JPS61276999A - Method for pickling steel sheet containing chromium - Google Patents

Abstract

PURPOSE:To obtain a steel sheet having fine finished surfaces by short-time treatment by electrolytically pickling a steel sheet contg. Cr with a soln. prepd. by adding a fluorosilicate or a fluoroborate and a nitrate or a sulfate to an aqueous sulfuric acid soln. having a specified concn. CONSTITUTION:A steel sheet contg. Cr and having a stuck oxide film is electrolytically pickled with a pickling soln. prepd. by adding a fluorosilicate such as Na2SiF6 or a fluoroborate such as NaBF4 and a nitrate such as NaNO3 and/or a sulfate such as Na2SO4 to an aqueous sulfuric acid soln. having 20-400g/l concn. Thus, the steel sheet is economically pickled at an increased pickling rate without causing the excessive pickling of the base.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a Cr-containing low alloy steel sheet and an austenitic,
The present invention relates to a method for pickling Cr-containing steel sheets such as ferritic, martensitic, and stainless steel sheets.

[Prior art]

Oxide films formed on the surface of Cr low-alloy steel sheets that have undergone thermal history such as hot rolling and hot-rolled sheet annealing, or on Cr alloy steel sheets that have been annealed after further cold rolling, impair the smoothness of the surface of the finished product, and There are many problems such as shortening the life of the die during drawing, so it is necessary to completely eliminate it.''2 [Steel Handbook]
April 5, 1960 “1, Marukubi KK, page 1258, Table 1
．． 5.3], various pickling solutions such as nitric acid and hydrofluoric acid, sulfuric acid, hydrofluoric acid and chromic acid, sulfuric acid, nitric acid and hydrofluoric acid, etc., and also the invention of JP-A-56-81688 Various pickling solutions are used, such as the sulfuric acid solution used, as well as a mixed solution of ferric sulfate and sulfuric acid.

[Problem to be solved by the invention]

These pickling solutions can effectively perform pickling using the immersion method, but if you want to complete pickling in a shorter time,
Electrolytic method must be adopted.

However, when using the above-mentioned pickling solution, the oxide film is removed in a relatively short time and the finished surface is quite beautiful, but the solution performance deteriorates quickly and the pickling cost increases. . In particular, pickling solutions mainly containing nitric acid and hydrofluoric acid tend to significantly deteriorate the finished surface of the steel plate during long pickling immersion times.

Other oxide film removal methods include electrolysis in a neutral salt aqueous solution such as sodium sulfate; however, the steel plate base metal is less likely to dissolve, and the finished surface is visually good; Since there is a problem that fine oxide films tend to remain and Cr-deficient debris remains, which deteriorates corrosion resistance, long-term treatment is necessary.

Further, as salt treatment, there is a method in which the oxide film is treated with a mixed molten salt of caustic soda, caustic potash, and sodium nitrate, and then electrolyzed in an aqueous nitric acid solution, but this method has the problem of high cost.

The present invention solves the above-mentioned drawbacks of the conventional pickling technology.An object of the present invention is to provide a pickling method for a Cr-containing steel plate, which allows a steel plate with a beautiful surface to be obtained by a short-time electrolytic treatment method. This is what I did.

[Means for solving problems]

In the present invention, the Cr-containing steel plate attached to the oxide film is
Solved the pickling method for Cr-containing steel sheets by electrolytically treating with a pickling solution containing one or more of nitrates, sulfates, fluorosilicates, and fluoroborates mixed in a 0 g/Q sulfuric acid aqueous solution. did.

[Effect]

The present invention will be explained in detail below.

Cr-containing steel sheets such as low-Cr-containing steel sheets or stainless steel sheets that have undergone thermal history during hot rolling and hot-rolled sheet annealing, or that have been annealed after cold rolling, that is, the surface of the steel sheet has a film that impairs various practical properties. 20~400 steel plate with thick oxide film
Electrolysis is carried out in a pickling solution in which one or more of the L agents nitrate, sulfate, fluorosilicate and fluoroborate are selectively mixed in a sulfuric acid aqueous solution of g/Q. Pickle.

Sulfuric acid used as the main agent in the present invention is added to dissolve the oxide film and improve conductivity, but when coexisting with other solvents used in the present invention, 20 g
/ If the concentration is less than 0, the pickling efficiency is significantly poor < 400
If the concentration exceeds g/Q, over-pickling will occur and the surface appearance will be impaired. Therefore, in the present invention, the amount of sulfuric acid is 20 to 400 g.
/ Use with Q. Further, the selectively mixed nitrate increases the removal rate of the oxide film by -1, but has the effect of suppressing overpickling of the substrate.

Sodium nitrate is the most common nitrate, but all nitrates such as potassium nitrate and ammonium nitrate are effective.

Sulfates represented by sodium sulfate have the effect of suppressing overpickling during electrolytic pickling. This effect is remarkable in Cr alloy steel with a relatively low Cr content.

Fluorosilicates such as sodium fluorosilicate and potassium fluorosilicate and fluoroborates such as sodium fluoroborate and ammonium fluoroborate improve the removal rate of the oxide film by a factor of 11.

The various additives mentioned above should be used depending on the steel type and the thickness of the oxide film, which is naturally determined by the process, but as a general rule, the higher the Cr content, the higher the temperature to which the steel will be exposed during the manufacturing process. The longer the length, the greater the number and concentration of additives.

The polarity of the electrolytic pickling method in the present invention is normally carried out by placing the steel plate at the anode, but depending on the purpose of the steel type, the polarity can be freely selected, such as first carrying out cathodic pickling for a short time, followed by anodic pickling. It is. In addition, if the oxide film is extremely thick or the removal is to be completed in a very short time, mechanical treatments such as skin pass treatment, repeated bending treatment, or shot blasting before pickling can facilitate the removal of the oxide film. .

〔Example〕

Next, the present invention will be explained in detail.

Example 1 430 series, 410 series, 409 series stainless steel plates and 7
%Cr cold-rolled steel sheets were annealed on a continuous annealing line, and the oxide film was removed under the pickling conditions shown in Table 1. As shown in Table 1, all of the Cr-containing steel sheets pickled under the conditions of the present invention exhibit performance comparable to the conventional method, which requires long-term appearance, in terms of appearance, contact resistance, and corrosion resistance.

-8-Example 2 The present invention is also effective in removing oxide films from extremely thick Cr alloy steel sheets such as hot-rolled sheets, and this method alone or in combination with the conventional immersion pickling method is effective. It is. Table 2 shows examples of oxide film removal.

Example 3 The present invention is also effective in removing the oxide film of a Cr-containing steel sheet that has been annealed at 800 to 1,000°C for about 1 minute after hot rolling. Combination with pickling is effective. Table 3 shows examples of oxide film removal.

〔Effect of the invention〕

As described above, the present invention provides a rapid oxide film removal method that is suitable for rice 1 to down production through high-speed mass production of Cr-containing steel sheets, and is of industrial value with excellent economic efficiency and anti-pollution properties. It is excellent and extremely expensive.

Patent applicant: Nippon Steel Corporation Representative Patent Attorney Furushima Nei Procedural Amendment August 3rd, 1985

Claims (1)

[Claims] A Cr-containing steel plate with an oxide film attached is electrolytically pickled in a pickling solution containing one or more of nitrates, sulfates, fluorosilicates, and fluoroborates mixed in a 20 to 400 g/l sulfuric acid aqueous solution. A pickling method for a Cr-containing steel plate, characterized in that: