JPH05140710A - Multi-layered alloyed fused Zn plated steel sheet excellent in workability without nicks and method for producing the same - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a multi-layered alloyed Zn-plated steel sheet which is excellent in workability without any flaws, which has reduced the flaws of the hot-dip Zn-based alloy-plated steel sheet and improved press formability. [Structure] A cold-rolled sheet or a hot-rolled sheet subjected to appropriate pretreatment is first electroplated with Zn of 0.1 to 20 g / m ² . This is heated to a temperature higher than the hot-dip galvanizing pot in the latter stage to make Fe content 15 to 85%, 0.1 to 10%.
A Zn / Fe alloy of g / m ² is formed in advance, and then hot-dip plating of Zn or a Zn-based alloy is performed for 10 to 100.
By carrying out g / m ² , there is provided a multi-layer type alloyed hot-dip Zn plating having excellent workability without any flaw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes hot-dip Zn-plated steel sheets and hot-dip alloyed Zn-plated steel sheets.
Super Zinc, Galfon or Zn containing Al as the main component
Melted Z such as galvalume containing 55% Al as the main component
The purpose of the present invention is to provide a new multi-layer hot-dip galvanized steel sheet, which is an improved n-based galvanized steel sheet. It is a hot-dip galvanized steel with improved appearance and workability for application to car body anticorrosion steel sheets for automobiles, building materials, and processing materials for home appliances The present invention relates to a Zn-based plated steel sheet.

[0002]

2. Description of the Related Art In recent years, the use of Zn-plated or Zn-alloy-plated steel sheets has been increasing in response to the demand for improved corrosion resistance of thin steel sheets. Since the corrosion resistance of a Zn-based plated steel sheet depends on the sacrificial anticorrosive action of the plated layer, how long the plated layer is allowed to exist on the surface has been studied. As a result, in electro-Zn plating, Zn-Ni alloy plated steel plate and Z
An n-Fe alloy plated steel sheet was developed and put into practical use. on the other hand,
In hot dip galvanizing, alloyed hot dip galvanized steel sheets, or Zn-5% Al-plated steel sheets and Zn-55% Al-plated steel sheets have been developed and put into practical use.

Generally, electric Zn or Zn alloy-plated steel sheet is obtained by making the current distribution during plating uniform.
It is characterized in that the amount of plating adhered and the alloy component of the plating layer can be made uniform, and the desired alloy composition can be obtained by controlling electrolysis. As a result, particularly excellent workability can be obtained, and therefore, it is used for deep drawing applications such as home electric appliances and automobiles, and outer panel applications. On the other hand, hot-dip Zn or Zn alloy-plated steel sheets have been used for applications where appearance and workability are not required so much, because thick plating is easy and productivity is high and high corrosion resistance can be imparted. However, recently, the demand for high corrosion resistance in applications requiring appearance and workability has become remarkable, and the demand for improving the appearance and workability of hot-dip galvanized steel sheets having excellent corrosion resistance has been particularly strong.

In hot-dip Zn-plated steel sheets, Zn-5% Al-plated steel sheets such as super zinc and galfan, Zn-55% Al-plated steel sheets such as Galvalume, and hot-dip Zn-based plated steel sheets such as alloyed hot-dip Zn-plated steel sheets, Researches on factors controlling workability have been actively conducted, and various factors have been cited so far. Among these factors, it has been found that the Fe-Zn alloy layer growing at the interface between the base iron and the plating layer is the largest factor for workability, and the control of this alloy layer is the control of molten Zn.
It is said to be important for ensuring the workability of plating. The thickness and properties of this alloy layer depend not only on the material and surface condition of the steel sheet that is the base, but also on the plating bath composition and plating bath temperature. Since it is difficult to completely control these factors in the manufacturing process of Zn plating by the current Zenzimer method, some improvement means have been proposed, but a perfect one has not yet been found.

In hot dip plating, the surface of a steel sheet is scraped by the contact between the steel sheet and a metal roll until it is immersed in a plating bath, iron powder is generated, and the iron powder is caught in the steel sheet to cause a flaw on the steel sheet. There are also problems.

[0006] A molten Zn-plated steel sheet forms a film when the steel sheet comes into contact with molten metal Zn or Zn alloy. At this time, Fe diffuses into Zn from the steel sheet surface, and at the same time, a Zn-Fe alloy layer is formed at the steel sheet / plating layer interface. As described above, the workability of the hot dip galvanized steel sheet largely depends on the properties of this alloy layer, and the influence of this alloy layer on the workability is particularly important in the case of the alloyed hot dip galvanized steel sheet. If an alloy layer mainly composed of the Γ phase develops at the interface between the base metal and the plating layer, the workability deteriorates, and in particular, the plating peels off from the plating layer during processing, and powdering becomes remarkable. Also, the low temperature chipping resistance after painting, which is required for automobile body rust-preventive steel sheets, becomes poor.

In order to improve the workability of the hot-dip Zn-plated steel sheet, a quality improvement plan has been proposed in which the plating layer has a multi-layer structure and the Fe-Zn alloy amount is controlled by controlling the heating and cooling conditions during plating. (JP-A-3-827
46). However, this method has not been able to achieve the workability equivalent to that of electric Zn-plated steel sheets currently required. Also,
A method has been proposed in which Fe is plated on the underlayer and then hot-dip Zn is plated on the upper layer to form a Fe—Zn alloy layer having excellent workability (Japanese Patent Laid-Open No. 2-15605).
6). However, since Fe as the base has a high melting point and does not become a semi-molten state, it is not effective as a countermeasure against the flaws that significantly deteriorate the appearance.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been devised to improve the workability, appearance, and flaws of hot-dip Zn-plated steel sheet. In the hot-dip Zn-plated steel sheet, when a Fe-Zn alloy formed by reacting a base metal with a plating bath containing molten metal Zn as a main component grows to form a layer, the non-uniformity and the surface Due to the appearance, the surface of the plated surface becomes rough and powdering occurs due to the destruction of the alloy layer during processing. Further, when the steel sheet is heated in the pre-stage of hot dip coating, the steel sheet rubs on the roll to generate iron powder, which is involved to cause push defects. As a solution to these problems, a pre-formed electroplating plating layer is heated and melted to form a stable alloy layer of Zn and Fe at the interface between the base iron and the Zn plating layer to improve workability. As a means for improving this, Zn is plated in advance by an electroplating method, and this is heated to provide lubricity and has excellent adhesiveness, and is stable and does not break during hot dipping. It is to make the alloy layer in advance. To study the multi-layering of plating film, in which the molten plating layer has lubricity so that iron powder is not generated in contact with the metal roll, and a stable alloy layer is formed before hot-dip plating. It was developed by.

[0009]

[Means for Solving the Problems] 0.1-10 g /
m ^{2 having} a uniform Fe content of 10% or more Fe—Zn alloy layer, and having a hot Zn plating layer of 10 to 100 g / m ² or a Zn alloy plating layer thereon. Multi-layered alloyed molten Zn with excellent workability without defects
Plated steel sheet.

In the production of a multi-layer type alloyed hot-dip galvanized steel sheet, a cold-rolled steel sheet or a hot-rolled steel sheet is degreased, washed with water, pickled with a nitric acid-free inorganic acid, and then fed with a current density of 3 to
A Zn plating layer of 0.1 to ²⁰ g / m ² is formed at 300 A / m ² , and then is heated to a temperature higher than the bath temperature of the subsequent hot dipping pot so that the Fe content is 10% or more,
A Fe—Zn alloy of 0.1 to 10 g / m ² is formed at the interface with the base iron, and then introduced into a Zn or Zn-based alloy hot-dip pot to perform an upper layer plating of 10 to 100 g / m ^2. Is a method for producing a multi-layered alloyed hot-dip Zn-plated steel sheet which is excellent in workability with no flaws.

[0011]

The function of the present invention is to apply the electric Z
n plating is performed, and this plating layer is heated and melted before hot dipping to provide lubricity and prevent push defects, and a uniform Fe-Zn alloy layer excellent in workability is formed in advance. The present invention relates to a multi-layer hot-dip galvanized steel sheet excellent in workability, which is obtained by hot-dip Zn plating by a method such as dipping in a hot-dip bath or coating with a roll coating method, and a method for producing the same. is there. Therefore, the point of the present invention lies in the state and forming method of the Fe—Zn alloy layer formed on the iron surface prior to hot dipping.

First, according to the present invention, Zn-Fe having a Fe content of 10% or more, preferably 15% to 85% is previously prepared.
The alloy plating layer is formed by heating and melting the Zn plating layer deposited by the electric Zn plating method and reacting with the base iron. At this time, the Fe content in the Fe-Zn alloy layer was 10%.
If it is less than this, the thickness of the Fe-Zn alloy plated layer is determined in consideration of the amount of redissolution in the subsequent hot dip plating process, but good workability as a composite steel sheet is 0.1 to 10 g /
m ² . If it is less than 0.1 g / m ² , η appears on the plating layer surface.
Phase and ζ phase tend to remain, and the flaking resistance is not sufficient. ^{On the other hand} , if it exceeds 10 g / m ² , the alloy layer becomes too thick and powdering occurs due to alloy breakdown during processing. Further, the alloying temperature is adjusted so as to have a melting point higher than the bath temperature of the subsequent hot dipping bath.

The amount of hot-dip galvanizing in the subsequent stage is 10 to 100.
g / m ² is the applicable range. If it is less than 10 g / m ² , corrosion resistance is insufficient, and if it exceeds 100 g / m ² , workability is significantly impaired.

The step of heating the electric Zn plating layer is as follows.
Depending on the latter hot-dip plating method, there are the following.

(1) When performing hot-dip Zn plating by the Sendzimir method, after performing electro-Zn plating in advance on a separate line, the hot-dip galvanizing line is passed through the hot-dip galvanizing line to adjust the furnace temperature of the preceding heating furnace. A desired Zn-Fe alloy plated layer is formed and then passed through a plating pot filled with molten Zn or a Zn alloy, followed by rapid cooling to finish a multilayer hot-dip galvanized steel sheet.

(2) An electroplating process having a degreasing and pickling treatment process is provided before the line of the hot-dip Zn plating method by the Sendzimir method, and after performing electro-Zn plating of a predetermined thickness, hot-dip plating is continuously performed. Pass to the line. Then, the furnace temperature of the heating furnace in the first stage of the hot dip coating line is adjusted to form a Zn-Fe alloy plating layer having a desired composition, and the Zn-Fe alloy plating layer is passed through a hot pot to be filled with hot-dip metal, followed by rapid cooling. And finish the multi-layer hot-dip galvanized steel sheet.

(3) After Zn electroplating, Zn-Fe alloying is performed to a predetermined composition in an induction heating furnace, and then hot-dip Zn plating is performed in a Sendzimir hot-dip galvanizing line, or directly introduced into a plating pot. After controlling the adhesion amount, it is cooled to finish the multi-layer hot-dip galvanized steel sheet.

In this way, Fe which was previously formed at the interface of the base metal
The alloy layer of Zn and Zn has the following characteristics as compared with the alloy layer that spontaneously grows in the hot dipping process.

The thickness of the alloy layer is uniform (in order to plate Zn with a uniform thickness by an electroplating method and then to alloy it by heating). The thickness of the alloy layer can be controlled (since it is an electroplating method, the amount of Zn deposited can be controlled). It is easy to control the composition of the alloy layer (the property is easy to control because it is a binary alloy layer of Zn and Fe). It is possible to add trace elements that are not stable in molten metal,
It is possible to improve the properties of the alloy layer. Furthermore, this Zn
Since the -Fe alloy is in a molten state, it also acts as a lubricant between the metal roll and the steel sheet, and is effective in reducing the push defects caused by the worn iron powder.

[0020]

【Example】

Example 1 Cold-rolled steel sheet was heated to 60 ° C. with 2% sodium carbonate and 0.5
% Degreasing with a mixed solution of caustic soda for 10 seconds, washing with water, and
After pickling with a 5% sulfuric acid solution at 5 ° C. for 5 seconds, it was washed with water at 30 ° C. to carry out a pretreatment for plating. Following the Zn and 20g / m ² plating from 0.1g / m ² by the electroplating method,
Distilled water at 40 ° C. was sprayed at a rate of 1 liter / minute for 10 seconds to wash with water, and then the temperature was raised to the melting point of Zn or higher in an induction heating furnace to alloy and form the first layer. Next, the steel sheet subjected to the alloying treatment of the first layer is immersed in a hot-dip Zn plating bath containing 0.1% Al for 0.1 seconds and then withdrawn, excess Zn is cut with cold air, and the adhesion amount At the same time, the cooled Zn was sprayed and rapidly cooled to finish the upper layer plating.

Example 2 Cold rolled steel sheet was heated to 60 ° C. with 2% sodium carbonate and 0.5
% Degreasing with a mixed solution of caustic soda for 10 seconds, washing with water, and
After pickling with a 5% sulfuric acid solution at 5 ° C. for 5 seconds, it was washed with water at 30 ° C. to carry out a pretreatment for plating. Following the Zn and 20g / m ² plating from 0.1g / m ² by the electroplating method,
Distilled water at 40 ° C. was sprayed at a rate of 1 liter / minute for 10 seconds to wash with water, and then the temperature was raised to the melting point of Zn or higher in an induction heating furnace to alloy and form the first layer. Next, the steel sheet subjected to the alloying treatment of the first layer is immersed in a hot-dip Zn plating bath containing 0.1% Al for 0.1 seconds and then withdrawn, excess Zn is cut with cold air, and the adhesion amount Was controlled and heated again to 530 ° C. within 1 second in the induction heating furnace to obtain a predetermined alloy composition, and then mist spray of cold water was performed to cool to finish the upper layer plating.

Example 3 Cold rolled steel sheet was heated to 60 ° C. with 2% sodium carbonate and 0.5
% Degreasing with a mixed solution of caustic soda for 10 seconds, washing with water, and
After pickling with a 5% sulfuric acid solution at 5 ° C. for 5 seconds, it was washed with water at 30 ° C. to carry out a pretreatment for plating. Following the Zn and 20g / m ² plating from 0.1g / m ² by the electroplating method,
Distilled water at 40 ° C. was sprayed at a rate of 1 liter / minute for 10 seconds to wash with water, and then the temperature was raised to the melting point of Zn or higher in an induction heating furnace to alloy and form the first layer. Next, the steel sheet subjected to the alloying treatment of the first layer was treated with 4.8% Al and 0.1% Mg.
While immersing in a hot dip Zn plating bath containing 0.2 seconds and then pulling it up, excess Zn was cut with cold air to control the amount of adhesion, and at the same time, cooled Zn was sprayed to be rapidly cooled to complete the upper layer plating.

Comparative Example 1 Cold rolled steel sheet was heated to 60 ° C. with 2% sodium carbonate and 0.5
% Degreasing with a mixed solution of caustic soda for 10 seconds, washing with water, and
After pickling with a 5% sulfuric acid solution at 5 ° C. for 5 seconds, it was washed with water at 30 ° C. to carry out a pretreatment for plating. Subsequently, Zn was plated by an electroplating method, and distilled water at 40 ° C. was sprayed at a rate of 1 liter / minute for 10 seconds to wash with water to form a first layer. Next, this steel sheet was immersed in a hot-dip Zn plating bath containing 0.1% Al for 0.1 seconds and then pulled up to cut off excess Zn with cold air to control the amount of adhesion and at the same time spray cooled Zn. The upper layer plating was finished by rapid cooling.

Comparative Example 2 Cold rolled steel sheet was heated to 60 ° C. with 2% sodium carbonate and 0.5
% Degreasing with a mixed solution of caustic soda for 10 seconds, washing with water, and
After pickling with a 5% sulfuric acid solution at 5 ° C. for 5 seconds, it was washed with water at 30 ° C. for pretreatment of plating. Subsequently, Zn is plated by an electroplating method, and distilled water at 40 ° C. is sprayed at a rate of 1 liter / min for 10 seconds to wash with water, and then alloyed by raising it to a temperature higher than the melting point of Zn in an induction heating furnace to form an alloy. Formed. Next, the steel sheet subjected to the alloying treatment of the first layer is immersed in a hot-dip Zn plating bath containing 0.1% Al for 0.1 seconds and then withdrawn, excess Zn is cut off with cold air, and the adhesion amount is reduced. Simultaneously with the control, the cooled Zn was sprayed and rapidly cooled to finish the upper layer plating.

Comparative Example 3 Cold rolled steel sheet was heated to 60 ° C. with 2% sodium carbonate and 0.5%.
% Degreasing with a mixed solution of caustic soda for 10 seconds, washing with water, and
After pickling with a 5% sulfuric acid solution at 5 ° C. for 5 seconds, it was washed with water at 30 ° C. to carry out a pretreatment for plating. Or no pretreatment was done. Subsequently, Zn was 10 g / m 2 by electroplating.
² plating was performed, and distilled water at 40 ° C. was sprayed at a rate of 1 liter / min for 10 seconds to wash with water, and then the temperature was raised to the melting point of Zn or higher in an induction heating furnace to form an alloy to form a first layer. Then this first
The steel sheet on which the layers have been alloyed is dipped in a hot-dip Zn plating bath containing 0.1% Al for 0.1 seconds and then pulled up, excess Zn is cut off with cold air to control the amount of adhesion and at the same time cooling. Zn was sprayed and rapidly cooled to finish the upper layer plating. The results are summarized in Table 1.

[0026]

[Table 1]

From A to F, according to the present invention, the powdering resistance during processing, the flaking resistance, the dent resistance and the appearance are excellent. Since G does not heat and melt in the lower electroplating, the alloy layer is easily peeled off. As a result, dents occur and the powdering resistance is poor. Since H has a small amount of upper Zn-Fe alloy, it has poor flaking resistance. I is the upper layer Z
Since the amount of n-Fe alloy is large, powdering resistance during processing is poor. Since J has a small amount of upper Zn, it has poor corrosion resistance. K
Has a large amount of Zn in the upper layer, and thus has poor powdering resistance. L
Zn has a small amount of Zn electroplating on the lower layer, so Zn-
Fe alloy content is small, resulting in poor flaking resistance. As for M, nitric acid pickling was used instead of sulfuric acid pickling in the pretreatment of the lower layer electric Zn plating. Therefore, the lower layer Zn
The adhesion of the plated layer to the base is poor, and even after heating and melting, sufficient adhesion cannot be obtained, and various performances deteriorate. N is the lower layer Zn
Since there is no pretreatment for plating, the adhesion of the plating layer is poor and various performances are poor.

[0028]

INDUSTRIAL APPLICABILITY The multi-layer hot-dip galvannealed steel sheet according to the present method has an effect of improving workability not only when it is used as a bare steel sheet but also as a base for coated steel sheet. A high-quality precoated steel sheet can be obtained.

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Claims (2)

[Claims] 1. The lower layer has a uniform F content of 0.1 to 10 g / m ^2.
e Fe-Zn alloy layer having an e content of 10% or more, and a hot-dip Zn plating layer of 10 to 100 g / m ² or Z
A multi-layer type alloyed hot-dip Zn-plated steel sheet having an n-alloy plated layer and excellent in workability with no flaws. 2. In the production of a multi-layer type alloyed hot-dip galvanized steel sheet, a cold-rolled steel sheet or a hot-rolled steel sheet is degreased, washed with water, pickled with a nitric acid-free inorganic acid, and then subjected to a current density of 3
To form a Zn plating layer of 0.1 to ²⁰ g / m ² at ˜300 A / m ² , and then temporarily heat it to a temperature higher than the bath temperature of the subsequent hot dip plating pot so that the Fe content is 10% or more, A Fe—Zn alloy of 0.1 to 10 g / m ² is formed at the interface with the base iron, and then introduced into a Zn or Zn-based alloy hot-dip pot to perform an upper layer plating of 10 to 100 g / m ^2. A method for producing a multi-layered alloyed hot-dip galvanized steel sheet having excellent workability and free from flaws.