Heat treating is a science in itself and should be left to specialists. One of the reasons the designer should stay with a minimum selection of tool steels is to avoid the many heat treatment specifications, which are usually different for each type of steel； this way both the designer and the heat treatment company both become familiar with particular steels and know what to expect.

Nearly all mold toolmakers use outside suppliers for heat treatment because it is a specialist process and also because of the investment that would otherwise be required for the necessary plant and equipment.

Sometimes two steels, even with an identical AISI number, may require significantly different heat treatment (as shown in the steel supplier’s specification sheets) to achieve the optimum properties required from the steel. The designer need only specify the required hardness of the part, as it is not necessary for the designer to have a deep knowledge of the heat treatmentprocess. It is desirable, however, that the basic procedures are understood so that the designer will be aware of the results that different hardening procedures give.

Where the same degree of hardness can be obtained by using alternative hardening procedures, the designer should specify which process is required since these may affect, wear, toughness and mechanical strength.

There are  several different hardening techniques available for mold took, the main ones being listed next:

                   Through-hardening

                  Pretoughening or prehardening

                   Carburizing or case hardening

                   Nitriding

                   Toftriding

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