Metal finishing Q&As since 1989

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410 stainless sheet with a mirror finish

2005

I am writing in to inquire if a directionless, mirror finish is possible on 410 stainless steel sheet. I have had small (0.03 x 1 x 3") parts polished to give a mirrored, #8 appearance. But, when ordering the finish on a sheet of material, the finish was not the same. I should say that the polishers of the small parts and sheet material are different. The sheet is 0.031 x 36 x 120", but when the part arrived from the polisher, there was unidirectional graining, though it was shiny. The polisher stated that is how a #8 appears on 410, but I'm no sure that is correct. Maybe the sheet requires another process in order to end up without graining. I am trying to find out if what I am calling out for in my specifications is possible or is this the only type of finish I can achieve on the 410 material?

John Walker
biotech devices - Fremont, California, USA of America

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Hmmmmm. If your material is coming directly from a mill, I might be able to understand the problem of the finish; however, if it is coming from a secondary source, then there is no excuse for mill or grain marks. Not sure you can solve this problem without a secondary source, but in the future, I suggest you specify an Ra, RMS, or Rz for the sheet, not just a #8 finish.

AF Kenton
retired business owner - Hatboro, Pennsylvania
2005

The best finish attainable on a given surface ultimately depends on the microstructure of the material. Most stainless steels are produced with a very fine grain structure, so, it is very likely your steel can be polished to a mirror. It may only be a matter of time and money. But again there are many definitions (or should I say opinions) of what a mirror must look like. What for do you need that finish?

Guillermo Marrufo
Monterrey, NL, Mexico
2005

First there shouldn't be any "grain" in the material but if you're saying that there are very light "lines" in the material that's impossible that's from the cloth buffing wheel. To have a plate buffed to a number #8 with absolutely no grain is impossible. You might be looking for super #8. Super #8 comes from the mill with no grain at all.

Brandt Hinton
- Elk River, MN, USA
2006