During the quenching of steels is the formation of martensite, a structure with high hardness and considerable tensile strength, but with a quite low toughness that may result in breakage due to shocks. Subjecting the steel to a tempering thermal treatment, transforms the martensite into tempered martensite. In fact, the martensite is a metastable phase, that is formed only because the carbon atoms are not able to escape from the lattice due to the high cooling rate that prevents the diffusive motions .. Generally steels used in this treatment have 0, 4 to 0.6% of C and are precisely those steels. Is defined remediation this sequence of treatments only in the case where the tempering takes place at a temperature higher than 550 ° C (except in the case of steel for springs which are found at about 450 ° C). Bringing the martensite at this temperature it comes to, becoming sorbitol, a structure which combines a good tensile strength, even if lower than that of martensite, to a greater toughness.
