For starters, I have never had the opportunity to forge any stainless steel and don't have any around the shop to try out.  Now, to the query...I made a pot rack out of mild steel for a fellow and he wanted me to try to use some hooks from an old pot rack he had (after I kindly offered to make some nice ones for him...).  I needed to reshape his hooks to fit the new pot rack.  They had sort of the shiny appearance of stainless.  After heating them in the forge (coal) to about bright red to orange, upon taking them out of the fire, there was absolutely no scale whatsoever.  Mild steel in my coal forge will usually have SOME scale at those temps, but these hooks had none.

Is it a characteristic of stainless to not form scale at red to orange temps?

The 304 and 316 Stainless I've been using for some hooks doesn't get the big flakey scale you'd see on mild, but I do usually end up with a surface that is roughened and black.  The black coating seems even more tenacious than scale, so I've had trouble getting things back to 100% shiny.

 

My experiences line up with HojPoj's.  Of course if you were just bending them a bit and they were only in the forge a short amount of time and running rich than little scaling might occur.

I didn't get the black, probably because the weren't in the fire long, just a med. grey. The finish wasn't coarse, but was sorta satin-like.

Next time I run across some stainless that I might want to work with, I'd like to try it out.....maybe some of my wife's stainless flatware! I DON'T THINK SO!

 

Yeah, it's likely a function of duration.  Seeing as I was using a gas forge even if I only wanted to heat the tip of the stock, most of it got up to heat anyways :-\ 

 

Come on Arkie; what could be more fun than taking a table knife and coiling up the cutting end and substituting it in your hand right before you tell her "this meat's a little tough"!  (Please remember to give her one of my "I deal with blacksmith estate sales" cards first.)

Thomas, great idea (except for using it at dinner.  Obtaining some scrap stainless ware at the flea market and putting a cute scroll on the end would make a neat "novel" item to put on the sale table at demos (if we ever get to have one again...).

To go with a Dieter's fork with the tines scrolled and a Dieter's spoon with the center of the bowl punched out?

LOL, once again great ideas!

Should be sold with a blood red napkin so the stains won't show after you give them to your SO.  ("Why a spoon....It will hurt more!")

A search of the site will turn up much more than I feel like typing.

Note that scale is oxidation and stainless is also known as non-ox or in-ox so no, there is generally no scale to speak of but in the case of highly polished S.S. colors of oxidation can be observed as well as utilized for decorative affect.

A thoroughly forged pieced will resemble mild steel and also could be a nice effect.

Tip; stainless is best worked at near white heat.

Good info, thanks.

We passivated the parts we machined to remove the surface iron exposed. We sent it out for that process as the customer could request either citric or nitric acid passivation.

Stainless steels do oxidise, even at room temperature, albeit slowly. Where the composition of alloy contains sufficient chromium, rather than a thick visible iron based oxide forming, as is typical of non-stainless alloys, chromium oxide is formed instead. This extremely thin, continuous layer is transparent to the eye and provides a protective barrier between the alloy substrate and the air; this slows down/prevents further oxidation.  

However, if the temperature is high, the chromia layer will grow quickly and become visible, or different types of oxide layers might form in preference. Furthermore, if the reservoir of chromium becomes depleted, iron can be incorporated in the oxide and a less protective, thicker spinel oxide will form. Finally, if conditions are such that chromium doesn’t diffuse at a sufficiently high rate from the alloy substrate toward the oxide, chromium oxide again will fail to form.

I am not sure exactly what the original post is describing but I suspect either the chromium oxide has grown to a thickness where it is no longer transparent, or that thick oxides, other than chromia have formed.

The chromium is what makes it stainless, chrome oxide is transparent and extremely stable.

Frosty The Lucky.