Annealing
Annealing is the process of softening steel, usually done in preparation for working and grinding the steel. Heating up the steel past the critical temperature (the austenizing temperature) and then letting it cool slowly does annealing.

Hardening
Hardenizing consists of two steps, austenizing and quenching. First, to austenize, the steel is heated to its critical temperature. To harden, the steel has to cool down more quickly than in the annealing step describe previously. So the steel is quenched -- allowed to cool -- in some medium such as oil, water, air, or molten salt, depending on the steel.

Tempering
Once the blade has been hardened, tempering is done to reduce the hardness and relieve internal stresses in the steel.

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