Plated steel material

Abstract

This plated steel material includes a plating layer that contains, in terms of mass%, 10.0-40.0% of Al, 5.0-12.5% of Mg, 0-1.0% of Ti, and 0-1.0% of Zr, the balance being at least 50% of Zn and impurities. The total of Ti plus Zr is 0.001% or greater, and the diffraction intensity as determined by X-ray diffraction of the plating layer satisfies formula (1). Formula (1): I(200)Al / {(I(111)Al + I(220)Al + I(200)Al + I(311)Al} ≥ 0.40. In formula (1), I(200)Al is the diffraction intensity of Al(200), I(111)Al is the diffraction intensity of (111) of Al, I(220)Al is the diffraction intensity of (220) of Al, and I(311)Al is the diffraction intensity of (311) of Al.

Description

Plated steel

[0001] This application claims priority to Japanese Patent Application No. 2023-131415, filed on August 10, 2023, the contents of which are incorporated herein by reference.

[0002] Plated steel has excellent corrosion resistance and is used in the fields of building materials and civil engineering. In particular, hot-dip Zn-Al-Mg plated steel has excellent corrosion resistance and is widely used in the above fields. Hot-dip Zn-Al-Mg plated steel is sometimes processed into various shapes before being made into various final products.

[0003] The typical phase structure of the hot-dip Zn-Al-Mg coating layer is MgZn. ２ Phase, [Al / Zn / MgZn ２ ] A ternary eutectic structure and Al primary crystals are formed. The Al primary crystals are Al dendrite structures containing Zn. Among these phase structures, MgZn ２ phase and [Al / Zn / MgZn ２ ) The ternary eutectic structure is said to have low plastic deformability. The primary Al phase is MgZn ２ phase and [Al / Zn / MgZn ２ ] Although it is said that the plastic deformability is higher than that of a ternary eutectic structure, it is hard to say that it is sufficient. Therefore, the coating layer of a hot-dip Zn-Al-Mg-plated steel material has poor workability. As a result, the coating layer of a hot-dip Zn-Al-Mg-plated steel material cannot follow the deformation caused by working, and the coating layer cracks in the worked area, resulting in a problem that the corrosion resistance of the worked area is inferior to that of a flat surface.

[0004] In Patent Document 1, MgZn is present in the primary crystal of Al. ２ Patent Document 1 discloses a technique for suppressing the progression of corrosion of the Al primary crystals by precipitating Al. Patent Document 1 aims to improve the corrosion resistance of the processed portion by suppressing the corrosion rate of the Al primary crystals, but does not consider improving the processability of the plating layer itself.

[0005] Japanese Patent Application Publication No. 2005-336546

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plated steel material that has excellent corrosion resistance and excellent workability of the plating layer.

[0007] In order to solve the above problems, the following configuration is adopted. [1] A steel sheet comprising a steel material and a plating layer on the steel material, wherein the plating layer has an average chemical composition, in mass%, of Al: 10.0% to 40.0%, Mg: 5.0% to 12.5%, Ti: 0% to 1.0%, Zr: 0% to 1.0%, Si: 0% to 5.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to 0.50%, Ce: 0% to 0.50%, Sr: 0% to 0.50%, Sn: 0% to 3.00%, Bi: 0% to 1.00%, In: 0% to 1.00%, B: 0% to 1.00%, P: 0% to 0.50%, Cr: 0% to 0.25%, V : 0% to 0.25%, Ni: 0% to 1.0%, Co: 0% to 0.25%, Nb: 0% to 0.25%, Cu: 0% to 1.0%, Mn: 0% to 0.25%, Mo: 0% to 0.25%, W: 0% to 0.25%, Ag: 0% to 1.00%, Li: 0% to 0.50%, Na: 0% to 0.05%, Ba: 0% to 0.25%, K: 0% to 0.05%, Fe: 0% to 5.0%, Sb: 0% to 0.50%, Pb: 0% to 0.50%, balance: 50.0% or more of Zn and impurities, wherein the total of Ti and Zr in the plating layer is 0.001% or more, A plated steel material, wherein the diffraction intensity obtained from the X-ray diffraction measurement of the plated layer satisfies the following formula (1): I(200) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ}≧0.40 (1) where I(200) in formula (1) Ａｌ is the diffraction intensity of Al (200), and I (111) Ａｌ is the diffraction intensity of Al (111), and I (220) Ａｌ is the diffraction intensity of Al (220), and I (311) Ａｌis the diffraction intensity of Al (311). [2] The plated steel material according to [1], wherein the total amount of Ti and Zr in the plated layer is 0.020% or more. [3] The plated steel material according to [1] or [2], wherein, in a cross section in the thickness direction of the plated layer, the ratio of the total area of ​​Al phases having a circle equivalent diameter of 20 μm or less to the total area of ​​Al phases is 50% or more.

[0008] According to the present invention, a plated steel material having excellent corrosion resistance and excellent workability of the plating layer can be provided.

[0009] 1 is a cross-sectional schematic view of a plated steel material according to an embodiment of the present invention.

[0010] When bending plated steel, if cracks occur in the plating layer and expose the steel substrate, the plating layer acts as a sacrificial corrosion protection around the exposed area, causing the constituent elements of the plating layer to leach out and partially wear away the plating layer itself. As a result, the corrosion resistance of the plating layer near the bent area may be reduced compared to the plating layer outside the bent area. To prevent this, it is necessary to prevent cracks in the plating layer in the bent area. The greater the plastic deformability of the plating layer, the less likely it is to crack.

[0011] The Zn-Al-Mg based plating layer has a phase structure containing multiple phases and structures, for example, MgZn ２ Phase, [Al / Zn / MgZn ２ The primary Al crystal has a crystal structure of Al dendrites containing Zn. ２ phase and [Al / Zn / MgZn ２ The ternary eutectic structure of Al is said to have low plastic deformability and poor workability. On the other hand, it is known that the workability of Al changes depending on the crystal orientation. Therefore, if the crystal orientation of Al, which is mainly contained in the Al primary crystal, can be controlled, it is expected that the overall workability of the plating layer will be improved and cracks in the plating layer in the processed area will be reduced.

[0012] The inventors conducted research aimed at improving the workability of the plating layer by controlling the crystal orientation of the Al phase, and found that when the plating layer contains either or both of Zr and Ti, the proportion of (100) planes among the crystal orientation planes of Al on the surface of the plating layer increases, thereby improving the workability of the plating layer.

[0013] In addition, Zr and Ti form compounds with Al in the plating layer, specifically Al ３ Zr, Al ３ Forms intermetallic compounds such as Ti. If Si is also present, Al ２．７ Si ０．３ Zr, Al ２．５ Si ０．５ These intermetallic compounds act as solidification nuclei for the primary Al crystals and refine the primary Al crystals, which further improves the workability of the plating layer.

[0014] Steel structures manufactured from such plated steel materials have excellent workability and corrosion resistance.

[0015] Hereinafter, a plated steel material according to an embodiment of the present invention will be described. The plated steel material of the present embodiment includes a steel material and a plating layer provided on the surface of the steel material, and the plating layer has an average chemical composition, in mass %, of Al: 10.0% to 40.0%, Mg: 5.0% to 12.5%, Ti: 0% to 1.0%, Zr: 0% to 1.0%, Si: 0% to 5.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to 0.50%, Ce: 0% to 0.50%, Sr: 0% to 0.50%, Sn: 0% to 3.00%, Bi: 0% to 1.00%, In: 0% to 1.00%, B: 0% to 1.00%, P: 0% to 0.50%, Cr: 0% to 0.25%, V: 0% to 0.25%, Ni: 0% to 1.0%, Co: 0% to 0.25%, Nb: 0% to 0.25%, Cu: 0% to 1.0%, Mn: 0% to 0.25%, Mo: 0% to 0.25%, W: 0% to 0.25%, Ag: 0% to 1.00%, Li: 0% to 0.50%, Na: 0% to 0.05%, Ba: 0% to 0.25%, K: 0% to 0.05%, Fe: 0% to 5.0%, Sb: 0% to 0.50%, Pb: 0% to 0.50%, and the balance: 50.0% or more of Zn and impurities, wherein the total amount of Ti and Zr in the plating layer is 0.001% or more, and the diffraction intensity obtained from the results of X-ray diffraction measurement of the plating layer satisfies the following formula (1): The surface of the steel material referred to here means the interface between the plating layer and the steel material. The plating layer provided on the surface of the steel material is a plating layer provided on the steel material.

[0016] I (200) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ} ≧ 0.40 ... (1)

[0017] However, I(200) in formula (1) Ａｌ is the diffraction intensity of Al (200), and I (111) Ａｌ is the diffraction intensity of Al (111), and I (220) Ａｌ is the diffraction intensity of Al (220), and I (311) Ａｌ is the diffraction intensity of Al (311).

[0018] The total content of Ti and Zr in the plating layer is preferably 0.020% or more.

[0019] In addition, in the plated steel material of this embodiment, in a cross section in the thickness direction of the plated layer, the ratio of the total area of ​​Al phases having a circle-equivalent diameter of 20 μm or less to the total area of ​​Al phases is preferably 50% or more.

[0020] In the following description, the "%" used to indicate the content of each element in the chemical composition means "mass %." 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. 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.

[0021] "Corrosion resistance" refers to the corrosion resistance of the plating layer itself. Zn-based plating layers have a sacrificial corrosion protection effect on steel materials, so the plating layer corrodes and turns to white rust before the steel material corrodes, and after the white rusted plating layer disappears, the steel material corrodes and turns to red rust. This is the corrosion process of plated steel sheets. "Workability" refers to the resistance to cracks in the plating layer when the plated steel material is bent.

[0022] As shown in FIG. 1 , the plated steel material 1 according to this embodiment has a steel material 11. There are no particular limitations on the shape of the steel material 11, and an example of the steel material 11 is a steel plate. The steel material 11 may also be a formed, bare steel material such as a steel pipe, civil engineering and construction material (fences, corrugated pipes, drainage ditch covers, sand-blocking plates, bolts, wire mesh, guardrails, water-blocking walls, etc.), home appliance components (casings for air conditioner outdoor units, etc.), or automobile parts (suspension components, etc.). Forming is performed by various plastic processing techniques such as pressing, roll forming, and bending.

[0023] There are no particular limitations on the material of the steel material 11. Various types of steel material can be used as the steel material 11, such as general steel, Ni-preplated steel, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, and some high-alloy steels (steels containing strengthening elements such as Ni and Cr). Furthermore, the steel material 11 is not particularly limited in terms of the conditions for the steel material manufacturing method and the steel sheet manufacturing method (hot rolling method, pickling method, cold rolling method, etc.). Furthermore, the steel material 11 may be a steel material on which a metal or alloy film of less than 1 μm, such as Zn, Ni, Sn, or an alloy thereof, is formed.

[0024] Next, the plating layer 12 will be described. The plated steel material 1 according to this embodiment has a plating layer 12 disposed on the surface of the steel material 11. When the steel material 11 is a steel plate, the plating layer 12 is disposed on at least one surface of the steel plate and the other surface opposite to the one surface. The plating layer 12 is also disposed on an end surface between the one surface and the other surface of the steel plate.

[0025] The plating layer 12 according to this embodiment is primarily composed of a Zn—Al—Mg alloy layer due to its chemical composition, which will be described later. The Zn—Al—Mg alloy layer is made of a Zn—Al—Mg alloy. The Zn—Al—Mg alloy refers to a ternary alloy containing Zn, Al, and Mg. A Zn—Al—Mg alloy layer, in which alloying elements such as Al and Mg are added to Zn, has improved corrosion resistance compared to a typical Zn plating layer. For example, even if the Zn—Al—Mg alloy layer is about half the thickness of a typical Zn plating layer, it has corrosion resistance equivalent to that of a Zn plating layer. Therefore, the plating layer according to this embodiment also has corrosion resistance equivalent to or greater than that of a Zn plating layer.

[0026] Furthermore, the plating layer 12 of the plated steel material 1 according to this embodiment may include an Fe-Al interfacial alloy layer (hereinafter referred to as an Al-Fe alloy layer) between the steel material 11 and the Zn-Al-Mg alloy layer. The Al-Fe alloy layer is an interfacial alloy layer between the steel material and the Zn-Al-Mg alloy layer.

[0027] The plating layer according to this embodiment may have a single-layer structure of a Zn—Al—Mg alloy layer, or a laminate structure including a Zn—Al—Mg alloy layer and an Al—Fe alloy layer. In the case of a laminate structure, the Zn—Al—Mg alloy layer is preferably the layer that constitutes the surface of the plating layer. However, although an oxide film of the plating layer constituent elements is formed on the outermost surface of the plating layer with a thickness of less than 1 μm, this is thin compared to the overall thickness of the plating layer and can therefore be ignored from the perspective of the main body of the plating layer.

[0028] Generally, the thinner the plating layer, the better the workability; however, considering the wear of the plating layer due to corrosion, the thicker the plating layer, the easier it is to ensure corrosion resistance. Therefore, the total thickness of the plating layer is preferably 10 to 70 μm. However, since the total thickness of the plating layer depends on the plating conditions, the total thickness of the plating layer is not limited to the range of 10 to 70 μm. In a typical hot-dip plating method, the total thickness of the plating layer is affected by the viscosity and specific gravity of the plating bath. The total thickness of the plating layer is adjusted by the drawing speed of the steel material (base plate) and the strength of wiping.

[0029] The Al-Fe alloy layer is formed on the surface of the steel material (specifically, between the steel material and the Zn-Al-Mg alloy layer), and has an Al structure. ５ The Fe2 phase is the main phase layer. The Al-Fe alloy layer is formed by mutual atomic diffusion between the base steel (steel material) and the plating bath. When hot dip plating is used as the manufacturing method, the Al-Fe alloy layer is likely to be formed in the plating layer containing Al element. This is because the plating bath contains Al at a certain concentration or more. Al ５ The Fe2 phase is formed most frequently. However, atomic diffusion takes time, and there are also areas where the Fe concentration is high near the base steel. Therefore, the Al-Fe alloy layer is partially composed of AlFe phase, Al ３ It may contain small amounts of Fe phase, AlFe phase, etc. In addition, since the plating bath contains a certain concentration of Zn, the Al-Fe alloy layer also contains a small amount of Zn.

[0030] When the plating layer contains Si, Si is particularly likely to be incorporated into the Al-Fe alloy layer, and may form an Al-Fe-Si intermetallic compound phase. Identified intermetallic compound phases include the AlFeSi phase, and isomers such as α-, β-, q1-, and q2-AlFeSi phases exist. Therefore, these AlFeSi phases may be detected in the Al-Fe alloy layer. An Al-Fe alloy layer containing these AlFeSi phases is also referred to as an Al-Fe-Si alloy layer.

[0031] 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 laminated structure of an Al—Fe alloy layer and a Zn—Al—Mg alloy layer, the average chemical composition is the combined average chemical composition of the Al—Fe alloy layer and the Zn—Al—Mg alloy layer.

[0032] Typically, in hot-dip galvanizing, the chemical composition of the Zn—Al—Mg alloy layer is almost identical to that of the galvanizing bath, since the reaction for forming the coating layer is almost always completed within the coating bath. Furthermore, in hot-dip galvanizing, the Al—Fe alloy layer is instantaneously formed and grows immediately after immersion in the coating bath. The reaction for forming the Al—Fe alloy layer is already completed within the coating bath, and its thickness is often sufficiently smaller than that of the Zn—Al—Mg alloy layer. Therefore, unless special heat treatment such as a thermal alloying treatment is performed after coating, the average chemical composition of the entire coating layer is substantially identical to that of the Zn—Al—Mg alloy layer, and components such as the Al—Fe alloy layer can be ignored.

[0033] The chemical composition of the plating layer according to this embodiment includes Zn, other alloying elements, and impurities. The chemical composition of the plating layer according to this embodiment may also include Zn, other alloying elements, and impurities. The chemical composition of the plating layer will be described in detail below. Elements whose lower limit concentration is 0% are not essential for solving the problems of the plated steel material according to this embodiment, but are optional elements that are allowed to be included in the plating layer for the purpose of improving characteristics, etc.

[0034] Al: 10.0% to 40.0% Like Zn, Al is an element that mainly constitutes the plating layer. Although Al has little sacrificial anticorrosion effect, the inclusion of Al in the plating layer improves the corrosion resistance of flat parts. Furthermore, without Al, Mg cannot be stably retained in the plating bath, so Al is included in the plating bath as an element essential for manufacturing.

[0035] The Al content of 10.0% or more is the content necessary to contain a large amount of Mg, which will be described later, and is also the content necessary to ensure workability. If the content is less than this, it becomes difficult to prepare the plating bath, it becomes difficult to ensure the workability of the plating layer, and it becomes difficult to ensure corrosion resistance. The Al content is set to 40.0% or less because Al has a weak sacrificial corrosion protection effect on steel, and if the content exceeds this, sufficient sacrificial corrosion protection cannot be obtained, so the upper limit is set to 40.0%.

[0036] Mg: 5.0% to 12.5% ​​Mg is an element that has a sacrificial anticorrosion effect and enhances the corrosion resistance of the plating layer. By including more than a certain amount of Mg, the plating layer ２ The higher the Mg content in the plating layer, the more the MgZn phase is formed. ２ More phases are formed. MgZn ２ The phase is known to have a structure called the Laves phase, and its hardness is known to be high. The Mg content of 5.0% or more is the concentration necessary to exhibit corrosion resistance, and if it is less than 5.0%, sufficient corrosion resistance cannot be obtained. ２ If the magnesium content is too high, the plating layer will not be sufficiently formed, and the corrosion resistance of the plating layer itself will be low. Since an excessive magnesium content makes it difficult to manufacture the plating layer and reduces the workability of the plating layer, the upper limit is 12.5%. A more preferable magnesium content is 6.0% to 8.0%.

[0037] Ti: 0% to 1.0% Zr: 0% to 1.0% When either or both of Ti and Zr are contained in the plating bath, ３ Zr, Al ３ In addition, when Si is present, it forms an intermetallic compound with Al. ２．７ Si０．３ Zr, Al ２．５ Si ０．５ These intermetallic compounds have good lattice matching with the Al phase and act as solidification nuclei for primary Al crystals. When intermetallic compounds containing Ti and Zr act as solidification nuclei for primary Al crystals, the (100) plane of Al is preferentially oriented parallel to the surface of the coating layer on the surface of the plated steel material. When the total concentration of Ti and Zr is 0.001% or more, the (100) plane of Al begins to form parallel to the surface of the coating layer, and the orientation of the (100) plane tends to become stronger as the concentrations of Ti and Zr increase. Therefore, the lower limit of the total concentration of Ti and Zr is 0.001% or more, and more preferably 0.020% or more.

[0038] Furthermore, when the total concentration of Ti and Zr is 0.020% or higher, the primary Al crystals begin to become finer, and as the concentration increases, the primary Al crystals tend to become finer. The effect of refining the crystal grains saturates when the total concentration of Ti and Zr is 0.5%. Since refining the crystal structure contributes to improved workability, a total concentration of Ti and Zr of 0.020% or higher is preferred for refining the primary Al crystals. On the other hand, higher Ti and Zr concentrations tend to make the preparation of the coating bath more difficult. Furthermore, when Ti and Zr concentrations exceed 1.0%, a large amount of dross is generated and uncoated areas frequently occur, resulting in poor appearance and corrosion resistance. Therefore, the Ti and Zr concentrations are each limited to 1.0% or less. The total Ti and Zr concentration is 0.001% to 2.0%, more preferably 0.001% to 1.5% or 0.010% to 0.5%, and even more preferably 0.1% to 0.5%.

[0039] Furthermore, when one or both of Ti and Zr are contained in the plating bath, Mg ２ Zn １１ This tends to suppress the precipitation of phases, improving workability.

[0040] Si: 0% to 5.00% Si is an optional element, but if Si is included in the plating bath, a single phase of Si or Mg ２Si precipitates, and when Ca is also present, Al-Ca-Si compounds precipitate. The precipitation of these Si or Si-based compounds on the surface of the coating layer improves water wettability and running water resistance. Furthermore, Si is incorporated into the Al-Fe alloy layer to form an Al-Fe-Si phase, which inhibits the growth of the Al-Fe alloy layer, thereby improving bending workability and coating adhesion. The Si content is preferably 0.05% or more. Furthermore, if the Si content exceeds 5.00%, a large amount of dross is generated and bare spots frequently occur. Therefore, the Si concentration is set to 5.00% or less. The Si concentration is preferably 0% to 5.00%, 0.05% to 3.00%, 0.05% to 1.0%, or 0.10% to 0.50%.

[0041] Element Group A Ca: 0% to 3.00% Y: 0% to 0.50% La: 0% to 0.50% Ce: 0% to 0.50% Sr: 0% to 0.50% Element Group A, Ca, Y, La, Ce, and Sr, are optional elements. However, these elements are easily oxidized in the atmosphere. When present in a coating bath, they form a dense oxide film on the bath surface, preventing oxidation of Mg. This effect stabilizes the Mg concentration and facilitates the production of coated steel sheets with the target composition. To optimally achieve this effect, the content of these elements should be greater than 0%, more preferably 0.01% or greater. Furthermore, each element has an upper limit. Exceeding the upper limit tends to make preparation of the coating bath more difficult. Furthermore, the deposition of dross and the like tends to increase, resulting in poor appearance and corrosion resistance.

[0042] Therefore, the Ca content is set to 0% to 3.00%, preferably more than 0% and less than 2.00%, more preferably 0.01% or more and less than 2.00%, and further preferably 0.01% or more and 1.50% or less. Furthermore, the Ca content may be 1.00% or less, 0.60% or less, or 0.50% or less.

[0043] Furthermore, the content of Y, La, Ce, and Sr is each 0% to 0.50%, preferably more than 0% and less than 0.50%, and more preferably 0.01% or more and less than 0.50%. Furthermore, each element may be 0.01% or more, 0.40% or less, or 0.30% or less. Element group A forms compounds with Al and Zn in the coating structure. Taking Ca as an example, when Ca is contained in an amount greater than 0%, preferably 0.01% or more, Al-Ca-Zn compounds are formed, and when Si is also present, Al-Ca-Si compounds are likely to be formed. Furthermore, when Y, La, Ce, or Sr is contained, the Ca in the above compounds is replaced by the respective element.

[0044] Element Group B Sn: 0% to 3.00%, Bi: 0% to 1.00%, In: 0% to 1.00%. The elements in element group B are optional, but they function to improve sacrificial corrosion protection. However, these elements tend to bond more strongly with Mg than Zn, reducing the effect of the contained Mg, so there is an upper limit to the content of these elements. Exceeding the upper limit increases the adhesion of dross and the like, and corrosion resistance tends to deteriorate. Therefore, the Sn content is set to 0 to 3.00%, more preferably, more than 0% and less than 3.00%. The Sn content may be 0.01% or more, 0.05% or more, and 2.50% or less, 2.00% or less, or 1.50% or less. The Bi content is set to 0% to 1.00%, more preferably, more than 0% and less than 1.00%. Bi may be 0.01% or more, 0.05% or more, 0.80% or less, 0.50% or less, or 0.40% or less. In is 0% to 1.00%, more preferably more than 0% and less than 1.00%. In may be 0.01% or more, 0.05% or more, 0.80% or less, 0.50% or less, or 0.40% or less.

[0045] Element group C B: 0% to 1.00% P: 0% to 0.50% B and P in element group C are elements belonging to semimetals. These elements are optional addition elements, but B is AlB ２B acts as a solidification nucleus for the primary Al crystals, refining them and improving their workability. However, its effect is not significant and is less than that of Ti and Zr. P does not have the effect of refining the primary Al crystals, but it does improve corrosion resistance. Each element has an upper limit, and exceeding the upper limit tends to increase the adhesion of dross and the like, deteriorating the appearance and corrosion resistance. Therefore, B is set to 0% to 1.00%, preferably greater than 0% and 0.50%, and more preferably greater than 0% and 0.10%. B may be 0.01% or greater, or 0.05% or greater. P is set to 0% to 0.50%, more preferably greater than 0% and less than 0.50%, and even more preferably greater than 0% and 0.01% or less. P may be 0.001% or greater, or 0.005% or greater.

[0046] Element Group D Cr: 0% to 0.25% V: 0% to 0.25% Ni: 0% to 1.0% Co: 0% to 0.25% Nb: 0% to 0.25% Cu: 0% to 1.0% Mn: 0% to 0.25% Mo: 0% to 0.25% W: 0% to 0.25% Ag: 0% to 1.00% Li: 0% to 0.50% Na: 0% to 0.05% Ba: 0% to 0.25% K: 0% to 0.05% Fe: 0% to 5.0% Element Group D is a metal element that can be added optionally, but the incorporation of these elements into the coating layer improves corrosion resistance. Each element has an upper limit on its content, and exceeding the upper limit tends to increase the adhesion of dross and the like. Therefore, the contents of Cr, V, Co, Nb, Mn, Mo, W, and Ba are each limited to 0% to 0.25%, preferably 0% to 0.25%, 0.01% to 0.20%, or 0% to 0.10%. Ni, Cu, and Ag are each limited to 0% to 1.0%, preferably 0% to 1.0%, 0% to 0.5%, 0% to 0.20%, or 0% to 0.10%. Ni, Cu, and Ag may each be 0.01% or more, or 0.05% or more. Li is limited to 0% to 0.50%, preferably 0% to 0.10%. Li may be 0.01% or more. Na and K are limited to 0% to 0.05%, preferably 0% to 0.03%. Na and K may be 0.01% or more. Furthermore, Fe may be inevitably contained in the coating layer. This is because Fe may diffuse from the base steel into the coating layer during coating production. Therefore, the Fe content is 0% to 5.0%, and preferably may be more than 0% and not more than 2.0%, more than 0% and not more than 1.5%, more than 0% and not more than 1.2%, or more than 0% and not more than 1.0%. Fe may be 0.1% or more, 0.3% or more, 0.5% or more, or not more than 0.9%.

[0047] Element Group E Sb: 0% to 0.50% Pb: 0% to 0.50% Element Group E's Sb and Pb are optional elements with properties similar to those of Zn. Therefore, the inclusion of these elements has the effect of facilitating the formation of a spangle pattern on the plating's appearance. However, excessive inclusion of these elements may result in a decrease in corrosion resistance. Therefore, the Sb and Pb contents are each set to 0% to 0.50%, preferably greater than 0% but not greater than 0.50%, greater than 0% but not greater than 0.40%, or greater than 0% but not greater than 0.10%. Sb and Pb may each be 0.01% or greater, or 0.05% or greater.

[0048] Balance: Zn: 50.0% or more and impurities. Zn is a low-melting-point metal and exists on the steel material as the main phase of the plating layer. Zn is an element necessary for ensuring corrosion resistance and providing sacrificial corrosion protection to the steel material. If the Zn content is less than 50.0%, the metal structure of the Zn-Al-Mg alloy layer will be dominated by Al phase, resulting in a shortage of Zn phase, which provides sacrificial corrosion protection. Therefore, the Zn content is set to 50.0% or more. More preferably, it is set to 60.0% or more, or 70.0% or more. The upper limit of the Zn content is the amount that constitutes the balance excluding elements other than Zn and impurities. The Zn content may be 85.0% or less.

[0049] Furthermore, the impurities in the coating layer refer to components contained in the raw materials, components mixed in during the manufacturing process, and components other than the above-mentioned optional added elements that are contained to the extent that they do not affect the effects of the present invention. For example, trace amounts of components other than Fe may be mixed into the coating layer as impurities due to mutual atomic diffusion between the steel material (base steel) and the coating bath.

[0050] The plating layer of this embodiment does not exclude the inclusion of elements other than those listed above, as long as they do not affect the effects of the present invention. "Not affecting the effects of the present invention" means that the plating layer can be rated A or higher in the corrosion resistance evaluation and workability evaluation described below.

[0051] Furthermore, in the plating layer according to this embodiment, the total content of Al, Mg, and Zn is preferably 83.7% or more, may be 90.0% or more, or may be 94.7% or more.

[0052] 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 can dissolve the plating layer. By measuring the area and weight before and after stripping, the plating deposition amount (g / m ２ ) can also be obtained at the same time.

[0053] Next, the structure of the plating layer will be described. The proportion of each phase contained in the plating layer significantly affects the performance of the plating layer. Even plating layers with the same component composition can have different performance due to the phases or structures contained in the metal structure, which vary depending on the manufacturing method. The metal structure of the plating layer can be easily confirmed using a scanning electron microscope with an energy dispersive X-ray analyzer (SEM-EDS). The approximate state of the metal structure of the plating layer can be confirmed by, for example, obtaining a backscattered electron image of any vertical cross section (thickness direction) of a mirror-finished plating layer. Since the thickness of the plating layer in this embodiment is approximately 10 to 70 μm, it is preferable to confirm the metal structure with an SEM at a magnification of 500 to 5000 times. For example, when a 25 μm-thick plating layer is observed at a magnification of 2000 times, the area per field of view is 25 μm (plating thickness) × 40 μm (SEM field width) = 1000 μm. ２ In this embodiment, since the SEM field of view for the plating layer may be a local field of view, 25 fields of view may be selected from any cross section to obtain average information on the plating layer. That is, a total of 25,000 μm ２ The metal structure in the field of view can be observed to determine the area ratio and size of the phases or structures that make up the metal structure of the plating layer.

[0054] Backscattered electron images taken by SEM are preferred because they allow easy identification of the phases or structures contained in the plating layer. Elements with small atomic numbers, such as Al, appear black, while elements with large atomic numbers, such as Zn, appear white, making it easy to determine the proportions of these structures.

[0055] To confirm each phase, the composition of the phase can be pinpointed using EDS analysis, and then the phase can be identified by reading phases with approximately the same components using elemental mapping, etc. For materials for which EDS analysis can be used, elemental mapping can be used to distinguish between phases with approximately the same composition. Once a phase with approximately the same composition can be identified, it is possible to determine the area of ​​that crystalline phase in the observation field. Once the area is known, the equivalent circular diameter can be calculated. Furthermore, the area proportion of each phase in the observation field can be determined. The area proportion of a specific phase in the plating layer corresponds to the volume proportion of that phase in the plating layer.

[0056] The plating layer according to this embodiment includes MgZn ２ phase, primary Al crystals including Al phase, and [Al / Zn / MgZn ２ The Al primary crystal is composed of an Al phase alone, or in a form in which the Al phase occupies the center of a dendrite and the Al-Zn phase occupies the outer periphery.

[0057] The content ratio of the phase and structure in the plating layer is the area fraction when observed in an arbitrary vertical cross section (thickness direction) of the plating layer using a scanning electron microscope. ２ The area ratio of the Al phase and the Al-Zn phase is 15% or more and 50% or less, the total area ratio of the Al phase and the Al-Zn phase is 15% or more and 70% or less, [Al / Zn / MgZn ２ It is preferable that the area fraction of the phases [ternary eutectic structure] is 0% or more and 60% or less, and the area fractions of the other phases are 0% or more and 10% or less. Note that, since the plating layer of this embodiment will have excellent corrosion resistance and workability if it satisfies the above chemical components and formula (1), the area fractions of the phases and structures in the plating layer are not limited to the above ranges.

[0058] MgZn ２ Phase MgZn according to this embodiment ２ The MgZn phase is a region in the coating layer where Mg is 16 mass% (±5%) and Zn is 84 (±5%). ２ In SEM backscattered electron images, the MgZn phase is often photographed as a gray color between Al and Zn.２ The phases are Al phase, Al-Zn phase, [Al / Zn / MgZn ２ It can be clearly distinguished from other ternary eutectic structures.

[0059] MgZn ２ When the ratio of the MgZn phase in the coating layer increases, the corrosion resistance improves. ２ The MgZn phase may reduce the workability of the plating layer. ２ The more the phase, the better, but an upper limit may be set from the viewpoint of ensuring workability. ２ The proportion of the MgZn phase may be 15% or more and 50% or less in terms of area ratio in order to balance corrosion resistance and workability. ２ The area ratio of the phase may be 20% or more, 25% or more, 45% or less, or 40% or less.

[0060] Al phase In this embodiment, the Al phase constituting the primary Al crystal is a region in the coating layer where the Al content exceeds 40 mass %. The Al phase may contain Zn, but the Zn content is less than 60 mass %. The Al phase can be clearly distinguished from other phases and structures in a backscattered electron image of an SEM. That is, the Al phase is often shown as the darkest in a backscattered electron image of an SEM. In this embodiment, the Al phase takes various forms in any cross section, such as appearing as a block, or as a dendritic cross section such as a circular or flat shape. In this embodiment, the Al phase is a dendritic phase composed of [Al / Zn / MgZn ２ The Al contained in the ternary eutectic structure is not included in the Al phase.

[0061] The area ratio of the Al phase in the plating layer is not particularly limited, but may be 5% or more, 10% or more, 20% or more, or 25% or more. The Al phase may be 60% or less, 55% or less, or 50% or less.

[0062] The Al phase is MgZn ２ Phase, [Al / Zn / MgZn ２Compared to a ternary eutectic structure (a ternary eutectic structure), the Al phase has excellent plastic deformability. The Al phase has a face-centered cubic crystalline structure and is known to have orientation dependency on processing. In the case of bending, if the preferred orientation on the surface of the plating layer is the (100) plane, the plastic deformability of the plating layer is improved, and the plating layer elongates in response to processing, resulting in fewer plating cracks in the processed area. Furthermore, the tendency for the development of the preferred orientation varies depending on the Al content of the plating layer; when the Al content is low and the Zn content is high, the preferred orientation is the (110) plane, and as the Al content increases, the preferred orientation changes to the (100) plane.

[0063] The preferred orientation of the Al phase on the surface of the coating layer can be determined by X-ray diffraction. For example, when X-ray diffraction is measured using a Cu source under output conditions of 50 kV-300 mA, the 2θ peaks for the (111) plane appear at approximately 38.47°, the (200) plane at approximately 44.74°, the (220) plane at approximately 65.13°, and the (311) plane at approximately 78.23°. Since the (200) plane is parallel to the (100) plane and the (220) plane is parallel to the (110) plane, when evaluating the preferred orientation on the surface of the coating layer using X-ray diffraction, the (200) plane can be substituted for the (100) plane and the (220) plane can be substituted for the (110) plane.

[0064] Whether the (100) plane appears as a preferred orientation on the surface of the plating layer can be confirmed by the ratio of the peak intensity of the (200) plane to the peak intensity of other orientation planes, and it can be said that the higher the peak intensity of the (200) plane, the more the (100) plane appears as a preferred orientation. In this embodiment, when the diffraction intensity obtained from the results of X-ray diffraction measurement of the plating layer satisfies the following formula (1), the (100) plane becomes the preferred orientation on the surface of the plating layer, and the processability of the plating layer can be improved.

[0065] I (200) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ} ≧ 0.4 ... (1)

[0066] However, I(200) in formula (1) Ａｌis the diffraction intensity of Al (200), and I (111) Ａｌ is the diffraction intensity of Al (111), and I (220) Ａｌ is the diffraction intensity of Al (220), and I (311) Ａｌ is the diffraction intensity of Al (311). In the plating composition of the present invention, the value of formula (1) may be 0.7 or less.

[0067] I(200) defined in equation (1) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ The measurement method for {} is as follows. First, the surface of the plating layer is mechanically polished, and if necessary, chemically polished to make the surface of the plating layer in a mirror-finished state. Next, for example, an X-ray diffraction measurement is performed using an X-ray diffractometer (manufactured by Rigaku Corporation (Model No. RINT-TTR III)) with an X-ray output of 50 kV, 300 mA, a copper target, a goniometer TTR (horizontal goniometer), a Kβ filter slit width of 0.05 mm, a longitudinal limiting slit width of 2 mm, a receiving slit width of 8 mm, and a receiving slit 2 open, under the measurement conditions of a scan speed of 5 deg. / min, a step width of 0.01 deg, and a scan axis 2θ (5 to 90°). Then, the diffraction intensity of Al (200) is measured. (maximum intensity in the range of 44.74°±0.20°), the diffraction intensity of Al (111) (maximum intensity in the range of 38.47°±0.20°), the diffraction intensity of Al (220) (maximum intensity in the range of 65.13°±0.20°), and the diffraction intensity of Al (311) (maximum intensity in the range of 78.23°±0.20°) are measured. The diffraction intensity is the intensity excluding the background intensity. From the obtained diffraction intensities, I(200) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ} is sought.

[0068] Furthermore, in any vertical cross section (thickness direction) of the plating layer, the total area of ​​Al phases contained in the plating layer, which have an equivalent circle diameter of 20 μm or less, is preferably 50% or more as a ratio to the total area of ​​all Al phases. That is, in a cross section in the thickness direction of the plating layer, the ratio of the total area of ​​Al phases having an equivalent circle diameter of 20 μm or less to the total area of ​​Al phases is preferably 50% or more. In this way, when Al phases having an equivalent circle diameter of 20 μm or less occupy 50% or more of the total area of ​​Al phases, the Al primary crystals are further refined, thereby further improving the workability of the plating layer. Since the refinement of the Al primary crystals tends to improve the workability of the plating layer, the area ratio of the total area of ​​Al phases having an equivalent circle diameter of 20 μm or less to the total area of ​​Al phases in the thickness direction of the plating layer may be 70% or more. The upper limit may be 100%.

[0069] The area ratio of the Al phase having an equivalent circle diameter of 20 μm or less is measured by extracting the Al phase from an image in a predetermined observation field and measuring the area of ​​each Al phase to derive the equivalent circle diameter. A specific measurement method will be described below.

[0070] The observation field is a total of 25,000 μm used to confirm the phase and structure of the plating layer. ２ The observation field is set to . In EDS analysis of this observation field, the phase composition is pinpointed, and phases with approximately the same components are identified by reading them from the contrast of the SEM image or element mapping. Since the Al phase is a light element, it can be seen as a black area in the SEM backscattered electron image. In EDS analysis, the Al phase can also be identified by element mapping. The Al phase identification method is not limited to the above, and EPMA mapping, for example, can also be used. Next, the Al phases in the observation field are extracted using image processing, and their respective areas are measured. Once the areas are known, the equivalent circular diameter of each Al phase can be calculated. Then, Al phases with a circular equivalent diameter of 20 μm or less are extracted, and their total area is determined. Then, the area ratio (%) of the Al phases with a circular equivalent diameter of 20 μm or less to the total area of ​​the Al phases in the observation field is determined.

[0071] Al-Zn Phase In this embodiment, the Al-Zn phase is a phase containing 60% or more of Zn and Al. The Al-Zn phase is an aggregate of a fine Zn phase with a grain size of approximately 1 μm (hereinafter referred to as the fine Zn phase) and a fine Al phase with a grain size of less than 1 μm (hereinafter referred to as the fine Al phase). In the molten coating layer, Al has a different crystal structure from that at room temperature (e.g., 25°C), allowing a large amount of Zn phase to be solid-dissolved, and exists as a high-temperature stable phase containing approximately 60% Zn phase. On the other hand, at room temperature, the content of the Zn phase in this high-temperature stable phase is drastically reduced, and Al and Zn are equilibrated and separated into an Al-Zn phase containing a fine Al phase and a fine Zn phase. In other words, the Al-Zn phase is a phase containing a fine Zn phase at a ratio of 60% or more by mass. This Al-Zn phase has different properties from the Al phase and Zn phase contained in the coating layer, and can be distinguished in backscattered electron SEM images and wide-angle X-ray diffraction. In wide-angle X-ray diffraction, for example, Al ０．４０３ Zn ０．５９７ (JCODF #00-052-0856) and Al ０．７１ Zn ０．２９ (PDF#00-019-0057) and the like. Therefore, in this embodiment, a phase having an Al component of 15 to 40 mass % and a Zn component of 60 to 85 mass % is defined as an Al—Zn phase.

[0072] As mentioned above, the Al-Zn phase is an aggregate of fine Al and Zn phases, so MgZn ２ Phase, [Al / Zn / MgZn ２ On the other hand, the corrosion resistance is superior to that of MgZn. ２ Phase, [Al / Zn / MgZn ２ ternary eutectic structure], which is considered to be inferior to the Al phase.

[0073] The area ratio of the Al—Zn phase is not particularly limited, but may be 5% or more, or 10% or more, and may be 20% or less, or 15% or less.

[0074] In the present invention, the total area ratio of the Al primary crystals, i.e., the Al phase and the Al-Zn phase, may be 15% or more and 70% or less. The total area ratio of the Al phase and the Al-Zn phase may be 20% or more, 25% or more, or 30% or more, or may be 65% or less, 60% or less, 55% or less, or 50% or less.

[0075] [Al / Zn / MgZn ２ ternary eutectic structure] [Al / Zn / MgZn ２ The ternary eutectic structure is composed of Al phase, MgZn ２ The backscattered electron SEM image shows that the MgZn phase is contained as the main phase of the plating layer. ２ It is clearly distinguishable from the Al phase and the Al phase.

[0076] Zn phase included [Al / Zn / MgZn ２ By having a certain amount of ternary eutectic structure, sacrificial corrosion protection is ensured and the end surface corrosion resistance is improved. On the other hand, water wetting resistance and water flow resistance are reduced, so when water wetting resistance and water flow resistance are taken into consideration, ２ The ternary eutectic structure of Al / Zn / MgZn may be 60% by area or less. It may also be 40% by area or less, 35% by area or less, or 30% by area or less. ２ There is no particular lower limit to the area ratio of the ternary eutectic structure, and it may be 0%, 5 area % or more, 10 area % or more, or 15 area % or more.

[0077] Mg ２ Zn １１ Phase Mg in this embodiment ２ Zn １１ The phase is a region where Mg is 5 mass% (±3%) and Zn is 93 (±4%). ２ Zn １１ The phase is gray, an intermediate color between Al and Zn, in the SEM backscattered electron image. ２ It is often photographed brighter than the Mg phase. ２ Zn １１ The phase is MgZn ２ Since the Mg phase has even poorer plastic deformability than the Zn phase, it is better not to precipitate it in the coating structure. ２ Phase, [Al / Zn / MgZn２ ternary eutectic structure], or Mg ２ It is desirable that the Si phase is Mg. ２ Zn １１ Diffraction intensity of the (322) plane of the phase (maximum intensity in the range of 43.60°±0.20°. Hereinafter, I(322) Ｍｇ２Ｚｎ１１ ) and MgZn ２ Diffraction intensity of the (201) plane of the phase (maximum intensity in the range of 41.30°±0.20°. Hereinafter, I(201) ＭｇＺｎ２ The ratio of I(322) Ｍｇ２Ｚｎ１１ / I (201) ＭｇＺｎ２ The plating bath composition and the cooling rate after pulling up from the plating bath may be such that Mg ２ Zn １１ The plated steel sheet produced in this embodiment has a I(322) Ｍｇ２Ｚｎ１１ / I (201) ＭｇＺｎ２ / ≦0.2, and the Mg content in the plating structure ２ Zn １１ The proportion of this phase is less than 1% by area.

[0078] The above phases and structures constitute the main phase of the coating layer, and they account for 90% or more of the area fraction of the coating layer. On the other hand, when elements other than Zn, Mg, and Al are contained in the coating layer, other metal phases are formed. For example, Si is present in the coating layer when Mg is present. ２ The Si phase is formed, and Ca forms the Al-Zn-Ca phase. The main components of the remaining structure are Mg ２ The coating layer may contain Si phase, AlZnCa phase, AlCaSi phase, etc. Although some of these are effective in improving weldability and corrosion resistance, the effects are not significant. Because it is difficult for the total amount of these to exceed 10 area % due to the composition of the coating layer, the total amount may be 10 area % or less.

[0079] Next, a case where the plated steel material of this embodiment is produced by a hot-dip galvanizing method will be described. The plated steel material of this embodiment can be produced by either an immersion-type plating method (batch type) or a continuous plating method.

[0080] There are no particular restrictions on the size, shape, or surface form of the steel material to be plated. Normal steel, high-tensile steel, stainless steel, and other steel materials are all applicable. Steel strips of general structural steel are most preferable. Surface finishing may be performed in advance using shot blasting, abrasive brushes, etc., and the surface may be coated with 3 g / m of Ni, Fe, Zn, Sn, or other metals. ２ There is no problem if the following metal or alloy film is attached before plating. As a pretreatment of the steel material, it is preferable to thoroughly clean the steel material by degreasing and pickling.

[0081] H ２ After the steel surface is sufficiently heated and reduced using a reducing gas such as HCl, the steel is immersed in a coating bath formulated to a predetermined composition. For high-tensile steels, the atmosphere during annealing is humidified, and internal oxidation is used to ensure coating adhesion, even on high-Si, high-Mn steels. By performing such treatments, it is possible to produce coated steel products with minimal uncoated areas or poor appearance, similar to ordinary steel products. While such steel products have a surface with fine grain size and an internal oxide film layer on the base steel side, these do not affect the performance of the present invention.

[0082] In the case of hot-dip plating, the composition of the plating layer can be controlled by the composition of the plating bath to be prepared. The plating bath is prepared by mixing predetermined amounts of pure metals to prepare an alloy of the plating bath components, for example, by a melting method in an inert atmosphere.

[0083] Immersing a steel material whose surface has been reduced in a plating bath maintained at a predetermined concentration forms a plating layer with approximately the same composition as the plating bath. If the immersion time is prolonged or if it takes a long time for solidification to be completed, the formation of the interfacial alloy layer becomes active, and the Fe concentration may become high. However, at temperatures below 500°C, the reaction with the plating layer rapidly slows, and the Fe concentration in the plating layer is usually kept at 5.0% or less.

[0084] To form the hot-dip coating layer, the coating bath is preferably kept at a temperature of 450°C to 550°C. The reduced steel material is then preferably immersed in the coating bath for several seconds. On the surface of the reduced steel material, Fe diffuses into the coating bath and reacts with the coating bath, which may result in the formation of an interfacial alloy layer at the interface between the coating layer and the steel material. The interfacial alloy layer is primarily an Al-Fe intermetallic compound layer (Al-Fe alloy layer). When the interfacial alloy layer (Al-Fe alloy layer) is formed, the steel material below the interfacial alloy layer (Al-Fe alloy layer) and the coating layer above are bonded more strongly metallurgically.

[0085] After immersing the steel material in the plating bath for a predetermined time, the steel material is removed from the plating bath, and the metal adhering to the surface is in a molten state. ２ By wiping, the plating layer is adjusted to a predetermined thickness. The thickness of the plating layer is preferably adjusted to 10 to 70 μm. This corresponds to a coating weight of the plating layer of 40 to 450 g / m. ２ (One-sided).

[0086] After adjusting the coating weight of the coating layer, the deposited molten metal is solidified. The cooling method during solidification of the coating may be performed by spraying nitrogen, air, or a hydrogen / helium mixed gas, or by mist cooling or submersion in water. Mist cooling is preferred, and mist cooling using nitrogen containing water is preferable. The cooling rate may be adjusted by adjusting the water content.

[0087] In this embodiment, when coating solidification conditions under normal operating conditions, for example, when cooling from the coating bath temperature to 150°C at an average cooling rate of 5 to 20°C / sec, the structure may not be controlled and the desired performance may not be achieved. Therefore, the cooling process that makes it possible to obtain the coating layer of this embodiment will be described below.

[0088] Average cooling rate between bath temperature and 380°C: More than 20°C / sec, less than 50°C / sec Between bath temperature and 380°C, Al phase precipitates as the primary crystal, followed by MgZn ２Even within the coating composition range of the present invention, if the degree of supercooling is large, orientation planes other than the (100) plane of the Al phase tend to grow easily. Therefore, in order to make the preferential growth of the Al phase the (100) plane, it is necessary to set the average cooling rate at least to less than 50°C / sec. On the other hand, if the average cooling rate is 20°C / sec or less, the primary Al crystals tend to become coarse and workability tends to decrease. Therefore, in the region between the bath temperature and 380°C, the average cooling rate needs to be more than 20°C / sec and less than 50°C / sec.

[0089] Average cooling rate between 380°C and 300°C: 5°C / sec or more, less than 15°C / sec. Between 380°C and 300°C, Al-Zn phase precipitation from the liquid phase, Zn-Al-MgZn ２ A ternary eutectic reaction occurs, the liquid phase disappears, and the coating layer completely solidifies. In the temperature range between 380°C and 300°C, if the degree of supercooling is large, Mg ２ Zn １１ Phases may be formed. ２ Zn １１ Since the precipitation of this phase tends to deteriorate workability, it is preferable that the average cooling rate between 380°C and 300°C is less than 15°C / s. On the other hand, if the average cooling rate is slower than 5°C / s, recrystallization of the Al phase occurs, increasing the proportion of orientation planes other than the (100) plane, which tends to deteriorate workability. Therefore, the average cooling rate should be 5°C / s or more but less than 15°C / s, and more preferably, 5°C / s or more but less than 10°C / s.

[0090] Average cooling rate between 300°C and 150°C: more than 10°C / sec, 20°C / sec or less In the temperature range between 300°C and 150°C, the fine Zn phase incorporated into the Al-Zn phase is suddenly expelled from the Al-Zn phase. Therefore, if cooling is performed slowly in this temperature range, the proportion of Al phase in the primary Al crystals increases. This tendency becomes particularly strong when the Al concentration is high, and when the cooling rate between 300°C and 150°C is 20°C / sec or less, the Al-Zn phase separates into the Al phase and the Zn phase. On the other hand, when the cooling rate is 10°C / sec or less, the ternary eutectic structure grows in grain size, resulting in the formation of coarse MgZn ２ Phase and Mg ２ Zn １１Therefore, in the temperature range of 300°C to 150°C, it is preferable to cool at an average cooling rate of more than 10°C / sec and not more than 20°C / sec.

[0091] Temperature Range Below 150°C During the solidification process, the cooling rate in the temperature range below 150°C does not affect the constituent phases in the plating layer, so there is no need to limit the cooling conditions and natural cooling is acceptable.

[0092] After cooling the plating layer, various chemical conversion treatments and painting treatments may be performed. In addition, in order to further improve corrosion resistance, touch-up paint for repair, thermal spraying treatment, etc. may be performed on welded parts, processed parts, etc.

[0093] In the plated steel material of this embodiment, a coating may be formed on the plating layer. The coating may be one layer or two or more layers. Examples of types of coatings that may be formed directly on the plating layer include chromate coatings, phosphate coatings, and chromate-free coatings. The chromate treatment, phosphate treatment, and chromate-free treatment for forming these coatings can be performed by known methods. However, since many chromate treatments can deteriorate the weldability of the plating layer surface, it is preferable that the thickness be less than 1 μm in order to fully utilize the weldability improvement effect in the plating layer.

[0094] 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.

[0095] 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.

[0096] Examples of the phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] <Corrosion Resistance Evaluation> The corrosion resistance of the plating layer can be evaluated by subjecting it to an accelerated corrosion test such as the JASO standard. Specifically, the number of cycles (time) until red rust appears is compared, and a longer cycle is evaluated as having better corrosion resistance, while a shorter cycle is evaluated as having worse corrosion resistance. The number of cycles until red rust appears also varies depending on the coating weight of the plating layer, so it is desirable to use the same coating weight for plated steel materials to be compared.

[0101] <Workability evaluation> The workability of the plating layer can be evaluated by bending the material and measuring the number of cracks in the plating layer in the bent area. The fewer cracks in the plating layer, the better the workability. If there are no cracks in the plating layer, the wear of the plating layer due to sacrificial corrosion protection is reduced, so the corrosion resistance of the bent area is equal to that of the flat area.

[0102] The original plate of the plated steel material was cut out from a cold-rolled steel sheet with a thickness of 0.8 mm to a size of 180 mm x 100 mm. Both were SS400 (general steel). A batch-type hot-dip galvanizing simulator (manufactured by Rhesca Co., Ltd.) was used, and a K thermocouple was attached to a part of the steel sheet. ２ Contains 5% of N ２ The steel sheet surface was annealed at 800°C in a reducing atmosphere to fully reduce the surface, and then immersed in a plating bath for 3 seconds, and then pulled out. ２ The plating thickness was adjusted to 20 μm (±1 μm) by gas wiping. The plating thickness on the front and back was the same. After being removed from the plating bath, plated steel materials were produced under various cooling conditions A to E below.

[0103] Condition A: After the steel material was pulled out of the coating bath, the average cooling rate was 30°C / s from the bath temperature to 380°C, 5°C / s from 380°C to 300°C, and 15°C / s from 300°C to 150°C. Cooling below 150°C was allowed to continue.

[0104] Condition B (comparative condition): After the steel material was removed from the plating bath, the average cooling rate was 20°C / s from the bath temperature to 150°C. Below 150°C, the steel material was allowed to cool naturally.

[0105] Condition C (comparative condition): After the steel material was removed from the plating bath, the average cooling rate was 2°C / s from the bath temperature to 150°C. Below 150°C, the steel material was allowed to cool naturally.

[0106] Condition D (comparative condition): After the steel material was removed from the plating bath, the average cooling rate from the bath temperature to 150°C was 60°C / s. Below 150°C, the steel material was allowed to cool naturally.

[0107] Condition E (comparative condition): After the steel material was pulled out of the coating bath, the average cooling rate was 30°C / s from the bath temperature to 380°C, the average cooling rate was 1°C / s from 380°C to 300°C, and the average cooling rate was 15°C / s from 300°C to 150°C. Cooling below 150°C was allowed to continue.

[0108] The average chemical composition of the plating layer was measured as follows. The plating layer was stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) to obtain an acid solution. The obtained acid solution was then measured using ICP atomic emission spectroscopy or ICP-MS to obtain the average chemical composition of the plating layer. The results are shown in Tables 1A to 1F.

[0109] Phase and structure in the plating layer (MgZn ２ phase, Al phase, Al-Zn phase, [Al / Zn / MgZn ２ The area ratio of the ternary eutectic structure and the remaining structure) was measured as described above by exposing a cross section of the plating layer in the thickness direction perpendicular to the surface of the steel material, and checking the metal structure in a field of view of 500 to 5000 times. ２ The metal structure was observed in the field of view to determine the area ratio of the phases or structures that make up the metal structure of the plating layer. To confirm each phase, the composition of the phase was pinpointed using EDS analysis, and phases with approximately the same components were identified by reading them from elemental mapping. Elemental mapping made it possible to distinguish phases with approximately the same composition.

[0110] The area ratio of the Al phase having a circle equivalent diameter of 20 μm or less is the above-mentioned 25000 μm ２ In EDS analysis of the observation field, the phase composition was pinpointed, and the Al phase was identified by reading approximately equivalent component phases from element mapping. Next, the Al phase in the observation field was extracted using image processing, the crystal area of ​​each was measured, and the equivalent circle diameter of each crystal was calculated. Furthermore, Al phases with a circle equivalent diameter of 20 μm or less were extracted, and their total area was calculated. Then, the area ratio (%) of Al phases with a circle equivalent diameter of 20 μm or less to the total area of ​​Al phases in the observation field was calculated.

[0111] Furthermore, in the X-ray diffraction pattern of the plating layer surface measured using Cu-Kα rays under conditions of an X-ray output of 50 kV and 300 mA, I(200) defined in the above formula (1) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ The measurement method was as follows. First, the surface of the plating layer was mechanically polished, and if necessary, chemically polished to make the surface of the plating layer mirror-finished. Next, X-ray diffraction measurement was performed using an X-ray diffractometer (manufactured by Rigaku Corporation (Model No. RINT-TTR III)) with an X-ray output of 50 kV, 300 mA, a copper target, a goniometer TTR (horizontal goniometer), a Kβ filter slit width of 0.05 mm, a longitudinal limiting slit width of 2 mm, a receiving slit width of 8 mm, and a receiving slit 2 open, under the measurement conditions of a scan speed of 5 deg. / min, a step width of 0.01 deg, and a scan axis 2θ (5 to 90°). Then, the diffraction intensity of Al (200) was measured. The diffraction intensity of Al (111) (maximum intensity in the range of 44.74°±0.20°), the diffraction intensity of Al (111) (maximum intensity in the range of 38.47°±0.20°), the diffraction intensity of Al (220) (maximum intensity in the range of 65.13°±0.20°), and the diffraction intensity of Al (311) (maximum intensity in the range of 78.23°±0.20°) were measured. The diffraction intensity was the intensity excluding the background intensity. From the obtained diffraction intensities, I(200) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ The results are shown in Tables 2A and 2B.

[0112] (Corrosion Resistance Evaluation) Test specimens were cut into 50 x 100 mm pieces, and the end faces were not painted or sealed. Corrosion resistance was evaluated by a combined cycle test in accordance with JASO M609 and M610. Specifically, a salt-dry-wet cycle test was conducted, in which salt spray, drying, and wetting were repeated. In the salt-dry-wet cycle test, the test specimens were subjected to a cycle of spraying with 5% NaCl aqueous solution (2 hours at 35°C), drying (4 hours at 30% relative humidity and 60°C), and wetting (2 hours at 95% relative humidity and 50°C). After each cycle, the specimens were rinsed with water and dried. The surface of the specimens was then observed and the area ratio of red rust was calculated. The area ratio of red rust was calculated by photographing the surface of the test specimens after the salt-dry-wet cycle test, binarizing the photographs using image analysis, calculating the area per pixel, and counting the number of pixels in the rusted area. The area ratio of red rust was calculated using the following formula:

[0113] Area ratio of red rust (%) = Area of ​​rusted part (mm 2 ) / area of ​​the entire observation area (mm 2 ) x 100

[0114] A red rust area ratio of 5% or more was considered to have occurred. The corrosion resistance was evaluated as follows: "B" was considered a failure, and "A" to "S" were considered to have passed. The results are shown in Tables 3A and 3B.

[0115] B: Red rust was observed after less than 200 cycles. A: Red rust was observed after 200 cycles. AA: Red rust was observed after more than 200 but less than 350 cycles. AAA: Red rust was observed after 350 or more but less than 500 cycles. S: No red rust was observed after 500 cycles.

[0116] (Workability Evaluation) The test material was cut into a size of 30 mm (C direction) x 100 mm (L direction) and subjected to a 5t 180° bending process. That is, when bending the test material, five plates of the same thickness as the test material were sandwiched and bent 180°. After that, the number of cracks in the area of ​​30 mm x 1.6 mm at the top of the bent part was measured at 40x magnification using a stereo microscope and evaluated as follows. The results are shown in Table 3.

[0117] B: 30 or more cracks A: 20 or more but less than 30 cracks AA: 10 or more but less than 20 cracks AAA: 5 or more but less than 10 cracks S: Less than 5 cracks

[0118] As shown in Tables 1A to 3B, Nos. 3 to 43, 53 and 54 (Examples) according to the present invention had appropriately controlled chemical compositions and metal structures of the plating layers, and were excellent in both corrosion resistance and workability. ２ Zn １１ No phases were included.

[0119] In Comparative Example No. 1, the Al content and Mg content of the hot-dip plating layer were insufficient, and the Ti and Zr contents were 0%. Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ} was less than 0.40. Therefore, No. 1 was insufficient in both corrosion resistance and workability.

[0120] In Comparative Example No. 2, the Al content of the hot-dip plated layer was insufficient, and the Ti and Zr contents were 0%. I(200) Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ} was less than 0.40. Therefore, No. 2 had insufficient processability.

[0121] Comparative Example No. 44 had excessive amounts of Al and Mg in the hot-dip plated layer, and therefore was deficient in both corrosion resistance and workability.

[0122] Comparative Example No. 45 had an excessive amount of Al in the hot-dip plated layer, and therefore had insufficient corrosion resistance.

[0123] In the comparative example No. 46, the contents of Ti and Zr in the hot-dip plating layer were 0%. Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ} was less than 0.40. Therefore, No. 46 had insufficient processability.

[0124] Comparative Example No. 47 had an excessive amount of Ca in the hot-dip plated layer. Furthermore, the manufacturing conditions were outside the range of preferred conditions. No. 47 was insufficient in both corrosion resistance and workability.

[0125] In the comparative examples Nos. 48, 49, and 50, the manufacturing conditions were outside the range of the preferred conditions. Ａｌ / {(I(111) Ａｌ +I (220) Ａｌ +I (200) Ａｌ +I(311) Ａｌ} was less than 0.40. Therefore, Nos. 48, 49, and 50 had poor processability.

[0126] Comparative Example No. 51 had an excessive amount of Zr in the hot-dip plated layer, and therefore, No. 51 had insufficient corrosion resistance.

[0127] In Comparative Example No. 52, the amount of Ti in the hot-dip plated layer was excessive, and therefore No. 52 had insufficient corrosion resistance.

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[0138] INDUSTRIAL APPLICABILITY The present invention has industrial applicability in that it can provide a plated steel material that has excellent corrosion resistance and excellent workability of the plated layer.

[0139] 1...plated steel material, 11...steel material, 12...plated layer

Claims

1. A steel material and a plating layer on the steel material, the plating layer having an average chemical composition, in mass%, of Al: 10.0% to 40.0%, Mg: 5.0% to 12.5%, Ti: 0% to 1.0%, Zr: 0% to 1.0%, Si: 0% to 5.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to 0.50%, Ce: 0% to 0.50%, Sr: 0% to 0.50%, Sn: 0% to 3.00%, Bi: 0% to 1.00%, In: 0% to 1.00%, B: 0% to 1.00%, P: 0% to 0.50%, Cr: 0% to 0.25%, V : 0% to 0.25%, Ni: 0% to 1.0%, Co: 0% to 0.25%, Nb: 0% to 0.25%, Cu: 0% to 1.0%, Mn: 0% to 0.25%, Mo: 0% to 0.25%, W: 0% to 0.25%, Ag: 0% to 1.00%, Li: 0% to 0.50%, Na: 0% to 0.05%, Ba: 0% to 0.25%, K: 0% to 0.05%, Fe: 0% to 5.0%, Sb: 0% to 0.50%, Pb: 0% to 0.50%, balance: 50.0% or more of Zn and impurities, the total of Ti and Zr in the plating layer is 0.001% or more, A plated steel material, wherein the diffraction intensity obtained from an X-ray diffraction measurement of the plated layer satisfies the following formula (1): I(200) Ａｌ / {(I(111) Ａｌ +I(220) Ａｌ + I (200) Ａｌ +I(311) Ａｌ }≧0.40 (1) where I(200) in formula (1) Ａｌ is the diffraction intensity of Al (200), and I (111) Ａｌ is the diffraction intensity of Al (111), and I(220) Ａｌ is the diffraction intensity of Al (220), and I (311) Ａｌ is the diffraction intensity of Al (311).

2. The plated steel material according to claim 1, wherein the total content of Ti and Zr in the plated layer is 0.020% or more.

3. The plated steel material according to claim 1 or 2, wherein in a cross section in the thickness direction of the plated layer, the ratio of the total area of ​​Al phases having a circle equivalent diameter of 20 μm or less to the total area of ​​Al phases is 50% or more.

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