WO2024219122A1 - Hot-dip galvanized steel material - Google Patents

Abstract

In this hot-dip galvanized steel material, a plating layer has a chemical composition containing more than 10.0% but less than 45.0% Al, 4.0-15.0% Mg, 0.01-2.0% Si, and 0.03-1.50% Sr, with the remainder being Zn and impurities. The plating layer contains a Zn-Sr-based compound and a Zn-Sr-Si-based compound. In an element distribution profile when GDS analysis is performed from the surface of the plating layer toward a steel material, an expression (1) is satisfied where t is the thickness of the plating layer, Sr(surf) is the average value of qualitative analysis values of Sr from the surface of the plating layer to 0.05t, Sr(centre) is a qualitative analysis value in the range from 0.05t to 0.66t, and Sr(deep) is a qualitative analysis value in the range from 0.66t to t. (1): Sr(surf) < Sr(deep) < Sr(centre)

Description

Hot-dip galvanized steel

The present invention relates to a hot-dip galvanized steel material.
This application claims priority based on Japanese Patent Application No. 2023-067060, filed on April 17, 2023, the contents of which are incorporated herein by reference.

If steel is to be used for a long period of time, it is preferable to apply some kind of rust-proofing treatment to the steel to make it resistant to corrosion. Hot-dip Zn plating is used in a variety of fields where rust prevention is required, such as civil engineering, construction, and automotive, as a means of inexpensively preventing rust on steel.

The corrosion prevention measures used by the plating layer are largely determined by the inherent corrosion resistance of the plating layer and the thickness of the plating layer. For example, Patent Document 1 describes the production of plated steel sheet by a so-called continuous hot-dip plating method in which the steel sheet is continuously immersed in a hot-dip plating bath. The plated steel sheet is then processed into the shape of the part, thereby producing the part.

In recent years, various elements other than Al and Mg have been added to Zn alloy plating baths to impart properties other than corrosion resistance to the plating layer.

For example, Patent Documents 1 and 2 describe Zn-Al-Mg-based plating layers that are used as highly corrosion-resistant plating. These Zn-Al-Mg-based plating layers improve their design and corrosion resistance through structural control, and also disclose techniques for improving corrosion resistance by adding elements to the plating layer or actively forming corrosion products.

International Publication No. 2018/139619 International Publication No. 2019/230894

In the Zn-Al-Mg-based plating layer disclosed in Patent Document 1, elements such as Si and Sn added to the plating layer tend to combine with Mg, Al, or Zn in the Zn alloy to form intermetallic compounds with high melting points. In addition, Si, Sn, etc. also combine with the steel components of the steel sheet passing through the plating bath to form intermetallic compounds with Fe, etc., which become fine particles (fine dross) and float or settle in the plating bath. These micro-sized intermetallic compounds adhere to the steel sheet during hot-dip plating, causing unplated areas (areas where the plating layer is not formed on the steel sheet) and making the plating layer surface uneven, resulting in problems with poor appearance.

Furthermore, in the conventional Zn-Al-Mg-based plating layers described in Patent Documents 1 and 2, the method of adding elements to the final plating layer and the form of the intermetallic compounds in the plating layer have not been fully considered, and there have been problems such as peeling of the plating layer (powdering phenomenon) caused by intermetallic compounds and reduced workability.

The problem that one embodiment of the present invention aims to solve is to provide a hot-dip galvanized steel material that combines excellent workability and corrosion resistance.

In order to solve the above problems, each aspect of the present invention employs the following configuration.
[1] A hot-dip plated steel material according to one embodiment of the present invention is a hot-dip plated steel material having a steel material and a plating layer disposed on a surface of the steel material,
The plating layer comprises, in mass %,
Al: more than 10.0% and less than 45.0%;
Mg: 4.0% or more, 15.0% or less,
Si: 0% or more, 2.0% or less,
Sr: 0.03% or more and 1.50% or less,
Sn: 0% or more, 0.7% or less,
Bi: 0% or more, 0.3% or less,
In: 0% or more, 0.3% or less,
Ca: 0% or more, 0.6% or less,
Y: 0% or more, 0.3% or less,
La: 0% or more, 0.3% or less,
Ce: 0% or more, 0.3% or less,
Li: 0% or more, 0.3% or less,
Ni: 0% or more, 1.0% or less,
Cu: 0% or more, 1.0% or less,
Ag: 0% or more, 0.25% or less,
Sb: 0% or more, 0.25% or less,
Pb: 0% or more, 0.25% or less,
B: 0% or more, 0.5% or less,
P: 0% or more, 0.5% or less,
Ti: 0% or more, 0.25% or less,
Co: 0% or more, 0.25% or less,
V: 0% or more, 0.25% or less,
Nb: 0% or more, 0.25% or less,
Mn: 0% or more, 0.25% or less,
Zr: 0% or more, 0.25% or less,
W: 0% or more, 0.25% or less,
Fe: 0% or more, 5.0% or less,
The balance has a chemical composition including Zn and impurities,
the plating layer contains a Zn—Sr-based compound and a Zn—Sr—Si-based compound,
In an element distribution profile obtained by performing a qualitative analysis by glow discharge optical emission spectrometry from the surface of the plating layer toward the steel material, when the thickness of the plating layer is t, the average value of the qualitative analysis value of Sr from the surface of the plating layer to 0.05t is Sr(surf), the qualitative analysis value in the range from 0.05t to 0.66t starting from the surface of the plating layer is Sr(centre), and the qualitative analysis value in the range from 0.66t to t starting from the surface of the plating layer is Sr(deep), the following formula (1) is satisfied.
Sr(surf)<Sr(deep)<Sr(centre)…(1)
[2] In the hot-dip plated steel material described in [1] above, the chemical composition of the plating layer contains Sr: 0.10% or more and 1.50% or less, and when the diffraction intensity of Zn-Sr compounds in an X-ray diffraction pattern of the surface of the plating layer measured using Cu-Kα radiation under conditions of an X-ray output of 50 kV and 300 mA is I(SrZn ₁₃ ), the following formula (2) may be satisfied:
{I(14.48)+I(32.74°)}/2×I(12.50°)}>2.0...(2)
In equation (2), I(n°) is the X-ray diffraction intensity at a diffraction angle of n°, where n is the diffraction angle (2θ) shown in equation (2).
[3] In the hot-dip plated steel material according to the above [1] or [2], in the chemical composition of the plating layer, Si is 0.05% or more and 0.5% or less, and in a cross section along a thickness direction of the plating layer, Zn-Sr-Si based compounds and Zn-Al-Sr-Si based compounds may be contained in an area ratio of 5% to 30%.

According to one embodiment of the present invention, it is possible to provide hot-dip galvanized steel material that combines excellent workability and corrosion resistance.

FIG. 2 is a graph showing an example of an element distribution profile, showing the results of a GDS analysis performed on a coating layer of a hot-dip coated steel material according to an embodiment of the present invention. 1 shows an example of an X-ray diffraction pattern of a plating layer according to an embodiment of the present invention.

Hereinafter, a hot-dip plated steel material according to one embodiment of the present invention will be described.
In this specification, the "%" designation for the content of each element in the chemical composition of the plating layer means "mass %" unless otherwise specified.
Furthermore, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits. When the numerical values before and after "to" are followed by "more than" or "less than," the numerical range does not include these numerical values as the lower or upper limit.

In this specification, "corrosion resistance" refers to the property of the plating layer itself being resistant to corrosion. A Zn-based plating layer has a sacrificial corrosion protection effect on steel material. Therefore, in the process of corrosion of a plated steel sheet, first, the plating layer corrodes and turns into white rust before the steel material corrodes, the white-rusted plating layer disappears, and then the steel material corrodes and red rust appears.
In addition, "sacrificial corrosion protection" as used in this specification refers to the property of suppressing corrosion of steel at exposed portions of the steel (for example, cut end surfaces of plated steel or portions where the steel is exposed due to cracking of the hot-dip plating layer during processing).

First, we investigated the relationship between the intermetallic compounds formed in the Zn-Al-Mg plating layer and the workability of plated steel. The results of this investigation are explained below.

In general, when intermetallic compounds with covalent bonds are included in a plating layer, they become hard particles, increasing the hardness of the entire plating layer. In addition, since intermetallic compounds also have excellent insulating properties, their inclusion in the plating layer provides high corrosion resistance.

On the other hand, if the plating layer contains an excessive amount of intermetallic compounds, the entire plating layer becomes hard, which makes the plating layer more susceptible to destruction when the plated steel material is subjected to forming processing, and peeling of the plating layer, such as powdering, may occur.
Therefore, it is not practically preferable to include a large amount of intermetallic compounds in the plating layer. Therefore, there has been a demand for a plating layer that has a desired level of hardness and high corrosion resistance, and has good workability without peeling or the like.

Here, there is a technology for including Ca in the plating layer to improve its hardness and corrosion resistance. If a large amount of Ca is included in the plating layer, an intermetallic compound is formed with Zn, Al, etc. in the plating layer. The melting point of this Ca-containing intermetallic compound is very high during the solidification process of Zn-Al-Mg hot-dip plating. Therefore, the Ca in the plating layer becomes a large Ca-containing intermetallic compound in the early stages after the steel material is pulled out of the plating bath, and grows in the plating layer.

In a normal hot-dip plating process, the surface of the plating layer is largely cooled by the outside air, so solidification of the plating layer progresses from the surface. In a bath containing Ca, a similar mechanism occurs, and precipitation of Ca-containing intermetallic compounds begins in areas with low free energy and stability, such as the surface or interface of the plating layer. As a result, Ca-containing intermetallic compounds tend to accumulate, particularly on the surface of the plating layer, and these can grow coarsely and form a layered structure of Ca-containing intermetallic compounds.

In the case of a plating layer in which Ca-containing intermetallic compounds are connected in layers, there is a risk that the Ca-containing intermetallic compounds will undergo brittle fracture during forming, causing the plating layer to peel off from the surface, a phenomenon known as "powdering." Therefore, in a plating layer that contains a high concentration of Ca, it has been difficult to improve the hardness, workability, and corrosion resistance.

The inventors therefore investigated elements that produce the same effect as Ca and found that Sr was effective. Specifically, they found that Sr forms covalent bonds with Zn, Al, Si, etc., to form Sr-based intermetallic compounds that have excellent corrosion resistance and hardness.

[Hot-dip galvanized steel]
The hot-dip plated steel material according to this embodiment will be described in detail below.
The hot-dip plated steel material of the present embodiment has a steel material and a plating layer disposed on the surface of the steel material.
The average chemical composition of the plating layer is, in mass%,
Al: more than 10.0% and less than 45.0%;
Mg: 4.0% or more, 15.0% or less,
Si: 0% or more, 2.0% or less,
Sr: 0.03% or more and 1.50% or less,
Sn: 0% or more, 0.7% or less,
Bi: 0% or more, 0.3% or less,
In: 0% or more, 0.3% or less,
Ca: 0% or more, 0.6% or less,
Y: 0% or more, 0.3% or less,
La: 0% or more, 0.3% or less,
Ce: 0% or more, 0.3% or less,
Li: 0% or more, 0.3% or less,
Ni: 0% or more, 1.0% or less,
Cu: 0% or more, 1.0% or less,
Ag: 0% or more, 0.25% or less,
Sb: 0% or more, 0.25% or less,
Pb: 0% or more, 0.25% or less,
B: 0% or more, 0.5% or less,
P: 0% or more, 0.5% or less,
Ti: 0% or more, 0.25% or less,
Co: 0% or more, 0.25% or less,
V: 0% or more, 0.25% or less,
Nb: 0% or more, 0.25% or less,
Mn: 0% or more, 0.25% or less,
Zr: 0% or more, 0.25% or less,
W: 0% or more, 0.25% or less,
Fe: 0% or more, 5.0% or less,
The balance includes Zn and impurities.

The plating layer in the hot-dip plated steel material of this embodiment contains Zn-Sr compounds and Zn-Sr-Si compounds. In addition, in the element distribution profile obtained by qualitatively analyzing the surface of the plating layer toward the steel material by glow discharge optical emission spectrometry, if the thickness of the plating layer is t, the average value of the qualitative analysis value of Sr from the surface of the plating layer to 0.05t is Sr(surf), the qualitative analysis value in the range from 0.05t to 0.66t starting from the surface of the plating layer is Sr(centre), and the qualitative analysis value in the range from 0.66t to t starting from the surface of the plating layer is Sr(deep), the following formula (1) is satisfied.

Sr(surf)<Sr(deep)<Sr(centre)...(1)

(Steel)
First, the steel material (original sheet) to be plated will be described.
The steel material is, for example, mainly a steel plate, but the size is not particularly limited. The steel plate may be any steel plate that can be applied to a normal hot-dip galvanizing process. Specifically, this applies to steel plates that can be applied to a process in which the steel plate is immersed in molten metal and solidified, such as a continuous hot-dip galvanizing line (CGL). The size of the steel plate may be, for example, a plate thickness of 10 mm or less and a plate width of 2000 mm or less, but the size of the steel plate is not limited to this.

The quality of the steel material is not particularly limited. Examples of applicable steel materials include various steel plates such as general steel, pre-plated steel thinly plated with various metals, Al-killed steel, ultra-low carbon steel, high carbon steel, various high tensile steels, some high alloy steels (steels containing elements that enhance corrosion resistance such as Ni and Cr), steel for bolts, and steel wire for bridge cables. More specifically, the steel material may be, for example, a hot-rolled steel plate defined in JIS G 3131 (2018), a cold-rolled steel plate defined in JIS G 3141 (2017), a material included in the general structural rolled steel material corresponding to the so-called SS material, a so-called general steel included in the hot-rolled steel plate shown in JIS G 3193 (2019), a pre-plated steel thinly plated with various metals described in JIS H 8641 (2021), JIS G 3302 (2019), 3303 (2017), 3313 (2017), 3314 (2019), 3315 (2017), 3317 (2019), and 3321 (2019), a rolled steel material for building structure described in JIS G 3136 (2012), a pre-plated steel thinly plated with various metals described in JIS G 3321 (2019 ...
Applicable steels include Al-killed steels, extra-low carbon steels, and high carbon steels described in JIS G 3126 (2015), various high tensile steels described in JIS G 3113 (2018), 3134 (2018), and 3135 (2018), and some high alloy steels (steels containing corrosion-resistant strengthening elements such as Ni and Cr, etc.).

Furthermore, the manufacturing process for steel materials includes common processes such as iron and steel making using blast furnaces or electric furnaces, hot rolling, pickling, cold rolling, and heat treatment.

(Plating layer)
Next, the plating layer provided on the steel material will be described.
The plating layer according to the present embodiment includes a Zn-Al-Mg alloy layer. When alloy elements such as Al and Mg are contained in the Zn phase, corrosion resistance is improved. Therefore, in the case of a plating layer including such a Zn phase, even if it is a thin film (for example, about half the thickness of a normal Zn plating layer), it can exhibit corrosion resistance equivalent to that of a normal Zn plating layer. Similarly, even if the plating layer according to the present embodiment is a thin film, it can ensure corrosion resistance equivalent to or greater than that of a conventional Zn plating layer.

The Zn-Al-Mg alloy layer is made of a Zn-Al-Mg alloy. A Zn-Al-Mg alloy refers to a ternary alloy containing Zn, Al, and Mg.

The plating layer may also include an Al-Fe-based interface alloy layer (however, the thickness is less than 5 μm). The Al-Fe-based interface alloy layer is an interface alloy layer between the steel material and the Zn-Al-Mg-based alloy layer, and is in contact with the surface of the steel material. In other words, the plating layer of this embodiment may have a single-layer structure composed of a Zn-Al-Mg-based alloy layer, or may have a laminated structure composed of a Zn-Al-Mg-based alloy layer and an Al-Fe-based interface alloy layer disposed between the Zn-Al-Mg-based alloy layer and the steel material. In the case of a single-layer structure, the plating layer on the steel material is composed of one layer composed of a Zn-Al-Mg-based alloy. In other words, the plating layer of this embodiment does not include a multi-layer structure in which, for example, an Al plating layer and a Zn plating layer are laminated. In addition, in the case of a laminated structure in this embodiment, the Zn-Al-Mg-based alloy layer may be a layer that constitutes the surface of the plating layer.

The Al-Fe interface alloy layer does not have a significant effect on corrosion resistance, but it does affect the adhesion of the plating layer during processing of hot-dip plated steel and the workability (presence or absence of cracks). In particular, the Al-Fe interface alloy layer may affect powdering resistance, which indicates the degree of peeling of the plating layer during processing. Usually, the thinner the Al-Fe interface alloy layer, the fewer the starting points for crack generation in the plating layer during processing, and the better the powdering resistance. For this reason, in hot-dip plated steel that may be subjected to high processing when used as a component, etc., it is preferable that the thickness of the Al-Fe interface alloy layer is as thin as possible. Specifically, the thickness of the intermetallic compound that constitutes the Al-Fe interface alloy layer is less than 5 μm. This thickness is preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less. It may be 0.3 μm or less. This makes it possible to suppress the generation of cracks during processing and further improve powdering resistance. Furthermore, the ratio of the thickness of the Al-Fe interfacial alloy layer to the thickness of the plating layer is, on average, less than 10%, and more preferably, less than 5%.

The Al-Fe-based interface alloy layer is formed on the surface of the steel material, specifically, between the steel material and the Zn-Al-Mg-based alloy layer. The Al-Fe-based interface alloy layer is a layer in which the Al ₅ Fe ₂ phase is the main phase in the structure. The Al-Fe-based interface alloy layer is formed by mutual atomic diffusion between the base steel (steel sheet) and the plating bath. When a continuous hot-dip plating method is used as the manufacturing method, the Al-Fe-based interface alloy layer is likely to be formed in the plating layer containing the Al element. In this embodiment, since the plating bath contains Al at a certain concentration or more, the Al ₅ Fe ₂ phase is formed most frequently in the Al-Fe-based interface alloy layer. However, since atomic diffusion takes time, the Fe concentration in the Al-Fe-based interface alloy layer is not uniform, and the Fe concentration may be high in the part close to the base steel. Therefore, the Al-Fe-based interface alloy layer may partially contain small amounts of the AlFe phase, the Al ₃ Fe phase, the Al ₅ Fe ₂ phase, etc. In addition, since the plating bath contains a certain concentration of Zn, the Al-Fe-based interface alloy layer may also contain a small amount of Zn. In addition, the Al-Fe-based interface alloy layer may also contain a small amount of Si, which tends to accumulate at the interface.

In this embodiment, the plating layer contains Si. A portion of the Si is incorporated into the Al-Fe interface alloy layer to form an Al-Fe-Si intermetallic compound phase. The identified intermetallic compound phase is the AlFeSi phase. Isomers of the AlFeSi phase include the α phase, β phase, q1 phase, q2 phase, and the like. Therefore, these AlFeSi phases and the like may be detected in the Al-Fe interface alloy layer. An Al-Fe interface alloy layer that contains these AlFeSi phases and the like is also referred to as an Al-Fe-Si alloy layer.

Next, the average chemical composition of the plating layer will be explained. When the plating layer has a single-layer structure of a Zn-Al-Mg alloy layer, the average chemical composition of the entire plating layer is the average chemical composition of the Zn-Al-Mg alloy layer. When the plating layer has a layered structure consisting of an Al-Fe interface alloy layer and a Zn-Al-Mg alloy layer, the average chemical composition of the entire plating layer is the average chemical composition of the Al-Fe interface alloy layer and the Zn-Al-Mg alloy layer combined.

In the plating layer of this embodiment, the thickness of the Al-Fe interfacial alloy layer is preferably 10% or less of the total thickness of the plating layer. In this way, when the thickness of the Al-Fe interfacial alloy layer is sufficiently small compared to the total thickness of the plating layer, the Fe concentration of the plating layer is often within 5%. Therefore, the average chemical composition of the plating layer is generally approximately the same as the components of the Zn-Al-Mg alloy layer. Furthermore, traces of the original plating material are unlikely to remain as chemical components of the plating layer. Therefore, the average chemical composition of the plating layer is approximately the same as the components of the plating bath used in production.

Al: more than 10.0% and less than 45.0% Al is an element that mainly constitutes the coating layer. If the Al content is 10.0% or less, a sufficient amount of Zn-Al phase may not be secured. Therefore, the Al content is more than 10.0%. On the other hand, if the Al content is 45.0% or more, the Al-Zn (α) phase becomes the main component in the coating layer, and the Al-Zn (β) phase is not formed. Therefore, the upper limit of the Al content is less than 45.0%. The lower limit of the Al content is preferably 15.0% or more. The upper limit of the Al content is preferably 30.0% or less, more preferably 25.0% or less.

Mg: 4.0% or more, 15.0% or less Like Zn, Mg is an element constituting the main part of the plating layer. Mg is an important element for improving the sacrificial corrosion protection in the plated steel sheet according to the present embodiment. If the Mg content in the plating layer is less than 4.0%, the effect of improving the sacrificial corrosion protection is not clear compared to the case where Mg is not contained. Therefore, the Mg content is set to 4.0% or more. On the other hand, if Mg is added excessively to a Zn-Al-Mg plating bath, a rapid oxidation reaction occurs on the bath surface of the plating bath, and plating cannot be performed stably. Therefore, in order to perform stable plating and ensure good manufacturability, the Mg content in the plating layer is set to 15% or less.

Si: 0% or more, 2.0% or less Si suppresses the Al-Fe reaction, thereby suppressing the formation of an Al-Fe-based interface alloy layer. Also, Si is incorporated into a part of the Al-Fe-based interface alloy layer to form an Al-Fe-Si compound. In this embodiment, Si may not be contained. However, if Si is not contained, the Al-Fe reaction becomes active, the thickness of the Al-Fe alloy layer becomes thick, powdering occurs during processing, and corrosion resistance may be impaired. On the other hand, if the Si content is 0.01% or more, the growth rate of the thickness of the interface alloy layer becomes slow. However, if the Si content exceeds 2.0%, a large amount of intermetallic compound having a composition of Mg ₂ Si is formed by bonding with Mg, and the viscosity of the plating bath becomes extremely high, so that the amount of molten metal attached to the steel material is reduced when the steel material is pulled out of the plating bath, and the thickness of the plating layer becomes extremely thin. Also, the plating appearance is significantly deteriorated. For this reason, the upper limit of the Si content is set to 2.0% or less. The preferred range is 0.05 to 0.50%, more preferably 0.10 to 0.40%, and further preferably 0.20 to 0.30%. If the Si content is 1.50% or less, almost no Mg2Si is formed.

Sr: 0.03% or more, 1.50%
Sr is an element that produces the same effect as Ca. Sr forms covalent bonds with Zn, Al, Si, etc. to form intermetallic compounds that have excellent corrosion resistance and hardness. Sr content is less than 0.03% In the case of 1.50%, the amount of intermetallic compounds formed is insufficient, and therefore the effect of improving corrosion resistance and hardness cannot be sufficiently obtained. Excessive intermetallic compounds are formed, making the entire plating layer hard. As a result, when the plated steel is used for forming, the plating layer is easily damaged, and peeling of the plating layer, such as powdering, occurs. Therefore, the Sr content is set to 0.03% or more and 1.50% or less.

Sn: 0% or more, 0.7% or less Bi: 0% or more, 0.3% or less In: 0% or more, 0.3% or less Total amount of Sn, Bi and In ΣX: 0% or more, 0.7% or less Each element of Sn, Bi and In is an element that promotes softening of the plating layer by being contained in the plating layer. Since Sn, Bi and In are elements that can be contained arbitrarily, the content of each is set to 0% or more. When Sn is contained, Mg ₉ Sn ₅ tends to be formed in the plating layer. Bi forms Mg ₃ Bi ₂ , and In forms Mg ₃ In, etc. These elements are softer than the MgZn ₂ phase and have good workability, and are elements that can clearly confirm the improvement of workability by being contained in the plating layer. In addition, these elements have a high sacrificial anticorrosion effect because they show very base electrochemical properties. By containing at least one of Sn, Bi and In within the above range, the effect of improving the corrosion resistance of the processed portion can be obtained.

Ca: 0% or more, 0.6% or less Y: 0% or more, 0.3% or less La: 0% or more, 0.3% or less Ce: 0% or more, 0.3% or less Li: 0% or more, 0.3% or less Ni: 0% or more, 1.0% or less Cu: 0% or more, 1.0% or less Ag: 0% or more, 0.25% or less Sb: 0% or more, 0.25% or less Pb : 0% or more, 0.25% or less B: 0% or more, 0.5% or less P: 0% or more, 0.5% or less Ti: 0% or more, 0.25% or less Co: 0% or more, 0 .25% or less V: 0% or more, 0.25% or less Nb: 0% or more, 0.25% or less Mn: 0% or more, 0.25% or less Zr: 0% or more, 0.25% or less 0% or more, 0.25% or less Ca, Y, La, Ce, Sr, Li, Ni, Cr, Mo, Sb, Pb, B, P, Ti, Co, V, Nb, Mn, Zr, and W are all similar to Si, Zn, and Al. However, when the content of these elements is within the above range, they do not affect the initial corrosion of the plating layer. On the other hand, when these elements are contained in excess, they can cause corrosion in the plating layer. Since a potential difference occurs and a large amount of initial white rust may occur, when it is contained, it is advisable to set the content within the above range.

Fe: 0% or more, 5.0% or less Since the hot-dip plated steel material of this embodiment is manufactured by a continuous hot-dip plating method, Fe may diffuse from the plated base material to the plated layer during manufacturing. As described above, in this embodiment, the Al concentration of the plated layer is high, and an Al-Fe-based interface alloy layer may be formed, but its thickness is thin. As a result, the plated layer may contain Fe up to a maximum of 5.0%, but as long as the Fe concentration is limited to 5.0% or less, there is no effect on the frequency of cracks in the plated layer. Therefore, the Fe content is set to 0 to 5.0%. The Fe content may be more than 0%.

Balance: Zn and impurities The balance preferably contains Zn. Since the hot-dip plated steel material of the present embodiment is a highly versatile Zn-based plated steel material, the element constituting the main phase of the plated layer is Zn.

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

To identify the average chemical composition of the plating layer, the plating layer is stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) to obtain an acid solution. The resulting acid solution is then measured using ICP emission spectroscopy or ICP-MS to obtain the chemical composition. There are no particular limitations on the type of acid, so long as it is an acid that can dissolve the plating layer. If the area and weight are measured before and after stripping, the plating coverage (g/ ^m2 ) can also be obtained at the same time.

Next, the intermetallic compounds contained in the plating layer will be described.
The plating layer according to this embodiment is a Zn-Al-Mg alloy plating, and therefore contains a Zn phase, an Al phase, and _two MgZn phases. The plating layer according to this embodiment also contains an Sr-containing intermetallic compound. Furthermore, the plating layer according to this embodiment may contain other intermetallic compounds.

_MgZn2 phase The _MgZn2 phase is a phase that is intentionally contained in the plating layer in order to improve the corrosion resistance of the plating layer. By containing a certain amount of _MgZn2 phase in the plating layer, the corrosion resistance in a water-wet environment can be further improved.

Zn phase (Al-Zn phase, Zn-Al phase)
The Zn phase mainly exists as a ternary eutectic structure (Zn/Al/MgZn _ternary eutectic structure). When the coating layer contains a large amount of Al, the Zn phase is a mixture of Al and Zn. In some cases, the two elements mix together in a solid state to form an Al-Zn phase, and then dissolve in the Al phase. On the other hand, in other cases, Al dissolves in the Zn phase to form a Zn-Al phase (with an Al concentration of 0.01% in the phase). The phase consisting of Zn and Al is very easy to work.

Al phase The Al phase exists in the plating layer as a lump of primary Al crystals. The Al phase dissolves various elements, particularly Zn, in the plating layer during the solidification process. Since the plating layer of this embodiment has a high Al content, the Al phase becomes supersaturated with elements such as Zn during the solidification process. The Al phase forms a dendrite structure that spreads in a tree-like shape in the plating layer during the solidification process, forming the skeleton of the plating layer. The Al phase is soft and highly workable, and therefore plays a role in hindering the progress of cracks that have occurred and reducing fatal defects in the plating layer.

Sr-containing intermetallic compounds The plating layer according to the present embodiment contains Sr-containing intermetallic compounds, such as Zn-Sr compounds, Zn-Sr-Si compounds, and Zn-Al-Sr-Si compounds. These are formed in the plating layer when Sr is contained in the plating layer.

Intermetallic compounds formed in the plating layer generally have the effect of increasing corrosion resistance and hardness, as individual atoms are bonded in a complex manner. On the other hand, if the content is too high, plastic deformability may be lost. In particular, if metal compounds are formed in continuous layers on the plating surface and interface, they may coagulate and peel off during bending, and during corrosion, differences in corrosion rates may cause surface and/or interface peeling. Therefore, it is necessary to reduce the accumulation of intermetallic compounds near the surface and interface.

Here, Ca is known as an element effective in improving the corrosion resistance and hardness of the plating layer, and as described above, Ca-containing intermetallic compounds are compounds that tend to form layers, and are particularly prone to accumulating at interfaces. This is because intermetallic compounds based on CaZn ₄ tend to form when an excessive amount of Ca is contained in a Zn-Al-Mg plating layer. In contrast, Sr has almost the same effect as Ca, but Zn-Sr compounds are intermetallic compounds based on SrZn ₁₃ , and tend to be less likely to accumulate at interfaces compared to Ca-containing intermetallic compounds.
In addition, the more the intermetallic compounds are accumulated in the center of the plating layer, the more the workability improves, so that powdering does not occur even under severe processing conditions. In particular, by containing an Sr-containing intermetallic compound so as to satisfy each formula described later, the hardness of the plating layer is further increased to improve the scratch resistance, and the corrosion resistance of the flat surface is improved, so that the plated steel material is hard and has good workability and corrosion resistance.

In this way, by incorporating an Sr-containing intermetallic compound in the center of the plating layer, the powdering phenomenon can be more efficiently avoided, and both workability and corrosion resistance can be improved.

In order to obtain the above-mentioned effects more effectively, it is preferable that the Zn--Sr--Si compound and the Zn--Al--Sr--Si compound are contained in an amount of 5 to 30% by area.
When Si is excessively contained in the plating layer, Mg ₂ Si is formed. However, Mg ₂ Si has strong sacrificial corrosion protection and is not a preferable compound for improving the corrosion resistance of the flat surface. On the other hand, Zn-Sr-Si compounds and Zn-Al-Sr-Si compounds have a potential slightly lower than Zn, do not show excessive sacrificial corrosion protection, and gradually corrode compared to Zn. In other words, Zn-Sr-Si compounds and Zn-Al-Sr-Si compounds having complex metal element bonds have a property of low corrosion rate, but also show an appropriate value in terms of potential, and the bonds are further strengthened by solid-solving Si, so that the inclusion of Zn-Sr-Si compounds and Zn-Al-Sr-Si compounds can significantly increase the corrosion resistance. In other words, the corrosion resistance can be significantly improved by appropriately controlling the area fraction of Zn-Sr-Si compounds and Zn-Al-Sr-Si compounds. The larger the area fraction of the Zn-Sr-Si compounds and the Zn-Al-Sr-Si compounds, the more preferable it is, but considering the upper limit of the amount of Sr that can be contained in the plating layer, the total area fraction of the Zn-Sr-Si compounds and the Zn-Al-Sr-Si compounds is substantially 30% or less.

These intermetallic compounds can be measured using an electron probe microanalyzer (EPMA). Specifically, first, an EPMA analysis is performed on a cross section along the thickness direction of the plating layer at an analytical magnification of 1000 times, and all structures in which Zn, Sr, and Si are detected in the same location are identified. Then, using the commercially available image editing software "Photoshop (registered trademark)", each of the structures identified above is surrounded, the number of px (pixels) within the surrounded range is calculated, and the px number of each structure is summed to obtain the total px number of intermetallic compounds within the field of view. The obtained total px number is then converted into an area to calculate the area distribution of the intermetallic compounds. In this embodiment, the same operation as above is performed for 20 fields of view. That is, 20 different fields of view are randomly selected in the cross section of the plating layer, the area ratio of the intermetallic compounds is calculated in each field of view by the above method, and the average value is taken as the area ratio of the metallic compounds in the plating layer.

Next, we will explain how to confirm the presence of Sr-containing intermetallic compounds in the plating layer according to this embodiment.

The component analysis method in the depth direction inside the plating layer may be performed by glow discharge optical emission spectrometry (GDS) using a glow discharge optical emission spectrometer. In this embodiment, a LECO Japan 850A is used as the glow discharge optical emission spectrometer, but the measurement device is not limited to this. In addition, when performing the analysis in the depth direction, it is preferable to perform the analysis while performing Ar sputtering, and the analysis conditions are argon pressure: 0.27 MPa, output power: 30 W, output voltage: 1000 V, and discharge area: within a circular area with a diameter of 4 mm.
The component analysis by GDS is carried out from the surface of the plating layer in the depth direction until the Fe concentration reaches 100% (reaching the base steel). Therefore, the analysis range of the depth direction analysis by GDS is a range from the plating surface to the Zn-Al-Mg plating layer, the Al-Fe alloy layer, and a part of the steel material. After the GDS analysis, the sputter depth of the cross section is measured using a Surfcom130A manufactured by Tokyo Seimitsu Co., Ltd. The component analysis by GDS provides an element distribution profile in the depth direction of the plating layer. The element distribution profile shows the distribution of the content of each element in the depth direction when the total amount of the detected elements is taken as 100%.

In this embodiment, in the element distribution profile obtained by performing a qualitative analysis using GDS from the surface of the plating layer toward the steel material, if the thickness of the plating layer is t, the average value of the qualitative analysis value of Sr from the surface of the plating layer to 0.05t is Sr(surf), the qualitative analysis value in the range of 0.05t to 0.66t starting from the surface of the plating layer is Sr(centre), and the qualitative analysis value in the range of more than 0.66t and t starting from the surface of the plating layer is Sr(deep), the following formula (1) is satisfied.

Sr(surf)<Sr(deep)<Sr(centre)...(1)

By accumulating Sr-based intermetallic compounds in the center of the plating layer so as to satisfy the above (1), workability can be improved and powdering can be avoided even under severe processing conditions. In other words, by satisfying formula (1), the hardness of the plating layer is increased, improving scratch resistance, and improving corrosion resistance of flat surfaces, ensuring a plated steel material that is hard and has good workability and corrosion resistance.

In this embodiment, the depth position at which an Fe intensity equivalent to 5% of the maximum Fe intensity is detected in the element distribution profile obtained by qualitative analysis using the GDS method from the surface of the plating layer toward the steel material is defined as the "interface," and the region up to this interface is the "plating layer."

Figure 1 shows an example of the results of depth direction analysis by GDS for the plating layer according to this embodiment. The graph shown in Figure 1 is an element distribution profile. The boundary between the plating layer and the steel is taken as the position where Fe exceeds 5% of its maximum strength, and the region deeper than that position is determined to be the base iron (steel). For example, in the case of the analysis results shown in Figure 1, the maximum strength of Fe is 1.5 cps, so the position of 5% of that strength, that is, the position where the strength of Fe is 0.075 cps, is taken as the boundary between the plating layer and the steel.

In order to achieve an appropriate distribution of Sr-containing intermetallic compounds in the plating layer, it is effective to appropriately control the manufacturing conditions. A suitable manufacturing method will be described later.

Next, we will explain the X-ray diffraction index of Sr-containing intermetallic compounds.

The plating layer of the present embodiment satisfies the following formula (2) when the diffraction intensity of the Zn-Sr compound in the X-ray diffraction pattern of the plating layer surface measured using Cu-Kα radiation at an X-ray output of 50 kV and 300 mA is defined as I(SrZn ₁₃ ).

{I(14.48°)+I(32.74°)}/2×I(12.50°)}>2.0...(2)
In the formula (2), I(n°) is the X-ray diffraction intensity at a diffraction angle of n°, and n is the diffraction angle (2θ) shown in the formula (2).

Figure 2 shows an example of an X-ray diffraction pattern for the plating layer according to this embodiment. As shown in Figure 2, peaks of Zn-Sr based compounds consisting of Sr-containing intermetallic compounds appear at around 14.48° and 32.74°. When the background intensity is I (12.50°), by satisfying the above formula (2), intermetallic compounds with excellent corrosion resistance and hardness are formed in the plating layer. As a result, high hardness and corrosion resistance can be achieved while maintaining the plastic deformability of the plating surface and interface.

[Method of manufacturing hot-dip plated steel material]
Next, a method for producing the hot-dip plated steel material according to this embodiment will be described.
As a method for forming the above-mentioned plating layer, it is possible to simply add Sr directly to a Zn-Al-Mg plating bath and plate it. However, with this method, there is a concern that Sr-based intermetallic compounds will be formed on the surface and its vicinity, rather than in the center of the plating layer. Therefore, as an example of a suitable manufacturing method for producing the hot-dip plated steel material of this embodiment, a method of supplying Sr to the plating layer from a pre-plating layer provided on the original plate to be plated will be described below. In this specification, such a method of forming a predetermined pre-plating layer on the original plate in advance and then applying Zn-Al-Mg hot-dip plating in this order is referred to as a "two-stage plating method."

First, an Al-Sr pre-plating layer is formed on a base plate to be plated, such as a cold-rolled or hot-rolled steel sheet. The pre-plating method may be hot-dip plating, electroplating, displacement plating, or vapor deposition. Furthermore, these pre-plating layers may be heated and alloyed.

If pre-plating on the base plate is performed by hot-dip plating, this can be done by adding Sr to the conditions for normal aluminum plating, such as an Al-0.3% Sr bath or an Al-5% Sr bath, and there are no particular restrictions.

Then, the original sheet for plating is heated to 450-600°C, preferably to a temperature similar to the temperature of the plating bath described below. This heating may also serve as annealing of the original sheet (hereinafter, this heating may be referred to as pre-annealing). By heating the steel sheet before immersion in the plating bath described below, it is possible to reduce temperature fluctuations in the plating bath.

The heated original sheet on which the pre-plating layer is formed is immersed in the plating bath and then pulled out. The temperature of the plating bath is preferably 450°C to 600°C. If the temperature of the plating bath is too low, the reaction between the pre-plating layer and the hot-dip plating bath does not proceed, and Sr cannot be sufficiently supplied to the plating bath. Also, if the temperature of the plating bath is too low, the plating adhesion of the resulting plated steel material is poor. Therefore, the bath temperature is preferably 450°C or higher. More preferably, it is 470°C or higher, even more preferably 500°C or higher, and even more preferably 550°C or higher. On the other hand, if the temperature of the plating bath is too high, the evaporation of Zn in the plating bath becomes significant, making stable operation difficult in practice. Therefore, the bath temperature is preferably 600°C or lower. More preferably, it is 580°C or lower.
Furthermore, in this embodiment, it is preferable to control the temperature when the plated original sheet is pulled up. In other words, by performing appropriate temperature control and cooling control after immersion, Sr is contained in the plated layer, and the desired Sr-based intermetallic compound can be formed.

Sr-based intermetallic compounds are an element that easily forms solid solutions. This is because the plating layer contains Mg.

In addition, to ensure sufficient formation of Zn-Sr-Si compounds and Zn-Al-Sr-Si compounds, it is preferable to set the average cooling rate in the temperature range of 450 to 350°C to 10°C/sec or less. If the average cooling rate in the temperature range of 450 to 350°C exceeds 10°C/sec, Sr and Si will be uniformly dispersed in the thickness direction of the plating layer, and the desired plating layer may not be obtained.

Cooling conditions in the temperature range below 350°C are not particularly limited as they do not affect the formation of intermetallic compounds.

In this way, by appropriately controlling the cooling rate after the plated base sheet is pulled out of the bath, it is possible to suppress the formation of Sr-based intermetallic compounds on the surface and interface of the plated layer, and to adequately disperse the Sr-based intermetallic compounds near the center of the plated layer. As a result, it is possible to achieve high plating hardness, workability, and corrosion resistance while maintaining the plastic deformability of the plated surface and interface.

In addition, when a steel sheet on which an Al-Sr pre-plated layer has been formed is used as the plating substrate, the plating bath and the Al-Sr intermetallic compound have a moderate reactivity, so that upon immersion in a Zn-Al-Mg plating bath at around 550°C, traces of the Al-Sr pre-plated layer immediately disappear, and the immersed plating bath and the Al-Sr intermetallic compound can easily blend together. As a result, the desired plating layer of this embodiment can be formed.

Next, we will explain how to evaluate the performance of hot-dip galvanized steel.

(Bending workability)
The bending workability of the plated steel material of this embodiment can be evaluated by measuring the amount of powdering (amount of peeling) when bending the material 0R to 5R-60 degrees-V and then bending it back.

Specifically, the material is molded using a 2R-60-degree V-shaped die press, and then bent back into a flat plate using a flat die. After V-shaping, a 24 mm wide cellophane tape is pressed against the valley and then pulled away, and a 90 mm long portion of the cellophane tape is visually inspected.
The evaluation criteria are as follows:

<Evaluation criteria>
A: No peeling occurred.
B: Peeling occurred partially at points (less than 5% of the processed area).
C: Linear peeling was observed (less than 5 to 10% of the processed area).
D: Linear peeling was observed (less than 10 to 20% of the processed area).
E: Peeling occurred in almost all areas (20% or more of the processed area).

(Corrosion resistance)
A flat test piece having a thickness of 2.3 mm is prepared, and the corrosion weight loss of JASO is measured after 120 cycles.
The evaluation criteria are as follows:

<Evaluation criteria>
E: The corrosion weight loss is 25 g/ ^m2 or more.
D: The corrosion weight loss is 20 g/ ^m2 or more.
C: The corrosion weight loss is 15 g/ ^m2 or more.
B: When the corrosion weight loss is 10 g/ ^m2 or more.
A: When the corrosion weight loss is 5 g/ ^m2 or more.
S: Corrosion weight loss is less than 5 g/ ^m2 .

(Hardness)
The hardness measured by the Vickers test is used as an index for evaluating the scratch resistance of the plating layer. Specifically, the Vickers hardness of the plating layer surface is measured under a load of 10 gf. The Vickers hardness is the average hardness of 10 points on the plating layer.

After the plating layer is formed, various chemical treatments and painting processes may be performed.

In the hot-dip plated steel material of this embodiment, a coating may be formed on the plating layer. The coating may be formed in one layer or in two or more layers. Types of coatings that may be formed directly on the plating layer include, for example, chromate coatings, phosphate coatings, and chromate-free coatings. These coatings may be formed by known methods such as chromate treatment, phosphate treatment, and chromate-free treatment.

There are three types of chromate treatment: electrolytic chromate treatment, which forms a chromate film by electrolysis; reactive chromate treatment, which uses a reaction with the material to form a film and then washes away excess treatment liquid; and paint-type chromate treatment, which applies the treatment liquid to the substrate and dries it without rinsing to form a film. Any of these treatments may be used.

Examples of electrolytic chromate treatments include those 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.

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

Chromate-free treatments are particularly suitable as they place no burden on the environment. There are electrolytic chromate-free treatments that form a chromate-free film by electrolysis, reactive chromate-free treatments that form a film by utilizing a reaction with the material and then wash away excess treatment liquid, and coating-type chromate-free treatments that apply a treatment liquid to the substrate and dry it without rinsing to form a film. Any of these treatments may be used.

Furthermore, one or more layers of an organic resin film may be provided on the film directly on the plating layer. The organic resin is not limited to a specific type, and examples include polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, and modified products of these resins. Here, the modified product refers to a resin in which a reactive functional group contained in the structure of these resins has been reacted with another compound (monomer, crosslinking agent, etc.) that contains a functional group in its structure that can react with the functional group.

As such organic resins, one or more organic resins (unmodified) may be used in combination, or one or more organic resins obtained by modifying at least one other organic resin in the presence of at least one organic resin may be used in combination. The organic resin film may also contain any coloring pigment or rust-preventive pigment. Water-based resins that have been dissolved or dispersed in water may also be used.

Next, an embodiment of the present invention will be described. However, the conditions in the embodiment are merely an example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this example of conditions. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

First, a cold-rolled steel sheet (SPCC) measuring 100 mm x 200 mm and 0.8 mm thick was prepared as the base sheet for plating. An Al-Sr pre-plated layer as described in Tables 1A and 1B was formed on the surface of this cold-rolled steel sheet using the Al-Sr-based plating bath shown below. Note that "two-stage" in the "Manufacturing method" column in Tables 1A and 1B indicates that the two-stage plating method described above was applied. "Sendzimer" in Tables 1A and 1B indicates that a method was applied that did not involve pre-plating. "SPCC" in the "Composition" item in the "Pre-plated layer" column in Tables 1A and 1B indicates that there is no pre-plated layer (and therefore the base cold-rolled steel sheet (SPCC) is exposed).

Al-Sr plating bath: Sr: 0.3-10 mass%, bath temperature: 650°C.

After forming an Al-Sr pre-plating layer on the plated original sheet, the plated original sheet was pre-annealed by heating it at 550°C for 0.5 to 3.0 minutes.

The obtained plated substrate was subjected to hot-dip plating using a hot-dip plating simulator.
First, an alloy having the plating bath components shown in Tables 1A and 1B was prepared by a vacuum melting method, and a plating bath was prepared in a completely oxygen-free, nitrogen-substituted atmosphere ( _O2 concentration less than 5 ppm).
Next, one point of the plated original sheet (the back side of the center of the evaluation surface) was attached to a K thermocouple by spot welding, and the temperature history until the completion of plating solidification was grasped. The plated steel sheet was heated to a predetermined temperature in a H ₂ (25%)-N ₂ atmosphere. The plating bath temperature was set to 550°C, and the plated substrate was immersed at a dipping speed of 600 mm/sec. After stopping in the bath for 3 seconds, the plated substrate was lifted up at a speed of 600 mm/sec.
Immediately after pulling up, the plating thickness was adjusted to 40 μm using N ₂ wiping gas, and then the plated material was cooled at the average cooling rate shown in Table 1 by blowing N ₂ gas at a controlled flow rate in an oxygen-free, nitrogen-substituted atmosphere.
Through the above steps, a plated steel sheet was obtained.

Next, evaluation samples were cut out from each type of plated steel sheet. Samples for GDS analysis and SEM observation were cut out at 30 mm square positions on the opposite side of the thermocouple position. Corrosion samples were taken from the center of the plated steel sheets, measuring 100 x 50 mm.

The cut samples were evaluated by bending tests, Vickers hardness tests, and corrosion tests (SST). The Fe content of the plating layer is not shown in the table, but it was in the range of 0 to 5%.
The evaluation results, the composition of the plating layer, the GDS analysis results, the X-ray diffraction (XRD) results, the area ratios of the Zn-Sr-Si compounds and the Zn-Al-Sr-Si compounds, etc. are shown in Tables 2A and 2B. Note that the underlines in each table indicate that the results are outside the scope of the present invention, that the manufacturing conditions are not within the ranges of the present invention, or that the characteristic values are not preferable.
In the comparative example, No. 49, the temperature of the plating bath was low, so the reaction between the Al-Sr pre-plating layer and the plating bath did not proceed sufficiently. As a result, the Al-Sr pre-plating layer remained between the base sheet and the plating layer, and a suitable hot-dip plated steel material could not be obtained. In addition, the plating adhesion of the plated steel material No. 49 deteriorated, so the GDS analysis results, X-ray diffraction (XRD) and each performance could not be properly evaluated (indicated as "-" in the table).

The above-mentioned aspects of the present invention provide hot-dip plated steel products that are excellent in plating hardness, corrosion resistance, and workability. The hot-dip plated steel products thus obtained are suitable for use in fields such as the automotive and building materials industries, and therefore have a high industrial applicability.

Claims (3)

Steel and
A plating layer disposed on a surface of the steel material;
A hot-dip galvanized steel material having the following properties:
The plating layer comprises, in mass %,
Al: more than 10.0% and less than 45.0%;
Mg: 4.0% or more, 15.0% or less,
Si: 0% or more, 2.0% or less,
Sr: 0.03% or more and 1.50% or less,
Sn: 0% or more, 0.7% or less,
Bi: 0% or more, 0.3% or less,
In: 0% or more, 0.3% or less,
Ca: 0% or more, 0.6% or less,
Y: 0% or more, 0.3% or less,
La: 0% or more, 0.3% or less,
Ce: 0% or more, 0.3% or less,
Li: 0% or more, 0.3% or less,
Ni: 0% or more, 1.0% or less,
Cu: 0% or more, 1.0% or less,
Ag: 0% or more, 0.25% or less,
Sb: 0% or more, 0.25% or less,
Pb: 0% or more, 0.25% or less,
B: 0% or more, 0.5% or less,
P: 0% or more, 0.5% or less,
Ti: 0% or more, 0.25% or less,
Co: 0% or more, 0.25% or less,
V: 0% or more, 0.25% or less,
Nb: 0% or more, 0.25% or less,
Mn: 0% or more, 0.25% or less,
Zr: 0% or more, 0.25% or less,
W: 0% or more, 0.25% or less,
Fe: 0% or more, 5.0% or less,
The balance has a chemical composition including Zn and impurities,
the plating layer contains a Zn—Sr-based compound and a Zn—Sr—Si-based compound,
A hot-dip plated steel material, in which, in an element distribution profile obtained by qualitatively analyzing from the surface of the plating layer toward the steel material by glow discharge optical emission spectrometry, when the thickness of the plating layer is t, an average value of the qualitative analysis value of Sr from the surface of the plating layer to 0.05t is Sr(surf), a qualitative analysis value in the range from 0.05t to 0.66t starting from the surface of the plating layer is Sr(centre), and a qualitative analysis value in the range from 0.66t to t starting from the surface of the plating layer is Sr(deep), the following formula (1) is satisfied:
Sr(surf)<Sr(deep)<Sr(centre)…(1) In the chemical composition of the plating layer,
Sr: 0.10% or more and 1.50% or less;
2. The hot-dip plated steel material according to claim 1, wherein the diffraction intensity of a Zn-Sr compound in an X-ray diffraction pattern of a surface of the plating layer measured using Cu-Kα radiation at an X-ray output of 50 kV and 300 mA is defined as I(SrZn ₁₃ ), and the following formula (2) is satisfied:
{I(14.48°)+I(32.74°)}/2×I(12.50°)}>2.0...(2)
In equation (2), I(n°) is the X-ray diffraction intensity at a diffraction angle of n°, where n is the diffraction angle (2θ) shown in equation (2). In the chemical composition of the plating layer,
Si: 0.05% or more and 0.5% or less;
3. The hot-dip plated steel material according to claim 1, wherein the Zn-Sr-Si based compound and the Zn-Al-Sr-Si based compound are contained in an area ratio of 5% to 30% in a cross section along a thickness direction of the plating layer.

Images