CF8M Sensitization
CF8M Sensitization
(OP)
Does it make sense for cast CF8M (i.e. 316 chemistry) to sensitize in the HAZ adjacent to the weld if the casting is post-cast weld repaired and is used in water service? Selective attack is occurring in the ferrite in the austenite matrix below selective corrosion adjacent to the weld. Carbon would be in the sensitization range if this were a wrought steel (actually, carbon is excessive at 0.13%). I can use feedback on my theory regarding sensitization of ferrite (theory being carbides precipitate on the ferrite interface with the austentite) in this instance.





RE: CF8M Sensitization
RE: CF8M Sensitization
RE: CF8M Sensitization
RE: CF8M Sensitization
residual ferrite has a very lean chemistry making it much less corrosion resistant.
Add the sensitization to this and you are assured of corrosion.
What FN did this material have? what was the actual FN of the welds?
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Plymouth Tube
RE: CF8M Sensitization
My personal opinion is that you always solution anneal CF8M after welding, unless there is a real good reason not to. Even CF3M, with it's reduced degree of sensitization, is better off with a solution anneal after welding. A lot of the corrosion issues with these materials are due to chromium depletion at the ferrite austenite interface caused by the carbon and chrome reacting preferentially to form a chromium carbide.
RE: CF8M Sensitization
Thanks for all of the helpful comments!
RE: CF8M Sensitization
CF3M again is a good alternative,if the cost permits. Unlike 316 and 316L the cost difference for CF8M and CF3M is significant. Of course those practising secondary refining processes are competitive in their pricing.
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"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year
RE: CF8M Sensitization
No, CF3M is no more expensive from a good foundry.
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Plymouth Tube