Hot dipped steel material

Abstract

This hot dipped steel material has a steel material and a plating layer that is disposed on the surface of the steel material, wherein the plating layer has a chemical composition that contains, in mass%, more than 10% and less than 40% of Al and 4.0% to 15.0% inclusive of Mg, with the balance being made up of Zn and impurities, and the total amount ΣTR1 of V and Mn being 0.05% to 3.0% inclusive. In the element distribution profile obtained by performing GDS analysis in the thickness direction of the steel material from the surface of the plating layer toward the steel material, if the depth position at which the Fe concentration reaches 95% is defined as the interface between the plating layer and the steel material, and the distance from the surface of the plating layer to the interface is defined as the thickness t of the plating layer, the ratio of the depth at which the total amount ΣTR1 is 0.1% or more is 10% or more with respect to the thickness t.

Description

Hot-dip galvanized steel

[0001] This application claims priority to Japanese Patent Application No. 2024-135644, filed on August 15, 2024, the contents of which are incorporated herein by reference.

[0002] When steel materials are used for a long period of time, it is preferable to apply some kind of rust prevention treatment to the steel materials to make them resistant to corrosion. Hot-dip Zn plating is used as a means of inexpensively preventing rust on steel materials in various fields where rust prevention of steel materials is required, such as civil engineering, construction, and automotive fields.

[0003] The corrosion protection provided by a coating layer is determined by the inherent corrosion resistance and thickness of the coating layer. For example, Patent Document 1 describes the production of a coated steel sheet by a so-called continuous hot-dip coating method in which a steel sheet is continuously immersed in a hot-dip coating bath. The coated steel sheet is then processed into the shape of a part. The continuous hot-dip coating method is used to form zinc coatings and Zn alloy coatings containing Al and Mg. The continuous hot-dip coating method produces a relatively thinner coating layer than the post-coating method described below.

[0004] Patent Document 2 describes a method in which a workpiece processed into a predetermined shape is immersed in a plating bath, and is called a batch-type hot-dip plating method or a post-plating method. The post-plating method involves immersing the workpiece in the plating bath for one minute or more, which tends to result in a thick plating layer. However, compared to the continuous hot-dip plating method, the post-plating method has greater restrictions on alloy components, tends to have poorer corrosion resistance, and is significantly less manufacturable.

[0005] However, in an environment where the time of wetting with water (wet time) is long, corrosion of plated steel sheets becomes extremely severe. Therefore, increasing the thickness of the plating layer is important for extending the life of the plated steel sheet. Therefore, if a Zn alloy plating layer containing a large amount of Al can be produced by a continuous hot-dip plating method to a thickness comparable to that of a post-plating method, it will be possible to efficiently produce steel sheets that provide long-term corrosion protection for steel materials.

[0006] The thickness of the coating layer of coated steel sheets produced by continuous hot-dip galvanizing is often about 20 to 30 μm. This is due to process characteristics of continuous hot-dip galvanizing, such as lifting of the molten metal when the steel sheet is pulled out of the coating bath, gas wiping, and air-cooling solidification. For example, increasing the pulling speed when pulling the steel sheet out of the coating bath increases the thickness of the coating layer, but it becomes difficult to control the surface appearance. Therefore, in practice, the upper limit of the coating layer thickness is strictly limited by adjusting the wiping rate. That is, when a Zn alloy coating layer containing Al and Mg is produced by continuous hot-dip galvanizing, it is generally difficult to produce a coating layer with a thickness of 30 μm or more. This is because a coating bath containing a large amount of Al has a low specific gravity and therefore a low viscosity, which results in a low amount of molten metal adhering to the steel sheet when it is pulled out of the coating bath.

[0007] In recent years, various elements other than Al and Mg have been added to Zn alloy plating baths in order to impart properties other than corrosion resistance to the plating layer. For example, as shown in Patent Document 1, Sn may be added to the plating layer. These elements tend to bond with Mg, Al, or Zn in the Zn alloy to form intermetallic compounds with high melting points.

[0008] International Publication No. 2018 / 139619 Japanese Patent Application Laid-Open No. 61-295361

[0009] One way to improve the lifespan of a plating layer, i.e., its corrosion resistance, is to increase the thickness of the plating layer. Increasing the viscosity of the plating bath is effective in obtaining a thick plating layer, and this can be achieved, for example, by adding an element with a relatively heavy specific gravity to the plating bath. That is, when an element with a heavy specific gravity is added to the plating bath, the specific gravity is restored, and it is expected that the plating coating weight can be increased.

[0010] However, when a heavy element is added to a coating bath, the heavy element is likely to change the reactivity between the elements in the coating bath and the base steel. For this reason, it has been difficult to obtain a thick, healthy coating layer by adding a heavy element to a coating bath while determining the effect of adding the heavy element.

[0011] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a hot-dip plated steel material that can increase the plating thickness even in the case of a plating layer that contains elements with a relatively high specific gravity.

[0012] To solve the above-mentioned problems, the present inventors have investigated a technique for adding elements with a high specific gravity, such as V and Mn (transition metals), which are difficult to add to a plating bath. Furthermore, while transition elements such as V and Mn have relatively high melting points, substances with high melting points can frequently cause plating defects, such as the generation of dross. Therefore, the inventors have investigated a technique for stably adding metal elements with high melting points to a plating bath. As a result, the inventors have discovered a technique for stably producing plated steel products even when using a plating bath containing elements with a high specific gravity and a high melting point. Furthermore, the inventors have discovered a plated steel product having a thick plating layer with excellent corrosion resistance. Furthermore, the inventors have discovered that a plating layer containing these elements with a high specific gravity and a high melting point and exhibiting an appropriate morphology can achieve excellent corrosion resistance due to V, Mn, etc.

[0013] In order to solve the above problems, the present disclosure employs the following configuration.[1] A hot-dip galvanized steel material according to one embodiment of the present disclosure is a hot-dip galvanized steel material having a steel material and a coating layer disposed on a surface of the steel material, wherein the coating layer contains, in mass %, Al: more than 10% and less than 40%, Mg: 4.0% to 15.0%, Si: 0% to 2.0%, V: 0% to 3.0%, Mn: 0% to 3.0%, Cr: 0% to 3.0%, Mo: 0% to 3.0%, Sn: 0% to 0.7%, Bi: 0% to 0.3%, In: 0% to 0.3%, Ca: 0% to 0.6%, Y: 0% to 0.3%, La: 0% to 0.3%, Ce: 0% to 0.3%. Sr: 0% or more, 0.3% or less, Li: 0% or more, 0.3% or less, Ni: 0% or more, 3.0% or less, Co: 0% or more, 3.0% or less, Cu: 0% or more, 0.25% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, B: 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, Nb: 0% or more, 0.25% or less, Zr: 0% or more, 0.25% or less, W: 0% or more, 0.25% or less, Fe: 0% or more, 5.0% or less, The remainder is Zn and impurities, The alloy has a chemical composition in which: total amount of V and Mn, ΣTR1: 0.05% or more and 3.0% or less; total amount of Cr and Mo, ΣTR1': 0% or more and 3.0% or less; ΣTR1+ΣTR1': 0.05% or more and 3.0% or less; total amount of Sn, Bi and In, Σα: 0% or more and 0.7% or less; total amount of Ca, Y, La, Ce, Sr and Li, Σβ: 0% or more and 0.6% or less; total amount of Ni and Co, ΣTR2: 0% or more and 3.0% or less; total amount of Cu, Ag, Sb, Pb, B, P, Ti, Nb, Zr and W, Σγ: 0% or more and 1.00% or less, In an element distribution profile obtained by GDS analysis from the surface of the plating layer toward the steel material in the thickness direction of the steel material, the depth position at which the Fe concentration reaches 95% is defined as the interface between the plating layer and the steel material, and the distance from the surface of the plating layer to the interface is defined as the thickness t of the plating layer, the proportion of the depth at which the total amount ΣTR1 is 0.1% or more is 10% or more of the thickness t.[2] When V and Mn in the chemical composition are defined as TR1, the hot-dip plated steel material of [1] above may contain a TR1-containing intermetallic compound in the coating layer, and the total area ratio of the TR1-containing intermetallic compound in a cross section of the coating layer may be 1% or more. [3] When Ni and Co in the chemical composition are defined as TR2, the hot-dip plated steel material of [1] or [2] above may satisfy the following formula (1) when the depth showing the maximum TR2 concentration in the element distribution profile is defined as t(TR2) and the depth showing the maximum TR1 concentration is defined as t(TR1): t(TR2) - t(TR1) ≦ 0.30t (1) [4] The hot-dip plated steel material of [1] or [2] above may satisfy the formula (4) I defined in the following formula (4) in an X-ray diffraction pattern of the surface of the coating layer measured using Cu-Kα radiation at an X-ray output of 50 kV and 300 mA. １ and I defined in the following formula (5) ２ However, the following formulas (2) and (3) may be satisfied: 1.5≦I １ ... (2) 1.5≦I ２ …(3) I １ =(Imax(10.5°~11.0°) / (I(10.5°)+0.2{|I(11.0°)−I(10.5°)|}) …(4) I ２ = (Imax (20.2° to 20.5°)) / (I(20.2°) + 0.667 {|I(20.5°) - I(20.2°)|}) ... (5) In equations (4) and (5), Imax (k to m°) 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 a diffraction angle n°, and k, m, and n are the diffraction angles (2θ) shown in equations (4) and (5), respectively.

[0014] According to an embodiment of the present invention, a hot-dip plated steel material having a large coating thickness can be provided. Furthermore, the hot-dip plated steel material of this embodiment can increase the thickness of the coating layer, thereby improving the coating life (corrosion resistance).

[0015] Fig. 1 is a graph showing an example of an element distribution profile, illustrating the results of a GDS analysis of a coating layer of a hot-dip coated steel material according to an embodiment of the present invention. Fig. 2 is a diagram illustrating an XRD analysis method.

[0016] Hereinafter, a hot-dip plated steel material according to one embodiment of the present invention will be described.

[0017] In this specification, the "%" used to indicate the content of each element in the chemical composition of a plating layer means "mass %" unless otherwise specified. Furthermore, when indicating the composition of an intermetallic compound, "%" means "atomic %" unless otherwise specified. Furthermore, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, when the numerical values ​​before and after "to" are followed by "greater than" or "less than," the numerical range does not include these numerical values ​​as the lower or upper limit.

[0018] The present inventors have conducted extensive research into hot-dip plated steel materials that have a plating layer containing Al, Mg, and Zn and are produced by a continuous hot-dip galvanizing method, and that have a large plating layer thickness (adhesion mass), excellent corrosion resistance, and excellent adhesion during processing, as well as a method for producing the same.

[0019] The melting point of a hot-dip galvanizing bath of a Zn alloy, in which Zn, a low-melting-point metal, is mixed with elements such as Al or Mg, tends to increase as the composition deviates from a ternary eutectic composition or Zn-3%Al-3%Mg (% by mass). The melting point of a plating bath containing more than 10% Al and 4% or more Mg is higher than that of pure Zn. In consideration of the hot-dip galvanizing process, such a Zn alloy plating bath is operated at around 500°C, which is 50°C or more higher than the melting point.

[0020] Alloying elements such as Al and Mg have a lower specific gravity than Zn. The specific gravity of alloying elements is closely related to the viscosity in the molten state. That is, molten metal containing high concentrations of Al, Mg, etc. has a lower viscosity. Therefore, in a continuous hot-dip coating process, when a steel sheet is passed through a coating bath at approximately 500°C at a constant line speed, the amount of hot-dip coating bath that adheres to the steel sheet and lifts up with the steel sheet is significantly less than in the case of pure Zn coating. Therefore, in order to stably produce a coating layer with a thickness exceeding 20 μm, the development of wiping technology, etc. is essential. However, because the molten metal that constitutes the coating layer is light due to its low specific gravity, the molten metal is easily blown away during wiping blowing, reducing the amount of hot-dip coating bath that adheres to the steel sheet and lifts up.

[0021] Furthermore, when Al is contained in the coating bath, the reaction between Al and Fe becomes active, and an Al-Fe interfacial alloy layer is easily formed when a steel material is passed through the coating bath. In this case, cracks originating from the Al-Fe alloy layer may propagate through the coating layer during bending tests, resulting in peeling of the coating layer. Such peeling becomes more pronounced as the temperature of the coating bath increases. Because of the immersion time and the loss of Al inside the coating layer due to Fe, a coating bath with a high Al concentration and high temperature makes it difficult to produce hot-dip coated steel materials with a coating layer with high adhesion that can be processed into various products.

[0022] Therefore, the present inventors conducted extensive research to solve the above problems. To produce a coating layer with a high adhesion weight under conditions of a high Al concentration and high bath temperature in the coating bath, it is first necessary to increase the viscosity of the coating bath, which can be achieved by adding elements with a high specific gravity to the coating bath. Adding transition metal elements such as V and Mn (TR1) in particular increases the specific gravity and viscosity of the coating bath, thereby increasing the coating weight on the steel material during threading.

[0023] On the other hand, when these transition metal elements are added to a coating bath, the transition metal elements tend to bond with elements such as Si, Ca, and Mg, which tends to cause floating dross to form in the coating bath. The coated steel material containing this dross has reduced adhesion or contains coating defects. However, since this floating dross is very fine, it is possible to redissolve the floating dross in the coating bath by raising the temperature of the coating bath to around 600°C if the concentration of the added transition metal elements is limited within a certain range.

[0024] On the other hand, in a plating bath at about 600°C, the Al-Fe alloying reaction is active, and even if a steel material is immersed for a short period of time, a thick Al-Fe-based interfacial alloy layer grows, which may significantly impair the adhesion of the subsequent hot-dip plated steel material.

[0025] Furthermore, the added transition metal elements have a similar reaction morphology to Fe and diffuse into the steel (Fe substrate). In particular, the accumulation of V and Mn on the steel surface immediately after immersion in the plating bath, which are elements less reducible than Fe, results in a large number of plating defects and deteriorated areas, such as non-plated areas (areas that do not react with the steel surface) due to poor reactivity with Fe. This is because, in Zn-Al-Mg-plated steel, fine oxides due to V and Mn formed below the steel surface (i.e., in the steel surface layer) inhibit plating adhesion. Therefore, when adding transition metal elements to the plating bath, taking measures to prevent excessive element diffusion into the steel can maintain the integrity of the plating layer, thereby enabling the production of plated steel with few defects and excellent corrosion resistance.

[0026] A hot-dip plated steel material according to one embodiment of the present invention, which has been made based on the above-mentioned new findings, will be described in detail below.

[0027] [Hot-dip plated steel material] A hot-dip plated steel material according to an embodiment of the present invention will be described. The hot-dip plated steel material of this embodiment has a steel material and a coating layer disposed on the surface of the steel material.

[0028] The average chemical composition of the plating layer is, in mass%, Al: more than 10% and less than 40%, Mg: 4.0% or more and 15.0% or less, Si: 0% or more and 2.0% or less, V: 0% or more and 3.0% or less, Mn: 0% or more and 3.0% or less, Cr: 0% or more and 3.0% or less, Mo: 0% or more and 3.0% or less, Sn: 0% or more and 0.7% or less, Bi: 0% or more and 0.3% or less, In: 0% or more and 0.3% or less, Ca: 0% or more and 0.6% or less, Y: 0% or more and 0.3% or less, La: 0% or more and 0.3% or less, Ce: 0% or more and 0.3% or less, Sr: 0% or more and 0.3% or less, Li: 0% or more and 0.3% or less, Ni: 0% or more, 3.0% or less, Co: 0% or more, 3.0% or less, Cu: 0% or more, 0.25% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, B: 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, Nb: 0% or more, 0.25% or less, Zr: 0% or more, 0.25% or less, W: 0% or more, 0.25% or less, Fe: 0% or more, 5.0% or less, the balance being Zn and impurities, and the total amount of V and Mn ΣTR1: 0.05% or more, 3.0% or less, The total amount of Cr and Mo ΣTR1': 0% or more and 3.0% or less, ΣTR1 + ΣTR1': 0.05% or more and 3.0% or less, The total amount of Sn, Bi, and In Σα: 0% or more and 0.7% or less, The total amount of Ca, Y, La, Ce, Sr, and Li Σβ: 0% or more and 0.6% or less, The total amount of Ni and Co ΣTR2: 0% or more and 3.0% or less, The total amount of Cu, Ag, Sb, Pb, B, P, Ti, Nb, Zr, and W Σγ: 0% or more and 1.00% or less. Note that V, Mn, Cr, and Mo are all transition metal elements, but in this specification, V and Mn may be referred to as "transition metal element TR1," and Cr and Mo may be referred to as "transition metal element TR1'." Furthermore, V, Mn, Cr and Mo may be collectively referred to as "transition metal elements TR."

[0029] Furthermore, in the hot-dip plated steel material of this embodiment, in an element distribution profile obtained by GDS analysis in the thickness direction of the steel material from the surface of the plated layer toward the steel material, the proportion of depths at which ΣTR1 is 0.1% or more is 10% or more of the thickness t of the plated layer in the region from the surface of the plated layer to the interface between the plated layer and the steel material. In other words, the total depth at which ΣTR1 is 0.1% or more is 0.1t or more. Note that the "thickness t of the plated layer" here refers to the distance from the surface of the plated layer to the interface, assuming that the depth position at which the Fe concentration is 95% of the maximum Fe concentration in the aforementioned element distribution profile is the interface between the plated layer and the steel material.

[0030] (Steel Material) The steel material to be plated will now be described. The steel material is, for example, mainly a steel plate, but there is no particular limitation on its size. The steel plate may be any steel plate that can be applied to a normal hot-dip galvanizing process. Specifically, this applies to steel plates that can be applied to a process in which the steel plate is immersed in molten metal and solidified, such as a continuous hot-dip galvanizing line (CGL). The size of the steel plate that can be applied is, for example, a plate thickness of 10 mm or less and a plate width of 2000 mm or less, but the size of the steel plate is not limited to this.

[0031] The steel material is not particularly limited, and examples of applicable steel materials include various steel plates, steel wire materials, and steel wires, such as general steel, pre-plated steel thinly plated with various metals, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, some high-alloy steels (steels containing elements that strengthen corrosion resistance, such as Ni and Cr), soft steel wire, hard steel wire, spring steel, steel cord, steel for bolts, and steel wire material for bridge cables. More specifically, for example, hot-rolled mild steel plates and steel strips specified in JIS G 3131:2018, cold-rolled steel plates and steel strips specified in JIS G 3141:2021, general structural rolled steel materials specified in JIS G 3101:2020, thinly plated steel sheets specified in JIS H 8641:2021, JIS G 3302:2022, JIS G 3303:2022, JIS G 3313:2021, JIS G 3314:2022, JIS G 3315:2022, JIS G 3317:2022, JIS G Applicable steels include various plated steels such as JIS G 3321:2022 (hereinafter, plating to make a plated steel sheet into a base steel material is also referred to as "pre-plating", and plated steel or plated steel sheet as a base steel material is also referred to as "pre-plated steel or pre-plated steel sheet"); rolled steel for building structures specified in JIS G 3136:2022; various high-tensile steels specified in JIS G 3113:2018, JIS G 3134:2018, JIS G 3135:2018, etc.; and some high-alloy steels (steels containing elements that strengthen corrosion resistance, such as Ni and Cr).

[0032] In addition, the surface of the steel material is pre-plated in advance with a thickness of 0.3 to 5 g / m ２ Alternatively, a Fe-plated layer, a Ni-plated layer, or a Co-plated layer having a coating amount of 0.01 to 0.01 may be provided. By using a steel material provided with such a pre-plated layer, the plating layer containing the transition elements V and Mn in this embodiment can be stably formed. Details will be described later.

[0033] Furthermore, the manufacturing process of steel material includes common processes such as pig iron and steel making processes using a blast furnace or an electric furnace, a hot rolling process, a pickling process, a cold rolling process, and a heat treatment process, but the steel material of this embodiment may have undergone any of these processes, and the processing conditions for each process are not limited.

[0034] (Plating Layer) Next, the plating layer provided on the steel material will be described. The plating layer according to this embodiment includes a Zn-Al-Mg alloy layer. When Zn contains alloying elements such as Al and Mg, corrosion resistance is improved. Therefore, in the case of the plating layer according to this embodiment including a Zn-Al-Mg alloy layer, even a thin plating layer with a small thickness, for example, about half the thickness of a normal Zn plating layer, can exhibit corrosion resistance equal to or greater than that of a Zn plating layer. The plating layer may include an Al-Fe interfacial alloy layer.

[0035] The Zn—Al—Mg alloy layer is made of a Zn—Al—Mg alloy, which means a ternary alloy containing Zn, Al, and Mg.

[0036] The thickness of the Zn—Al—Mg alloy layer may be 4 to 100 μm. If necessary, the lower limit of the thickness of the Zn—Al—Mg alloy layer may be 7 μm, 10 μm, 15 μm, or 20 μm, and the upper limit of the thickness of the Zn—Al—Mg alloy layer may be 90 μm, 80 μm, or 70 μm.

[0037] In many cases, the Al--Fe interfacial alloy layer is an interfacial alloy layer between the steel material and the Zn--Al--Mg alloy layer, and is in contact with the surface of the steel material.

[0038] The thickness t of the entire coating layer depends on the coating conditions, and therefore the upper and lower limits of the thickness t of the entire coating layer are not particularly limited. Furthermore, the thickness of the entire coating layer is affected by the withdrawal speed of the steel material from the coating bath and the wiping conditions. That is, in the continuous hot-dip coating method, the thickness t of the entire coating layer is affected by the viscosity and specific gravity of the coating bath. Since the maximum thickness t of the coating layer formed by the continuous hot-dip coating method is often 100 μm or less, the coating thickness t of the hot-dip coated steel material of this embodiment may be, for example, 100 μm or less, 80 μm or less, 70 μm or less, or 60 μm or less. The thickness t of the coating layer may be 30% or less of the steel sheet thickness, or, if necessary, 20% or less of the steel sheet thickness. The thickness t of the coating layer may be 15 μm or more, 20 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, or 45 μm or more, if necessary.

[0039] <Chemical Composition> Next, the average chemical composition of the plating layer will be described. When the plating layer has a single-layer structure of a Zn-Al-Mg alloy layer, the average chemical composition of the entire plating layer is the average chemical composition of the Zn-Al-Mg alloy layer. When the plating layer has a laminate structure of an Al-Fe interfacial alloy layer and a Zn-Al-Mg alloy layer, the average chemical composition is the average chemical composition of the sum of the Al-Fe interfacial alloy layer and the Zn-Al-Mg alloy layer. Note that when a pre-plating layer is provided on the surface of the steel material (base sheet) before plating, Ni, Co, etc. derived from the pre-plating layer are also included in this chemical composition.

[0040] In the plating layer of this embodiment, the thickness of the Al-Fe-based interface alloy layer is small, preferably 10% or less of the total thickness of the plating layer, and therefore the Fe concentration of the plating layer is often 5.0% or less.

[0041] Al: More than 10% and Less than 40% Al is the main constituent element of the coating layer. When the Al content exceeds 10%, the melting point of the coating layer becomes higher than that of pure Zn. Furthermore, the transition metal elements necessary to increase the thickness of the coating layer in this embodiment are hardly dissolved in Zn or Mg. Therefore, a certain amount of Al is required to contain the transition metal elements. Since the minimum concentration required for this purpose is more than 10%, the Al content is more than 10%. Furthermore, Al is an essential element for forming V-containing intermetallic compounds and / or Mn-containing intermetallic compounds (hereinafter, V-containing intermetallic compounds and Mn-containing intermetallic compounds are collectively referred to as TR1-containing intermetallic compounds). The Al content is preferably 11% or more, more preferably 12% or more, even more preferably 18% or more, and even more preferably 25% or more. On the other hand, when the Al content exceeds 40%, the reactivity between the coating bath and the base steel increases, making it difficult to suppress the formation of an Al-Fe-based interfacial alloy layer, and ensuring workability at a thick coating thickness becomes difficult. Furthermore, the thickness of the Zn-Al-Mg alloy layer is reduced by the amount of the thick Al-Fe alloy layer formed. Therefore, the Al content is set to less than 40%. The Al content is preferably 38% or less, and more preferably 35% or less.

[0042] Mg: 4.0% or more, 15.0% or less Like Zn, Mg is an element that constitutes the main component of the plating layer. Mg is an element that ensures the corrosion resistance of the plating layer. Mg is added to the Zn-Al-Mg alloy layer to form MgZn, which has excellent corrosion resistance and is relatively hard. ２ Mg forms a phase. Furthermore, Mg is an effective element for improving various performances by bonding with transition metal elements. If the Mg content is less than 4.0%, Mg does not form appropriate compounds with transition metal elements, etc., which promotes the formation of compounds between Al and transition metal elements, resulting in the generation of dross and the inability to form a sound coating layer. Therefore, the Mg content is set to 4.0% or more. The Mg content is preferably 4.5% or more, more preferably 4.8% or more, even more preferably 5.0% or more, and even more preferably 6.0% or more. On the other hand, if the Mg content exceeds 15.0%, the amount of dross generated increases, which may increase the number of unplated areas where the coating layer does not adhere. Therefore, the Mg content is set to 15.0% or less. The Mg content is preferably 13.0% or less, or 10.0% or less.

[0043] Si: 0% or more, 2.0% or less. Si has the effect of suppressing the reaction between the plating bath and Fe. Generally, containing a large amount of transition metal element TR in the plating bath results in excessive reaction, so the use of Si or other additives can suppress the diffusion of transition metal elements to a certain extent. On the other hand, the mixture of transition metal elements and large amounts of Si can cause oxides to form partially at the interface or on the steel surface (Fe surface), resulting in poor adhesion of the plating layer, which is known as "bad plating." Therefore, the Si content is 2.0% or less. The Si content is preferably 1.5% or less, 1.0% or less, or 0.30% or less. When a pre-plating layer is used, reactivity with the substrate can be sufficiently suppressed even without Si. Since Si is not necessary, the lower limit of the Si content is 0%. The Si content is preferably 0.01% or more, more preferably 0.1% or more.

[0044] V: 0% or more, 3.0% or less Mn: 0% or more, 3.0% or less Total amount of V and Mn ΣTR1: 0.05% or more, 3.0% or less When V and Mn (transition metal element TR1) are contained in a Zn-based coating bath containing Al and Mg, they have the effect of increasing the specific gravity of the coating bath and improving the viscosity of the coating bath. As a result, when the steel material is pulled out of the coating bath, the amount of molten metal adhering to the steel material increases, and the thickness of the coating layer increases. In addition, the presence of transition metal element TR1 in the coating bath prevents Al from adhering to the steel material during the initial stage of solidification of the coating phase. １８ (TR1) ２ Mg ３ This results in the formation of Al-Mg-TR1-based intermetallic compounds (TR1-containing intermetallic compounds), which further promotes an increase in the thickness of the plating layer. It is difficult to distinguish between the effect of increasing thickness due to the formation of such intermetallic compounds and the effect of increasing specific gravity and viscosity, but both effects are considered to be the effects of adding transition metals. When Al and Mg are within the appropriate concentration ranges, these effects tend to increase the plating coverage when the transition metal element TR1 is 0.05% or more. Therefore, it is preferable that the content of each of V and Mn (transition metal element TR1) is 0.05% or more. More preferably, the content of each of the transition metal element TR1 is 0.1% or more, 0.3% or more, 0.5% or more, 0.7% or more, or 1.0% or more.

[0045] On the other hand, TR1-containing intermetallic compounds form floating dross in the coating bath. The floating dross causes coating defects such as non-coating and dross adhesion scratches, significantly affecting the shape and performance of the product and degrading corrosion resistance. Therefore, it is preferable to completely dissolve the floating dross in the coating bath. For this reason, in this embodiment, the temperature of the coating bath containing the transition metal element TR1 must be 570°C or higher. It is preferably 600°C or higher. If the content of the transition metal element TR1 exceeds 3.0%, it is difficult to completely dissolve the floating dross even if the temperature of the coating bath is increased. Furthermore, the viscosity of the coating bath becomes extremely high, reducing the amount of molten metal adhering to the steel material when it is pulled out of the coating bath, resulting in an extremely thin coating layer. Furthermore, the coating appearance is significantly deteriorated. Therefore, the content of each of V and Mn (transition metal element TR1) is set to 3.0% or less. More preferably, the content of each of the transition metal element TR1 is 2.5% or less, or 2.0% or less.

[0046] In this embodiment, the chemical composition of the plating layer may contain at least one of V and Mn, or may contain both. In this embodiment, to obtain the above-described effects of V and Mn, the total concentration ΣTR1 of V and Mn is set to 0.03 to 3.0%. It is not necessary to contain both V and Mn; the concentration of either V or Mn may be within this range. Therefore, the lower limit of the concentration of V and Mn is 0%. The total concentration ΣTR1 is preferably 0.2% or more, 0.3% or more, 0.5% or more, 0.7% or more, or 1.0% or more. Furthermore, the total amount ΣTR1 is preferably 2.5% or less, 2.0% or less.

[0047] In this embodiment, when Ca is contained in the plating layer, the TR1-containing intermetallic compound is Al. １０ Ca(TR1) ２ However, Al may be generated. １０ Ca(TR1) ２ is Al in terms of crystal structure and atomic arrangement. １８ Mg ３ (TR1) ２ It is difficult to distinguish between １８ Mg ３(TR1) ２ It can also be considered that the compound in which part of the Mg in the above is substituted with Ca. Therefore, in this embodiment, there is no problem in considering both as the same kind of substance.

[0048] Cr: 0% or more, 3.0% or less Mo: 0% or more, 3.0% or less Cr and Mo (transition metal elements TR1') are elements that have effects similar to those of V and Mn. When V and Mn are contained, a portion of the V and Mn can be substituted for Cr and / or Mo to exhibit effects similar to those of V and Mn. Therefore, Cr and Mo are defined as transition metal elements TR1'. The respective contents of Cr and Mo are 3.0% or less, similar to V and Mn. More preferably, the respective contents of Cr and Mo are 2.5% or less, 2.0% or less. Note that the respective contents of Cr and Mo may be 0%. The respective contents of Cr and Mo are preferably 0.05% or more, more preferably 0.1% or more, 0.3% or more, 0.5% or more, 0.7% or more, or 1.0% or more.

[0049] The transition metal elements TR, Cr, Mo, V, and Mn, all form characteristically similar intermetallic compounds. However, when examining the properties of each intermetallic compound by focusing on the individual elements, slight differences were found. Intermetallic compounds containing Cr and Mo (transition metal element TR1') tend to have a weak sacrificial corrosion protection effect. This is thought to be because the formed intermetallic compounds are predicted to exhibit a high potential due to the Cr and Mo oxide film, which tends to delay the timing of dissolution into the plating layer during corrosion. On the other hand, V and Mn (transition metal element TR1) do not have the effect of strengthening the oxide film of the intermetallic compound, so they are found to dissolve at the appropriate time during corrosion of the plating layer and clearly contribute to corrosion resistance. Furthermore, it was also found that even in intermetallic compounds mainly composed of Cr and / or Mo, the delay in corrosion timing due to the oxide film as described above can be suppressed by containing a certain amount of Mn and V. Therefore, by incorporating V and Mn (transition metal element TR1) into an intermetallic compound mainly composed of Cr and / or Mo, the timing of corrosion of the intermetallic compound can be controlled.

[0050] In this embodiment, in order to obtain the above-described effects of Cr and Mo, the total concentration ΣTR1′ of Cr and Mo is 0% or more and 3.0% or less. It is not necessary to include both Cr and Mo, and the concentration of either Cr or Mo may be within this range.

[0051] ΣTR1 + ΣTR1': 0.05% or more, 3.0% or less. As described above, when the transition metal elements TR (V, Mn, Cr, and Mo) are added to a Zn-based plating bath containing Al and Mg, the specific gravity of the plating bath increases, improving the viscosity of the plating bath and thereby increasing the thickness of the resulting plating layer. Therefore, the total content of the transition metal elements TR1 and TR1' is 0.05% or more. On the other hand, if the total content of the transition metal elements TR1 and TR1' (ΣTR1 + ΣTR1') exceeds 3.0%, the viscosity of the plating bath becomes extremely high, reducing the amount of molten metal adhering to the steel when the steel is pulled out of the plating bath and resulting in an extremely thin plating layer. Therefore, the total content of the transition metal elements TR1 and TR1' is set to 3.0% or less. More preferably, the total content of the transition metal elements TR1 and TR1' is set to 2.5% or less, 2.0% or less.

[0052] Element group α Sn: 0% or more, 0.7% or less Bi: 0% or more, 0.3% or less In: 0% or more, 0.3% or less Total amount of Sn, Bi and In Σα: 0% or more, 0.7% or less Each element of element group α (Sn, Bi, In) is an element that promotes softening of the plating layer when contained in the plating layer. Since Sn, Bi and In are elements that can be contained optionally, the lower limit of each content is 0%. When Sn is contained, Mg is contained in the plating layer. ９ Sn ５ Bi tends to form Mg ３ Bi ２ , In is Mg ３ It also forms In etc. The element group α can be contained as needed for the purpose of improving properties such as corrosion resistance and workability.

[0053] However, there is an upper limit to the content of each element of element group α, and if it is contained in a large amount, Mg will be absorbed from the TR1-containing intermetallic compound, preventing the TR1-containing intermetallic compound from forming, resulting in a deterioration in corrosion resistance and a poor appearance of the plating layer due to the formation of intermetallic compounds with element group α. Therefore, the upper limit for element group α is set to 0.7% or less for Sn, and 0.3% or less for Bi and In. Furthermore, the total amount Σα of these elements is also set to 0.7% or less. The total amount Σα is preferably 0.5% or less, or 0.4% or less.

[0054] Next, each of the elements of element groups β and γ described below is an optional added element, and the lower limit thereof is set to 0% or more.

[0055] Element group β Ca: 0% to 0.6% Y: 0% to 0.3% La: 0% to 0.3% Ce: 0% to 0.3% Sr: 0% to 0.3% Li: 0% to 0.3% Total amount of Ca, Y, La, Ce, Sr and Li ΣY: 0% or more and 0.6% or less

[0056] Ca, which is one of the element group β, is preferably contained because it brings about various effects in the plating bath. Of the elements in the plating bath, Ca is most likely to bond with transition metal elements. Therefore, in a plating bath containing Ca and transition metal elements, a part of Mg is replaced by Ca, resulting in Al. １８ (Mg, Ca) ３ (TR1) ２ Ya, Al １０ Ca(TR1) ２ is formed in accordance with the content of the element group β. When such intermetallic compounds are formed, the viscosity of the plating increases, and a thick plating layer can be easily obtained.

[0057] If the Ca content exceeds 0.6%, various floating dross is formed in the coating bath, resulting in an increase in coating defects. Furthermore, the viscosity of the coating bath becomes extremely high, which reduces the amount of molten metal adhering to the steel material when it is pulled out of the coating bath, resulting in an extremely thin coating layer and a deterioration in corrosion resistance. Furthermore, the coating appearance is significantly deteriorated. Therefore, the Ca content is set to 0.6% or less. The Ca content is preferably 0.5% or less, more preferably 0.4% or less.

[0058] Each element of the element group β other than Ca can obtain almost the same effect as Ca, so it can be contained as a substitute for Ca. However, elements other than Ca are expensive, and there is a concern that the inclusion of a large amount of Ca may impair economic efficiency, so it is not preferable for the total content of elements other than Ca to be equal to or greater than the Ca content. The intermetallic compounds formed by the inclusion of the element group β other than Ca are Al １０ Ca(TR1) ２ As a substitute of Al １０ (β) (TR1) ２ When either Ca or any one of the elements is contained, almost no difference in corrosion resistance or performance is observed. As with Ca, if the concentration is high, Mg is absorbed from the TR1-containing intermetallic compound, and this compound is no longer formed, resulting in a thin plating thickness, so there is an upper limit to the concentration. Therefore, the concentration of each element in the element group β other than Ca is set to 0 to 0.3%. The concentration of each element in the element group β other than Ca is preferably 0.2% or less, 0.1% or less, respectively. Furthermore, the total concentration Σβ of the concentrations of each element in the element group β including Ca is set to 0 to 0.6%. The total concentration Σβ is preferably 0.5% or less, 0.4% or less.

[0059] Ni: 0% or more, 3.0% Co: 0% or more, 3.0% Total amount of Ni and Co ΣTR2: 0 to 3.0% or less Ni and Co are elements that can be used as materials for forming a pre-plating layer. When, for example, a Ni layer or a Co layer is formed as a pre-plating layer on a steel material (base sheet) before plating, these elements are ultimately contained in the plating layer. Typically, when a metal layer containing Ni or Co is formed on a base sheet for plating as a pre-plating layer, Ni or Co is often mixed into the plating layer in a range of 3.0% or less. Note that these pre-plating layers are often ultimately unevenly distributed as layers at the interface between the plating layer and the steel material, so the concentrations of Ni and Co are low as component concentrations in the Zn-Al-Mg alloy layer. Note that trace amounts of Ni and Co (e.g., 0.25% or less) can also be added to the plating bath in addition to the pre-plating layer.

[0060] Element group γ Cu: 0% or more, 0.25% or less Ag: 0% or more, 0.25% or less Sb: 0% or more, 0.25% or less Pb: 0% or more, 0.25% or less B: 0% or more, 0.50% or less P: 0% or more, 0.50% or less Ti: 0% or more, 0.25% or less Nb: 0% or more, 0.25% or less Zr: 0% or more, 0.25% or less W: 0% or more, 0.25% or less Total amount of Cu, Ag, Sb, Pb, B, P, Ti, Nb, Zr and W Σγ: 0% or more, 1.00% or less The elements of element group γ are elements that can be added optionally. When the concentration of one of these elements is 0.10% or more, the effect of improving corrosion resistance is obtained. Therefore, it is preferable that the concentration of at least one of these elements is 0.10% or more. However, if the total concentration of these elements Σγ becomes excessive, plating defects such as bare spots may occur. Therefore, the total concentration Σγ is set to 1.00% or less. The total concentration Σγ is preferably set to 0.50% or less. From the viewpoint of corrosion resistance, the concentrations of Cu, Ag, Sb, Pb, Ti, Nb, Zr, and W are each set to 0.25% or less. The concentrations of B and P are each set to 0.50% or less.

[0061] Fe: 0% or more, 5.0% or less. The hot-dip plated steel material of this embodiment is produced by a continuous hot-dip plating method, so Fe may diffuse from the base material to the plated layer during production. As mentioned above, in this embodiment, the Al concentration of the plated layer is high, and an Al-Fe-based interface alloy layer may be formed, but its thickness is thin. Furthermore, when an Fe pre-plated layer or the like is used, Fe inevitably diffuses into the plated layer, and Fe is contained in the Zn-Al-Mg alloy layer. As a result, the plated layer may contain up to 5.0% Fe. The Fe concentration may be 0%, but as long as the Fe concentration is 5.0% or less, there is no effect on the frequency of cracks in the plated layer. Therefore, the Fe content is set to 5.0% or less. The Fe concentration is preferably 4.0% or less, 3.0% or less, 2.0% or less, or 1.0% or less. The Fe content may be greater than 0%.

[0062] Balance: Zn and impurities The balance contains Zn and impurities. Since the hot-dip plated steel material of this embodiment is a highly versatile Zn-based plated steel material, the element constituting the main phase of the plated layer is Zn. There is no need to particularly specify the Zn concentration, but the Zn concentration may be 30 to 96% by mass. If necessary, the upper limit may be 90%, 80%, 70%, or 60%, and the lower limit may be 35%, 45%, 50%, or 55%.

[0063] Impurities refer to components contained in raw materials or components mixed in during the manufacturing process, but not intentionally included. For example, trace amounts of components other than Fe may be mixed into the plating layer as impurities due to atomic diffusion between the steel material (base steel) and the plating bath. Furthermore, since metals with 3N purity are typically used to manufacture plating alloys, the total concentration of impurities may be approximately 0.03% or less.

[0064] To identify the average chemical composition of the plating layer, the plating layer is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) to obtain an acid solution. The resulting acid solution is then measured using ICP atomic emission spectroscopy or ICP-MS to obtain the chemical composition. There are no particular restrictions on the type of acid, as long as it is an acid that can dissolve the plating layer. By measuring the area and weight before and after stripping, the plating adhesion amount (g / m ２ ) can also be obtained at the same time.

[0065] <Intermetallic Compounds> Next, the intermetallic compounds contained in the plating layer will be described. Since the plating layer according to this embodiment is a Zn-Al-Mg alloy plating, the plating layer contains a Zn phase, an Al phase, an MgZn phase, and the like. ２ The plating layer of this embodiment also contains an intermetallic compound containing a transition metal element TR1 (TR1-containing intermetallic compound).

[0066] MgZn ２ Phase MgZn ２ The MgZn phase is formed in the plating layer to improve the corrosion resistance of the plating layer. ２ The phase provides corrosion resistance to the plating layer and is a hard phase.

[0067] Zn phase (Al-Zn phase, Zn-Al phase) The Zn phase exists in the coating layer and has a ternary eutectic structure (Zn / Al / MgZn ２ The Zn phase mainly exists as a ternary eutectic structure. In addition, because the coating layer contains a large amount of Al, fine Al crystals and fine Zn crystals are mixed together, and when the amount of Al phase is large, it exists as an Al-Zn phase (mixed phase). On the other hand, when a large amount of Al phase is contained within the Zn phase, it exists as a Zn-Al phase (mixed phase). Since the amount of this phase is small compared to the entire coating layer, it is often not possible to confirm deterioration or improvement of corrosion resistance. Furthermore, a phase composed of Zn and Al is extremely easy to work.

[0068] The Al phase exists as fine grains in the Zn-Al phase and Al-Zn phase, and also in the ternary eutectic structure. In areas with high Al concentration, the grains grow and the Al phase may exist as coarse grains.

[0069] Intermetallic compound containing transition metal element (TR1) (TR1-containing intermetallic compound) The plating layer according to this embodiment contains (Al, Zn) １８ (Mg) ３ (TR1) ２ Such TR1-containing intermetallic compounds are formed in the plating layer when TR1 is contained in the plating layer. When Ca is contained in the plating layer, TR1 bonds with Ca and Al to form Al. １０ Ca(TR1) ２ In addition, when Ca is insufficient, TR1 combines with Al and Mg to form Al １８ Mg ３ (TR1) ２ In addition, since the atomic radii of Al and Zn, and Mg and Ca are close to each other, in the plating layer, part of Al is replaced by Zn, and part of Mg is replaced by Ca, forming (Al, Zn). １８ (Ca, Mg) ３ (TR1) ２ In addition, in areas where Ca is insufficient in the plating layer, (Al, Zn) １８ (Mg) ３ (TR1) ２may also be formed.

[0070] These intermetallic compounds all have similar crystal structures and are difficult to distinguish from one another. These intermetallic compounds exhibit diffraction peaks at approximately the same positions in XRD. However, from the perspective of enjoying the effects of this embodiment, it does not matter which intermetallic compound is formed, and the performance when contained in the plating layer is approximately the same, so there is no need to distinguish between them. Details will be described later.

[0071] By adding TR1 to the coating bath, the viscosity of the coating bath is significantly improved, and the lifting amount of the coating bath when the steel material is pulled up from the coating bath increases. In other words, according to this embodiment, by using TR1 as a constituent element of the coating layer, it is possible to manufacture a thick coated steel sheet, and a coated steel sheet with an excellent coating life can be easily manufactured.

[0072] To achieve this effect, it is effective to contain a certain amount of TR1-containing intermetallic compounds in the plating layer. Specifically, in a cross section along the thickness direction of the plating layer, the total area fraction of the TR1-containing compounds is preferably 1% or more. By increasing the total area fraction of the TR1-containing compounds, it is possible to ensure sufficient plating thickness and obtain a plating layer with excellent adhesion. This area fraction in a plating layer produced by an appropriate manufacturing method is mainly proportional to the concentration of the transition metal TR1 added. TR1-containing compounds can be observed using a scanning electron microscope (SEM). Details of measuring the area fraction of intermetallic compounds such as TR1-containing compounds will be described later.

[0073] Furthermore, when a large amount of these TR1-containing intermetallic compounds is contained in the plating layer, the TR1-containing intermetallic compounds grow coarsely, and in this case, the intermetallic compounds can also be detected by XRD.

[0074] The role of the TR1-containing intermetallic compounds is not only to increase the thickness of the plating layer, but also to incorporate transition metals into corrosion products during the corrosion process of the plating layer. The effect of the corrosion products is particularly evident in sacrificial corrosion protection. For example, in a plating layer containing these coarse TR1-containing intermetallic compounds, the coexistence of these coarse TR1-containing intermetallic compounds and Mg at the cut end surface of the plated steel material allows corrosion products to be stably formed, making it possible to suppress the generation of red rust from the cut end surface in the early stages of corrosion. Furthermore, as the TR1-containing intermetallic compounds grow coarse, unevenness appears on the plating surface, changing the appearance.

[0075] The presence of the TR1-containing intermetallic compound can be indirectly confirmed by the GDS method (glow discharge optical emission spectroscopy), which is a highly sensitive and quantitative detection method.

[0076] The transition metal elements remaining in the plating layer preferentially form these intermetallic compounds. On the other hand, because transition metal elements easily diffuse into Fe, diffusing a large amount of transition metal elements into the steel material (inside Fe) reduces the amount of transition metal elements in the plating layer. It is also possible to easily detect cases where the TR1 addition concentration is low, fine crystal grains are present, and TR1 is distributed throughout the plating layer.

[0077] Furthermore, when a large amount of the TR1 intermetallic compound is contained in the plating layer, the cross section of the plating layer can be observed with a scanning electron microscope (SEM) to directly identify the intermetallic compound, and the effect of containing the compound can be determined by measuring the area fraction of the contained intermetallic compound. These measurement methods will be described later.

[0078] Other intermetallic compounds When Ca and Si are contained, in addition to the TR1-containing metal compounds described above, Al-Ca-Si compounds may be formed. Furthermore, in the TR1-containing metal compounds, a portion of Al may be substituted with Zn. Ca may also be substituted with a portion of Mg.

[0079] Si is Mg ２ However, when the amount of Si exceeds the Ca concentration, Mg２ Si, but this Mg ２ It is not preferable to form a large amount of Si because it reduces corrosion resistance. However, a small amount of Mg ２ If it is Si, the deterioration of corrosion resistance of the entire plating layer is small.

[0080] Sn and In tend to bond with Mg, ２ Sn, Mg ９ Sn ５ , Mg ３ As described above, these phases have excellent sacrificial corrosion resistance. ３ Ni and the like may be contained. In this embodiment, the elements constituting the plating layer are grouped according to their atomic radius and properties. Therefore, when other elements are contained, there is a possibility that substitution products of these representative intermetallic compounds may be formed. Generally, these intermetallic compounds do not occupy the main phase in the plating layer, and therefore their impact on performance is small.

[0081] Next, a method for confirming the presence of intermetallic compounds containing the transition metal element TR1 in the plating layer according to this embodiment will be described. To eliminate the influence of solidification and structural characteristics of the plating layer on the evaluation, it is preferable that the plating thickness of the sample used for SEM, GDS, and XRD for cross-sectional observation of the plating layer be 25 μm (±2 μm). This allows for a relative evaluation between each plating component.

[0082] A glow discharge optical emission spectrometer (GDS) is preferably used to analyze the components in the depth direction within the plating layer. The inventors used a LECO Japan 850A glow discharge optical emission spectrometer, but the measurement device is not limited to this. Depth direction analysis is preferably performed while Ar sputtering is performed, under the following analysis conditions: argon pressure: 0.27 MPa, output power: 30 W, output voltage: 1000 V, and discharge area: a circular area with a diameter of 4 mm. Measurement is performed from the surface of the plating layer toward the depth direction until the Fe concentration reaches 100% (reaching the base steel). Therefore, the analysis range of depth direction analysis using GDS extends from the plating surface to the Zn-Al-Mg plating layer, and in some cases, alloy layers such as Fe-Al present between the plating layer and the pre-plating layer, and even to a portion of the steel material. After GDS analysis, the sputter depth of the cross section is measured using a "surfcom 130A" manufactured by Tokyo Seimitsu Co., Ltd. The GDS analysis provides an element distribution profile in the depth direction of the coating layer. The element distribution profile shows the distribution of the content of each element in the depth direction, assuming that the total amount of detected elements is 100%. The boundary (interface) between the coating layer and the steel material is defined as the position (t) where the Fe content exceeds 95 mass %, and the region deeper than that position is determined to be the base steel (steel material).

[0083] In this embodiment, in an element distribution profile obtained by GDS analysis from the surface of the plating layer toward the steel material, when the distance from the surface of the plating layer to the interface is defined as the thickness of the plating layer, a region of 0.1t or more (10% of the total thickness of the plating layer) exists in the region from the surface of the plating layer to the interface, where the total concentration ΣTR1 of the transition metal elements TR1 exhibits an intensity of 0.1% or more. Note that when two or more types of transition metal elements TR1 are contained in the plating layer, the total concentration ΣTR1 of the transition metal elements TR1 is used to obtain a total (concentration) intensity profile of the transition metal elements TR1 in the obtained element distribution profile.

[0084] Figure 1 shows an example of the results of depth profile analysis by GDS for the plating layer according to this embodiment. The graph shown in Figure 1 is an element distribution profile. In the example shown in Figure 1, the plating thickness t is 26 μm.

[0085] Within the above evaluation range, i.e., in the region from the surface to the interface of the coating layer, if a region showing ΣTR1 of 0.1% or more exists continuously for 0.1t or more in the depth direction, it can be said that a clear effect of increased viscosity was observed during the production of the coating layer. Specifically, under the same coating conditions with constant wiping and strip threading speed, the thickness of the coating layer increases. When considering the amount of corrosion of the coating layer, an increase in coating thickness is desirable from the standpoint of corrosion resistance, as it leads to an improvement in the corrosion protection period of the steel material.

[0086] In order to achieve the appropriate distribution of transition metal elements in the plating layer as described above, it is effective to appropriately control the production conditions, i.e., to appropriately manage the temperature of the plating bath, the base sheet to be plated, etc.

[0087] Furthermore, when a pre-plating layer such as a Ni layer or a Co layer is present on the original plate for plating, GDS can be used to confirm whether the Ni layer or the Co layer remains even after plating.

[0088] In this embodiment, when Ni and Co in the chemical composition are defined as the transition metal element TR2, it is preferable that the following formula (1) be satisfied when the depth showing the maximum value of the TR2 concentration in the element distribution profile is defined as t(TR2) and the depth showing the maximum value of the TR1 concentration is defined as t(TR1).

[0089] t(TR2)-t(TR1)≦0.30t...(1)

[0090] It has been found that when formula (1) is satisfied, i.e., when layers of transition metal elements TR1 and TR2 remain near the interface, not only excellent adhesion but also high sacrificial corrosion protection is obtained. This is thought to be because exposure of the base steel is suppressed and a large amount of intermetallic compounds containing TR1, which has excellent sacrificial corrosion protection, is present near the interface. In order to satisfy formula (1), it is effective to previously provide a Ni layer, a Co layer, or the like, and to ensure a coating amount sufficient to sufficiently suppress the diffusion of the transition metals.

[0091] The area ratio occupied by the intermetallic compound containing the transition metal element TR1 (TR1-containing intermetallic compound) is measured using an electron probe microanalyzer (EPMA). The cross section of the plating layer is exposed, and a vertical cross section in the depth direction of the plating layer is observed using a scanning electron microscope attached to the EPMA, and the regions where V and Mn exist are identified. These identified regions are then identified as intermetallic compounds containing TR1. Furthermore, these identified regions are quantitatively analyzed using point analysis or the like, and the intermetallic compound is identified from the atomic percentage. For example, the intermetallic compound obtained in this embodiment is Al １０ Ca(TR1) ２ , Al １８ Mg ３ (TR1) ２ etc., as long as the atomic ratio is close to these. Note that when the concentration of the transition metal element is low, the particles become fine, which may make EPMA analysis difficult. In such cases, it is advisable to identify the intermetallic compounds from the electron beam diffraction image using a TEM or the like. After identifying the intermetallic compounds, the total area fraction of the TR1-containing intermetallic compounds is calculated.

[0092] More specifically, an elemental mapping image is obtained using EPMA at a magnification of 1000x. Since the map image of the transition metal to be detected corresponds to the position of the intermetallic compound, the area ratio of the intermetallic compound to the plating layer can be determined from the elemental mapping image. In this embodiment, the TR1-containing intermetallic compound is contained in an area ratio of 1% or more in the cross section of the plating layer, which tends to increase the coating weight of the plating layer. More preferably, the area ratio of the TR1-containing intermetallic compound is 5% or more, 15% or more, or 25% or more. Furthermore, from the viewpoint of improving sacrificial corrosion protection, a content of 15% or more is preferable. The area ratio in the plating layer is correlated with the concentration of the added transition metal element.

[0093] Once the mapping images of each element are obtained, they are analyzed using image analysis software such as Image J. The Zn mapping image (in this embodiment, trace amounts of Zn are distributed in any part of the plating layer) is binarized, a threshold is set so that the entire plating layer is white or black, and the number of pixels in the Zn map is calculated in pixel units.

[0094] Next, the transition metal element TR1 mapping image is also binarized, and the number of TR1 pixels is obtained so that the TR1-containing intermetallic compounds (regions where the detection position of TR1 coincides with the location of the intermetallic compounds in the SEM image) can be identified. The value obtained by dividing the number of TR1 pixels by the number of Zn pixels represents the area fraction of the TR1-containing intermetallic compounds. The same operation is performed across 20 fields of view. That is, 20 different fields of view are randomly selected on the cross section of the plating layer, the area fraction is determined for each field of view, and the average value is calculated.

[0095] Next, the indexes of the TR1-containing intermetallic compounds determined by X-ray diffraction will be described.

[0096] X-ray diffraction measurement has lower detection sensitivity than GDS analysis, so it is assumed that the plating layer contains intermetallic compounds containing a certain amount of transition metal elements. Specifically, it is desirable that the area ratio of TR1-containing intermetallic compounds determined by the above-mentioned EPMA is 5% or more. In other words, when crystals of a size large enough to exhibit a specific orientation appear in the plating layer, these intermetallic compounds can also be detected by XRD. When nuclei within the plating layer grow and crystals of a specific orientation grow within the plating layer, unevenness forms on the plating layer surface, suppressing metallic reflection and making it easier to achieve a uniform concrete-like appearance. This moderately reduces gloss, making it a desirable performance for plated steel sheets used in a variety of building materials.

[0097] In the X-ray diffraction measurement, Cu-Kα rays were used and the X-ray output was measured under conditions of 50 kV and 300 mA. In the X-ray diffraction pattern of the plating layer surface, I defined by the following formula (4) was １ and I defined in the following formula (5) ２ and preferably satisfy the following formulas (2) and (3), respectively.

[0098] 1.5≦I １ ... (2) 1.5≦I ２ …(3) I １ =(Imax(10.5°~11.0°) / (I(10.5°)+0.2{|(I(11.0°)−I(10.5°)|}) …(4) I ２= (Imax (20.2° to 20.5°)) / (I (20.2°) + 0.667 {| I (20.5°) - I (20.2°) |}) ... (5)

[0099] Here, Imax (k to m°) 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 a diffraction angle n°, and k, m, and n are the diffraction angles (2θ) shown in formulas (4) and (5), respectively.

[0100] I in formula (4) and formula (5) １ , I ２ is (TR1) ２ Mg ３ Al １８ These are peaks related to intermetallic compounds represented by, for example, JCPDS Card #00-040-1153 (V ２ Mg ３ Al ８ ) and #04-007-9047 (Mn ２ Mg ３ Al １８ ), #04-008-7169(Cr ２ Mg ３ Al １８ ) includes intermetallic compounds defined in (TR1) and (TR1'), but even if the elements in (TR1) and (TR1') change, the diffraction peak positions do not change much. Therefore, these intermetallic compounds can be treated as the same kind, and I １ , I ２ The diffraction position of I does not overlap with other diffraction peaks, so it is a diffraction peak suitable for detection. １ , I ２ represents the specifications for the X-ray diffraction peaks of V-containing intermetallic compounds and Mn-containing intermetallic compounds. ２ Al ２０is defined in JCPDS card #00-051-1061. Note that these intermetallic compounds have similar diffraction peaks, making it difficult to distinguish them from one another; that is, Al and Mg are solid-solubilized together, and Zn and Ca are solid-solubilized together, so they are assumed to have almost the same components and structures, and the diffraction peaks appear at almost the same positions. Therefore, there is no need to distinguish these transition metal-containing intermetallic compounds from one another in X-ray diffraction measurements.

[0101] On the other hand, in the plating layer according to this embodiment, many of the diffraction peaks of these TR1-containing intermetallic compounds are different from the other main constituent phases, MgZn ２ , Al, and Zn. Therefore, among the many diffraction peaks of the TR1-containing intermetallic compound, it is necessary to pay attention to the diffraction peaks that do not overlap with other constituent phases. One of them is a diffraction peak appearing in the vicinity of 2θ = 10.6°, and the other is a diffraction peak appearing in the vicinity of 2θ = 20.4°.

[0102] Equation (4) focuses on the diffraction peak near 2θ = 10.6°. Imax (10.5° to 11.0°) in equation (4) is the maximum value of the X-ray diffraction intensity between diffraction angles of 10.5° and 11.0°. Imax (10.5°) is the X-ray diffraction intensity at a diffraction angle of 10.5°, and Imax (11.0°) is the X-ray diffraction intensity at a diffraction angle of 11.0°.

[0103] Furthermore, equation (5) focuses on the diffraction peak near 2θ = 20.4°. Imax (20.2° to 20.5°) in equation (4) is the maximum value of the X-ray diffraction intensity between diffraction angles of 20.2° and 20.5°. Imax (20.2°) is the X-ray diffraction intensity at a diffraction angle of 20.2°, and Imax (20.5°) is the X-ray diffraction intensity at a diffraction angle of 20.5°.

[0104] The numerators in formulas (4) and (5) are the intensities corresponding to the diffraction peaks of the TR1-containing compound, and are the maximum diffraction intensities of the diffraction peaks, including the background intensity. Because measurement errors in X-ray diffraction can cause the diffraction peaks to deviate from 10.6° or 20.4°, the maximum values ​​between 10.5° and 11.0° and between 20.2° and 20.5° are obtained.

[0105] The denominators of the formulas (4) and (5) are the background intensities at diffraction angles of 10.6° and 20.4°, calculated from the diffraction intensities at 10.6° and 20.4°.

[0106] For example, for the denominator of equation (4), as shown in FIG. 2, a straight line is drawn connecting the diffraction line at 10.5° and the diffraction line at 11.0°. This line becomes the baseline of the diffraction peak. Next, the absolute value of I(10.5°) - I(11.0°) is calculated. Also, the ratio (0.1 / 0.5 = 0.2) of the difference between diffraction angles 10.5° and 11.0° (0.5°) to the difference between diffraction angles 10.5° and 10.6° (0.1°) is calculated. The background intensity at a diffraction angle of 10.6° is then calculated using the formula given in the denominator of equation (4) above.

[0107] For the denominator of equation (5), as in the case of Figure 2, a straight line is drawn connecting the diffraction line at 20.2° and the diffraction line at 20.5°. This line becomes the baseline of the diffraction peak. Next, the absolute value of I(20.2°) - I(20.5°) is calculated. The ratio of the difference between the diffraction angles of 20.2° and 20.4° (0.2°) to the difference between the diffraction angles of 20.2° and 20.5° (0.3°) (0.2 / 0.3 = 0.667) is also calculated. The background intensity at a diffraction angle of 20.4° is then calculated using the formula given in the denominator of equation (5) above.

[0108] The conditions for obtaining the X-ray diffraction image are as follows.

[0109] X-ray diffraction using Cu as the target X-ray source is the most convenient method, as it can obtain average information about the constituent phases of the plating layer. As an example of measurement conditions, the X-ray conditions are a voltage of 50 kV and a current of 300 mA. There are no particular limitations on the X-ray diffraction device, but for example, a horizontal sample-type high-power X-ray diffraction device RINT-TTR III manufactured by Rigaku Corporation can be used.

[0110] [Method for manufacturing hot-dip plated steel material] Next, a method for manufacturing the hot-dip plated steel material of this embodiment will be described. The hot-dip plated steel material of this embodiment is preferably manufactured by a continuous hot-dip plating method. However, due to size restrictions of the steel material, it can also be manufactured by a batch-type hot-dip plating method, if necessary.

[0111] <Production Method A: Sendzimir Method> As described above, in this embodiment, the diffusion of the transition metal element TR1 added to the bath is sufficiently suppressed, leaving the transition metal element TR1 inside the plating layer and forming a specific intermetallic compound (a TR1-containing intermetallic compound) within the plating layer. However, when the plating layer is formed using the conventional Sendzimir method, the diffusion of the transition metal element TR1 to the steel surface (Fe surface) becomes active, and the transition metal element TR1 collects on the Fe surface during immersion in the plating bath, which tends to cause a loss of the reduction effect and the formation of an oxide film made of the transition metal element TR1. A plating layer in this state is undesirable because it can lead to non-plating in non-plated areas and peeling during processing.

[0112] <Manufacturing Method B> The present inventors have therefore investigated the optimum manufacturing conditions and found that forming a physical diffusion barrier on the original sheet for plating is effective in leaving the transition metal element TR1 in the plating layer. The "physical diffusion barrier" means, for example, forming a mismatched surface with the Fe crystals deposited by electroplating on the Fe surface of the surface of the original sheet for plating. Specifically, an Fe plating layer (for example, 0.5 to 2.0 g / m) is formed on the Fe surface of the surface of the original sheet for plating. ２) is attached to the base sheet. This forms a continuous crystal grain between the Fe surface and the Fe plating layer, providing a temporary diffusion barrier. Then, by immersing the base sheet with the Fe plating layer in a high-temperature bath, the Fe dissolves and diffuses into the plating bath. Much of the Fe acts as a nucleus for the growth of transition-metal intermetallic compounds, leaving almost no trace of them, effectively retaining the transition metal element TR1 in the plating layer. In this manufacturing method B, the plating bath temperature is preferably in the range of 590 to 620°C to simultaneously promote the dissolution of the Fe layer. Temperatures outside this range may result in unplated areas or adverse effects on adhesion. Furthermore, because a portion of the transition metal element TR1 diffuses to the Fe surface, it is necessary to thoroughly control the oxidation conditions of the base sheet. Specifically, a dew point of 0°C or higher is effective in inhibiting the reaction between oxygen and the transition metal element TR1. On the other hand, in the case of the above-mentioned manufacturing method A (Sendzimer method), Cr, Mo, Mn, and V, which are the causes of non-plating, tend to gather at the interface during the reaction, which makes it easy to cause non-plating. Furthermore, the above-mentioned manufacturing method A (Sendzimer method) is not preferable in terms of manufacturing method because it cannot exhibit the function and effect of the Fe plating layer, which is to prevent these elements from gathering at the interface during the reaction and keep them offshore in the plating bath.

[0113] <Manufacturing Method C> Furthermore, in order to more efficiently retain transition metal elements in the plating layer, it is preferable to form a Ni pre-plating layer or a Co pre-plating layer before forming the Fe plating layer as a pre-plating layer. The Ni pre-plating layer or the Co pre-plating layer functions as an additional barrier against the diffusion of transition metal elements into the Fe surface. As with Manufacturing Method B above, the Fe plating layer present on the Ni pre-plating layer or the Co pre-plating layer reacts with the transition metal elements during plating and then rapidly diffuses into the plating layer. In other words, the reaction between the Fe plating layer and the transition metal elements during plating moves the plating bath accumulated at the interface offshore, thereby achieving the repeated reduction effect of regenerating a fresh Fe surface. This is thought to be due to the inconsistency in the crystal planes of the Fe base material and the Fe crystals (fine grains) of the Fe plating layer deposited by electroplating, which is involved in the reaction with the transition metal elements. Ni in the Ni pre-plated layer and Co in the Co pre-plated layer tend to diffuse toward the Fe surface of the base material rather than toward the plating bath, and are likely to remain on the Fe surface even after immersion in the plating bath. On the other hand, Fe in the Fe plating layer formed on the upper surface tends to diffuse toward the plating bath. Note that when a Ni pre-plated layer or a Co pre-plated layer is provided on the base, dew point control, as employed in Manufacturing Method B, is not required. The effective Ni or Co deposition amount for Manufacturing Method C is 0.5 g / m. ２ The deposition amount is 2.0 g / m or more. ２ In the above cases, the transition metal elements can be concentrated further near the interface, which is preferable in terms of sacrificial corrosion protection.

[0114] <Manufacturing Method D> On the other hand, when a Ni pre-plated layer or a Co pre-plated layer is used alone, immediately after immersion in the plating bath, Ni or Co diffuses to the steel material side, and at the same time, transition metals accumulate on the Ni pre-plated layer or the Co pre-plated layer, making it easy for an oxide film to form. As a result, Fe-Ni-transition metal elements are formed, making it difficult to reduce, and an oxide film forms. In this case, plating adhesion is poor and bare spots occur.

[0115] As explained above, the above-mentioned manufacturing method B and manufacturing method C are preferable as the manufacturing method of the plated steel material of this embodiment.

[0116] <Other Manufacturing Conditions> The continuous hot-dip galvanizing method is carried out by the Sendzimir method after preparing the base sheet to be plated so as to satisfy the above-mentioned manufacturing methods B and C. That is, before immersing the steel material in the plating bath, the steel material is heated at the annealing temperature of a nitrogen-hydrogen mixed gas until the steel material temperature reaches or exceeds the plating bath temperature. Typically, the annealing atmosphere is a nitrogen atmosphere containing hydrogen, with a hydrogen concentration of 5%, and the steel material is heated at a temperature of around 600 to 800°C to sufficiently reduce the steel material surface. When a pre-plating layer such as a Ni pre-plating layer or a Co pre-plating layer is not applied to the plated substrate, it is effective to humidify the substrate and adjust the dew point as described above. Note that when the base sheet to be plated is immersed in the plating bath, N is used to heat the steel material until the steel material temperature reaches the plating bath temperature. ２ Gas cooling is used to prevent fluctuations in the plating bath temperature during the manufacturing process.

[0117] Next, the steel material whose surface has been sufficiently reduced is immersed in a reduced state in a coating bath at a temperature of 570°C or higher, preferably 600°C or higher.

[0118] The immersion time of the steel material in the plating bath is in the range of 1 to 5 seconds. If the immersion time exceeds 5 seconds, a thick interfacial alloy layer will be formed, which is not preferable.

[0119] After immersion in the plating bath, the thickness of the plating layer is adjusted by wiping immediately. After wiping is complete, the workpiece is cooled.

[0120] If the cooling rate at high temperatures above 550°C is too slow, the Ni pre-plating layer, Co pre-plating layer, and Fe layer will dissolve significantly into the plating bath, affecting plating properties. Therefore, cooling from the bath temperature to 550°C should be completed within 10 seconds.

[0121] After immersion in the plating bath, the Fe in the Fe layer immediately diffuses, and these diffuse as nuclei to form intermetallic compounds containing transition metal elements. On the other hand, if the cooling rate after immersion is high, the crystal size of each phase becomes small, while if the cooling rate is low, the crystal size becomes large. A large crystal size in the plating layer is preferable because it increases the plating thickness. In other words, a low cooling rate after immersion is preferred. Furthermore, the plating structure is determined by 350°C, where the liquid phase remains. For these reasons, the upper limit of the cooling rate to 350°C after removal from the plating bath is set to 100°C / s or less, and preferably 50°C / s or less. The lower limit of the cooling rate may be set to 1°C / s or more after removal from the plating bath, taking into account equipment constraints on the production line.

[0122] <Manufacturing Method E> Here, the cooling rate in the liquid phase between 600 and 300°C affects the process from nucleation by Fe in the Fe layer to growth. In other words, between 600 and 300°C, the higher the temperature, the easier the growth, and the lower the temperature, the more nuclei are generated and the more difficult the growth. For this reason, it is preferable to cool slowly in the high-temperature region between 600 and 450°C to suppress the amount of nuclei generated. Specifically, for example, it is preferable to suppress the cooling rate in this high-temperature region to between 5 and 20°C / second. In addition, it is necessary to use a plating base sheet that promotes nucleus growth using pre-plated Fe.

[0123] After the plating layer is formed, various chemical conversion treatments and painting treatments may be carried out.

[0124] In the hot-dip plated steel material of this embodiment, a coating may be formed on the plating layer. One or more layers of the coating may be formed. Examples of the type of coating directly on the plating layer include a chromate coating, a phosphate coating, and a chromate-free coating. These coatings can be formed by known methods such as chromate treatment, phosphate treatment, and chromate-free treatment.

[0125] Chromate treatments include electrolytic chromate treatments that form a chromate film by electrolysis, reactive chromate treatments that form a film by utilizing a reaction with the material and then wash away excess treatment solution, and paint-on chromate treatments that apply a treatment solution to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0126] Examples of electrolytic chromate treatments include electrolytic chromate treatments using chromic acid, silica sol, resins (phosphoric acid, acrylic resins, vinyl ester resins, vinyl acetate acrylic emulsions, carboxylated styrene butadiene latex, diisopropanolamine-modified epoxy resins, etc.), and hard silica.

[0127] Examples of the phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0128] Chromate-free treatments are particularly suitable because they do not place a burden on the environment. Chromate-free treatments include electrolytic chromate-free treatments that form a chromate-free film by electrolysis, reactive chromate-free treatments that form a film by utilizing a reaction with the material and then wash away excess treatment liquid, and paint-on chromate-free treatments that apply a treatment liquid to the substrate and dry it without rinsing with water to form a film. Any of these treatments may be used.

[0129] Furthermore, one or more organic resin coatings may be provided on the coating directly on the plating layer. The organic resin is not limited to a specific type, and examples thereof include polyester resins, polyurethane resins, epoxy resins, acrylic resins, polyolefin resins, and modified versions of these resins. Here, the term "modified version" refers to a resin obtained by reacting a reactive functional group contained in the structure of these resins with another compound (such as a monomer or a crosslinking agent) containing a functional group capable of reacting with the functional group.

[0130] Such organic resins may be a mixture of one or more unmodified organic resins, or a mixture of one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin. The organic resin film may also contain any coloring pigment or anti-rust pigment. Water-based organic resins obtained by dissolving or dispersing them in water may also be used.

[0131] As explained above, it is difficult to increase the coating weight of a coating layer with an increased Al content due to a decrease in the specific gravity of the coating bath. However, according to the hot-dip coated steel material of this embodiment, by adding V or Mn, the viscosity of the coating bath is increased, making it possible to produce a hot-dip coated steel material with a coating layer with a large coating weight. Furthermore, since the coating layer contains a V-containing intermetallic compound or a Mn-containing intermetallic compound, corrosion resistance can be improved. Furthermore, by adding V or Mn to the coating layer, the thickness of the interfacial alloy layer can be reduced, thereby improving adhesion. Furthermore, since the coating weight of the coating layer is large, corrosion resistance can be further improved.

[0132] Next, examples of the present invention will be described, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0133] Details of the examples are shown in Tables 1 to 3. First, two types of cold-rolled steel sheets (corresponding to JIS G 3141 (2017)) with different thicknesses of 100 mm × 200 mm × 0.8 mmt and 100 mm × 200 mm × 2.3 mm were prepared as base steel sheets to be plated (base steel materials) ("0.8 mm sheet" and "2.3 mm sheet" in the tables).

[0134] These base steel materials were subjected to continuous hot-dip galvanization using the Sendzimir method. A K-type thermocouple was spot-welded to the center of the backside of the plated original sheet so that temperature changes during the plating process could be monitored. A hot-dip galvanization simulator manufactured by Rhesca was used for the galvanization.

[0135] [Conditions for producing the plating layer] The plating layer was produced by employing one of the following production methods A to E. In each production method, pure metals (purity 3N or higher) of Zn, Al, and Mg were mixed as the plating bath to prepare a Zn-Al-Mg hot-dip plating bath so as to obtain a plating layer having the chemical composition shown in Table 1. The elements listed under "base sheet" in the table are the constituent elements of the pre-plating layer formed in advance on the base sheet for plating, and the numerical values ​​attached to the elements indicate the coating weight (g / m ２ ) means

[0136] <Production Method A> The Sendzimir method was used as the hot-dip galvanizing method. That is, before immersing the base steel sheet in the galvanizing bath, the steel sheet was heated at the annealing temperature of a nitrogen-hydrogen mixed gas until the steel sheet temperature reached the galvanizing bath temperature or higher. The annealing atmosphere was a nitrogen atmosphere containing 5% hydrogen (N ２ -5% H ２ ) and heated to a temperature of around 800°C for about 1 minute to fully reduce the steel surface. Humidification was not performed and the dew point was set to -40°C. When the original sheet to be plated was immersed in the plating bath, N was blown into the plating bath until the temperature of the original sheet reached the plating bath temperature so that the plating bath temperature would not fluctuate during the manufacturing process. ２ Cooling was carried out using gas. The plating bath temperature was set to 600°C. The immersion time in the plating bath was set to 3 seconds. The pulling speed and N ２ Gas wiping was applied to set the plating thickness t to 25 μm (±2) μm. After pulling up the plated original sheet, it was cooled in the temperature range of 600 to 200°C at a cooling rate of 10°C / sec. Thereafter, it was allowed to cool naturally.

[0137] <Production Method B> The Sendzimir method was used as the hot-dip plating method, but an Fe plating layer was previously formed on the plating base sheet. ４ ・7H ２ O: 600g / L, 6.7A / dm ２The plating was carried out under the condition of a bath temperature of 47°C, with the current application time adjusted so as to obtain a predetermined Fe content. The subsequent plating conditions were the same as those of Production Method A, except that the dew point was set to 0°C.

[0138] <Production Method C> The Sendzimir method was used as the hot-dip plating method, but a Ni layer or a Co layer was formed in advance as a pre-plating layer on the base sheet to be plated, and then Fe plating was carried out in the same manner as in Production Method B. The Ni pre-plating was carried out using NiSO ４ ・6H ２ O: 340g / L, NiCl ２ ・6H ２ O: 70 g / L, H ３ BO ３ :40g / L, bath temperature 50℃, 5A / dm ２ The current application time was adjusted to obtain a predetermined amount of Ni under the conditions of ２ SO ４ :0.5g / L, CoSO ４ ・6H ２ O: 246g / L, H ３ BO ３ :45g / L, bath temperature 50℃, 5A / dm ２ The current application time was adjusted so as to obtain a predetermined amount of Co under the above conditions. The subsequent plating conditions were the same as those in Manufacturing Method A.

[0139] <Production method D> The Sendzimir method was used as the hot-dip plating method, but only a Ni layer or a Co layer was formed in advance as a pre-plating layer on the plating base sheet. The subsequent plating conditions were the same as those of Production method A.

[0140] <Production method E> Production method E is similar to production method C. In production method E, plating was performed by production method C, and after the base sheet was pulled out of the plating bath, mist cooling was performed to cool it to 30°C at a cooling rate of 30°C / second.

[0141] Plated steel materials were manufactured by the above manufacturing methods A to E. A 4 cm area was cut from the center of the obtained plated steel material. ２A sample of 10 ...

[0142] [Performance] Next, the performance of the obtained plated steel material was evaluated using the "0.8 mm sheet" and the "2.3 mm sheet." Specifically, the effect of plating thickness, adhesion, sacrificial corrosion protection, and gloss were investigated.

[0143] (Effect of plating thickness) The effect of plating thickness was evaluated by the following test. Before immersing a sample of a plating base sheet having a size of 100×200×0.8 mm in a plating bath, N ２ -5% H ２ The original steel sheet was annealed in a reducing atmosphere at 100°C to reduce the surface. The original steel sheet was then immersed in the plating bath for at least 3 seconds and pulled up vertically. Tests were conducted at three pull-up speeds: 10 mm / s, 50 mm / s, and 100 mm / s. Wiping was not performed during testing. The thickness of the plating layer was calculated from the coating weight. Specifically, a 50 mm diameter sample was taken from the center of the resulting plated steel sheet and immersed in 10% hydrochloric acid containing an inhibitor to remove only the plating layer. The coating weight was calculated from the weight difference before and after removal. The thickness of the plating layer was calculated by dividing the coating weight by the theoretical density of the components. These three levels were tested repeatedly with N = 3, and the average plating thickness was calculated from the average of all samples. The evaluation criteria were as follows: "S," "A," "B," "C," and "D" were considered pass, and "E" was considered fail.

[0144] Average plating thickness over 31.5 μm... "S" Average plating thickness over 30 μm and 31.5 μm or less... "A" Average plating thickness over 27 μm and 30 μm or less... "B" Average plating thickness over 24 μm and 27 μm or less... "C" Average plating thickness over 21 μm and 24 μm or less... "D" Average plating thickness 21 μm or less... "E"

[0145] (Adhesion) The adhesion of the plating layer (unplated) was evaluated by a 1-ton bending test. First, a sample measuring 40 mm x 120 mm x 0.8 mm was taken from the obtained plated steel material so as to include the plating layer. Next, the taken sample was bent at the center in the longitudinal direction (120 mm) (60 mm length per side). Tape was firmly attached to both sides of the plated steel sheet beforehand. A 1-ton (the thickness of one steel sheet) was sandwiched inside, bent at 180° in a jig, and completely pressed to prepare a bending test specimen with a space equivalent to one steel sheet inside. Then, the inner steel sheet was removed, and the tape was forcefully pulled and peeled off. At this time, the inner and outer tapes were attached to black cardboard to check for the presence of peeled plating powder in the processed area. The evaluation criteria were as follows: "G" was considered pass, and "B" was considered fail.

[0146] Peeling powder on both sides... "Bad (B)" No peeling powder on both sides... "Good (G)"

[0147] (Sacrificial Corrosion Protection) Three rectangular samples measuring 50 × 100 × 2.3 mm were taken from different positions on the resulting plated steel material. The four end faces were mirror-polished to eliminate the effects of shearing on the cut end faces. The samples were completely immersed in a 0.01 M NaCl aqueous solution for 10 seconds and then placed horizontally at 45% humidity and 30°C for 240 hours. This cycle was repeated three times. The red rust area ratio on the four end faces after 240 hours was measured. The same test was performed on three samples, and the average was taken as the red rust area ratio. The evaluation criteria were as follows: "EX," "VG," and "G" were considered pass, and "B" was considered fail.

[0148] Red rust area ratio less than 10%... "Excellent (EX)" Red rust area ratio 10% or more but less than 20%... "Very Good (VG)" Red rust area ratio 20% or more but less than 30%... "Good (G)" Red rust area ratio more than 30%... "Bad (B)"

[0149] (Glossiness) A sample for gloss testing was cut out from the center of a 2.3 mm plate sample, and the sample was used to measure glossiness. Specifically, the 60° gloss (G60) defined in JIS Z 8741:1997 was measured on the surface of the sample using a glossmeter. A sample manufactured with a thickness of 0.8 mm was used. The 60° gloss was measured at 10 random locations on the surface of the plated steel material, and the average value was calculated. The evaluation criteria were as follows: "FA" was judged to be good (i.e., low glossiness).

[0150] 60° gloss (G60) is 40 or less... "Favorable (FA)" 60° gloss (G60) is over 40... "Dazzling (DZ)"

[0151]

[0152]

[0153]

[0154] According to the above-described aspects of the present invention, it is possible to provide a hot-dip plated steel material that can ensure a sufficient plating thickness even in the case of a plating layer containing elements with a relatively high specific gravity (particularly, transition metal elements), and as a result, it is possible to provide a hot-dip plated steel material that can exhibit good corrosion resistance over a long period of time and has a long life.

Claims

1. A hot-dip galvanized steel product having a steel material and a coating layer disposed on a surface of the steel material, wherein the coating layer contains, in mass %, Al: more than 10% and less than 40%, Mg: 4.0% to 15.0%, Si: 0% to 2.0%, V: 0% to 3.0%, Mn: 0% to 3.0%, Cr: 0% to 3.0%, Mo: 0% to 3.0%, Sn: 0% to 0.7%, Bi: 0% to 0.3%, In: 0% to 0.3%, Ca: 0% to 0.6%, Y: 0% to 0.3%, La: 0% to 0.3%, Ce: 0% to 0.3%, Sr: 0% to 0.3%, Li: 0% or more, 0.3% or less, Ni: 0% or more, 3.0% or less, Co: 0% or more, 3.0% or less, Cu: 0% or more, 0.25% or less, Ag: 0% or more, 0.25% or less, Sb: 0% or more, 0.25% or less, Pb: 0% or more, 0.25% or less, B: 0% or more, 0.50% or less, P: 0% or more, 0.50% or less, Ti: 0% or more, 0.25% or less, Nb: 0% or more, 0.25% or less, Zr: 0% or more, 0.25% or less, W: 0% or more, 0.25% or less, Fe: 0% or more, 5.0% or less, the balance being Zn and impurities, and the total amount of V and Mn ΣTR1: 0.05% or more, 3.0% or less, The alloy has a chemical composition in which the total amount of Cr and Mo, ΣTR1', is 0% or more and 3.0% or less, ΣTR1+ΣTR1', is 0.05% or more and 3.0% or less, the total amount of Sn, Bi and In, Σα, is 0% or more and 0.7% or less, the total amount of Ca, Y, La, Ce, Sr and Li, Σβ, is 0% or more and 0.6% or less, the total amount of Ni and Co, ΣTR2, is 0% or more and 3.0% or less, and the total amount of Cu, Ag, Sb, Pb, B, P, Ti, Nb, Zr and W, Σγ, is 0% or more and 1.00% or less, In an element distribution profile obtained by GDS analysis from the surface of the plating layer toward the steel material in the thickness direction of the steel material, the depth position at which the Fe concentration reaches 95% is defined as the interface between the plating layer and the steel material, and the distance from the surface of the plating layer to the interface is defined as the thickness t of the plating layer, the proportion of the depth at which the total amount ΣTR1 is 0.1% or more is 10% or more of the thickness t.

2. The hot-dip galvanized steel material according to claim 1, wherein, when V and Mn in the chemical composition are defined as TR1, the plating layer contains a TR1-containing intermetallic compound, and the total area ratio of the TR1-containing intermetallic compounds in a cross section of the plating layer is 1% or more.

3. The hot-dip galvanized steel material according to claim 1 or 2, wherein, when Ni and Co in the chemical composition are defined as TR2, the depth at which the TR2 concentration is at its maximum in the element distribution profile is defined as t(TR2), and the depth at which the TR1 concentration is at its maximum is defined as t(TR1), the following formula (1) is satisfied: t(TR2) - t(TR1) ≦ 0.30t (1) 4. In the X-ray diffraction pattern of the surface of the plating layer measured using Cu-Kα rays under conditions of an X-ray output of 50 kV and 300 mA, I defined by the following formula (4) １ and I defined in the following formula (5) ２ The hot-dip plated steel material according to claim 1 or 2, wherein the following formulas (2) and (3) are satisfied: 1.5≦I １ ... (2) 1.5≦I ２ …(3) I １ =(Imax(10.5°~11.0°) / (I(10.5°)+0.2{|I(11.0°)−I(10.5°)|}) …(4) I ２ = (Imax (20.2° to 20.5°)) / (I(20.2°) + 0.667 {|I(20.5°) - I(20.2°)|}) ... (5) In equations (4) and (5), Imax (k to m°) 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 a diffraction angle n°, and k, m, and n are the diffraction angles (2θ) shown in equations (4) and (5), respectively.

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