ABSTRACT
One of the most important properties of metals is their ability to be shaped or formed, enabling the production of parts with a variety of shapes and forms. However, the ability to plastically deform metals is limited at room temperature. Once a strain is applied, the number of dislocations increases, causing strain hardening and the reduction of ductility; and with continued application of strain, this will eventually lead to cracks in the formed part. One way to increase the amount of ductility is by avoiding strain hardening, by means of reducing the number of accumulated dislocations in the microstructure, and which in turn is possible by increasing the temperature. Above a certain temperature, usually above 600°C in steels, several microstructure mechanics causing softening may take place, promoting dislocation arrangements (restoring) or creating new grains (recrystallization). Through both mechanisms, the ductility increases and then the metal can be deformed to a much higher extent. At a higher temperature, dislocations will move faster and overcome easily their obstacles, meaning that the strength of the metal being hot-formed then decreases. The net effect is that, at high temperatures, metals can be deformed to a much larger extent and with lower forces. And softening is faster and more effective once the temperature is increased, for instance above 1000°C (1830°F) for steels.
