[Simonpie]

You're mixing two different processes. The "heat and quench" and carbon deposition (case hardening) are to change the hardness and strength of the metal. Straightening isn't really dependent on the cooling rate so much as the shape of the area you heat. I'd scan some welding or metalworking books or even Utube for a good description. I've seen it done on angles and I beams, but I'd think a C channel would need a slightly different technique. Also, I've usually seen it done to take a "wow" out of a flange, not to take out a bend across the whole area of a beam. I'm not saying it can't be done, just haven't seen it.