Effect of compressive plastic deformation on mean lattice strains, dislocation densities and flow stresses of martensitically hardened steels

Mean strains and domain sizes of different steels with nearly 0.4 wt.% carbon were determined by an X-ray interference line profile analysis after martensitic hardening and annealing at temperatures Ta≲700 °C, and after plastic deformation in compression tests. The mean strains and micro-residual stresses are caused by the stress fields of dislocations, and in the case of the alloyed steels, by additional contributions of the solute carbon atoms for appropriate low Ta-values. The mean strains of the hardened and low-tempered states decrease considerably with increasing plastic deformation εp for εp<5% despite large hardening rates of the stress-strain curves due to rearrangements of dislocations in low energy structures. The solute carbon atoms in the alloyed steels generate an additional reduction effect in the mean strains due to stress-induced changes into energetically more favorable octahedral sites. The deformation dependence of the dislocation densities, which can be determined from the mean strains and domain sizes are discussed.