Annealing, like hardening is another heat processes where the entire mechanical characteristics of the work-piece are changed.
Annealing is usually applied after hardening. That means; the annealing process takes place immediately after the work-piece has been rapidly quenched and has is completely cold. Depending on the composition of the steel, it can exhibit very high values of hardness. In this hardened state the component is also very brittle and therefore it cannot be used or further processed.
As a rule; the higher the hardness, the lower the toughness. When a component is annealed, the hardness is reduced until the required toughness index has been reached. The consequential loss of hardness is taken into account. Hardness and toughness are cross-related and therefore cannot be selected independently from one another.