JPH0892798A - Method for producing Cr-containing corrosion-resistant steel strip excellent in corrosion resistance - Google Patents

Abstract

PURPOSE: To improve the corrosion resistance of a steel strip by annealing a Cr-contg. steel strip after cold rolling in a specified atmosphere, subjecting an oxidized film on the surface to mechanical grinding under specified conditions and executing finish pickling and passivating treatment. CONSTITUTION: A Cr-contg. steel strip is annealed in an atmosphere having -70 to -30 deg.C dew point to regulate the thickness of an oxidized film formed on the surface of the steel strip to >=1000Å. In the case of >-30 deg.C dew point, it is hard to regulate the thickness of the oxidized film to <=1000Å. It is costed to reduce the dew point to -70 deg.C. The oxidized film formed at the time of the annealing is first subjected to mechanical grinding so as to regulate the amt. to be ground to >=1g/m<2> and the loss in pickling to >=0.5g/m<2> and is thereafter subjected to finish pickling and passivating treatment by a pickling soln. contg. nitric acid. Since the oxidized film is removed away by the mechanical grinding, the concn. of the pickling soln. can be regulated to a low one, and furthermore, the increase of the temp. of the pickling soln. can be reduced.

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 Cr-containing corrosion resistant steel strip, and more particularly to a method for producing a Cr-containing corrosion resistant steel strip containing Cr in an amount of 1 to 19 wt% and having excellent corrosion resistance after cold rolling. Is.

[0002]

2. Description of the Related Art Conventionally, a Cr-containing steel strip after cold rolling has been subjected to continuous annealing and pickling treatment by continuous annealing and pickling equipment. As shown in FIG. 3, Cr after cold rolling
The steel strip 10 contains pre-tropical zone 12, heating zone 14, cooling zone 16
After that, it is water-cooled in the water cooling zone 18 and then descaled and passivated in the pickling tank 20.
2. It is manufactured by passing through the dryer 24. The pickling solution in the pickling tank 20 is cooled by the cooling device 26 after the pickling. The pickling treatment is carried out by combining neutral salt electrolysis, nitric acid electrolysis, nitric acid and nitric hydrofluoric acid, etc.
The contained steel strip is descaled and passivated.

[0003]

In the conventional continuous annealing / pickling treatment of the Cr-containing steel strip after the cold rolling described above, the chemical reaction by the acid is utilized to descale the steel strip surface after the annealing. Since the passivation treatment is performed, if the descaling is incomplete, the subsequent passivation will not be performed sufficiently and satisfactory corrosion resistance of the product cannot be obtained. In addition, in order to promote descaling, a high concentration, acid solution kept at high temperature is required, and the iron content of the steel sheet dissolves in the pickling solution to change the pickling ability, so acid concentration management is extremely troublesome. is there. Further, a cooling device for the acid solution is necessary to prevent the temperature of the solution from rising due to a chemical reaction of the acid solution, and equipment such as piping for high-concentration acid solution is also required. On the other hand, if the acid concentration is not increased, the pickling tank becomes longer, leading to an increase in equipment cost, and if it is left as it is, the pickling rate becomes a rate-decreasing production capacity.

An object of the present invention is to solve the above problems and provide a method for producing a Cr-containing corrosion-resistant steel strip which is superior in corrosion resistance to conventional ones and which has reduced pickling costs.

[0005]

According to the present invention, in a method for producing a Cr-containing corrosion-resistant steel strip, a cold-rolled Cr-containing steel strip is annealed in an atmosphere having a dew point of −70 to −30 ° C., and then, Grinding amount of oxide film on the surface formed during annealing is 1.0g
/ m ² or more and a pickling weight loss range of 0.5 g / m ² or more, characterized by first performing mechanical grinding, and then performing final pickling and passivation treatment with a pickling solution containing nitric acid. Is a method for producing a Cr-containing corrosion-resistant steel strip having excellent corrosion resistance.

[0006]

According to the present invention, since the annealing is performed in the atmosphere with the dew point adjusted in the range of -70 to -30 ° C, the thickness of the oxide film formed on the surface of the steel strip can be 1000 Å or less. Dew point is-
Above 30 ° C, it is difficult to reduce the oxide film thickness to less than 1000Å, which is not preferable. On the other hand, lowering the dew point below −70 ° C. leads to an increase in operating cost, which is not preferable.

In the present invention, after the oxide film is first removed by mechanical grinding, the passivation treatment by pickling is performed. Therefore, the pickling solution required for descaling and passivation treatment is different from the conventional one. Can be reduced in concentration. Moreover, since the temperature rise of the pickling solution due to the descaling reaction in the pickling tank can be reduced, the cooling device for the pickling solution can be reduced or omitted. Also, since the pickling time can be shortened, the pickling equipment can be reduced,
Further, improvement in productivity can be achieved by increasing processing speed.

The present inventors have conducted various investigations on the relationship between the amount of mechanical grinding and the amount of pickling loss on the corrosion resistance of cold rolled steel strips containing 1 to 19 wt% of Cr, and as a result, the grinding amount shown in FIG. And, in the range of pickling weight loss, first, mechanical grinding is performed, and then finish pickling and passivation treatment with a pickling solution containing nitric acid are performed, whereby a Cr-containing corrosion-resistant steel strip with excellent corrosion resistance can be manufactured. I found it.

As the mechanical grinding means, brush grinding, belt grinding or the like can be used. Further, as the pickling solution, in addition to an acid containing nitric acid having a passivation treatment function, nitric acid alone, nitric acid hydrochloric acid, nitric hydrofluoric acid, etc., an acid solution containing halide, chloride, sodium sulfate, etc. may be used. Can be used.

[0010]

EXAMPLE FIG. 2 is a schematic diagram showing an example of an apparatus used in the method for producing a Cr-containing corrosion-resistant steel strip according to the present invention. The Cr-containing steel strip 10 after cold rolling has a pre-tropical zone 12 and a heating zone 1
4, sequentially passing through the cooling zone 16, then water-cooled in the water-cooling zone 18, the oxide film is removed by the grinding brush 34, finish pickling and passivation treatment is performed in the pickling tank 20, the rinse tank 22, It is manufactured by passing through the dryer 24. The pickling solution in the pickling tank 20 is cooled by the cooling device 26 after the pickling. As the pickling condition, the pickling solution contains 5% by weight of nitric acid and 10%.
An aqueous solution containing 7 wt% and 15 wt% was used, the electrolysis current density was 7 A / dm ² , and the electrolysis time was 5 seconds.

Using the apparatus shown in FIG. 2, a steel strip containing 11 wt% of Cr was placed in an atmosphere having a dew point of -40 ° C. and a temperature of 880 ° C.
After that, it was annealed by the grinding brush 34, and was ground with various grinding amounts by the grinding brush 34. Subsequently, final pickling and passivation treatment were performed in the pickling tank 20 so as to reduce various pickling amounts. The corrosion resistance test was carried out at a temperature of 35 ° C. for 4 hours according to the method specified in JIS Z2371-1955. The results are shown in FIG.

In this case, since the dew point is -40 ° C., the Cr content is not included.
The thickness of the oxide film formed on the surface of the steel strip is about 500Å
Met. Area in the upper right of FIG. 1, for example, grinding amount 1.0 g
/ M ²Above (total of both sides), pickling loss 0.5g / m²that's all
Good corrosion resistance is obtained in the area of (total of both sides).
I understand. In addition, the steel strip that has been ground (the pickling loss is 0) is
Many defects (microscale, grinding flaws, steps, etc.) on the surface
Since it is still introduced, it is prone to crevice corrosion
Corrosion resistance is poor because

Further, an increase in the pickling weight loss leads to an increase in the acid cost because it accelerates the deterioration of the pickling solution. On the other hand, an increase in the amount of grinding shortens the life of the grinding brush and leads to an increase in grinding cost. Therefore, the dew point during annealing is kept at -30 ° C or lower, the grinding amount is changed according to the dew point, and the pickling reduction amount is 0.5 to 1.
It is advantageous to produce in the range of 0 g / m ² .

[0014]

According to the present invention, since the Cr-containing steel strip after cold rolling is annealed in an atmosphere having a controlled dew point, the oxide film formed is thin, and the grinding amount and pickling shown in FIG. Within the range of weight reduction, mechanical grinding is performed first, and then final pickling and passivation treatment are performed with a pickling solution containing nitric acid, so it has better corrosion resistance than before and contains less Cr. A corrosion resistant steel strip can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of grinding amount and pickling loss amount on corrosion resistance.

FIG. 2 is a schematic configuration diagram showing an example of an apparatus used in the method for producing a Cr-containing corrosion-resistant steel strip of the present invention.

FIG. 3 is a schematic configuration diagram showing an example of an apparatus used in a conventional method for producing a Cr-containing corrosion-resistant steel strip.

[Explanation of symbols]

 10 Steel band containing Cr 12 Pretropical zone 14 Heating zone 16 Cooling zone 18 Water cooling zone 20 Pickling tank 22 Rinsing tank 24 Dryer 26 Cooling device for pickling solution 34 Grinding brush

Front page continued (72) Inventor Hiroshi Yaginuma 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Junsuke Takasaki 1 Kawasaki-cho, Chuo-ku, Chiba Chiba Pref. Company Chiba Steel Works (72) Inventor Motoki Imamura 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Works Chiba Works

Claims (1)

[Claims] 1. A method for producing a Cr-containing corrosion-resistant steel strip, wherein the cold-rolled Cr-containing steel strip has a dew point of −70 to −30 ° C.
Annealing is performed in an atmosphere of the following range, and then the surface oxide film formed during annealing is ground at a rate of 1.0 g / m ² or more and the pickling loss is reduced.
Corrosion-resistant steel containing Cr with excellent corrosion resistance, characterized by first mechanically grinding in the range of 0.5 g / m ² or more, and then performing final pickling and passivation treatment with a pickling solution containing nitric acid. Method of manufacturing obi.