Effect of tempering on the microstructure and strength of martensitically hardened plain carbon steels

The X-ray interference line profile analysis was applied to plain carbon steels with 0.4 wt.% carbon after martensitic hardening and tempering in order to investigate the mean strains and domain sizes. From these parameters micro residual stresses and dislocation densities have been estimated. The mean strains of the hardened samples are only caused by the stress fields of dislocations. Tempering leads to decreasing mean strains and micro residual stresses as well as increasing domain sizes due to rearrangements and annihilations of dislocations. The hardening contributions of dislocations and carbide particles in the yield strength of the quenched and tempered states which increase with increasing carbon content, are evaluated.