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Cleaning burned-on oil from high strength titanium, SS, and alloy steels

My company makes aircraft fasteners. We roll threads on titanium, stainless steels, and alloy steels. Occasionally we must heat the part to roll the threads, not enough to affect the heat treat, but enough to slightly soften the material. When this is done, the oil used to lubricate the part during thread rolling burns onto the threads. This burned on oil must be removed prior to penetrant inspection, which we just installed in-house. Can anyone suggest a cleaning process to remove the burned on oil? A chemical process is preferred, because mechanical processes like blasting and wire brushing cause problems with penetrant inspection by roughening the surface.

Guy Lester
- Apple Valley, California
2003

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In the one sentence, you say you soften the material and that you don't change its properties. Whoa! Softening the material by heat is of course a direct change of one of its properties - it is applying a heat treatment to change the properties that were established by the previous heat treatment. In this case, reducing hardness and of course automatically and simultaneously reducing strength. I hope any plane that I'm in doesn't rely on those fasteners to stay in the air!

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
2003

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Degrease the parts (and handle with clean gloves) prior to heat treatment. Possible cleaning techniques: molten salt bath, oxidizing flame, electropolishing.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2003

In response to Mr. Reynolds, we heat the part to approximately 400 F to TEMPORARILY soften the material due to the temperature increase, not altering the grain structure by heat treating temperatures. If you are an engineer I suggest you dust off your Engineering Materials textbook and read the section on material property changes due to temperature.

Guy Lester
- Apple Valley, California
2003

G'day mate,

Mr Lester and I must agree to disagree on the point. From my position as a consultant metallurgist specialising in ferrous alloys, I have no inclination to change the opinion I expressed earlier.

Cheers,

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
2003

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2003

I am dealing with similar issues, a couple of suggestions:

Use a synthetic oil. Synthetics do not form carbon residues as readily as petroleum base, and are capable of higher ( 600 F ) temperatures.

Blast clean the work following rolling using fine grit walnut shell media ⇦this on eBay or Amazon [affil links] which will not smear metal so as to obscure indications.

You are of course correct that all you are doing with warm rolling is momentarily lowering the yield strength of the titanium to facilitate the rolling.

Harold Jason
- Carson, California