1. Metallurgical reminders

1.1 Thin sheet annealing metallurgy for deep drawing

Cold rolling of thin sheet results in hardening of the metal, which becomes brittle and unsuitable for forming. Recrystallization annealing is therefore carried out almost systematically after cold rolling.

The structure of work-hardened steel is characterized by the rotation and elongation of grains in the rolling direction and by an increasing density of dislocations as a function of the work-hardening rate. Second-phase particles and inclusions with little or no ductility are broken and aligned in strings separated by microcracks. The energy stored in the dislocations is the driving force behind recrystallization, which starts at a lower temperature the higher the cold work hardening rate; the heating rate...