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Forging Sensitized 347 SS

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Has anyone ever forged sensitized 347 stainless?   If so is this an issue or not?   I think this is primarily a polythionic acid issue but I am not sure...???   And if you are aware it is an issue is there a heat treat that may solve this problem such as a stabilize or solution anneal?   Just looking for someone with practical hands on experience with this material in a sensitized condition...   :)   Maybe it will just crumble if not handled correctly...????   :(    I kinda doubt it but if no one here knows for sure I will be finding out in the coming days/weeks....   Prior to that it would be good to start out with others learning and experience prior to my experimenting.... 

Before you ask how I know it is sensitized you can either just take it for granted (my preference) or...    

Because I know it has been in ~1000F service for many years and that we also have metalography of similar service 347 material that shows clear sensitization as determine by a metalurgist.   

This is potentially a heat treat question depending on the answer?    But it may be a non issue so I placed it in general discussion.


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Sensitized vs. non-senstized will make no difference during forging. This has to do with corrosion resistance. The sensitized condition is not as corrosion resistant as non-sensitized material. Maximum corrosion resistance is typically achieved in this and most other austentic grades by heating to 1900 F or higher and rapidly cooling to prevent chrome from reacting with carbon. T-347 and T-321 are stabalized versions in which either titanium or niobium is added to grab carbon before the chrome has a chance to reacte with it. If chrom combines with carbon, you get a reduction in the corrosion resistance. But at forging temperatures none of this matters since carbon will be dissoved in the austenite.You should be able to completely restore maximum corrosion resistance after forging by solution annealing. The nice thing about T-347 and T-321 is that they are less suseceptible to sensitization than are the regular austenitcs. This make them easier to fabricate, since often welded structures can't be solution annealed.

Patrick Nowak (Metallurgist at Scot Forge for the past 12 years)

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