Hardening is one of many metalworking processes involving heating (to a given temperature) and holding it at this temperature until changes to the external structure of the hardened material occur and it is quickly cooled down.
After applying hardening, the strength properties increase, such as:
- resilience
- hardness
- plasticity
- resilience
- abrasion resistance.
By hardening steel, we increase its hardness and strength. Correctly performed hardening must have well-chosen parameters, such as e.g. cooling rate. Because if the cooling temperature is too low, we can lead to the release of cementite. This situation will prevent the martensitic transformation of the steel. On the other hand, cooling the steel too quickly will lead to high hardening stresses. Stress can contribute to permanent deformation and cracks.
The rate of cooling also affects the depth of hardening of the steel. To prevent this from happening, we must remember the following factors:
- cooling rate
- heating rate
- temperature
- material holding time.
The methods of hardening steel are:
- ordinary hardening: consists in quick cooling of steel in water or oil
- surface hardening: only the surface of the object is heated; This method includes: flame, blind, laser, induction and bath hardening
- gradual hardening: consisting in very quick cooling of the steel in a quenching bath so that the temperature is slightly higher than the martensitic transformation temperature
- isothermal hardening: no martensitic transformation takes place here.
