Where the
world gathers for metal finishing
Q&As since 1989


-----

I want to remove orange dichromate discoloration from stainless

I am trying to find an inexpensive process to remove a light oxide (from an annealing furnace) from 316 stainless steel. Several solutions containing sodium dichromate at high temperatures have yielded the result I want with the exception that they leave the surface with an orange tint. Nitric acid doesn't remove the tint. High temperature (220 °F) phosphoric acid (85%) for two hours has worked, but it etches the surface. Can anyone suggest alternative processes for either removing light oxides or for removing orange discoloration?

Craig

Craig Tupelo
metallurgical consultant - Oxnard, California, United States
March 23, 2011

In the lab/bucket, try adding ammonium bifluoride to your nitric solution. Start at a rate of 1/4 pound per gal and see what results you get. You can increase it by 1/8 pound at a time until you find the best solution. Do not exceed 1 pound to the gal or expect pits as the solution is used/ages.

James Watts
- Navarre, Florida
March 24, 2011