JP2018090885A - MOLTEN Zn-Al-Mg GROUP PLATED SHEET STEEL, AND MOLTEN Zn-Al-Mg GROUP PLATED SHEET STEEL MANUFACTURING METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molten Zn-Al-Mg alloy plated sheet metal having a molten Zn-Al-Mg alloy plated layer, in which the exposure of a base material steel plate hardly occurs due to cracking and peel in a processing part of a molten Zn-Al-Mg alloy plated layer so that the reduction of anticorrosion in the processing part is suppressed and so that the plated sheet can be manufactured not by the rapid low-temperature heating.SOLUTION: A molten Zn-Al-Mg alloy plated sheet metal of the invention comprises a base material steel plate, a Ni plated layer having a thickness of 0.3 μm to 4.0 μm, and a molten Zn-Al-Mg alloy plating layer of Al: 1.0 weight % to 22.0 weight %; Mg: 0.5 weight % to 10.0 weight %, and the remainder being made of Zn, and a Ni-Al based inter-metallic compound between the Ni plated layer and the molten Zn alloy plated layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a molten Zn—Al—Mg-based plated steel sheet and a method for producing a molten Zn—Al—Mg-based plated steel sheet.

  The Zn-based plated steel sheet has a low manufacturing cost and has an effect of protecting the steel material from rust by a sacrificial anticorrosive effect. Therefore, Zn-based plated steel sheets are used in a wide range of fields such as automobiles, building materials, home appliances, and civil engineering.

  A Zn-55% Al alloy-plated steel sheet has been developed as a Zn-based plated steel sheet with higher corrosion resistance and longer life due to Al passivation. However, the Zn-55% Al alloy plated steel sheet has a relatively low Zn content due to the addition of high Al, so that the sacrificial corrosion protection effect is lower than that of the Zn plated steel sheet, and the surface of the plated steel is damaged. When exposed, corrosion is likely to occur. Furthermore, alloy plating generally contains an intermetallic compound in the plating layer, so it is difficult to be plastically deformed, and the plating layer is cracked or peeled off by various processing, and the base steel sheet is likely to be exposed. It's easy to do.

  As a Zn-based plated steel sheet in which both the passivation by Al and the sacrificial anticorrosive effect by Zn have been enhanced, a molten Zn-Al-Mg-based plated steel sheet has been developed. The hot-dip Zn-Al-Mg-based plated steel sheet is a base steel sheet in the periphery of the processed part because Zn corrosion products produced by the sacrificial anticorrosive effect are densified by Mg in addition to the increase in corrosion resistance due to Al passivation. The corrosion resistance of the processed part is greatly improved.

  However, even alloy-plated steel sheets such as hot-dip Zn-Al-Mg-plated steel sheets contain intermetallic compounds in the plating layer, so that the plating layer is difficult to be plastically deformed, and cracks and peeling of the plating layer occur due to various processing, and the base steel sheet Is still easy to expose. Moreover, it cannot be said that the corrosion resistance of the processed part where the base steel sheet is exposed is increased to the same level as that of the unprocessed part even in a molten Zn—Al—Mg-based plated steel sheet.

  With respect to this problem, in Patent Document 1, various alloy platings such as molten Zn—Al alloy plating, molten Zn—Al—Mg alloy plating, and Al—Si alloy plating are kept heated in a temperature range of 50 ° C. or more and less than 150 ° C. By processing (warm processing), the crack of the plating layer is greatly reduced, and the deterioration of the corrosion resistance in the processed portion is suppressed. Further, in Patent Document 2, the Zn-based alloy plating is heat-treated at a temperature of 90 ° C. or higher and lower than 300 ° C. to generate a fine crystal layer in the plating layer, and the cracking of the plating layer due to the processing is refined, thereby providing corrosion resistance in the processed portion. Is suppressed.

  In Patent Document 3, a thermosetting resin coating film having an elongation of 100% or more is laminated on a molten Zn—Al—Mg alloy plating layer through an epoxy resin coating film having excellent adhesion, and the elongation described above is achieved. By covering the plated layer with cracks in a coating film having a high rate and making it difficult to expose the base steel plate, a decrease in corrosion resistance in the processed portion is suppressed.

Moreover, in patent document 4, a Ni plating layer is provided in the lower layer of a hot-dip Zn type alloy plating layer, a Ni-Al-Fe-Zn compound is produced | generated in the interface of a plating layer and a base-material steel plate, The binder of this intermetallic compound By improving the adhesion of the molten Zn-based alloy plating layer by the effect, cracking and peeling of the molten Zn-based alloy plating layer are suppressed, and a decrease in corrosion resistance in the processed portion is suppressed. In Patent Document 4, after applying a pre-Ni plating with an adhesion amount of 0.2 g / m ² or more to 2 g / m ² or less to a base steel sheet, rapid low temperature heating is performed in a non-oxidizing or reducing atmosphere, and then It is described that a hot-dip Zn-based alloy-plated steel sheet having the intermetallic compound can be produced by hot-dip plating in a Zn plating bath containing Al.

Moreover, in patent document 5, the layer by a Ni-Al-Zn compound is formed in the interface of a molten Zn-type alloy plating layer and a base-material steel plate by providing a Ni plating layer in the lower layer of a hot-dip Zn-type alloy plating layer, By suppressing the growth of the Γ phase in the Fe—Zn-based intermetallic compound in the layer and enhancing the adhesion of the molten Zn-based alloy plating layer, cracking and peeling of the molten Zn-based alloy plating layer are suppressed, and the processed part The deterioration of the corrosion resistance is suppressed. In Patent Document 5, after a pre-Ni plating having an adhesion amount of 0.2 g / m ² or more and 2 g / m ² or less is applied to a base steel sheet, the plate temperature is 430 ° C. or more and 500 ° C. or less in a non-oxidizing or reducing atmosphere. It is described that a hot-dip Zn-based alloy-plated steel sheet having the above-described configuration can be manufactured by performing rapid heating at a heating rate of 30 ° C./second in the range, and then performing hot-dip plating in a Zn plating bath containing Al. Yes.

In Patent Document 6, Ni ₂ Al ₃ derived from the Ni plating layer is generated in the plating layer, thereby suppressing plating peeling during processing due to overalloying and deterioration in appearance quality due to uneven alloying. ing. Patent Document 6, after the deposition amount is subjected to a pre-Ni plating 0.05 g / ^{m 2} or more 0.25 g / ^{m 2} or less to the substrate steel sheet, the range of the plate temperature 405 ° C. or higher 415 ° C. or less in a reducing atmosphere It is described that a hot-dip Zn-based alloy-plated steel sheet having the above-described configuration can be manufactured by performing rapid heating at a heating rate of 50 ° C./second and then performing hot-dip plating in a Zn plating bath containing Al. .

  When forming the molten Zn-based alloy plating layer, the base steel sheet is heated to a temperature near or higher than the melting point of Zn (about 430 ° C.). Therefore, the formation of the molten Zn-based alloy plating layer has an advantage that the annealing of the base steel plate and the formation of the plating layer can be performed continuously in the same apparatus as a series of steps. Annealing means heating and gradual cooling of the base steel sheet to recrystallize the crystal structure crushed by rolling, soften the base steel sheet, and reduce the surface of the base steel sheet to improve the plateability. Usually, for example, as described in Patent Document 7, the base steel sheet is heated to a temperature higher than 500 ° C.

JP 2008-1111189 A JP 2011-190507 A JP 2003-277903 A JP 2000-325871 A Japanese Patent Laid-Open No. 4-147533 JP 2009-280859 A JP 2014-189812 A

  As described in Patent Documents 1 to 6, various methods have been proposed for suppressing a decrease in corrosion resistance in a processed part in a plated steel sheet having an alloy plating layer. Among these, as described in Patent Documents 4 to 6, the method of forming the hot-dip Zn-based alloy plating layer after forming the Ni plating layer on the base steel sheet is based on the additional apparatus and the manufacturing conditions of the plated steel sheet. Close control is unnecessary, and there is an advantage that the reduction of the effect due to an external corrosion factor hardly occurs.

Here, Patent Document 4 and Patent Document 5, the adhesion amount of the Ni plating has a 0.2 g / ^{m 2} or more 2.0 g / ^{m 2} or less. Since the density of Ni at room temperature is about 8.9 g / cm ³ (about 8.9 × 10 ⁶ g / m ³ ), the thickness of the Ni plating layer in Patent Document 4 and Patent Document 5 is about 0.02 μm. This is considered to be about 0.22 μm or less (about 0.2 × 10 ⁻⁷ m or more and about 2.2 × 10 ⁻⁷ m or less). Similarly, Patent Document 6, adhesion of Ni plating is for the 0.05 g / ^{m 2} or more 0.25 g / ^{m 2} or less, the film thickness of the Ni plating layer is less than about 0.006μm than about 0.028μm It is believed that there is. The film thickness of the Ni plating layer in Patent Documents 4 to 6 is relatively thin, and there may be a region where the base steel plate cannot be sufficiently covered. In a region where the Ni plating layer cannot sufficiently cover the base steel plate, an intermetallic compound containing Ni is not sufficiently generated, and thus a decrease in corrosion resistance in the processed portion cannot be sufficiently suppressed.

  Furthermore, in Patent Document 4, the adhesion of the molten Zn-based alloy plating layer is enhanced by the binder effect of the Ni—Al—Fe—Zn compound generated at the interface between the plating layer and the base steel sheet, and the base material in the processed part is obtained. The exposure of the steel sheet is suppressed. In Patent Document 5, the growth of the Γ phase is suppressed by the Ni—Al—Zn compound, the adhesion of the molten Zn-based alloy plating layer is improved, and the exposure of the base steel sheet in the processed portion is suppressed. In order to obtain the effects of the intermetallic compounds in these documents, it is necessary that a sufficient amount of Ni plating remains when immersed in the plating bath. For this reason, in Patent Document 4 and Patent Document 5, it is necessary to lower the heating temperature of the pretreatment heating before hot dipping and to more rapidly heat to suppress the diffusion of Ni into the base steel sheet. is there. Moreover, also in patent document 6, in order to suppress rapid elution of Ni in a plating bath, the heating temperature of pre-processing heating is set to low temperature.

  However, if the heating temperature of the pretreatment heating is low, annealing of the base steel sheet may be insufficient and an unrecrystallized part may occur, and if an unrecrystallized part occurs, it is difficult to process the steel sheet. Special methods may be required for processing. In addition, if pretreatment heating is performed rapidly, temperature unevenness (particularly temperature unevenness in the width direction of the plate) occurs in the base steel plate, and warpage is likely to occur in the base steel plate. Strict management of pretreatment heating conditions may be required.

  The present invention has been made in view of the above circumstances, and in a molten Zn-Al-Mg alloy-plated steel sheet having a molten Zn-Al-Mg alloy plated layer, in a processed portion of the molten Zn-Al-Mg alloy plated layer. Since the exposure of the base steel sheet due to cracking and peeling is difficult to occur, the deterioration of the corrosion resistance in the processed part is suppressed, and the molten Zn-Al-Mg alloy-plated steel sheet that can be manufactured without rapid low temperature heating, and such It aims at providing the manufacturing method of a hot-dip Zn-Al-Mg alloy plating steel plate.

  As a result of intensive studies, the inventors of the present invention have made the Ni plating layer thicker, and before forming the molten Zn—Al—Mg alloy plating layer, the Ni plating layer is usually heated at a normal temperature increase rate in pretreatment heating. It was found that by heating to the ultimate temperature and softening the Ni plating layer, exposure of the base steel sheet due to cracking and peeling in the processed part is less likely to occur, and a decrease in corrosion resistance in the processed part is suppressed.

  That is, according to one embodiment of the present invention, a base steel plate, a Ni plating layer having a thickness of 0.3 μm to 4.0 μm, Al: 1.0% by mass to 22.0% by weight, Mg: 0 A molten Zn—Al—Mg alloy plating layer composed of 0.5% by mass to 10.0% by weight and the balance of Zn being laminated in this order, and between the Ni plating layer and the molten Zn alloy plating layer, The present invention relates to a molten Zn—Al—Mg plated steel sheet containing a Ni—Al based intermetallic compound.

  Another aspect of the present invention provides a Ni-plated steel sheet having a Ni-plated layer having a film thickness of 0.3 μm or more and 4.0 μm or less on the surface of the base steel sheet, the surface temperature of the Ni-plated layer being higher than 500 ° C. Heating at a heating rate of 4 ° C./second or more and 28 ° C./second or less until reaching a temperature of 860 ° C. or less, and heat-treating the Ni-plated steel sheet subjected to the heat treatment. Dipping in a Mg alloy plating bath and forming a molten Zn-Al-Mg alloy plated layer on the surface of the Ni plated steel plate having the Ni plated layer, It relates to a manufacturing method.

  According to the present invention, in a molten Zn-Al-Mg alloy-plated steel sheet having a molten Zn-Al-Mg alloy plating layer, the base steel sheet is caused by cracking and peeling in the processed portion of the molten Zn-Al-Mg alloy plating layer. A molten Zn—Al—Mg alloy-plated steel sheet that is less likely to be exposed, has a reduced corrosion resistance in a processed part, and can be manufactured without rapid low-temperature heating, and such a molten Zn—Al—Mg alloy-plated steel sheet A manufacturing method is provided.

FIG. 1 is a schematic cross-sectional view of a hot-dip Zn—Al—Mg alloy-plated steel sheet according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view after processing the hot-dip Zn—Al—Mg alloy-plated steel sheet shown in FIG.

1. As shown in FIG. 1, a molten Zn—Al—Mg-based plated steel sheet (hereinafter, also simply referred to as “plated steel sheet”) 100 according to an embodiment of the present invention is a base material. Steel plate 110, Ni plating layer 120 having a film thickness of 0.3 μm or more and 4.0 μm or less, Al: 1.0% by mass or more and 22.0% by weight or less, Mg: 0.5% by mass or more and 10.0% by weight %, And a molten Zn—Al—Mg alloy plating layer 130 with the balance being Zn is laminated in this order. Further, the molten Zn—Al—Mg based plated steel sheet 100 includes a Ni—Al based intermetallic compound 140 between the Ni plated layer 120 and the molten Zn—Al—Mg alloy plated layer 130.

  The plated steel plate 100 may be a plate-like plated steel plate, a processed product obtained by plating a processed steel plate, or a processed product obtained by processing a plated steel plate that has been plated. .

  In addition, the composition of each plating layer and intermetallic compound contained in the plated steel sheet 100 can be measured by a known method such as energy dispersive X-ray analysis (EDX) or nanobeam electron diffraction (NBD).

[Substrate steel plate 110]
The kind of the base steel plate 110 is not particularly limited. For example, the base steel plate 110 may be carbon steel including low carbon steel, medium carbon steel, high carbon steel, or the like, or may be alloy steel containing Mn, Cr, Si, Ni, or the like. Further, the base steel plate 110 may be killed steel including Al killed steel or rimmed steel. When good press formability is required, a steel sheet for deep drawing including a low carbon Ti-added steel and a low carbon Nb-added steel is preferable as the base steel sheet 110. Moreover, you may use the high strength steel plate which adjusted the quantity of P, Si, Mn, etc. to the specific value as the base-material steel plate 110. FIG.

[Ni plating layer 120]
The Ni plating layer 120 is a layer formed by Ni plating with a film thickness of 0.3 μm or more and 4.0 μm or less.

  When the film thickness of the Ni plating layer 120 is 0.3 μm or more, even if the pretreatment heating when performing the molten Zn—Al—Mg based plating is higher than 500 ° C., it is caused by the diffusion of Ni into the base steel plate 110. The disappearance of the Ni plating layer 120 does not occur. Therefore, the Ni plating layer 120 sufficiently covers the base steel plate 110, and the intermetallic compound 140 is sufficiently generated in a wider range between the Ni plating layer 120 and the molten Zn—Al—Mg plating layer. As a result, the adhesion of the molten Zn—Al—Mg-based plating layer is enhanced, and the exposure of the processed part due to the molten Zn—Al—Mg-based plated layer being cracked or peeled off at the processed part is suppressed. A reduction in corrosion resistance can be suppressed.

  Moreover, when the film thickness of the Ni plating layer 120 is 0.3 μm or more, when the pretreatment heating when performing the molten Zn—Al—Mg based plating is higher than 500 ° C., the Ni plating layer is softened, As shown in FIG. 2, even if the plated steel sheet is processed after cooling the Ni plating layer, the Ni plating layer 120 becomes more difficult to break. Therefore, even if the molten Zn—Al—Mg alloy plating layer 130 or the intermetallic compound 140 is cracked during processing, the softened Ni plating layer 120 covers the base steel plate 110 without cracking, so that the base steel plate 110 is exposed. It is difficult to reduce the corrosion resistance even in the processed part due to the barrier type anticorrosion effect of the Ni plating layer 120. On the other hand, when the low temperature rapid heating is performed as shown in Patent Documents 4 to 6, since the Ni plating layer 120 is not sufficiently softened, the Ni plating layer 120 is easily broken during processing, and the base steel plate 110 is also exposed. Cheap.

  Furthermore, when the film thickness of the Ni plating layer 120 is 0.3 μm or more, a sufficient amount of Ni during immersion in the plating bath can be obtained regardless of rapid low-temperature heating as described in Patent Documents 4 to 6. Plating can remain. Therefore, the base steel plate 110 can be sufficiently annealed and softened at a higher ultimate temperature, and the processing of the plated steel plate 100 can be made easier. In addition, since the base steel plate 110 can be heated at a slower temperature increase rate, temperature unevenness is less likely to occur in the base steel plate 110 and warpage of the base steel plate 110 can be prevented.

  In Patent Document 4, when the thickness of the Ni plating layer exceeds 0.22 μm, the adhesion of the hot-dip Zn-based alloy plating layer decreases and the corrosion resistance of the plated steel sheet decreases. In Patent Document 5, the Ni plating layer If the film thickness exceeds 0.2 μm, the corrosion resistance of the plated steel sheet is said to decrease. Moreover, in patent document 6, in order to produce | generate a specific intermetallic compound, the film thickness of Ni plating layer shall be 0.028 micrometer or less. On the other hand, even if the film thickness of the Ni plating layer is 0.3 μm or more, the corrosion resistance of the plated steel sheet is enhanced by softening the Ni plating layer by heating at a temperature higher than 500 ° C. Is neither described nor suggested.

  On the other hand, when the thickness of the Ni plating layer 120 is 4.0 μm or less, the manufacturing cost is not increased more than necessary.

  From the viewpoint of further suppressing the manufacturing cost while sufficiently suppressing the deterioration of the corrosion resistance in the processed part, the thickness of the Ni plating layer 120 is preferably 0.5 μm or more and 2.0 μm or less, and 0.5 μm or more and 1 More preferably, it is 0.0 μm or less.

[Hot Zn-Al-Mg Alloy Plating Layer 130]
The molten Zn—Al—Mg alloy plating layer 130 is a molten Al-containing Mg plating containing 1.0% by mass or more and 22.0% by mass or less of Al and 0.5% by mass or more and 10.0% by mass or less of Mg. Is a layer. The molten Zn—Al—Mg alloy plating layer 130 is substantially made of Zn, but may contain other elements including Si, Ti, and B, as long as the corrosion resistance of the processed portion is not significantly reduced. .

  Al in the molten Zn—Al—Mg alloy plating layer 130 is passivated to enhance the corrosion resistance of the plated steel sheet 100 and suppress the generation of dross during manufacturing. When the Al content is less than 1.0% by weight, the corrosion resistance of the plated steel sheet 100 is not sufficiently increased, and the generation of dross is not sufficiently suppressed. If the Al content exceeds 22.0% by weight, the adhesion of the molten Zn-based alloy plating layer 130 is lowered, and the sacrificial anticorrosive effect by Zn may not be sufficiently exhibited.

  Mg in the molten Zn—Al—Mg alloy plating layer 130 uniformly generates a dense corrosion product on the surface of the molten Zn—Al—Mg alloy plating layer 130, thereby preventing corrosion factors from being eroded. Increase corrosion resistance. When the Mg content is less than 0.5% by weight, the dense and uniform corrosion product is not easily generated, and the corrosion resistance of the plated steel sheet 100 is not sufficiently increased. When the Mg content exceeds 10.0% by weight, the effect of improving the corrosion resistance is saturated, while the sacrificial anticorrosive effect by Zn is reduced, and dross is likely to occur.

In the molten Zn-Al-Mg alloy plating layer 130 in which the contents of Al and Mg are both in the above range, [Al / Zn / Zn ₂ Mg] or [Al / Zn / Zn ₁₁ ] in the metal structure in the plating layer. A ternary eutectic of Mg ₂ ] may be crystallized. Of these ternary eutectics, the Zn ₂ Mg phase contained in [Al / Zn / Zn ₂ Mg] is more difficult to discolor and less susceptible to corrosion.

Therefore, from the viewpoint of making the discoloration of the plated steel plate 100 less likely to occur and enhancing the corrosion resistance of the plated steel plate 100, the molten Zn—Al—Mg alloy plated layer 130 has [Al / It preferably has a ternary eutectic of [Zn / Zn ₂ Mg]. Further, from the viewpoint of suppressing the crystallization of Zn ₁₁ Mg ₂ to improve the surface appearance and to further improve the corrosion resistance, [Al / Zn / Zn ₂ Mg] ternary eutectic structure in the substrate [ More preferably, it has a metal structure mixed with primary Al]. From the viewpoint of facilitating the formation of such a metal structure, the molten Zn—Al—Mg alloy plating layer 130 has an Al content of 4.0% by mass or more and 10.0% by mass or less and 1.0% by mass or more and 4.0% by mass. It is preferable to contain not more than mass% Mg.

  The molten Zn—Al—Mg alloy plating layer 130 contains Si in the plating layer in a range of 0.005% by mass to 2.0% by mass in order to improve the adhesion between the base steel plate 110 and the plating layer. You may do it. Further, Ti, B, Ti—B alloy, Ti-containing compound or B-containing compound may be contained in the plating layer. The content of these compounds is preferably set so that B is 0.0005 mass% or more and 0.045 mass% or less so that Ti is 0.001 mass% or more and 0.1 mass% or less. . When an excessive amount of Ti or B is contained, there is a possibility that precipitates are grown on the plating layer.

  The thickness of the molten Zn—Al—Mg alloy plating layer 130 is not particularly limited, but is preferably 3 μm or more and 100 μm or less. When the thickness of the plating layer is less than 3 μm, scratches that reach the base steel plate 110 are likely to occur during handling, and thus there is a concern that the external appearance retainability and the corrosion resistance may be reduced. On the other hand, when the thickness of the plating layer 130 is more than 100 μm, the ductility when subjected to compression differs between the plating layer 130 and the base steel plate 110, so that the plating layer and the base steel plate 110 peel at the processed portion. There is a risk that.

[Ni-Al intermetallic compound 140]
The Ni—Al-based intermetallic compound 140 exists at the interface between the Ni plating layer 120 and the molten Zn—Al—Mg alloy plating layer 130. The Ni—Al-based intermetallic compound 140 may form a continuous layer at the interface, or may be distributed in a discontinuous island shape at the interface.

  Since the Ni—Al-based intermetallic compound 140 has high affinity with both the Ni plating layer 120 and the molten Zn—Al—Mg alloy plating layer 130, the adhesion of the molten Zn—Al—Mg alloy plating layer 130 is further increased. Further, cracking and peeling of the molten Zn—Al—Mg alloy plating layer 130 are made difficult to occur. Therefore, the Ni—Al-based intermetallic compound 140 makes it difficult to expose the base steel plate 110 when the plated steel plate 100 is processed, and suppresses a decrease in corrosion resistance in the processed portion.

  Further, the Ni—Al-based intermetallic compound 140 has high oxidation resistance. Therefore, the Ni—Al-based intermetallic compound 140 can further improve the corrosion resistance of the plated steel sheet 100.

The Ni—Al-based intermetallic compound 140 may be an intermetallic compound mainly composed of Ni and Al, and may be NiAl ₃ , NiAl, Ni ₃ Al, Ni ₂ Al ₃ , or the like. Of these, NiAl ₃ is preferable from the viewpoint of improving oxidation resistance.

2. Manufacturing method of hot-dip Zn—Al—Mg-based plated steel plate The hot-dip Zn—Al—Mg-based plated steel plate 100 described above includes (1) a Ni-plated layer having a film thickness of 0.3 μm or more and 4.0 μm or less. The Ni-plated steel sheet (hereinafter also simply referred to as “Ni-plated steel sheet”) on the surface has a maximum surface temperature of the Ni plating layer (hereinafter also simply referred to as “attainable temperature”) higher than 500 ° C. and 860 ° C. or lower. A process of heating at a rate of temperature rise of 4 ° C./second or more and 28 ° C./second or less (hereinafter also simply referred to as “heat treatment process”), and (2) The Ni-plated steel sheet is made of a molten Zn—Al—Mg alloy comprising Al: 1.0% by mass to 22.0% by weight, Mg: 0.5% by mass to 10.0% by weight, and the balance being Zn. Immerse it in the plating bath to make the Ni A surface having come layer, prepared by a method comprising forming a hot-dip Zn-Al-Mg alloy plating layer (hereinafter, simply referred to as "the step of forming the alloy plating layer".) And the.

  In the method for producing the hot-dip Zn—Al—Mg-based plated steel sheet, (3) a step of forming a Ni plating layer on the surface of the base steel plate (hereinafter, also simply referred to as “step of forming a Ni plating layer”) ( 1) It may be included before the heat treatment step, and further, (4) a step of producing a base steel plate may be included before (3) a step of forming the Ni plating layer.

  Since the Ni—Al intermetallic compound is formed when the alloy plating layer is formed, the film thickness of the Ni plating layer is actually slightly reduced after the step (2) of forming the alloy plating layer. . However, there is little change in the film thickness of the Ni plating layer at this time, and it can be considered that the film thickness hardly changes.

(1) Heat treatment process At this process, the Ni plating steel plate which has a Ni plating layer on the surface is heated.

  Heating is performed so that the ultimate temperature is higher than 500 ° C and lower than 860 ° C. When the temperature reached is higher than 500 ° C., the Ni plating layer is sufficiently softened to maintain the softened state even when cooled. Therefore, even if the molten Zn—Al—Mg alloy plating layer cracks during processing, the softened Ni plating Since the layer covers the base steel plate without cracking, the base steel plate is difficult to be exposed, and the corrosion resistance is also unlikely to deteriorate in the processed portion. Also, when the ultimate temperature is higher than 500 ° C, the crystal structure of the base steel sheet is sufficiently recrystallized, so that the internal stress is sufficiently warmed and the base steel sheet is sufficiently softened, making it easier to process the plated steel sheet. become. When the ultimate temperature is 860 ° C. or lower, the crystal grains due to recrystallization do not become too coarse, and the toughness of the base steel sheet does not deteriorate too much, so that the plated steel sheet can be processed more easily. From the above viewpoint, the ultimate temperature is preferably 550 ° C. or higher and 800 ° C. or lower.

  The heating rate of heating is 4 ° C./second or more and 28 ° C./second or less. When the rate of temperature increase is 4 ° C./second or more, the plate speed of the production line can be sufficiently increased, and the productivity can be increased. In addition, when the heating rate is 4 ° C./second or more and 28 ° C./second or less, temperature unevenness (particularly temperature unevenness in the width direction of the plate) hardly occurs in the base steel plate, and thus the base steel plate hardly warps. . From the above viewpoint, the temperature rising rate is preferably 8 ° C./second or more and 20 ° C./second or less.

  The other heat treatment conditions can be the same as the annealing that is normally performed as the pretreatment for forming the molten Zn—Al—Mg alloy plating layer. For example, the Ni-plated steel sheet heated to the above-mentioned temperature is preferably held for 30 seconds or more. When the suitable temperature of the Ni-plated steel sheet in the next step (2) of forming the alloy plating layer is lower than the ultimate temperature, the surface temperature of the Ni plating layer is preferably the above at a temperature decreasing rate of 5 ° C./second or more. What is necessary is just to perform the process of cooling a Ni plating steel plate until it becomes temperature and forming the next alloy plating layer.

(2) Step of forming an alloy plating layer The alloy plating layer can be formed by a known method for forming a molten Zn-Al-Mg alloy plating layer on the surface of a base steel sheet. For example, the same composition as the above-described molten Zn—Al—Mg alloy plating layer (Al: 1.0 mass% to 22.0 wt%, Mg: 0.5 mass% to 10.0 wt%, balance: What is necessary is just to immerse the Ni plating steel plate which heat-processed at the said (1) heat processing process in the hot-dip Zn-Al-Mg alloy plating bath which has Zn).

  The adhesion amount of the molten Zn—Al—Mg alloy plating may be adjusted so that the film thickness of the molten Zn—Al—Mg alloy plating layer is in the above-described range.

  Note that (1) the heat treatment step and (2) the step of forming the alloy plating layer can be continuously performed in the same apparatus that performs a continuous molten Zn plating line (CGL).

(3) Step of forming Ni plating layer The Ni plating layer can be formed by a known method of applying Ni plating to the surface of the steel sheet. The Ni plating layer may be formed by either electroplating or electroless plating. As the electroplating method, for example, an electroplating method using a total sulfate bath, an electroplating method using a watt bath, a sulfamic acid bath, or the like can be used. In the electroless plating method, hypophosphorous acid, dimethylamine borane, hydrazine, or the like can be used as a reducing agent. Of these, the electroplating method is preferable from the viewpoint of enabling continuous production and facilitating the control of the film thickness.

  The composition of the plating bath is not particularly limited, and may be arbitrarily set according to the type of steel sheet, the plating film thickness, the current density of electrolytic plating, the reducing agent for electroless plating, and the like.

  Moreover, before performing Ni plating, you may perform pretreatment, such as alkali degreasing and pickling.

(4) Process for producing base steel sheet The base steel sheet is obtained by refining the hot metal taken out of the blast furnace into a molten steel and rolling a slab obtained by casting the molten steel (hot rolling, cold rolling, etc.) And can be manufactured. During this process, after hot rolling, the steel sheet may be heated to a temperature higher than 500 ° C. and annealed (intermediate annealing) before the heating process. However, since the effect of annealing is obtained in the heating step, the steel plate may not be heated to a temperature higher than 500 ° C. after the hot rolling and before the heating step.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not limited by these Examples.

[Experimental Example 1]
(1) Base steel plate SPCC having a thickness of 0.8 mm was used as a base steel plate, a cold-rolled steel plate for general use. Table 1 shows components other than Fe contained in the SPCC used in this example.

(2) Formation of Ni plating layer The above steel sheet was subjected to alkali degreasing and pickling, and a Ni plating layer was formed by an electroplating method to obtain a Ni plated steel sheet. Table 2 shows the bath composition and conditions for electroplating. The amount of current that flows in the plating bath is 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 1.0 μm, 2.0 μm, as calculated from the first law of Faraday. Or it adjusted so that it might become 4.0 micrometers. In addition, the film thickness was confirmed with an electrolytic film thickness meter (manufactured by Chuo Seisakusho, TH-11).

(3) Test 1: Evaluation of softening of Ni-plated layer A Ni-plated steel sheet on which a Ni-plated layer having a thickness of 1.0 μm was formed was placed in a reduction furnace, and the ultimate temperatures were 400 ° C., 450 ° C., 500 ° C., 550 ° C. , 600 ° C., or 700 ° C. at a rate of temperature increase of 10 ° C./s for heat treatment. In order to investigate the degree of softening of the Ni plating layer, the Vickers hardness of the Ni plating layer after the heat treatment and after cooling to room temperature was measured. Vickers hardness was measured with a micro hardness tester (manufactured by Mitutoyo Corporation, HM-221). Table 3 shows the measurement results. In addition, Vickers hardness has shown the average value measured 3 times.

  From the measurement result of the Vickers hardness, it can be seen that when the ultimate temperature is 500 ° C. or less, the Ni plating layer is not sufficiently softened.

(4-1) Test 2: Formation of hot-dip Zn-Al-Mg alloy plating layer The Ni-plated steel sheet on which the Ni plating layer was formed was heat-treated at a temperature of 500 ° C or 700 ° C. Each heat-treated Ni-plated steel sheet was immersed in a molten Zn—Al—Mg alloy plating bath at a bath temperature of 400 ° C., 430 ° C., 450 ° C., 500 ° C. or 600 ° C. for 2 seconds, and then cooled at a temperature drop rate of 12 ° C./second. Then, a molten Zn—Al—Mg alloy plated layer was formed to obtain a molten Zn—Al—Mg alloy plated steel sheet. The composition of the molten Zn—Al—Mg alloy plating bath was changed as shown in Tables 4 and 5. The single-side adhesion amount of the molten Zn—Al—Mg alloy plating was adjusted to 60 g / m ² by wiping.

(4-2) Test 2: Evaluation [Ni plating layer]
A cross section of each of the above-described hot-dip Zn—Al—Mg alloy-plated steel sheets was observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to confirm whether or not the Ni plating layer remained.

[Intermetallic compounds]
In addition, the composition of the intermetallic compound formed between the Ni plating layer and the molten Zn-Al-Mg alloy plating layer is irradiated with an electron beam to the measurement region of 40 nmφ, and the nanobeam for measuring and analyzing the crystal structure information It was measured by electron diffraction (NBD).

[Processed part exposure]
The hot-dip Zn—Al—Mg alloy-plated steel sheet was subjected to a 2T bending test by a method according to JIS Z 2248. The cross section of each molten Zn-Al-Mg alloy-plated steel sheet after the 2T bending test is observed with SEM or TEM to observe whether the Ni plating layer and the intermetallic compound are cracked. At that time, it was determined that the base steel plate was exposed at the processed portion.

[Corrosion resistance]
The corrosion resistance of the molten Zn—Al—Mg alloy-plated steel sheet subjected to the 2T bending test was evaluated by a combined cycle corrosion test (CCT) by a method according to JASO M609 and JASO M610. In CCT, salt spray (2 hr, 35 ° C.), drying (4 hr, 60 ° C.) and wet (2 hr, 50 ° C.) are defined as one cycle, and the number of cycles where the generated red rust area ratio is 5% is evaluated as corrosion resistance. did.

  Base steel plate, Ni plating layer having a film thickness of 0.3 μm or more and 4.0 μm or less, Al: 1.0 mass% or more and 22.0 wt% or less, Mg: 0.5 mass% or more and 10.0 weight %, A molten Zn—Al—Mg alloy plating layer consisting of Zn in the balance is laminated in this order, and a Ni—Al intermetallic compound is included between the Ni plating layer and the molten Zn alloy plating layer. In Examples 1 to 6, the base steel plate was sufficiently covered with the remaining Ni plating layer, and the exposure of the base steel plate in the processed part was not confirmed. In addition, in Examples 1 to 6, it was confirmed that the number of cycles until the area ratio of red rust reached 5% was higher and the corrosion resistance was higher. As a result of analysis by nanobeam electron diffraction, Ni was not present in the molten Zn—Al—Mg alloy plating layer.

  On the other hand, in Comparative Example 1 in which the Ni plating layer was not formed, the molten Zn—Al—Mg alloy plating layer was cracked in the processed part, and the base steel sheet was exposed, and the corrosion resistance of the processed part was also low.

  Further, in Comparative Example 2 where the thickness of the formed Ni plating layer was 0.1 μm, the Ni plating layer disappeared when the ultimate temperature was set to 700 ° C. When analyzed by EDX, Ni was diffused in the steel sheet. Therefore, the molten Zn-Al-Mg alloy plating layer was cracked in the processed part, and the base steel sheet was exposed, and the corrosion resistance of the processed part was also low.

  In Comparative Example 3 in which the reached temperature was 500 ° C., although the Ni plating layer remained, the Ni plating layer was not softened sufficiently, so that the Ni plating layer cracked in the processed part, and the base steel plate was exposed. Moreover, the corrosion resistance of the processed part was also low. In addition, although some corrosion resistance improvement is seen, even if compared with Example 4 etc. with the same film thickness of Ni plating layer, the extent is not so high, and it is the effect by the adhesive improvement by Ni plating, and Ni plating layer It is not recognized to be due to the barrier type anticorrosive effect

  Also in Examples 7 to 14 in which the plating bath components were changed, similarly, the exposure of the base steel sheet in the processed part was not confirmed, and the corrosion resistance of the processed part was higher.

  On the other hand, in Comparative Examples 5 to 12 in which the Ni plating layer was not formed, the molten Zn—Al—Mg alloy plating layer was cracked in the processed part and the base steel sheet was exposed, and annealing was performed at the same temperature. The corrosion resistance of the processed part was also lower than in Examples 1-6.

  The hot-dip Zn-Al-Mg alloy-plated steel sheet of the present invention has high corrosion resistance in the processed part, and therefore is required for corrosion resistance of plated steel sheets used for building roofing materials, exterior materials, home appliances, automobiles, etc. Can be suitably used. Moreover, since the hot-dip Zn—Al—Mg alloy-plated steel sheet of the present invention is easy to manufacture and process, it can be manufactured at low cost.

DESCRIPTION OF SYMBOLS 100 Hot-dip Zn-Al-Mg alloy plating steel plate 110 Base steel plate 120 Ni plating layer 130 Hot-melt Zn-Al-Mg alloy plating layer 140 Ni-Al type intermetallic compound

Claims (5)

A base steel plate;
A Ni plating layer having a film thickness of 0.3 μm or more and 4.0 μm or less;
Al: 1.0% by mass or more and 22.0% by weight or less, Mg: 0.5% by mass or more and 10.0% by weight or less, and a molten Zn—Al—Mg alloy plating layer composed of Zn in the order of lamination. And
Between the Ni plating layer and the molten Zn—Al—Mg alloy plating layer, a Ni—Al-based intermetallic compound is included.
Fused Zn-Al-Mg-based plated steel sheet.   2. The molten Zn—Al—Mg based plated steel sheet according to claim 1, wherein the molten Zn—Al—Mg alloy plating layer contains an element selected from the group consisting of Si, Ti, and B. 3. A Ni plated steel sheet having a Ni plated layer having a film thickness of 0.3 μm or more and 4.0 μm or less on the surface of the base steel sheet is 4 ° C. until the surface temperature of the Ni plated layer is higher than 500 ° C. and lower than 860 ° C. Heating at a temperature rising rate of 28 ° C./second or more and performing a heat treatment;
The Ni-plated steel sheet subjected to the heat treatment is Al: 1.0% by mass to 22.0% by weight, Mg: 0.5% by mass to 10.0% by weight, and the balance is molten Zn— Dipping in an Al-Mg alloy plating bath to form a molten Zn-Al-Mg alloy plating layer on the surface of the Ni-plated steel sheet having the Ni plating layer;
The manufacturing method of the hot dip Zn-Al-Mg system plating steel plate containing this.   The molten Zn-Al-Mg-based plated steel sheet according to claim 3, wherein the step of performing the heat treatment and the step of forming the molten Zn-Al-Mg alloy plating layer are continuously performed in the same apparatus. Manufacturing method.   5. The molten Zn—Al— according to claim 3, comprising a step of forming a Ni plating layer having a thickness of 0.3 μm or more and 4.0 μm or less on the surface of the base steel plate before the heating step. Manufacturing method of Mg-based plated steel sheet.

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