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WO2025033539A1 - Matériau d'acier plaqué - Google Patents

Matériau d'acier plaqué Download PDF

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Publication number
WO2025033539A1
WO2025033539A1 PCT/JP2024/028649 JP2024028649W WO2025033539A1 WO 2025033539 A1 WO2025033539 A1 WO 2025033539A1 JP 2024028649 W JP2024028649 W JP 2024028649W WO 2025033539 A1 WO2025033539 A1 WO 2025033539A1
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WIPO (PCT)
Prior art keywords
plating layer
phase
less
plating
steel material
Prior art date
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PCT/JP2024/028649
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English (en)
Japanese (ja)
Inventor
康太郎 石井
公平 ▲徳▼田
靖人 後藤
完 齊藤
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Nippon Steel Corp
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Nippon Steel Corp
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Priority to AU2024322687A priority Critical patent/AU2024322687A1/en
Publication of WO2025033539A1 publication Critical patent/WO2025033539A1/fr
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment

Definitions

  • the present invention relates to a plated steel material.
  • This application claims priority based on Japanese Patent Application No. 2023-131415, filed on August 10, 2023, the contents of which are incorporated herein by reference.
  • Hot-dip Zn-Al-Mg plated steel has excellent corrosion resistance and is used in the fields of building materials and civil engineering.
  • Hot-dip Zn-Al-Mg plated steel in particular has excellent corrosion resistance and is widely used in the above fields.
  • Hot-dip Zn-Al-Mg plated steel may be processed into various shapes before being made into various final products.
  • the MgZn 2 phase, the [Al/Zn/MgZn 2 ] ternary eutectic structure, and the Al primary crystal are formed as typical phase structures.
  • the Al primary crystal is considered to be an Al dendrite structure containing Zn.
  • the MgZn 2 phase and the [Al/Zn/MgZn 2 ] ternary eutectic structure are considered to have low plastic deformability.
  • the Al primary crystal is considered to have higher plastic deformability than the MgZn 2 phase and the [Al/Zn/MgZn 2 ] ternary eutectic structure, it is difficult to say that it is sufficient.
  • the plating layer of the hot-dip Zn-Al-Mg-based plated steel material has poor workability.
  • the plating layer of the hot-dip Zn-Al-Mg-based plated steel material cannot follow the deformation caused by processing, and the plating layer cracks at the processed part, resulting in a problem that the corrosion resistance of the processed part is inferior to that of a flat surface.
  • Patent Document 1 discloses a technique for suppressing the progress of corrosion of the Al primary crystals by precipitating MgZn2 in the Al primary crystals. Patent Document 1 aims to improve the corrosion resistance of the processed part by suppressing the corrosion rate of the Al primary crystals, but does not consider improving the processability of the plating layer itself.
  • the present invention was made in consideration of the above circumstances, and aims to provide a plated steel material that has excellent corrosion resistance and excellent workability of the plating layer.
  • a steel material and a plating layer on the steel material The average chemical composition of the plating layer is, in mass%, Al: 10.0% to 40.0%, Mg: 5.0% to 12.5%, Ti: 0% to 1.0%, Zr: 0% to 1.0%, Si: 0% to 5.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to 0.50%, Ce: 0% to 0.50%, Sr: 0% to 0.50%, Sn: 0% to 3.00%, Bi: 0% to 1.00%, In: 0% to 1.00%, B: 0% to 1.00%, P: 0% to 0.50%, Cr: 0% to 0.25%, V: 0% to 0.25%, Ni: 0% to 1.0%, Co: 0% to 0.25%, Nb: 0% to 0.25%, Cu: 0% to 1.0%, Mn: 0% to 0.25%, Mo: 0% to 0.25%,
  • the present invention provides plated steel that has excellent corrosion resistance and excellent workability of the plating layer.
  • FIG. 1 is a schematic cross-sectional view of a plated steel material according to an embodiment of the present invention.
  • the plating layer acts as a sacrificial anti-corrosion agent around the exposed area, causing the constituent elements of the plating layer to leach out and the plating layer itself to be partially worn away.
  • the corrosion resistance of the plating layer in the vicinity of the processed area may be reduced compared to the plating layer outside the processed area. To prevent this, it is necessary to prevent cracks in the plating layer in the processed area. The greater the plastic deformability of the plating layer, the less likely it is to crack.
  • the Zn-Al-Mg-based coating layer has a phase structure containing a plurality of phases and structures, for example, MgZn 2 phase, [Al/Zn/MgZn 2 ternary eutectic structure], and Al primary crystal.
  • the Al primary crystal has a crystal structure of Al dendrites containing Zn.
  • the MgZn 2 phase and [Al/Zn/MgZn 2 ternary eutectic structure] are said to have low plastic deformability and low workability.
  • the workability of Al changes depending on the crystal orientation state. Therefore, if the crystal orientation state of Al mainly contained in the Al primary crystal can be controlled, it is expected that the overall workability of the coating layer will be improved and cracks of the coating layer in the processed part can be reduced.
  • Zr and Ti form compounds with Al in the coating layer, specifically intermetallic compounds such as Al 3 Zr and Al 3 Ti. Furthermore, when Si is present, Al 2.7 Si 0.3 Zr and Al 2.5 Si 0.5 Ti are formed. These intermetallic compounds act as solidification nuclei for the primary Al crystals and refine the primary Al crystals. It has been found that this further improves the workability of the coating layer.
  • the plated steel material of the present embodiment includes a steel material and a plating layer provided on the surface of the steel material, and the plating layer has an average chemical composition, in mass %, of Al: 10.0% to 40.0%, Mg: 5.0% to 12.5%, Ti: 0% to 1.0%, Zr: 0% to 1.0%, Si: 0% to 5.00%, Ca: 0% to 3.00%, Y: 0% to 0.50%, La: 0% to 0.50%, Ce: 0% to 0.50%, Sr: 0% to 0.50%, Sn: 0% to 3.00%, Bi: 0% to 1.00%, In: 0% to 1.00%, B: 0% to 1.00%, P: 0% to 0.50%, Cr: 0% to 0.25%, V: 0% to 0.25%, Ni: 0% to and the balance: 50.0% or more of Zn and impurities, wherein the total of Ti and Zr in
  • I(200) Al is the diffraction intensity of Al (200)
  • I(111) Al is the diffraction intensity of Al (111)
  • I(220) Al is the diffraction intensity of Al (220)
  • I(311) Al is the diffraction intensity of Al (311).
  • the total amount of Ti and Zr in the plating layer is preferably 0.020% or more.
  • the ratio of the total area of Al phases with a circle equivalent diameter of 20 ⁇ m or less to the total area of Al phases is 50% or more.
  • Corrosion resistance refers to the property of the plating layer itself being resistant to corrosion. Since a Zn-based plating layer has a sacrificial corrosion protection effect on steel materials, the plating layer corrodes and turns to white rust before the steel material corrodes, and after the white rusted plating layer disappears, the steel material corrodes and turns to red rust. This is the corrosion process of plated steel sheets.
  • “Workability” refers to the property of preventing cracks from occurring in the plating layer when the plated steel material is bent.
  • the plated steel material 1 has a steel material 11.
  • the steel material 11 may also be a formed base steel material such as steel pipes, civil engineering and building materials (fences, corrugated pipes, drainage ditch covers, sand prevention boards, bolts, wire mesh, guardrails, water cut-off walls, etc.), home appliance parts (casings for air conditioner outdoor units, etc.), and automobile parts (suspension parts, etc.).
  • Forming is, for example, various plastic processing techniques such as pressing, roll forming, and bending.
  • the steel material 11 There are no particular limitations on the material of the steel material 11.
  • Various types of steel material can be used as the steel material 11, such as general steel, Ni pre-plated steel, Al killed steel, ultra-low carbon steel, high carbon steel, various high tensile steels, and some high alloy steels (steels containing strengthening elements such as Ni and Cr).
  • the steel material 11 may be a steel material on which a metal or alloy film of less than 1 ⁇ m is formed, such as Zn, Ni, Sn, or alloys thereof.
  • the plated steel material 1 has a plating layer 12 disposed on the surface of the steel material 11.
  • the plating layer 12 is disposed on at least one side of the steel plate and the other side opposite the one side.
  • the plating layer 12 is also disposed on the end face between the one side and the other side of the steel plate.
  • the plating layer 12 according to this embodiment is mainly composed of a Zn-Al-Mg alloy layer due to its chemical composition, which will be described later.
  • the Zn-Al-Mg alloy layer is made of a Zn-Al-Mg alloy.
  • the Zn-Al-Mg alloy refers to a ternary alloy containing Zn, Al, and Mg.
  • the Zn-Al-Mg alloy layer which contains Zn and alloy elements such as Al and Mg, has improved corrosion resistance compared to a normal Zn plating layer. For example, even if the Zn-Al-Mg alloy layer is about half the thickness of a normal Zn plating layer, it has the same corrosion resistance as the Zn plating layer. Therefore, the plating layer according to this embodiment also has corrosion resistance equal to or greater than that of the Zn plating layer.
  • the plating layer 12 of the plated steel material 1 may include an Fe-Al-based interfacial alloy layer (hereinafter referred to as an Al-Fe alloy layer) between the steel material 11 and the Zn-Al-Mg alloy layer.
  • the Al-Fe alloy layer is an interfacial alloy layer between the steel material and the Zn-Al-Mg alloy layer.
  • the plating layer according to this embodiment may be a single-layer structure of a Zn-Al-Mg alloy layer, or a laminated structure including a Zn-Al-Mg alloy layer and an Al-Fe alloy layer.
  • the Zn-Al-Mg alloy layer is preferably the layer that constitutes the surface of the plating layer.
  • an oxide film of the plating layer constituent elements is formed on the outermost surface of the plating layer with a thickness of less than 1 ⁇ m, this is thin compared to the overall thickness of the plating layer and can be ignored from the perspective of the main body of the plating layer.
  • the thinner the plating layer the better the workability; however, when considering the wear of the plating layer due to corrosion, the thicker the plating layer, the easier it is to ensure corrosion resistance. Therefore, it is preferable for the total thickness of the plating layer to be 10 to 70 ⁇ m. However, since the total thickness of the plating layer depends on the plating conditions, it is not limited to the range of 10 to 70 ⁇ m. In normal hot-dip plating methods, the viscosity and specific gravity of the plating bath affect the total thickness of the plating layer. The total thickness of the plating layer is adjusted by the drawing speed of the steel material (original plate) and the strength of wiping.
  • the Al-Fe alloy layer is formed on the surface of the steel material (specifically, between the steel material and the Zn-Al-Mg alloy layer), and the Al 5 Fe 2 phase is the main phase of the structure.
  • the Al-Fe alloy layer is formed by mutual atomic diffusion between the base steel (steel material) and the plating bath.
  • the hot-dip plating method is used as the manufacturing method, the Al-Fe alloy layer is likely to be formed in the plating layer containing the Al element. Since the plating bath contains Al at a certain concentration or more.
  • the Al 5 Fe 2 phase is formed most frequently. However, atomic diffusion takes time, and there are also parts where the Fe concentration is high near the base steel.
  • the Al-Fe alloy layer may partially contain small amounts of the AlFe phase, Al 3 Fe phase, Al 2 Fe phase, etc. Since the plating bath also contains Zn at a certain concentration, the Al-Fe alloy layer also contains a small amount of Zn.
  • the plating layer contains Si, it is particularly likely to be incorporated into the Al-Fe alloy layer, and may become an Al-Fe-Si intermetallic compound phase.
  • Identified intermetallic compound phases include the AlFeSi phase, with ⁇ , ⁇ , q1, q2-AlFeSi phases and other isomers. As a result, these AlFeSi phases may be detected in the Al-Fe alloy layer.
  • An Al-Fe alloy layer that contains these AlFeSi phases is also referred to as an Al-Fe-Si alloy layer.
  • the average chemical composition of the plating layer is the average chemical composition of the Zn-Al-Mg alloy layer.
  • the average chemical composition is the combined average chemical composition of the Al-Fe alloy layer and the Zn-Al-Mg alloy layer.
  • the chemical composition of the Zn-Al-Mg alloy layer is almost the same as that of the plating bath, since the reaction of forming the plating layer is almost always completed within the plating bath.
  • the Al-Fe alloy layer is formed and grows instantly immediately after immersion in the plating bath. The reaction of forming the Al-Fe alloy layer is completed within the plating bath, and its thickness is often sufficiently smaller than that of the Zn-Al-Mg alloy layer.
  • the average chemical composition of the entire plating layer is substantially the same as that of the Zn-Al-Mg alloy layer, and the components of the Al-Fe alloy layer and the like can be ignored.
  • the chemical composition of the plating layer according to this embodiment includes Zn, other alloying elements, and impurities.
  • the chemical composition of the plating layer according to this embodiment may also include Zn, other alloying elements, and impurities.
  • the chemical composition of the plating layer is described in detail below. Note that elements described as having a lower limit of 0% concentration are optional elements that are not essential for solving the problems of the plated steel according to this embodiment, but are permissible to be included in the plating layer for the purpose of improving characteristics, etc.
  • Al 10.0% to 40.0% Like Zn, Al is an element that constitutes the main part of the plating layer. Although Al has a small sacrificial anticorrosive effect, the inclusion of Al in the plating layer improves the corrosion resistance of the flat surface. Furthermore, without Al, Mg cannot be stably held in the plating bath, so Al is included in the plating bath as an element essential for manufacturing.
  • the Al content is set to 10.0% or more is that this content is necessary to contain a large amount of Mg, which will be described later, and also to ensure workability. If the content is less than this, it will be difficult to prepare the plating bath, it will be difficult to ensure the workability of the plating layer, and it will be difficult to ensure corrosion resistance. Also, the reason why the Al content is set to 40.0% or less is that Al has a weak sacrificial corrosion protection effect on steel, and if the content exceeds this, sufficient sacrificial corrosion protection cannot be obtained, so the upper limit is set to 40.0% or less.
  • Mg 5.0% to 12.5%
  • Mg has a sacrificial anticorrosive effect and is an element that enhances the corrosion resistance of the plating layer.
  • the MgZn 2 phase is formed in the plating layer. The higher the Mg content in the plating layer, the more the MgZn 2 phase is formed. It is known that the MgZn 2 phase has a structure called a Laves phase, and its hardness is known to be high.
  • the Mg content of 5.0% or more is a concentration necessary for exerting corrosion resistance, and if it is less than 5.0%, sufficient corrosion resistance cannot be obtained.
  • the MgZn 2 phase is not sufficiently formed in the plating layer, and the corrosion resistance of the plating layer itself is also low. If the Mg content is excessive, it becomes difficult to manufacture the plating layer and the workability of the plating layer decreases, so the upper limit is 12.5% or less. A more preferable Mg content is 6.0% to 8.0%.
  • Ti 0% to 1.0%
  • Zr 0% to 1.0%
  • intermetallic compounds of Al 3 Zr and Al 3 Ti respectively.
  • Si When Si is present, they form Al 2.7 Si 0.3 Zr and Al 2.5 Si 0.5 Ti. These have good lattice matching with the Al phase in the crystal structure and act as solidification nuclei of the primary crystal of Al.
  • an intermetallic compound containing Ti and Zr acts as a solidification nuclei of the primary crystal of Al, the (100) plane of Al is preferentially oriented parallel to the surface of the plating layer on the surface of the plated steel material.
  • the lower limit of the total concentration of Ti and Zr is 0.001% or more, and more preferably 0.020% or more.
  • the total concentration of Ti and Zr is 0.020% or more, the primary Al crystals start to become finer, and as the concentration increases, the primary Al crystals tend to become finer.
  • the total concentration of Ti and Zr is 0.5%, the effect of refining the crystal grains saturates. Since refining the crystal structure contributes to improving workability, in order to refine the primary Al crystals, it is preferable that the total concentration of Ti and Zr is 0.020% or more.
  • the Ti and Zr concentrations are high, it tends to become difficult to make a plating bath, and when Ti and Zr each exceed 1.0%, a large amount of dross is generated and non-plating occurs frequently, which tends to deteriorate the appearance and corrosion resistance. Therefore, the Ti and Zr concentrations are each set to 1.0% or less.
  • the total concentration of Ti and Zr is 0.001% to 2.0%, more preferably 0.001% to 1.5% or 0.010% to 0.5%, and even more preferably 0.1% to 0.5%.
  • Si 0% to 5.00% Si is an optional element, but when Si is included in the plating bath, a single phase of Si or Mg 2 Si precipitates in the plating layer, and when Ca is further included, an Al-Ca-Si compound precipitates. Precipitation of these Si or Si-based compounds on the surface layer of the plating layer has the effect of improving water wettability and running water resistance.
  • Si is incorporated into the Al-Fe alloy layer to form an Al-Fe-Si phase, which inhibits the growth of the Al-Fe alloy layer, thereby improving bending workability and plating adhesion.
  • the Si content is preferably 0.05% or more.
  • the Si concentration is set to 5.00% or less.
  • the Si concentration is preferably 0% to 5.00%, 0.05% to 3.00%, 0.05% to 1.0%, or 0.10% to 0.50%.
  • Element group A Ca: 0% to 3.00% Y: 0% to 0.50% La: 0% to 0.50% Ce: 0% to 0.50% Sr: 0% to 0.50%
  • the elements of element group A, Ca, Y, La, Ce, and Sr are optional elements, these elements are easily oxidized in the atmosphere, and when present in the coating bath, they form a dense oxide film on the bath surface, which has the effect of preventing oxidation of Mg.
  • the above effect stabilizes the Mg concentration, facilitating the production of coated steel sheets of the target composition.
  • it is preferable that the content of these elements is more than 0%, more preferably 0.01% or more.
  • Ca is set to 0% to 3.00%, preferably more than 0% and less than 2.00%, more preferably 0.01% or more and less than 2.00%, and even more preferably 0.01% or more and 1.50% or less. Ca may also be 1.00% or less, 0.60% or less, or 0.50% or less.
  • Y, La, Ce, and Sr are each 0% to 0.50%, preferably more than 0% and less than 0.50%, and more preferably 0.01% or more and less than 0.50%. Furthermore, each element may be 0.01% or more, 0.40% or less, or 0.30% or less.
  • Element group A forms compounds with Al and Zn in the plating structure. Taking Ca as an example, when it contains more than 0%, preferably 0.01% or more, Al-Ca-Zn compounds are formed, and when Si is also present, Al-Ca-Si compounds are easily formed. Furthermore, when Y, La, Ce, and Sr are contained, the Ca in the above compounds is replaced by the respective elements.
  • Element group B Sn: 0% to 3.00% Bi: 0% to 1.00% In: 0% to 1.00%
  • the elements in element group B are optional elements, but these elements have the function of improving sacrificial corrosion protection. However, these elements tend to bond more strongly with Mg than Zn, and the effect of the contained Mg is reduced, so there is an upper limit to the content of these elements. If the upper limit is exceeded, adhesion of dross and the like increases, and corrosion resistance also tends to deteriorate. Therefore, Sn is set to 0 to 3.00%, more preferably more than 0% and less than 3.00%. Sn may be 0.01% or more, 0.05% or more, 2.50% or less, 2.00% or less, or 1.50% or less.
  • Bi is set to 0% to 1.00%, more preferably more than 0% and less than 1.00%.
  • Bi may be 0.01% or more, 0.05% or more, 0.80% or less, 0.50% or less, or 0.40% or less.
  • In is set to 0% to 1.00%, more preferably more than 0% and less than 1.00%.
  • In may be 0.01% or more, 0.05% or more, 0.80% or less, 0.50% or less, or 0.40% or less.
  • Element group C B 0% to 1.00%
  • P 0% to 0.50%
  • B and P which are elements of element group C, are elements belonging to metalloids. These elements are optional, but B acts as a solidification nucleus of the Al primary crystal as AlB2 , and refines the Al primary crystal, thereby improving the workability of the Al primary crystal. However, the effect is not large and does not reach the effect of Ti and Zr. P does not have the effect of refining the Al primary crystal, but improves corrosion resistance.
  • There is an upper limit to the content of each element and if the upper limit of the content is exceeded, adhesion of dross etc. increases, and the appearance and corrosion resistance tend to deteriorate.
  • Element group D Cr 0% to 0.25% V: 0% to 0.25% Ni: 0% to 1.0% Co: 0% to 0.25% Nb: 0% to 0.25% Cu: 0% to 1.0% Mn: 0% to 0.25% Mo: 0% to 0.25% W: 0% to 0.25% Ag: 0% to 1.00% Li: 0% to 0.50% Na: 0% to 0.05% Ba: 0% to 0.25% K: 0% to 0.05% Fe: 0% to 5.0%
  • the element group D is a metal element and is an optional added element, but the incorporation of these elements into the plating layer improves the corrosion resistance.
  • the content of each element has an upper limit, and if the content exceeds the upper limit, the adhesion of dross and the like tends to increase. Therefore, Cr, V, Co, Nb, Mn, Mo, W, and Ba are each set to 0% to 0.25%, preferably 0% to 0.25%, 0.01% to 0.20%, or 0% to 0.10%.
  • Ni, Cu, and Ag are each set to 0% to 1.0%, preferably 0% to 1.0%, 0% to 0.5%, 0% to 0.20%, or 0% to 0.10%.
  • Ni, Cu, and Ag may each be 0.01% or more, or 0.05% or more.
  • Li is set to 0% to 0.50%, preferably 0% to 0.10%. Li may be 0.01% or more.
  • Na and K are 0% to 0.05%, preferably more than 0% and 0.03% or less. Na and K may be 0.01% or more.
  • Fe may be inevitably contained in the plating layer. This is because Fe may diffuse from the base steel into the plating layer during plating production. Therefore, the Fe content is 0% to 5.0%, and may be preferably more than 0% and 2.0% or less, more than 0% and 1.5% or less, more than 0% and 1.2% or less, or more than 0% and 1.0% or less. Fe may be 0.1% or more, 0.3% or more, 0.5% or more, or 0.9% or less.
  • Element Group E Sb: 0% to 0.50%
  • Pb 0% to 0.50%
  • Sb and Pb, which are in element group E are optional elements with properties similar to those of Zn.
  • the inclusion of these elements has the effect of making it easier to form a spangle pattern on the appearance of the plating.
  • excessive inclusion of these elements may reduce corrosion resistance. Therefore, the contents of Sb and Pb are each set to 0% to 0.50%, and preferably set to more than 0% and not more than 0.50%, more than 0% and not more than 0.40%, or more than 0% and not more than 0.10%.
  • Sb and Pb may each be 0.01% or more, or 0.05% or more.
  • Zn 50.0% or more and impurities
  • Zn is a low melting point metal and exists on the steel material as the main phase of the plating layer.
  • Zn is an element necessary for ensuring corrosion resistance and obtaining sacrificial corrosion protection for the steel material. If the Zn content is less than 50.0%, the main component of the metal structure of the Zn-Al-Mg alloy layer is the Al phase, and the Zn phase that exhibits sacrificial corrosion protection is insufficient. Therefore, the Zn content is set to 50.0% or more. More preferably, it is set to 60.0% or more, or 70.0% or more. The upper limit of the Zn content is the amount that is the balance other than elements other than Zn and impurities. The Zn content may be 85.0% or less.
  • impurities in the plating layer refer to components contained in the raw materials, components mixed in during the manufacturing process, and components other than the above-mentioned optional added elements that are contained to the extent that they do not affect the effects of the present invention.
  • trace amounts of components other than Fe may be mixed into the plating layer as impurities due to mutual atomic diffusion between the steel material (base steel) and the plating bath.
  • the plating layer of this embodiment does not exclude the inclusion of elements other than those listed above, so long as they do not affect the effects of the present invention. "Does not affect the effects of the present invention” refers to a case in which an evaluation of A or higher is obtained in the corrosion resistance evaluation and workability evaluation described below.
  • the plating layer according to this embodiment preferably has a total of Al, Mg, and Zn of 83.7% or more, may be 90.0% or more, or may be 94.7% or more.
  • the plating layer is stripped and dissolved with 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.
  • ICP emission spectroscopy or ICP-MS to obtain the chemical composition.
  • 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/m 2 ) can also be obtained at the same time.
  • the ratio of the phases contained in the plating layer greatly affects the performance of the plating layer. Even if the plating layer has the same component composition, the phase or structure contained in the metal structure changes depending on the manufacturing method, resulting in different performance.
  • the metal structure of the plating layer can be easily confirmed by a scanning electron microscope with an energy dispersive X-ray analyzer (SEM-EDS). By obtaining, for example, a reflected electron image in any vertical cross section (thickness direction) of the mirror-finished plating layer, the approximate state of the metal structure of the plating layer can be confirmed.
  • the SEM field of view for the plating layer may be a local field of view, 25 fields of view may be selected from any cross section to obtain average information of the plating layer. In other words, the metal structure in a total field of view of 25,000 ⁇ m2 may be observed to determine the area ratio and size of the phase or structure that constitutes the metal structure of the plating layer.
  • Backscattered electron images taken by SEM are advantageous in that they allow easy identification of the phases or structures contained in the plating layer. Elements with small atomic numbers, such as Al, appear black, while elements with large atomic numbers, such as Zn, appear white, making it easy to read the proportions of these structures.
  • the composition of the phase can be pinpointed in EDS analysis, and the phase can be identified by reading the phases with approximately the same components through element mapping, etc.
  • element mapping can be used to distinguish phases with approximately the same composition. If a phase with approximately the same composition can be identified, it is possible to know the area of that crystalline phase in the observation field. Once the area is known, the equivalent circular diameter can be calculated. In addition, the area ratio of each phase in the observed field of view can be determined. The area ratio of a specific phase to the plating layer corresponds to the volume ratio of that phase in the plating layer.
  • the plating layer according to the present embodiment includes an MgZn 2 phase, an Al primary crystal containing an Al phase, and an [Al/Zn/MgZn 2 ternary eutectic structure].
  • the plating layer may further include a remaining structure.
  • the Al primary crystal is composed of an Al phase alone, or is composed in a form in which the Al phase occupies the center of the dendrite and the Al-Zn phase occupies the outer periphery.
  • the content ratio of the phases and structures in the plating layer is preferably, in terms of area fraction when observed in a scanning electron microscope in any vertical cross section (thickness direction) of the plating layer, the area fraction of the MgZn 2 phase is 15% to 50%, the total area fraction of the Al phase and the Al-Zn phase is 15% to 70%, the area fraction of the [Al/Zn/MgZn 2 ternary eutectic structure] is 0% to 60%, and the area fraction of the other phases is 0% to 10%.
  • the area fraction of the phases and structures in the plating layer is not limited to the above range.
  • the MgZn 2 phase is a region in the coating layer where Mg is 16 mass% ( ⁇ 5%) and Zn is 84 ( ⁇ 5%).
  • the MgZn 2 phase is often photographed in a backscattered electron image of an SEM as a gray intermediate color between Al and Zn.
  • the MgZn 2 phase can be clearly distinguished from the Al phase, the Al-Zn phase, the [Al/Zn/MgZn 2 ternary eutectic structure], etc.
  • the MgZn 2 phase in the plating layer When the ratio of the MgZn 2 phase in the plating layer is high, the corrosion resistance is improved.
  • the MgZn 2 phase which is called the Laves phase, may reduce the workability of the plating layer. Therefore, from the viewpoint of corrosion resistance, the more the MgZn 2 phase, the more preferable it is, but from the viewpoint of ensuring workability, an upper limit may be set.
  • the ratio of the MgZn 2 phase in the plating layer may be 15% or more and 50% or less in area ratio in order to balance corrosion resistance and workability.
  • the area ratio of the MgZn 2 phase may be 20% or more, 25% or more, 45% or less, or 40% or less.
  • the Al phase constituting the Al primary crystal is a region in the plating layer where the Al content exceeds 40 mass%.
  • the Al phase may contain Zn, but the Zn content is less than 60 mass%.
  • the Al phase can be clearly distinguished from other phases and structures in the backscattered electron image of the SEM. That is, the Al phase is often shown as the darkest in the backscattered electron image of the SEM.
  • the Al phase takes various forms in any cross section, such as a block shape, or a dendritic cross section such as a circular or flat shape.
  • the Al contained in the [Al/Zn/MgZn 2 ternary eutectic structure] is not included in the Al phase.
  • the area ratio of the Al phase in the plating layer is not particularly limited, but may be 5% or more, 10% or more, 20% or more, or 25% or more.
  • the Al phase may be 60% or less, 55% or less, or 50% or less.
  • the Al phase has superior plastic deformability compared to the MgZn 2 phase and the ternary eutectic structure of Al/Zn/MgZn 2.
  • the Al phase has a face-centered cubic crystal structure and is known to have orientation dependency on processing. In the case of bending, if the preferred orientation on the surface of the plating layer is the (100) plane, the plastic deformability of the plating layer is improved, and the plating layer stretches in response to processing, so that plating cracks in the processed part are reduced.
  • the tendency of the development of the preferred orientation differs depending on the Al content of the plating layer. When the Al content is low and the Zn content is high, the (110) plane becomes the preferred orientation, and as the Al content increases, the preferred orientation changes to the (100) plane.
  • the preferred orientation of the Al phase on the surface of the plating layer can be derived by performing X-ray diffraction. For example, when X-ray diffraction is measured with a Cu source under output conditions of 50 KV-300 mA, the 2 ⁇ peak appears at around 38.47° for the (111) plane, around 44.74° for the (200) plane, around 65.13° for the (220) plane, and around 78.23° for the (311) plane.
  • the (200) plane is parallel to the (100) plane and the (220) plane is parallel to the (110) plane, when evaluating the preferred orientation on the surface of the plating layer by X-ray diffraction, the (200) plane can be substituted for the (100) plane, and the (220) plane can be substituted for the (110) plane.
  • the (100) plane appears as the preferred orientation on the surface of the plating layer can be confirmed by the ratio of the peak intensity of the (200) plane to the peak intensity of other orientation planes.
  • the (100) plane becomes the preferred orientation for the surface of the plating layer, and the workability of the plating layer can be improved.
  • I(200) Al is the diffraction intensity of Al (200)
  • I(111) Al is the diffraction intensity of Al (111)
  • I(220) Al is the diffraction intensity of Al (220)
  • I(311) Al is the diffraction intensity of Al (311).
  • the value of formula (1) may be 0.7 or less.
  • the measurement method for I(200) Al / ⁇ (I(111) Al +I(220) Al +I(200) Al +I(311) Al ⁇ defined in formula (1) is as follows. First, the surface of the plating layer is mechanically polished, and if necessary, chemically polished to make the surface of the plating layer in a mirror state.
  • an X-ray diffraction measurement is performed using an X-ray diffractometer (manufactured by Rigaku Corporation (model number RINT-TTR III)) with an X-ray output of 50 kV, 300 mA, a copper target, a goniometer TTR (horizontal goniometer), a K ⁇ filter slit width of 0.05 mm, a longitudinal limiting slit width of 2 mm, a receiving slit width of 8 mm, and a receiving slit 2 open, and with the measurement conditions of a scan speed of 5 deg./min, a step width of 0.01 deg, and a scan axis 2 ⁇ (5 to 90°).
  • the diffraction intensity of Al (200) is (maximum intensity in the range of 44.74° ⁇ 0.20°), the diffraction intensity of Al (111) (maximum intensity in the range of 38.47° ⁇ 0.20°), the diffraction intensity of Al (220) (maximum intensity in the range of 65.13° ⁇ 0.20°), and the diffraction intensity of Al (311) (maximum intensity in the range of 78.23° ⁇ 0.20°) are measured.
  • the diffraction intensity is the intensity excluding the background intensity. From the obtained diffraction intensities, I(200) Al / ⁇ (I(111) Al +I(220) Al +I(200) Al +I(311) Al ⁇ is calculated.
  • the total area of the Al phases contained in the plating layer that have a circle equivalent diameter of 20 ⁇ m or less is preferably 50% or more as a ratio to the total area of all the Al phases. That is, in a cross section in the thickness direction of the plating layer, the ratio of the total area of the Al phases that have a circle equivalent diameter of 20 ⁇ m or less to the total area of the Al phases is preferably 50% or more. In this way, the Al phases that have a circle equivalent diameter of 20 ⁇ m or less occupy an area of 50% or more of the total area of the Al phases, so that the Al primary crystals become finer and the workability of the plating layer can be further improved.
  • the area ratio of the total area of the Al phases that have a circle equivalent diameter of 20 ⁇ m or less to the total area of the Al phases in the thickness direction of the plating layer may be 70% or more.
  • the upper limit value may be 100%.
  • the method for measuring the area ratio of Al phases with a circle equivalent diameter of 20 ⁇ m or less is to extract the Al phases from an image in a specified observation field, measure the area of each Al phase, and derive the circle equivalent diameter.
  • the specific measurement method is explained below.
  • the observation field is a total of 25,000 ⁇ m2 used to confirm the phase and structure of the plating layer.
  • the composition of the phase is pinpointed, and the Al phase is identified by reading the approximately equivalent component phase from the contrast of the SEM image, element mapping, etc. Since the Al phase is a light element, it can be grasped as a black area in the backscattered electron image of the SEM.
  • the Al phase can be identified by element mapping.
  • the method of identifying the Al phase is not limited to the above, and for example, EPMA mapping may be used.
  • the Al phase in the observation field is extracted by image processing, and the area of each is measured.
  • the equivalent circle diameter of each Al phase can be calculated. Then, the Al phase with a circle equivalent diameter of 20 ⁇ m or less is extracted, and the total area is calculated. Then, the area ratio (%) of the Al phase with a circle equivalent diameter of 20 ⁇ m or less to the total area of the Al phase in the observation field is calculated.
  • the Al-Zn phase is a phase containing 60% or more of Zn and Al.
  • the Al-Zn phase is an aggregate of a fine Zn phase with a grain size of about 1 ⁇ m (hereinafter referred to as a fine Zn phase) and a fine Al phase with a grain size of less than 1 ⁇ m (hereinafter referred to as a fine Al phase).
  • a fine Zn phase a fine Zn phase with a grain size of less than 1 ⁇ m
  • Al has a structure different from the crystal structure at room temperature (e.g., 25° C.), making it possible to dissolve a large amount of Zn phase, and exists as a high-temperature stable phase containing about 60% of Zn phase.
  • the content of the Zn phase in this high-temperature stable phase is extremely reduced, and Al and Zn are equilibrated and exist as an Al-Zn phase containing a fine Al phase and a fine Zn phase. That is, the Al-Zn phase is a phase containing a fine Zn phase at a ratio of 60% or more by mass.
  • This Al-Zn phase has different properties from the Al phase and Zn phase contained in the plating layer, and is distinguished on a backscattered electron SEM image and wide-angle X-ray diffraction.
  • a phase in which the Al component is 15 to 40 mass % and the Zn component is 60 to 85 mass % is defined as an Al-Zn phase.
  • the Al-Zn phase is an aggregate of fine Al and Zn phases, and therefore has superior plastic deformability compared to the MgZn 2 phase and the [Al/Zn/MgZn 2 ternary eutectic structure].
  • its corrosion resistance is considered to be inferior to the MgZn 2 phase, the [Al/Zn/MgZn 2 ternary eutectic structure] and the Al phase.
  • the area ratio of the Al-Zn phase there are no particular restrictions on the area ratio of the Al-Zn phase, but it may be 5% or more or 10% or more. Also, the area ratio of the Al-Zn phase may be 20% or less, or 15% or less.
  • the total area ratio of the Al primary crystals i.e., the Al phase and the Al-Zn phase
  • the total area ratio of the Al phase and the Al-Zn phase may be 20% or more, 25% or more, or 30% or more, and may be 65% or less, 60% or less, 55% or less, or 50% or less.
  • the [Al/Zn/MgZn 2 ternary eutectic structure] is a eutectic structure consisting of an Al phase, an MgZn2 phase, and a Zn phase, and is clearly distinguished from the MgZn2 phase contained as the main phase of the plating layer and the above-mentioned Al phase in a backscattered electron SEM image.
  • [Al/Zn/MgZn 2 ternary eutectic structure] containing Zn phase By allowing a certain amount of [Al/Zn/MgZn 2 ternary eutectic structure] containing Zn phase to exist, sacrificial corrosion protection is ensured and end surface corrosion resistance is improved.
  • [Al/Zn/MgZn 2 ternary eutectic structure] may be 60 area% or less. Furthermore, it may be 40 area% or less, 35 area% or less, or 30 area% or less. There is no particular limit to the lower limit of the area ratio of [Al/Zn/MgZn 2 ternary eutectic structure], and it may be 0%, 5 area% or more, 10 area% or more, or 15 area% or more.
  • the Mg2Zn11 phase is a region where Mg is 5 mass % ( ⁇ 3%) and Zn is 93 ( ⁇ 4%).
  • the Mg2Zn11 phase is often photographed in a backscattered electron image of an SEM as a gray intermediate color between Al and Zn, and is brighter than the MgZn2 phase.
  • the Mg2Zn11 phase has even poorer plastic deformability than the MgZn2 phase, so it is better not to precipitate it in the coating structure.
  • the presence of Mg in the coating structure is preferably in the form of the MgZn2 phase, [a ternary eutectic structure of Al/Zn/ MgZn2 ], or the Mg2Si phase described below.
  • the ratio of the diffraction intensity of the (322) plane of the Mg 2 Zn 11 phase (maximum intensity in the range of 43.60° ⁇ 0.20°; hereinafter referred to as I(322) Mg2Zn11 ) to the diffraction intensity of the (201) plane of the MgZn 2 phase (maximum intensity in the range of 41.30° ⁇ 0.20°; hereinafter referred to as I(201) MgZn2 ) may satisfy I(322) Mg2Zn11 /I(201) MgZn2 / ⁇ 0.2, or more preferably, may satisfy 0.1 or less.
  • the plating bath composition and the cooling rate after pulling up from the plating bath affect the precipitation of the Mg 2 Zn 11 phase, and the plated steel sheet produced in this embodiment satisfies I(322) Mg2Zn11 /I(201) MgZn2 / ⁇ 0.2, and the proportion of the Mg 2 Zn 11 phase in the plating structure is less than 1 area %.
  • the above phases and structures constitute the main phase of the coating layer, and they account for 90% or more of the area fraction of the coating layer.
  • elements other than Zn, Mg, and Al are contained in the coating layer to form other metal phases.
  • Si forms Mg 2 Si phase, etc.
  • Ca forms Al-Zn-Ca phase, etc.
  • Representative components of the remaining structure may include Mg 2 Si phase, AlZnCa phase, AlCaSi phase, etc. Although some of these are effective in improving weldability and corrosion resistance, their influence is not significant. Because of the composition of the coating layer, it is difficult for these to exceed 10 area % in total, so they may be 10 area % or less.
  • the plated steel material of this embodiment can be manufactured using either an immersion plating method (batch method) or a continuous plating method.
  • the size, shape, surface form, etc. of the steel material to be plated There are no particular restrictions on the size, shape, surface form, etc. of the steel material to be plated. Any steel material, including ordinary steel, high-tensile steel, and stainless steel, can be used. Steel strips of general structural steel are most preferable. Surface finishing may be performed in advance using shot blasting, abrasive brushes, etc., and there is no problem in plating after attaching a metal or alloy film of 3 g/m2 or less of Ni, Fe, Zn, Sn, plating, etc. to the surface. In addition, as a pre-treatment of the steel material, it is preferable to thoroughly clean the steel material by degreasing and pickling.
  • the steel surface is sufficiently heated and reduced by a reducing gas such as H2
  • a reducing gas such as H2
  • the steel is immersed in a plating bath prepared with a predetermined composition.
  • a reducing gas such as H2
  • a steel surface with fine grain size and an internal oxide coating layer are observed on the base steel side, but this does not affect the performance of the present invention.
  • the composition of the plating layer can be controlled by the composition of the plating bath that is prepared.
  • the plating bath is prepared by mixing a specified amount of pure metals, for example by melting in an inert atmosphere, to produce an alloy of the plating bath components.
  • a plating layer with approximately the same composition as the plating bath is formed. If the immersion time is extended or if it takes a long time for solidification to be completed, the formation of the interface alloy layer becomes active, and the Fe concentration may become high, but below 500°C, the reaction with the plating layer slows rapidly, so the Fe concentration in the plating layer is usually below 5.0%.
  • the hot-dip plating layer it is preferable to keep the plating bath at 450°C to 550°C. It is then preferable to immerse the reduced steel material for several seconds. On the surface of the reduced steel material, Fe diffuses into the plating bath and reacts with the plating bath, which may result in the formation of an interfacial alloy layer at the interface between the plating layer and the steel material.
  • the interfacial alloy layer is mainly an Al-Fe intermetallic compound layer (Al-Fe alloy layer).
  • Al-Fe alloy layer Al-Fe intermetallic compound layer
  • N2 wiping is performed to adjust the plating layer to a predetermined thickness.
  • the thickness of the plating layer is preferably adjusted to 10 to 70 ⁇ m. This corresponds to a coating weight of the plating layer of 40 to 450 g/ m2 (one side).
  • the applied molten metal is solidified.
  • the cooling method during plating solidification may be by spraying nitrogen, air, or a hydrogen/helium mixed gas, or it may be mist cooling or submersion in water. Mist cooling is preferred, and mist cooling using nitrogen containing water is preferable.
  • the cooling rate may be adjusted by the water content.
  • the structure when the plating solidification conditions are normal operating conditions, for example, when cooling from the plating bath temperature to 150°C at an average cooling rate of 5 to 20°C/sec, the structure may not be controlled, and the specified performance may not be met. Therefore, the cooling process that makes it possible to obtain the plating layer of this embodiment is described below.
  • Average cooling rate between bath temperature and 380°C more than 20°C/sec, less than 50°C/sec
  • the Al phase precipitates as the primary crystal, followed by the MgZn2 phase.
  • the average cooling rate it is necessary to set the average cooling rate to at least less than 50°C/sec.
  • the average cooling rate is 20°C/sec or less, the Al primary crystal tends to become coarse and the workability tends to decrease. Therefore, in the region between the bath temperature and 380°C, the average cooling rate needs to be more than 20°C/sec, less than 50°C/sec.
  • Average cooling rate between 380°C and 300°C 5°C/sec or more, less than 15°C/sec
  • Al-Zn phase precipitation from the liquid phase and ternary eutectic reaction of Zn-Al-MgZn 2 occur, the liquid phase disappears and the plating layer is completely solidified.
  • Mg 2 Zn 11 phase may be formed. If the Mg 2 Zn 11 phase precipitates, the workability tends to deteriorate, so it is preferable that the average cooling rate between 380°C and 300°C is less than 15°C/sec.
  • the average cooling rate is preferably 5° C./sec or more and less than 15° C./sec, and more preferably 5° C./sec or more and 10° C./sec or less.
  • Average cooling rate between 300°C and 150°C more than 10°C/sec, 20°C/sec or less
  • the fine Zn phase incorporated in the Al-Zn phase is rapidly expelled from the Al-Zn phase. Therefore, if cooling is performed slowly in this temperature range, the proportion of the Al phase in the primary Al crystal increases. This tendency becomes stronger especially when the Al concentration is high, and when the cooling rate between 300°C and 150°C is 20°C/sec or less, the Al-Zn phase separates into the Al phase and the Zn phase.
  • the cooling rate is 10°C/sec or less
  • the grains of the ternary eutectic structure grow, forming coarse MgZn 2 phase and Mg 2 Zn 11 phase, and the workability tends to deteriorate. Therefore, in the temperature range between 300°C and 150°C, it is preferable to cool at an average cooling rate of more than 10°C/sec, 20°C/sec or less.
  • the cooling rate in the temperature range below 150° C. during the solidification process does not affect the constituent phases in the plating layer, so there is no need to limit the cooling conditions, and natural cooling may be used.
  • 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 directly on the plating layer include, for example, chromate coatings, phosphate coatings, and chromate-free coatings.
  • the chromate treatment, phosphate treatment, and chromate-free treatment for forming these coatings can be performed by known methods. However, since many chromate treatments can deteriorate the weldability on the surface of the plating layer, it is preferable to keep the thickness less than 1 ⁇ m in order to fully bring out the effect of improving weldability in the plating layer.
  • 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
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the corrosion resistance of the plating layer can be evaluated by subjecting it to an accelerated corrosion test such as JASO. Specifically, the number of cycles (time) until red rust appears is compared, and a longer number of cycles until rust appears is evaluated as having better corrosion resistance, and a shorter number of cycles until rust appears is evaluated as having worse corrosion resistance. Since the number of cycles until red rust appears also varies depending on the coating weight of the plating layer, it is desirable to make the coating weight of the plating steel materials to be compared the same.
  • the workability of the plating layer can be evaluated by bending the plated material and measuring the number of cracks in the plated layer in the bent area. The fewer the cracks in the plated layer, the better the workability. If there are no cracks in the plated layer, the wear of the plated layer due to sacrificial corrosion protection is reduced, and the corrosion resistance of the bent area becomes equal to that of the flat area.
  • the plated steel material was cut out from a cold-rolled steel sheet with a thickness of 0.8 mm to a size of 180 mm x 100 mm. Both were SS400 (general steel). Using a batch-type hot-dip galvanizing simulator (manufactured by Rhesca), a K thermocouple was attached to a part of the steel sheet, and the steel sheet surface was sufficiently reduced by annealing at 800°C in a reducing atmosphere of N2 containing 5% H2 , and then immersed in a plating bath for 3 seconds, and then pulled out and N2 gas wiped to make the plating thickness 20 ⁇ m ( ⁇ 1 ⁇ m). The plating thickness on the front and back was the same. After pulling out from the plating bath, plated steel materials were produced under various cooling conditions A to E below.
  • Condition B (comparison condition): After the steel was removed from the plating bath, the average cooling rate between the bath temperature and 150°C was 20°C/s. Below 150°C, it was left to cool naturally.
  • Condition C (comparison condition): After the steel was removed from the plating bath, the average cooling rate between the bath temperature and 150°C was 2°C/s. Below 150°C, it was left to cool naturally.
  • Condition D (comparison condition): After the steel was removed from the plating bath, the average cooling rate between the bath temperature and 150°C was 60°C/s. Below 150°C, it was left to cool naturally.
  • Condition E (comparison condition): After the steel was removed from the plating bath, the average cooling rate was 30°C/s between the bath temperature and 380°C, 1°C/s between 380°C and 300°C, and 15°C/s between 300°C and 150°C. Below 150°C, it was left to cool.
  • the average chemical composition of the plating layer was measured as follows. The plating layer was stripped and dissolved using an acid containing an inhibitor that suppresses corrosion of the base steel (steel material) to obtain an acid solution. The resulting acid solution was then measured using ICP atomic emission spectrometry or ICP-MS to obtain the average chemical composition of the plating layer. The results are shown in Tables 1A to 1F.
  • the method for measuring the area ratio of the phases and structures (MgZn 2 phase, Al phase, Al-Zn phase, [Al/Zn/MgZn 2 ternary eutectic structure], and the remaining structure) in the coating layer was as described above, in which a cross section of the coating layer in the thickness direction perpendicular to the surface of the steel material was exposed, and the metal structure was confirmed in a field of view of 500 to 5000 times. Specifically, the metal structure in a field of view of 25000 ⁇ m 2 in total was observed to determine the area ratio of the phase or structure constituting the metal structure of the coating layer.
  • the composition of the phase was pinpointed in the EDS analysis, and the phases with approximately the same composition were identified by reading them from elemental mapping. By performing elemental mapping, it was possible to distinguish phases with approximately the same composition.
  • the area ratio of the Al phase with a circle equivalent diameter of 20 ⁇ m or less was determined by pinpointing the phase composition in the EDS analysis of the above-mentioned 25,000 ⁇ m2 observation field, reading approximately equivalent component phases from element mapping, and identifying the Al phase. Next, the Al phase in the observation field was extracted by image processing, the crystal area of each was measured, and the equivalent circle diameter of each crystal was calculated. Furthermore, the Al phase with a circle equivalent diameter of 20 ⁇ m or less was extracted, and the total area was calculated. Then, the area ratio (%) of the Al phase with a circle equivalent diameter of 20 ⁇ m or less to the total area of the Al phase in the observation field was calculated.
  • the test material was cut to 50 x 100 mm, the end faces were not painted and sealed, and a composite cycle test was performed in accordance with JASO M609 and M610 to evaluate the corrosion resistance. Specifically, a salt-dry-wet cycle test was performed in which salt spray, drying and wetting were repeated. In the salt-dry-wet cycle test, the test material was sprayed with 5% NaCl aqueous solution (2 hours at 35°C), dried (4 hours at 30% relative humidity and 60°C), and wetting (2 hours at 95% relative humidity and 50°C) as one cycle. After washing and drying at the end of each cycle, the surface of the test material was observed and the area ratio of red rust was calculated.
  • the area ratio of red rust was calculated by taking a photograph of the surface of the test material after the salt-dry-wet cycle test, binarizing the photograph by image analysis, calculating the area per pixel, and counting the number of pixels in the rusted area.
  • the area ratio of red rust was calculated by the following formula.
  • Area ratio of red rust (%) area of rusted part (mm 2 ) / total area of observed part (mm 2 ) ⁇ 100
  • Red rust was considered to have occurred when the red rust area ratio was 5% or more.
  • Corrosion resistance was evaluated as follows. “B” was a failure, and “A” to “S” were passes. The results are shown in Tables 3A and 3B.
  • B Red rust was observed within less than 200 cycles.
  • A Red rust occurred after 200 cycles.
  • AA Red rust occurred after more than 200 but less than 350 cycles.
  • AAA Red rust occurred after 350 to less than 500 cycles.
  • S No red rust was observed after 500 cycles.
  • the test material was cut into a size of 30 mm (C direction) x 100 mm (L direction) and subjected to 5t 180° bending. That is, when bending the test material, five plates of the same thickness as the test material were sandwiched and bent 180°. After that, the number of cracks in the range of 30 mm x 1.6 mm at the top of the bent part was measured with a stereo microscope at 40 times magnification and judged as follows. The results are shown in Table 3.
  • A Number of cracks is 20 or more but less than 30 AA: Number of cracks is 10 or more but less than 20 AAA: Number of cracks is 5 or more but less than 10 S: Number of cracks is less than 5
  • Nos. 3 to 43, 53 and 54 had appropriately controlled chemical compositions and metal structures of the plating layers, and were excellent in both corrosion resistance and workability.
  • the Mg 2 Zn 11 phase was not included.
  • Comparative example No. 44 had excessive amounts of Al and Mg in the hot-dip plating layer. As a result, No. 44 was deficient in both corrosion resistance and workability.
  • Comparative example No. 45 had an excessive amount of Al in the hot-dip plating layer. No. 45 had insufficient corrosion resistance.
  • Comparative example No. 47 had an excessive amount of Ca in the hot-dip plating layer. In addition, the manufacturing conditions were outside the range of preferred conditions. No. 47 lacked both corrosion resistance and workability.
  • the comparative examples Nos. 48, 49, and 50 were produced under conditions outside the range of preferred conditions.
  • I(200) Al / ⁇ (I(111) Al +I(220) Al +I(200) Al +I(311) Al ⁇ was less than 0.40. Therefore, Nos. 48, 49, and 50 had poor processability.
  • Comparative example No. 51 had an excessive amount of Zr in the hot-dip plating layer. As a result, No. 51 had insufficient corrosion resistance.
  • the present invention has industrial applicability in that it can provide plated steel material that has excellent corrosion resistance and excellent workability of the plating layer.

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  • Physical Vapour Deposition (AREA)

Abstract

Le matériau d'acier plaqué selon la présente invention comprend une couche de placage qui contient, en termes de % en masse, 10,0 à 40,0 % d'Al, 5,0 à 12,5 % de Mg, 0 à 1,0 % de Ti, et 0 à 1,0 % de Zr, le reste étant au moins 50 % de Zn et des impuretés. Le total de Ti plus Zr est de 0,001 % ou plus, et l'intensité de diffraction telle que déterminée par diffraction aux rayons X de la couche de placage satisfait la formule (1). Formule (1) : I(200)Al / {(I(111)Al + I(220)Al + I(200)Al + I(311)Al} ≥ 0,40. Dans la formule (1), I(200)Al est l'intensité de diffraction de l'Al (200), I(111)Al est l'intensité de diffraction de (111) de l'Al, I(220)Al est l'intensité de diffraction de (220) de l'Al, et I(311)Al est l'intensité de diffraction de (311) de l'Al.
PCT/JP2024/028649 2023-08-10 2024-08-09 Matériau d'acier plaqué Pending WO2025033539A1 (fr)

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AU2024322687A AU2024322687A1 (en) 2023-08-10 2024-08-09 Plated steel material

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JP2023-131415 2023-08-10

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011001662A1 (fr) * 2009-06-30 2011-01-06 新日本製鐵株式会社 TÔLE D'ACIER TREMPÉE À CHAUD DANS UN BAIN DE Zn-Al-Mg ET SON PROCÉDÉ DE FABRICATION
JP2023530374A (ja) * 2020-06-19 2023-07-14 ポスコ カンパニー リミテッド 耐食性、加工性及び表面品質に優れためっき鋼板、並びにその製造方法

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011001662A1 (fr) * 2009-06-30 2011-01-06 新日本製鐵株式会社 TÔLE D'ACIER TREMPÉE À CHAUD DANS UN BAIN DE Zn-Al-Mg ET SON PROCÉDÉ DE FABRICATION
JP2023530374A (ja) * 2020-06-19 2023-07-14 ポスコ カンパニー リミテッド 耐食性、加工性及び表面品質に優れためっき鋼板、並びにその製造方法

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