Heat Treatment Of Steel
Heat treatment of steel may be defined as an operation or combination of operations which involve the heating and cooling of the metal in its solid state in order to obtain certain desirable characteristics or properties. Metal and alloys are primarily heat treated to increase their hardness and strength, to improve ductility, and to soften them for later forming or cutting operations.
Alloy steels and plain carbon steels with a carbon content of 0.35 percent or higher can be hardened to the limits attainable for the particular carbon content, or softened as required by controlling the rate of heating, the rate of cooling, and the method of cooling.
One of the most important factors in heat treating steels is that the metal should never be heated to a temperature close to its melting point. When this occurs, certain elements in the metal are oxidized (burned out), and the steel becomes coarse and brittle. Steel in this condition usually cannot be restored by any subsequent heat treatment. In general, the lower the carbon content, the higher the temperature to which steels can be heated without being oxidized.
The must common problem related to heat treatment are warping, dimensional changes, cracking, failure to harden, soft spots, and excessive brittleness. The following table lists some problems, possible causes, and remedies.