Matt,

You just ran up against the red hard property of stainless. When I forge stainless steel, I do it at a high yellow heat, not at a red heat. At a red heat, you might just as well anneal it and work it cold.

the thicker bars need a good soak .... bright red or orange is then fine as a forging heat .... the important difference is in the way you forge .... a small number of hard blows with curved tools is better than lots of light blows because of the work hardening.

304 is great to forge provided it is low carbon ( 304L )

I assume that you are using propane ... try to avoid a situation where a bar is half out of the oven with a red heat ... keep the entrance deep to force the gas to burn well .... if not, you will get excess carbon reacting with the junction between hot and cold and this will leave nasty patches when you electropolish.

write to me direct metalgarden at mac dot com if you want immediate response .. I am on site around the world and do not often visit artmetal.
G

Matt,

As Guiseppe said, stainless needs to be soaked at heat to get the heat into the core of the stock. Stainless has a lower rate of thermal conductivity than mild steel. Also, it work hardens something fierce when forged at too cold a temperature. It anneals somewhat like non-ferrous metals, by heating and quenching, so keep that in mind. If you want it hard for the finished piece, you'll want to end on a forging cycle, not a heating cycle.

304-L Stainless is a low-carbon alloy designed to reduce the precipitationof carbides on the surface and therefore be less prone to corrosion. It is also a bit easier to work. At a good yellow heat, I can't tell any real difference under the hammer between it and regular 304, though your mileage may vary.

Stainless steel worked with regular steel hammers, anivls and wire brushes will become contaminated with vagrant iron on the surface and will then rust in a damp or marine environment. To prevent this, finish with a solution annealing stage and then passivate in a hot solution of citric acid in water. 10% citric acid by weight in distilled water used at 140F for an hour should do it. Better yet, send it out for electropolishing.

In a dry environment, forged stainless can be left as is, and shouldn't rust. If you want to do this, I suggest using 316 marine grade, but the stuff is pretty pricey.

I recommend 304L not simply for its softness but because there is less likelyhood of a carbon reaction on the surface between heat soaked areas and cooler ones at the entrance to the oven. These areas become chromium depleted and do not polish well.

Only use 316 bar if you have a heavy power hammer because it needs to flow fast and it will also spoil your tools at lower temperatures.

Of course with sheet 316 things are not so bad and it will polish and colour beautifully.

have fun

G