blaksdc

Annealing and passivating stainless steel

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Hello,

It is to my understanding, from what I've read here and in other forums, that after you forge stainless steel (I'll be using mainly 316 and 304), you need to anneal and passivate it to maximize the stainlessness. But I've seen a few videos and read of people that do not anneal it after forging. Or some people that say, if you want to keep the black hammer marks on (if you want this kind of finish), not to passivate it, as they will be removed.

My question is, since I will be using stainless to make mostly BBQ tools, pendants, bottle openers and such, how much of the stainlessness will be lost IF I skip these processes?

As soon as I fix my forge I will compare how an annealed+passivated, just annealed, and brand new piece behave in saltwater or something like that, but I was wondering if someone has already answered this question.

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any forging  benefits with a normalizing after the hot work, some more than others, I dont know why anyone would say it needs annealing, Some stainless varieties need a slow furnace cool (40F/Hr) to anneal.

Passivating is jump starting the chrome oxide layer that will form naturally anyway after a while.

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I'm sorry I might have explained myself badly, I was referring to annealing to 1950°F followed by water quench, to prevent chromium precipitation(as written here https://www.steelforge.com/stainless-304-stainless-304l/ ). My question was more like, how much does this precipitation modify corrosion resistance?

I'm not sure if it could be important only in "extreme" environments, or it's important for everyday use too.

Thanks for the answer, Steve.

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Heating and quenching is not annealing, unless you are dealing with nonferrous metals like brass or copper. Steels normally get harder with quenching.

For passivation we sent our parts out, and the company either used citric or nitric acid to remove the surface iron after machining. It all depended on what the customer required.

 

Staff note: Edited for clarity

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Generally yes, steel does get harder with quenching. But from what I've read around the net this does not apply to the 3xx series stainless steel. Quenching in water is apparently used to only stop chromium migration, so to have more corrosion resistance that is lost if simply forging. I was wondering if this loss of corrosion resistance is just barely noticeable, or if the aisi 3xx series become as rust prone as mild steel.

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For the kind of items you are making, no additional treatment is typically needed to maintain corrosion resistance. The main issue you may have is if you use a non-stainless wire brush on your items that can transfer iron onto the surface. This can lead to more surface rust though much less than on a mild steel item. It is true that if you passivate with (preferably) citric acid or nitric acid, you will change the as-forged look. I have items forged without further treatment and used outside for 15 years that are rust free or with only a few specks of rust on them. They still look pretty much the same as when I first finished them.

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I forged a scrap SS spoon around 30 years ago that was part of my camp eating set.  No passivation but much abuse and exposure to food acids and moisture and it has not rusted---yet.

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Hey! Thanks everybody! Your experiences have been very helpful to me, thank you all for sharing.

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