JP2005042177A - Electrolytic polishing method for stainless steel increasing its 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 by one or more additives remarkably improving the corrosion resistance of stainless steel by a trace amount of addition in an electrolytic polishing method to a stainless steel surface. <P>SOLUTION: In the electrolytic polishing method, using a solution obtained by adding ≥1 wt.% of one or more kinds selected from the group consisting of potassium zirconium fluoride, sodium zirconium fluoride and ammonium zirconium fluoride to one kind selected from sulfuric acid, phosphoric acid, citric acid, tartaric acid and malic acid, and their sodium salts, potassium salts and ammonium salts or two or more their combination is used as an electrolytic solution, water passable nonwoven fabric is inserted between the stainless steel to be treated and an electrode, and AC electrolysis is performed. <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 processed by applying a direct current or an alternating voltage while being in contact with an electrolytic solution. In stainless steel, for example, the burnt portion after welding of stainless steel is subjected to surface polishing. The electrolytic polishing method by electrolytic processing is performed 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 performed (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, but 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 passivating film having excellent corrosion resistance on the surface of stainless steel, potassium fluoride, sodium fluoride, ammonium fluoride or fluoride A method in which hydrogen acid is added 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 has been 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 and electrode to be treated with a solution obtained by adding one or more selected from the group consisting of potassium zirconium fluoride, sodium zirconium fluoride, and ammonium zirconium fluoride to a combination of two or more. This is an electrolytic polishing method for stainless steel that is electrolyzed by alternating current with a water-permeable non-woven fabric between.

  This invention succeeded in improving the corrosion resistance of the stainless steel surface by adding an ultrathin film of iron fluoride and zirconium oxide to the stainless steel surface by adding potassium zirconium fluoride or the like into the electrolytic solution.

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

  Specifically, the corrosion resistance is almost the same as when 0.3 wt% to 1 wt% of potassium fluoride, sodium fluoride, or ammonium fluoride is added. In the case of zirconium ammonium fluoride, it could be obtained by adding only 0.1% by weight.

  Therefore, it is effective when added in an amount of about 0.1% by weight, and it 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% of potassium zirconium fluoride, etc. This is because iron in the electrolyte reacts with iron, which is the main component of stainless steel, It is presumed that zirconium reacts with oxygen generated during electrolysis to form zirconium oxide, and these oxides become ultrathin films to improve the corrosion resistance by covering 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 electrolyte in the nonwoven fabric at the tip of the electrode, and what was soaked as electrolyte with only 10% sodium sulfate added to 10% sodium sulfate 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 the weight reduction ratio after 24 hours. .

  10% sodium sulfate as the electrolyte had a weight before measurement of 31.018 g, a weight after measurement of 28.833 g, and a decrease of 7.0%, whereas potassium zirconium fluoride was added by 0.1% by weight. As a result, it was confirmed that the weight before the measurement was 31.307 g and the weight after the measurement was reduced by 30.987 g to 1.1%. Similar results were obtained with sodium zirconium fluoride and ammonium zirconium fluoride.

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 A solution containing one or more selected from the group consisting of potassium, sodium zirconium fluoride, and ammonium zirconium fluoride is used as an electrolyte solution, and an alternating current is inserted between the stainless steel to be treated and the electrode with a water-permeable nonwoven fabric sandwiched between them. An electrolytic polishing method characterized by electrolyzing.