Air Products Home

Ask the Experts Metals

What causes discoloration and oxidation of stainless steels in brazing, sintering or annealing processes?

Tom Philips
Sr. Principal Industry Engineer

All grades of stainless steels are iron-based alloys with significant percentages of chromium. Typically, stainless steels contain less than 30% chromium and more than 50% iron. Their stainless characteristics stem from the formation of an invisible, adherent, protective and self-healing chromium-rich oxide (Cr2O3) surface film. While stainless steels are resistant to rusting at room temperatures, they're prone to discoloration by oxidation at elevated temperatures due to the presence of chromium and other alloying elements such as titanium and molybdenum.

Factors that contribute to increased oxidation include high dew points, high oxygen and oxides of lead, boron and nitrides on the surface. For bright stainless steels, process them in a highly reducing atmosphere with a dew point lower than –40oF and a minimum of 25% hydrogen.

For an audit and troubleshooting tips, call us at 800-654-4567.
← Back to Heat Treating
An error has occured, please fix the highlighted fields.
To request a quote or for more information about Air Products, please fill out the form below, and an Air Products representative will contact you shortly.
Please use the form below to contact us.

What can we answer for you?

  1. What kind of inquiry?

If you would prefer to contact us by phone, you can call any of our Air Products locations worldwide by visiting Worldwide Locations & Phone Numbers.


This site uses cookies to store information on your computer. Some are essential to make our site work; others help us to better understand our users. By using the site, you consent to the placement of these cookies. Read our Legal Notice to learn more.