JP2000087257A - Production of cold rolled steel sheet excellent in coating suitability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively improve the coating suitability of a steel sheet with high productivity and to improve its durability by subjecting a steel sheet to annealing in a continuous annealing line, subsequently applying it by electrogalvanizing of specified zinc coating weight and then executing chemical conversion treatment of phosphate treatment or chromate treatment. SOLUTION: In a continuous annealing line, a steel sheet S recoiled from an inlet side payoff reel 1 is cleaned by a pretreating device 2 and is thereafter passed through annealing equipment 4 via an inlet side looper 3. In this place, the steel sheet S is subjected to annealing by heat treatment of heating, soaking and cooling, is applied by required light rolling reduction with a skinpass rolling device 5 according to need and is carried into electroplating equipment 6. The steel sheet S is applied by electroplating to form a galvanizing layer of <=4 g/m2 coating weight in which the lower limit is about 0.5 g/m2. Then, the galvanized steel sheet S is subjected to phosphate treatment or coating type chromate treatment with chemical conversion treating equipment 7 or a roll coating device 8 and is dried or baked by an oven 9, and the obtd. cold rolled steel sheet S is recoiled round a tension reel 11 via an outlet side looper 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inexpensively producing a cold-rolled steel sheet having excellent paintability.

[0002]

2. Description of the Related Art Cold-rolled steel sheets used for automobiles, home appliances and the like are often used for painting. In the case of using a paint, a chemical conversion treatment such as a phosphate treatment is performed in advance to improve the durability after the paint.

[0003] In recent years, cold rolled steel sheets of various materials can be manufactured in a continuous annealing line. Therefore, cold rolled steel sheets are mainly manufactured in a continuous annealing line.

[0004] In the continuous annealing line, the steel sheet is directly heated by a heating furnace in order to heat the steel sheet efficiently in a short time, or the steel sheet after heating and soaking is cooled by water cooling or in order to adjust the material of the steel sheet. The cooling rate and the cooling end temperature are adjusted by cooling means such as steam cooling.

[0005] However, even when the air ratio of the combustion gas is strictly controlled at the time of the direct fire heating, an oxidation phenomenon occurs on the steel sheet surface. This oxidation phenomenon is reduced in the reducing atmosphere in the subsequent heating zone and solitary zone. However, if the degree of oxidation varies greatly, the degree of activation of the steel sheet surface after reduction varies.

Further, when cooling the steel sheet after heating and soaking, the steel sheet is oxidized and a thin oxide film is formed. This oxide film remains on the steel sheet surface after annealing without being reduced.

When a phosphate treatment is applied to a steel sheet having a difference in the degree of activation of the surface or a steel sheet having an oxide film remaining thereon, the phosphate treatment film becomes non-uniform, resulting in poor paintability. The durability is reduced. Therefore, the steel sheet manufactured by the continuous annealing line may have poor paintability.

In a continuous annealing line, a trace amount of Ni is deposited (Ni flash plating) on an annealed steel sheet to uniformly form a phosphate treatment film and improve coating properties. No. 8132 has been proposed.

[0009]

SUMMARY OF THE INVENTION The aforementioned Japanese Patent Publication No. 61-81
The method proposed in Japanese Patent Publication No. 32 and the like presupposes that a phosphate treatment is performed by a customer. Steel plate manufacturer, N
If not only the phosphating treatment such as i-flash plating but also the phosphating treatment can be performed at a low cost, the phosphating process at the consumer becomes unnecessary and It can contribute to cost reduction at home.

An object of the present invention is to provide a method for manufacturing a cold-rolled steel sheet which is inexpensive and has excellent paintability in consideration of the above circumstances.

[0011]

Means of the present invention for solving the above problems are as follows.

(1) In the continuous annealing line, electrogalvanizing is performed on the steel sheet after annealing, and the amount of plating is 4
A method for producing a cold-rolled steel sheet having excellent coatability, wherein a galvanized layer having a thickness of g / m ² or less is formed and further subjected to a chemical conversion treatment.

(2) The method for producing a cold-rolled steel sheet having excellent coatability according to the above (1), wherein the chemical conversion treatment is a phosphate treatment or a chromate treatment.

(3) The method for producing a cold-rolled steel sheet having excellent coatability according to the above (2), wherein the chromate treatment is a coating type chromate treatment.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS When a phosphate treatment is applied to a steel sheet,
As compared with the case where the base is Ni flash plating, when a small amount of zinc adheres, the reactivity becomes better and a good phosphate film is formed, so that excellent paintability is obtained.

In order to deposit a small amount of zinc on a steel sheet, it is possible to insert a steel sheet annealed in a continuous annealing line into another electrogalvanizing line and perform galvanizing. Therefore, the manufacturing cost is not low.

If an electroplating facility is provided downstream of the annealing facility in the continuous annealing line, annealing and zinc plating can be performed in one line. However, since the optimal processing speed of steel sheets in annealing equipment is mainly determined by the steel sheet size, the optimal processing speed of steel sheets in the electroplating equipment is not dependent on the steel sheet size, but is mainly determined by the plating amount. The optimum processing speed of the annealing equipment and the optimum processing speed of the electroplating equipment generally do not match. If they do not match, the processing speed of the entire continuous annealing line is limited by the processing speed of the equipment whose optimum processing speed is lower. When the amount of galvanized steel increases like a normal galvanized steel sheet, a large-scale galvanizing equipment is required, which not only increases the equipment cost, but also increases the processing speed of the electroplating equipment to reduce the processing speed of the entire continuous annealing line. It becomes rate-limiting, compared to the case where no electroplating equipment is installed.
The production capacity of the continuous annealing line decreases, and the production cost increases.

In the present invention, by limiting the amount of zinc plating to 4 g / m ² or less, the processing speed of the entire continuous annealing line does not decrease due to the rate control in the electroplating equipment. The productivity of the continuous annealing line does not decrease as compared with the continuous annealing line where no equipment is provided. In addition, the electroplating equipment is inexpensive because it can be a compact equipment.

When the amount of zinc plating is less than 0.5 g / m ² , the plating layer dissolves non-uniformly in the subsequent chemical conversion treatment, so that the chemical conversion coating becomes non-uniform. In order to obtain excellent paintability after the chemical conversion treatment, the amount of zinc plating is 0.5 g / m ^2.
It is desirable to make the above.

The steel sheet having a galvanized layer on its surface is excellent not only in phosphate treatment but also in chemical conversion such as chromate treatment. In a continuous annealing line, a steel sheet having excellent coatability can be obtained at low cost by subjecting a steel sheet annealed and galvanized to a chemical conversion treatment. In order to obtain excellent coating properties, the chemical conversion treatment is preferably a phosphate treatment or a chromate treatment, and the chromate treatment is more preferably a coating type chromate treatment.

Hereinafter, the present invention will be further described with reference to FIG. FIG. 1 is a diagram showing a main part of a continuous annealing line for explaining an embodiment of the present invention. In FIG. 1, 1 is an incoming payoff reel, 2 is a pretreatment device, 3 is an incoming looper, 4 is an annealing facility, 5 is a temper rolling device, 6 is an electroplating facility, 7 is a chemical treatment facility, and 8 is a roll. An application device, 9 is an oven, 10 is an output looper, and 11 is an output tension reel.

As the pretreatment device 2, a known device such as an electrolytic cleaning device for removing rolling oil, iron powder and the like adhering to the surface of the steel sheet as a treatment prior to annealing can be used.

As the annealing equipment 4, a known equipment can be used. For example, the heating furnace for heating the steel sheet S may be any of a direct-fired heating furnace and a radiation tube heating furnace. Also heating
The cooling of the steel sheet after soaking may be any of gas cooling, water cooling, steam-water cooling, roll cooling and the like. A facility for performing overaging treatment after cooling may be provided.

As the electroplating equipment 6, equipment having a known structure, for example, equipment having a plating section and a pretreatment section for performing degreasing and / or pickling before the plating section can be used.
In the present invention, the amount of zinc plating in the electroplating facility 6 may be 4 g / m ² or less, so that the electroplating facility 6 can be a compact facility.

As the chemical conversion treatment facility 7, a device having a known configuration can be used. For example, a phosphate treatment equipment such as a spray method or a chromate treatment equipment can be provided. As the roll coating device 8 and the oven 9, a device having a known configuration can be used.

In the continuous annealing line shown in FIG. 1, the steel sheet S paid out from the pay-off reel 1 is transported to the pretreatment device 2 to clean the surface of the steel sheet. Next, the steel sheet S is conveyed to the annealing equipment 4 via the entry-side looper 3 and subjected to a required heat treatment. The temper rolling is performed on the steel sheet S annealed by the annealing equipment 4 by the temper rolling device 5 as necessary.

Next, the steel sheet S is transported to the electroplating equipment 6 and is subjected to zinc plating with a coating weight of 4 g / m ² or less.
In order to make the equipment as compact as possible, when plating, the current density should be as high as possible,
Plating at 0 A / dm ² or more is advantageous.

Next, using the chemical conversion treatment equipment 7 and / or the roll coating device 8, necessary chemical conversion treatments such as a phosphate treatment by a spray method or a chromate treatment are performed. Phosphate treatment or chromate treatment is performed in the chemical conversion treatment equipment 7, and dried with a built-in dryer. When performing the coating type chromate treatment, the treatment liquid is applied by the roll coating device 8,
The required drying or baking is performed in the oven 9. If necessary, after performing a base chromate treatment in the chemical conversion treatment equipment 7,
The coating type chromate treatment can also be performed by the roll coating device 8. As the chemical conversion treatment liquid used above, a known treatment liquid used for chemical conversion treatment of an electrogalvanized steel sheet can be used.

Next, the steel sheet S is wound around the output side tension reel 11 through the output side looper 10 to obtain a required cold-rolled steel sheet.

The steel sheet obtained as described above has excellent paintability and is inexpensive because it is manufactured in one line. Further, since the productivity of the continuous annealing line does not decrease due to the galvanization, the continuous annealing line is excellent in productivity.

[0031]

EXAMPLES (Example 1) Cold rolled steel sheets having a thickness of 0.8 mm and 1.6 mm were annealed in the continuous annealing line shown in FIG. 1, and after galvanizing with a plating amount of 4 g / m ^2. , Palbond 3 manufactured by Nippon Parkerizing Co., Ltd.
Cold-rolled steel sheet was manufactured by spraying phosphate treatment using 312 (trade name). The plating amount of the cold-rolled steel sheet and the adhesion amount of the phosphate film obtained above were examined, and the paint adhesion was examined as follows (Example of the present invention).

A melamine resin paint (Amirac White Conc (trade name) manufactured by Kansai Paint Co., Ltd.) is applied to the cold-rolled steel sheet obtained above with a bar coater to a thickness of 20 to 25 μm.
A test piece was prepared by baking at 120 ° C. for 20 minutes, and a cross cut test, an Erichsen test, and a bending test were performed.

In the cross-cut test, 100 cross-cuts (10 × 10) were formed on the coating surface of the test piece with a safety razor to reach the plating surface at 1 mm intervals, and a cellophane tape was stuck thereon and immediately peeled off. Evaluation was made as shown in Table 1 based on the number of grids in which the coating film did not peel.

In the Erichsen test, an orthogonal line reaching the plating surface was inserted into the coating surface of the test piece with a safety razor, extruded with an Erichsen tester, and based on the extruded length when the coating film was peeled off, as shown in Table 1. Was evaluated.

In the bending test, a mandrel having a constant curvature was bent at 180 ° C. for 1 second, and the outer coating surface was observed and evaluated as shown in Table 1 based on the state of the coating surface. .

[0036]

[Table 1]

The lowest evaluation point of the above three tests was regarded as the coating adhesion evaluation point. The results of the survey are shown in Table 2.

[0038]

[Table 2]

For comparison, the thickness after continuous annealing is 0.8 m.
Palbond 30 manufactured by Nippon Parkerizing Co., Ltd. on a steel plate obtained by performing Ni flash plating on a 1.6 mm steel plate.
Phosphate treatment was performed using 30M (trade name), and paint adhesion was similarly investigated (Comparative Example 2). In addition, a steel sheet having a thickness of 0.8 mm and 1.6 mm after continuous annealing is subjected to the same electrogalvanizing and phosphate treatment as in the above-described present invention example in a separate electrogalvanizing line, and the paint adhesion is similarly reduced. Investigation was conducted (Comparative Example 1). The results of the survey are shown in Table 2.

The paint adhesion of the present invention is superior to Comparative Example 2 in which Ni flash plating is performed, and is equivalent to Comparative Example 1.

(Example 2) In a continuous annealing line shown in FIG. 1, cold-rolled steel sheets having a thickness of 0.8 mm and 1.6 mm were annealed, and electrogalvanized at a plating amount of 4 g / m ² . A cold-rolled steel sheet was manufactured by performing a spray-type chromate treatment using a chromate treatment liquid (Zinchrome # 357S manufactured by Nippon Parkerizing Co., Ltd.) in a chemical conversion treatment facility 7. The plating amount and Cr adhesion amount of the steel sheet obtained above were investigated, and paint adhesion was investigated in the same manner as in Example 1. Table 3 shows the results of the survey.

[0042]

[Table 3]

For comparison, the thickness after continuous annealing is 0.8 m.
A 1.6 mm steel plate was subjected to electrogalvanizing and chromate treatment as described above in another electrogalvanizing line, and paint adhesion was examined in the same manner as described above. The results are shown in Table 3. In the present invention example, the same paint adhesion as the comparative example was obtained.

Example 3 Cold rolled steel sheets having a thickness of 0.8 mm and 1.6 mm were annealed in the continuous annealing line shown in FIG. 1 and electrogalvanized to a plating amount of 4 g / m ² . 3
Chromate treatment liquid (Zinchrome # 3399 (trade name) manufactured by Nippon Parkerizing Co., Ltd.) in a roll type coating device 8
Was applied and chromated, and baked in an oven 9 to produce a cold-rolled steel sheet. The plating amount and Cr adhesion amount of the steel sheet obtained above were investigated, and paint adhesion was investigated in the same manner as in Example 1. Table 4 shows the results of the survey.

[0045]

[Table 4]

For comparison, the thickness after continuous annealing is 0.8 m.
A 1.6 mm steel plate was subjected to the same electrogalvanizing and coating type chromate treatment as described above in another electrogalvanizing line, and the paint adhesion was examined in the same manner as described above.
Table 4 also shows the results of the investigation.

In the examples of the present invention, paint adhesion equivalent to that of the comparative example is obtained.

[0048]

According to the present invention, in the continuous annealing line, the steel sheet after the annealing is successively coated with a coating amount of 4 g / m ^2.
Since the following electrogalvanizing and chemical conversion treatment are performed, a cold rolled steel sheet which is inexpensive and has excellent paintability can be manufactured. In addition, by performing electrogalvanizing, the line speed of the continuous annealing line does not decrease, so that the continuous annealing line is excellent in productivity.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of a continuous annealing line for explaining an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Incoming payoff reel 2 Pre-processing device 3 Incoming looper 4 Annealing equipment 5 Temper rolling equipment 6 Electroplating equipment 7 Chemical conversion equipment 8 Roll coating device 9 Oven 10 Outgoing looper 11 Outgoing tension reel S Steel plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K024 AA05 AB01 BA03 BB02 BB18 BC01 DA10 DB04 DB05 GA12 4K026 AA02 AA12 AA22 BA04 BA06 BB06 CA20 CA21 CA22 CA23 DA02 DA06 4K043 AA01 DA05 EA07 GA06 HA01 HA04 HA07 4K04 ABA BB03 BC04 CA02 CA16 CA18 CA53

Claims (3)

[Claims] 1. In a continuous annealing line, electrogalvanizing is performed on a steel sheet after annealing, and the amount of plating is 4 g /
A method for producing a cold-rolled steel sheet having excellent coatability, wherein a galvanized layer having a thickness of m ² or less is formed and further subjected to a chemical conversion treatment. 2. The method according to claim 1, wherein the chemical conversion treatment is a phosphate treatment or a chromate treatment. 3. The method according to claim 2, wherein the chromate treatment is a coating type chromate treatment.