C CHEMISTRY; METALLURGY
C21 METALLURGY OF IRON
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
1/00 General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
C21D1/18 Hardening; Quenching with or without subsequent tempering
C21D1/25 Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")