Ferrite
Ferrite
(OP)
Will passivation or pickling remove ferrite from the surface layer of 316L stainless steel? I'm not talking about free iron contamination, but the actual ferrite as part of the grain structure of the metal.
I have a customer that I'm building a vessel for and the product is sensitive to ferrite levels above 5 FN. My base material is at 2-3 FN but the welds go up to 9-13 FN, even using special "low ferrite forming" weld rod gives me a 5-6 FN. Since I'm only worried about the exposed/wetted surface ferrite level, I was wondering whether passivation or pickling will lower this surface ferrite level.
I have a customer that I'm building a vessel for and the product is sensitive to ferrite levels above 5 FN. My base material is at 2-3 FN but the welds go up to 9-13 FN, even using special "low ferrite forming" weld rod gives me a 5-6 FN. Since I'm only worried about the exposed/wetted surface ferrite level, I was wondering whether passivation or pickling will lower this surface ferrite level.





RE: Ferrite
RE: Ferrite
Thanks!
RE: Ferrite
RE: Ferrite
I have seen people use 904L filler when they needed low weld ferrite levels.
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Plymouth Tube
RE: Ferrite
RE: Ferrite
RE: Ferrite
RE: Ferrite
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Plymouth Tube
RE: Ferrite
Thanks for reminding me about 904L; forgot about that one. Used it over 30 years ago for a pharmaceutical application on 316L vessel.
RE: Ferrite
No chemical or mechanical surface treatment will change the ferrite content.
For welding you don't need to mess around with fancy gases or other metallurgical tricks like cover passing or even alternative filler metal classes. You just need to source consumables formulated for cryogenic applications, and request deposit ferrite on the MTR. I have specified Metrode products for a couple of clients recently. Standard issue E316L will consistently deposit 5-6FN.
Caution: low-FN covered electrode may not weld as smoothly as the regular stuff.