Hardening

Hardening. A piece of steel is rendered extremely hard and brittle by being heated to red heat and suddenly cooled. In the process of tempering, which means the reduction of the metal to a special degree of softness, it is usual to perform the first operation of rendering the steel glass-hard, and then to raise its temperature to a certain lower temperature before cooling suddenly again. This gives it a degree of softness depending upon the temperature to which it is raised during the latter part of the process. [Tempering.]