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  for Metal Finishing since 1989
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Need help polishing hardened steel without introducing pits

1998

As an ever-growing part of my graduate work, I'm trying to produce thin, electrically isolating coatings on bearing-grade 52100 steel (bearing grade means ASTM A295).

A machinist friend (whose friendship I'm fast losing) and I are trying to reduce the height of all defects to 50nm (2 microinches) or less on the surfaces of some four inch (100 mm) diameter disks. We sent the disks out for lapping, which seemed to replace scratches with pits 5-15 microns (0.0002" to 0.0006") in diameter and 0.3 microns deep. Polishing seems to help somewhat, but after we get to a point, we seem to be moving pits around rather than removing them.

I'd like to find out either

1. how not to introduce pits while making scratches less deep, or
2. how to eliminate pits already on the surface

Any suggestions would be much appreciated. If it helps,

• we've tried both diamond sprays (4-6 micron and 0-1 micron) and pastes, all oil-based
• we've polished by hand and on a small (8") metallurgical polishing wheel available to us
• we've tried both napped (synthetic suede) and napless cloths.

Again, thanks for any help -- I'll answer any questions as best I can.

Dave Nickel
Purdue University

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Have you tried electropolishing? Doesn't the metallurgist sometimes use electropolishing to develop the grain of a sample, using various electrolytes? Graham's Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] (page 117) gives formulas for polishing of metallographic samples, I believe for the purpose of brightening them.

  
Tom Pullizzi
Falls Township, Pennsylvania
1998

Try using and mixing different grades of natural[very important] diamond powder with veg/olive oil and lap with bamboo. Synth diamond powders or paste can produce pitting. Also lapping is dam near an art. patience patience patience

Thomas L Malo
S.P. Carbide Die - Lewis Center, Ohio
2001