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Heat treatment causes dark blue discoloration of 13-8 SST

We have received 13-8 SST weldments after heat treatment to H1050 which are discolored. We have cleaned the parts prior to heat treatment with acetone ⇦this on eBay or Amazon [affil links] Warning! highly Flammable! followed by Isopropal Alcohol and packaged carefully to preserve cleanliness. The weldments sometimes are bright shiney silver colored (desirable) but other times they vary from light to dark straw colored or dark bluish purple. Two questions: What is the most likely reason for the discoloration? Is the discoloration detrimental to the material strength of the parts?

Ronald James Corces
Project Engineer - St. Petersburg, Florida, USA
2003

The color is from oxygen in the system. It is being run in some type of inert atmosphere or reducing atmosphere or in a vacuum. Your variable colors are from variable amounts of oxygen in the furnace. Cosmetics is probably the worst problem if your use is reasonably far enough from the ultimate design strength of the part.

James Watts
- Navarre, Florida
2003

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Another problem with heat treat discoloration of stainless steels, especially those alloys like 13-8 which only THINK they are stainless : ) is that the discoloration lowers the corrosion resistance. See Publication 14050 from the Nickel Development Institute (www.nidi.org), an article by Tuthill and Avery on how heat tints cause corrosion problems.

Lee Gearhart
metallurgist - E. Aurora, New York
2003