[TheForge] Stainless steel Forging?

[Ries Niemi]

Steve- I have forged about 5 tons of stainless in the last few years. 
And no, I am not exagerating about the amount- I had to pay for every 
pound of it, and lift it 3 or 4 times too.
We use 304- its available in all kinds of profiles, its the cheapest, 
and easiest to get.
It forges just fine- you have to hit it harder than mild, and so we try 
to do as much as possible with the power hammer.
It also anneals when you water quench it, which can be handy when you 
need to cold bend parts after forging.
As far as passivation goes, you can try to set up and do it yourself- a 
lot of guys have put stuff together with battery chargers. But 
personally, I dont like to mess with the chemicals, so I send it out. I 
have found that many large commercial platers do passivation and 
electroplating- these are two related processes. Both involve using a 
dc power supply to kind of "reverse plate"- that is, instead of coating 
the stainless, like you would when plating, you are actually stripping 
off the outer layer. This cleans off the black oxides formed when 
forging, and cleans off the steel pollution you get on the stainless 
when working it with mild steel tools. It still helps to avoid using 
sanding or grinding discs that have also been used on mild, though.
Passivation leaves a matte dull gray finish, kind of like sandblasting. 
Not real attractive, in my book, but it may be the look you want.
Electropolishing can take the material to a bright, shiny finish, even 
areas that have been extensively forged. Electropolishing uses stronger 
acids in the bath, as well as the electricity.
You should be able to find some local places to do the work- if not, I 
have a good place on the west coast you could ups small parts to- I 
think their minimum is 75 bucks, and they have lots of experience doing 
heavily forged stuff for me.

Usually, the electropolishing will result in a great finish. 
Occasionally, with very heavy forging, there may be some tiny particles 
of steel still in the piece- these will rust in a month or so, and then 
you can go back and mechanically finish just that spot, with a wire 
brush or fine sander. Also, sometimes on large pieces, the magnetic 
fields of the electrical process make it so that some areas get shinier 
than others- then you may have to blend it by buffing. I have only had 
this happen on pieces over about 4 feet by 8 feet. Small stuff usually 
works great.
You can also buy or build small portable electropolishers to touch up 
site welds- we often will make up subassemblies, have them polished, 
and then tig weld them together on site- and just polish up the welds 
themselves. I use a unit from a company in LA called screenpro for 
this- screenpro.net.

hope this helps- I will be happy to answer more questions if you have 
them.

ries