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  for Metal Finishing since 1989
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Removing heat stains on steel

I have had a mould die (P20 Steel) welded and during this process they had to heat the block. It now has colours ranging from straw to a deep blue. I would like to remove this colouring. Can you help?

Peter Bramer
Mould Making - Dandenong, Victoria, Australia
2005

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You didn't say anything about size, configuration, or tolerances; therefore, a standard quick and dirty answer is a mechanical abrasive system such as blasting.

AF Kenton
retired business owner - Hatboro, Pennsylvania
2005

P-20 alloy is supplied in a pre-hardened condition from the mill. Preheating temperature should be around 400oF and heat input during welding must be low. Overheating it to the extent that it will discolor as described indicates that its hardness and temper could have been affected. It could also be distorted and internally stressed. Dies and moulds have hardness requirements and very tight tolerances. In my opinion, there could be other concerns more important than just the color. A full metallurgical and dimensional examination and restoration are advisable. Now, regarding superficial rust and oxidation, blasting is an option in some cases, but most often the surface finish is also so important that it will require a final bench work by a professional mold polisher.

Guillermo Marrufo
Monterrey, NL, Mexico
2005