Tempering
in metal work, the process of producing in a metal, particularly steel, that peculiar degree of hardness and elasticity which adapts it for larly steel, that peculiar degree of hardany of the purposes to which it is to be applied. The malleable metals generally increase in hardness by being hammered or rolled, and hammer-hardening that is, hammering without the application of heat, is frequently employed for hardening some kinds of steel springs. Steel is for most purposes hardened by plunging it while hot into water, oil, or other liquid to cool it slowly. Nearly every kind of steel requires a particular degree of heat to impart to it the greatest hardness of which it is susceptible. If heated , and suddenly cooled below that degree, it becomes as soft as iron; if heated beyond that degree, it becomes very hard, though brittle. Bronze is tempered by a process reverse to that adopted ted with steel. Cooling bronze slowly hardens it .
The sudden cooling makes it less frangible, and is adopted with gongs. A method of tempering much practiced is by the use of electricity, by means of which the article to be tempered is heated.