The same metal can behave very differently during forming depending on temperature.

Cold working is deformation performed low enough that recovery and recrystallization do not substantially erase the deformation structure while forming. Plastic strain accumulates, dislocation density rises and the material usually work-hardens. Forces can increase as deformation proceeds, while strength after forming can increase and ductility can decrease.

Hot working is performed at a temperature where thermally activated restoration processes operate rapidly enough to reduce stored deformation. Large strains can then be imposed with lower flow stress and less accumulated work hardening.

The distinction is not set by one universal temperature such as room temperature. It depends on the material and is often interpreted relative to its melting temperature on an absolute scale.

Warm forming occupies an intermediate regime and can trade lower forces against oxidation, heating cost, dimensional control and tooling life.

For example, a large reduction that would require excessive force or cause cracking when cold may be feasible hot. Conversely, a final cold-forming operation may be chosen to obtain good dimensions and a strengthened surface condition.

Temperature therefore changes both process mechanics and resulting microstructure. Choosing forming temperature is a coupled decision involving required strain, force, dimensional accuracy, surface condition and final material properties.