Re: forging stainless

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Bramblebush

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Posted by Chris Ray on November 12, 1997 at 08:34:28:

In Reply to: forging stainless posted by Steven Bronstein on November 11, 1997 at 21:59:58:

Steven: I can't answer the question about which specific stainless alloy to use for forging but can say a little something about forging stainless.

I have sucessfully forged stainless steel from stock that I've had around the studio and though I don't know which alloy it was, I found it to be fairly easy to forge although not as easy as mild steel of course. Oddly enough when I had gone to a suppliers show one time, I had asked the supplier of stainless which alloy was best for forging and could not get an answer from them.

Back to the question of the permanence of firescale which you asked about. Well stainless has a beautiful grey firescale that is quite tight on the metal and in my opinion would weather quite well. When abraided with fine emery cloth you can pick out the highlights of the textured metal and leave the rest as is. Since you won't be coating the finished work with a varnish or other coating, you will find that the color of the natural blue grey scale is left intact. It's not quite black but a very dark shade of grey instead. I think you will like the finish.

Here is one thing you might keep in mind though. Whatever the alloy is that is forgable probably has less chrome in it than the harder stainless stock which means that you may have some discoloration around the weld zones after completion. The discoloration will, of course, be brownish so you might take this into consideration when designing the work or working on the final finish. The brown oxide may not show up for a while after weathering but will eventually appear.

I personally don't believe that this seriously affects the integrity of the welds or the metal itself since the metal will not rust in the same fashion as a carbon based steel. I might suggest that during the final finish stage of your work that you not highlight the areas around your weld zones too much but leave more of the firescale intact which will mask the eventual oxide that may appear later. By the way, the discoloration that does show up later is very tight on the metal, not flakey as it would be with mild steel.

You will have to be careful about your forging heat, however while shaping and make sure that you don't bring it up so high that the chrome is burned out of the parent metal. This is an important thing to remember. I would keep the color of the heated metal at a bright cherry red or less although this is going to make forging a bit more difficult. Any metal that is alloyed has a much lower melting temperature than in it's purest form, or at least it usually does.

Finally an important point to keep in mind. Do NOT use any steel wire brushes on the stainless, whether powered or hand since it will streak your metal later with rust color which is difficult to then remove. Use only stainless steel wirebrushes for this work and make certain that the wire brush is used only for stainless and not any other metal.

Chris Ray

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