Metal finishing Q&As since 1989

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Effect on Electropolish of carbon content in 304 stainless

Q. I have an electropolish line that has been running for over a decade with reasonable consistency. Recently, I have received some deep drawn 304 stainless parts that went through a series of heat treatments. In the past these were not a problem, but now they end our normal EP process time with a white haze all over the part.

Is it possible that the extra heat treat added carbon in the surface that is causing the white finish?

Thanks,

Sean Casarotti
- Yreka, California, USA
December 13, 2011

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Sean,

What color are the parts after heat treatment? Do you see any film on the surface?

Anna Berkovich
Russamer Lab

Pittsburgh, Pennsylvania

December 16, 2011

The parts come to me washed and degreased. They are a similar dull grey to the tubing that we use. There is evidence of heat treat scale on the parts that are failing which prompted the question about carbon content.

Sean Casarotti
- Yreka, CA
December 21, 2011

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We have seen such white haze all over some parts when electrolyte is old. We suspect that when parts are heat treated, the oxides penetrate deep into the surface. During electropolishing such oxides react with the phosphates in the electrolyte (this is only our guess). When electrolyte is old, its acidity decreases. Try to play with the regimes at the end of the polishing - decrease voltage, or change temperature. It helped in our electrolyte. If it does not work, replace the electrolyte by the fresh one.

Anna Berkovich
Russamer Lab

Pittsburgh, Pennsylvania

December 23, 2011