore, it is necessary not to contain the Zn phase. In the present invention, the presence or absence of the Zn phase is strictly restricted, so that the Zn contained in the coating is dissolved in the Al phase or made into an intermetallic compound as the MgZn2 phase. Thus, the corrosion resistance of the coating in water (simulating acid rain and seawater (brine)) can be ensured.

[0170] Al phase

[0171] The Al phase exists in the coating as massive Al primary crystals. In the coating of the present invention, a certain amount of Zn is contained, but the massive Al phase contains up to about 35% of Zn at most. Therefore, strictly speaking, the massive Al primary crystal is the Al-Zn phase. The Al-Zn phase is a collection of extremely fine grains. If confirmed by crystal size, it is a structure formed by the aggregation of fine grains of several nm to about 3 μm. Sometimes, through X-ray diffraction or TEM, etc., it is confirmed as a structure containing fine Al and Zn phases. In the present invention, such a fine structure is also called the Al phase. The Al phase that can contain up to about 35% of Zn forms a stable oxide film such as Al2O3 on the surface, and has high corrosion resistance in water (simulating acid rain) in particular. It is speculated that the Al concentration in this oxide film needs to exceed 35%. On the other hand, in water containing salts, Al2O3 cannot exist stably, and the corrosion resistance deteriorates extremely.

[0172] MgZn2 phase

[0173] The MgZn2 phase exists in the coating. In addition to existing as massive MgZn2, it also contains a certain amount as fine grains in the dendritic structure or ternary eutectic structure (Zn / Al / MgZn2 ternary eutectic structure) formed when solidifying with the Al phase on the Al-MgZn2 eutectic line. The MgZn2 phase has good corrosion resistance in water and high corrosion resistance in both simulated acid rain / sea water. On the other hand, the corrosion resistance of the MgZn2 phase has a particle size dependence, and the MgZn2 etc. contained in the ternary eutectic structure tend to be easily corroded by coupling reactions etc. The MgZn2 contained in the ternary eutectic structure shows a diffraction peak of the (102) plane in X-ray diffraction measurement. Therefore, by reducing the MgZn2 phase showing the orientation of the (102) plane, there is a tendency to improve the corrosion resistance in water (simulating acid rain and seawater (brine)).

[0174] As described above, the inventors of the present invention sought to improve the coating for the purpose of ensuring corrosion resistance in water (simulated acid rain and seawater (brine)). As a result, it was found that corrosion resistance in water can be ensured by forming a specific intermetallic compound. In order to determine the presence of a specific intermetallic compound in the coating, X-ray diffraction is preferably used. This detection method can obtain average information of the coating compared to SEM observation, TEM observation, etc., has less selectivity in the measurement site (field of view), and is excellent in quantification. In addition, if the measurement conditions are specified, when a specific intermetallic compound is present, the diffraction peak intensity is obtained at a specific ratio at the same angle (2θ), so the internal structure of the coating can be simply estimated.

[0175] The conditions for obtaining the X-ray diffraction image are set as described below.

[0176] As the X-ray source, the X-ray diffraction method using Cu as the target is the most convenient because it can obtain average information of the constituent phases in the coating. As an example of the measurement conditions, the conditions of the X-ray are set to a voltage of 50 kV and a current of 300 mA. There is no particular limitation on the X-ray diffraction apparatus, but for example, a sample horizontal type high-power X-ray diffraction apparatus RINT-TTR III manufactured by Rigaku Corporation can be used.

[0177] Hereinafter, the substances to be measured in the X-ray diffraction measurement will be described. The substances to be measured are Zn, Al, MgZn2, and Al2O5Si.

[0178] Zn

[0179] Zn is a substance represented by database number (ICDD-JCPDS powder diffraction database) 00-004-0831. In the coating composition range of the present embodiment, there is 1 angle convenient for detecting Zn. That is, the diffraction angle 2θ is 36.30° ((002) plane).

[0180] Al

[0181] In the coating composition range of the present embodiment, there is 1 angle convenient for detecting Al. That is, the diffraction angle 2θ is 38.47° ((111) plane).

[0182] MgZn2

[0183] In the coating composition range of the present embodiment, there is 1 angle convenient for detecting this intermetallic compound. That is, the diffraction angle 2θ is 19.67° ((100) plane).

[0184] Al2O5Si

[0185] Al2O5Si is a substance represented by database number (ICDD-JCPDS powder diffraction database) 01-075-4827. In the composition range of the coating in this embodiment, the diffraction angle convenient for detecting this intermetallic compound is 16.18° (110 plane) in terms of 2θ.

[0186] Since the diffraction peaks at the above diffraction angles do not overlap with the diffraction peaks of the main crystal structure of the coating, it is convenient for quantification and determination of the content. That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target substance is indeed contained.

[0187] In the X-ray diffraction pattern of the coating surface obtained by X-ray diffraction using a Cu target for the coating surface (X-ray output is 50 kV, 300 mA), I1 is defined by formula (A-1) from the X-ray diffraction peaks of Zn, Al, and MgZn2. In this case, in order to ensure the corrosion resistance of the hot-dip galvanized steel sheet in water (simulating acid rain and seawater (brine)), it is necessary to satisfy formula (A-2).

[0188]

[0189] I1 ≤ 0.10 (A-2)

[0190] In formula (A-1), Imax(k~m°) is the maximum value of the X-ray diffraction intensity between diffraction angles k~m°, and k and m are the diffraction angles shown in formula (A-1) respectively.

[0191] That is, Imax(36.00~36.60°) in formula (A-1) is the maximum value of the X-ray diffraction intensity between diffraction angles 36.00~36.60°, corresponding to the diffraction intensity of the (002) plane of Zn.

[0192] Imax(38.00~39.00°) is the maximum value of the X-ray diffraction intensity between diffraction angles 38.00~39.00°, corresponding to the diffraction intensity of the (111) plane of Al.

[0193] Imax(19.20~20.00°) is the maximum value of the X-ray diffraction intensity between diffraction angles 19.20~20.00°, corresponding to the diffraction intensity of the (100) plane of MgZn2.

[0194] Therefore, I1 defined by formula (A-1) represents the ratio of the diffraction intensity of Zn to the total diffraction intensity of Zn, Al, and MgZn2. The smaller I1 is, the less Zn phase there is in the coating. In this embodiment, I1 is set to 0.10 or less. Thereby, the corrosion resistance in water can be ensured. That is, in the coating, the low ratio of the Zn phase leads to an improvement in the corrosion resistance in water, and the coating can be maintained in water. The lower limit of I1 does not need to be particularly limited, but it can also be 0 or more.

[0195] Next, when Al exceeds 30.0% and is less than 35.0%, the Al concentration in the coating is relatively low, and there is a lack of a highly blocking film such as Al2O3 that maintains the corrosion resistance in water (especially simulated acid rain). On the other hand, when Al exceeds 30.0% and is less than 35.0%, Si is contained in an amount exceeding 0.5% and being 1.0% or less. However, within the composition range of Al and Si, Al2O5Si that exhibits high corrosion resistance in water can be obtained as the oxide film of the coating. It should be noted that even when the Al content is 35.0% or more, this oxide film is formed, and there is a tendency for the corrosion resistance in simulated acid rain to increase. Therefore, when I2 is defined by formula (B-1) from the X-ray diffraction peak of Al2O5Si, formula (B-2) needs to be satisfied.

[0196]

[0197] 1.05 ≤ I2 (B-2)

[0198] Among them, Imax(k~m°) in formula (B-1) 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) and formula (B-1), respectively.

[0199] Imax(15.60°~16.60°) in formula (B-1) is the maximum value of the X-ray diffraction intensity between diffraction angles 15.60°~16.60°, corresponding to the diffraction intensity of the (110) plane of Al2O5Si. I(15.60°) and I(16.60°) are the X-ray diffraction intensities at diffraction angles 15.60° and 16.60°, respectively, corresponding to the background intensity of the diffraction peak of the (110) plane of Al2O5Si.

[0200] The numerator of formula (B-1) (Imax (15.60 to 16.60°)) is the intensity of the diffraction peak corresponding to 2θ = 16.18° ((110) plane) of Al2O5Si, which is the maximum diffraction intensity of the diffraction peak including the background intensity. Due to the measurement error of X-ray diffraction, it is possible that the diffraction angle of the (110) plane deviates from 16.18°, so the maximum value between 15.60 and 16.60° is obtained.

[0201] The denominator of formula (B-1) is a value obtained by calculating the background intensity at the diffraction angle of 16.18° from the diffraction intensities at 15.60° and 16.60°. That is, as Figure 1 shown, draw a straight line connecting the diffraction line at 15.60° and the diffraction line at 16.60°. This straight line becomes the baseline of the diffraction peak. Then, calculate I(15.60°) - I(16.60°). In addition, calculate the ratio of the difference between the diffraction angles of 15.60° and 16.18° (0.58°) to the difference between the diffraction angles of 15.60° and 16.60° (1.00°) (0.58 / 1.00 = 0.58). Then, calculate the background intensity at the diffraction angle of 16.18° through the mathematical formula described in the denominator of the above formula (B-1).

[0202] By setting formula (B-1) through the above operations, even if there are measurement errors or background variations due to different measurement conditions, the intensity of the diffraction peak of 2θ = 16.18° (110) of Al2O5Si can be accurately measured.

[0203] As shown in formula (B-2), by having I2 be 1.05 or more, corrosion resistance in water (especially simulated acid rain) can be ensured. A larger value of I2 is also preferred, but no obvious effect can be confirmed when Al is more than 30.0% and less than 35.0%.

[0204] When the Al concentration is 35.0% or more, there is a tendency for the corrosion resistance in salt water to increase in the range of I2 = 1.05 to 20. In addition, I2 is more preferably I2 = 3 to 20. When the Si concentration is high, there is a tendency to become a large value. The lower limit of I2 does not need to be particularly limited, but it can be 0 or more, or more than 0.

[0205] In order to satisfy formula (A-2) and (B-2), it is necessary for the chemical composition of the coating to meet the scope of the present invention, and appropriate plating manufacturing methods, heat treatment, and atmosphere control are carried out in the manufacturing method.

[0206] Next, within the compositional range of the coating in the present embodiment, the MgZn2 phase crystallizes. The MgZn2 phase inherently has high corrosion resistance in water, but if it is surrounded by fine Al and Zn phases, corrosion is promoted through the coupling reaction between these phases. In addition, the corrosion potential of the MgZn2 phase is lower than that of the Zn phase. Therefore, the MgZn2 phase surrounded by the Al and Zn phases dissolves out early in water. Examples of such MgZn2 phases include the MgZn2 phase contained in the ternary eutectic structure in the coating. 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.

[0207] As a diffraction angle that facilitates the detection of the MgZn2 phase contained in the ternary eutectic structure by X-ray diffraction, there is one angle. The diffraction intensity of the (102) plane of most of the MgZn2 phase contained in the ternary eutectic structure is strong. That is, the diffraction peak that appears at the diffraction intensity of the (102) plane with a diffraction angle of 2θ = 28.73° does not overlap with the diffraction peaks of the main crystal structure of the coating, so it is convenient for quantification and determination of the content. That is, if a diffraction peak with a diffraction intensity exceeding a certain amount is obtained at these diffraction angles, it can be said that the target phase is indeed contained.

[0208] The MgZn2 phase showing a crystal orientation other than the (102) plane is a coarse MgZn2 phase that covers the Al phase through a peritectic reaction or a coarse MgZn2 phase precipitated by other than the ternary eutectic reaction, and has high corrosion resistance in water. These MgZn2 phases with excellent corrosion resistance in water show diffraction intensities at diffraction angles of 2θ = 20.78° ((002) plane) and 22.26° ((101) plane) in addition to 19.67° ((100) plane). The diffraction peaks that appear at these diffraction angles do not overlap with the diffraction peaks of the main crystal structure of the coating, so it is convenient for quantification and determination of the content.

[0209] Most of the MgZn2 phase contained in the coating mostly shows one of the above four diffraction peaks. Then, in the hot-dip galvanized steel sheet of the present embodiment, in the X-ray diffraction pattern of the coating surface measured under the conditions of using Cu-Kα rays and an X-ray output of 50 kV and 300 mA, when I3 is obtained from the X-ray diffraction peak of MgZn2 defined by formula (C-1), it is preferable to satisfy formula (C-2).

[0210]

[0211] I3 ≤ 0.03 (C-2)

[0212] Among them, Imax(k~m°) in formula (C-1) is the maximum value of the X-ray diffraction intensity between diffraction angles k~m°, and k and m are the diffraction angles shown in formula (C-1) respectively.

[0213] That is, Imax(28.52~28.92°) in formula (C-1) is the maximum value of the X-ray diffraction intensity between diffraction angles 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.

[0214] Imax(19.20~20.00°) is the maximum value of the X-ray diffraction intensity between diffraction angles 19.20~20.00°, corresponding to the diffraction intensity of the (100) plane of MgZn2.

[0215] Imax(20.58~20.98°) is the maximum value of the X-ray diffraction intensity between diffraction angles 20.58~20.98°, corresponding to the diffraction intensity of the (002) plane of MgZn2.

[0216] Imax(22.06~22.45°) is the maximum value of the X-ray diffraction intensity between diffraction angles 22.06~22.45°, corresponding to the diffraction intensity of the (101) plane of MgZn2.

[0217] Therefore, I3 defined by formula (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 contained in the coating. The smaller I3 is, the less the MgZn2 phase contained in the ternary eutectic structure and even the ternary eutectic structure. In this embodiment, I3 is set to be 0.03 or less. Thus, the MgZn2 phase existing as the ternary eutectic structure basically disappears, and the corrosion resistance in simulated acid rain / salt water is further improved. The lower limit of I3 does not need to be particularly limited, but it can also be 0 or more. In order to control I3, it is appropriate to control the immersion time in the plating bath in the two-stage plating method.

[0218] The plated steel sheet of this embodiment includes a steel sheet and a coating formed on the surface of the steel sheet. Generally, the Zn-Al-Mg-based coating is formed by the deposition and solidification reaction of metals. The easiest means for forming the coating is to form the coating on the steel sheet surface by the hot-dip plating method, and it can be formed by the Sendzimir strip nitriding immersion galvanizing method, the flux method, the two-stage plating method, etc.

[0219] In the present embodiment, in order to appropriately control the morphology of the interfacial alloy layer, a manufacturing method equivalent to a two-stage plating method is preferably used. The reasons for preferably using the two-stage plating method are as follows. For a plating bath with more than 30.0% Al, in order to dissolve the plating bath for hot dip plating, a bath temperature of 520°C or higher is generally required. If such a plating bath is used and the Morikawa strip nitriding immersion galvanizing method or the like is adopted, the reduced Fe surface reacts rapidly with the plating bath, and there is a tendency for the Al-Fe alloy layer to grow quite thick. The hot dip galvanized steel sheet of the present embodiment is sometimes used as a raw material for pre-plated products, but such a thick interfacial alloy layer can cause various problems such as peeling of the coating during processing of the hot dip galvanized steel sheet and early generation of Fe rust during corrosion. Therefore, in the manufacturing method of the present embodiment, it is necessary to adopt a manufacturing method equivalent to the two-stage plating method, and as the plating substrate, a plating substrate that can suppress the reaction between the Fe surface and the plating bath is used. In the plating substrate, in order to ensure the plating thickness required for the performance of the coating manufactured as the product of the present invention, the plating thickness needs to be at least 10 μm or more, and more preferably 20 μm or more. In addition, at this time, the interfacial alloy layer needs to be set to less than 10% of the entire coating, and more preferably set to less than 1 μm. In addition, from the viewpoint of poor plating appearance such as sagging patterns, the thickness of the coating is more preferably 80 μm or less.

[0220] It should be noted that in the case where the Morikawa strip nitriding immersion galvanizing method has to be adopted, it is allowed when using a plating bath containing more than 35.0% Al. However, as the plating substrate, a plating steel sheet that is hardly soluble in Fe and has a barrier film effect of suppressing the reaction between the plating bath and Fe is required, and a steel sheet with a Ni or Cr pre-plating layer of 0.7 g / m or more attached to each side needs to be used as the substrate. Ni and Cr exert a barrier effect on Fe diffusion. However, even in this case, there is a tendency to suppress the formation of the Al-Ca-Si alloy layer that should be included in the coating of the present embodiment, and the influence of Fe diffusion is suppressed to the minimum by forcibly solidifying the coating to cause appropriate coating solidification. Furthermore, in order to ensure corrosion resistance in water, Al-Si-O oxides are required. Although corrosion resistance in simulated acid rain can be ensured, there is a tendency for corrosion resistance to deteriorate in salt water. It is considered that this phenomenon is due to the fact that even if the thickness of the coating can be manufactured within the preferred range, the thickness of the interfacial alloy layer becomes around 10% or more, so the specified performance cannot be exhibited. 2 Hereinafter, a manufacturing method for a preferred hot dip galvanized steel sheet of the present embodiment will be described.

[0221] Hereinafter, a manufacturing method for a preferred hot dip galvanized steel sheet of the present embodiment will be described.

[0222] The manufacturing method of the hot-dip galvanized steel sheet according to this embodiment is manufactured by a continuous hot-dip plating method in which a plating base plate is continuously immersed in a hot-dip plating bath and then lifted out. However, as described above, since the hot-dip plating bath used in the manufacturing method of this embodiment has a high Al content, the bath temperature becomes relatively high. If a steel sheet is directly immersed as the plating base plate, the reaction between the plating bath and the base metal becomes active. As a result, a large amount of Fe diffuses into the coating layer, and an interfacial alloy layer formed of Fe-Al alloy is formed relatively thickly, and the adhesion of the coating layer is significantly reduced. Therefore, in this embodiment, as the plating base plate, a galvanized steel sheet or a pre-plated steel sheet having a coating layer of a specified amount or more is used. Thereby, the reaction between the plating bath and the base metal can be suppressed, and the interfacial alloy layer can be thinned.

[0223] The plating adhesion amount per single side of the galvanized steel sheet used as the plating base plate is at least 40 g / m 2 Above, preferably 100 g / m 2 Above is appropriate. This is the intention of a plating thickness of about 10 μm or more, more preferably about 21 μm or more in terms of the converted coating layer thickness. There is no restriction on the manufacturing method of the coating layer of the plating base plate, and it can be any method of hot-dip plating method or electroplating method. It is necessary to make the interfacial alloy layer of the plating base plate less than 1 μm, and the main body of the coating layer is Zn, but for example, the coating layer can also contain 1% or less of Al. If a plating steel sheet having an interfacial alloy layer formed from the beginning is used as the base plate, the reaction will change, so it is not preferred. That is, the interfacial alloy layer formed at the time of manufacturing the plating base plate also remains directly as the interfacial alloy layer after two-stage plating, so this alloy layer is strictly restricted, preferably set to less than 1 μm, and must be set to less than 10% of the overall thickness of the coating layer.

[0224] In addition, as the galvanized steel sheet, a Zn-Al-Mg series plated steel sheet containing elements such as Al and Mg contained in the coating layer of the present invention in the coating layer can also be used as the base plate. Even for such a Zn-Al-Mg series plated steel sheet, the thickness of the interfacial alloy layer needs to be less than 1 μm. It should be noted that generally, in hot-dip galvanized / Zn-based alloy steel sheets manufactured by a continuous hot-dip plating production line, due to the relationship of the immersion time, the thickness of the interfacial alloy layer basically does not exceed 1 μm. Therefore, as the plating base plate, it is more preferable to use a hot-dip galvanized steel sheet / Zn-based alloy plated steel sheet.

[0225] If a galvanized steel sheet is immersed in a hot-dip plating bath, the coating layer provided in these steel sheets and the metal elements of the hot-dip plating bath are easily displaced, and a coating layer containing the components of the plating bath is formed in a state where the reaction between the plating bath and the base metal is suppressed. A galvanized steel sheet refers to a steel sheet having a coating layer mainly composed of zinc on the steel sheet, and in the case of a hot-dip galvanized steel sheet, there is an interfacial alloy layer between the coating layer and the steel sheet.

[0226] In addition, examples of the pre-coated steel sheet for the coated base plate include a pre-coated steel sheet pre-coated with a coating layer of Zn, Ni, Cr, Sn, or an alloy system formed by combining these elements with a coating thickness of 30 μm or less. If the pre-coated steel sheet is immersed in a hot-dip plating bath, the metal elements of the pre-coating layer and the hot-dip plating bath are likely to undergo replacement, and a coating layer containing the components of the plating bath is formed while suppressing the reaction between the plating bath and the base metal. The constituent elements of the pre-coating layer such as Sn, Ni, and Cr react with Al and Si in the plating bath and act as a barrier layer for suppressing the diffusion of Fe. Furthermore, it is also possible to eliminate uncoated areas (areas where the plated metal bounces off due to an oxide film or the like) caused by the components contained in the plating bath.

[0227] In addition, it is also possible to use a low-temperature coating layer, that is, a Sn-plated steel sheet or an electroplated Zn-Ni steel sheet, as the coated base plate.

[0228] In the manufacturing method of the present embodiment, the above-mentioned coated base plate is immersed in a hot-dip plating bath and then lifted out. The composition of the coating layer can be controlled by the composition of the plating bath for bath building. The bath building of the plating bath is carried out by mixing pure metals in a specified amount, for example, by a dissolution method in an inert atmosphere to produce an alloy of the plating bath components.

[0229] By immersing the coated base plate in a plating bath maintained at a specified concentration, a coating layer having substantially the same composition as the plating bath is formed. The immersion time can also be changed according to the plating adhesion amount for the base plate. When the value of the plating adhesion amount (g / m 2 ) per single side is set to M, the immersion time (seconds) is preferably set in the range of M / 30 (seconds) to M / 10 (seconds).

[0230] Furthermore, in order to satisfy the above formula (C-2), it is preferable to set the immersion time (seconds) in the range of M / 15 (seconds) to M / 10 (seconds).

[0231] In addition, it is not necessary to raise the temperature of the coated base plate during immersion to match the plating bath temperature, and it can be at room temperature (for example, 50 °C or less), but in the case of Zn-based plating, it can be raised up to about 600 °C (the temperature at which the coating layer on the surface does not melt) without problems.

[0232] After various coating layers formed on the coated base plate are immersed in the plating bath, they are exposed to a plating bath at 500 °C or higher and instantaneously dissolve. On the other hand, since the temperature of the base metal of the coated steel sheet does not rise sufficiently, there is a tendency to suppress the reaction between Fe and the plating bath, and the diffusion of Fe into the coating layer and the formation of intermetallic compounds caused by Fe can be significantly suppressed. By short-time immersion, replacement from the coating layer of the coated base plate to the hot-dip coating layer is caused before the diffusion of Fe, and it is lifted out in this state.

[0233] When an oxide of Al-Si-O is formed in the coating layer immediately after it is lifted out of the plating bath, the atmosphere needs to be set to an atmospheric environment (oxygen concentration of 2000 ppm or more). In addition, immediately after lifting out, the plating thickness can be controlled by wiping. In addition, in a series of plating solidification reactions, it is preferably controlled in such a way that the steel plate temperature does not exceed 500 °C. This is because if the temperature exceeds this value, Fe diffuses rapidly into the plating bath.

[0234] A series of manufacturing methods can be carried out in an atmospheric environment. When the Al content in the plating bath exceeds 35.0%, it can also be manufactured in an inert atmosphere such as a nitrogen atmosphere, but in this case, an Al-Si-O oxide film is not formed.

[0235] There is no particular limitation on the cooling of the coating layer, and it can be solidified by blowing N2 gas or mist, etc.

[0236] After plating, various chemical conversion treatments and painting treatments can also be carried out. The uneven patterns on the plating surface can also be utilized to further apply coatings of Cr, Ni, Au, etc., and then painting can be carried out to impart a pattern design. In addition, in order to further improve the corrosion resistance, repair correction coatings, spraying treatments, etc. can also be implemented at the welded parts, processed parts, etc.

[0237] For the hot-dip galvanized steel sheet of this embodiment, a film can also be formed on the coating layer. One layer or two or more layers of films can be formed. As the types of films directly above the coating layer, for example, chromate films, phosphate films, and chromium-free films can be cited. The chromate treatment, phosphate treatment, and chromium-free treatment for forming these films can be carried out by known methods.

[0238] For chromate treatment, there are the following chromate treatments: electrolytic chromate treatment for forming a chromate film by electrolysis; reaction-type chromate treatment for forming a film by reacting with the raw material and then rinsing off the excess treatment liquid; coating-type chromate treatment for coating the treatment liquid on the object to be coated and drying it without water washing to form a film. Any treatment can be adopted.

[0239] As the electrolytic chromate treatment, an electrolytic chromate treatment using chromic acid, silica sol, resin (phosphoric acid, acrylic resin, vinyl ester resin, vinyl acetate-acrylic emulsion, carboxylated styrene-butadiene latex, diisopropanolamine-modified epoxy resin, etc.) and hard silica can be exemplified.

[0240] As the phosphate treatment, for example, zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment can be exemplified.

[0241] Chromate-free treatment is particularly suitable because it has no environmental load. For chromate-free treatment, there are the following chromate-free treatments: electrolytic chromate-free treatment that forms a chromate-free film by electrolysis; reactive chromate-free treatment that forms a film by reacting with the raw material and then rinses off the excess treatment liquid; and coating-type chromate-free treatment that coats the treatment liquid on the object to be coated and dries it without water washing to form a film. Any of these treatments can be adopted.

[0242] Furthermore, on the film directly above the plating layer, there may also be one or two or more layers of organic resin films. As the organic resin, it is not limited to a specific type, and examples include polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, or modified products of these resins. Here, the modified product refers to a resin obtained by reacting the reactive functional groups contained in the structure of these resins with other compounds (monomers, crosslinking agents, etc.) containing functional groups that can react with the functional groups in the structure.

[0243] As such an organic resin, one or two or more organic resins (unmodified resins) can be mixed and used, or one or two or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin can be mixed and used. In addition, arbitrary coloring pigments and anti-rust pigments can be included in the organic resin film. These organic resins can also use resins made water-based by dissolving or dispersing them in water.

[0244] It should be noted that in this embodiment, the corrosion resistance in acid rain and the corrosion resistance in salt water are measured and evaluated as follows. The case where the evaluations of the corrosion resistance in acid rain and the corrosion resistance in salt water are both "E" is set as unqualified, and the others are set as qualified.

[0245] (Corrosion resistance in acid rain)

[0246] The corrosion resistance in acid rain is evaluated by a simulated acid rain corrosion resistance test. This test is a test that assumes the situation where acid rain in the atmosphere flows in. As the simulated acid rain, test water is prepared, and this test water is adjusted to Cl - : 10 ppm, NO 3- : 20 ppm, SO4 2-: 40 ppm, pH 5.0 ± 0.2. Add 60 L of test water to a container in the shape of a cube with a side length of 50 cm. At the front end of a stainless-steel shaft (φ25 mm), a plated steel sheet test piece is installed through a clamp and bolts. The test piece is set as a circular plate with a diameter of 130 mm. A hole is set in the center of the circular plate, and the front end of the stainless-steel shaft is embedded in this hole for fixation. Immerse the test piece in the test water, and rotate the test piece at high speed so that the peripheral speed of the test piece becomes 2.2 m / s. The part where the test piece contacts the clamp is insulated by means of tape sealing, etc. The pH is monitored constantly, and when it deviates from the range of pH 5.0 ± 0.2, it is restored to pH 5.0 with dilute hydrochloric acid or an aqueous NaOH solution. The water temperature is maintained within the range of 23 - 25 °C. Replace the test solution every 250 hours. After 1000 hours, take out the test piece, immerse it in a 30% chromic acid (VI) aqueous solution for 15 minutes, measure the weight difference before and after immersion, and calculate the corrosion loss (g / m 2 ). For the test piece, the end face part is in an open state, and the central hole part is taken as the evaluation part. The evaluation criteria are set as follows.

[0247] The corrosion loss is less than 5 g / m 2 : The corrosion resistance in simulated acid rain is "A"

[0248] The corrosion loss is 5 g / m 2 or more and less than 10 g / m 2 : The corrosion resistance in simulated acid rain is "B"

[0249] The corrosion loss is 10 g / m 2 or more and less than 20 g / m 2 : The corrosion resistance in simulated acid rain is "C"

[0250] The corrosion loss is 20 g / m 2 or more and less than 30 g / m 2 : The corrosion resistance in simulated acid rain is "D"

[0251] The corrosion loss is 30 g / m 2 or more: The corrosion resistance in simulated acid rain is "E"

[0252] (Corrosion resistance in salt water)

[0253] The corrosion resistance in salt water is evaluated through a corrosion resistance test in a salt water aqueous solution. Except that the test water is set as a 5% NaCl aqueous solution, this test is carried out in the same way as the simulated acid rain corrosion resistance test. After 1000 hours, immerse it in a 30% chromic acid (VI) aqueous solution for 15 minutes, and calculate the corrosion loss before and after immersion. The evaluation criteria are set as follows.

[0254] The corrosion weight loss is less than 15 g / m 2 : The corrosion resistance in salt water is "S"

[0255] The corrosion weight loss is 15 g / m 2 or more and less than 20 g / m 2 : The corrosion resistance in salt water is "A"

[0256] The corrosion weight loss is 20 g / m 2 or more and less than 30 g / m 2 : The corrosion resistance in salt water is "B"

[0257] The corrosion weight loss is 30 g / m 2 or more and less than 40 g / m 2 : The corrosion resistance in salt water is "C"

[0258] The corrosion weight loss is 40 g / m 2 or more and less than 50 g / m 2 : The corrosion resistance in salt water is "D"

[0259] The corrosion weight loss is 50 g / m 2 or more: The corrosion resistance in salt water is "E"

[0260] Examples

[0261] Manufacture the plated steel sheets shown in Tables 2A to 5C and conduct performance evaluation.

[0262] For the preparation of various plating baths, pure metals are blended to prepare the bath. After the composition of the plated alloy is prepared, Fe powder is added to prevent the increase of Fe concentration in the test.

[0263] The manufacturing conditions are set as shown in Table 1 below. The unit of the single-sided coating amount of the base plate is g / m 2 . The heating temperature of the steel sheet before the plating bath is set from normal temperature to 800 °C. The normal temperature is 50 °C or lower. The immersion time is set from 2 to 15 seconds.

[0264] [Table 1]

[0265]

[0266] Production methods A, A1, A2: The plating base plate is set as cold-rolled steel sheet, Ni pre-plated steel sheet or Cr pre-plated steel sheet. The thickness of the interfacial alloy layer of the pre-plated steel sheet is less than 1 μm. As the production method, the CGL Morishita strip nitriding immersion galvanizing method is used. That is, before immersion in the plating bath, the plating base plate is heated in a nitrogen atmosphere with 5% H2 (oxygen concentration is 20 ppm or less, dew point is -40 °C) at a specified heating temperature for 60 seconds for surface reduction. After that, the steel sheet is cooled to the plating bath temperature by N2 gas and immersed in the plating bath. After being fished out, it is adjusted by wiping so that the thickness of each single side becomes 20 μm, and cooled in the atmosphere at an average cooling rate of 10 °C / second. It should be noted that the plating adhesion amount is also set to 20 μm in thickness for each single side for production methods B to L.

[0267] Production methods B, B1, B2: Regarding their production methods, until immersion in the plating bath, they are the same as the above production methods A, A1, A2. After being fished out from the plating bath, the steel sheet is covered with a sealed box and cooled in a nitrogen atmosphere with an oxygen concentration of less than 2000 ppm.

[0268] Production methods C, D, E: As the plating base plate, a hot-dip galvanized Zn steel sheet produced by the CGL Morishita strip nitriding immersion galvanizing method is used. The details are as described in Table 1. The thickness of the interfacial alloy layer of the hot-dip galvanized Zn steel sheet is less than 1 μm, which is less than 10% of the overall thickness of the coating. The plating base plate is immersed in the plating bath without heating. The plating bath is maintained so that the plating bath temperature does not change before and after immersion. For the treatment after being fished out, production methods C and E are set to be the same as production methods A to A2, and production method D is set to be the same as production methods B to B2.

[0269] Production methods F, G, H: As the plating base plate, a hot-dip Zn-Al-Mg alloy steel sheet produced by the CGL Morishita strip nitriding immersion galvanizing method is used. The details are as described in Table 1. The thickness of the interfacial alloy layer of the hot-dip Zn-Al-Mg alloy steel sheet is less than 1 μm, which is less than 10% of the overall thickness of the coating. The plating process is as described in Table 1.

[0270] Production methods I, J, K, L: As the plating base plate, the plated steel sheets described in Table 1 are used. The thickness of the interfacial alloy layer of these plated steel sheets is less than 1 μm, which is less than 10% of the overall thickness of the coating. The plating process is as described in Table 1.

[0271] Regarding the plating bath temperature, the plating bath with an Al content of less than 35.0% is set to 550 °C, and the plating bath with an Al content of 35.0% or more is set to 600 °C.

[0272] The intensity of the X-ray is measured as follows.

[0273] The hot-dip galvanized steel sheet after plating was cut into pieces with a size of 20 mm square. Using a high-angle X-ray diffractometer manufactured by Rigaku Corporation (model RINT-TTR III), the X-ray output was set to 50 kV, 300 mA, copper (Cu) target, goniometer TTR (horizontal goniometer), the slit width of the Kβ filter was 0.05 mm, the length limit slit width was 2 mm, the light-receiving slit width was 8 mm, and the light-receiving slit 2 was open. As the measurement conditions, the scanning speed was set to 5 deg. / min, the step size was 0.01 deg, and the scanning axis was 2θ (5 - 90°) to perform the measurement, and the cps intensity at each angle was obtained.

[0274] The corrosion resistance in simulated acid rain and salt water was measured and evaluated as follows. The results are shown in the table.

[0275] (Corrosion resistance in acid rain)

[0276] The corrosion resistance in acid rain was evaluated through a simulated acid rain corrosion resistance test. This test is a test that assumes the situation where acid rain in the atmosphere flows in. As the simulated acid rain, test water was prepared. This test water was adjusted to 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 in the shape of a cube with a side length of 50 cm. At the front end of a stainless steel shaft (φ25 mm), a plated steel sheet test piece was installed through a clamp and bolts. The test piece was set as a circular plate with a diameter of 130 mm. A hole was set in the center of the circular plate, and the front end of the stainless steel shaft was inserted into this hole for fixation. The test piece was immersed in the test water, and the test piece was rotated at a high speed so that the peripheral speed of the test piece became 2.2 m / s. The part where the test piece contacted the clamp was insulated by tape sealing, etc. The pH was monitored constantly. In the case of deviating from the range of pH 5.0 ± 0.2, it was restored to pH 5.0 by dilute hydrochloric acid or an aqueous NaOH solution. The water temperature was maintained within the range of 23 - 25°C. The test solution was replaced every 250 hours. After 1000 hours, the test piece was taken out, immersed in a 30% chromic acid (VI) aqueous solution for 15 minutes, the weight difference before and after immersion was measured, and the corrosion loss (g / m 2 ) was obtained. For the test piece, the end face part was in an open state, and the central hole part was used as the evaluation part. The evaluation criteria were set as follows. "E" was set as unqualified.

[0277] The corrosion loss was less than 5 g / m 2 : The corrosion resistance in simulated acid rain was "A"

[0278] The corrosion weight loss is 5 g / m 2 or more and less than 10 g / m 2 : The corrosion resistance in simulated acid rain is "B"

[0279] The corrosion weight loss is 10 g / m 2 or more and less than 20 g / m 2 : The corrosion resistance in simulated acid rain is "C"

[0280] The corrosion weight loss is 20 g / m 2 or more and less than 30 g / m 2 : The corrosion resistance in simulated acid rain is "D"

[0281] The corrosion weight loss is 30 g / m 2 or more: The corrosion resistance in simulated acid rain is "E"

[0282] (Corrosion resistance in salt water)

[0283] The corrosion resistance in salt water is evaluated by the corrosion resistance test in a salt water aqueous solution. Except that the test water is set as a 5% NaCl aqueous solution, this test is carried out in the same way as the simulated acid rain corrosion resistance test. After 1000 hours, it is immersed in a 30% chromic acid (VI) aqueous solution for 15 minutes, and the corrosion weight loss before and after immersion is calculated. The evaluation criteria are set as follows. "E" is set as unqualified.

[0284] The corrosion weight loss is less than 15 g / m 2 : The corrosion resistance in salt water is "S"

[0285] The corrosion weight loss is 15 g / m 2 or more and less than 20 g / m 2 : The corrosion resistance in salt water is "A"

[0286] The corrosion weight loss is 20 g / m 2 or more and less than 30 g / m 2 : The corrosion resistance in salt water is "B"

[0287] The corrosion weight loss is 30 g / m 2 or more and less than 40 g / m 2 : The corrosion resistance in salt water is "C"

[0288] The corrosion weight loss is 40 g / m 2 or more and less than 50 g / m 2 : The corrosion resistance in salt water is "D"

[0289] The corrosion weight loss is 50 g / m 2 or more: The corrosion resistance in salt water is "E"

[0290] For No.1 and 44, since the Al content is outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0291] For No.54, 66, 69, 73, since the Si content is outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0292] For No.5 to 11, 14, 28 to 32, 35, 115 to 119, 122, since the manufacturing conditions are outside the preferred range, I1 or I2 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0293] For No.45 and 50, since the Mg content is outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0294] For No.51 to 53, since the elements of element group A are outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0295] For No.55, 56, 58, 60, 62, 64, 65, since the elements of element group B are outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0296] For No.77, 79, 81, 83, 85, 87, 89, 91, 93, 95, since the elements of element group C are outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0297] For No.97, since Fe is outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0298] For No.99, 101, 103, 105, 107, 109, 111, 128, 130, 132, 135, since the elements of element group D are outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0299] For No.137, since Si≤Sn is not satisfied, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0300] For No.139, since Si / Ca is outside the scope of the present invention, I1 is outside the scope of the invention, and the corrosion resistance in water is reduced.

[0301] On the other hand, the hot-dip galvanized steel sheets other than the above are excellent in corrosion resistance in water.

[0302] [Table 2A]

[0303]

[0304] The underlined part indicates outside the scope of the present invention or outside the scope of preferred manufacturing conditions.

[0305] [Table 2B]

[0306]

[0307] The underlined part indicates outside the scope of the present invention or outside the scope of preferred manufacturing conditions.

[0308] [Table 2C]

[0309]

[0310] The underlined part indicates outside the scope of the present invention or outside the scope of preferred manufacturing conditions.

[0311] [Table 3A]

[0312]

[0313] The underlined part indicates outside the scope of the present invention.

[0314] [Table 3B]

[0315]

[0316] The underlined part indicates outside the scope of the present invention.

[0317] [Table 3C]

[0318]

[0319] The underlined part indicates outside the scope of the present invention.

[0320] [Table 4A]

[0321]

[0322] The underlined part indicates outside the scope of the present invention.

[0323] [Table 4B]

[0324]

[0325] The underlined part indicates outside the scope of the present invention.

[0326] [Table 4C]

[0327]

[0328] The underlined part indicates outside the scope of the present invention.

[0329] [Table 5A]

[0330]

[0331] The underlined part indicates outside the scope of the present invention.

[0332] [Table 5B]

[0333]

[0334] The underlined part indicates outside the scope of the present invention.

[0335] [Table 5C]

[0336]

[0337] The underlined part indicates outside the scope of the present invention.

[0338] Industrial Applicability

[0339] According to the present invention, it is possible to provide a hot-dip galvanized steel sheet that can exhibit high corrosion resistance in water (such as simulated acid rain or salt water like seawater) or a constantly water-wetted environment that can cause water wetting. Therefore, the industrial applicability of the present invention is high.

Claims

1. A hot-dip galvanized steel sheet, which is a hot-dip galvanized steel sheet having a coating layer on the surface of the steel sheet, The average chemical composition of the coating layer is by mass%: Al: more than 30.0% and 50.0% or less, Mg: more than 5.0% and 15.0% or less, Sn: 0% to 0.70%, Bi: 0% to 0.30%, In: 0% to 0.30%, Ca: 0.03% to 0.60%, Y: 0% to 0.30%, La: 0% to 0.30%, Ce: 0% to 0.30%, Si: more than 0.5% and 1.0% or less when Al is more than 30.0% and less than 35.0%, 0.03% to 1.0% when Al is 35.0% to 50.0%, Cr: 0% to 0.25%, Ti: 0% to 0.25%, Ni: 0% to 1.0%, 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: 0% to 5.0%, Sr: 0% to 0.5%, Sb: 0% to 0.5%, Pb: 0% to 0.5%, B: 0% to 0.5%, Li: 0% to 0.5%, Zr: 0% to 0.5%, Mo: 0% to 0.5%, W: 0% to 0.5%, Ag: 0% to 0.5%, P: 0% to 0.5%, The balance contains Zn and impurities, The total amount ΣA of Sn, Bi and In is 0% to 0.70%, The total amount ΣB of Ca, Y, La and Ce is 0.03% to 0.60%, and the total amount ΣC of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is 0% to 1.00%, The total content ΣD of Sr, Sb, Pb, B, Li, Zr, Mo, W, Ag and P is 0% to 0.5%, satisfies the following formulas (1) to (3), In the X-ray diffraction pattern of the surface of the coating layer measured under the conditions of using Cu-Kα rays and with an X-ray output of 50 kV and 300 mA, when I1 is defined by formula (A-1) from the X-ray diffraction peaks of Zn, Al and MgZn2, formula (A-2) is satisfied, When I2 is defined by formula (B-1) from the X-ray diffraction peaks of Al2O5Si, formula (B-2) is satisfied, Sn ≤ Si (1) 15 ≤ Mg / Si (2) 1.0 ≤ Si / Ca ≤ 5.0 (3) I1 ≤ 0.10 (A-2) 1.05 ≤ I2 (B-2) wherein, In formulas (1) to (3), Sn, Si, Mg, and Ca are the contents of the respective elements in the coating by mass%, and Imax(k to m°) in formulas (A-1) and (B-1) is the maximum value of the X-ray diffraction intensity between diffraction angles k and m°, I(n°) is the X-ray diffraction intensity at diffraction angle n°, and k, m, and n are the diffraction angles shown in formulas (A-1) and (B-1), respectively.

2. The hot-dip galvanized steel sheet according to claim 1, in the X-ray diffraction pattern of the surface of the coating layer measured under the conditions of using Cu-Kα rays and with an X-ray output of 50 kV and 300 mA, when I3 is defined by formula (C-1) from the X-ray diffraction peaks of MgZn2, formula (C-2) is satisfied, I3 ≤ 0.03 (C-2) wherein, In formula (C-1), Imax(k to m°) is the maximum value of the X-ray diffraction intensity between diffraction angles k and m°, and k and m are the diffraction angles shown in formula (C-1), respectively.

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