Hot working entails plastic deformation of metals at temperatures where strain hardening does not occur. Hot working is done for two reasons: to shape metal into useful objects; and to improve the properties of the metal. During hot working annealing occurs, and recrystallization takes place following plastic deformation. The annealing action prevents hardening and loss of ductility, which are characteristic of cold working. Hot working is done to plastically deform metal into a desired shape, using a minimum of energy, and to get the best possible mechanical properties of the metal, being worked. During hot working, various defects such as blowholes, internal porosity, and segregation can be largely eliminated, consolidating the metal and increasing its density. Mechanisms of plastic deformation during hot working are similar to those of cold working.
There are many hot working methods, but only a few processes are widely used. The greatest tonnage of ingot metal is hot-rolled into plate, sheet, and structural shapes, while forging under hammers or presses is also common. Extrusion, drawing, spinning, and other forming processes are also employed. Each method has its advantages and disadvantages.