Recrystallization

The hardness of steel increases through deformation hardening when it is cold formed, limiting the degree of further cold forming. Recrystallization annealing is therefore applied between cold forming passes like cold rolling of sheet, cold drawing of wire, deep drawing of plate or other plastic forming operations carried out to such a degree that further plastic forming becomes difficult.

However, the steel can be recrystallized by annealing at above about 600 ºC, which results in new, unstressed, undeformed grains being created and growing at the expense of the deformed grains when recrystallization temperature is reached. The resulting microstructure often has a finer grain size than the original. Through deformation hardening, the material has high hardness prior to recrystallization, but this process reduces the hardness to the level of the original, undeformed microstructure through the formation of new grains.

Another way to make the steel softer is to recrystallize it at a lower temperature, below A1, approximately 720 ºC for carbon steel. If the steel is then not converted to austenite the material could – after the heat treatment – be rapidly quenched in water or - if you do not want any oxide material - forced gas. In principle this is a type of short-time high tempering .

Ref. Steel and its Heat Treatment – A Handbook (8.2.4)