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Effect of Electropolishing on Stainless Steel Grain Size

2003

Does electropolishing of Stainless Steel affect grain size? Since chemical composition of grain boundary is different, would that cause preferred etching of grain boundaries during electropolishing?

I am a consultant at a medical device company working on developing new in-house electropolishing process for very small and thin stainless steel part which is implanted in heart in California. My MS thesis is actually on these parts, developing various test procedures, and heat treatments and corresponding modeling of the procedures.

Thanks,

Mazdak Rooein
- Irvine, California, USA

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The grain size is set when it manufactured/heat treated. Electropolish will remove some metal, so does that effect how you view it. In metallographic evaluation, we electro etch the mechanically polished sample to highlite the grain boundaries. Electropolish should not be attacking the grain boundaries that much. The purpose of electropolish is to find the right density so that it eats off the very top of the surface roughness while the diffusion layer does not exchange enough ions to affect the lower areas. I would guess that you would need to look at formulation /temperature /voltage. It is my somewhat educated guess that your problem should not be happening.

James Watts
- Navarre, Florida
2003

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First of two simultaneous responses --

The grain size is only dependent on the casting process...EP only can highlight the existing grains. My guess is you're making stents from 316L VimVar. This material has an awful tendency to pit along one axis and polish along the other two due to the way the sulfur is incorporated. Switching to 316LS VimVar will help, but low Sulfur grades are not free machining so it may require changes to the machining procedures.

Dave Kinghorn
Chemical Engineer
SUNNYvale, California
2003

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Second of two simultaneous responses --

What is the alloy? If implanted I would guess 316, 316L or 316VAR. A good electropolishing solution and procedure should not attack grain boundaries, we also do a lot of parts for heart management, as well as back, eyes and all the other body parts.

One more thought if the company you are consulting for starts with a G and not an M. The G company tends to have process specifications that sometimes do not work. The M company tends to have performance specifications which makes life easier as you have some flex as to how you get there.

Jon Quirt
- Minneapolis, Minnesota
2003

I WANT ETCH SOLUTION FOR GRAIN SIZE STEEL AISI4340

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- ROM, ITALYA
May 18, 2008