JPH09263964A - Manufacture of hot-dip galvannealed steel sheet excellent in surface property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a hot-dip galvannealed steel sheet excellent in the surface property by uniformizing the alloying degree in the longitudinal direction and in the width direction of the hot-dip galvannealed steel sheet to form the Fe-Ni-O coating film of appropriate coating weight. SOLUTION: An alloying furnace 4 is provided with an induction heating device 4a and an edge heater 4b to uniformly heat a hot-dip galvannealed steel sheet in the longitudinal direction and in the width direction. The hot-dip galvannealed steel sheet 1b heated in the alloying furnace 4 is heated at a low temperature for a long time by a heat insulating device 5, and coated with the coating solution in a coating equipment 7 in the next process. The hot-dip galvannealed steel sheet 1b heated in the alloying furnace 4 is cooled by a cooling device 6a, and a cooling device 6b, and further cooled by cooling devices 6c, 6d, and heated at high temperature for a short time, and then, coated with the coating solution in the coating equipment 7 in the next process. The coating suitable for the layer structure of the plated layer can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a galvannealed steel sheet, and more particularly to a method for producing a galvannealed steel sheet having excellent surface properties.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheets are widely used as various anticorrosion steel sheets because they have various excellent characteristics.

In order to use this alloyed hot-dip galvanized steel sheet as an anticorrosion steel sheet for automobiles, in addition to corrosion resistance and paint compatibility, the performance required in the vehicle body manufacturing process is as follows.
It is important that it is excellent in press formability, spot weldability, adhesiveness, and chemical conversion treatment property, and that it can be supplied to customers at low cost, that is, the manufacturing cost is low.

However, alloyed hot-dip galvanized steel sheets generally have the disadvantage that they are inferior in press formability to cold-rolled steel sheets. This is because the sliding resistance between the galvannealed steel sheet and the press die is higher than that in the case of cold-rolled steel sheet.If this sliding resistance is high, the bead of the press die is pressed during pressing. The alloyed hot-dip galvanized steel sheet in the vicinity of the part is less likely to flow into the press die, and the steel sheet is likely to break.

As a method for improving the press formability of an alloyed hot-dip galvanized steel sheet, a method of applying a high-viscosity lubricating oil is widely used. In this method,
Due to the high viscosity of the lubricating oil, there are problems such as coating defects due to poor degreasing in the next coating process, unstable press molding due to running out of lubricating oil, and unstable press performance.

Therefore, in recent years, a double-layer plated steel sheet in which an iron-based plating film is formed on the surface of a galvannealed steel sheet by an electroplating method has come to be used.

This iron-based plating film has the effect of reducing sliding resistance during press molding and improving coating compatibility.

However, in order to manufacture this double-layer galvanized steel sheet with a hot dip galvanizing facility (CGL), it is necessary to add an electrogalvanizing facility, and the fixed cost and the variable cost due to the electrogalvanizing operation increase due to the capital investment. That is, there is a problem that the manufacturing cost is increased.

As a method for solving the above problem, Japanese Patent Laid-Open No. Hei 2
JP-A-190483 discloses that an electrolytic film, a dipping process, a coating oxidation process, or a heating process is applied to the surface of a zinc-based plated steel sheet to generate an oxide film mainly composed of ZnO, thereby improving weldability or workability. Japanese Patent Laid-Open No. 3-17282 discloses a technique (hereinafter, referred to as Prior Art 1).
Disclosed is a method (hereinafter referred to as Prior Art 2) in which one or more metals selected from Fe, Ni and Co are substitutionally deposited on the surface of a zinc-based plated steel sheet.
Japanese Patent No. 093 discloses a technique for generating Ni oxide to improve press formability and chemical conversion treatability (hereinafter, Prior Art 3).
JP-A-60-63394 discloses a method of applying an aqueous solution of an inert coating component (hereinafter referred to as Prior Art 4).

[0010]

The above-mentioned prior art 1 has the following problems. In Prior Art 1,
Since this is a method of producing an oxide mainly composed of ZnO on the plating surface by various treatments, the effect of reducing the sliding resistance between the press die and the plated steel sheet is small, and the effect of improving press formability is small. Further, an oxide mainly composed of ZnO deteriorates the adhesiveness.

Prior art 2 has the following problems. In the prior art 1, since metals such as Ni and Fe are deposited, sufficient wettability cannot be obtained because the wettability with respect to the adhesiveness of the metal is small. In addition, there is a problem in that the effect of improving press formability and spot weldability is small because the coating has strong metallic properties.

Further, since the pH of the aqueous solution is low and the substitution precipitation efficiency is low, it is impossible to secure a sufficient amount of deposition, and it is necessary to raise the temperature of the aqueous solution in order to secure the amount of deposition. However, there is a problem that the equipment cost rises due to such problems as the rise of the water temperature and the provision of the heating equipment for the aqueous solution.

In the prior art 3, since it is a Ni oxide single-phase coating, press formability is improved, but there is a problem that adhesiveness is deteriorated.

In the prior art 4, since it is a method of forming an inactive film, there is a problem that the chemical conversion treatment property and the adhesive property are deteriorated.

In order to solve the above-mentioned problems, the present applicant has filed Japanese Patent Application No. 7-216589 with FeCl ₂
And NiCl ₂ and Fe content (g / l) and Ni
Fe content (g / l) relative to the sum with the content (g / l)
Ratio is in the range of 0.004 to 0.9 and the pH is 2.0 to 3.
A Fe-Ni-O-based coating film is formed on the surface of a zinc-based plated steel sheet by preparing an aqueous solution in the range of 5 and a temperature in the range of 20 to 70 ° C and treating the zinc-based plated steel sheet with the aqueous solution. An application has been filed for the above zinc-based plated steel sheet manufacturing method (hereinafter referred to as prior art 5). Prior art 5 is excellent in press formability, spot weldability, adhesiveness and chemical conversion treatment,
Furthermore, it is possible to expect an effect that it can be supplied to customers at low cost.

On the other hand, among the zinc-based plated steel sheets, particularly the case of alloyed hot-dip galvanized steel sheet, in many cases, due to the characteristics, it is often used for applications where the required quality of appearance of automobile outer panels is very strict. In addition to the above-mentioned characteristics, the alloyed hot-dip galvanized steel sheet on which the Fe-Ni-O-based coating is formed also has a non-uniform alloying and a visual unevenness of the surface due to the unevenness of the coating treatment after the alloying. There is a demand for an excellent surface property that does not have

The present invention was made in order to solve the above problems, and made the alloying hot-dip galvanized steel sheet uniform in the alloying degree in the longitudinal direction and the width direction, and Fe-Ni.
-Forms a proper amount of the -O-based coating, press moldability,
It is an object of the present invention to provide a method for producing an alloyed hot-dip galvanized steel sheet having excellent spot weldability, adhesiveness, and chemical conversion treatability and having excellent surface properties.

[0018]

The invention according to claim 1 is a method for producing an alloyed hot-dip galvanized steel sheet having a Fe-Ni-O-based coating film in a hot-dip galvanizing line, wherein an induction heating device is provided in the hot-dip galvanizing line. Between the alloying furnace equipped with the edge heater and the cooling device, a heat retaining device that can be put in and out is provided, and then a Fe-Ni-O type coating treatment facility is provided to heat the alloying treatment heat cycle. And cooling zone, or heating zone, heat retaining zone and cooling zone to control the underlying structure of the galvannealed steel sheet, and then FeCl ₂ and N
It contains iCl ₂ , the ratio of the Fe content (g / l) to the sum of the Fe content (g / l) and the Ni content (g / l) is in the range of 0.004 to 0.9, and the pH is 2.0. To treat the alloyed hot-dip galvanized steel sheet with an aqueous solution in the range of 3.5 to 3.5 and the temperature in the range of 20 to 70 ° C to form a coating film having an adhesion amount of 10 to 550 mg / m ² on the alloyed hot-dip galvanized steel sheet. And a method for producing an alloyed hot-dip galvanized steel sheet having excellent surface properties.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a description will be given based on the above-mentioned reasons for limiting the present invention. In the present invention, an aqueous solution containing FeCl ₂ and NiCl ₂ is used as an aqueous solution (hereinafter referred to as a coating treatment solution) used for forming a Fe—Ni—O-based coating on the surface of a galvannealed steel sheet. The reason for selecting is that when a chloride is used as the metal salt, substitutional precipitates are high.

That is, when compared with nitrates and sulfates at the same salt concentration and the same treatment time, the metal salt of chloride is Ni.
This is because the amount of Fe and Fe deposited is large and the productivity is improved.

As a method for treating the alloyed hot-dip galvanized steel sheet with the coating treatment solution for forming the Fe-Ni-O-based coating, the dipping method is adopted to uniformly and uniformly coat the Fe-Ni-O-based coating. Let it form.

F relative to the sum of the Fe content (g / l) and the Ni content (g / l) in the coating treatment liquid used in the present invention.
By controlling the ratio of the e content (g / l) within an appropriate range, desired Fe on the surface of the galvannealed steel sheet can be obtained.
It is possible to form a —Ni—O-based coating. If Fe / (Fe + Ni) in the coating solution is less than 0.004, there is no effect of improving the adhesiveness. On the other hand, Fe / (Fe + in the coating solution does not exist.
When Ni) exceeds 0.9, the effect of improving spot weldability is reduced. Therefore, Fe / (Fe + Ni) in the coating solution
Was in the range of 0.004 to 0.9.

Further, the film can be formed efficiently by setting the pH in the film treatment liquid to an appropriate range. When the pH is less than 2.0, the amount of hydrogen gas generated is extremely increased, so that the effect of substitution precipitation of Ni and Fe is reduced, and the adhesion amount of Ni and Fe is reduced at a constant salt concentration and a predetermined treatment time. Lower.

Further, the coating mainly consists of Ni and Fe metals, and the effect of improving press formability, spot weldability and adhesiveness cannot be obtained.

Even if the pH is low, it is possible to increase the amount of Ni and Fe deposited per unit time by increasing the salt concentration, but this causes an increase in the cost of the treatment liquid and an increase in sludge. , Not preferable.

On the other hand, if the pH exceeds 3.5, Fe in the coating solution is oxidized so strongly that surface defects of the product due to sludge are likely to occur, which is not preferable.

When the temperature of the coating solution is high, the substitution precipitation reaction rate is high, the Ni and Fe precipitation efficiency is good, and the productivity is improved.

If this temperature is less than 20 ° C., the reaction rate is slow and Ni necessary for improving the properties of the galvannealed steel sheet is formed.
Also, it takes a long time to secure the amount of Fe deposited and the productivity is reduced. On the other hand, if the temperature exceeds 70 ° C., deterioration of the coating solution due to an increase in the amount of impurity ions mixed into the coating solution accelerates, and equipment and heat energy for maintaining the coating solution at a high temperature are increased. Therefore, the manufacturing cost is increased.

[0029] Fe-Ni-O based film according to the present invention should be formed in the range of the attached amount of ^{10mg / m 2 ~550mg / m 2} .

When the adhesion amount is less than 10 mg / m ² , the press moldability cannot be improved and the adhesion amount is 550 mg.
If it exceeds / m ² , the surface appearance of the alloyed hot dip galvanized steel sheet on which the Fe—Ni—O-based coating is formed is poor as shown in the examples described later, and defects such as microscopic flaws Difficult to find.

When the adhered amount exceeds 600 mg / m ² , there is a risk of overlooking the defects of the galvannealed steel sheet and flowing out the products containing the defects to the customer.
Furthermore, there is a risk that defects may be overlooked in the product manufacturing process of the consumer, the product value of the final product may be impaired, and the consumer may be greatly annoyed.

On the other hand, the alloying degree (Fe%) of the galvannealed steel sheet is in the range of 8% to 12%.

If the degree of alloying (Fe%) is less than 8%, alloying is undeveloped and baking unevenness is likely to occur. In addition, the flaking resistance is reduced. If the alloying degree (Fe%) exceeds 12%, powder links are likely to occur during press molding.

In this case, even if the alloying degree (Fe%) of the galvannealed steel sheet is in the range of 8% to 12%, Fe
When the —Ni—O-based coating is formed, there is an inverse correlation shown in FIG. 1 with the Ni deposition amount mg / m ² which is a parameter of the deposition amount of the Fe—Ni—O-based coating.

Here, 115 g / l of NiCl ₂ and Fe
The galvannealed steel sheets having different alloying degrees were treated with a coating treatment liquid containing Cl ₂ at 28 g / l.
The coating treatment time is 11 seconds and the temperature of the coating treatment liquid is 50 ° C.

As is clear from FIG. 1, when the alloying degree (Fe%) of the alloyed hot-dip galvanized steel sheet increases, the Ni adhesion amount mg / m ² decreases. That is, the amount of the Fe-Ni-O-based coating attached decreases.

In FIG. 1, the structure of the underlying plating layer having a low alloying degree (Fe%) of the galvannealed steel sheet is ζ phase A, and the structure of the underlying plating layer having a high alloying degree (Fe%) is It was δ1 phase B.

From the above, in the case of the underlying plating layer mainly composed of ζ phase, a large amount of Ni adhered mg / m ² adheres,
In the case of the underlying plating layer mainly composed of the δ1 phase, it was found that the Ni adhesion amount mg / m ² was small and adhered.

In the present invention, based on FIG. 1, the alloying degree (Fe%) in the longitudinal direction and the width direction of the galvannealed steel sheet.
In order to make the temperature uniform, in the hot dip galvanizing line, between the alloying furnace equipped with an induction heating device and an edge heater, and a cooling device, a heat retention device that can be put in and taken out is provided, and then Fe-
Ni-O coating treatment equipment is installed to switch the heat cycle of alloying treatment between heating zone and cooling zone, or heating zone and heat retaining zone and cooling zone to control the underlying structure of the galvannealed steel sheet. is there.

FIG. 2 is an explanatory view of an alloying treatment step and a coating treatment step according to one embodiment of the present invention. In FIG.
The hot-dip galvanized steel sheet 1 a is hot-dip galvanized in the hot-dip zinc pot 2, and the wiping nozzle 3 adjusts the amount of the applied coating. The hot-dip galvanized steel sheet 1b with the attached amount adjusted is alloyed in the alloying furnace 4.

In this case, an induction heating device 4a and an edge heater 4b are provided, and the longitudinal direction of the hot dip galvanized steel sheet,
It is designed so that it can be heated uniformly in the width direction.

The hot-dip galvanized steel sheet 1b heated in the alloying furnace 4 is heat-treated at a low temperature for a long time by the heat retaining device 5, passes through the cooling devices 6c and 6d, and is fed to Fe-Ni- in the next step.
The film is processed by the O-based film processing facility 7 with the film processing liquid.

On the other hand, the hot-dip galvanized steel sheet 1b heated in the alloying furnace 4 is cooled by the cooling devices 6a and 6b, further cooled by the cooling devices 6c and 6d, and heat-treated at a high temperature for a short time. In the Fe-Ni-O-based coating treatment equipment 7, the coating treatment is performed with the coating treatment liquid. 8 is a skin pass mill.

As described above, as shown in FIG. 3, the heat cycle of alloying treatment indicated by an arrow is a high temperature short time heat treatment by a heating zone and a cooling zone, or a low temperature length by a heating zone, a heat retaining zone and a cooling zone indicated by a thick arrow. The time heating treatment is switched to control the underlying structure of the galvannealed steel sheet. That is, while the alloying degree (Fe%) of the galvannealed steel sheet is regulated to 8 to 12%, the structure of the plating layer is mainly composed of the ζ phase by the low temperature long time heat treatment and the high temperature short time heat treatment. The Fe-Ni alloy layer is controlled so that the variation of the alloying degree (Fe%) in the longitudinal direction and the width direction of the alloyed hot-dip galvanized steel sheet can be reduced by controlling the underlying plating layer mainly composed of the δ1 phase. The alloyed hot-dip galvanized steel sheet on which the -O-based coating is formed has excellent surface properties.

Next, the present invention will be specifically described with reference to examples. Table 1 shows the composition% of the steel sheet used in the present invention.

[0046]

[Table 1]

This steel sheet is hot dip galvanized in a hot dip galvanizing line as shown in FIG. 2 and further subjected to the low temperature long-term heat treatment or the high temperature short-time heat treatment in the alloying step so that the structure of the plating layer is changed to ζ phase. It is controlled to the underlying plating layer mainly composed of the δ1 phase and the underlying plating layer mainly composed of the δ1 phase.
A Ni—O based coating is formed.

The temperature of the low temperature long time heat treatment is 470 ° C. to 4 ° C.
80 ℃, high temperature short time heat treatment temperature is 500 ~ 510 ℃
And In the case of the comparative example, the temperature was set to 450 ° C. to 470 ° C., the alloying degree (Fe%) was low, and a part thereof was out of the alloying degree (Fe%) 8 to 12%.
The dipping treatment conditions with the coating treatment liquid were as follows.

Immersion time: 11 seconds Coating treatment liquid temperature: 50 ° C. Coating treatment liquid composition: FeCl ₂ -115 g / l, NiCl
₂ ─ 28 g / l, pH ─ 2.0

In the evaluation of the surface properties, ○ marks are intended for consumers, and there is no visual unevenness of the surface due to non-uniform alloying and uneven coating treatment after alloying, and X marks the surface. The visual unevenness and the like are included. The results in that case are shown in Table 2.

[0051]

[Table 2]

As is clear from Table 2, in Examples No. 1 to No. 8 according to the present invention, the degree of alloying is entirely within 8 to 12%, the variation is small, and the base of ζ phase is the main component. An underlying plating layer mainly composed of the plating layer and the δ1 phase is obtained. As a result, the Ni deposition amount is maintained in an appropriate range, and the Fe—Ni—O-based coating film deposition amount calculated in terms of Ni deposition amount is maintained in an appropriate range. On the other hand, in No. 9 and No. 10 of the comparative examples, the alloying degree (Fe%) has a value in which a part of the alloy width is less than 8.0%, and the surface quality becomes x due to variations and uneven baking. became.

As shown in the above examples, according to the present invention, the alloying degree (Fe%) of the galvannealed steel sheet is maintained in an appropriate range, and the alloying degree in the longitudinal direction and the width direction is maintained. The Fe-Ni-O film forming alloyed hot dip galvanized steel sheet having excellent surface properties can be manufactured uniformly.

Further, in the present embodiment, Fe-Ni-
The alloyed hot-dip plated steel sheet on which the O-based coating was formed was excellent in press formability, spot weldability, adhesiveness, and chemical conversion treatability in addition to the above-mentioned excellent surface properties.

[0055]

As described above, according to the present invention, the alloying degree of the galvannealed steel sheet is made uniform in the longitudinal direction and the width direction, and the proper amount of the Fe-Ni-O coating film is formed. As a result, it is possible to produce an alloyed hot-dip galvanized steel sheet having excellent press formability, spot weldability, adhesiveness, and chemical conversion treatability, and further having excellent surface properties.

[Brief description of drawings]

FIG. 1 is an alloying degree (Fe%) of a plating layer of a galvannealed steel sheet on which an Fe—Ni—O-based coating film of the present invention is formed.
And Fe-Ni-O based Ni deposition amount in the coating (mg / m ²⁾
FIG.

FIG. 2 is an explanatory diagram of an alloying treatment step and a coating treatment step according to an embodiment of the present invention.

FIG. 3 is a diagram showing a heat cycle of alloying treatment according to the present invention.

[Explanation of symbols]

A Area mainly composed of ξ phase having low alloying degree (Fe%) B Area mainly composed of δ1 phase having large alloying degree (Fe%) 1a Original plate of hot dip galvanized steel sheet 1b Hot dip galvanized steel sheet 1c Alloying fusion Galvanized steel plate 2 Hot-dip zinc pot 3 Wiping nozzle 4 Alloying furnace 4a Induction heating device 4b Edge heater 5 Heat retention device 6a to 6d Cooling device 7 Fe-Ni-O type coating treatment facility 8 Skin pass mill

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noritaka Sakurai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (1)

[Claims] 1. Fe-Ni-O in a hot dip galvanizing line
In the method for producing an alloyed hot-dip galvanized steel sheet having a system coating, between the alloying furnace equipped with an induction heating device and an edge heater in the plating line, and a cooling device, a heat retention device that can be put in and taken out is provided, After that, an Fe-Ni-O-based coating treatment facility is provided, and the heat cycle of alloying treatment is switched between a heating zone and a cooling zone or a heating zone, a heat retaining zone and a cooling zone to form a base structure of the galvannealed steel sheet. Control, then F
It contains eCl ₂ and NiCl ₂ , and Fe content (g /
The ratio of Fe content (g / l) to the sum of 1) and Ni content (g / l) is in the range of 0.004 to 0.9, and pH
Is in the range of 2.0 to 3.5 and the temperature is in the range of 20 to 70 ° C, and the alloyed hot dip galvanized steel sheet is treated to form a coating film with an adhesion amount of 10 to 550 mg / m ² on the alloyed hot dip galvanized steel sheet. A method for producing an alloyed hot-dip galvanized steel sheet having excellent surface properties.