JP2005146364A - Electrolytic polishing method for stainless steel increasing corrosion resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the use of the neutral salt of fluoride exerting adverse influence on the human body to a minimum with an additive remarkably improving the corrosion resistance of stainless steel by a trace amount to be added. <P>SOLUTION: In the electrolytic polishing method, a solution obtained by adding cobalt fluoride to one or more kinds selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, citric acid, tartaric acid and malic acids, and their sodium salts, potassium salts and ammonium salts in ≥1 wt.% is used as an electrolytic solution, and, in a state where a water-passable nonwoven fabric is held between the stainless steel to be treated and an electrode, electrolysis is performed by AC, DC, or in the combined use thereof. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrolytic polishing method for a stainless steel surface used for scoring after welding of stainless steel, etc., and can improve the corrosion resistance after processing by adding a specific material to the electrolytic solution. It is about the law.

  As a metal processing method, electrolytic processing is widely used in which a metal is applied with a direct current or an alternating voltage while being in contact with an electrolytic solution. In stainless steel, for example, the burned portion after welding of stainless steel is surface-polished. Electrolytic polishing is performed by electrolytic processing as a method, but the electrolyte and applied voltage are devised so that chromium contained in stainless steel does not elute as harmful hexavalent chromium and pollutes the environment. An electropolishing method is applied (see, for example, Patent Document 1).

  By the way, the electrolytic polishing method is performed by various energization methods such as direct current, alternating current, and AC / DC combined use. However, the alternating current electrolytic method is widespread because of its high processing speed. However, in this AC electropolishing, an anodizing reaction does not occur on the workpiece surface, so that a passive film cannot be formed on the stainless steel surface, and it is difficult to increase the corrosion resistance.

  Here, even when an alternating current electrolytic method is used, as a method of forming a passivated film having excellent corrosion resistance on the surface of stainless steel, potassium fluoride, sodium fluoride, ammonium fluoride or fluoride A method of adding a hydrogen acid has been invented (see, for example, Patent Document 2 and Patent Document 3).

JP 7-185940 A JP 2003-27296 A JP 2003-82495 A

  The corrosion resistance of stainless steel was improved by the electropolishing method described in Patent Document 2 and Patent Document 3.

  However, since neutral salt of fluoride is toxic, reduction of the amount of these additives has been demanded from the viewpoint of easy handling of the electrolytic solution and disposal of the waste solution.

  Therefore, the inventor has studied and studied various additives to the electrolyte solution that can solve the above problems, and as a result, found an additive that drastically improves the corrosion resistance of stainless steel with a slight addition amount, The inventors have invented an electropolishing method that minimizes the use of fluoride neutral salts that adversely affect the human body.

  In order to solve the above-mentioned problems, the present invention is one or more kinds selected from the group of 1% by weight or more of sulfuric acid, nitric acid, phosphoric acid, citric acid, tartaric acid, malic acid, or sodium, potassium or ammonium salts thereof. Stainless steel that is electrolyzed by alternating current, direct current, or alternating current with a water-permeable nonwoven fabric sandwiched between the stainless steel to be treated and the electrode, using a solution in which cobalt fluoride is added to a combination of two or more types as an electrolytic solution This is an electropolishing method.

  The present invention has succeeded in improving the corrosion resistance of the stainless steel surface by adding cobalt fluoride to the electrolytic solution to form an ultrathin film of iron fluoride and cobalt oxide on the stainless steel surface.

  The addition amount of cobalt fluoride to be added is not particularly limited, but for the purpose of the invention, it is desirable to keep the addition amount small within a range where the corrosion resistance of the stainless steel can be improved.

  Specifically, the corrosion resistance of about the same level as when 0.3 wt% to 1 wt% of potassium fluoride, sodium fluoride, or ammonium fluoride is added is only 0.1 for the cobalt fluoride of the present invention. It could be obtained with the addition of wt%.

  Therefore, it is effective at an addition amount of about 0.1% by weight, and is limited to at most 1% by weight in order to reduce the toxicity of the electrolytic solution, preferably within the range of 0.01 to 0.1% by weight. Just do it.

  Corrosion resistance is greatly improved by adding only about 0.1% cobalt fluoride. This is because the fluorine in the electrolyte reacts with iron, which is the main component of stainless steel, and iron fluoride and cobalt are It is presumed that the corrosion resistance is improved by reacting with oxygen generated during electrolysis to form cobalt oxide and these oxides become ultrathin and cover the stainless steel surface.

  Due to this effect, it was possible to significantly reduce the neutral salt of fluoride having toxicity as compared with the electrolytic solution of the conventional method, and to improve the handling property of the electrolytic solution and reduce the processing cost of the waste liquid.

  What was impregnated with 10% sodium sulfate as an electrolyte in the non-woven fabric at the tip of the electrode and what was impregnated with 10% sodium sulfate as an electrolyte with only 0.1% cobalt fluoride added, Each was pressed against SUS304 (30 mm × 90 mm × 1.6 mm), which is an austenitic stainless steel, applied with an alternating current of 20 V, immersed in a 10% ferric chloride aqueous solution, and compared in weight reduction ratio after 24 hours.

  In the case of using 10% sodium sulfate as the electrolyte, the weight before measurement was 31.132 g, the weight after measurement was 28.264 g and the decrease was 7.0%, whereas cobalt fluoride was added by 0.1% by weight. As a result, it was confirmed that the weight of the sample treated with the electrolytic solution was 31.288 g, and the weight after measurement was 30.825 g.

Claims (1)

1% by weight or more of sulfuric acid, nitric acid, phosphoric acid, citric acid, tartaric acid, malic acid, or one or a combination of two or more thereof selected from the group of sodium, potassium and ammonium salts, zirconium fluoride An electrolytic polishing method characterized in that a solution containing potassium and cobalt fluoride is used as an electrolytic solution, and electrolysis is performed by alternating current, direct current, or alternating current using a water-permeable nonwoven fabric between a stainless steel to be treated and an electrode.