"ASTM Specification A493 for CF8M Stainless"

Question:

"My question is to the corrosion resistance of CF8M when it is lacking the post solution annealing process. We have received information from a investment cast supplier that there is no need to post heat treat Investment Cast components, as the inherent procedures of Investment Casting eliminates the needs to do so for corrosion resistance."

Answer:

CF8M (316SS), if cooled too slowly through the temperature range of ~ 1500F-800F, will form intergranular chromium carbides, which can reduce the corrosion resistance in some aqueous media. Normal practice is to solution anneal the material after forming, hot working, casting, etc. to assure that the carbides are in solution. Whether or not the investment cast component will cool sufficiently fast to avoid carbide precipitation is a function of the carbon content, the part section thickness and the cooling rate. If the casting will be in critical and/or corrosive service I would require the casting supplier to prove through testing (i.e., protocol test piece) that the component will not form detrimental intergranular carbides.

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