In article ,
"DoN. Nichols" wrote:

Makes sense. The coal should contribute more carbon, if the
workpiece is kept in contact with the coal.

Contact is not really needed. There is gas between the coal chunks, and
where you are in the fire determines if there's (much) oxygen in that
gas.

And, of course, if you have a small electric furnace, *and* a
TIG setup, flow argon (or some other inert gas) into the oven to push
out the air with its oxygen.

Nitrogen is way cheaper. AFAIK, most electric kiln/furnace elements
(Kanthal or the like) depend on an oxide coating, so you may burn them
out faster that way - not a problem with the stainless foil envelope and
a bit of something to burn inside the envelope to use up oxygen/supply
carbon.

You can't see it directly in a forge (all that coal gets in the way) but
it's similar to an oxy/acetylene or propane/air flame in that there's
fuel-rich and oxygen rich areas. You want to heat the steel in a
fuel-rich area (not really the coal, as such, but the gases given off
from the coal.) When doing small things the expensive way (OA) you use a
"soft" or carburizing (fuel-rich) flame with a long feather. With a coal
forge, if you get the steel too deep in the fire, or don't build the
fire up with enough coal, or use to much air blast, you burn out the
carbon by having the steel hot (for a prolonged time) in an oxygen-rich
environment. It's obviously going to see a little of that when it's out
of the fire and hot, but not for such a long time.

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