JP7393640B2 - Manufacturing method of multi-layer plated steel sheet - Google Patents

Description

The present invention relates to a multilayer plated steel sheet and a method for manufacturing the same.

Plated steel sheets are used in various fields such as building materials, automobiles, and home appliances. It is generally known that Zn-based plated steel sheets have sacrificial corrosion resistance, and Al-based plated steel sheets have high corrosion resistance. As a plated steel plate that combines the characteristics of these two plated steel plates, a multilayer plated steel plate in which the lower layer is coated with Al-based plating and the upper layer is coated with Zn-based plated is disclosed in Patent Document 1.

The multilayer plated steel sheet described in Patent Document 1 is manufactured by applying first hot-dip plating (Al-based) to the surface of a base steel sheet and then applying second hot-dip plating (Zn-based) thereon. . Furthermore, Patent Document 1 describes that the steel plate temperature of the intermediate product is important when the intermediate product that has been subjected to the first hot-dip plating is subjected to the second hot-dip plating. Patent Document 1 discloses, as a preferred embodiment, a steel sheet temperature of an intermediate product of 300 to 550°C.

Japanese Patent Application Publication No. 2010-144193

However, when drawing is performed on the multilayer plated steel sheet described in Patent Document 1, a phenomenon occurs in which the upper layer Zn-based plating falls off in dots. A multilayer plated steel sheet in which such a phenomenon occurs does not exhibit the excellent characteristics of both the sacrificial corrosion resistance of Zn-based plating and the high corrosion resistance of Al-based plating. Therefore, the multilayer plated steel sheet described in Patent Document 1 is not suitable for drawing.

One aspect of the present invention aims to realize a multilayer plated steel plate suitable for drawing.

In order to solve the above problems, a multi-layer plated steel sheet according to one aspect of the present invention includes a base steel plate and a Si: 0.1 to 12% by mass % applied to the surface of the base steel plate. a molten Zn-based plating layer containing Al: 0 to 20% and Mg: 0.5 to 8% in mass %, which is applied to the molten Al-based plating layer; Formed between the Al-based plating layer and the hot-dip Zn-based plating layer, Al: 30 to 50%, Mg: 0.5 to 10%, O: 40 to 60%, and Si: 0 to 5% in mass %. and an intermediate layer containing the sum of these is 100% or less.

Further, a method for manufacturing a multilayer plated steel sheet according to one embodiment of the present invention includes immersing a base steel sheet in a hot-dip Al-based plating bath containing Si: 0.1 to 12% by mass. a first step of forming a hot-dip Al-based plating layer on the surface; heating the hot-dip Al-based plated steel sheet on which the surface of the base steel sheet has been provided with the hot-dip Al-based plating layer in the first step; A second step in which the temperature of the steel sheet reaches 380 to 550°C and is held for 10 seconds or more, and a hot-dip Zn-based plating bath containing Al: 0 to 20% and Mg: 0.5 to 8% by mass%. and a third step of immersing the hot-dip Al-based plated steel sheet heated in the second step to form a hot-dip Zn-based plating layer on the surface of the hot-dip Al-based plated steel sheet.

According to one aspect of the present invention, it is possible to realize a multilayer plated steel plate suitable for drawing.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the outline of the multilayer plating steel plate in one embodiment of this invention. It is a figure which shows the result of cross-sectional observation and elemental analysis about an example of the multilayer plating steel plate produced in the verification experiment.

[Embodiment 1]
Hereinafter, one embodiment of the present invention will be described in detail. It should be noted that the following description is provided for better understanding of the gist of the invention, and is not intended to limit the invention unless otherwise specified. Furthermore, in this application, "A to B" indicates that the number is greater than or equal to A and less than or equal to B. The description of "%" regarding chemical composition means "% by mass" unless otherwise specified.

<Schematic explanation of the findings of the invention>
It is thought that the multilayer plated steel sheet described in Patent Document 1 has defective parts that cannot be recognized from the appearance or by cross-sectional observation of the 2T bent portion (adhesion evaluation method described in Patent Document 1). In the defective part, it is thought that the intermediate layer between the upper layer Zn-based plating and the lower layer Al-based plating has a brittle porous structure.

During drawing, a large force is applied to the steel plate due to stretching, compression, and contact with a die. Therefore, if the intermediate layer is brittle, it is thought that the intermediate layer will be destroyed during drawing and the upper layer will fall off. In order to prevent the upper layer from falling off even after drawing, it is necessary to make the intermediate layer between the upper layer and the lower layer dense and strong throughout.

The present inventors have conducted intensive studies on a method of making the entire intermediate layer dense and strong in a multilayer plated steel sheet, and have obtained the following knowledge. That is, by holding a plated steel plate for forming the lower layer at 380 to 550°C for 10 seconds or more in an air atmosphere and then applying plating to form the upper layer, the intermediate layer is completely coated. By making it dense and strong, it can prevent the upper layer from falling off after drawing.

(Verification experiment)
Preheating in the air before applying the upper layer plating is also performed on the multilayer plated steel sheet described in Patent Document 1. As mentioned above, in the preferred embodiment described in Patent Document 1, the target temperature for preheating is 300 to 550°C. However, in the multilayer plated steel sheet described in Patent Document 1, holding the target temperature for a predetermined time (heat holding) after reaching the target temperature is not performed.

The present inventors conducted a verification experiment on the effect of heating and holding. In the verification experiment, after forming a molten Al-based plating layer to form a lower layer on the surface of a base steel plate, it was heated to 450° C. in an air atmosphere and kept heated for 60 seconds. Thereafter, a hot-dip Zn-based plating layer was applied to form an upper layer over the hot-dip Al-based plating layer, thereby producing a multilayer plated steel sheet. The results of the verification experiment will be explained below.

FIG. 2 is a diagram showing the results of cross-sectional observation and elemental analysis of an example of a multilayer plated steel sheet produced in a verification experiment. For cross-sectional observation and elemental analysis, a scanning transmission electron microscope with a spherical aberration correction function (Cs-STEM-EDX, Corrector-Spherical Aberration Scanning Transmission Electron Microscope Energy Disper) was used. sive X-ray spectrometry) was used.

In FIG. 2, a cross section of a plating layer having a lower layer 2, an upper layer 3 and an intermediate layer 4 is indicated by reference numeral 2001. Further, photographs showing the distribution states of Zn, Al, Si, O, and Mg in the cross section are shown with reference numerals 2002 to 2006, respectively. In the symbols 2002 to 2006, the areas where each element exists in a larger amount are shown brighter. Further, in reference numeral 2002, the boundary between the lower layer 2 and the intermediate layer 4 is indicated by a broken line.

As shown in FIG. 2, the elements constituting the intermediate layer 4 are mainly Al, O, and Mg. In addition, even if a multilayer plated steel plate with varying compositions of the lower layer 2 and upper layer 3 was separately prepared and elemental analysis was conducted in the same manner, no major variation was observed in the composition of the intermediate layer 4, and Al: 30 to 50. %, O: 40-60%, Mg: 0.5-10%, Si: 0-5% (the sum of the ratios of each element does not exceed 100%). This is because the intermediate layer 4 is formed by replacing Al in the oxide film on the surface of the lower layer 2 with Mg, which has a more base natural potential than Al. This is thought to be because the ratio of Al and Mg only changes depending on the .

Further, when the upper layer does not contain Mg and only contains Zn, a large number of plating repellents (non-plating) occur in the upper layer, making it impossible to produce a multilayer plated steel sheet.

Next, the state of the surface of the molten Al-based plating layer for forming the lower layer was analyzed using attenuated total reflection (ATR) of infrared spectroscopy (IR). In the ATR method, a peak derived from hydroxyl groups appears at 3500 to 3900 cm ^-1 .

After forming a hot-dip Al-based plating layer on the surface of the base steel plate, (i) heating up to 400°C and not holding it, (ii) heating up to 450°C and not holding it, (iii) heating up to 450°C Table 1 shows the measurement results of the amount of hydroxyl groups before and after heating for each of the cases where the sample was heated and then held for 60 seconds. For the measurement, FT-IR6600 manufactured by JASCO Corporation was used, and the amounts of hydroxyl groups were compared using values obtained by automatically integrating peaks appearing at 3500 to 3900 cm ^-1 .

As shown in Table 1, in all of the cases described above, the peak derived from hydroxyl groups was reduced by heating. This is thought to be due to the fact that part of the aluminum hydroxide present on the surface of the molten Al-based plating layer before heating is changed into aluminum oxide by heating. Further, it is thought that aluminum oxide hydrate is also present on the surface of the molten Al-based plating layer before heating, and it is thought that at least a portion of this is also converted to aluminum oxide.

By applying a hot-dip Zn-based plating layer containing Mg to the surface of a hot-dip Al-based plating layer, a substitution reaction occurs between Mg and a portion of Al, forming an intermediate layer having strong Al-O-Mg bonds. . Generally, aluminum hydroxide and aluminum oxide hydrate are porous compared to aluminum oxide. Therefore, if a large amount of aluminum oxide with a dense structure exists on the surface of a molten Al-based plating layer, applying a molten Zn-based plating layer containing Mg to the surface will increase the density of Al-O-Mg bonds. It is believed that this results in the formation of a strong intermediate layer.

In particular, the peak derived from hydroxyl groups when a molten Al-based plating layer was formed and heated to 450°C and then held for 60 seconds was compared with the case where the heating was not held after heating to 400°C or 450°C. has decreased significantly. That is, on the surface of the heated and maintained molten Al-based plating layer, most of the aluminum hydroxide and aluminum oxide hydrate has changed to aluminum oxide. It is thought that by applying a hot-dip Zn-based plating layer to such a hot-dip Al-based plating layer, the above-mentioned strong intermediate layer is formed, and the upper layer does not fall off even when drawing is performed.

On the other hand, the peak derived from hydroxyl groups in the case of not being heated and held does not decrease compared to the case of being heated and held. This is considered to be because the amount of heat required for aluminum hydroxide (and aluminum oxide hydrate) to change into aluminum oxide was smaller than that in the case of heating and holding, because the heating and holding were not carried out. In this case, even if a hot-dip Zn-based plating layer is applied to the molten-Al-based plating layer to form an upper layer, a strong intermediate layer is not formed, and the upper layer falls off in dots during the drawing process.

Note that the intermediate layer may also contain other elements such as Fe or Zn. However, it is thought that these elements do not affect the adhesion of the upper layer.

〔Definition of terms〕
In the following description, forming a hot-dip Al-based plating layer on the surface of the base steel plate by immersing the base steel plate in a hot-dip Al-based plating bath may be referred to as first hot-dip plating. Then, immersing the steel plate after the first hot-dip plating in a hot-dip Zn-based plating bath to form a hot-dip Zn-based plating layer on the surface may be referred to as second hot-dip plating.

<Multi-layer plated steel plate>
Hereinafter, a multilayer plated steel sheet according to an embodiment of the present invention will be described.

FIG. 1 is a diagram schematically showing a multilayer plated steel sheet 10 in an embodiment of the present invention. As shown in FIG. 1, the multilayer plated steel sheet 10 includes a base steel sheet 1, a lower layer 2 (hot-dip Al-based plating layer) applied to the surface of the base steel sheet 1, and an upper layer applied to the lower layer 2. 3 (molten Zn-based plating layer), and an intermediate layer 4 formed between the lower layer 2 and the upper layer 3. Below, the base steel plate and various layers will be explained in detail.

[Base material steel plate 1]
As the base steel plate 1 serving as a plating original plate, various steel plates that are generally used as base materials for Zn-based plated steel sheets and Al-based plated steel plates can be used.

[Lower layer 2]
In this specification, the term "lower layer" refers to the molten Al-based plating layer formed by the first hot-dip plating, which is present in the multilayer plating layer after the first hot-dip plating and the second hot-dip plating are applied. This refers to the layer from which it originates (excluding the intermediate layer described below).

This lower layer 2 exhibits the excellent corrosion resistance characteristic of a hot-dip Al-based plating layer and is responsible for the long-term corrosion resistance of the steel plate surface. The component composition of the lower layer 2 (molten Al-based plating bath composition in the first hot-dip plating) contains Si: 0.1 to 12% by mass %. The remainder may be Al. Further, the remainder may contain various additive elements. Examples of additional elements include B: 0 to 0.5%, Cr: 0 to 2.0%, Sr: 0 to 0.5%, Ti: 0 to 0.5%, etc. The remainder may contain unavoidable impurities.

Si in the lower layer 2 has the effect of lowering the liquidus temperature of the Al-based plating bath. However, if the Si content of the plating bath exceeds 12%, it tends to exceed the eutectic composition and enter a region where the liquidus temperature increases. Furthermore, when such a large amount of Si is contained, a large amount of Si crystallized phase is formed at the interface between the lower layer 2 and the upper layer 3 described below, and the adhesion between the lower layer 2 and the upper layer 3 tends to deteriorate. In this case, cracks may occur between the lower layer 2 and the upper layer 3 due to the bending process, which causes the sacrificial anticorrosion effect of the Zn in the upper layer 3 to not be sufficiently exerted. On the other hand, if the lower layer 2 does not contain Si, a thick Fe--Al alloy layer with no extensibility and brittleness grows between the lower layer 2 and the base steel plate 1, so that the plating tends to fall off during drawing. Therefore, the lower layer 2 contains Si in a range of 0.1% to 12% or less.

[Upper layer 3]
In this specification, the "upper layer" is derived from a Zn-based plating layer formed by the second hot-dip plating, which is present in the multilayer plating layer after the first hot-dip plating and the second hot-dip plating. (excluding the middle layer). This upper layer 3 is a Zn-based plating layer optionally containing Al and Mg. The upper layer 3 mainly has a sacrificial anticorrosion effect, a protective effect on the plated surface by forming a Zn-based corrosion product containing Al and Mg, and a protective effect by the Zn-based corrosion product containing Mg.

The component composition of the upper layer 3 (the composition of the hot-dip Zn-based plating bath in the second hot-dip plating) includes Al: 0 to 20% and Mg: 0.5 to 8% in mass %. The remainder may be Zn. Further, the remainder may contain various additive elements. The remainder may contain unavoidable impurities. In particular, the component composition of the upper layer 3 more preferably contains Mg: 3 to 8% by mass. Further, as other examples of additive elements, B: 0-0.05%, Si: 0-2.0%, Ca: 0-1.0%, Ti: 0-0.1%, Sn: 0-0. Examples include 1.0%.

Mg in the upper layer 3 has the effect of stably maintaining corrosion products generated on the surface of the plating layer as protective corrosion products and significantly increasing the corrosion resistance of the plating layer. In addition, Mg-containing Zn-based corrosion products generated by the sacrificial corrosion protection are deposited on the exposed portions of the steel substrate, such as the cut end surface, to form a protective film, which acts to protect the exposed portions of the steel substrate. However, if the Mg content of the plating bath exceeds 8%, a large amount of Mg oxide will be generated on the surface of the plating bath, making it difficult to create a multilayer plated steel sheet by hot-dip Mg plating. Therefore, the upper limit of the Mg content in the upper layer 3 is set to 8%.

[Middle layer 4]
In this specification, the term "intermediate layer" refers to a layer formed between the lower layer 2 and the upper layer 3 in the multilayer plated steel sheet 10 after the first hot-dip plating and the second hot-dip plating have been applied. This intermediate layer 4 serves to join the lower layer 2 and the upper layer 3 together.

The component composition of the intermediate layer 4 is Al: 30 to 50%, Mg: 0.5 to 10%, O: 40 to 60%, and Si: 0 to 5%, and the total of these is 100% or less. Including as there is. If the intermediate layer 4 has such a component composition, it is possible to prevent the plating from falling off in dots during the drawing process. Therefore, the multilayer plated steel sheet 10 becomes suitable for drawing. Intermediate layer 4 may contain other impurities.

(Production method)
The multi-layer plated steel sheet in one aspect of the present invention includes a first hot-dip plating (hot-dip Al-based plating) applied to the surface of the base steel sheet 1 (first step), The Al-based plated steel plate is heated, and the temperature of the base steel plate reaches 380 to 550°C and held for 10 seconds or more (second step), and the heated hot-dip Al-based steel plate is coated with a second hot-dip plate ( It can be manufactured by applying molten Zn-based plating (third step). Specifically, a hot-dip Al-based plated steel sheet is created by performing first hot-dip plating on a continuous hot-dip plating line. Next, the produced hot-dip Al-based plated steel sheet is heated to 380 to 550°C in a furnace and held for 10 seconds or more. Finally, second hot-dip plating may be applied to the hot-dip Al-plated steel sheet after being heated and maintained in a continuous hot-dip plating line. By the above manufacturing method, a multilayer plated steel sheet suitable for drawing can be manufactured.

In particular, in the second step, it is preferable that the temperature of the base steel plate 1 reaches 400 to 500° C. and is maintained for 60 seconds or more. By heating and maintaining the temperature within the above range, a sufficient amount of heat is given to the aluminum hydroxide and aluminum oxide hydrate on the surface of the first hot-dip plating to change into aluminum oxide. Therefore, the upper layer of the multilayer plated steel sheet becomes stronger.

A cold-rolled ordinary steel sheet with a thickness of 0.8 mm was used as the base steel sheet, and hot-dip Al-based plating (plating weight: 30 to 90 g/m ² on one side) was applied using a continuous hot-dip plating line, and the sheet was cooled to room temperature. , a hot-dip Al-based plated steel sheet was obtained. Next, using a batch-type hot-dip plating tester, heat the hot-dip Al-plated steel sheet to 300 to 600°C, hold the temperature for a certain period of time, and then apply hot-dip Zn-based plating (no plating adhesion) on the surface at a plating bath temperature of 400°C. Amount: 30 to 180 g/m ² on one side) to obtain a multilayer plated steel sheet. The plating composition, preheating temperature of the hot-dip Al-based plated steel sheet, and coating weight are listed in Tables 2 and 3.

The following investigation was conducted on the obtained multilayer plated steel sheet.

(1) Evaluation of upper layer plating properties The appearance of the multi-layer plated steel sheet was visually observed, and the ratio of the area of the unplated portion to the area of the region coated with the upper layer was measured. Those with less than 5% non-plating were judged to have good plating properties. Samples with poor plating properties and 5% or more of unplated samples were not used in the evaluation of post-drawing adhesion and post-drawing corrosion resistance, which will be described later. In Tables 2 and 3, those with plating repellency (unplated) of 5% or more are ×, those with 1% or more and less than 5% are △, those with less than 1% are ○, and those with no unplated at all are ◎ It is shown as

(2) Analysis of intermediate layer composition A cross-section of a flat multilayer plated steel plate was cut using a focused ion beam (FIB) device, and the cross-section was cut using a scanning transmission electron microscope (Cs-STEM-) with a spherical aberration correction function. EDX) was used to analyze the composition of the intermediate layer from the cross section. In Tables 2 and 3, the composition of the intermediate layer is classified into three types, A, B, and C. Specific compositions of each of A to C will be described later with reference to Table 4.

(3) Evaluation of adhesion after drawing The appearance of the multilayer plated steel sheet was visually confirmed, and the unplated portion was punched out to a diameter of 68 mm. The punched multilayer plated steel plate was drawn into a cylindrical shape up to a height of 16 mm at a speed of 30 mm/min using a 40 mmφ5R punch and a 42 mmφ5R die to obtain a cylindrical drawn sample. Adhesive tape was attached to each of the shoulder and side wall of the cylindrical drawing sample and then peeled off, and the peeled area of the upper layer was evaluated. A sample with a peeled area of less than 10% was judged to have good adhesion. In Tables 2 and 3, cases in which there was no peeling of the upper layer at all are shown as ◎, cases in which the peeled area was less than 10% are shown as ○, and cases in which the peeled area was 10% or more are shown as ×.

(4) Evaluation of corrosion resistance after drawing The end face of the cylindrical drawing sample prepared in (3) was sealed with fluorine tape as a corrosion resistance evaluation sample, and 200 cycles of cyclic corrosion testing (CCT) were conducted. Thereafter, red rust on the shoulders and sidewalls of the cylindrical drawing sample was visually observed. Those with a red rust occurrence area ratio of less than 5% were judged to have good corrosion resistance. In Tables 2 and 3, those with an area ratio of red rust occurrence of less than 5% are indicated as ○, and those with an area ratio of 5% or more are indicated as ×.

Regarding the above-mentioned investigation, the results for the invention examples are shown in Table 2. Table 3 also shows the results for comparative examples.

Invention example no. Nos. 1 to 26 all showed good results in terms of "upper layer plating properties," "adhesion after drawing," and "corrosion resistance after drawing." Among these, Invention Example No. 1 had an upper layer Mg content of 3 to 8% and a heating temperature of 400 to 500°C. Samples Nos. 1 to 4, 6 to 10, 14 to 19, and 23 to 26 showed better results with "upper layer plating properties" of ○ or ◎. In particular, invention example No. 1, in which the heating temperature is 450° C. and the holding time is 60 seconds or more. Samples Nos. 1 to 4, 6 to 8, 10, and 23 to 26 showed outstandingly good results, with both "upper layer plating properties" and "post-drawing adhesion" being ◎.

In addition, invention example No. 23 to 26, and Invention Example No. 3 differs only in the amount of plating deposited. From the results of comparing these invention examples, no influence on "upper layer plating properties", "adhesion after drawing", and "corrosion resistance after drawing" was observed for the amount of plating on either the lower layer or the upper layer. Ta.

Regarding the "intermediate layer composition" in Tables 2 and 3, the compositions of A, B, and C are shown in Table 4. For comparison, the composition of the oxide film on the surface of the lower layer before the second hot-dip plating is also shown in Table 4. The sum of each component in Table 4 does not exceed 100%.

As shown in Table 4, the Mg content in the composition of the intermediate layer is the lowest in A to C, and the highest in C. Conversely, regarding the content of Al in the composition of the intermediate layer, A has the highest content and C has the lowest content. However, regardless of the composition of the intermediate layer from A to C, there is no major difference between the composition of the intermediate layer and the composition of the oxide film on the surface of the lower layer.

In Table 2, Invention Example No. 1 has a low Mg concentration in the upper layer. In Invention Example No. 5, the intermediate layer composition is A, and the Mg concentration is high. In No. 8, the intermediate layer composition was C. In other invention examples, the intermediate layer composition was all B. That is, as the Mg concentration in the upper layer increased, the Mg concentration in the intermediate layer increased and the Al concentration decreased. From this, it is considered that Al was replaced with Mg in the intermediate layer depending on the Mg concentration of the upper layer.

Comparative Example No. 1, in which heating was not maintained in the heating step before applying the second hot-dip plating (that is, heating was immediately terminated when the heating temperature was reached). In samples Nos. 27 to 31, both "adhesion after drawing" and "corrosion resistance after drawing" were inferior to the invention examples. This result is considered to be because the amount of heat given to the lower layer in the heating step was insufficient, so that the aluminum oxide hydrate and aluminum hydroxide on the surface of the lower layer were not sufficiently converted to aluminum oxide.

Comparative example No. 1 containing no Mg in the upper layer. In samples No. 32 to 39, the "upper layer plating properties" were inferior to the invention examples, regardless of the composition of the lower layer. From this result, it is considered that in the invention example, Mg contained in the upper layer improved the plating properties of the multilayer plated steel sheet.

Comparative example No. 1 containing no Si in the lower layer. In No. 40, although the "upper layer plating properties" were good, the "post-drawing adhesion" and "post-drawing corrosion resistance" were inferior to the invention examples. This result is because there was no Si in the lower layer, which is hot-dip Al plating, so a brittle and inextensible Fe-Al alloy layer grew significantly at the bottom of the lower layer, and the alloy layer was destroyed during drawing. This is thought to be because the lower layer itself fell off from the base steel plate.

Comparative Example No. in which Si is excessive in the lower layer. In No. 41, the "upper layer plating property" was inferior to that of the invention example. This result is considered to be because a large amount of Si and Si compounds precipitated on the surface of the lower layer, reducing the plating properties of the upper layer.

No. 2 has a lower heating temperature before applying the second hot-dip plating. Samples No. 42 to No. 44 had inferior "upper layer plating properties" compared to the invention examples. This result was due to the fact that the plating bath temperature in the second hot-dip plating was 400°C, but the heating temperature was more than 40°C lower, so the replacement of Mg and Al between the upper and lower layers did not proceed. it is conceivable that.

Comparative Example No. 1 has a higher heating temperature before applying the second hot-dip plating. In No. 45 to No. 47, the lower layer was melted, so it was not possible to produce a multilayer plated steel sheet in which the upper layer and the lower layer had different compositions.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

1 Base steel plate 2 Lower layer (hot-dip Al-based plating layer)
3 Upper layer (hot-dip Zn-based plating layer)
4 Intermediate layer 10 Multi-layer plated steel plate

Claims (3)

A first step of forming a hot-dip Al-based plating layer on the surface of the base steel plate by immersing the base steel plate in a hot-dip Al-based plating bath containing Si: 0.1 to 12% by mass%;
The hot-dip Al-plated steel sheet on which the hot-dip Al-based plating layer has been applied to the surface of the base steel sheet in the first step is heated, and the temperature of the base steel sheet reaches 380 to 550° C. for 10 seconds. a second step of holding the above;
The hot-dip Al-plated steel sheet heated in the second step is immersed in a hot-dip Zn-based plating bath containing Al: 0 to 20% and Mg: 0.5 to 8% by mass%, and the molten Al A method for producing a multi-layer plated steel sheet, comprising: a third step of forming a hot-dip Zn-based plating layer on the surface of the Zn-based plated steel sheet. 2. The method for manufacturing a multilayer plated steel sheet according to claim 1 , wherein in the second step, the temperature of the base steel sheet reaches 400 to 500° C. and is maintained for 60 seconds or more. 3. The method for producing a multilayer plated steel sheet according to claim 1 , wherein in the third step, the hot-dip Zn-based plating bath contains Mg: 3 to 8% by mass.

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