JP7315826B2 - Plated steel and method for producing plated steel - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to plated steel and methods of manufacturing plated steel.

For example, steel structures are used in the civil engineering and infrastructure fields. Steel structures are exposed to severe corrosive environments such as coastal areas and areas where snow-melting salt is sprayed. Therefore, stainless steel materials are used to suppress corrosion over a long period of time and maintain steel structures.

On the other hand, stainless steel materials use high cost alloying elements such as Cr and Ni. For this reason, the installation of steel structures using stainless steel is expensive. Therefore, pre-plated products (for example, Zn-Al-Mg-based plated steel) have come to be used as a substitute for stainless steel.

However, large steel structures, pipe-shaped steel structures, etc., have the following problems: 1) the plating layer disappears due to welding; 3) It is originally difficult to manufacture steel parts such as bolts and washers from plate materials.
For this reason, post-plating (so-called soaking plating) is applied to such members.

Hot-dip Zn plating is widely used as a post-plating treatment, but Zn--Al--Mg-based plating is also being used in order to improve corrosion resistance.

On the other hand, post-plating treatment by hot-dip plating other than Zn (Zn-Al-Mg system plating treatment, etc.) is because plating components such as Al and Mg hinder reactivity with flux and cause some kind of poor adhesion. A two-stage plating method is employed in which the steel material is subjected to hot-dip Zn plating treatment in the first stage, and the steel material is immersed in a Zn--Al--Mg-based plating bath in the second stage for post-plating.

For example, the two-step plating method disclosed in Patent Documents 1 to 3, etc. is a representative two-step plating method of Zn--Al--Mg-based plating that is mainly used at present.

JP-A-61-295361 JP-A-11-117052 JP 2017-8390

Here, the advantage of the two-step plating method is that compared to the normal plating method (single-step plating method), there are fewer restrictions on the composition of the plating bath used in the second-step plating process, and various plating baths can be tried. It is possible to make mistakes.
On the other hand, the disadvantage of the two-step plating method is that the plated layer formed in the first-step plating process somehow participates in the reaction for forming the plated layer in the second-step plating process. As a result, the balance of components of the plating layer and the determination of the texture are different from those of simple one-step plating. In addition, it is necessary to confirm the structure of the plated layer that is comprehensively excellent, and to clarify the manufacturing method for incorporating it.

Against this background, in order to avoid complicating the reaction even in the second-stage plating process of the Zn-Al-Mg-based plating bath, a plating bath with relatively similar components to the first-stage plating process is used. In many cases, the concentrations of alloying components such as Al and Mg are kept low.

Therefore, there is room for improvement in corrosion resistance of post-plated steel materials (that is, plated steel materials having a surface layer plating layer and an intermediate plating layer) by the two-step plating method. At present, there is a demand for improved corrosion resistance in areas where salt or the like is sprayed.

Accordingly, an object of the present invention is to provide a plated steel material having a surface layer plating layer and an intermediate plating layer as plating layers and having excellent corrosion resistance in a severe corrosion-resistant environment.

Means for solving the above problems includes the following aspects.
(1) a steel material;
A surface plating layer arranged on the surface of the steel material and composed of a Zn-Al-Mg alloy layer having an Fe concentration of less than 3% by mass, and a surface plating layer arranged between the steel material and the surface plating layer, wherein the Fe concentration is a plating layer comprising a Zn-Al-Mg alloy layer of 3% by mass or more and less than 30% by mass and having a layer thickness of 3 μm or more,
The total layer thickness of the surface plating layer and the intermediate plating layer is 8 μm or more and less than 300 μm,
The average chemical composition of the plating layer is mass%,
Zn: more than 65.00%,
Al: more than 6.5% to less than 22.5%,
Mg: more than 3.0% to less than 12%,
Sn: 0% to less than 4.00%,
Bi: 0% to less than 0.30%,
In: 0% to less than 0.30%,
Ca: 0.05% to less than 1.00%,
Y: 0% to less than 0.30%,
La: 0% to less than 0.30%,
Ce: 0% to less than 0.30%,
Si: 0% to less than 1.00%,
Cr: 0% to less than 0.25%,
Ti: 0% to less than 0.25%,
Ni: 0% to less than 0.25%,
Co: 0% to less than 0.25%,
V: 0% to less than 0.25%,
Nb: 0% to less than 0.25%,
Cu: 0% to less than 0.25%,
Mn: 0% to less than 0.25%,
Fe: 0% to less than 15.0%,
Sr: 0% to less than 0.50%,
Sb: 0% to less than 0.50%,
B: 0% to less than 0.50%, and consists of impurities,
A plated steel material, wherein the intermediate plated layer has a Mg concentration of more than 3.0% by mass.
(2) In the X-ray diffraction image of the surface of the surface plating layer, measured under the conditions that the X-ray output is 40 kV and 150 mA using Cu-Kα rays,
Intensity sum I (Zn) = I (36.30° intensity (cps)) + I (38.99° intensity (cps)) + I (43.23° intensity (cps)) + I (54.34° intensity (cps) ) + I (70.06° intensity (cps)),
Intensity sum I (Al) = I (38.47° intensity (cps)) + I (44.74° intensity (cps)) + I (65.14° intensity (cps)),
Intensity sum I (MgZn ₂ ) = I (19.67° intensity (cps)) + I (20.79° intensity (cps)) + I (22.26° intensity (cps)) + I (40.47° intensity (cps) )) + I (41.31° intensity (cps)) + I (45.378° intensity (cps)),
Intensity sum Io=I(Zn)+I(Al)+I(MgZn ₂ )
, the plated steel material according to (1) that satisfies the following formulas 1 to 3 below.
Formula 1: I(Zn)/Io≤0.70,
Formula 2: 0.05≦I(Al)/Io≦0.30
Formula 3: 0.25≤I( _MgZn2 )/Io≤0.70
(3) the Sn concentration of the surface plating layer is 0.03 to less than 2.00% by mass;
In the X-ray diffraction image of the surface of the surface plating layer, measured using Cu-Kα rays under the conditions that the X-ray output is 40 kV and 150 mA, the intensity I (Mg-Sn intermetallic compound) = I (22. 8° intensity (cps)) is 1000 cps or more, or 500 cps or more when the average intensity at 11° to 12° without a diffraction peak is taken as the background intensity (cps), (1) or (2) Plated steel as described.
(4) The plated layer is disposed between the steel material and the intermediate plated layer, and is composed of an Al—Fe alloy layer having a Fe concentration of 30% by mass or more and less than 85% by mass) and a layer thickness of 1 μm or more. The plated steel material according to any one of (1) to (3), which has an interfacial alloy layer.
(5) A method for producing a plated steel material according to any one of claims 1 to 4,
in % by mass,
Zn: more than 65.0%,
Al: more than 12.0% to 25.0%,
Mg: more than 5.0% to less than 8.0%,
Sn: 0 to less than 5.00%,
Bi: 0% to less than 1.0%,
In: 0% to less than 0.50%,
Ca: 0.10% to less than 3.00%,
Y: 0% to less than 0.50%,
La: 0% to less than 0.50%,
Ce: 0% to less than 0.50%,
Si: 0% to less than 1.00%,
Cr: 0% to less than 0.25%,
Ti: 0% to less than 0.25%,
Ni: 0% to less than 0.25%,
Co: 0% to less than 0.25%,
V: 0% to less than 0.25%,
Nb: 0% to less than 0.25%,
Cu: 0% to less than 0.25%,
Mn: 0% to less than 0.25%,
Fe: 0% to less than 5.0%,
Sr: 0% to less than 0.50%,
Sb: 0% to less than 0.50%,
B: A molten Zn-Al-Mg alloy plating bath having a chemical composition consisting of 0% to less than 0.50% and impurities, and a bath temperature of +20°C (but at least above 420°C) to 520°C. and a plated steel base material having a coating layer with a thickness of 30 μm or more, which is selected from a Zn-plated steel base material, a Zn-Al alloy-plated steel base material, and a Zn-Al-Mg alloy-plated steel base material. a step of immersing the steel base material for 20 seconds or more and less than 240 seconds, and then withdrawing the steel base material;
a step of cooling the plated steel base material to 380° C. within 60 seconds immediately after being pulled up from the molten Zn—Al—Mg alloy plating bath;
A method for producing a plated steel material having
(6) The plating layer of the plated steel substrate has an interfacial alloy layer composed of a Zn—Fe alloy layer having a Fe concentration of 3% by mass or more and less than 80% by mass and a layer thickness of 10 μm or more; A method for producing the plated steel described.

ADVANTAGE OF THE INVENTION According to this invention, it is a plated steel material which has a surface layer plating layer and an intermediate plating layer as a plating layer, and can provide the plated steel material excellent in corrosion resistance to a severe corrosion-resistant environment.

1 shows a backscattered electron image of a SEM (magnification: 100) showing an example of a cross section of a plating layer of a plated steel material of the present invention. FIG. 2 shows a backscattered electron image of an SEM (magnification: 500) showing an example of the cross section of the intermediate plating layer of the plated steel material of the present invention. In addition, FIG. 2 is an enlarged cross-sectional photograph of a region surrounded by a white line of the intermediate plating layer among the plating layers shown in FIG. FIG. 2 shows a backscattered electron image of a SEM (magnification: 2000) showing an example of a cross section of a plating layer of a conventional plated steel.

An example of the present invention will be described below.
In addition, in this specification, "%" display of content of each element of a chemical composition means "mass %."
A numerical range represented using "to" means a range including the numerical values described before and after "to" as lower and upper limits.
Numerical ranges in which "greater" or "less than" are attached to numerical values written before and after "to" mean ranges that do not include these numerical values as lower or upper limits.
The content of an element in a chemical composition may be expressed as element concentration (for example, Zn concentration, Mg concentration, etc.).
The term "process" includes not only independent steps, but also if the intended purpose of the step is achieved even if it cannot be clearly distinguished from other steps.
The expression “X% or X+element symbol (for example, 19% Al or 19Al)” indicates that the target element concentration is X% (for example, Al concentration is 19%). The Zn concentration indicated together with "X% or X+element symbol" is the balance concentration. For example, when written as "Zn-10Al-5.1Mg-0.1Ca" or "Zn-10%Al-5.1%Mg-0.1%Ca", Al concentration = 10%, Mg concentration = 5.1%, Ca concentration = 0.1%, Zn concentration = balance.
A “layer cross section” refers to a cross section obtained by cutting a layer along the thickness direction.
The term “layer surface” refers to a surface facing the thickness direction of the layer and facing the outside of the steel sheet.

The plated steel material of the present invention has a steel material and a plating layer.
The plating layer is arranged on the surface of the steel material, and is arranged between the surface plating layer composed of a Zn-Al-Mg alloy layer having an Fe concentration of less than 3% by mass, and the steel material and the surface plating layer, and the Fe concentration is and an intermediate plated layer having a thickness of 3 μm or more, which is composed of a Zn—Al—Mg alloy layer containing an Al—Fe intermetallic compound phase and containing 3% by mass or more and less than 30% by mass.
The total layer thickness of the surface plating layer and the intermediate plating layer is 8 μm or more and less than 300 μm, and the average chemical composition of the surface plating layer and the intermediate plating layer combined, and the average chemical composition of the surface plating layer will be described later. A predetermined average chemical composition is used, and the Mg concentration of the intermediate plating layer is more than 3% by mass.

The plated steel material of the present invention is a plated steel material having a surface layer plating layer and an intermediate plating layer as the plating layers, and has excellent corrosion resistance in severe corrosion-resistant environments (coastal areas, areas where snow-melting salts are sprayed, etc.). It becomes a plated steel material.

Here, the plated steel material of the present invention was discovered based on the following findings.
Conventionally, as a post-plated steel material by a two-step plating method (that is, a plated steel material having a surface layer plating layer and an intermediate plating layer as a plating layer), hot-dip Zn post-plating steel material with an increased thickness of the plating layer, second-step plating After forming a Zn-Al-Mg-based plating layer (for example, a Zn-5%Al-1%Mg plating layer) by treatment, plated steel materials have been used.

In order to evaluate the corrosion resistance of these post-plated steel materials, the salt spray test (SST) accelerated corrosion test is commonly used. As a market evaluation, endurance for 10,000 hours with a layer thickness of 50 μm is one index of high corrosion resistance. If the plating layer has high corrosion resistance, the plating layer can be made thinner, and if the plating layer is made thicker, a longer rust prevention period can be obtained.

And if the composition and structure of the plating layer with higher corrosion resistance can be imparted by the post-plating treatment (second-stage plating treatment), the applications of post-plating steel materials by Zn-Al-Mg-based plating treatment will be expanded. is possible. As a result, these post-plated steel materials can be applied to parts where stainless steel materials and the like have conventionally been used, and as a result, cost reduction can be realized.

Therefore, the inventors studied corrosion resistance in severe corrosion-resistant environments (coastal areas, areas where snow-melting salt is sprayed, etc.), and obtained the following findings.
In addition, the inventors have determined that the minimum durability level of post-plated steel materials in severe corrosion-resistant environments (coastal areas, areas where snow-melting salt is sprayed, etc.) is 6000 hours with a layer thickness of 25 μm or less, and a layer thickness of 50 μm or less. 11000 hours at 100 μm, and 21000 hours or more with a layer thickness of 100 μm or less (that is, plating thickness×200 hours+1000 hours) in SST, no occurrence of red rust was examined based on the acceptance criteria.

First, as a condition for carrying out the two-step plating method, at least a plating layer having a layer thickness of 10 μm or more (for example, a dipping molten Zn plating layer (5 μm or more as ζ phase)) is formed in the first plating process. There is a need.
If the thickness of the first-stage plating layer is not sufficient, non-plating occurs after the second-stage plating process. Alternatively, the entire plated layer or the intermediate plated layer cannot be formed with a sufficient thickness by the two-step plating method. Since the .zeta. phase changes to the intermediate plating layer, it is preferable that the .zeta.
Therefore, even if the chemical composition or structure of the plating layer is suitable, the post-plated steel material does not meet the following acceptance conditions. However, if the thickness of the plating layer as a whole is too thick, the components of the second plating process will tend to change. Since it tends to deteriorate, it becomes a post-plated steel material that does not meet the following acceptance conditions.

In other words, the second-stage plating involves a reaction with the first-stage plating layer (for example, hot-dip Zn plating layer). 2) The thickness of the entire plating layer is kept within an appropriate range, and traces of the first plating layer are appropriately left.

Specifically, as a trace of the first plated layer, an intermediate plated layer composed of a Zn-Al-Mg alloy layer with a layer thickness of 3 µm or more containing an Al-Fe intermetallic compound is formed with a layer thickness of 3 µm or more. In addition, by setting the thickness of the entire plating layer (total thickness of the surface plating layer and the intermediate plating layer) to 8 μm or more and less than 300 μm, corrosion resistance to severe corrosion resistance environments is enhanced.

That is, as the plating layer by the two-step plating method, the surface plating layer is a Zn-Al-Mg alloy layer having a structure derived from the second plating bath, and the intermediate plating layer is a structure containing an Al-Fe intermetallic compound. and a Zn--Al--Mg alloy layer having a suitable layer thickness, both the outermost plating layer and the intermediate plating layer can exhibit high corrosion resistance.

On the other hand, among the plating layers by the two-step plating method, the chemical composition of the surface plating layer is the first plating layer (for example, the dipping Zn plating layer) and the plating bath used in the second plating process (hereinafter referred to as (also referred to as a “second-stage plating bath”). That is, when a plated steel base material having a thick plating layer is used as the plated steel base material on which the first-stage plating layer is formed, the chemical composition of the entire plating layer is Zn concentration increases. In addition, since Fe diffuses by a maximum of about 15% from the steel material (base iron), the Al concentration tends to be low.

Further, for example, when a hot-dip Zn-plated steel base material on which a hot-dip Zn-plated layer is formed as the first-stage plating layer is immersed in the second-step plating bath, the η phase of the surface layer of the hot-dip Zn-plated layer dissolves at the same time. The lower layers (ζ phase and δ phase) of the hot-dip Zn plating layer remain, and the surface η phase is replaced with the plating layer having the composition of the second plating bath. Thereby, it is possible to form a second plated layer. The surface plating layer of the second-stage plating layer becomes a plating layer close to the bath composition of the second-stage plating bath. Al in the plating bath of the second step repeats reaction with Fe diffused from the base iron, and changes to an intermediate plating layer. Since the intermediate plating layer reacts with Al and the base iron component, the concentration of these components is higher than that of the surface plating layer.

Judging from these tendencies, the plating layer by the two-stage plating method does not show much variation in the Zn concentration, and the concentration of major elements such as Al is at least 10% lower than that of the second-stage plating bath. occurs, and a component reduction of up to about 50% can occur.

Therefore, regarding the chemical composition of the entire plating layer, even if a plating bath having a high Al concentration is used as the second-stage plating bath, the Al concentration may be low when viewed as the entire plating layer. Needless to say, the chemical composition of the surface layer of the plating layer is closer to the chemical composition of the plating bath in the second stage, and the closer to the interface of the steel material (base iron), the more the Fe component is, and the second stage Unlike the chemical composition of the plating bath, the plating layer has a large difference in composition distribution. That is, the surface plated layer and the intermediate plated layer have different chemical compositions, resulting in a plated layer with a large difference in composition distribution.

By creating these component differences, it is possible to impart a high corrosion resistance with a thick plating layer and a complicated corrosion path, which cannot be exhibited by a single-layer plated steel material or a single-layer plated steel material.

Conventionally, in the second-stage plating process using a Zn--Al--Mg-based plating bath, a plating bath with relatively similar components to the first-stage plating process is used in order to avoid complicating the reaction. The concentrations of alloying components such as Al and Mg can also be kept low. On the other hand, compared with the Zn--Al--Mg-based plating bath used in the conventional second-stage plating process, the composition system with relatively high Al concentration and Mg concentration enhances the corrosion resistance.
In other words, the composition of the entire plating layer by the two-step plating method (average chemical composition of the surface plating layer and the intermediate plating layer) is compared to the composition of the entire plating layer by the conventional two-step plating method, and the Al concentration and Mg concentration are A relatively high component system increases the corrosion resistance in a severe corrosion-resistant environment.

Among the plating layers produced by the two-stage plating method, the main corrosion resistance in a general corrosive environment is the outermost plating layer, which has a low Zn concentration and a high Al and Mg concentration. In such a corrosive environment, if the Mg concentration is relatively high even in the intermediate plating layer, a considerable amount of MgZn ₂ phase can be present, so that even higher corrosion resistance can be exhibited.

As described above, the plated steel material of the present invention is a plated steel material having a surface layer plating layer and an intermediate plating layer as plating layers, and has excellent corrosion resistance to severe corrosion resistance environments (coastal areas, areas where snow melting salt, etc. is sprayed, etc.) It was found to be a plated steel material.

The inventors also made detailed studies on the chemical composition and structure of the surface plating layer and the intermediate plating layer, which are endowed with corrosion resistance to severe corrosion-resistant environments.

First, FIG. 1 shows a backscattered electron image (magnification: 100) of an SEM showing an example of a cross section of the plating layer of the plated steel material of the present invention. In addition, FIG. 2 shows a backscattered electron image of an SEM (magnification: 500) showing an example of a cross section of the intermediate plating layer of the plated steel material of the present invention. In addition, FIG. 2 is an enlarged cross-sectional photograph of a region surrounded by a white line of the intermediate plating layer among the plating layers shown in FIG.
On the other hand, FIG. 3 shows a backscattered electron image (magnification: 2000) of an SEM showing an example of a cross section of a plating layer of a conventional plated steel material.

1 to 3, SL is the surface plating layer, ML is the intermediate plating layer, IL is the interfacial alloy layer, St is the steel material (base iron), Zn is the Zn phase, Al is the Al phase, _MgZn2 is the _MgZn2 phase, Al--Zn is an Al--Zn binary eutectic phase, Al--Fe is an Al--Fe intermetallic compound phase, and Zn (Mg ₂ Sn) is an Mg--Sn intermetallic compound phase present in the Zn phase (for example, Mg ₂ Sn phase).
In FIG. 3, in the surface plated layer, the white region is the Zn phase, and the gray region is the region in which at least one of the Al phase and the _MgZn2 phase exists.

The plated steel material shown in FIG. 1 is HDZ45 (hot-dip Zn-plated steel sheet) standardized by JIS H 8641: 2007 as a plated steel base material, and the second-stage plating is performed using a plating bath (Zn-Al-Mg alloy plating bath). It is a plated steel material that has been treated (hereinafter also referred to as "developed two-stage plated steel material").
On the other hand, the comparative plated steel material shown in FIG. It is a plated steel material (hereinafter also referred to as "comparative two-stage plated steel material") that has undergone a second-stage plating treatment by. This comparative two-stage plated steel is the plated steel with the highest corrosion resistance in the market.

Compared to the comparative two-step plated steel, the developed two-step plated steel has a lower Zn concentration in the surface layer plating layer, and a higher Al concentration and Mg concentration. That is, the proportion of Zn phase is low, and Al phase and _MgZn2 phase (especially _MgZn2 phase) are high.
In the developed two-step plated steel material, even the middle plated layer that leaves traces of the first plated layer (hot-dip Zn plated layer) has a high Mg concentration and contains a considerable amount of MgZn ₂ phase. As a result, the overall coating layer of the developed two-step plated steel has a lower ratio of Zn phase and a higher ratio of Al phase and _MgZn2 phase (particularly _MgZn2 phase) than the comparative two-step plated steel.

Since the developed two-stage plated steel material contains Sn in the plating layer, an Mg—Sn intermetallic compound phase (for example, Mg ₂ Sn phase) is generated.
Furthermore, in the developed two-step plated steel material, an interfacial alloy layer composed of an Al—Fe alloy layer is formed between the intermediate plated layer and the base iron (steel material). This intermediate plated layer contains a high concentration of Mg, which is not found in the comparative two-step plated steel.

Due to the composition and structure of the intermediate plating layer, the developed two-stage plated steel has the same plating layer thickness as the comparison two-stage plated steel (corrosion resistance that can withstand 10,000 hours with a plating layer thickness of 50 μm) ), it is considered to exhibit even higher corrosion resistance.

Based on these findings, the following findings were obtained.

1) Among the plating layers by the two-step plating method, the surface plating layer has a lower proportion of the Zn phase than the plating layer by the conventional two-step plating method, and the phases caused by the alloy components such as the Al phase and the MgZn _two- phase can exhibit even higher corrosion resistance.

Specifically, the structure of the surface plating layer is a structure having Zn phase, Al phase, and MgZn ₂ phase, and the ratio of Zn phase is less than 70% in terms of strength (corresponding to volume fraction) measured by X-ray diffraction. , Al phase and MgZn ₂ phase at a ratio of 30% or more, even higher corrosion resistance can be exhibited.

2) When Sn is contained in the surface plating layer, an Mg—Sn intermetallic compound phase (for example, Mg ₂ Sn phase) is generated, which complicates the direction in which corrosion progresses, thereby exhibiting even higher corrosion resistance.

3) If an interfacial alloy layer composed of an Al—Fe alloy layer is formed between the steel material (base iron) and the intermediate plating layer, this layer has a certain degree of corrosion resistance, so that even higher corrosion resistance can be exhibited. Moreover, the thickness of the entire plating layer can be increased, and corrosion resistance can be obtained by increasing the thickness. In addition, due to mutual diffusion of atoms between the base steel and the plating layer, a certain degree of plating adhesion can be ensured.

From these findings, it was found that the plated steel material of the present invention preferably has, for example, the following aspects.

-Aspect (1)-
In the X-ray diffraction image of the surface of the surface plating layer measured using Cu-Kα rays and under the conditions that the X-ray output is 40 kV and 150 mA,
Intensity sum I (Zn) = I (36.30° intensity (cps)) + I (38.99° intensity (cps)) + I (43.23° intensity (cps)) + I (54.34° intensity (cps) ) + I (70.06° intensity (cps)),
Intensity sum I (Al) = I (38.47° intensity (cps)) + I (44.74° intensity (cps)) + I (65.14° intensity (cps)),
Intensity sum I (MgZn ₂ ) = I (19.67° intensity (cps)) + I (20.79° intensity (cps)) + I (22.26° intensity (cps)) + I (40.47° intensity (cps) )) + I (41.31° intensity (cps)) + I (45.378° intensity (cps)),
Intensity sum Io=I(Zn)+I(Al)+I(MgZn ₂ )
Then, the following formulas 1 to 3 are satisfied.
Formula 1: I(Zn)/Io≤0.70
Formula 2: 0.05≦I(Al)/Io≦0.30
Formula 3: 0.25≤I( _MgZn2 )/Io≤0.70

-Aspect (2)-
The Sn concentration of the surface plating layer is 0.03 to less than 2.00% by mass,
In the X-ray diffraction image of the surface plating layer surface, measured using Cu-Kα rays and under the conditions that the X-ray output is 40 kV and 150 mA, the intensity I (Mg-Sn intermetallic compound) = I (22.8 ° intensity (cps)) is greater than or equal to 1000 cps, or greater than or equal to 500 cps over the background intensity (cps) at 11°-12°.

-Aspect (3)-
The plating layer is disposed between the steel material and the intermediate plating layer, and has an interface alloy layer composed of an Al-Fe alloy layer having a thickness of 1 μm or more with an Fe concentration of 30% by mass or more and less than 85% by mass. .

Details of the plated steel material of the present invention will be described below.

(steel)
A steel material to be plated (hereinafter sometimes referred to as a "plating raw material") will be described.
There are no particular restrictions on the shape of steel materials. Steel materials include steel plates, steel pipes, civil engineering and construction materials (fences, corrugated pipes, drain covers, sand prevention plates, bolts, wire nets, guardrails, water stop walls, etc.) , home appliances and automobile parts (small bolts, complex-shaped housings, punching metals), and other molded steel materials. Various plastic working methods such as press working, roll forming, and bending can be used for forming.

There are no particular restrictions on the material of the steel material. Steel materials include, for example, general steel, Ni pre-plated steel, Al-killed steel, ultra-low carbon steel, high carbon steel, various high-strength steels, and some high-alloy steels (steel containing strengthening elements such as Ni and Cr), etc. Various steel materials can be applied.
There are no particular restrictions on conditions such as the steel material manufacturing method and the steel sheet manufacturing method (hot rolling method, pickling method, cold rolling method, etc.).

The steel may be pre-plated pre-plated steel. A pre-plated steel material is obtained, for example, by an electrolytic treatment method or a displacement plating method. In the electrolytic treatment method, a pre-plated steel material is obtained by immersing a plating raw material in a sulfuric acid bath or a chloride bath containing metal ions of various pre-plating components and performing electrolytic treatment. In the displacement plating method, a pre-plated steel material is obtained by immersing a plating raw material in an aqueous solution containing metal ions of various pre-plating components and pH-adjusted with sulfuric acid to cause displacement deposition of metals.
Ni pre-plated steel is a representative example of the pre-plated steel.
In other words, dipping plating is possible if the plating raw material is steel, and there are no restrictions on the surface condition and shape.

(Plating layer)
Next, the plating layer will be explained.
The plating layer is arranged between the surface plating layer composed of a Zn-Al-Mg alloy layer having an Fe concentration of less than 3% by mass and the steel material and the surface plating layer, and the Fe concentration is 3% by mass or more and 30% by mass. and an intermediate plating layer composed of less than a Zn-Al-Mg alloy layer.
The plating layer may have an interfacial alloy layer composed of an Al—Fe alloy layer in addition to the surface plating layer and the intermediate plating layer. The interfacial alloy layer (Al—Fe alloy layer) is provided between the steel material and the intermediate plating layer.

The surface of the plating layer (that is, the surface of the surface plating layer) has an oxide film of about 50 nm of the constituent elements of the plating layer, but the thickness is thin compared to the thickness of the entire plating layer and does not correspond to the plating layer. Consider.

Next, the chemical composition of the plating layer will be explained.
In the hot-dip plating method, the formation of the interfacial alloy layer composed of the Al-Fe alloy layer completes the reaction in the plating bath, so the formation of the Al-Fe alloy layer reduces the Al and Zn components of the entire plating layer. is usually small.

In order to achieve corrosion resistance in a severe corrosion-resistant environment, the average chemical composition of the plating layer is as follows.

However, Sn, Bi, In, Ca, Y, La, Ce, Si, Cr, Ti, Ni, Co, V, Nb, Cu, Mn, Fe, Sr, Sb, and B are optional elements and is an ingredient. In other words, the lower limit of the content of these elements is 0%, and the plating layer does not have to contain them. When these optional components are included, the content of each optional element is preferably within the range described later.

In addition, the average chemical composition of the plating layer indicates the average chemical composition of the surface layer plating layer and the intermediate plating layer when there is no interfacial alloy layer (Al-Fe alloy layer), and the interfacial alloy layer (Al-Fe alloy layer) means the average chemical composition of the surface plating layer, the intermediate plating layer and the Al—Fe alloy layer.

・ Zn: more than 65.00% (whole plating layer)
Zn is an element that constitutes the main component of the plating layer. In the present invention, since a two-stage plating method is employed, it is an element necessary to have affinity with the first-stage plating layer. If the concentration of Zn is too low, the concentration of Al, which is the second element, will increase, which will control the reactivity with Fe, ensure the wettability with the first-stage plating, and the intermediate plating layer that is the main subject of the present invention. formation becomes uncontrolled.
Therefore, the Zn concentration should be over 65.00%. Zn concentration is preferably 68.00% or more, more preferably 71.00% or more.
Note that the upper limit of the Zn concentration is the concentration of elements other than Zn and the remainder other than impurities.

・ Al: more than 6.5% to less than 22.5% (whole plating layer)
Al is an essential element for forming an intermediate plating layer in the plating layer.
If the Al concentration is too low, the amount of Fe component supplied from the base iron is reduced, and the intermediate plating layer is not formed.
If the Al concentration is too high, as described above, the reactivity with Fe becomes active, making it impossible to control the intermediate plating layer. Excess Al also increases the amount of Al phase and Al--Fe phase formed, and reduces the MgZn ₂ phase essential for the intermediate plating layer. As a result, the corrosion resistance balance is lost, and the expected corrosion resistance cannot be exhibited.
Therefore, the Al concentration should be more than 6.5% and less than 22.5%.
The lower limit of Al concentration is preferably 10.0% or more, more preferably 15.0% or more.
The upper limit of the Al concentration is preferably 21.0% or less, more preferably 20.0% or less.

・ Mg: more than 3.0% to less than 7.2% (whole plating layer)
Mg is an essential element for forming the MgZn ₂ phase that constitutes the intermediate plating layer. In particular, by containing a large amount of elements, a large amount of MgZn2 phase can be formed in the intermediate plating layer, and corrosion resistance under corrosive environments that could not be endured conventionally can be obtained.
If the Mg concentration is too low, the Mg component in the intermediate plating layer becomes insufficient, resulting in a structure similar to that of conventional two-step plating. In such cases, corrosion resistance cannot be obtained in a severely corrosive environment.
If the Mg concentration is too high, the wettability of Mg with the first-stage plating layer becomes poor, making it difficult to form the two-stage plating itself. Also, excess Mg promotes the formation of MgZn ₂ phase and at the same time reduces the amount of Al phase formation. As a result, the corrosion resistance balance is lost, and the expected corrosion resistance cannot be exhibited.
Therefore, the Mg concentration should be more than 3.0% and less than 7.2%.
The lower limit of the Mg concentration is preferably 3.5% or higher, more preferably 4.0% or higher.
The upper limit of the Mg concentration is preferably 7.0% or less, more preferably 6.3% or less.

・Sn: 0% to less than 4.00%, Bi: 0% to less than 0.30%, In: 0% to less than 0.30% (whole plating layer)
Sn, Bi and In are not elements that themselves improve corrosion resistance. Rather, it is an element that promotes the formation of Mg ₂ Sn phase, Mg ₃ In phase, etc., which have low corrosion resistance and are easily soluble, thereby deteriorating corrosion resistance.
If the respective concentrations of Sn, Bi and In are too high, their formation is activated and corrosion resistance deteriorates.
Therefore, the Sn concentration is set to 0% to less than 4.00%, and the respective concentrations of Bi and In are set to 0% to less than 0.30%.

However, when intermetallic compound phases such as Mg ₂ Sn phase and Mg ₃ In phase are dispersed in the plating layer, the corrosion path can be changed. That is, normal corrosion progresses from the surface in the depth direction centering on one point, but single-point breakthrough corrosion can be prevented by including more easily corroded locations in the plating layer. As a result, the corrosion path becomes complicated, and the period during which corrosion reaches the intermediate plating layer as well as the interfacial alloy layer can be lengthened. If corrosion reaches the intermediate plating layer and interfacial alloy layer, the sacrificial anti-corrosion action will act on the surroundings, making it easier for corrosion to progress all at once. is. When the member is placed vertically, such corrosion considerations are largely unnecessary, but when the member is placed flat, this corrosion path becomes an important factor. Therefore, it can be achieved by including a certain amount of Sn, Bi, In, etc. in the plating layer and finely dispersing these phases.
That is, Sn, Bi and In are preferably contained in appropriate amounts. On the other hand, the intermetallic compound phases such as the Mg ₂ Sn phase and the Mg ₃ In phase are hard, and therefore, when formed in a large amount, they adversely affect the adhesion of the plating layer.
Therefore, the lower limit of the Sn concentration is preferably over 0%, more preferably 0.05% or more, and even more preferably 0.10% or more.
The lower limit of each concentration of Bi and In is preferably over 0%, preferably 0.10% or more.
The upper limit of the Sn concentration is preferably 3.00% or less, more preferably 1.00% or less.
The upper limit of each concentration of Bi and In is preferably 0.25% or less.

・ Ca: 0.05% to less than 1.00% (whole plating layer)
Ca is an element necessary to ensure the wettability of the plating bath.
If the Ca concentration is too low, that is, in a plating bath containing a high concentration of Mg, such as the plating bath for forming the plating layer of the present invention, a large amount of Mg oxide film is formed, resulting in a two-stage It becomes impossible to ensure the wettability with the first-stage plating bath when immersed in the plating bath, and it becomes difficult to form the plating layer itself.
If the Ca concentration is too high, a large amount of hard intermetallic compounds are formed in the plating layer, making the plating layer brittle and making it difficult to ensure adhesion to the steel material.
Therefore, the Ca concentration should be 0.05% to less than 1.00%.
The lower limit of Ca concentration is preferably 0.10% or more.
The upper limit of Ca concentration is preferably 0.50% or less.

・ Y: 0% to less than 0.30%, La: 0% to less than 0.30%, Ce: 0% to less than 0.30% (whole plating layer)
Y, La and Ce are elements that have the same function as Ca.
If the respective concentrations of Y, La and Ce are too high, they also form intermetallic compounds.
Therefore, each concentration of Y, La and Ce is set to 0% to less than 0.30%.
The lower limit of each concentration of Y, La and Ce is preferably over 0%, more preferably 0.05% or more.
The upper limit of each concentration of Y, La and Ce is preferably 0.25% or less.

・ Si: 0% to less than 1.00% (whole plating layer)
Si is an element that improves the corrosion resistance of the plating layer. A Mg--Si compound and a Ca--Si compound having high corrosion resistance are formed in the plating layer.
If the Si concentration is too high, the plating adhesion of the plating layer deteriorates, and furthermore, diffusion of Fe into the plating bath is suppressed, making it difficult to form an intermediate plating layer.
Therefore, the Si concentration should be 0% to less than 1.00%.
The lower limit of the Si concentration is preferably over 0%, more preferably 0.05% or more, and even more preferably 0.10% or more.
The upper limit of the Si concentration is preferably 0.50% or less, more preferably 0.40% or less.

・Cr: 0% to less than 0.25%, Ti: 0% to less than 0.25%, Ni: 0% to less than 0.25%, Co: 0% to less than 0.25%, V: 0% to Less than 0.25%, Nb: 0% to less than 0.25%, Cu: 0% to less than 0.25%, Mn: 0% to less than 0.25% (whole plating layer)
Cr, Ti, Ni, Co, V, Nb, Cu and Mn are elements that can be added to the plating bath. When these elements are contained in the plating bath, they exist in a substitution state in the phases constituting the plating layer, or form fine intermetallic compounds, and these effects slightly change the corrosion resistance. is an element that can
If the respective concentrations of Cr, Ti, Ni, Co, V, Nb, Cu and Mn are too high, the formation of intermetallic compounds increases, and the original structure and corrosion resistance of the plating layer cannot be exhibited.
Therefore, each concentration of Cr, Ti, Ni, Co, V, Nb, Cu, and Mn should be 0% to less than 0.25%.
The lower limit of each concentration of Cr, Ti, Ni, Co, V, Nb, Cu and Mn is preferably over 0%, more preferably 0.05% or more, and even more preferably 0.1% or more.

・ Fe: 0% to less than 15.0% (whole plating layer)
When forming a plating layer by a hot dip plating method, a surface plating layer (Zn-Al-Mg alloy layer), an intermediate plating layer (Zn-Al-Mg alloy layer containing an Al-Fe metal intermetallic layer) and an interfacial alloy layer (Al—Fe alloy layer) contains a constant Fe concentration.
It has been confirmed that up to a Fe concentration of less than 15.0%, there is no adverse effect on performance even if Fe is included in the plating layer formed by the two-stage plating method. Since most of Fe is often contained in the Al—Fe alloy layer, the Fe concentration generally increases as the thickness of this layer increases.

・ Sr: 0% to less than 0.50%, Sb: 0% to less than 0.50%, B: 0% to less than 0.50% (whole plating layer)
Like the above elements, Sr, Sb and B are also elements that can be added, and bring about the same effects. is an element.
Too high concentrations of Sr, Sb and B not only saturate the effect, but also increase dross and lower workability.
Therefore, each concentration of Sr, Sb and B is set to 0% to less than 0.50%.
The lower limit of each concentration of Sr, Sb and B is preferably over 0%, more preferably 0.05% or more, and even more preferably 0.1% or more.
The upper limit of each concentration of Sr, Sb and B is preferably 0.40% or less, more preferably 0.30% or less.

・Impurities (whole plating layer)
Impurities refer to components contained in raw materials or components mixed in during the manufacturing process and not intentionally included. For example, the plating layer may contain a small amount of components other than Fe as impurities due to mutual atomic diffusion between the steel material (base iron) and the plating bath.

(Surface plating layer)
The surface plated layer is composed of a Zn--Al--Mg alloy layer having an Fe concentration of less than 3% by mass.

The average chemical composition of the surface plating layer is the following average chemical composition in order to achieve corrosion resistance in general corrosion-resistant environments.

Here, the general corrosive environment refers to a normal outdoor environment, a rural environment, a corrosive environment with a low SOx concentration, and an environment where seawater droplets do not directly hit even in a coastal area. Severe corrosive environments for two-stage plated steel materials are assumed to be, for example, coastal areas where they are directly exposed to seawater splashes, and conditions where they are constantly wet with water in environments where snowmelt salt is sprayed. are doing.

The plating components of the surface plating layer, that is, the plating bath components used in the two-stage plating bath always contain the components Zn and Fe of the first stage. That is, Zn and Fe affect the components of the two-step plating bath, and these components are usually greater in the surface layer plating layer. On the other hand, other elements tend to be relatively low due to the increase in these elements. For example, Zn may be higher than the plating bath in the range of 0 to +10% in the surface layer plating layer, and Fe may be contained up to around 1%. On the other hand, Al is a representative element that decreases in the surface layer plating layer, and since it moves to the intermediate plating layer, the surface layer plating layer may decrease to about 1/5 of the original two-stage plating bath composition. The increase or decrease of other components is not specified, but when the decrease in Al component is large compared to the increase in Zn and Fe components, the increase is relatively high, and when the decrease in Al component is small, the other elements are also included. descend.

Specifically, for the same reason as the reason for limitation explained in the average chemical composition of the plating layer, the average chemical composition of the surface plating layer is
Zn: more than 70.00%,
Al: more than 3.0% to less than 25.0%,
Mg: more than 5.0% to less than 12.0%,
Sn: 0% to less than 5.00%,
Bi: 0% to less than 0.30%,
In: 0% to less than 0.30%,
Ca: 0.05% to less than 1.00%,
Y: 0% to less than 0.30%,
La: 0% to less than 0.30%,
Ce: 0% to less than 0.30%,
Si: 0% to less than 1.00%,
Cr: 0% to less than 0.25%,
Ti: 0% to less than 0.25%,
Ni: 0% to less than 0.25%,
Co: 0% to less than 0.25%,
V: 0% to less than 0.25%,
Nb: 0% to less than 0.25%,
Cu: 0% to less than 0.25%,
Mn: 0% to less than 0.25%,
Fe: 0% to less than 3.0%,
Sr: 0% to less than 0.50%,
Sb: 0% to less than 0.50%,
B: Average chemical composition consisting of 0% to less than 0.50% and impurities.

Next, the constituent phases of the surface plated layer will be described.
The surface plated layer preferably has a Zn phase, an Al phase and a _MgZn2 phase. From the viewpoint of improving corrosion resistance, it is preferable to lower the proportion of the Zn phase and increase the proportions of the Al phase and the _MgZn2 phase.

Here, the presence and ratio of Zn phase, Al phase and _MgZn2 phase can be confirmed by X-ray diffraction (XRD) using Cu-Kα rays.
Usually, in XRD, if it is a diffraction peak of Zn, for example, JCPDS card: PDF#00-004-0831 is represented. In the surface plating layer (Zn-Al-Mg alloy layer), the optimum diffraction peaks for identifying the Zn phase are 36.30°, 38.99°, 43.23°, 54.34° and 70.06° is.
Further, in XRD, if it is an Al diffraction peak, for example, JCPDS card: PDF#00-004-0787 is representative. In the surface layer plating layer (Zn-Al-Mg plating layer), the optimum diffraction peaks for identifying the Al phase are 38.47°, 44.74° and 65.14°.
Moreover, in XRD, if it is a diffraction peak of _MgZn2 , for example, JCPDS card: PDF#00-034-0457 is represented. In the surface plating layer (Zn-Al-Mg plating layer), the optimum diffraction peaks for identifying the MgZn ₂ phase are 19.67°, 20.79°, 22.26°, 41.31°, and 45°. .378°.

Then, in the X-ray diffraction image of the surface of the surface plating layer, measured under the conditions that the X-ray output is 40 kV and 150 mA using Cu-Kα rays,
Intensity sum I (Zn) = I (36.30° intensity (cps)) + I (38.99° intensity (cps)) + I (43.23° intensity (cps)) + I (54.34° intensity (cps) ) + I (70.06° intensity (cps)),
Intensity sum I (Al) = I (38.47° intensity (cps)) + I (44.74° intensity (cps)) + I (65.14° intensity (cps)),
Intensity sum I (MgZn ₂ ) = I (19.67° intensity (cps)) + I (20.79° intensity (cps)) + I (22.26° intensity (cps)) + I (40.47° intensity (cps) )) + I (41.31° intensity (cps)) + I (45.378° intensity (cps)),
Intensity sum Io=I(Zn)+I(Al)+I(MgZn ₂ )
, it is preferable that the following formulas 1 to 3 are satisfied.

When the following formula 1 is satisfied, the ratio of the Zn phase is lower than that of the plated layer formed by the conventional two-step plating method, for example, the Zn phase has a volume fraction of less than 70%.
On the other hand, when the formulas 2 and 3 are satisfied, the ratio of the Al phase and _{the MgZn2} phase is higher than that of the plating layer formed by the conventional two-step plating method. indicates that it has
By satisfying the following formulas 1 to 3, further high corrosion resistance is exhibited. From the viewpoint of improving corrosion resistance, it is more preferable to satisfy the following formulas 1-2 to 3-2.

Formula 1: I(Zn)/Io≤0.70
Formula 2: 0.05≦I(Al)/Io≦0.30
Formula 3: 0.25≤I( _MgZn2 )/Io≤0.70

Formula 1-2: I (Zn) / Io ≤ 0.60
Formula 2-2: 0.10 ≤ I (Al) / Io ≤ 0.25
Formula 3-2: 0.30≦I(MgZn ₂ )/Io≦0.50

Next, the "effect of containing Sn" for improving the corrosion resistance of the surface plating layer will be described.
When Sn is included in the surface plating layer, it forms an Mg--Sn intermetallic compound phase with Mg, compared to the MgZn ₂ phase. Therefore, when the Mg—Sn intermetallic compound phase is present in the surface plating layer, higher corrosion resistance is exhibited.
In order to exhibit high corrosion resistance and to form an Mg—Sn intermetallic compound phase, the Sn concentration in the surface plating layer is preferably 0.03 to less than 2.00%.

Here, the Mg—Sn intermetallic compound phase includes intermetallic compound phases corresponding to the following (1) to (5). The Mg—Sn intermetallic compound phase may contain an element such as Si in an interstitial solid solution.
(1) Mg ₂ Sn phase (2) Mg ₉ Sn ₅ phase (3) Part of Sn is substituted with at least one of Bi, In, Cr, Ti, Ni, Co, V, Nb, Cu, and Mn Substituted Mg ₂ Sn phase and Mg ₉ Sn ₅ phase (phases of substitutes of Mg ₂ Sn phase and Mg ₉ Sn ₅ phase)
(4) Substituted Mg ₂ Sn phase and Mg ₉ Sn 5 phase in _{which at least one of Ca, Y, La and Ce is substituted for part of Mg (Mg 2 Sn phase and Mg 9 Sn 5 substituted phase )}
(5) At least one of Ca, Y, La and Ce is substituted for a portion of Mg, and Bi, In, Cr, Ti, Ni, Co, V, Nb, Cu, and Mn are substituted for a portion of Sn. Substituted Mg ₂ Sn phase and Mg ₉ Sn ₅ phase with at least one substitution (Mg ₂ Sn phase and substituted phase of Mg ₉ Sn ₅ )
The Mg ₂ Sn phase and the Mg ₉ Sn ₅ -substituted phase are sometimes collectively referred to as the "Mg ₂ Sn-substituted phase."

The presence of the Mg—Sn intermetallic compound phase in the surface plating layer can be confirmed by X-ray diffraction (XRD) using Cu—Kα rays.
Usually, XRD diffraction peaks of Mg ₂ Sn are represented by, for example, JCPDS cards: PDF#00-007-0274, #00-006-0190, and #00-002-1087. However, in the surface plating layer (Zn-Al-Mg alloy layer), the optimum diffraction peak for identifying the Mg-Sn intermetallic compound phase is the Zn phase, MgZn ₂ phase, Al phase and the diffraction peaks do not overlap 22 .8°. The diffraction peaks used to identify the Mg—Sn intermetallic compound phase were 22.8°, 23.3°, and 24.2°, which did not overlap with other constituent phases of the plating layer, and Zn—Al - is a convenient diffraction peak for identifying Mg alloys.

Specifically, in the X-ray diffraction image of the surface layer plating layer surface measured using Cu-Kα rays under the conditions that the X-ray output is 40 kV and 150 mA, the intensity I (Mg-Sn intermetallic compound) = When I (22.8 ° intensity (cps)) is 1000 cps or more, or 500 cps or more higher than the background intensity (cps) at 11 to 12 °, the surface plating layer has a sufficient amount of Mg-Sn intermetallic compound phase. It is an index that exists in
If the intensity I (Mg-Sn intermetallic compound) is 1000 cps or more, or if the intensity is 500 cps against the background intensity (cps) at 11 to 12 °, the Mg-Sn intermetallic compound is dispersed in the surface plating layer. The higher the strength, the higher the content.
However, if the strength I (Mg—Sn intermetallic compound) exceeds 5000 cps, the corrosion resistance deteriorates, which is not preferable.

As a method for calculating the intensity of the background, there is software that can remove the background in recent years, but from the data of the obtained diffraction peak intensity, create a 2θ and intensity (cps) graph, An approximation line (straight line) of the plateau confirmed at 12° is created. From the plated layer surface of the present disclosure, no diffraction peaks appear at 15 ° and 25 °, so simply taking the average value of the intensity cps at 11 ° and 12 ° will reveal the background intensity at 11 to 12 °. do.

(Intermediate plating layer)
Next, the intermediate plated layer will be explained.
The intermediate plated layer is composed of a Zn--Al--Mg alloy layer having an Fe concentration of 3% by mass or more and less than 30% by mass.

The average chemical composition of the intermediate plating layer is not particularly limited, but the Mg concentration should be over 3.0%. When the Mg concentration is over 3%, the _MgZn2 phase with corrosion resistance increases. Therefore, even higher corrosion resistance is exhibited. The Mg concentration is preferably more than 3.0% and less than 15.0%.
The lower limit of Mg concentration may be 3.2%, 3.5%, 4.0%.
The upper limit of Mg concentration may be 10.0%, 8.0%, 6.0%.

Next, the constituent phases of the Zn--Al--Mg alloy layer will be described.
The intermediate plated layer contains 3% by mass or more and less than 30% by mass of Fe. Fe in the intermediate plated layer is contained as, for example, an Al--Fe intermetallic compound phase by reaction with Al.
The Al—Fe intermetallic compound phase is a phase mainly composed of Al ₅ Fe. _{The Al—Fe intermetallic compound phase may contain AlFe, Al 3 Fe} , Al ₅ Fe ₂ and the like in addition to Al 5 Fe.
The Al--Fe intermetallic compound phase may become an Al--Fe--Si intermetallic compound phase when Si is contained in the plating layer. The identified Al--Fe--Si intermetallic compound phase includes the AlFeSi phase, and α, β, q1, q2-AlFeSi phases and the like exist as isomers.
Al and Fe compounding ratios other than those mentioned above are conceivable, but there is almost no change in corrosion resistance due to changes in the AlFe ratio. , not so much as to affect the corrosion resistance of the entire plating layer. That is, the Al--Fe intermetallic compound has a certain sacrificial anti-corrosion property against Fe due to its binding action with Al rather than with Fe (therefore, until the Al--Fe intermetallic compound phase disappears, does not corrode ₎ , and since it is an intermetallic compound, it is highly insulating and _resistant to corrosion in any environment. However, if there is a large amount of Mg component in the surroundings, this yellow rust is hardly conspicuous) and acts as a strong framework (column) of the plating layer.

In addition to the Al--Fe intermetallic compound phase, the intermediate plating layer includes, for example, MgZn ₂ phase, Zn--Al phase (or Al--Zn phase, depending on the component concentration), between Al--Fe intermetallic compounds, It may have Mg ₂ Sn phase, Zn—Al—MgZn ₂ ternary eutectic structure, Zn phase, and Mg ₂ Si phase. In addition, although the amount of other intermetallic compound phases in the intermediate plating layer is small, Al—Ca—Si intermetallic compound phase, Al—Ca intermetallic compound phase, Mg—Ca—Si intermetallic compound phase, Zn- It may have a compound phase in which Sn, Bi, In, and B elements added to the Al—Mg-based plating bath and Zn, Al, and Mg atoms are incorporated and bonded.
These phases basically have the same properties as the surface plating layer, and corrode to produce white rust. Moreover, except for a small amount of the intermetallic compound phase, it is always in a less noble electrochemical relationship than the Al—Fe intermetallic compound phase, so corrosion precedes the Al—Fe intermetallic compound phase during corrosion.

It is a feature of the plated steel material of the present invention that these multiple phases are incorporated into the intermediate plating layer, and it is almost impossible to incorporate Mg into the intermediate plating layer in conventional Zn-Al-Mg-based plated steel materials. Therefore, many of the intermediate plating layers of conventional Zn-Al-Mg-based plated steels have Zn, Fe or Al, that is, only Zn-Fe phases and Al-Fe phases in a state close to 100%. ing. This is because, unlike Zn and Al, Mg inherently has low reactivity with Fe, so that it cannot move to the interface side during plating and solidifies on the plating layer surface.

In the plated steel material of the present invention, it is possible to incorporate Mg into the intermediate plating layer by appropriately controlling the concentration range of high-concentration Mg, Al, Zn, and other elements.
The intermediate plating layer of the plating layer is composed of these compound phases, and the intermediate plating layer has stable corrosion resistance in any corrosive environment. A metal layer composed only of Zn, Al, and Mg exhibits high corrosion resistance in a general corrosive environment, an atmospheric environment, etc., but corrodes relatively quickly in water, seawater, or the like. This is presumed to be due to excessive sacrificial corrosion resistance due to the large potential difference with the base iron.

On the other hand, the Al—Fe intermetallic compound phase has a small potential difference with Fe, and does not exhibit excessive sacrificial corrosion resistance. However, the corrosion rate is stable. The intermetallic compound phase composed of Zn, Al, and Mg, which occupies the space between the Al—Fe intermetallic compound phases, makes the yellow rust due to Al—Fe corrosion inconspicuous, and further, the corrosion order of the Al—Fe intermetallic compound phase. By slowing down, it is possible to exhibit corrosion resistance that cannot be achieved with a plating layer consisting of only a simple metal layer.
This is greatly related to the concentration of Mg, and by increasing the ratio of this element in the plating bath and intermediate plating layer, when it is composed only of Zn, Al, and Fe, the Al-Fe intermetallic Corrosion between compound phases is also rapid, and corrosion of Al--Fe intermetallic compound phases is also rapid. Furthermore, red rust becomes conspicuous.

(interface alloy layer)
The interfacial alloy layer is composed of an Al—Fe alloy layer having an Fe concentration of 30% by mass or more and less than 85% by mass.

The interfacial alloy layer (Al—Fe alloy layer) is a layer whose main phase is the Al ₅ Fe phase as a structure. The Al—Fe alloy layer is formed by mutual atomic diffusion of the base iron (steel material) and the first and second plating baths. When hot-dip plating is used as a manufacturing method, an Al—Fe alloy layer is likely to be formed in a plating layer containing Al element. At least, since the second-stage plating bath contains Al at a certain concentration or more, the Al ₅ Fe phase is formed most. However, atomic diffusion takes a long time, and there are areas where the Fe concentration is high in areas close to the base iron. Therefore, the interfacial alloy layer may partially contain a small amount of an AlFe phase, an Al ₃ Fe phase, an Al ₅ Fe ₂ phase, or the like. In addition, since the plating bath contains Zn at a certain concentration, the Al—Fe alloy layer also contains a small amount of Zn.

In terms of corrosion resistance, there is no great difference between the Al ₅ Fe phase, the Al ₃ Fe phase, the AlFe phase, and the Al ₅ Fe ₂ phase. The corrosion resistance referred to here is the corrosion resistance of portions not affected by welding. The thickness of the interfacial alloy layer, which occupies the plating layer, is small, and the corrosion resistance is lower than that of the surface plating layer (Zn-Al-Mg alloy layer) and the intermediate plating layer. Even if the phase ratio is changed, there is no big difference.

Here, when Si is contained in the plating layer, Si is particularly easily incorporated into the interfacial alloy layer (Al—Fe alloy layer), and the Al—Fe intermetallic compound phase is the Al—Fe—Si intermetallic compound phase. can be The identified intermetallic compound phase includes the AlFeSi phase, and α, β, q1, q2-AlFeSi phases and the like exist as isomers. Therefore, these AlFeSi phases and the like may be detected in the Al--Fe alloy layer. The Al--Fe alloy layer containing these AlFeSi phases and the like is also called an Al--Fe--Si alloy layer.
Since the Al--Fe--Si alloy layer is also smaller than the total thickness of the surface layer plating layer (Zn--Al--Mg alloy layer) and the intermediate plating layer, it has little effect on the corrosion resistance of the entire plating layer.
The composition of the Al—Fe intermetallic compound is almost the same as that of the intermediate plating layer, but the intermediate plating layer exhibits needle-like, columnar, branch-like, etc. forms, while the interfacial alloy layer is formed in layers. There is a difference. That is, in the interfacial alloy layer, the Al—Fe intermetallic compound tends to grow parallel to the thickness direction of the plating layer, spreads over the entire surface, and then grows onto the plating surface.

In addition, when various pre-plated steel materials are used as the plating raw material (plating base plate, etc.), the structure of the interfacial alloy layer (Al—Fe alloy layer) may change depending on the amount of pre-plating deposited. Specifically, when the pure metal layer used for pre-plating remains around the Al-Fe alloy layer, the surface layer plating layer (Zn-Al-Mg alloy layer) or the plating layer by the first plating process When an intermetallic compound phase (for example, an Al ₃ Ni phase, etc.) in which a constituent component and a pre-plating component are combined forms an alloy layer, when an Al—Fe alloy layer in which some of the Al atoms and Fe atoms are substituted is formed, Alternatively, an Al--Fe--Si alloy layer in which part of Al atoms, Fe atoms and Si atoms are substituted may be formed. In any case, these alloy layers also have a total thickness of the surface layer plating layer (Zn-Al-Mg alloy layer) and the intermediate plating layer, and the interfacial alloy layer itself is thicker than the intermediate plating layer and the metal layer. Since it is small, it has little effect on the corrosion resistance of the entire plating layer.

Further, the interfacial alloy layer (Al--Fe alloy layer) may partially incorporate the phases (Zn phase, MgZn ₂ phase, etc.) constituting the surface plated layer (Zn--Al--Mg alloy layer).

In other words, the interfacial alloy layer (Al--Fe alloy layer) is a layer including alloy layers of the above-described various aspects in addition to the alloy layer mainly composed of the Al ₅ Fe phase.

Among various pre-plated steel materials, when a plating layer is formed on a Ni pre-plated steel material, an Al--Ni--Fe alloy layer is formed as an interfacial alloy layer (Al--Fe alloy layer). The Al--Ni--Fe alloy layer also has a smaller thickness than the total thickness of the surface plating layer (Zn--Al--Mg alloy layer) and the intermediate plating layer, and thus has little effect on the corrosion resistance of the entire plating layer.

Since the interfacial alloy layer (Al—Fe alloy layer) is often composed mainly of the Al ₅ Fe phase, the chemical composition of the Al—Fe alloy layer is Fe: 30 to 85%, Al: 15 to 75%, Zn : 10% or less, and the balance: a composition containing impurities can be exemplified.

(Thickness of plating layer)
Next, the layer thickness of the plating layer will be described.
When the total layer thickness of the surface plating layer and the intermediate plating layer is less than 8 μm, it becomes difficult to exhibit high corrosion resistance.
Judging from the manufacturing method of two-stage dipping, a plating layer thickness of at least 5 μm is usually obtained in many cases. On the other hand, there are portions such as screw threads that are extremely thin due to the uneven shape, and the thinnest portion is about 8 μm at these portions. If centrifugal separation or other sagging removal is performed, the thickness of the special portion can be as high as 3 to 5 μm.
Therefore, the total layer thickness of the surface plated layer and the intermediate plated layer is set to 8 μm or more. The total layer thickness of the surface plating layer and the intermediate plating layer is preferably 10 μm or more, more preferably 25 μm or more.

On the other hand, if the total layer thickness of the surface plating layer and the intermediate plating layer exceeds 300 μm, strain such as thermal contraction during solidification becomes excessive, cracks occur in the plating layer, and corrosion resistance may deteriorate. , The total layer thickness of the surface plating layer and the intermediate plating layer shall be less than 300 μm

Regarding the upper limit of the total layer thickness of the surface layer plating layer and the intermediate plating layer, the thicker the layer, the better the corrosion resistance. Normally, dipping plating produces a plated product with a thickness of around 100 μm, but depending on the unevenness, sagging occurs even if the target is 100 μm, and the thickness of the plating layer partially increases to around 300 μm. Sometimes. It is preferable that the thickness is 150 μm or less when the appearance is important, because it causes sagging, deterioration of the appearance, projections, and the like.

If the layer thickness of the surface plating layer is too thin, it becomes difficult to exhibit high corrosion resistance. Therefore, the layer thickness of the surface plating layer is preferably 1 μm or more, more preferably 10 μm or more.
On the other hand, if the layer thickness of the surface layer plating layer is too thick, the plating appearance may deteriorate. Therefore, the layer thickness of the surface plating layer is preferably 100 μm or less, more preferably 50 μm or less.

If the layer thickness of the intermediate plating layer is less than 3 μm, it becomes difficult to exhibit high corrosion resistance. That is, the structure is such that corrosion can easily reach the base metal interface. Therefore, the total layer thickness of the intermediate plating layers is set to 3 μm or more. The layer thickness of the intermediate plating layer is preferably 5 μm or more, more preferably 10 μm or more.
On the other hand, if the total layer thickness of the intermediate plating layer is too thick, cracks are likely to occur, resulting in a structure that is likely to peel off due to some impact. Therefore, the layer thickness of the intermediate plating layer is preferably 175 μm or less, more preferably 100 μm or less.
The intermediate plated layer is a layer generated by atomic diffusion of the plated layer and the base iron. Generally, in the case of plated plated steel, the plated layer is often formed with an appropriate thickness in the range of 1/5 to 2/3 of the total thickness. That is, it is formed within a range of 2 μm to 200 μm. Depending on the shape of the member, the amount of formation may partially change, and there are cases where the lower limit is 1/50 to 1/5 of the total thickness.

The interfacial alloy layer (Al—Fe alloy layer) may remain even if the upper surface plating layer and the intermediate plating layer are eluted and rusted to prevent corrosion of the base iron (steel material). Electrochemically, the Al--Fe alloy layer that constitutes the interfacial alloy layer is more noble than the Zn--Al--Mg layer that constitutes the surface plating layer and the intermediate plating layer, but is less noble than the base iron (steel). Because it is located. Therefore, the interfacial alloy layer (Al--Fe alloy layer) also has a certain degree of corrosion resistance. However, the anti-corrosion effect requires a thickness of a very small amount. In addition, the adhesion between the upper intermediate plating layer and the base iron (steel material) is also enhanced.
Therefore, when an interfacial alloy layer (Al—Fe alloy layer) is formed, the layer thickness of the interfacial alloy layer is preferably 1 μm or more.

On the other hand, if the interfacial alloy layer (Al—Fe alloy layer) is too thick, the Al component in the upper surface plating layer and the intermediate plating layer will be insufficient, and the adhesion and workability of the plating layer will be extremely deteriorated. tend to Therefore, the layer thickness of the interfacial alloy layer is preferably 5 μm or less, more preferably 2 μm or less.

(Various measurement methods regarding the properties of the plating layer)
Next, various methods for measuring the properties of the plating layer will be described.

-Average chemical composition of plating layer-
The average chemical composition of the plating layer is measured by the following method.
First, an acid solution is obtained by stripping and dissolving the plating layer with an acid containing an inhibitor that suppresses the corrosion of the base iron (steel material). Next, the chemical composition of the plating layer can be obtained by measuring the obtained acid solution by ICP analysis. The acid species is not particularly limited as long as it is an acid capable of dissolving the plating layer.

-Each average chemical composition of the constituent layers of the plating layer-
Each average chemical composition of the constituent layers of the plating layer (that is, the surface plating layer, the intermediate plating layer, and the interfacial alloy layer) uses, for example, GDS (high frequency glow discharge spectroscopy). Specifically, for example, it is measured as follows.
First, a calibration curve for quantitative analysis of each element is obtained by GDS (high frequency glow discharge spectroscopy). After that, the chemical components in the depth direction of the target layer are measured. For example, several pieces of 30 mm square are taken from the produced plated steel sample and used as a GDS sample. Argon ion sputtering is performed on the surface of the plating layer to obtain an element intensity plot in the depth direction.
On the other hand, a standard sample such as a pure metal plate for each element is prepared, and an element intensity plot is obtained in advance.
Then, the concentration of each element is calculated by converting the element intensity plot of the GDS from the element intensity plot of the standard sample.
This operation is performed 10 or more times and the mean value of the component at each location is taken.

Note that the sputtering speed is, for example, in the range of approximately 0.04 to 0.1 μm/sec.

Specific measurement conditions include, for example, the following:
As a measuring device, for example, a Marcus-type high-frequency glow discharge emission analyzer (GD-Profiler 2) manufactured by Horiba, Ltd. is used.
Measurement conditions are, for example, a discharge area of 4 mmφ, an RF output of 35 W, and an argon pressure of 600 Pa.
The measurement interval is, for example, 0.02 seconds for the initial 60 seconds and 0.5 seconds thereafter.

When measuring the average chemical composition of the surface plating layer, at each GDS analysis point, the Fe element strength from the surface to less than 3% of the total elemental analysis (that is, the Fe concentration is 3% by mass or more and less than 30% by mass) A region is defined as a surface layer plating layer, and an element intensity plot of a width corresponding to the layer thickness of the surface layer plating layer is obtained. The component average value of each element concentration obtained from the obtained element intensity plot is employed. However, in order to remove the influence of the outermost oxide layer, the element intensity plots from the surface to a depth of 1 μm are ignored.

Also, when measuring the average chemical composition of the intermediate plating layer, at each GDS analysis point, the Fe element intensity is 3% or more and less than 30% of the entire elemental analysis (that is, the Fe concentration is 3% or more and less than 30% by mass. ) is defined as an intermediate plating layer, and an element intensity plot with a width corresponding to the layer thickness of the intermediate plating layer is obtained. The component average value of each element concentration obtained from the obtained element intensity plot is employed.

Further, when measuring the average chemical composition of the interfacial alloy layer, at each GDS analysis point, the Fe element intensity is 30% or more and less than 85% of the entire elemental analysis (that is, the Fe concentration is 30% by mass or more and 85% by mass less than) is defined as the interfacial alloy layer. An elemental intensity plot is obtained with a width corresponding to the layer thickness of the interfacial alloy layer. The component average value of each element concentration obtained from the obtained element intensity plot is adopted.

Here, in the GDS analysis, after the Fe element strength reaches 30% or more (that is, the Fe concentration is 30% by mass or more) near the interface between the intermediate plating layer and the interface alloy layer, the Fe element strength (that is, the Fe concentration) Although there may appear a place (specifically, the surface layer portion of the interfacial alloy layer) where is temporarily reduced to less than 30%, the element intensity plot at that place is ignored. Then, when the Fe element strength reaches 30% or more (that is, the Fe concentration is 30% by mass or more) again, it is regarded as the interfacial alloy layer.

It is also possible to obtain individual chemical compositions of the surface plating layer, the intermediate plating layer, and the interfacial alloy layer from elemental analysis values by EPMA or SEM-EDS.

-X-ray diffraction (XRD) measurement conditions-
Although the X-ray diffraction (XRD) intensity can be used as a radiation source such as Cu, Co, etc., it is finally necessary to calculate and change the diffraction angle to match the Cu radiation source. The X-ray output is 40 kV and 150 mA. It is preferable that the measurement range is 5° to 90° and the step is about 0.01°. To obtain the intensity (cps) at a particular diffraction angle, take an average value of ±0.05° before and after. That is, the intensity at 23.3° gets an average value between 22.25° and 22.35°. In addition, it is necessary to obtain each intensity index without taking measures such as background removal for clarifying the peak before calculating the average value of the intensity.
In addition, in order to remove the influence of the oxide layer of the outermost layer, the intensity of X-ray diffraction (XRD) is measured with respect to the surface of the surface layer plating layer after cutting from the surface to a depth of 1 μm.

Specific measurement conditions are, for example, as follows.
As a measuring device, for example, an X-ray diffractometer (RINT1500) manufactured by Rigaku Corporation and a RINT1000 wide-angle goniometer are used.
The measurement conditions are, for example, an X-ray output of 40 kV-150 mA, a scan speed of 2°/min, a step of 0.01°, a scan range of 5 to 90°, an incident slit of 1°, a receiving slit of 1°, and 0.15 mm.

-Layer thickness of plating layer-
The layer thickness of each layer of the plating layer is measured as follows.
When measuring the average chemical composition of each layer of the plating layer, the region width set by the Fe element strength (that is, Fe concentration) at the GDS analysis point is defined as each layer (surface plating layer, intermediate plating layer, interfacial alloy layer) Calculated as layer thickness.
Then, the average value of the width of each region obtained by performing this GDS at 10 locations is taken as the thickness of each layer (surface plating layer, intermediate plating layer, interfacial alloy layer).

(Manufacturing method of plated steel)
Next, an example of the method for producing the plated steel material of the present invention will be described.

The plated steel material of the present invention is obtained by forming a plating layer on the surface (that is, one side or both sides) of the plating raw material (plating base plate, etc.) by a two-step plating method (specifically, a two-step hot dip plating method). can get.

Specifically, the method for producing the plated steel material of the present invention includes:
A plated steel base material having a plating layer with a thickness of 30 μm or more is placed in a molten Zn-Al-Mg alloy plating bath with a bath temperature of +20° C. (but at least above 420° C.) to 520° C. for 20 to 240 seconds. After immersing less than, pulling up;
A method for producing a plated steel material can be exemplified, which includes a step of cooling the plated steel base material to 380° C. within 60 seconds immediately after pulling it out of the molten Zn—Al—Mg alloy plating bath.

Here, the molten Zn-Al-Mg alloy plating bath contains Zn: more than 65.0%, Al: more than 12.0% to 25.0%, Mg: more than 5.0% to less than 8.0%, Sn : 0% to less than 5%, Bi: 0% to less than 1%, In: 0% to less than 0.5%, Ca: 0.10% to less than 3.00%, Y: 0% to less than 0.5% , La: 0% to less than 0.5%, Ce: 0% to less than 0.5%, Si: 0% to less than 1.0%, Cr: 0% to less than 0.25%, Ti: 0% to Less than 0.25%, Ni: 0% to less than 0.25%, Co: 0% to less than 0.25%, V: 0% to less than 0.25%, Nb: 0% to less than 0.25%, Cu: 0% to less than 0.25%, Mn: 0% to less than 0.25%, Fe: 0% to less than 5%, Sr: 0% to less than 0.5%, Sb: 0% to 0.5% %, B: 0% to less than 0.5%, and a chemical composition consisting of impurities.

On the other hand, the plated steel base material (that is, the plated steel material plated in the first stage) is selected from a Zn-plated steel base material, a Zn-Al alloy-plated steel base material, and a Zn-Al-Mg alloy-plated steel base material. An example is a plated steel substrate.
Among these, a Zn-plated steel substrate is suitable as the plated steel substrate. HDZ (HDZ45, 55, etc.) standardized by JIS H 8641:2007 can be exemplified as a representative plated steel base material for the Zn-plated steel base material.

In the method for producing a plated steel material of the present invention, a plated steel base material having a plating layer with a layer thickness of 30 μm or more is used as the plated steel base material, and as the second-stage plating treatment, the predetermined plating bath temperature and immersion time are performed. By applying the plating process with the cooling time conditions, it is possible to appropriately leave traces of the first-stage plating layer while keeping the thickness of the entire plating layer in an appropriate range.

That is, an intermediate plating layer composed of a Zn-Al-Mg alloy layer having a layer thickness of 3 μm or more containing an Al-Fe intermetallic compound and having a predetermined average chemistry of the plating layer as a trace of the first plating layer is formed with a layer thickness of 3 μm or more, and the thickness of the entire plating layer (the total thickness of the surface plating layer and the intermediate plating layer) is 8 μm and less than 300 μm.

Further, by performing the second-stage plating process under the above conditions, the first-stage plating layer and the second-stage plating bath react to form an intermediate plating layer. Therefore, a plated steel material having a surface layer plating layer and an intermediate plating layer with the predetermined phase composition described above can be obtained.

Here, in the method for producing a plated steel material of the present invention, as a pretreatment for the second-stage plating treatment, for the purpose of cleaning the surface of the first-stage plating layer, dilute hydrochloric acid treatment, flux treatment (for example, aqueous ammonium chloride solution, A process of immersing the plated steel base material in a flux such as a ZnCl ₂ aqueous solution and drying it) may also be performed.

In addition, in the method for producing a plated steel material of the present invention, the method of applying the second-stage plating treatment to the plated steel substrate on which the first-stage plating layer has already been formed and the substrate temperature has been lowered has been described. On the other hand, a method in which the first-stage and second-stage plating processes are performed continuously without an interval may be used.

Post-treatments that can be applied to the plated steel material of the present invention are described below.

A film may be formed on the plating layer of the plated steel material of the present invention. The coating can form one layer or two or more layers. Examples of the types of films directly on the plating layer include chromate films, phosphate films, and chromate-free films. Chromate treatment, phosphate treatment, and chromate-free treatment for forming these films can be performed by known methods.

Chromate treatment includes electrolytic chromate treatment, in which a chromate film is formed by electrolysis, reactive chromate treatment, in which a film is formed by using a reaction with the material, and then excess treatment liquid is washed away, and treatment liquid is applied to the object to be coated. There is a coating type chromate treatment that forms a film by drying without washing with water. Either process may be adopted.

Electrolytic chromate treatment using chromic acid, silica sol, resin (phosphoric acid, acrylic resin, vinyl ester resin, vinyl acetate acrylic emulsion, carboxylated styrene-butadiene latex, diisopropanolamine-modified epoxy resin, etc.), and hard silica. Chromate treatment can be exemplified.

Examples of phosphate treatment include zinc phosphate treatment, zinc calcium phosphate treatment, and manganese phosphate treatment.

Chromate-free treatment is particularly suitable because it does not burden the environment. Chromate-free treatment includes electrolytic-type chromate-free treatment that forms a chromate-free film by electrolysis, reaction-type chromate-free treatment that forms a film by using a reaction with the material, and then rinses off the excess treatment solution. There is a coating-type chromate-free treatment in which a coating is applied to an object to be coated and dried without washing with water to form a film. Either process may be adopted.

Furthermore, one or more organic resin films may be provided on the film 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, modified products of these resins, and the like. Here, the modified product is a reaction of the reactive functional group contained in the structure of these resins with another compound (monomer, cross-linking agent, etc.) containing a functional group capable of reacting with the functional group in the structure. It refers to resin.

As such an organic resin, one or two or more organic resins (unmodified) may be mixed and used, or in the presence of at least one organic resin, at least one other One or a mixture of two or more organic resins obtained by modifying the organic resin may be used. Further, the organic resin film may contain any color pigment or rust preventive pigment. A water-based product obtained by dissolving or dispersing in water can also be used.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, each of these examples does not limit the present invention.

Using a predetermined amount of pure metal ingots so as to have the chemical compositions shown in Tables 1 and 2, melt the ingots in a vacuum melting furnace, and then heat the plating bath for the second plating process in the atmosphere. I built a bath. A batch-type hot-dip plating apparatus was used to produce the plated steel sheets. Then, a second-stage plating treatment was performed to produce a plated steel material.

The following steel plate or bolt was used as the plated steel base material to be subjected to the second-stage plating treatment (the plated steel material subjected to the first-stage plating treatment).
1) Dipped galvanized steel sheet (200 mm × 150 mm × 4.5 mm hot-dip galvanized steel sheet equivalent to HDZ45 standardized by JIS H 8641: 2007)
2) Dipped galvanized hexagon bolts (half-threaded hexagon bolts with a length of 100 mm, a diameter of M16, equivalent to HDZ35 standardized in JIS H 8641:2007, and a plated layer thickness of 100 μm at the thread portion).

Then, the second-stage plating treatment was carried out in the following three ways. A part of the plated layer of the plated steel base material was removed, and a K-type thermocouple was attached to control the temperature during the plating process.

・Manufacturing method A: After setting the set plating bath temperature to the bath melting point + 40 ° C. and immersing the plated steel base material in flux (ZnCl ₂ /NaCl / SnCl ₂ = 220 g / 20 g / 10 g / L) at 80 ° C. for 30 seconds, It was sufficiently dried in a drying oven at 150°C. After that, the plated steel substrate was immersed in the plating bath in air for 240 seconds, and then withdrawn from the plating bath. Immediately after the plated steel substrate was lifted from the plating bath, it was cooled to 380° C. within 60 seconds by spraying compressed air gas or the like, and then naturally cooled to room temperature.

・Manufacturing method B: After setting the set plating bath temperature to the bath melting point + 40 ° C. and immersing the plated steel base material in flux (ZnCl ₂ /NaCl / SnCl ₂ = 220 g / 20 g / 10 g / L) at 80 ° C. for 30 seconds, It was sufficiently dried in a drying oven at 150°C. After that, the plated steel substrate was immersed in the plating bath in air for 240 seconds, and then pulled out of the plating bath. Then, the plated steel substrate was placed in an atmospheric furnace set at 400° C. or higher, and immediately after the plated steel substrate was lifted from the plating bath, it was cooled to 380° C. in more than 60 seconds, and then naturally cooled to room temperature.

・Manufacturing method C: The set plating bath temperature is set to the bath melting point + 10°C, and the plated steel base material is immersed in flux (ZnCl ₂ /NaCl/SnCl ₂ =220g/20g/10g/L) at 80°C for 30 seconds, It was sufficiently dried in a drying oven at 150°C. After that, the plated steel substrate was immersed in the plating bath in the air for 20 seconds and then pulled out of the plating bath. Then, immediately after being pulled up, the plated steel substrate was subjected to a centrifugal separator to remove sagging. Centrifugation was completed in the temperature range above 380°C. After the plated steel substrate was taken out from the centrifuge and reached about 380°C, it was submerged in 100 L water at a water temperature of 25°C. The cooling to 380° C. immediately after the plated steel substrate was lifted from the plating bath was completed within 60 seconds.

(evaluation)
－Various measurements－
A sample was cut out from the obtained plated steel sheet. Then, the following items were measured according to the method described above.
・Average chemical composition and layer thickness of plating layer (denoted as “thickness” in the table)
・Average chemical composition (Mg concentration) and layer thickness of the intermediate plating layer (denoted as “thickness” in the table)
・Layer thickness of interfacial alloy layer (denoted as “thickness” in the table)
・ Sum intensity ratio (I (Zn) / Io, I (Al) / Io, I (MgZn ₂ ) / Io) in the X-ray diffraction image of the surface of the surface plating layer
・ In the X-ray diffraction image of the surface of the surface plating layer, the intensity I (Mg-Sn intermetallic compound) (indicated as I (Mg2Sn) in the table) and the intensity I (Mg-Sn intermetallic compound) and 11 ° ~ Difference from background intensity at 12° (denoted as “BG difference” in the table)
In the table, in the column of strength I (Mg—Sn intermetallic compound) (denoted as I (MgSn) in the table),
"○" indicates that the intensity I (Mg-Sn intermetallic compound) is 1000 cps or more,
"-" indicates that Sn is not intentionally added, and a clear diffraction peak cannot be obtained at the diffraction peak position of the Mg-Sn metal compound in the plating layer. "×" indicates that the BG difference is less than 100. Indicates judgment.
Further, in the steel sheets corresponding to the examples, the Fe concentration of the surface plating layer is less than 3% by mass, the Fe concentration of the intermediate plating layer is 3% by mass or more and less than 30% by mass, and the Fe concentration of the interfacial alloy layer is 30% by mass. % or more and less than 85% by mass.

- Corrosion resistance (SST) -
As a method for evaluating corrosion resistance, a salt spray test (corrosion resistance test specified in JIS Z 2371:2015) was performed. The number of samples was N = 10, and all the samples exceeded the red rust suppression time (thickness of the plating layer x 200 hours + 1000 hours) on the surface of the plating layer of the plated steel material. When 6 samples or more out of the number of samples N (=10) satisfied the above criteria (that is, when red rust was generated on the surface of the plating layer within 4 samples), it was evaluated as A. A B evaluation was given when five or more samples had red rust.
When the plated steel material was a bolt, the corrosion resistance of the screw thread portion was evaluated by standing it upright, and the other parts were painted to evaluate the red rust generation time only on the screw thread portion.

- Hammer test -
The hammer test was carried out according to the method specified in JIS H0401:2013. A 50 mm square sample with a thickness of 4.5 mm was taken from a plated steel sheet and used.
Five points of impact were applied in parallel at intervals of 4 mm, and peeling and lifting between the impact marks were examined. However, areas within 10 mm from corners or edges are excluded from the test, and the same point should not be hit more than twice.
If the hammer test shows that there is no continuous lifting or peeling between the dents, it is acceptable.
When the plated steel material was a bolt, visual evaluation was performed instead of the same evaluation. Specifically, the unplated portion of the screw thread portion was confirmed by visual observation using a magnifying glass, and the acceptance condition was that there was no clear unplated portion of 0.3 mmφ or more.

From the above results, it can be seen that the examples corresponding to the plated steel materials of the present invention have corrosion resistance to severe corrosion-resistant environments compared to the comparative examples.
The examples corresponding to the plated steel materials of the present invention also passed the hammer test, and it can be seen that the adhesion of the plated layer is high.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

Claims (5)

steel and
A surface plating layer arranged on the surface of the steel material and composed of a Zn-Al-Mg alloy layer having an Fe concentration of less than 3% by mass, and a surface plating layer arranged between the steel material and the surface plating layer, wherein the Fe concentration is a plating layer including an intermediate plating layer having a layer thickness of 3 μm or more, which is composed of a Zn-Al-Mg alloy layer of 3% by mass or more and less than 30% by mass,
The total layer thickness of the surface plating layer and the intermediate plating layer is 8 μm or more and less than 300 μm,
The average chemical composition of the plating layer is mass%,
Zn: more than 65.00%,
Al: more than 6.5% to less than 22.5%,
Mg: more than 3.0% to less than 12%,
Sn: 0% to less than 4.00%,
Bi: 0% to less than 0.30%,
In: 0% to less than 0.30%,
Ca: 0.05% to less than 1.00%,
Y: 0% to less than 0.30%,
La: 0% to less than 0.30%,
Ce: 0% to less than 0.30%,
Si: 0% to less than 1.00%,
Cr: 0% to less than 0.25%,
Ti: 0% to less than 0.25%,
Ni: 0% to less than 0.25%,
Co: 0% to less than 0.25%,
V: 0% to less than 0.25%,
Nb: 0% to less than 0.25%,
Cu: 0% to less than 0.25%,
Mn: 0% to less than 0.25%,
Fe: 0% to less than 15.0%,
Sr: 0% to less than 0.50%,
Sb: 0% to less than 0.50%,
B: 0% to less than 0.50%, and consists of impurities,
A plated steel material, wherein the intermediate plated layer has a Mg concentration of more than 3.0% by mass. In the X-ray diffraction image of the surface of the surface plating layer measured using Cu-Kα rays and under the conditions that the X-ray output is 40 kV and 150 mA,
Intensity sum I (Zn) = I (36.30° intensity (cps)) + I (38.99° intensity (cps)) + I (43.23° intensity (cps)) + I (54.34° intensity (cps) ) + I (70.06° intensity (cps)),
Intensity sum I (Al) = I (38.47° intensity (cps)) + I (44.74° intensity (cps)) + I (65.14° intensity (cps)),
Intensity sum I (MgZn ₂ ) = I (19.67° intensity (cps)) + I (20.79° intensity (cps)) + I (22.26° intensity (cps)) + I (40.47° intensity (cps) )) + I (41.31° intensity (cps)) + I (45.378° intensity (cps)),
Intensity sum Io=I(Zn)+I(Al)+I(MgZn ₂ )
The plated steel material according to claim 1, which satisfies the following formulas 1 to 3 when
Formula 1: I(Zn)/Io≤0.70,
Formula 2: 0.05≦I(Al)/Io≦0.30
Formula 3: 0.25≤I( _MgZn2 )/Io≤0.70 The Sn concentration of the surface plating layer is 0.03 to less than 2.00% in mass%,
In the X-ray diffraction image of the surface of the surface plating layer, measured using Cu-Kα rays under the conditions that the X-ray output is 40 kV and 150 mA, the intensity I (Mg-Sn intermetallic compound) = I (22. 8° intensity (cps)) is 1000 cps or more, or 500 cps or more when the average intensity at 11° to 12° without a diffraction peak is taken as the background intensity (cps),
The plated steel material according to claim 1 or 2. The plating layer is arranged between the steel material and the intermediate plating layer, and has an Fe concentration of 30% by mass or more and less than 85% by mass) and an interface alloy layer composed of an Al-Fe alloy layer having a layer thickness of 1 μm or more. having
The plated steel material according to any one of claims 1 to 3. A method for producing a plated steel material according to any one of claims 1 to 4,
in % by mass,
Zn: more than 65.0%,
Al: more than 12.0% to 25.0%,
Mg: more than 5.0% to less than 8.0%,
Sn: 0 to less than 5.00%,
Bi: 0% to less than 1.0%,
In: 0% to less than 0.50%,
Ca: 0.10% to less than 3.00%,
Y: 0% to less than 0.50%,
La: 0% to less than 0.50%,
Ce: 0% to less than 0.50%,
Si: 0% to less than 1.00%,
Cr: 0% to less than 0.25%,
Ti: 0% to less than 0.25%,
Ni: 0% to less than 0.25%,
Co: 0% to less than 0.25%,
V: 0% to less than 0.25%,
Nb: 0% to less than 0.25%,
Cu: 0% to less than 0.25%,
Mn: 0% to less than 0.25%,
Fe: 0% to less than 5.0%,
Sr: 0% to less than 0.50%,
Sb: 0% to less than 0.50%,
B: A molten Zn-Al-Mg alloy plating bath having a chemical composition consisting of 0% to less than 0.50% and impurities, and a bath temperature +20°C (but at least above 420°C) to 520°C. and a plated steel base material having a plating layer with a thickness of 30 μm or more, which is selected from a Zn-plated steel base material, a Zn-Al alloy-plated steel base material, and a Zn-Al-Mg alloy-plated steel base material. a step of immersing the steel base material for 20 seconds or more and less than 240 seconds, and then withdrawing the steel base material;
a step of cooling the plated steel base material to 380° C. within 60 seconds immediately after being pulled up from the molten Zn—Al—Mg alloy plating bath;
has
A method for producing a plated steel material, wherein the plated layer of the plated steel substrate has an interfacial alloy layer composed of a Zn—Fe alloy layer having an Fe concentration of 3% by mass or more and less than 80% by mass and a layer thickness of 10 μm or more.