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Etching during electropolishing

2005

I have been electropolishing stainless steel successfully for awhile now. I electropolish stainless steel in a cold bath and I replace the bath weekly. I have made a fresh bath with sulfuric acid and methanol [affil links], and using the same parameters on the power supply that I have always used the parts are etched. This etching occurs within seconds of turning on the power supply. The voltage is lower than it normally is 2.3 V and it does not increase the way it normally does; the current is fixed at what I normally have it 0.40 A.
I suspect it might be the solution. I have opened new bottles of sulfuric acid and methanol and made multiple new solutions and the parts are still etched.
I have performed electrochemical analyzing with a potentiostat and it confirms that I am only etching and not forming an anodic film.
Is the solution the only thing that could be causing this etching or could anything else be responsible for this behavior?

Migdalis Cintron
R&D - San Antonio, Texas

A few possibilities: 1) Are you processing the same number and size of pieces? It's the current per unit area that is important, not total current. 2) Make sure the electrical connections are good to ALL the electrodes in the tank. 3) Check that you REALLY are working with the same material you have been; it's not unheard of for a stray sheet or roll to get mixed in with an order. Would be curious to hear about what you find.

Tom Gallant
- Long Beach, California
2005

The answer above, it is absolutely right. Years ago, I faced a similar problem when electropolishing stainless steel. Then I was in charge of the chemical area at certain manufacturing plant. I performed a lot of experiments and spent many days cracking my head on what the problem was, only to find at the end that bars from different alloys were mixed up at the beginning of the manufacturing process. That mistake did cost thousands of dollars in raw material scrapped and machining time, tools, etc, and I still don't know how the guy responsible kept his position.

Manuel Sandez
Medical Device Company - Empalme, Sonora, Mexico
December 19, 2008