forged 316 SS -- corrosion afterwards?

I forge lots of very simple wall hooks from mild steel, usually 3/16" rounds, and either donate them to a non-profit for sale in their gift shop, or just give them away as personal gifts. Finishes range from rattle-can paint to fancy-shmancy beeswax/linseed oil/turpentine/japan drier .

All indoor finishes.

Now I want to make some out 0f 3/16" SS, grade 316, for outdoor use. The forging messes with the metallurgy I think, and I went to return them to a reasonably corrosion-resistant condition. No welding required.

So is an acid bath reasonable? Nitric, Hydrochloric (muriatic), citric, vinegar? If not, any other methods that are better?

They don't need to be shiny.

I suspect no treatment would be necessary as long as you don't get the material too hot. If you should see some corrosion, simple passivation with nitric acid should be adequate.

Cold forming is what makes the change that becomes slightly less corrosion resistant.
If you could do the forming before it cools, while still glowing orange, that would result in the annealed, more corrosion resistant/non-magnetic state.
It's still stainless steel and may not matter for your parts.
Either way, you WILL get rusting is you do not passivate, your forming tools will deposit iron particles galore that will cause rust spots if not passivated.

So whether not too hot, or glowing orange, passivation is the key

Since they won't be welded and strength isn't critical, will soaking them in muriatic acid for a few hours be adequate?

I'm sure they pick up iron particles from the hammer and anvil.

When people are paying me ten grand, or a hundred grand, I absolutely send the stainless out to be electropolished.
but for knickknacks, I just wire brush them with a stainless steel wire brush. I have a 2hp 10"x 1 1/2" wire brush, and it gets the stuff clean enough.

Yes, you can soak em in acid- If you do, I would recommend buying some citric acid powder from Citrisurf, and soaking the hooks in it for a while.
http://www.citrisurf.com/products.htm

that way, you wont rust every piece of steel in your shop, and burn holes in your pants- which always happens to me if I bring real acids near my shop.

workplace cleanliness helps- I make sure there is no loose mild scale on my anvil or tools, and I dont use sanding or grinding discs that have been used on mild steel.
Keep sparks from grinding mild steel from hitting your stainless.

Thanks Ries, that's about what I figured.

Adding electricity to a citric/phosphoric acid mix can make it go a little faster and safer.
Either set up like an electroplating tank or with a more direct approach like a surfox unit.
SURFOX™ 34 – Walter Surface Technologies
Either set up can be accomplished with a decent car battery charger and a little bit of winging it...
If you going to set up a tank and leave it alone for some amount of time, make sure you have enough ventilation around to prevent hydrogen build up.
When stainless is brought above ~2000F and quenched it solution anneals it vs hardening it like carbon steels. I *think* that the solution annealed state is the more corrosion resistant structure for stainless.
Or it had something to do with high temp service and some strange "sigma" phase (Welder problems...) and had little to do with corrosion... Stainless can do some funky things
If you take an annealed bit of stainless a rare earth magnet will not stick to and bend it, the magnet will stick right at the bend. It had something to do with forming ferrite due to cold working and the crystal structures changing...

Ries said:

When people are paying me ten grand, or a hundred grand, I absolutely send the stainless out to be electropolished.
but for knickknacks, I just wire brush them with a stainless steel wire brush. I have a 2hp 10"x 1 1/2" wire brush, and it gets the stuff clean enough.

Yes, you can soak em in acid- If you do, I would recommend buying some citric acid powder from Citrisurf, and soaking the hooks in it for a while.
http://www.citrisurf.com/products.htm

that way, you wont rust every piece of steel in your shop, and burn holes in your pants- which always happens to me if I bring real acids near my shop.

workplace cleanliness helps- I make sure there is no loose mild scale on my anvil or tools, and I dont use sanding or grinding discs that have been used on mild steel.
Keep sparks from grinding mild steel from hitting your stainless.

Click to expand...

100% agree with all of the above. We use the citric acid method all the time and find that an overnight soak works the best. All you have to do after soaking is a quick rinse in clean water (Not Well Water). Also make sure you order a test kit from the same source.

We also purchased a couple of plastic storage tubs from Target to keep all our Stainless and Aluminum polishing, sanding and cleaning consumables separate. That alone saved us many headaches and lost money.

Walter

Also beware carbon pickup from the forge. C binds to Cr, lowering the corrosion resistance

Sea Farmer said:

So is an acid bath reasonable?

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Nitric: acceptable but difficult to handle
Hydrochloric (muriatic): keep it away from stainless
citric: works quite well
vinegar: not really going to do anything

Ries said:

Yes, you can soak em in acid- If you do, I would recommend buying some citric acid powder from Citrisurf, and soaking the hooks in it for a while.
http://www.citrisurf.com/products.htm

Click to expand...

Thanks! We don't sell raw citric acid powder though. We formulate our products to be an improvement over a plain citric bath, though in many situations a plain citric bath would serve the purpose just fine as well.

Ray Kremer said:

Nitric: acceptable but difficult to handle
Hydrochloric (muriatic): keep it away from stainless
citric: works quite well
vinegar: not really going to do anything



Thanks! We don't sell raw citric acid powder though. We formulate our products to be an improvement over a plain citric bath, though in many situations a plain citric bath would serve the purpose just fine as well.

Click to expand...

Thank you. Very informative website.