Passivation surface treatment of stainless steel

Patent metadata

Field	Value
Publication number	US-11230782-B2
Application number	US-201815984853-A
Country	US
Kind code	B2
Filing date	May 21, 2018
Priority date	Jan 4, 2018
Publication date	Jan 25, 2022
Grant date	Jan 25, 2022

Abstract

A passivation surface treatment method of stainless steel that improves corrosion resistance including in a brine environment without changing the appearance of the surface of stainless steel. A passivation surface treatment method for stainless steel includes: performing degreasing of stainless steel, performing electrolytic pickling where the stainless steel that underwent the degreasing is immersed in a pickling solution having phosphoric acid (H 3 PO 4 ) and is connected to the anode and a voltage of about 0.5 to 5.0 V for about 10 seconds or more is applied, performing electrolytic degreasing of the stainless steel, and performing electrolytic passivation where the stainless steel that underwent the electrolytic degreasing is immersed in a passivation solution including dichromic acid and chromium sulfate and a voltage of about 0.5 to 5.0 V is applied for 5 seconds or more.

First claim

What is claimed is:

1. A method of passivation surface treatment for stainless steel, the method comprising:
performing electrolytic pickling by immersing the stainless steel that underwent degreasing in a pickling solution having phosphoric acid (H 3 PO 4 ) while the stainless steel is connected to an anode and applying a voltage of between 0.5 to 5.0 V to the pickling solution during a time of between 30 to 180 seconds;
performing electrolytic degreasing of the stainless steel;
neutralizing an alkaline degreasing solution used for the electrolytic degreasing with sulfuric acid;
performing electrolytic passivation by immersing the stainless steel that underwent the electrolytic degreasing in a passivation solution including dichromic acid and chromium sulfate while applying a voltage over a time; and
pickling the stainless steel with sulfuric acid,
wherein the passivation solution comprises between 0.1 to 10.0% by weight (wt %) of dichromic acid, between 0.1 to 3.0 wt % of chromium sulfate, and 5 wt % or less of corrosion inhibitor (excluding 0).

2. The method of claim 1 , wherein a temperature of the pickling solution is between 50 to 70° C.

3. The method of claim 1 , wherein the pickling solution further comprises sulfuric acid (H 2 SO 4 ).

4. The method of claim 3 , wherein the pickling solution comprises phosphoric acid (H 3 PO 4 ) equal to or more than 70% by weight and less than 100% by weight and sulfuric acid (H 2 SO 4 ) more than 0% by weight and equal to or less than 30% by weight.

5. The method of claim 3 , wherein the pickling solution further comprises chromic acid, glycerin, ammonium citrate and sodium nitrate as additives.

6. The method of claim 1 , wherein a temperature of the passivation solution is between 50 to 70° C.

7. The method of claim 1 , wherein a pH of the passivation solution is between 3.5 to 5.5.

8. The method of claim 1 , wherein the voltage applied during the performing of the electrolytic passivation is between 3.0 to 5.0 V and the time is between 60 to 180 seconds.

9. A method of passivation surface treatment for stainless steel, the method comprising:
performing immersion degreasing of stainless steel;
performing electrolytic pickling by immersing the stainless steel that underwent the immersion degreasing in a pickling solution having phosphoric acid (H 3 PO 4 ) while the stainless steel is connected to an anode and applying a voltage between 0.5 to 5.0 V to the pickling solution during a time of 30 to 180 seconds;
performing electrolytic degreasing of the stainless steel;
neutralizing an alkaline degreasing solution used for the electrolytic degreasing with sulfuric acid;
performing electrolytic passivation where the stainless steel that underwent the electrolytic degreasing is immersed in a passivation solution including dichromic acid and chromium sulfate and applying a voltage between 0.5 to 5.0 V for 5 seconds or more during the performing of the electrolytic passivation; and
pickling the stainless steel with sulfuric acid;
wherein the passivation solution comprises between 0.1 to 10.0% by weight (wt %) of dichromic acid, between 0.1 to 3.0 wt % of chromium sulfate, and 5 wt % or less of corrosion inhibitor (excluding 0).

10. The method of claim 9 , further comprising: drying after the performing of the electrolytic passivation.

11. The method of claim 9 , further comprising: water washing before and after the performing of the electrolytic pickling.

12. The method of claim 9 , further comprising: creating a passive layer having a thickness of between 15 to 20 nm.

Assignees

• Samsung Electronics Co Ltd

Inventors

• Lee Kyung Hwan
• Yoo Young Min
• Koh Young Deog
• Kim Kwang Joo
• Kim Beom Gon
• Shin Hyun Seok

Classifications

• C25F1/06 Primary

  Iron or steel · CPC title

• C25D11/38 Primary

  Chromatising · CPC title

• C25D5/36 Primary

  of iron or steel · CPC title

• C25D5/50

  by heat-treatment · CPC title