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Spotting after vacuum heat treatment

Spotting on 304 stainless steel heat treated at 1050deg C in a vacuum furnace. I am looking into a project where a heat treating company are experiencing big problems with spotting on 304 ss heat treated in vacuum furnace for 2 hours at 1050 degrees C. I have had the samples sent away for EDAX analysis and the results showed the area was found to mainly consist of iron, chromium and nickel (which is understandable). The centre of the surface spots were found to contain mainly manganese oxygen with some iron and small amounts of carbon, sodium , aluminium, copper, chromium and tin. The three samples analyzed were consistent with the above.

I would be much obliged if anyone could assist me in any way as this very important.

Richard Greenough
- UK

Since it is "spots" I think that the parts are not clean when they went into the furnace. Second, it costs a goodly chunk of money to do a "burn out cycle", so it is done as infrequently as possible. It is not uncommon for metals or ? to revaporize and deposit on the parts. Vacuum furnaces are great when well maintained.

James Watts
- Navarre, Florida

What you are experiencing is a very common problem in both the open air and hydrogen annealing of stainless steel in its production as cold-rolled sheet. The most common source of the spots you describe are the minerals in the last water used to clean the steel. These minerals on the surface disrupt the normal protective oxide growth which happens at any terrestially attainable vacuum. Pre-cleaning with a solvent is better than with water unless you can be very sure that the water won't be leaving any residue.

Dr. Michael McGuire
- Pittsburgh, Pennsylvania, USA

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Hello everybody,
I am working in a manufacturing company and we manufacture aerospace parts here. Sometimes we have similar problem on 15-5 stainless steel, in other words there are black stains all over the part when we received them from Stress relieve process.
After my research, I realized that this company (Our processing supplier) use vacuum furnace in order to perform stress relieve process.
I was wondering that, is this case similar to Richard's case or not. And if yes, what do you think, how can I prevent this problem.
I would appreciate if you guys could assist me with this problem.

Thank you

Ali Zarrin
- Valencia, California, USA
August 3, 2011