If my memory is not too bad, I think OB was a metallurgist or related pro. So, he's probably spot on with the 300F from a purely technical perspective, but I'll step out on a limb and say heating would unlikely be of any functional detriment on a cased frame until it got well above 400F and more likely above 500F.
One of the 'rust and blueing removers' should do the deed quickly but will remove any "patina" oxides as well.
I have a question for OB (if you're the metallurgist I'm thinking of). Since the outer layer of a case hardened steel is of high carbon and hardness, would embrittlement be a concern with the use of acids like it is with high strenth/hardness martensitic steels like 300M etc?
