Annealing is the process of heating, soaking and cooling of steel in order to achieve specific material properties. When batch annealing, e.g. with the Ebner Hicon/H2, several coils are put into a closed furnace and remain there for an annealing time of up to several days.
The batch annealer consists of an annealing base and a batch. In order to meet the high demands of the strip surface, the annealing is performed under protective gas atmosphere.
To create this protective gas atmosphere, hydrogen is specifically suitable, but nitrogen and certain gas mixtures can be used as well.
There are different annealing processes, but in the production of cold rolled steel strip, soft annealing and recrystallization annealing are used in particular.
Soft annealing of steel minimizes existing precipitations of cementites and perlites to reduce the strength of steel to facilitate deformation. Common temperatures for this range from 680°C and 780°C.
Recrystallization annealing reconstitutes the crystallite forms to their pre-cold forming state. The coil is heated up to temperatures between 550°C and 700°C, slightly above recrystallization temperature. The recrystallization temperature depends on the material and the degree of deformation.