Tempering Tool Steel
The 7th process to discuss is tempering. Tempering is key in developing the final properties of the steel and, in the sequence of the heat treat cycle, is extremely important to perform immediately after quenching.
Tempering is reheating hardened steel to convert untempered martensite produced by the proper quenching cycle, to tempered martensite & also reduce the volume of the tooling (a much tighter microstructure) which increases the mechanical properties of the material (increases toughness & enhances wear).
Tool steels should never be used in an as quenched (untempered) condition.
All grades of tool steels have many tempering temperatures to achieve the best operational hardness that will optimize the performance of the tooling or part.
Note: always use the highest tempering temperature to achieve the rockwell hardness you want.
Note: 2-3 tempers are highly recommended in all tooling steels as this will assure you of total transformation to tempered martensite & a very homogeneous (tight) microstructure.