You can use stainless foil and charcoal granules to avoid oxidizing the surface, if that's important to you. Make a sealed package with the foil that has the steel and the granules inside; the charcoal will eat up most of the oxygen as you bring it up to heat in a kiln.. Unwrap and quench it in oil when it's red hot to harden it; the tempering process happens at a low heat (about 400F, depending on what you're going for) so the wrap isn't necessary for that part. Careful of the foil - the edges are very sharp...