TWI504754B - Plated steel sheet with quasicrystal - Google Patents

Description

Plated steel plate with quasicrystal Field of invention

The present invention relates to a surface treated steel sheet having excellent corrosion resistance, and more particularly to a plated steel sheet containing a quasicrystal.

Background of the invention

Quasicrystal system A crystal structure first discovered by Daniel Shechtman in 1982, which has an atomic arrangement of icosahedron. It is known that the crystal structure has an excellent rotational symmetry which is not obtained by a usual metal or alloy, a non-periodic crystal structure such as a fifth-order symmetry, and a non-period represented by a three-dimensional Penrose pattern. Sex structure and equivalent crystal structure.

It has been found that after the configuration of the novel metal atom, that is, the novel crystal structure, a quasicrystal system having a quasi-periodic structure and excellent rotational symmetry is attracting considerable attention. In recent years, it has been clearly understood that a quasicrystal can also be obtained by crystal growth. Conventionally, a method of producing a quasicrystal is usually a liquid quenching method. Therefore, since the shape is limited to powders, foils, and small pieces, practical examples of products using quasicrystals are very few.

Patent Documents 1 and 2 disclose a high strength Mg-based alloy and Production method. These Mg-based alloys are alloys having excellent strength and elongation in which a hard quasicrystal phase having a particle diameter of several tens of nm to several hundreds nm is dispersed and precipitated in a metal structure. In these Patent Documents 1 and 2, the quasicrystal is used as a hard property.

Patent Document 3 discloses a thermoelectric material using an Al reference crystal. In Patent Document 3, a quasicrystal is used as a property having excellent thermoelectric characteristics. Patent Document 4 discloses a heat-resistant catalyst using a quasi-crystalline Al alloy (Al-based crystal) as a precursor and a method for producing the same. In Patent Document 4, a quasi-crystalline system having no periodic crystal structure is used to be brittle and easily broken. As described above, in the conventional invention, the quasicrystal is dispersed as fine particles or the quasicrystals of fine particles are solidified.

As a form of utilization of another type of these inventions, Patent Document 8 discloses that a conditioning tool containing a quasicrystal is coated with a metal. In Patent Document 8, the alloy powder containing quasicrystals excellent in corrosion resistance composed of Al, Fe, and Cr is plasma-sprayed to impart abrasion resistance and corrosion resistance to salt to the conditioning tool. Excellent coating.

As described above, the Mg-based crystal system is used as a material having excellent strength, and the Al-based crystal system is used as a member having excellent strength, a thermoelectric material, a conditioning tool, or the like. However, such utilization is limited, and quasicrystals may not be said to have been utilized in many fields.

Quasicrystal systems have excellent properties derived from unique crystalline structures. However, its characteristics are only partially explained, and it cannot be said that it is a material that has been widely used in industry at present. The present inventors attempted to apply a quasicrystal which is almost unutilized in the industry to gold used for surface-treated steel sheets. It is a coating layer that improves corrosion resistance.

In general, when the steel sheet is continuously used for a long period of time, the steel sheet has a certain anti-corrosion function by performing surface treatment such as metal coating, coating treatment, chemical treatment, or organic coating lamination. Many steels used in the fields of automobiles, home appliances, and building materials are mainly subjected to metal coating treatment. By the metal coating layer, the barrier corrosion resistance of the shielding base iron (steel material) to the external environment can be preferentially provided, and the sacrificial corrosion prevention effect of the base iron corrosion can be prevented by preferentially causing corrosion than the base iron.

As an industrial method for forming a metal coating layer, various methods are employed. In order to have a thickness of the metal coating layer, a melt method, a hot-dip plating method, or the like is suitable, and in order to uniformly form the metal coating layer, a sputtering method, an ion plating method, a vapor deposition method, a plating method, or the like is used. Suitable for. Among these, the hot-dip plating method is widely used because it can mass-produce a steel material having a metal coating layer at low cost.

Further, in general, the plating method is limited to the deposited metal and is limited to the elements constituting the metal coating layer. On the other hand, a method of forming a metal coating layer by metal melting, evaporation, precipitation, solidification reaction or the like by a spray method, a vapor deposition method or the like can theoretically form a metal coating layer similar to the molten plating method. However, since the metal has its own melting point and boiling point, in the spray method and the vapor deposition method, the chemical components of the alloy to be used and the chemical composition of the formed metal coating layer are likely to be separated.

In this way, it is possible to form a metal coating layer having a target chemical component by a hot-dip plating method of forming a metal coating layer having a chemical composition substantially equal to the chemical composition of the alloy used in the molten plating bath. Any other method is more excellent.

At present, a general surface-treated steel sheet which can be obtained on the market is a surface-treated steel sheet mainly having a metal coating layer of a Zn-based alloy or a metal coating layer of an Al-based alloy. The metal coating layer of the Zn-based alloy is a metal coating layer containing a small amount of elements such as Al or Mg in the main component Zn, and the metal structure as the metal coating layer contains the Al phase and the Mg _{2 in} addition to the Zn phase. Zn is equal. On the other hand, the metal coating layer of the Al-based alloy contains a small amount of a metal coating layer of an element such as Si or Fe as a main component Al, and the metal structure of the metal coating layer contains a Si phase in addition to the Al phase. Fe ₂ Al _{5 is} equal.

In the inventors of the present invention, Patent Literatures 5 to 7 disclose a Mg-based alloy plated steel material which is a plated alloy material which is completely different from the so-called ordinary surface-treated steel sheets. In order to improve the corrosion resistance of the plating layer (metal coating layer), the inventors of the present invention have further studied the improvement of the corrosion resistance by improving the corrosion resistance of the plating layer (metal coating layer).

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-113235

Patent Document 2: Japanese Patent Laid-Open Publication No. 2008-69438

Patent Document 3: Japanese Patent Publication No. 08-176762

Patent Document 4: Japanese Patent Laid-Open Publication No. 2004-267878

Patent Document 5: Japanese Patent Laid-Open Publication No. 2008-255464

Patent Document 6: Japanese Patent Laid-Open Publication No. 2010-248541

Patent Document 7: Japanese Patent Laid-Open Publication No. 2011-219823

Patent Document 8: Japanese National Official Publication No. 2007-525596

Summary of invention

The problem to be solved by the present invention is to provide a plated steel sheet which is required to be greatly improved in corrosion resistance when used in the fields of building materials, automobiles, and home appliances.

In particular, attention has been paid to the quasi-crystals which have been hardly considered for improving the corrosion resistance of the plating layer, and the composition of the metal structure which can most improve the corrosion resistance is clarified. The objective of the result is to provide an excellent corrosion resistance and sacrifice. Corrosion-resistant coated steel sheet. Specifically, the purpose is to improve the corrosion resistance, but the preferred morphology of the quasi-crystal phase that has not been studied in the past is clarified in the metal coating layer (plating layer), and The method of producing well in the coating layer is clarified to improve the corrosion resistance of the plated steel sheet and the sacrificial corrosion resistance.

The gist of the present invention is as follows.

(1) A plated steel sheet containing a quasi-crystal according to an aspect of the present invention includes a steel sheet and a metal coating layer disposed on a surface of the steel sheet; and the chemical composition of the metal coating layer is in atom%, and contains: Zn: 20%~ 60%, Al: 0.3% to 15%, Ca: 0% to 3.5%, Y: 0% to 3.5%, La: 0% to 3.5%, Ce: 0% to 3.5%, Si: 0% to 0.5% , Ti: 0%~0.5%, Cr: 0%~0.5%, Fe: 0%~2%, Co: 0%~0.5%, Ni: 0%~0.5%, V: 0%~0.5%, Nb :0%~0.5%, Cu: 0% to 0.5%, Sn: 0% to 0.5%, Mn: 0% to 0.2%, Sr: 0% to 0.5%, Sb: 0% to 0.5%, Pb: 0% to 0.5%, and remaining a part consisting of Mg and an impurity; the zinc content and the aluminum content in the chemical composition of the metal coating layer satisfy 25% ≦Zn+Al in atomic %; the metal structure of the metal coating layer contains a quasicrystal phase; The magnesium content, the zinc content, and the aluminum content contained in the quasi-crystalline phase satisfy 0.5 ≦Mg / (Zn + Al) ≦ 0.83 in atomic %; the quasi-crystalline phase has an average circular equivalent diameter of more than 1 μm to 200 μm.

(2) The plated steel sheet containing the quasicrystal according to the above (1), wherein the calcium content, the indium content, the niobium content, and the niobium content in the chemical composition of the metal coating layer are 0.3% by weight in terms of atomic %. +Y+La+Ce≦3.5%.

(3) The plated steel sheet containing the quasicrystal according to (1) or (2) above, wherein the ruthenium content, the titanium content, and the chromium content in the chemical composition of the metal coating layer are 0.005% in terms of atomic %. Si + Ti + Cr ≦ 0.5%.

(4) The quasi-crystal-containing plated steel sheet according to any one of (1) to (3) above, wherein the zinc content and the aluminum content in the chemical composition of the metal coating layer are in atom%, Satisfy 30% ≦Zn+Al≦50%, and 3≦Zn/Al≦12.

(5) The plated steel sheet containing the quasicrystal according to any one of the above items (1) to (4), wherein the metal coating layer is observed when the metal coating layer is observed in a cross section parallel to the cutting direction in the thickness direction of the sheet. The metal structure is a bimodal structure composed of a fine region and a coarse region, and the fine region is composed of crystal grains having a circle equivalent diameter of 1 μm or less, and the coarse region is larger than a circle equivalent diameter. 1 μm of crystal grains; the coarse region containing the quasicrystal phase; and the fine region containing at least one of Mg ₅₁ Zn ₂₀ phase, Mg ₃₂ (Zn, Al) ₄₉ phase, MgZn phase, MgZn ₂ phase, and Zn phase can.

(6) The plated steel sheet containing a quasicrystal according to any one of the above items (1) to (5), wherein an area fraction of the coarse region may be 5% to 80% with respect to the metal structure; In the metal structure, the area ratio of the fine region may be 20% to 95%.

(7) The plated steel sheet containing a quasicrystal according to any one of the above items (1) to (6), wherein an area fraction of the quasicrystalline phase contained in the coarse region is 80 with respect to the coarse region. % to less than 100%; and the total area fraction of the Mg ₅₁ Zn ₂₀ phase, the Mg ₃₂ (Zn, Al) ₄₉ phase, the MgZn phase, the MgZn ₂ phase, and the Zn phase contained in the fine region, It may be 80% to less than 100% with respect to the aforementioned fine area.

(8) The plated steel sheet containing the quasicrystal according to any one of the above items (1) to (7), wherein the thickness of the metal coating layer is D when viewed from the cross section, and the metal coating layer is The surface of the surface of the metal coating layer is 0.3×D in the thickness direction of the sheet, and the surface of the metal coating layer is 0.3× from the interface between the steel sheet and the metal coating layer toward the metal coating layer. When the range of D is set to a deep portion of the metal coating layer, the area ratio of the coarse region may be 10% to less than 100% with respect to the surface portion of the metal coating layer, and the coarse region may be formed with respect to the deep portion of the metal coating layer. The area fraction may be from 10% to less than 100%, and when the surface of the metal coating layer and the deep portion of the metal coating layer in the metal coating layer are the center portion of the metal coating layer, the metal coating layer is formed. The area of the aforementioned fine area of the center portion may be 50% to less than 100%.

(9) The plated steel sheet containing a quasicrystal according to any one of the above (1) to (8), wherein the metal structure of the metal coating layer may not contain a Mg phase.

(10) The quasi-crystal-containing plated steel sheet according to any one of the above (1) to (9), further comprising an Fe-Al-containing alloy layer; wherein the Fe-Al-containing alloy layer is disposed in the foregoing The steel sheet and the metal coating layer are contained; the Fe-Al-containing alloy layer contains at least one of Fe ₅ Al ₂ and Al _3.2 Fe; and the Fe-Al-containing alloy layer may have a thickness of 10 nm to 1000 nm.

(11) A method of producing a quasi-crystal-containing plated steel sheet according to any one of the above (1) to (10), wherein the method for producing a quasi-crystal-coated steel sheet according to any one of the above items (1) to (10); The hot-plating step is performed by immersing the steel sheet in a molten plating bath of an adjusted component to form a metal coating layer on the surface of the steel sheet; and the first cooling step is a step of setting the liquidus temperature of the metal coating layer in units. °C is set to T _melt , and the metal coating layer is in a state in which the solid phase and the liquid phase coexist, and the temperature ratio of the solid phase to the metal coating layer is 0.3 to 0.8, and the temperature is expressed in units of ° C. _{In the case of solid-liquid} , the melting of the metal coating layer is carried out under the conditions of a temperature range from T _melt to T _solid-liquid and an average cooling rate of the metal coating layer of 15 ° C / sec to 50 ° C / sec. The steel sheet after the plating step is cooled; the second cooling step is performed by the temperature of the metal coating layer from the temperature at the end of the cooling of the first cooling step to a temperature range of 250 ° C, and the average cooling of the metal coating layer Speed becomes 1 The steel sheet after the first cooling step is cooled under the conditions of 00 ° C / sec to 3000 ° C / sec.

(12) The method for producing a quasi-crystal-containing plated steel sheet according to the above (11), wherein in the hot-dip plating step, the oxide in the plating bath may be 1 g/l or less; and the gas atmosphere when the steel sheet is immersed The oxygen concentration may be 100 ppm or less by volume; the plating tank for maintaining the plating bath may be made of steel; the scum in the plating bath may be discharged by a metal pump; The temperature of the bath, that is, T _bath, may be 10 ° C to 100 ° C higher than the T _melt ; the immersion time of the steel sheet in the plating bath may be 1 second to 10 seconds.

According to the aspect of the invention, it is possible to provide a plated steel sheet which is required to be improved in corrosion resistance when used in the fields of building materials, automobiles, and home appliances. Therefore, it is possible to realize a member that has a longer life than the previous surface-treated steel sheet.

1‧‧‧ steel plate

2‧‧‧Metal coating

2a‧‧‧Large area

2b‧‧‧Micro-area

2a1, 2b1‧‧‧ local area

Fig. 1 is a SEM photograph of a plated steel sheet according to an embodiment of the present invention, and is a photograph of a metal structure obtained by observing a cross section in which the cutting direction is parallel to the plate thickness direction of the plated steel sheet.

2 is a TEM photograph of a metal coating layer of a plated steel sheet according to the same embodiment, and is a photograph of a metal structure obtained by observing a cross section in which the cutting direction is parallel to the plate thickness direction of the plated steel sheet.

Fig. 3A is an electron ray diffraction image obtained from the partial region 2a1 in the coarse region 2a shown in Fig. 2.

Fig. 3B is an electron ray diffraction image obtained from the partial region 2b1 in the fine region 2b shown in Fig. 2.

Fig. 4 is a SEM photograph of a plated steel sheet according to the same embodiment, and is obtained by observing a cross section in which the cutting direction is parallel to the plate thickness direction of the plated steel sheet. A photo of the organization.

Figure 5 is a liquid phase diagram of the Zn-Al-Mg ternary system.

Form for implementing the invention

Hereinafter, suitable embodiments of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in the embodiment, and various modifications can be made without departing from the scope of the invention.

The plated steel sheet according to the present embodiment includes a steel sheet (base iron) and a metal coating layer (plating layer) disposed on the surface of the steel sheet. The metal coating layer exhibits a film shape and ensures an adhesion to the steel sheet, and has a task of resisting corrosion and imparting a function to the base iron. On the other hand, it does not impair the material strength and rigidity of the base iron. . In other words, the plated steel sheet according to the present embodiment is a composite material obtained by combining two kinds of metal alloy materials, a steel sheet and a metal coating layer. Further, as a method of compositing, an interface alloy layer (an alloy layer containing Fe-Al) or a diffusion portion may be present at the interface between the steel sheet and the metal coating layer by interdiffusion of metal atoms, and as a result, Interfacial adhesion can be obtained by atomic bonds of metals. First, the characteristics required for the metal coating layer of the plated steel sheet according to the present embodiment will be described.

The metal coating of the plated steel sheet is required to have excellent corrosion resistance. Corrosion resistance is distinguished by corrosion resistance and sacrificial corrosion resistance. The corrosion resistance of the metal coating layer generally refers to the corrosion resistance of the metal coating layer itself. In various corrosion tests, it is often evaluated that the corrosion reduction of the metal coating layer after a certain period of time has elapsed.

When the corrosion reduction is small, it means that the metal coating layer can be long. During this period, it remains as a protective film for the steel sheet (base iron), that is, it is excellent in corrosion resistance. When corrosion reduction is performed using a pure metal, the corrosion resistance is generally higher in Zn than Mg, and Al tends to be higher than Zn.

On the other hand, the sacrificial corrosion resistance of the metal coating layer is such that when the steel sheet (base iron) is exposed to a corrosive environment for some reason, the surrounding metal coating layer acts to protect the steel sheet by causing corrosion instead of the steel sheet. When evaluated using a pure metal, a metal having low electrical properties and corrosion of the material has a high sacrificial corrosion resistance, and generally Zn is higher than Al and Mg tends to be higher than Zn.

The Zn-Mg alloy-plated steel sheet of the present embodiment is excellent in sacrificial corrosion resistance because it contains a large amount of Mg in the metal coating layer. On the other hand, the subject is how to reduce the corrosion reduction of the metal coating layer, that is, how to improve the corrosion resistance of the metal coating layer.

In order to minimize the corrosion reduction of the metal coating layer of the Zn-Mg alloy-plated steel sheet, the inventors of the present invention have studied the constituent phase of the metal structure of the metal coating layer. As a result, it was found that when the quasi-crystal phase was contained in the metal coating layer, the corrosion resistance was drastically improved.

The main feature of the plated steel sheet according to the present embodiment is the metal structure of the metal coating layer. When a plated steel sheet is produced by a specific chemical composition and a specific production condition to be described later, a quasi-crystal phase is generated in the metal coating layer, and the corrosion resistance can be greatly improved. In the present embodiment, the quasi-crystal phase generated in the metal coating layer has an average circular equivalent diameter of more than 1 μm to 200 μm.

Compared to a metal coating that does not contain a quasi-crystal phase, because Since the metal coating layer of the plated steel sheet of the embodiment contains the quasi-crystal phase described above, the corrosion resistance is improved. Further, since the metal coating layer of the plated steel sheet according to the present embodiment contains a large amount of Mg, it has excellent sacrificial corrosion resistance to the steel sheet. In other words, the plated steel sheet according to the present embodiment is preferably a metal coating layer which is excellent in both corrosion resistance and sacrificial corrosion resistance.

Hereinafter, the chemical composition of the metal coating layer, the metal structure of the metal coating layer, and the production conditions will be described in detail with respect to the plated steel sheet according to the present embodiment.

In general, when a metal phase such as Zn, Al, Mg ₂ Zn, or Fe ₂ Al ₅ or a structural formula of an intermetallic compound is used, the atomic ratio is used instead of the mass ratio. In the description of the present embodiment, the atomic ratio is utilized because attention is paid to the quasi-crystal phase. That is, in the following description, it is indicated that % of the chemical component means atomic % unless otherwise notified.

First, the numerical range of the metal coating layer and the reasons for its limitation will be described.

The metal coating layer of the plated steel sheet according to the present embodiment contains Zn and Al as essential components and contains optional components as necessary, and the remainder is composed of Mg and impurities.

Zn (zinc): 20%~60%

In order to obtain a metal structure in which the quasicrystal phase is a metal coating layer, it is necessary to contain Zn in the above range. Therefore, the Zn content of the metal coating layer is set to 20 to 60%. When the Zn content is less than 20%, a quasi-crystal phase cannot be produced in the metal coating layer. Further, similarly, when the Zn content is more than 60%, a quasi-crystal phase cannot be generated in the metal coating layer. Also, in order to control the generation of the quasicrystal phase well The generation of the intermetallic compound described above can set the lower limit of the Zn content to 25% and the upper limit of the Zn content to 52%. It is preferable to set the lower limit of the Zn content to 30% and the upper limit of the Zn content to 45%.

Further, in order to cause the quasicrystal to be favorably generated and to further improve the corrosion resistance, it is preferable to set the Zn content to 33% or more. When it is 33% or more, the quasi-crystal phase tends to grow as a composition range of the primary crystal, and the Mg phase does not easily grow as a primary crystal. In other words, the phasor (area fraction) of the quasi-crystal phase in the metal coating layer can be increased, and the Mg phase which deteriorates the corrosion resistance can be reduced as much as possible. It is preferred to set the Zn content to 35% or more. In general, when a plated steel sheet is produced in this composition range and using the production method of the present embodiment, the Mg phase system hardly exists.

Al (aluminum): 0.3% to 15%

Al is an element which improves the corrosion resistance of the flat portion of the metal coating layer. Further, Al promotes the generation of elements of the quasi-crystal phase. In order to obtain such effects, the Al content of the metal coating layer is set to 0.3% or more. In order to favorably control the average circular equivalent diameter of the quasi-crystal phase, the Al content of the metal coating layer may be set to 5% or more. When the Al content is 5% or more, the average circular equivalent diameter of the quasi-crystal phase is likely to be more than 1 μm, and when the Al content is 10% or more, the average circular equivalent diameter of the quasi-crystal phase is likely to become more than 2 μm. When the average circular equivalent diameter of the quasicrystal phase is controlled to be larger than 2 μm, the corrosion resistance of the flat portion is further improved. Further, when the Zn content is in the above range and is in a small amount, it is preferable to control the Zn content and the Al content in order to form a quasi-crystal phase favorably in the metal coating layer. Specifically, the Zn content and the Al content in the chemical composition of the metal coating layer are in atomic %, preferably satisfying 25% ≦Zn+Al, and 28.5% ≦Zn+Al is better. Further, the upper limit of Zn + Al is not particularly limited, and the upper limit is preferably 50%. On the other hand, when a large amount of Al is contained, red rust is likely to be generated, and at the same time, a quasi-crystal phase is not easily generated, resulting in low corrosion resistance. Therefore, the upper limit of the Al content of the metal coating layer was set to 15%. Further, in order to form an Fe-Al interface alloy layer to be described later, Al is preferably contained as an element.

Moreover, in order to produce a quasicrystal phase more favorably in the metal coating layer, it is preferable to control the Zn content and the Al content as follows. That is, the Zn content and the Al content in the chemical composition of the metal coating layer are in atom%, preferably 30% ≦Zn+Al≦50% and preferably 3≦Zn/Al≦12. When the Zn content and the Al content satisfy the above conditions, it is possible to produce a quasi-crystal phase at a preferable area fraction in the metal coating layer. For example, in the metal coating layer, since the quasi-crystal phase system can be produced in an area ratio of about 30 to 80% with respect to the entire metal coating layer, it is preferable. The rationale for this technology is not clear. However, it is considered that the quasi-crystal phase of the present embodiment has a crystal structure mainly composed of Zn and Mg, and the substitution of Al by Zn can promote the generation of a quasi-crystal phase, and the substitution amount of Al is present in an optimum value system. There are relationships. The quasi-crystal phase is favorably generated in the metal coating layer, and is particularly long during the period in which the corrosion resistance of the processed portion is increased and the base iron is red rust. It is presumed that this effect is such that the quasi-crystal phase can be well dispersed in the metal coating layer by strictly controlling the contents of Zn and Al.

Like Mg and Al, Mg (magnesium) is a main element constituting a metal coating layer, and is an element which promotes sacrificial corrosion resistance. Further, Mg is an important element that promotes the generation of a quasicrystal phase. In this embodiment, for gold The content of Mg in the coating layer is not particularly limited, and is a content obtained by removing the content of the impurities in the remaining portion described above. That is, the Mg content is set to be more than 25% to less than 79.7%. However, the Mg content in the remaining portion is preferably 50% or more, and more preferably 55% or more. In the present embodiment, it is necessary to contain Mg. However, in order to improve the corrosion resistance, it is preferable to suppress precipitation of Mg contained in the metal coating layer so as to form a Mg phase. In other words, since the Mg phase deteriorates the corrosion resistance, it is preferable that the contained Mg is a constituent of a quasicrystal phase or another intermetallic compound.

The metal coating layer of the plated steel sheet according to the present embodiment contains an impurity other than the above-described basic components. Here, the term "impurity" means an element such as C, N, O, P, S, or Cd which is mixed from a raw material of a steel or a plating alloy or a manufacturing environment when a plated steel sheet is industrially produced. These elements each contain about 0.1% in the form of impurities, and the above effects are not impaired.

The metal coating layer of the plated steel sheet according to the embodiment may further contain Ca, Y, La, Ce, Si, Ti, Cr, Fe, Co, Ni, V, Nb, Cu, Sn, Mn, Sr, At least one or more selected components of Sb and Pb are substituted for a part of the remaining Mg. These optional components may be contained according to the purpose. Therefore, it is not necessary to limit the lower limit of the selected components, and the lower limit may be 0%. Moreover, the selected components are contained as impurities and do not impair the above effects.

Ca (calcium): 0%~3.5%

Y (indium): 0%~3.5%

La (镧): 0%~3.5%

Ce (铈): 0%~3.5%

In order to improve the workability of the molten plating, Ca, Y, La, and Ce may be contained as necessary. When the plated steel sheet of the present embodiment is produced, a molten Mg alloy having high oxidizability is maintained in the atmosphere as a plating bath. Therefore, it is preferred to take some of the antioxidant means of Mg. Ca, Y, La, and Ce are more susceptible to oxidation than Mg and form a stable oxide film on the plating bath surface in a molten state, thereby preventing oxidation of Mg in the bath. Therefore, the Ca content of the metal coating layer can be set to 0% to 3.5%, the Y content can be set to 0% to 3.5%, the La content can be set to 0% to 3.5%, and the Ce content can be set to 0% to 3.5%. . More preferably, the Ca content, the Y content, the La content, and the Ce content may be set to 0.3% and the upper limit to 2.0%.

The plating bath having a high Mg content can be kept non-oxidized in the air, and it is preferable that at least one element selected from the group consisting of Ca, Y, La, and Ce is contained in a total amount of 0.3% or more. On the other hand, since Ca, Y, La, and Ce are easily oxidized, and there is a case where the corrosion resistance is adversely affected, the upper limit of the contents of Ca, Y, La, and Ce is preferably 3.5% in total. That is, the Ca content, the Y content, the La content, and the Ce content in the chemical composition of the metal coating layer are preferably in atom%, so as to satisfy 0.3% ≦Ca+Y+La+Ce≦3.5%.

In addition, the content of Ca, Y, La, and Ce is preferably 0.3% or more and 2.0% or less in total in order to cause a quasi-crystal phase to be favorably formed in the metal coating layer. Although these elements are substituted for Mg constituting the quasi-crystal phase, it is considered that when a large amount of these elements are contained, there is a case where the quasi-crystal phase is hindered from being generated. When these elements are contained in an appropriate amount, the red rust suppressing effect of the quasicrystal phase and other phases is improved. It is speculated that this effect is derived from the melting analysis of the quasicrystal phase. The effect of timing on the retention of white rust. That is, after the melting of the quasi-crystal phase in the metal coating layer is estimated, the elements are contained in the formed white rust, so that the rust prevention force of the white rust is improved, and the red rust is caused by the corrosion of the base iron. The period until then becomes longer.

Further, among these elements, the above effects (antioxidation and quasi-crystal phase generation) can be obtained largely by containing Ca, La, and Ce. On the other hand, compared with Ca, La, and Ce, the above effects obtained by containing Y are clearly small. The putative system is related to the fact that Y, Ca, La, and Ce are elements that are easily oxidized and are reactive. When the chemical composition of the quasi-crystal phase is analyzed by EDX (Energy Dispersive X-ray Spectroscopy), since Y cannot be detected in most cases, it is estimated that the Y system is not easily accommodated in the quasicrystal. On the other hand, Ca, La, and Ce tend to have a concentration higher than the concentration of the quasi crystal. That is, it is not necessary to contain Y in the metal coating layer. When the metal coating layer does not contain Y, it may be 0.3% ≦Ca+La+Ce≦3.5%, and 0.3%≦Ca+La+Ce≦2.0%.

Further, when an inert gas (for example, Ar) is used in place of the gas atmosphere of the plating bath or vacuum, that is, when the oxygen barrier means is provided in the manufacturing apparatus, it is not necessary to intentionally add Ca, Y, La, and Ce.

Further, the total content of Al, Ca, La, Y, and Ce is preferably controlled as follows. That is, the Al content, the Ca content, the La content, the Y content, and the Ce content in the chemical composition of the metal coating layer are in atomic %, preferably 6% Al+Ca+La+Y+Ce≦18.5%, It is more preferable to satisfy 6.5% ≦Al+Ca+La+Y+Ce≦18.5%. Combination of Al, Ca, La, Y, and Ce When the content is such that the above conditions are satisfied, a quasi-crystal phase having a preferred average circular equivalent diameter can be produced in the metal coating layer. By satisfying these conditions, the average circular equivalent diameter of the quasi-crystal phase can be controlled to be 3 μm or more. Further, it is possible to ensure a certain corrosion resistance by the quasi-crystal phase, and to increase the powdering property (peeling resistance to compressive stress) of the plating layer by a certain amount or more. It is estimated that Al, and a small amount of added Ca, La, Y, and Ce are precipitated to the grain boundary of the quasicrystal phase and grain boundary strengthening is performed. On the other hand, when it is more than 18.5%, the pulverization property tends to be deteriorated.

Si (矽): 0%~0.5%

Ti (titanium): 0% to 0.5%

Cr (chromium): 0% to 0.5%

In order to form a quasi-crystal phase well in the metal coating layer, Si, Ti, and Cr may be contained as necessary. When a trace amount of Si, Ti, and Cr is contained in the metal coating layer, the quasi-crystal phase is easily generated and the structure of the quasi-crystal phase is stabilized. It is considered that Si is formed by bonding with Mg to form fine Mg ₂ Si, and Ti and Cr which are deficient in Mg are formed into a fine metal phase to form a starting point (core) for generating a quasi-crystal phase. Moreover, the generation of the quasi-crystal phase is affected by the cooling rate at the time of manufacture. However, when Si, Ti, and Cr are contained in the metal coating layer, the dependence of the cooling rate on the generation of the crystal phase tends to be small. Therefore, the Si content of the metal coating layer can be set to 0% to 0.5%, the Ti content can be set to 0% to 0.5%, and the Cr content can be set to 0% to 0.5%. More preferably, the Si content, the Ti content, and the Cr content may be set to 0.005% each of the lower limits and 0.1% of the upper limit.

Also, because the structure of the quasicrystal is further stabilized, in total It is preferred to contain at least one element selected from the group consisting of Si, Ti, and Cr in an amount of 0.005% to 0.5%. That is, the Si content, the Ti content, and the Cr content in the chemical composition of the metal coating layer are preferably in atom%, so as to satisfy 0.005% ≦Si+Ti+Cr≦0.5%. Further, when these elements are contained in an appropriate amount, since the quasicrystal system is generated in a large amount, the corrosion resistance of the surface of the metal coating layer is improved. The corrosion resistance in a humid environment is improved and the generation of white rust can be suppressed.

Co (cobalt): 0% to 0.5%

Ni (nickel): 0% to 0.5%

V (vanadium): 0% to 0.5%

Nb (铌): 0%~0.5%

Co, Ni, V, and Nb have the same effects as Si, Ti, and Cr described above. In order to obtain the above effects, the Co content may be set to 0% to 0.5%, the Ni content may be set to 0% to 0.5%, the V content may be set to 0% to 0.5%, and the Nb content may be set to 0% to 0.5%. More preferably, the Co content, the Ni content, the V content, and the Nb content may be set to 0.05% each and the upper limit to 0.1%. However, compared with Si, Ti, and Cr, these elements have less effect of improving corrosion resistance.

Further, in the metal coating layer, an element constituting the steel sheet from the base material, that is, the steel sheet is mixed. In particular, in the hot-dip plating method, the adhesion is improved by the mutual diffusion of the elements from the steel sheet to the metal coating layer and the metal coating layer to the steel sheet. Therefore, in the metal coating layer, a certain amount of Fe (iron) is contained. For example, there is a case where about 2% of Fe is contained as a chemical component of the entire metal coating layer. However, most of the Fe diffused to the metal coating layer is in the vicinity of the interface between the steel sheet and the metal coating layer, and reacts with Al and Zn to produce an intermetallic compound. Therefore, the corrosion resistance of the metal coating layer The possibility of sexual impact is small. Therefore, the Fe content of the metal coating layer can be set to 0% to 2%. In the same manner, the elements constituting the steel sheet (the elements diffused from the steel sheet to the metal coating layer other than the elements described in the embodiment) diffuse into the metal coating layer, but the possibility of affecting the corrosion resistance of the metal coating layer is small. .

Cu (copper): 0% to 0.5%

Sn (tin): 0% to 0.5%

In order to improve the adhesion between the steel sheet and the metal coating layer, there is a case where the steel sheet before the hot-plating step is pre-plated with Ni, Cu, Sn, or the like. When a plated steel sheet is formed by using a steel sheet which has been subjected to pre-plating, the metal coating layer may contain such elements as about 0.5%. Among Ni, Cu, and Sn, Cu and Sn do not have the above-described effects of Ni. However, even if the metal coating layer contains about 0.5% of Cu or Sn, there is little possibility of affecting the behavior of generating a quasicrystal and the corrosion resistance of the metal coating layer. Therefore, the Cu content of the metal coating layer can be set to 0% to 0.5%, and the Sn content can be set to 0% to 0.5%. More preferably, the Cu content and the Sn content may be set to 0.005% each of the lower limits and 0.4% of the upper limit.

Mn (manganese): 0% to 0.2%

As a base material of a plated steel sheet, that is, a steel sheet, high-tensile steel (high-strength steel) has been gradually used in recent years. When a plated steel sheet is produced by using high-tensile steel, elements such as Si and Mn contained in the high-tensile steel may be diffused into the metal coating layer. Among Si and Mn, Mn does not have the above-described effects of Si. However, even if the metal coating layer contains about 0.2% of Mn, there is little possibility of affecting the behavior of generating a quasicrystal and the corrosion resistance of the metal coating layer. thus, The Mn content of the metal coating layer can be set to 0% to 0.2%. More preferably, regarding the Mn content, the lower limit may be set to 0.005% and the upper limit may be set to 0.1%.

Sr (锶): 0%~0.5%

Sb (锑): 0%~0.5%

Pb (lead): 0% to 0.5%

Sr, Sb, and Pb are elements that enhance the appearance of plating and have an effect of improving anti-glare. In order to obtain this effect, the Sr content of the metal coating layer may be set to 0% to 0.5%, the Sb content may be set to 0% to 0.5%, and the Pb content may be set to 0% to 0.5%. When the Sr content, the Sb content, and the Pb content are in the above ranges, the corrosion resistance is hardly affected. More preferably, the Sr content, the Sb content, and the Pb content may be set to 0.005% and the upper limit to 0.4%.

The chemical composition of the metal coating layer described above is ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). And measurement. The plated steel sheet was immersed in 10% hydrochloric acid to which an inhibitor was added for about 1 minute to partially peel off the metal coating layer, and a molten metal obtained by melting the metal coating layer was prepared. The melt was analyzed by ICP-AES, ICP-MS or the like, and the chemical composition was obtained as a whole of the metal coating layer.

Moreover, in the hot-dip plating method, it is possible to form a metal coating layer having a chemical component substantially equivalent to the chemical composition of the molten plating bath. Therefore, regarding the element which can neglect the mutual diffusion between the steel sheet and the metal coating layer, the chemical composition of the plating bath to be used can be measured, and the measured value can be replaced. The chemical composition of the metal coating layer is used. A small piece of metal ingot is taken from the plating bath, and the molten powder is prepared by taking the drilling powder and preparing the molten powder. The chemical composition of the plating bath is obtained by analyzing the melt by ICP or the like. The measured value of the chemical composition of the plating bath can be used as a chemical component of the metal coating layer.

Next, the metal structure of the metal coating layer will be described.

The plated steel sheet according to the present embodiment contains a quasi-crystal phase as a metal structure in the metal coating layer. The quasi-crystal phase can be defined as a quasicrystalline phase in which the Mg content, the Zn content, and the Al content in the quasi-crystal phase satisfy 0.5 ≦Mg/(Zn+Al)≦0.83 in atomic %. That is, it can be defined as a ratio of a total of Mg atoms, Zn atoms, and Al atoms, that is, Mg:(Zn+Al) becomes a quasi-crystal phase of 3:6 to 5:6. In terms of theoretical ratio, it is considered that Mg:(Zn+Al) is 4:6. The chemical composition of the quasi-crystal phase is quantified by TEM-EDX (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy), EPMA (electron probe microanalysis) It is better to calculate the quantitative analysis of the Electron Probe Micro-Analyzer. Also, it is not easy to define a quasicrystal system such as an intermetallic compound with the correct chemical formula. Since the quasi-crystal phase cannot define a repeating lattice unit as a unit lattice of crystals, the atomic positions of specific Zn and Mg are also difficult.

Further, in the present embodiment, the quasi-crystal phase contained in the metal coating layer has an average circular equivalent diameter of more than 1 μm to 200 μm. The lower limit of the average circular equivalent diameter of the quasi-crystal phase is not particularly limited. However, in the configuration of the metal structure of the metal coating layer to be described later, it is preferable to set the lower limit of the average circular equivalent diameter of the quasicrystal phase to be more than 1 μm. Also, in order to further enhance the metal The corrosion resistance of the coating layer is preferably such that the lower limit of the average circular equivalent diameter of the quasicrystal phase is 1.5 μm, more preferably the lower limit is more than 2.0 μm, and the lower limit is preferably more than 5 μm. Further, a quasi-crystalline phase system having an average circular equivalent diameter of more than 200 μm is not easily produced. Therefore, the upper limit of the average circular equivalent diameter of the quasicrystal phase is set to 200 μm. Further, as the quasi-crystal phase, the quasi-crystal phase can be identified to about 0.01 μm by the average circular equivalent diameter by the electron microscope image of the TEM and the electron beam diffraction image.

Further, when the metal structure of the metal coating layer is observed in a cross section parallel to the cutting direction in the thickness direction of the sheet, it is preferable to form a bimodal structure composed of a coarse region and a fine region, wherein the coarse region is composed of a circle equivalent diameter. It is composed of crystal grains larger than 1 μm; and the fine region is composed of crystal grains having a circle equivalent diameter of 1 μm or less. Further, it is preferable that the coarse region contains a quasicrystal phase and the fine region contains at least one of a Mg ₅₁ Zn ₂₀ phase, a Mg ₃₂ (Zn, Al) ₄₉ phase, a MgZn phase, a MgZn ₂ phase, and a Zn phase. More than one species. The corrosion resistance is favorably improved by controlling the metal structure of the metal coating layer to a bimodal structure composed of the above-described coarse region and fine region. In addition, the upper limit of the equivalent diameter of the crystal grain contained in the coarse region and the lower limit of the circle equivalent diameter of the crystal grain contained in the fine region are not particularly limited. However, the upper limit may be set to 500 μm, 300 μm, or 200 μm as necessary, and the lower limit may be set to be larger than 0 μm or 0.01 μm or more.

In general, the bimodal structure means a structure in which the degree distribution such as the circle equivalent diameter of the crystal grains contained in the metal structure is bimodal. The plated steel sheet according to the embodiment is contained in the metal structure of the metal coating layer. The degree distribution of the equivalent diameter of some crystal grains is also preferably a bimodal distribution. However, in the plated steel sheet according to the present embodiment, the degree distribution does not necessarily need to be a bimodal distribution. For example, the above-described effects can be obtained even if the degree distribution is a wide distribution. In other words, the bimodal structure in the present embodiment means that the degree distribution of the circle equivalent diameter of the crystal grains contained in the metal structure of the metal coating layer is not in accordance with the normal distribution, and the metal structure of the metal coating layer is The fine region is composed of a crystal grain composed of a circle equivalent diameter of 1 μm or less, and the coarse region is composed of crystal grains having a circle equivalent diameter of more than 1 μm.

Further, as described above, the quasi-crystal phase contained in the metal structure of the metal coating layer of the plated steel sheet according to the present embodiment has an average circular equivalent diameter of more than 1 μm to 200 μm. That is, when the crystal grains of the quasicrystal phase are individually considered, the metal structure of the metal coating layer contains a quasicrystal phase having a circle equivalent diameter of more than 1 μm; and a quasicrystal phase having a circle equivalent diameter of 1 μm or less. However, since the quasi-crystal phase has an average circular equivalent diameter of more than 1 μm to 200 μm, the quasi-crystal phase is mainly contained in the above-mentioned coarse region of the above-mentioned metal coating layer.

Further, regarding the Mg ₅₁ Zn ₂₀ phase, the Mg ₃₂ (Zn, Al) ₄₉ phase, the MgZn phase, the MgZn ₂ phase, or the Zn phase other than the quasi-crystal phase, the average circular equivalent diameter of these is 0.01 μm to 1 μm. good. In this case, the metal structure of the metal coating layer contains the crystal grains having a circle equivalent diameter of 1 μm or less; and the crystal grains having a circle equivalent diameter of more than 1 μm. However, since the average circular equivalent diameter of these is preferably 0.01 μm to 1 μm, the Mg ₅₁ Zn ₂₀ phase, the Mg ₃₂ (Zn, Al) ₄₉ phase, the MgZn phase, the MgZn ₂ phase, or the Zn phase system are mainly It is contained in the above fine area. In other words, the metal structure of the metal coating layer of the plated steel sheet according to the present embodiment is mainly composed of a quasi-crystal phase mainly contained in a coarse region and mainly containing Mg ₅₁ Zn ₂₀ phase and Mg ₃₂ (Zn, Al) ₄₉ phase in the fine region. At least one of the MgZn phase, the MgZn ₂ phase, and the Zn phase is preferred.

Fig. 1 is an electron micrograph of a plated steel sheet according to the present embodiment, and is a photograph of a metal structure obtained by observing a cross section in which the cutting direction is parallel to the plate thickness direction of the plated steel sheet. This cross-sectional photograph was observed using a SEM (Scanning Electron Microscope) and was a reflected electron composition image (COMPO image). 1 shown in Fig. 1 is a steel plate, and 2 is a metal coating layer. Further, 2a shown in Fig. 1 is a coarse area, and 2b is a fine area. The coarse region 2a contains a quasi-crystal phase. The fine region 2b contains at least one of Mg ₅₁ Zn ₂₀ phase, Mg ₃₂ (Zn, Al) ₄₉ phase, MgZn phase, MgZn ₂ phase, and Zn phase. From Fig. 1, the metal structure of the metal coating layer shows a bimodal structure.

Further, strictly speaking, a fine intermetallic compound having a circular equivalent diameter of 1 μm or less and a metal phase are also dispersed in the coarse region 2a. However, the fine particles existing in such a coarse region 2a are not so-called fine regions 2b. In the so-called fine region 2b of the present embodiment, a plurality of fine particles having a circle equivalent diameter of 1 μm or less are continuously and aggregated, and the observation system at the SEM level is a region in which an equivalent area can be observed.

2 is an electron micrograph of a metal coating layer of a plated steel sheet according to the same embodiment, and a photograph of a metal structure obtained by observing a cross section parallel to the thickness direction of the plated steel sheet is observed. This section photo is used TEM observation is a bright field image. 2a shown in Fig. 2 is a coarse area, and 2b is a fine area. In Fig. 2, similarly to Fig. 1, the metal structure of the metal coating layer shows a bimodal structure.

Fig. 3A is an electron ray diffraction image obtained from the partial region 2a1 in the coarse region 2a shown in Fig. 2. Fig. 3B is an electron ray diffraction image obtained from the partial region 2b1 in the fine region 2b shown in Fig. 2. In Fig. 3A, an electron ray diffraction image derived from a radial regular pentagon of a regular icosahedral structure is shown. The electron ray diffraction image shown in Fig. 3A can only be obtained from a quasicrystal and cannot be obtained from any other crystal structure. According to the electron beam diffraction image shown in FIG. 3A, it can be confirmed that the quasi-crystal phase is contained in the coarse region 2a. Further, in Fig. 3B, an electron ray diffraction image derived from the Mg ₅₁ Zn ₂₀ phase is shown. According to the electron beam diffraction image shown in FIG. 3B, it was confirmed that the Mg ₅₁ Zn ₂₀ phase was contained in the fine region 2b. Further, although not shown, it was confirmed that the fine region 2b contains Mg ₃₂ (Zn, Al) ₄₉ phase, MgZn phase, MgZn ₂ phase, and Zn.

Further, in the fine region 2b, when the Mg content is high, many Mg ₅₁ Zn ₂₀ can be observed, and when the Mg content is low, many Mg ₃₂ (Zn, Al) ₄₉ can be observed. Further, the presence of an intermetallic compound and a metal phase of Mg ₅₁ Zn ₂₀ phase, Mg ₃₂ (Zn, Al) ₄₉ phase, MgZn phase, MgZn ₂ phase, and Zn are as described above, and can be irradiated by electron beam of TEM. The image is confirmed or can also be confirmed by XRD (X-Ray Diffractometer).

Further, the Mg ₅₁ Zn ₂₀ phase system is defined as: JCPDS card (JCPDS card) (Joint Committee on Powder Diffraction Standards, JCPDS, Joint Committee on Powder Diffraction Standards): PDF#00-008-0269, or #00-065- 4290, or the non-patent literature of Dong et al. (Journal of Solid state chemistry 36, 225-233 (1981)) can identify the constituent phases. Further, the Mg ₃₂ (Zn, Al) ₄₉ phase system is defined as a constituent phase which can be identified in the JCPDS card: PDF #00-019-0029, or #00-039-0951.

Further, the chemical components of the above-described intermetallic compound and metal phase can be easily quantitatively analyzed by TEM-EDX or EPMA. Further, from the quantitative analysis result, it is possible to easily identify whether each crystal grain in the constituent phase is a quasicrystal phase, a Mg ₅₁ Zn ₂₀ phase, a Mg ₃₂ (Zn, Al) ₄₉ phase, a Mg ₄ Zn ₇ phase, a MgZn phase, MgZn ₂ phase, Mg phase, Zn phase, or other phase.

Further, according to the non-patent literature of Dong et al. (Journal of solid state chemistry 36, 225-233 (1981)), it is revealed that the Mg ₅₁ Zn ₂₀ system has a unit lattice close to a cubic crystal and has a formation in a unit lattice. The atomic structure of the icosahedron. Since the unit lattice of the Mg ₅₁ Zn ₂₀ is different from the icosahedral structure of the quasicrystal, the Mg ₅₁ Zn ₂₀ system is strictly different from the quasicrystal. However, since Mg ₅₁ Zn ₂₀ is similar to the crystal structure of the quasicrystal, it is considered that the Mg ₅₁ Zn ₂₀ phase influences the generation of the quasicrystal phase. Further, Mg ₃₂ (Zn, Al) _{49 is} also referred to as a Frank-Kasper phase, and the Mg ₃₂ (Zn, Al) ₄₉ also has a complex atomic configuration (diamond icosahedron). It is presumed that the Mg ₃₂ (Zn, Al) ₄₉ phase is also closely related to the generation of the quasicrystal phase, similarly to the Mg ₅₁ Zn ₂₀ phase.

Further, the MgZn phase, the MgZn ₂ phase, and the Zn phase contained in the fine region 2b are largely different from the chemical components and crystal structures of the quasicrystal phase. When the MgZn phase, the MgZn ₂ phase, and the Zn phase are sufficiently diffused at a high temperature in the production of a plated steel sheet, it is possible to determine that a stable phase is generated. From the viewpoint of improving corrosion resistance, the fraction of these stable phases is preferably lower.

The corrosion resistance of the constituent phase of the metal coating layer is excellent in the order of quasicrystal phase > Mg ₃₂ (Zn, Al) ₄₉ phase > Mg ₅₁ Zn ₂₀ phase > MgZn phase = MgZn ₂ phase > Zn phase >> Mg phase. tendency. In the case of doping the constituent phases, it is advantageous to improve the corrosion resistance of the metal coating layer by increasing the fraction of the phase having high corrosion resistance. In other words, in the plated steel sheet according to the present embodiment, it is preferable that the area ratio of the quasi-crystal phase is the highest among all the constituent phases contained in the metal structure of the metal coating layer. In other words, in the metal structure of the metal coating layer of the plated steel sheet according to the present embodiment, the quasi-crystal phase is preferably the main phase.

However, when a plurality of metal phases and intermetallic compounds coexist in the metal coating layer, corrosion resistance is lowered when a coupling cell is formed and a single phase is formed as compared with the metal coating layer. Usually, when a complex phase is mixed in the metal coating layer, a portion having high and low electric energy is generated in the metal coating layer to cause a coupling reaction. Moreover, the low portion is first corroded to cause a decrease in corrosion resistance. However, in the plated steel sheet according to the present embodiment, when the metal coating layer is the bimodal structure described above, it is almost impossible to observe that the corrosion resistance is lowered due to the formation of the coupling cells, and it is negligible, and it is possible to observe by containing a quasicrystal. The corrosion resistance is significantly improved.

Further, in general, the intermetallic compound lacks plastic deformability. When the fraction of the coarse intermetallic compound which is inferior in plastic workability is reduced, the crack of the metal coating layer is fine during the processing of the plated steel sheet, so that the exposed area of the steel sheet (base iron) is small and can be satisfactorily Improve and improve corrosion resistance Corrosion performance. In addition, since the peeling of the metal coating layer can be suppressed, the period from the processing portion to the occurrence of red rust becomes long, and the corrosion resistance can be satisfactorily improved.

The quasi-crystal phase is non-equilibrium and the heat is not stable. Therefore, when exposed to a high temperature environment of around 250 to 330 ° C for a long time, phase decomposition occurs, and the Mg ₅₁ Zn ₂₀ phase also has a Mg phase which lacks corrosion resistance. As a result, there is a possibility that the corrosion resistance is deteriorated as a whole of the plated steel sheet. Care must be taken when using plated steel in high temperature environments.

In the metal coating layer of the plated steel sheet according to the present embodiment, the area ratio of the coarse region (the area of the coarse region to the area of the metal coating layer) is preferably 5% to 80% with respect to the metal structure of the entire metal coating layer. Further, the area fraction of the fine regions (the area of the fine regions and the area of the metal coating layer) is preferably 20% to 95% with respect to the metal structure of the entire metal coating layer. When this condition is satisfied, the corrosion resistance of the metal coating layer is further improved. 4 is a SEM photograph of the plated steel sheet of the present embodiment, and is a photograph of a metal structure obtained by observing a cross section in which the cutting direction is parallel to the plate thickness direction of the plated steel sheet. In Fig. 4, the metal coating layer is shown when the area fraction of the coarse region is 63% and the area fraction of the fine region is 37%. In the plated steel sheet, it was confirmed that the corrosion resistance of the metal coating layer was further improved.

When the corrosion resistance of the metal coating layer is further improved, the lower limit of the area fraction of the coarse region may be set to 10%, 15%, or 25%, and the upper limit of the area fraction of the fine region may be set to 90. %, 85%, or 75%. On the other hand, compared with the corrosion resistance of the metal coating layer, the peeling at the time of bending processing is preferentially suppressed, and the area of the coarse area can be divided. The upper limit of the ratio is set to 50%, 35%, or 25%, and the lower limit of the area fraction of the fine region is set to 50%, 65%, or 75%.

In the metal coating layer of the plated steel sheet according to the present embodiment, the area fraction of the quasi-crystal phase contained in the coarse region with respect to the coarse region is 80% (the area of the quasi-crystal phase in the coarse region, the area of the coarse region). It is preferably less than 100%, and the total area fraction of Mg ₅₁ Zn ₂₀ phase, Mg ₃₂ (Zn, Al) ₄₉ phase, MgZn phase, MgZn ₂ phase, and Zn phase contained in the fine region with respect to the fine region It is preferable that the total area of the above-mentioned respective constituent phases in the fine region 面积 the area of the fine region is 80% to less than 100%. When this condition is satisfied, the corrosion resistance of the metal coating layer is further improved. It is presumed that there is some correlation between the fraction of the quasicrystal phase, the size of the coarse region in the plating structure (metal coating layer), and the electrochemical property. For example, the higher the fraction of the quasicrystal phase, the metal coating layer The corrosion potential is shifted from a low (-1.3V~-1.1V vs. Ag/AgCl reference electrode) to a high (-1.0V~-0.8V vs. Ag/AgCl reference electrode), and the cathode current value at the corrosion potential and The anode current value becomes small and the corrosion current density becomes small. This is presumed to be because the quasi-crystal phase has a characteristic potential and a near-passive nature. As a result, it is considered that the corrosion resistance of the metal coating layer is improved. Further, in the remaining portion of the coarse region and the remaining portion of the fine region, the intermetallic compound or the metal phase other than the above may be contained, but the above effects of the embodiment are not impaired. The potential of the coarse region can be measured, for example, using a scanning Kelvin probe microscope method and the tissue can be mapped. In the case where the quasicrystal, Mg ₃₂ (Zn, Al) is usually more than ₄₉ , the potential becomes high and shows a value close to -0.8 V. On the other hand, the Mg ₅₁ Zn ₂₀ system showed about -1.1 V. The potential and the corrosion current density vary depending on the phasors, and usually show -1.3V to -0.8V. Generally, the corrosion current density tends to decrease as the value is close to -0.8V.

In the plated steel sheet according to the present embodiment, it is preferred that the metal structure of the metal coating layer does not contain a Mg phase. Since the Mg phase contained in the metal coating layer deteriorates the corrosion resistance in any of the coarse region and the fine region, it is preferable to reduce the precipitation of the Mg phase as much as possible. The presence or absence of the Mg phase can be confirmed by TEM-EDX or SEM-EDX, or can be confirmed by XRD. For example, in the XRD diffraction pattern, relative to the diffraction angle in the Mg ₅₁ Zn ₂₀ phase (or Mg ₇ Zn ₃ phase): 2 θ = 36.496° diffraction intensity, diffraction from the (110) plane of the Mg phase When the strength is 1% or less, it can be said that the metal structure of the metal coating layer does not contain the Mg phase. Similarly, when 100 or more arbitrary crystal grains are sampled in the TEM diffraction image, when the number of crystal grains of the Mg phase is 3% or less, it can be said that the metal structure of the metal coating layer does not contain the Mg phase. . The number of crystal grains of the Mg phase is preferably less than 2%, and the number of crystal grains of the Mg phase is preferably less than 1%.

In the metal coating layer, the Mg phase tends to generate primary crystals directly below the melting point. Whether or not the Mg phase is generated as a primary crystal is roughly determined by the chemical composition and production conditions of the metal coating layer. Compared with the eutectic composition (Mg72%-Zn28%) of the equilibrium state diagram of the Mg-Zn binary system, the Mg content is higher, and the Mg phase has the possibility of crystallizing in the form of primary crystal. On the other hand, in the case where the Mg content is lower than this value, in principle, the possibility that the Mg phase generates crystals in a primary crystal form is small. Further, in the process of the present embodiment, since the quasicrystal is generated by the primary crystal, even if the Mg content is higher than the eutectic composition, the Mg phase is extremely unlikely to be generated, and even if it is confirmed, the main phase is There is little possibility that the Mg phase exists. The presence of the crystal grains of the Mg phase is, in terms of a fraction, up to about 3%. In addition, when the Zn content is 28.5% or more, the inventors of the present invention have less than 2% of the crystal grains of the Mg phase in terms of the number of the crystal grains contained in the metal structure of the metal coating layer. tendency. In addition, when the Zn content is 33% or more, the crystal grains of the Mg phase tend to be less than 1% in terms of the number of the crystal grains contained in the metal structure of the metal coating layer. Further, when the Mg phase is present in the metal coating layer, particularly in a wet environment, the surface of the metal coating layer changes to black in time and causes a poor appearance of the plating. In this regard, particularly in the surface layer of the metal coating layer, it is preferred to avoid the incorporation of the Mg phase. The surface change of the metal coating layer is a black appearance defect, and it is possible to determine the state of occurrence of the plated steel sheet by storing it in a constant temperature and humidity chamber for a certain period of time.

The metal coating layer of the plated steel sheet according to the present embodiment is an area fraction of the quasi-crystal phase contained in the coarse region with respect to the coarse region (the area of the quasi-crystal phase in the coarse region, the area of the coarse region). 80% to less than 100%, and the area fraction of the Mg ₅₁ Zn ₂₀ phase contained in the fine region with respect to the fine region (the area of the Mg ₅₁ Zn ₂₀ phase in the fine region ÷ the area of the fine region), It is preferably from 80% to less than 100%. When the conditions are satisfied, the fraction of the Mg ₅₁ Zn ₂₀ phase excellent in corrosion resistance is improved, so that the corrosion resistance of the metal coating layer is further improved.

When the metal coating layer of the plated steel sheet according to the present embodiment is viewed in a cross section parallel to the cutting direction in the thickness direction of the sheet, the thickness of the metal coating layer is set to D in units of μm, and the surface of the metal coating layer is along the thickness of the sheet. The range from the direction of the steel plate to 0.3×D is set to the surface of the metal coating layer, and will be When the range of the interface between the steel sheet and the metal coating layer in the thickness direction of the metal coating layer is 0.3×D is the depth of the metal coating layer, the area ratio of the coarse region to the surface portion of the metal coating layer (the surface portion of the metal coating layer) The area of the coarse area in the area of the surface of the metal coating layer is from 10% to less than 100%, and the area fraction of the coarse area with respect to the deep part of the metal coating layer (the area of the coarse area in the deep part of the metal coating layer, the area of the metal The area of the deep portion of the coating layer is 10% to less than 100%, and when the surface of the metal coating layer of the metal coating layer and the deep portion of the metal coating layer are the center portions of the metal coating layer, the center portion of the metal coating layer is The area fraction of the fine region (the area of the fine region in the central portion of the metal coating layer, the area of the central portion of the metal coating layer) is 50% to less than 100%. When the above conditions are satisfied, the constituent phase contained in the metal coating layer is preferably disposed, so that the corrosion resistance of the metal coating layer is further improved. Moreover, the adhesion of the metal coating layer tends to increase. Further, when the crystal grains in the coarse region exist at positions along the surface portion of the metal coating layer and the center portion of the metal coating layer, or the crystal grains in the coarse region exist in the deep portion of the metal coating layer and the center portion of the metal coating layer. In the case of the position, the area of the surface of the metal coating layer or the area covered by the deep portion of the metal coating layer may be used to calculate the area fraction. Similarly, when crystal grains in the fine region exist at positions along the surface portion of the metal coating layer and the center portion of the metal coating layer, or crystal grains in the fine region exist in the deep portion of the metal coating layer and the center portion of the metal coating layer. In the case of the position, the area included in the center portion of the metal coating layer among the crystal grains may be used, and the above-mentioned area fraction may be calculated.

The plated steel sheet according to the present embodiment further has an alloy layer containing Fe-Al, the alloy layer containing Fe-Al is disposed between the steel sheet and the metal coating layer, and the alloy layer containing Fe-Al contains Fe ₅ Al _{2 .} The thickness of the alloy layer containing at least one of Al _3.2 Fe and containing Fe-Al is preferably 10 nm to 1000 nm. When an alloy layer containing Fe-Al satisfying the above conditions is disposed at the interface between the steel sheet and the metal coating layer, peeling of the metal coating layer can be satisfactorily suppressed. Moreover, when the alloy layer containing Fe-Al is formed, the adhesion of the metal coating layer tends to be improved.

The thickness D of the metal coating layer of the plated steel sheet according to the present embodiment is not particularly limited. This thickness D may be controlled as necessary. Usually, the thickness D is usually 35 μm or less.

The metal structure of the above metal coating layer was observed as follows. The cross section parallel to the cutting direction and the cutting direction were used as the observation surface, and the plated steel sheet was cut off to take a sample. This section is polished or subjected to CP (Cross Section Polisher) processing. After the polishing, the cross section was subjected to NITAL (nitric acid etching solution) etching. The cross section was observed using an optical microscope or SEM and photographs of metal structures were taken. Further, when the cross section observed by the SEM is a COMPO image as shown in FIG. 1, since the chemical composition derived from the coarse region and the fine region is greatly different, it is easy to recognize the coarse region and the fine region. Boundary. Further, the chemical composition of the constituent phase can be measured by analysis of EDX or EPMA. From the results of the chemical analysis, the constituent phases can be easily identified. The metal structure photograph is binarized by, for example, image analysis, and the area ratio of the white portion or the black portion of the metal coating layer is measured, and the area fraction of the constituent phase can be measured. Also, from the area of the individual coarse areas sought, The average circle equivalent diameter can be obtained by calculation. Alternatively, the metal structure of the metal coating layer may be observed by an EBSD (Electron Back Scattering Diffraction Pattern) method to identify the constituent phase and determine the area fraction and the average circle equivalent diameter of the constituent phase.

In order to identify the constituent phases in more detail, the metal structure of the metal coating layer was observed as follows. The cross section parallel to the cutting direction and the cutting direction were used as the observation surface, and the plated steel sheet was cut off to take a sample. The sheet sample was subjected to ion milling. Alternatively, the plated steel sheet is subjected to FIB (Focused Ion Beam) processing to take a sheet sample in such a manner that the cross section parallel to the cutting direction and the cutting direction becomes the observation surface. These sheet samples were observed using TEM and photographs of metal structures were taken. The constituent phase can be correctly identified by the electron beam diffraction image. The area fraction and the average circle equivalent diameter of the constituent phase can be obtained by analyzing the photo of the metal structure by image analysis.

Further, although the existence state of the unknown space is the easiest, the existence of the constituent phase can be confirmed from the diffraction peak of the XRD of the metal coating layer. However, since the quasicrystal, Mg ₅₁ Zn ₂₀ , and Mg ₃₂ (Zn, Al) ₄₉ are overlapped with each other at the diffraction peak position, it is possible to confirm the presence, but it is difficult to perform the identification.

In addition, the plated steel sheet of the present embodiment is not particularly limited as the base material of the base material of the plated steel sheet. As the steel sheet, aluminum killed steel, extremely low carbon steel, high carbon steel, various high tensile steels, steel containing Ni or Cr, or the like can be used.

Next, a method of producing the plated steel sheet according to the embodiment will be described.

The method for producing a plated steel sheet according to the present embodiment includes a hot-plating step of immersing the steel sheet in a molten plating bath having an adjusted component to form a metal coating layer on the surface of the steel sheet; and the first cooling step is performed The liquidus temperature of the metal coating layer is T _melt in units of ° C, and the metal coating layer is in a state in which a solid phase and a liquid phase coexist, and a volume ratio of the solid phase to the metal coating layer (solid phase) ÷ volume of the volume of the metal coating layer) becomes a temperature range of 0.3 to 0.8 of a unit ℃ timer set T _{solid-liquid,} the temperature of the metal coating layer at a temperature T _melt from T _solid-liquid to the range and the metal The steel sheet after the hot-melt plating step is cooled under the condition that the average cooling rate of the coating layer is 15 ° C / sec to 50 ° C / sec. The second cooling step is based on the temperature of the metal coating layer. 1 the temperature at the end of the cooling step of the cooling step is in the temperature range of 250 ° C, and the average cooling rate of the metal coating layer is 100 ° C / sec to 3000 ° C / sec, the above after the first cooling step The steel plate is cooled.

Further, the liquidus temperature of the metal coating layer, that is, the value of T _melt , can be, for example, a non-patent document of Liang et al. (Liang, P., Tarfa, T., Robinson, JA, shown in Fig. 5). Wagner, S., Ochin, P., Harmelin, MG, Seifert, HJ, Lukas, HL, Aldinger, F., "Experimental Investigation and Thermodynamic Calculation of the Al-Mg-Zn System (Experimental Investigation Thermodynamic Calculation Al-Mg- The Zn system), Thermochim. Acta (Journal of Thermochemistry), 314, 87-110 (1998)) is obtained by the liquidus temperature (liquidus surface temperature). Thus, the value of T _melt can be roughly estimated by the ratio of Zn, Al, and Mg contained in the metal coating layer.

The value of T _solid-liquid can be determined explicitly from the alloy state diagram. Specifically, the alloy state diagram corresponding to the chemical composition of the metal coating layer can be used to determine the volume ratio (volume fraction) of each constituent phase in the complex phase coexistence according to the Libra rule. In other words, the alloy state diagram can be used to determine the temperature at which the volume ratio of the solid phase is 0.3 and the volume ratio of the solid phase to 0.8. In the method for producing a plated steel sheet according to the present embodiment, the value of T _solid-liquid can also be obtained by using an alloy state diagram. At this time, a calculation state map based on the thermodynamic calculation system may also be used as the alloy state map. However, since the alloy state diagram represents the equilibrium state in the end, the configuration obtained from the alloy state diagram is not exactly the same as the configuration performed in the metal coating layer during cooling. The inventors of the present invention have focused on T _solid-liquid , which is a temperature range in which the solid phase of the metal coating layer in the solid phase and the liquid phase in the cooling phase is in the range of 0.3 to 0.8, which is a temperature range of 0.3 to 0.8. found in accordance with the following equation _{{345 + 0.35 × (T melt} -345)} - 5 ≦ T solid-liquid ≦ {345 + 0.35 × (T melt -345)} + 5, can be empirically obtaining T _{solid-liquid.} Therefore, in the method for producing a plated steel sheet according to the present embodiment, the value of T _solid-liquid can also be obtained from the formula.

In the hot-dip plating step, the chemical composition of the metal coating layer formed on the surface of the steel sheet contains, in atom%, Zn: 20% to 60%, Al: 0.3% to 15%, Ca: 0% to 3.5%, Y: 0%~3.5%, La: 0%~3.5%, Ce: 0%~3.5%, Si: 0%~0.5%, Ti: 0%~0.5%, Cr: 0%~0.5%, Fe: 0% ~2%, Co: 0%~0.5%, Ni: 0%~0.5%, V: 0%~0.5%, Nb: 0%~0.5%, Cu: 0%~0.5%, Sn: 0%~0.5 %, Mn: 0%~0.2%, Sr: 0%~0.5%, Sb: 0%~0.5%, Pb: 0%~0.5%, the remainder is composed of Mg and impurities; the chemical of the metal coating Zn in the composition The chemical composition of the plating bath was adjusted in such a manner that the amount and the Al content were 25% ≦Zn+Al in atomic %.

Further, in the present embodiment, the hot-plating step is selected as an example. However, the method of forming a metal coating layer on the surface of the steel sheet is not limited as long as it can form a metal coating layer of the above chemical composition on the surface of the steel sheet. A melt plating method, a spray method, a sputtering method, an ion plating method, a vapor deposition method, and a plating method can be applied.

The metal coating layer formed on the surface of the steel sheet by the hot-dip plating step is in a molten state (liquid phase) immediately after being pulled up from the plating bath. By cooling the metal coating layer in the molten state by the first cooling step and the second cooling step peculiar to the present embodiment, the metal coating layer can be controlled to the above-described metal structure containing the quasicrystal.

When a method of forming a metal coating layer other than the hot-dip plating step is selected, the plated steel sheet having the metal coating layer formed thereon is reheated in a heating furnace, and only after the metal coating layer is melted, the present embodiment is used. The specific first cooling step and the second cooling step are cooled, and the metal coating layer can be controlled to the above-described metal structure containing a quasicrystal.

The melting point of the metal coating layer containing Mg and Zn as main components is completely different from the melting point of the steel sheet which is a base material. Therefore, only the temperature and time at which the molten metal coating layer of the metal coating layer is melted can be easily optimized and determined as long as it is the manufacturer.

For example, when heated at 700 ° C, the metal coating layer is completely melted and the base material, that is, the steel sheet is not melted. In particular, rapid heating by a high-temperature gas environment is preferred because it preferentially heats the plated steel sheet in contact with the gaseous environment. It is a coating, which is preferred.

Further, in the hot-dip plating step, the oxide in the plating bath is 0 g/l to 1 g/l, and the oxygen concentration in the gas atmosphere when the steel sheet is immersed is 0 ppm to 100 ppm by volume, and the plating bath is held. The plating tank is made of steel, and the scum in the plating bath is discharged by using a metal pump, and the temperature of the plating bath, that is, the T _bath is 10 ° C to 100 ° C higher than T _melt , and the steel sheet is immersed in The time in the above plating bath is preferably from 1 second to 10 seconds.

When the oxide in the plating bath is 1 g/l or less, a quasicrystal is favorably generated in the metal structure of the metal coating layer. The oxide in the plating bath is preferably 0.1 g/l or less. When the oxygen concentration is 100 ppm or less by volume, the oxidation of the plating bath can be satisfactorily suppressed. The oxygen concentration is preferably 50 ppm by volume. When the plating tank is made of steel, since the inclusions in the plating bath can be reduced, the metal structure of the metal coating layer can satisfactorily generate quasicrystals. Further, when the plating tank is made of steel and the plating tank is made of steel, it is possible to suppress the occurrence of loss in the inner wall of the plating tank. When the scum in the plating bath is discharged by the metal pump, since the inclusions in the plating bath can be reduced, the metal structure of the metal coating layer can satisfactorily generate quasicrystals. When the temperature of the plating bath, that is, T _bath is 10 ° C to 100 ° C higher than T _melt , the metal coating layer can be favorably formed on the surface of the steel sheet, and the alloy layer containing Fe-Al is formed on the steel sheet and the metal coating layer. between. Further, the temperature of the plating bath, that is, the T _bath is preferably 30 ° C to 50 ° C higher than T _melt . When the steel sheet is immersed in the plating bath for 1 second to 10 seconds, the metal coating layer can be formed well on the surface of the steel sheet, and an alloy layer containing Fe-Al is formed between the steel sheet and the metal coating layer. . Further, the time during which the steel sheet is immersed in the plating bath is preferably 2 seconds to 4 seconds.

In the first cooling step, the temperature of the metal coating layer is controlled from the liquidus temperature of the metal coating layer, that is, T _melt , to the metal coating layer (liquid phase + solid phase), and the volume ratio of the solid phase is 0.3 to 0.8. The temperature range, that is, the average cooling rate of the metal coating in the case of T _solid-liquid , is important. In the first cooling step, the average cooling rate is controlled so as to be 15 ° C / sec to 50 ° C / sec, and the steel sheet on which the metal coating layer is formed is cooled.

By cooling in the first cooling step, in the metal coating layer in the molten state (liquid phase) before the start of cooling, the quasicrystal system is crystallized as a primary crystal. Preferably, the quasicrystal system after crystallization grows slowly under the controlled cooling rate range, and finally becomes a quasi-crystal phase containing an average circle equivalent diameter of more than 1 μm in the coarse region.

When the average cooling rate in the first cooling step is less than 15 ° C / sec, it is difficult to generate a quasicrystal because the cooling rate of the quasi-crystal phase originally generated in the non-equilibrium phase is not reached. On the other hand, when the average cooling rate in the first cooling step is more than 50 ° C / sec, since the quasi-crystal phase does not reach 1 μm, the average circular equivalent diameter which does not become the quasi-crystal phase is more than 1 μm. Further, it is impossible to form a coarse region mainly containing a quasi-crystal phase, and there is a case where the above-described bimodal structure is not obtained. Further, when the cooling rate is particularly large, since the constituent phase such as the amorphous phase is also generated, the upper limit of the average cooling rate in the first cooling step is set to 50 ° C / sec.

In the first cooling step, when the temperature lower than T _{melt and} the average cooling rate of the metal coating layer are controlled to the above conditions, the primary crystal which is crystallized in the metal coating layer cannot be made into a quasicrystal phase. The Al phase, the Zn phase, and the Mg which are constituent phases other than the quasi-crystal may be crystallized in the form of primary crystals, and may be formed by incomplete quasicrystals which have not grown to a predetermined size. The area fraction of the coarse area is also not well controlled. Further, when the temperature above the T _solid-liquid is controlled to stop the above-described average cooling rate, or when the average cooling rate is controlled to a lower temperature than the T _solid-liquid , the above-described average cooling rate cannot be controlled to the above condition. Good control of the average circular equivalent diameter and area fraction of the quasicrystalline phase. Further, there is a case where it is impossible to control the bimodal structure composed of the coarse region and the fine region described above. In particular, there is a case where a specific phase grows in a fine region and does not become the above-described bimodal structure. In addition, when the volume ratio of the solid phase to the metal coating layer is set to a temperature not lower than 0.3 to 0.8 and the first cooling step is performed, the average circular equivalent diameter and area of the quasicrystal phase cannot be satisfactorily controlled. The rate. Further, there is a case where it is impossible to control the bimodal structure composed of the above-described coarse region and fine region. Thus, in order to stably grow without destroying the crystallized quasicrystal, the specific cooling conditions as described above are necessary.

In the second cooling step, the temperature of the metal coating layer is controlled from the temperature at the end of the cooling in the first cooling step, that is, from the first cooling end temperature in the T _solid-liquid to the average cooling of the metal coating layer at 250 ° C. Speed is important. The average cooling rate is controlled so as to be 100 ° C / sec to 3000 ° C / sec, and the steel sheet after the first cooling step is cooled. The lower limit of the above temperature range is preferably 200 ° C, more preferably 150 ° C, and most preferably 100 ° C.

In the metal coating layer in which the quasicrystal is crystallized and the solid phase and the liquid phase coexist in the cooling in the second cooling step, Mg ₅₁ Zn ₂₀ phase, Mg ₃₂ (Zn, Al) ₄₉ phase At least one of the MgZn phase, the MgZn ₂ phase, and the Zn phase generates crystals. The Mg ₅₁ Zn ₂₀ phase, the Mg ₃₂ (Zn, Al) ₄₉ phase, the MgZn phase, the MgZn ₂ phase, or the Zn phase after crystallization is preferably a constituent phase contained in the fine region at the end.

In the second cooling step, when the average cooling rate is controlled to the above condition from a temperature higher than T _solid-liquid or a temperature lower than T _solid-liquid , the average circle of the quasi-crystal phase cannot be well controlled. Equivalent diameter and area fraction. Further, there is a case where it is impossible to control the bimodal structure composed of the coarse region and the fine region described above. When the above-described average cooling rate is controlled to a temperature higher than 250 ° C, the quasi-crystal phase of the non-equilibrium phase, the Mg ₅₁ Zn ₂₀ phase, and the Mg ₃₂ (Zn, Al) ₄₉ phase are decomposed. Further, there is a case where it is impossible to control the bimodal structure composed of the above-described coarse region and fine region. Further, when the average cooling rate in the second cooling step is less than 100 ° C / sec, the Mg ₅₁ Zn ₂₀ phase, the Mg ₃₂ (Zn, Al) ₄₉ phase, the MgZn phase, the MgZn ₂ phase, or the Zn phase may not be generated, or It is a metal structure that is particularly rich in Mg. Further, there may be cases where the Mg ₅₁ Zn ₂₀ phase, the Mg ₃₂ (Zn, Al) ₄₉ phase, the MgZn phase, the MgZn ₂ phase, or the Zn phase are not in a fine region. When the average cooling rate in the second cooling step is more than 3,000 ° C / sec, a constituent phase such as an amorphous phase may be generated and the above-described bimodal structure may not be controlled.

As described above, the liquidus temperature of the metal coating layer, that is, T _melt , can be obtained from the liquid phase map of the Zn-Al-Mg ternary system. Further, with respect to the metal coating layer, the volume ratio of the solid phase is a temperature range of 0.3 to 0.8, that is, T _solid-liquid , which can be from the following formula, {345 + 0.35 × (T _melt -345)} -5 ≦ T _{solid -liquid} ≦ {345+0.35×(T _melt -345)}+5. In the case where the volume ratio of the solid phase to the metal coating layer is in the range of 0.3 to 0.8, the reason why the cooling in the first cooling step is completed is because the solid phase system is explosively increased in the vicinity of the temperature range. By controlling {345 + 0.35 × (T _{melt -} 345)} as a reference and cooling at least ± 5 ° C, the average circular equivalent diameter and the area fraction of the quasi-crystal phase can be favorably controlled. Thus, in order to form the metal coating layer described above, precise temperature control is necessary.

In the present embodiment, a method of measuring the temperature of the metal coating layer in the case of producing a plated steel sheet may be a contact type thermocouple (K-type). By mounting the contact type thermocouple on the original plate, the average temperature of the entire metal coating layer can be constantly monitored. When the pulling speed and the thickness control are controlled mechanically, and the preheating temperature of the steel sheet, the temperature of the molten plating bath, and the like are unified, the temperature of the entire metal coating layer at this point under the manufacturing conditions can be substantially accurately monitored. Therefore, it is possible to precisely control the cooling in the first cooling step and the second cooling step. Moreover, although it is not as correct as the contact type, the surface temperature of the metal coating layer can also be measured using a non-contact radiation thermometer.

Further, the relationship between the surface temperature of the metal coating layer and the average temperature of the entire metal coating layer can be obtained by performing cooling simulation of heat conduction analysis. Specifically, it is based on the preheating temperature of the steel sheet, the temperature of the molten plating bath, the drawing speed of the steel sheet from the plating bath, the thickness of the steel sheet, the layer thickness of the metal coating layer, the heat exchange heat between the metal coating layer and the manufacturing equipment, The surface temperature of the metal coating layer and the average temperature of the entire metal coating layer may be determined under various production conditions such as the heat release amount of the metal coating layer. Then, the relationship between the surface temperature of the metal coating layer and the average temperature of the entire metal coating layer may be determined. Its knot Therefore, since the average temperature of the entire metal coating layer at this point in the production condition can be analogized by actually measuring the surface temperature of the metal coating layer during the production of the plated steel sheet, the first cooling step and the second cooling step can be performed. Precise control of cooling.

The cooling method in the first cooling step and the second cooling step is not particularly limited. As the cooling method, the rectified high-pressure gas cooling, the spray cooling (Mist cooling), and the flooding cooling may be performed. However, in order to favorably control the surface state of the metal coating layer and generate quasicrystals, it is preferred to use a rectified high pressure gas for cooling. When H ₂ and He are used, the cooling rate increases.

In the hot-dip plating method applied in the present embodiment, all known plating methods such as a Sendzimir method, a pre-plating method, a two-stage plating method, and a flux method can be applied. The pre-plating system can use a substitution plating, an electroplating, a vapor deposition method, or the like.

The steel material used as the base material of the plated steel sheet is not particularly limited as the method for producing the plated steel sheet according to the embodiment. The above effects are not affected by the chemical composition of the steel, and aluminum all-steel steel, ultra-low carbon steel, high carbon steel, various high-tensile steels, and steels containing Ni and Cr can be used.

Further, in the method for producing a plated steel sheet according to the present embodiment, the steps of the steel making step, the hot rolling step, the pickling step, and the cold rolling step before the hot-plating step are also not particularly limited. That is, the production conditions of the steel sheet to which the hot-dip plating step is provided and the material of the steel sheet are not particularly limited.

However, the steel sheet to which the melt plating step is provided has a temperature difference between the surface and the inside thereof. Specifically, it is immersed in the plating bath before The steel plate is preferably such that its surface temperature is higher than the internal temperature. For example, the surface temperature of the steel sheet before being immersed in the plating bath is preferably about 10 ° C to 50 ° C higher than the center temperature of the sheet thickness direction of the steel sheet. At this time, since the metal coating layer can be exhausted by the steel sheet immediately after being pulled up from the plating bath, the metal coating layer can be favorably controlled to the above-described metal structure containing the quasicrystal. The method of causing the steel sheet before being immersed in the plating bath to have a temperature difference between the surface and the inside is not particularly limited. For example, the steel sheet immersed in the plating bath is rapidly heated by a high-temperature gas atmosphere, and only the surface temperature of the steel sheet is controlled to a preferred temperature for melt plating. At this time, the surface area of the steel sheet is preferentially heated, and it can be immersed in the plating bath in a state where the surface of the steel sheet has a temperature difference from the inside.

In order to evaluate the corrosion resistance of the metal coating layer, an exposure test capable of evaluating the corrosion resistance of the metal coating layer in an actual environment is preferred. The corrosion resistance can be evaluated by evaluating the corrosion reduction of the metal coating layer in a certain period of time.

When the corrosion resistance of the metal coating layer having high corrosion resistance is compared, it is preferable to carry out the corrosion resistance test for a long period of time. The corrosion resistance was evaluated based on the magnitude of the period until red rust was generated. Further, when evaluating the corrosion resistance, it is also considered that the corrosion prevention period of the steel sheet is important.

In order to evaluate the corrosion resistance more easily, a corrosion promotion test such as a combined cycle corrosion tester or a salt spray test can be used. By evaluating the corrosion reduction and red rust rust prevention period, it is possible to judge the merits of corrosion resistance. When comparing the corrosion resistance of the metal coating with high corrosion resistance, it is preferable to use a corrosion promotion test using a high concentration of about 5% NaCl water. Melt. When a thin concentration (1% or less) of NaCl water melt is used, it is not easy to judge the merits of corrosion resistance.

Further, organic or inorganic chemical treatment may be performed on the metal coating layer. Since the metal coating layer of the present embodiment contains a certain amount or more of Zn in the metal coating layer, the same chemical treatment as the Zn-based plated steel sheet can be performed. The same applies to the chemical treatment of the coating on the film. Moreover, the original board which is a laminated steel plate can also be utilized.

The use of the plated steel sheet according to the present embodiment is considered to be possible in a place where the corrosion environment is particularly severe. It is possible to use various kinds of plated steel sheets that are used in the fields of building materials, automobiles, home appliances, and energy.

[Example 1]

Next, the effects of one aspect of the present invention will be described in more detail by way of examples, but the conditions of the examples are a conditional example employed to confirm the implementation possibilities and effects of the present invention, and the present invention is not This conditional example is limited. The present invention can be applied to various conditions without departing from the gist of the present invention and achieving the object of the present invention.

The plated steel sheet containing the quasicrystal was produced by the melt plating step, the first cooling step, and the second cooling step of the manufacturing conditions shown in Tables 1 to 5. The plating bath is obtained by melting a predetermined amount of each pure metal ingot. The plating bath is controlled to a predetermined oxygen concentration by being covered with a sealed box and substituted with Ar gas.

As a plated original plate (a steel plate which is a base material of a plated steel plate), a hot-rolled steel sheet having a thickness of 0.8 mm (carbon content: 0.2% by mass) was used. The steel plate system was cut to be 100 mm × 200 mm. Melt plating uses batch type melt plating Apply the test device. The temperature of the plated steel sheet in production is the center portion of the steel sheet.

Before immersing the steel sheet in the plating bath, the surface of the steel sheet heated to 800 ° C was reduced using a N ₂ -5% H ₂ gas in a furnace having a controlled oxygen concentration. The steel crucible was air-cooled using N 2 gas, and after the surface temperature of the steel sheet reached a temperature higher than the bath temperature of the plating bath by 20 ° C, the steel sheet was immersed in the plating bath for a predetermined time. After immersing in the plating bath, the steel sheet was pulled up at a pulling speed of 100 mm/sec. When the lift is applied, the high-pressure N ₂ gas or the mixed gas of H ₂ and N _{2 which is obtained} by rectifying the blowout port by the parallel slit is blown to control the plating adhesion amount (thickness of the metal coating layer) and the cooling rate. .

A sample of 20 (C direction: plate width direction) mm × 15 (L direction: rolling direction) mm was used from any ten of the produced plated steel sheets. These oxides were immersed in a 10% HCl water melt for 1 second to remove the oxide film. The metal structure of the cross section of each sample (the cutting direction was parallel to the plate thickness direction) was observed by SEM, and the circle equivalent diameter and the area fraction of each constituent phase (each crystal grain) were measured, and the average value was calculated. Further, the circle equivalent diameter and the area fraction of each constituent phase are obtained by image analysis. Further, the chemical components of the constituent phases were measured by EPMA analysis.

Further, the metal structure of any three of the ten samples was observed using an optical microscope (×1000 times), and Vickers Identation was applied to the target. A Vickers indentation was used as a reference to cut a sample of 8 mm square. A sample for TEM observation was produced from each sample by a low temperature ion etching method.

Electron ray diffraction images of the main crystal grains observed by TEM were used to analyze and identify the constituent phases contained in the metal structure (quasi-crystal, Mg ₅₁ Zn ₂₀ , Mg ₃₂ (Zn, Al) ₄₉ , MgZn, Zn Wait). Further, the circle equivalent diameter and the area fraction of each constituent phase were determined by image analysis as necessary, and the chemical composition of each constituent phase was measured by analysis using EDX. The determination of the presence or absence of the Mg phase was confirmed by XRD. When the diffraction intensity of the Mg phase of the XRD diffraction pattern is smaller than the regulation, it is judged that the metal structure of the metal coating layer does not contain the Mg phase.

The corrosion resistance, sacrificial corrosion resistance, antiglare effect, appearance, and adhesion of the metal coating layer of the produced plated steel were evaluated. Further, in terms of corrosion resistance, corrosion reduction, red rust generation, white rust generation, and red rust in the processed portion were evaluated.

The corrosion reduction was evaluated by a corrosion promotion test (CCT: Combined Cycle Corrosion Test) according to JASO (M609-91) cycle. Specifically, a sample of 50 (C direction) mm × 100 (L direction) mm was cut out from the produced plated steel sheet and a corrosion promotion test was provided to evaluate the corrosion loss. The corrosion promotion test (CCT) was carried out using a 0.5% NaCl water melt and the corrosion loss after 150 cycles was evaluated.

In the evaluation of the corrosion reduction, the plated steel sheet having a corrosion loss of less than 20 g/m ² was judged as "Excellent", and the plated steel sheet having a corrosion loss of 20 g/m ² to less than 30 g/m ² was judged as "Good", and the plated steel sheet having a corrosion loss of 30 g/m ² or more was judged to be "Poor". Moreover, "excellent" means that the corrosion loss is evaluated to be the most excellent.

The red rust generation was evaluated by the above corrosion promotion test (CCT). Specifically, the corrosion-promoting test (CCT) using a 5% NaCl water melt was carried out using the produced plated steel sheet to investigate the plane portion of the plated steel sheet. The number of test cycles of red rust greater than 5% in area % was produced.

In the evaluation of the occurrence of red rust, the plated steel sheet in which the red rust was not confirmed after 300 cycles was judged as "Excellent", and the plated steel sheet in which the red rust could not be confirmed after 150 cycles was judged as "" Very good (Very. Good), the plated steel sheet in which the red rust was not confirmed after 100 cycles was judged as "Good", and the plated steel sheet which was able to confirm the red rust was judged to be less than 100 cycles. "Poor". In addition, "(Excellent)" indicates that the red rust is evaluated to be the most excellent.

White rust generation was evaluated by a salt spray test (SST: Salt Spray Test) according to JIS Z2371:2000. Specifically, a salt spray test (SST) using a 5% NaCl water melt was used to test a white rust having a surface area of more than 5% in the plane portion of the plated steel sheet using the produced plated steel sheet. Elapsed time.

In the evaluation of the occurrence of white rust, the plated steel sheet in which the white rust cannot be confirmed after 120 hours has been judged as "Excellent", and the plated steel sheet in which the white rust cannot be confirmed after 24 hours has passed is determined. It is "Good", and the plated steel sheet which can confirm the white rust after less than 24 hours is judged as "Poor". Moreover, "excellent" means that white rust is evaluated to be the most excellent.

The red rust generation in the processed portion was evaluated by using the above-described salt spray test (SST) using a plated steel sheet subjected to bulging processing. Specifically, the embossing process according to JIS Z2247:2006 was carried out using the produced plated steel sheet under the conditions of a press-in depth (moving distance of the punch) of 7 mm. A salt spray test using a 5% NaCl water melt using the plated steel sheet In the test (SST), the test elapsed time in which the top portion of the bulging process (the region having the top of the center of the diagonal of the square is 45 mm) was produced in area % yielded red rust of more than 5%.

In the evaluation of the red rust in the processing unit, the plated steel sheet in which the red rust was not confirmed after 600 hours was judged as "Excellent", and the plated steel sheet in which the red rust could not be confirmed after 240 hours passed was determined. It is "Good", and the plated steel sheet which can confirm the red rust is less than 240 hours and is judged as "Poor". Moreover, "excellent" means that the red rust is evaluated to be the most excellent.

Sacrificial corrosion resistance is evaluated according to electrochemical methods. Specifically, the produced plated steel sheet was immersed in a 0.5% NaCl water melt, and the corrosion potential of the produced plated steel sheet was measured using an Ag/AgCl reference electrode. At this time, the corrosion potential of Fe showed about -0.62V.

In terms of evaluating the sacrificial corrosion resistance, the plated steel sheet having a corrosion potential of -0.9 V to -0.62 V was judged to be "Excellent" with respect to the Ag/AgCl reference electrode, and the corrosion potential was less than -1.0 to - The plated steel sheet of 0.9 V was judged to be "Very Good", and the plated steel sheet having a corrosion potential of -1.3 to less than -1.0 V was judged as "Good", and the corrosion potential was not -1.3. The plated steel sheet of V~-0.62V was judged as "Poor". Further, "excellent" means excellent, and the potential difference from iron is small, and sacrificial anticorrosive action is appropriately generated.

The anti-glare effect was evaluated using a spectrophotometric method. Originally by visual evaluation, it is better to confirm the visual correlation with the L* value of the color meter, and then use a spectrophotometer (D65 light source, 10° field of view) and The SCI (including specular reflection light) was evaluated. Specifically, the L* value was examined under the conditions of measuring the diameter of 8φ, the field of view of 10°, and the D65 light source using the spectrophotometer CM2500d manufactured by Konica Minolta.

In the anti-glare effect, the plated steel sheet having an L* value of less than 75 was judged as "Excellent", and the plated steel sheet having an L* value of not less than 75 was judged as "Poor". Moreover, "Excellent" means that the anti-glare effect is excellent.

The appearance of the plated steel sheet was evaluated by a storage test in a constant temperature and humidity chamber. Specifically, the produced plated steel sheet was stored in a constant temperature and humidity chamber at a temperature of 40 ° C and a humidity of 95% for 72 hours, and the area % of the blackening portion of the flat portion of the plated steel sheet after storage was investigated. .

In terms of the appearance evaluation, the plated steel sheet having a blackened portion of less than 1% in terms of the area of evaluation was judged to be "Excellent" with respect to the evaluation area of 45 mm × 70 mm, and the blackened portion was 1% to less than 3% of the plated steel sheets were judged to be "good", and the plated steel sheets having a black portion of 3% or more were judged as "Poor". Moreover, "excellent" means that the appearance is evaluated to be the most excellent.

The adhesion of the metal coating layer was evaluated by a 4T bending test (180 degree bending test). Specifically, a 20 mm × 80 mm sample was cut out from the produced plated steel sheet and a 4T bending test (180 degree bending test) was provided. Further, T means the thickness of the plated steel sheet and is about 0.8 mm. Further, the bending direction is the C direction of the steel sheet. The peeling test of the metal coating layer was examined by performing a tape peeling test on the inner side of the bending of the test piece after the bending test.

In the evaluation of the adhesion of the metal coating layer, the plated steel sheet in which the metal coating layer was not peeled off was judged to be "Excellent", and the plated steel sheet having the metal coating layer peeled off of less than 5 mm ² was judged to be "very good". (Very Good), the plated steel sheet having a metal coating layer peeled off from 5 mm ² to less than 10 mm ² was judged as "good", and the plated steel sheet having a metal coating layer peeled off of 10 mm ² or more was judged as "good". Poor. Moreover, "excellent" means that the adhesion is evaluated to be the most excellent.

The corrosion resistance after pulverization of the plated steel sheet can be evaluated by using the test of the conditions shown below. Specifically, a sample of a size of 300 mm × 600 mm was cut out using the produced plated steel sheet (thickness 0.8 mm, plating thickness 10 μm). A bending process of a 90° processed portion was performed at the center of the sample. Using a sample after bending, a salt spray test (SST) using a 5% NaCl water melt was used to investigate the occurrence of red rust on the inner surface of the processed portion. Further, in the salt spray test, the sample after the bending process was subjected to tape repair around, and then the height was set to 300 mm.

In the evaluation of the corrosion resistance after the pulverization, the plated steel sheet in which the red rust was not confirmed after 720 hours from the start of the salt spray test was judged as "Excellent", and the red rust could not be confirmed after 480 hours passed. The plated steel sheet was judged to be "good", and it was confirmed that the plated steel sheet of the red rust was "Poor" at the time of 480 hours. Moreover, "excellent" means that the corrosion resistance after pulverization is evaluated to be the most excellent.

The above production conditions, production results, and evaluation results are shown in Tables 1 to 30. Also, in the table, the additional bottom line value indicates the scope of the present invention. Outside, the empty column indicates that the alloying elements are not intentionally added.

Each of Examples Nos. 1 to 58 is a plated steel sheet which satisfies the scope of the present invention and is excellent in corrosion resistance and sacrificial corrosion resistance. On the other hand, in Comparative Examples Nos. 1 to 25, since the conditions of the present invention were not satisfied, the corrosion resistance or the sacrificial corrosion resistance was insufficient.

Industrial availability

According to the above aspect of the present invention, it is possible to provide a plated steel sheet which is required to be improved in corrosion resistance when used in the fields of building materials, automobiles, and home appliances. Therefore, the life of the member can be longer than that of the prior surface treated steel sheet. Therefore, the possibility of utilization in the industry is high.

1‧‧‧ steel plate

2‧‧‧Metal coating

2a‧‧‧Large area

2b‧‧‧Micro-area

Claims (12)

A plated steel sheet containing a quasi-crystal, comprising a steel sheet and a metal coating layer disposed on a surface of the steel sheet; the plated steel sheet characterized in that the chemical composition of the metal coating layer is in atom%, and contains: Zn: 20% to 60% %, Al: 0.3% to 15%, Ca: 0% to 3.5%, Y: 0% to 3.5%, La: 0% to 3.5%, Ce: 0% to 3.5%, Si: 0% to 0.5%, Ti: 0% to 0.5%, Cr: 0% to 0.5%, Fe: 0% to 2%, Co: 0% to 0.5%, Ni: 0% to 0.5%, V: 0% to 0.5%, Nb: 0%~0.5%, Cu: 0%~0.5%, Sn: 0%~0.5%, Mn: 0%~0.2%, Sr: 0%~0.5%, Sb: 0%~0.5%, Pb: 0% to 0.5%, and the remainder is composed of Mg and impurities; the zinc content and the aluminum content in the aforementioned chemical composition of the metal coating layer are in atom%, satisfying 25% ≦Zn+Al; the aforementioned metal coating The metal structure of the layer contains a quasi-crystal phase; the magnesium content, the zinc content and the aluminum content contained in the quasi-crystal phase satisfy 0.5 ≦Mg / (Zn + Al) ≦ 0.83 in atomic %; the average circle of the quasi-crystal phase, etc. The effect diameter is greater than 1 μm to 200 μm. The plated steel sheet containing the quasi-crystal according to claim 1, wherein the calcium content, the indium content, the niobium content, and the niobium content in the chemical composition of the metal coating layer are 0.3% ≦Ca+Y+La+ in atomic %. Ce≦ 3.5%. The quasi-crystal-containing plated steel sheet according to claim 1, wherein the ruthenium content, the titanium content, and the chromium content in the chemical composition of the metal coating layer satisfy 0.005% ≦Si+Ti+Cr≦0.5% in atom%. The quasi-crystal-containing plated steel sheet according to claim 1, wherein the zinc content and the aluminum content in the chemical composition of the metal coating layer are 30% ≦Zn+Al≦50%, and 3≦ in terms of atomic %. Zn/Al≦12. In the plated steel sheet containing the quasi-crystal of claim 1, when the metal coating layer is observed in a cross section parallel to the cutting direction in the thickness direction of the plate, the metal structure of the metal coating layer is composed of a fine region and a coarse region. a bimodal structure consisting of crystal grains having a circle equivalent diameter of 1 μm or less, and the coarse region is composed of crystal grains having a circle equivalent diameter of more than 1 μm; the coarse region containing the quasicrystal phase; The fine region contains at least one of a Mg ₅₁ Zn ₂₀ phase, a Mg ₃₂ (Zn, Al) ₄₉ phase, a MgZn phase, a MgZn ₂ phase, and a Zn phase. The quasi-crystal-containing plated steel sheet according to claim 5, wherein an area fraction of the coarse region is 5% to 80% with respect to the metal structure; and an area fraction of the fine region is 20 with respect to the metal structure. %~95%. The plated steel sheet containing a quasi-crystal according to claim 5, wherein an area fraction of the quasi-crystal phase contained in the coarse region is 80% to less than 100% with respect to the coarse region; and the aforementioned fine region contains The total area fraction of the Mg ₅₁ Zn ₂₀ phase, the Mg ₃₂ (Zn, Al) ₄₉ phase, the MgZn phase, the MgZn ₂ phase, and the Zn phase is 80% to less than 100% with respect to the fine region. The plated steel sheet containing the quasi-crystal according to Item 5, wherein the thickness of the metal coating layer is D when viewed from the cross section, and the surface of the metal coating layer is oriented toward the steel sheet 0.3 along the thickness direction of the sheet. When the range of the surface of the metal coating layer is the surface of the metal coating layer, and the range from the interface between the steel sheet and the metal coating layer toward the metal coating layer 0.3×D in the thickness direction of the sheet is the depth of the metal coating layer, The area ratio of the coarse region is 10% to less than 100% with respect to the surface portion of the metal coating layer, and the area ratio of the coarse region is 10% to less than 100% with respect to the deep portion of the metal coating layer; When the surface of the metal coating layer and the deep portion of the metal coating layer in the metal coating layer are the center portion of the metal coating layer, the area ratio of the fine region is 50% to the center portion of the metal coating layer. Less than 100%. The quasi-crystal-containing plated steel sheet according to claim 1, wherein the metal structure of the metal coating layer does not contain a Mg phase. The quasi-crystal-containing plated steel sheet according to claim 1, wherein the plated steel sheet further has an alloy layer containing Fe-Al; and the Fe-Al-containing alloy layer is disposed between the steel sheet and the metal coating layer; The Fe-Al-containing alloy layer contains at least one of Fe ₅ Al ₂ or Al _3.2 Fe; and the Fe-Al-containing alloy layer has a thickness of 10 nm to 1000 nm. A method for producing a plated steel sheet containing a quasi-crystal, the method for producing a quasi-crystal-containing plated steel sheet according to any one of claims 1 to 10, wherein the method comprises: a hot-plating step of impregnating the steel sheet In the molten plating bath of the adjusted component, a metal coating layer is formed on the surface of the steel sheet; and in the first cooling step, the liquidus temperature of the metal coating layer is set to T _melt in units of ° C, and the metal coating is applied. The layer is a state in which the solid phase and the liquid phase coexist, and the temperature of the metal coating layer is set to T _solid-liquid in a temperature range of 0.3 to 0.8 with respect to the metal coating layer when the volume ratio of the solid phase is 0.3 to 0.8. The steel sheet after the hot-melt plating step is cooled under the conditions of a temperature range from T _melt to T _solid-liquid and an average cooling rate of the metal coating layer of 15 ° C / sec to 50 ° C / sec; The cooling step is performed in a temperature range from a temperature at which the cooling of the first cooling step is completed to a temperature range of 250 ° C, and an average cooling rate of the metal coating layer is 100 ° C / sec to 3000 ° C / Under the conditions, after the first cooling step of the steel sheet is cooled. The method for producing a quasi-crystal-containing plated steel sheet according to claim 11, wherein in the molten plating step, the oxide in the plating bath is 1 g/l or less; and the oxygen concentration of the gas atmosphere when the steel sheet is immersed is in a volume The ratio is 100 ppm or less; the plating bath for holding the plating bath is made of steel; the scum in the plating bath is discharged by a metal pump; and the temperature of the plating bath is T _bath The T _melt is 10 ° C to 100 ° C high; the immersion time of the steel sheet in the plating bath is 1 second to 10 seconds.