JP7653049B1 - Hot-dip galvanized steel - Google Patents

Abstract

This hot-dip plated steel has a chemical composition in which the plating layer contains, by mass%, Al: more than 10.0% and 60.0% or less, Mg: 4.0 to 15.0%, Si: 3.5% to 8.0%, and the balance Zn and impurities. In the element distribution profile obtained by qualitatively analyzing the surface of the plating layer toward the steel material by the GDS method, if the thickness of the region from the surface of the plating layer to the depth position where an Fe intensity equivalent to 5% of the maximum Fe intensity is detected is Tg, the average value of Si from the surface of the plating layer to Tg/3 is Si(surf), the average value of Si in the range from Tg/3 to 2Tg/3 starting from the surface of the plating layer is Si(centre), and the average value of Si in the range from 2Tg/3 to Tg starting from the surface of the plating layer is Si(deep), the following formula (1) is satisfied. Si(surf)<Si(deep)<Si(centre) ... (1)

Description

The present invention relates to a hot-dip galvanized steel material.
This application claims priority based on Japanese Patent Application No. 2023-125776, filed on August 1, 2023, the contents of which are incorporated herein by reference.

When using steel materials for a long period of time, it is preferable to apply some kind of rust-proofing treatment to the steel materials to make them resistant to corrosion. Hot-dip galvanizing is used as a cheap method of rust-proofing steel materials in various fields where rust prevention is required, such as civil engineering, construction, and automotive fields.

The corrosion protection measures provided by the plating layer are roughly 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 studies have been conducted to improve the performance of plated steel sheets.

For example, Patent Documents 1 and 2 describe Zn-Al-Mg plated steel materials (steel sheets) as plated steel materials with high corrosion resistance. In these Zn-Al-Mg plated steel materials, the corrosion resistance and other performance properties are improved by controlling the structure of the plated layer, adding elements to the plated layer, or actively forming corrosion products.

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

In conventional Zn-Al-Mg plated steel materials as described in Patent Documents 1 and 2, the morphology of intermetallic compounds in the plating layer has not been fully studied, except for the major ones. Therefore, under severe processing conditions, problems such as reduced workability, such as peeling (powdering) of the plating layer, may occur due to intermetallic compounds. Furthermore, in conventional Zn-Al-Mg plated steel materials, the hardness of the plating layer is insufficient, and it may be difficult to stably ensure good scratch resistance.

The problem that one embodiment of the present invention aims to solve is to provide a hot-dip plated steel material that can achieve sufficient plating hardness, excellent workability, and excellent 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 aspect of the present invention has 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%, less than 60.0%,
Mg: 4.0% or more, 15.0% or less,
Si: 3.5% or more, 8.0% or less,
and further comprising
Sn: 0% or more, 0.7% or less,
Sr: 0% or more, 1.5% 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 an Mg ₂ Si intermetallic 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 a region from the surface of the plating layer to a depth position at which an Fe intensity equivalent to 5% of the maximum intensity of Fe is detected is defined as Tg, the average value of the qualitative analysis values of Si from the surface of the plating layer to Tg/3 is defined as Si(surf), the average value of the qualitative analysis values of Si in the range from Tg/3 to 2Tg/3 starting from the surface of the plating layer is defined as Si(centre), and the average value of the qualitative analysis values of Si in the range from 2Tg/3 to Tg starting from the surface of the plating layer is defined as Si(deep), the following formula (1) is satisfied.
Si(surf)<Si(deep)<Si(centre)…(1)
[2] In the hot-dip plated steel material described in the above [1], an X-ray diffraction pattern of a surface of the plating layer measured using Cu-Kα radiation under conditions of an X-ray output of 50 kV and 300 mA may satisfy the following formula (2):
{I(26.19°)+I(44.6°)}/{2×I(12.5°)}>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).

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

FIG. 2 is a graph showing the results of a GDS analysis performed on a coating layer of a hot-dip galvanized steel material according to an embodiment of the present invention, and is a graph showing an example of an element distribution profile. 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.

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.

Generally, when a plating layer contains intermetallic compounds with covalent bonds, 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 may become hard, reducing the plastic deformability of the plating layer. Furthermore, if the entire plating layer becomes hard, the plating layer may be easily destroyed when the plated steel material is used for forming processing, and peeling of the plating layer, such as powdering, may occur. For this reason, it is not practically preferable to contain a large amount of intermetallic compounds in the plating layer.

Furthermore, when intermetallic compounds are formed continuously and in layers, particularly on the surface and interface of the plating layer, peeling may occur during bending, or the difference in corrosion rate during corrosion may cause interfacial peeling at the interface between the plating layer and the base material. Therefore, there has been a demand for a plating layer that has the desired level of hardness and high corrosion resistance, while also having good workability and does not cause peeling.

Here, there is a technology for incorporating Ca into the plating layer in order to improve the hardness and corrosion resistance of the plating layer. When a large amount of Ca is incorporated into the plating layer, intermetallic compounds are formed with the 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-based hot-dip plating. Therefore, the Ca in the plating layer becomes large Ca-containing intermetallic compounds in the early stages after the steel material is pulled out of the plating bath, and grows in the plating layer.

In a typical hot-dip plating process, the surface of the plating layer is largely cooled by the outside air, so solidification of the plating layer proceeds 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 may 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, the Ca-containing intermetallic compounds may 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 of the plating layer.

Therefore, the present inventors investigated elements that can exert the same effect as Ca and found that Si is effective. Specifically, they found that Si forms Mg-Si intermetallic compounds, but that these Mg-Si intermetallic compounds have the property of being less likely to accumulate at the interface between the plating layer and the base material than Ca-containing intermetallic compounds. In other words, by including Si in the plating layer, it is possible to exert substantially the same effect as Ca, while allowing the formed Mg-Si intermetallic compounds to accumulate in the center of the plating layer in the thickness direction, thereby improving workability compared to conventional methods.

[Hot-dip plated 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 is a hot-dip plated steel material having a steel material and a plating layer disposed on a surface of the steel material, and the average chemical composition of the plating layer is, in mass%,
Al: more than 10.0%, less than 60.0%,
Mg: 4.0% or more, 15.0% or less,
Si: 3.5% or more, 8.0% or less,
and further comprising
Sn: 0% or more, 0.7% or less,
Sr: 0% or more, 1.50% 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.

Furthermore, the plating layer in the hot-dip plated steel material of this embodiment contains an Mg ₂ Si intermetallic compound, and in an element distribution profile obtained by qualitatively analyzing the plating layer from the surface toward the steel material by glow discharge optical emission spectrometry, when the thickness of the region from the surface of the plating layer to the depth position where an Fe intensity equivalent to 5% of the maximum Fe intensity is detected is Tg, the average value of the qualitative analysis values of Si from the surface of the plating layer to Tg/3 is Si(surf), the average value of the qualitative analysis values of Si in the range from Tg/3 to 2Tg/3 starting from the surface of the plating layer is Si(centre), and the average value of the qualitative analysis values of Si in the range from 2Tg/3 to Tg starting from the surface of the plating layer is Si(deep), the following formula (1) is satisfied.

Si(surf)<Si(deep)<Si(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 material of the steel material is not particularly limited. For example, various steel plates and steel materials such as general steel, Al-killed steel, ultra-low carbon steel, high carbon steel, various high tensile steels, some high alloy steels (steels containing corrosion-resistant strengthening elements such as Ni and Cr), steel for bolts, and steel wire for bridge cables can be used. 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 general structural rolled steel material corresponding to so-called SS material, a so-called general steel included in hot-rolled steel plate shown in JIS G 3193 (2019), pre-plated steel thinly plated with various metals as 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 as described in JIS G 3136 (2012), a rolled steel material for building structure as described in JIS G 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.).

(Plating layer)
Next, the plating layer provided on the steel material will be described.
The plating layer according to this embodiment includes a Zn-Al-Mg alloy layer. The Zn-Al-Mg alloy layer contains a Zn phase, an Al phase, and an MgZn ₂ phase. The plating layer according to this embodiment also contains an Mg ₂ Si intermetallic compound. Furthermore, the plating layer according to this embodiment may contain other intermetallic compounds.

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 containing 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 of this embodiment is made thin, it ensures corrosion resistance equivalent to or greater than that of a conventional Zn plating layer.

MgZn ₂ phase The plating layer according to the present embodiment contains MgZn ₂ phase. When a certain amount of MgZn ₂ phase is contained 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 plating layer contains a large amount of Al, the Zn phase may be dissolved in the Al phase by mixing Al and Zn in a solid state to form an Al-Zn phase. On the other hand, Al may be dissolved in the Zn phase to form a Zn-Al phase (the Al concentration in the phase is up to about 20%). The phase composed of Zn and Al is very easy to work.

Al phase The Al phase exists in the plating layer in the form of a mass as 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.

Mg ₂ Si intermetallic compound The plating layer according to this embodiment contains an Mg ₂ Si intermetallic compound. The Mg ₂ Si intermetallic compound is an intermetallic compound observed in the form of islands with clear boundaries in the solidification structure of the plating layer containing Si. It is considered that Zn, Al and other additive elements are not solid-dissolved in the Mg ₂ Si intermetallic compound, or even if they are solid-dissolved, they are in very small amounts. The Mg ₂ Si intermetallic compound can be clearly distinguished from other phases in the plating layer when observed under a microscope. The Mg ₂ Si intermetallic compound is formed in the plating layer when the plating layer contains Si.

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, when intermetallic 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.

Here, Ca is known as an element effective in improving the corrosion resistance and hardness of the plating layer. However, 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 _CaZn4 are likely to be formed when an excessive amount of Ca is contained in a Zn-Al-Mg-based plating layer. In contrast, it has been found that Si tends to improve the corrosion resistance and hardness of the plating layer in a manner similar to Ca, and that _Mg2Si intermetallic compounds in particular tend to be less likely to accumulate at interfaces compared to Ca-containing intermetallic compounds.
In addition, the more the intermetallic compound accumulates in the center of the plating layer, the less likely powdering occurs even under severe processing conditions. By incorporating the Mg ₂ Si intermetallic compound in the plating layer so as to satisfy the various formulas described below, the hardness of the plating layer can be further increased, the corrosion resistance can be improved, and good processability can be ensured.

The presence of intermetallic compounds such as the Mg ₂ Si intermetallic compound can be confirmed by the GDS method (glow discharge optical emission spectroscopy).

Next, we will explain the method for analyzing the components in the depth direction inside the plating layer in this embodiment.

The method for analyzing the components in the depth direction inside the plating layer is preferably 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 measuring device is not limited to this. In addition, when performing an 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.

Component analysis using GDS is carried out from the surface of the plating layer in the depth direction towards the steel material until the Fe concentration reaches 100% (reaching the base steel). Therefore, the analysis range of depth direction analysis using GDS is the range from the surface of the plating layer to the Zn-Al-Mg plating layer, the Al-Fe alloy layer and part of the steel material. After GDS analysis, the sputter depth of the cross section is measured using a "surfcom130A" manufactured by Tokyo Seimitsu Co., Ltd. Component analysis using 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 detected elements is taken as 100%.

In this embodiment, in the element distribution profile obtained by performing a qualitative analysis from the surface of the plating layer toward the steel material by GDS, if the thickness of the region from the surface of the plating layer to the depth position where an Fe intensity equivalent to 5% of the maximum Fe intensity is detected is Tg, the average value of the qualitative analysis value of Si from the surface of the plating layer to Tg/3 is Si(surf), the average value of the qualitative analysis value of Si in the range from Tg/3 to 2Tg/3 starting from the surface of the plating layer is Si(centre), and the average value of the qualitative analysis value of Si in the range from 2Tg/3 to Tg starting from the surface of the plating layer is Si(deep), the following formula (1) is satisfied. Note that Si(surf), Si(centre), and Si(deep) are obtained by performing a qualitative analysis by GDS 10 times and averaging the qualitative analysis values in the obtained element distribution profile. The qualitative analyses are performed at positions on the surface of the plating layer that do not overlap with each other.

Si(surf)<Si(deep)<Si(centre)…(1)

By accumulating the Mg ₂ Si intermetallic compound in the center of the thickness direction of the plating layer (specifically, the aforementioned region) so as to satisfy the above (1), the workability can be improved and powdering can be avoided even under severe processing conditions. In other words, by satisfying the formula (1), the hardness and corrosion resistance of the plating layer can be increased, and as a result, a plated steel material that is hard and has good workability and corrosion resistance can be obtained. It is considered that the presence of an insulator such as the Mg ₂ Si intermetallic compound in a portion where the potential is likely to change significantly, such as the center of the thickness direction of the plating layer or the boundary between the plating layer and Fe, suppresses the promotion of corrosion and improves the corrosion resistance.

The Mg ₂ Si intermetallic compound has the effect of increasing corrosion resistance and hardness. On the other hand, if a large amount of Mg ₂ Si intermetallic compound is formed on the surface and interface of the plating layer, the Mg ₂ Si intermetallic compound may peel off during processing. In addition, due to the difference in corrosion rate, surface peeling and/or interface peeling of the Mg ₂ Si intermetallic compound may occur during corrosion, which may impair workability and corrosion resistance. The Mg ₂ Si intermetallic compound formed on the surface of the plating layer has a greater effect on the deterioration of workability and corrosion resistance. Therefore, in this embodiment, Si (surf) is made smaller than Si (deep). That is, by making the amount of Si in the region from the surface of the plating layer to Tg/3 smaller than the amount of Si in the range from 2Tg/3 to Tg, peeling due to the Mg ₂ Si intermetallic compound during processing and corrosion can be suppressed, and workability and corrosion resistance can be further improved.

In this embodiment, the above formula (1) is satisfied in the element distribution profile obtained by qualitatively analyzing the steel material from the surface of the plating layer using the GDS method up to the depth position where an Fe intensity equivalent to 5% of the maximum Fe intensity is detected. This region is roughly the same as the region where the Zn-Al-Mg alloy layer exists.

Figure 1 shows an example of the results of depth-wise analysis by GDS of the plating layer according to this embodiment. The graph shown in Figure 1 is an element distribution profile. In this embodiment, the region that defines the above formula (1) is from the surface of the plating layer to a position that is 5% of the maximum Fe intensity when analyzed in the depth direction from the surface of the plating layer. For example, in the case of the analysis results shown in Figure 1, since the maximum Fe intensity is 53 V, the above formula (1) is defined in the region up to the position of 5% of that intensity, that is, the position where the Fe intensity is 2.7 V.

Next, the indices of the Mg ₂ Si intermetallic compound based on X-ray diffraction will be described.

The plating layer of this embodiment satisfies the following formula (2) when the diffraction intensities of the Mg ₂ Si intermetallic compound are I (26.19°) and I (44.6°) and the background intensity is I (12.5°) 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.

{I(26.19°)+I(44.6°)}/{2×I(12.5°)}>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).

FIG. 2 shows an example of an X-ray diffraction pattern of the plating layer according to this embodiment. As shown in FIG. 2, the peaks of the Mg ₂ Si intermetallic compound appear near 26.19° and near 44.6°. That is, I (26.19°) and I (44.6°) in formula (2) represent the X-ray diffraction intensity of the Mg ₂ Si intermetallic compound at the diffraction angles of 26.19° and 44.6°, respectively. In this embodiment, when the background intensity is I (12.5°), by satisfying the above formula (2), an intermetallic compound having excellent corrosion resistance and hardness is formed in the plating layer. As a result, it is possible to develop high hardness and corrosion resistance while maintaining the plastic deformability of the plating surface and interface.

The plating layer of this embodiment may include an interface alloy layer (Al-Fe-based interface alloy layer) containing Al and Fe. The average thickness of the Al-Fe-based interface alloy layer 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 be a single-layer structure composed of a Zn-Al-Mg-based alloy layer, or may be a laminated structure including a Zn-Al-Mg-based alloy layer and an Al-Fe-based interface alloy 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 the 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 crack initiation points 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 member, 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 suppresses the occurrence of cracks during processing and further improves powdering resistance. Furthermore, the ratio of the thickness of the Al-Fe interface 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 coating bath. When a continuous hot-dip coating method is used as the manufacturing method, the Al-Fe-based interface alloy layer is likely to be formed in the coating layer containing the Al element. In this embodiment, since the coating 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. Furthermore, 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 the plating layer according to this embodiment, some of the Si may be incorporated into the Al-Fe-based interface alloy layer to form an Al-Fe-Si intermetallic compound phase. The identified Al-Fe-Si 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 may be detected in the Al-Fe-based interface alloy layer. An Al-Fe-based interface alloy layer that contains these AlFeSi phases 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 composed of an Al-Fe interfacial 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 interfacial 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. 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%.

Al: more than 10.0% and not more than 60.0% Al is an element that mainly constitutes the coating layer. If the Al content is not more than 10.0%, 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 exceeds 60.0%, the corrosion resistance may decrease. Therefore, the upper limit of the Al content is not more than 60.0%. The lower limit of the Al content is preferably not less than 15.0%. Moreover, the upper limit of the Al content is preferably not more than 45.0%, more preferably not more than 30.0%.

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 corrosion resistance 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 corrosion resistance 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: 3.5% or more, 8.0% or less Si combines with Mg to form an intermetallic compound having a composition of Mg ₂ Si. Si also suppresses excessive Al-Fe reaction, thereby suppressing the formation of an Al-Fe based interface alloy layer.
If the Si content is less than 3.5%, the amount of Mg ₂ Si produced will be small, the hardness of the plating layer will be low, and the corrosion resistance may also be reduced. On the other hand, if the Si content exceeds 8.0%, the amount of Mg ₂ Si produced in the plating layer will be too large, the plating layer will undergo brittle fracture, and the plating layer will coagulate and peel off from the plating surface, causing a powdering phenomenon, which may result in a decrease in corrosion resistance. Therefore, the Si content is set to 3.5% or more and 8.0% or less.

Sr: 0% or more, 1.5% or less Sr forms covalent bonds with Zn, Al, Si, etc., to form intermetallic compounds with excellent corrosion resistance and hardness. On the other hand, if the Sr content exceeds 1.5%, Sr-based intermetallic compounds are excessively generated in the plating layer, and the entire plating layer becomes hard. As a result, when the plated steel material is used as a material for forming, the plating layer is easily destroyed, and peeling of the plating layer, such as powdering, may occur. Therefore, the Sr content is set to 0.03% or more, 1.5% 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 Each 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, 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 anticorrosive 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 part can be obtained.

Ca: 0% or more, 0.6% or less,
Ca is an element that contributes to improving the hardness and corrosion resistance of the plating layer. On the other hand, when a large amount of Ca is contained in the plating layer, an intermetallic compound is formed with Zn and/or Al in the plating layer. The Ca-containing intermetallic compound thus formed is particularly likely to accumulate on the plating layer surface, and in some cases, the accumulated Ca-containing intermetallic compound may grow coarsely and the Ca-containing intermetallic compound may be connected in layers. In the case of a plating layer in which Ca-containing intermetallic compounds are connected in layers, the Ca-containing intermetallic compound may undergo brittle fracture during forming, causing the plating layer to peel off from the plating layer surface, resulting in a decrease in workability. Therefore, the Ca content is set to 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 Y, La, Ce, Li, Ni, Cu, Ag, Sb, Pb, B, P, Ti, Co, V, Nb, Mn, Zr, and W all form intermetallic compounds with Si, Zn, Al, etc. However, when the contents of these elements are within the above ranges, they do not affect the initial corrosion of the plating layer. On the other hand, when these elements are contained in excess, a potential difference occurs in the plating layer, and a large amount of initial white rust may occur, so when these elements are contained, it is preferable to keep them within the above ranges.

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 Zn-based plated steel material having high versatility, 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. In addition, 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, an acid solution is obtained by peeling and dissolving the plating layer with an acid containing an inhibitor that suppresses corrosion of the base steel (steel material). The acid solution is filtered to remove the insoluble matter, and the resulting residue is liquefied by an alkali fusion treatment. The resulting acid solution and the solution obtained by the alkali fusion treatment are then measured by 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 peeling, the plating coverage (g/m ² ) can also be obtained at the same time.

[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.
The manufacturing method of the plated steel material according to this embodiment is not particularly limited.
Therefore, as a method for forming the above-mentioned Si-containing plating layer, a simple method of plating by directly adding Si to a Zn-Al-Mg-based plating bath is considered. However, in this method, Mg ₂ Si intermetallic compounds are likely to be formed on the surface and its vicinity, not 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 Si to the plating layer from a Si-containing pre-plating layer provided on the original plate for plating will be described below. In this specification, such a method of forming a predetermined pre-plating layer on the original plate for plating in advance and then performing Zn-Al-Mg-based hot-dip plating in this order is called a "two-stage plating method".

First, an Al-Si 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, vapor deposition, etc. Furthermore, these pre-plating layers may be heated and alloyed.

In addition, when pre-plating on the original sheet is performed by hot-dip plating, it can be performed under conditions for forming normal aluminum plating, such as an Al-8 to 10% Si bath, and there are no particular restrictions.

Next, the original sheet to be plated 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 base sheet with the pre-plated layer is immersed in a Zn-Al-Mg plating bath adjusted to obtain the desired plating components, and then pulled out, whereby the pre-plated layer is incorporated into the Zn-Al-Mg alloy layer to form the final plating layer. The plating bath temperature is preferably 480 to 550°C.

In addition, in order to incorporate the pre-plating layer into the Zn-Al-Mg alloy layer and obtain a plating layer with a single-layer structure, it is preferable to ensure that the original sheet is immersed in the plating bath for a certain period of time or more. Specifically, the immersion time is preferably between 3 and 10 seconds. In order to sufficiently incorporate the pre-plating layer into the Zn-Al-Mg alloy layer, the immersion time is preferably 4 seconds or more. Note that if the immersion time is excessively long, the alloy layer at the interface between the plating and the steel sheet may become thick, which may result in plating peeling. Therefore, the immersion time is preferably 8 seconds or less.

In this embodiment, it is preferable to control the temperature when the plated original sheet is pulled up. That is, by controlling the cooling conditions appropriately after immersion, Si is contained in the plated layer, and the desired Mg ₂ Si intermetallic compound can be formed.

Specifically, in order to sufficiently form the Mg ₂ Si intermetallic compound, it is preferable to set the average cooling rate in the temperature range of 550 to 450° C. to 25° C./sec or less. If the average cooling rate in the temperature range of 550 to 450° C. exceeds 25° C./sec, Si may be uniformly dispersed in the thickness direction of the plating layer, and the desired plating layer may not be obtained.

Cooling conditions in temperature ranges other than 550 to 450°C are not particularly limited as they do not affect the formation of intermetallic compounds, etc.

In this way, by appropriately controlling the cooling conditions after the plating base sheet is pulled out of the bath, the formation of Mg ₂ Si intermetallic compounds on the plating layer surface and interface can be further suppressed, and the Mg ₂ Si intermetallic compounds can be appropriately dispersed near the center of the plating layer, thereby achieving high plating hardness, workability, and corrosion resistance while maintaining the plastic deformability of the plating surface and interface.

In addition, when a steel sheet on which an Al-Si pre-plating layer is formed is used as the plating substrate, the Mg ₂ Si intermetallic compounds can be more concentrated in the center and in the vicinity of the interface of the plating layer, rather than on the plating surface, and as a result, the desired plating layer of this embodiment can be formed.

Next, we will describe the performance evaluation method for 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 back after bending it 0R to 5R-60 degrees-V.

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: Peeling occurred in a linear fashion (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 with a thickness of 0.8 mm is prepared, and a salt spray combined cycle corrosion test (CCT, JASO-M609-91) is carried out to measure the area ratio of red rust that has developed. The number of cycles is 600.
The evaluation criteria are as follows:

<Evaluation criteria>
A: No red rust was observed.
B: Red rust area ratio: less than 10%.
C: Red rust area ratio: 10% or more and less than 20%.
D: Red rust area ratio: 20% or more.

(Hardness)
The hardness measured by the Vickers test (Vickers hardness) is used as an evaluation index for 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 measured at 10 points on a cross section including the thickness direction of the plating layer, and the average of these measurements is used.

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. Examples of the type of coating directly on the plating layer include a chromate coating, a phosphate coating, and a chromate-free coating. These coatings can be formed by known methods such as chromate treatment, phosphate treatment, and chromate-free treatment.

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 a treatment liquid to the substrate and then dries it without rinsing to form a film. Any of these treatments may be used.

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

Chromate-free treatments are particularly suitable as they do not place a 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 with water 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 thereof include polyester resin, polyurethane resin, epoxy resin, acrylic resin, polyolefin resin, and modified products of these resins. The modified product here refers to a resin in which a reactive functional group contained in the structure of these resins is 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 organic 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-Si pre-plating layer as shown in Tables 1A and 1B was first formed on the surface of this cold-rolled steel sheet using an Al-Si-based plating bath (bath temperature: 650°C). Note that "two-stage plating" in the "Manufacturing method" column in Tables 1A and 1B indicates that the above-mentioned two-stage plating method was applied. "Sendzimer" in Tables 1A and 1B indicates that a method was applied in which the surface of the cold-rolled steel sheet was reduction-annealed and plated without applying pre-plating.

An Al-Si pre-plating layer was formed on the original sheet to produce a plated substrate, and the plated substrate was then heated at 400° C. in a H ₂ (25%)-N ₂ atmosphere for 0.5 to 3.0 minutes.

After the above pre-annealing, hot-dip plating was performed on the plated substrate using a hot-dip plating simulator.

First, alloys having the plating bath components shown in Tables 1A and 1B were prepared by a vacuum melting method, and plating baths were prepared in a completely oxygen-free, nitrogen-substituted atmosphere ( _O2 concentration less than 5 ppm). The remainder of the plating bath components in Tables 1A and 1B was essentially Zn.
Next, one point of the plated substrate (the back surface at 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 substrate was then heated to a predetermined temperature in a H ₂ (25%)-N ₂ atmosphere. The plating bath temperature was set as shown in Tables 1A and 1B, and the plated substrate was immersed in the plating bath at an immersion speed of 500 mm/sec for the immersion time shown in Tables 1A and 1B. The plated substrate was then pulled out of the plating bath at a speed of 500 mm/sec.

Immediately after pulling up, the average plating thickness Tp was adjusted to 40 μm using _N2 wiping gas, and then _N2 gas with a flow rate controlled in an oxygen-free, nitrogen-substituted atmosphere was sprayed onto the workpiece to cool it in the temperature range of 550 to 450 ° C. at the average cooling rate shown in Table 1.

The above-mentioned steps resulted in the production of plated steel sheets. The thicknesses (μm) of the plating layers shown in Tables 2A and 2B include the thicknesses of the interfacial alloy layer, and were measured from the cross section of the plating layer using an electron microscope.

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 to the thermocouple position. Samples (100 x 50 mm) for evaluating various characteristics were taken from the center of the plated layer in the planar direction.

To evaluate the various cut samples, bending tests, Vickers hardness measurements, and corrosion tests (SST) were conducted. Note that the composition of the Fe in the plating layer is not listed in the table, but all were within the range of 0 to 5%.

The evaluation results, plating layer composition, GDS analysis results, XRD measurement results, etc. are shown in Tables 2A and 2B. The remainder of the plating layer composition in Tables 2A and 2B is essentially Zn. Note that underlines in each table indicate that the results are outside the scope of the present invention, are outside the preferred manufacturing conditions, or have undesirable characteristic values.

In the example of No. 52, the immersion time of the plated substrate in the plating bath was short, so the pre-plating layer could not be sufficiently incorporated into the Zn-Al-Mg alloy layer, and as a result, a single-layered plating layer could not be obtained.

In the example of No. 53, the temperature of the plating bath was low, so the pre-plating layer could not be sufficiently incorporated into the Zn-Al-Mg alloy layer, and as a result, a plating layer with a single layer structure could not be obtained.

In the example of No. 54, the plating substrate was immersed in the plating bath for a long time, which caused an excessive reaction between the plating bath and the original plate (base steel sheet). Specifically, an interface alloy layer approximately 5 μm thick was observed in a cross-sectional view of the plating layer using an electron microscope. Furthermore, the results of the GDS analysis of No. 54 showed no accumulation of Si in the center of the plating layer in the thickness direction.

In the case of No. 55, the high temperature of the plating bath caused excessive alloying between the plating bath and the base steel sheet. Specifically, an interfacial alloy layer with an average thickness of about 5 μm was observed in a cross-sectional view of the plating layer using an electron microscope. Furthermore, the results of the GDS analysis of No. 55 showed no accumulation of Si in the center of the plating layer in the thickness direction.

According to the above aspect of the present invention, a hot-dip plated steel material having excellent plating hardness, corrosion resistance, and workability can be obtained. Therefore, the hot-dip plated steel material obtained can be suitably applied to the automotive field, building material field, and the like, and has high industrial applicability.

Claims (2)

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%, less than 60.0%,
Mg: 4.0% or more, 15.0% or less,
Si: 3.5% or more, 8.0% or less,
and further comprising
Sn: 0% or more, 0.7% or less,
Sr: 0% or more, 1.5% 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 an Mg ₂ Si intermetallic compound,
A hot-dip plated steel material that satisfies the following formula (1): in an element distribution profile obtained by qualitatively analyzing a region from the surface of the plating layer toward the steel material by glow discharge optical emission spectrometry, the thickness of the region from the surface of the plating layer to a depth position at which an Fe intensity equivalent to 5% of the maximum intensity of Fe is detected is Tg, the average value of the qualitative analysis values of Si from the surface of the plating layer to Tg/3 is Si(surf), the average value of the qualitative analysis values of Si in the range from Tg/3 to 2Tg/3 starting from the surface of the plating layer is Si(centre), and the average value of the qualitative analysis values of Si in the range from 2Tg/3 to Tg starting from the surface of the plating layer is Si(deep),
Si(surf)<Si(deep)<Si(centre)…(1) The hot-dip plated steel material according to claim 1, wherein an X-ray diffraction pattern of a surface of the plating layer measured using Cu-Kα rays under conditions of an X-ray output of 50 kV and 300 mA satisfies the following formula (2):
{I(26.19°)+I(44.6°)}/{2×I(12.5°)}>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).

Images