C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material