On the strain-hardening of tempered martensitic alloys

The strain-hardening behaviour of a tempered martensitic iron-chromium-carbon model was examined in terms of dislocation mechanics. Tensile tests of this body-centered cubic alloy were carried out from 77 up to 293 K. A specific relationship between the flow stress σ and the dislocation density ρ was considered below the transition temperature (T < 200 K) where the Peierls lattice friction becomes the single rate controlling mechanism. This relationship is different from the usual Taylor equation, where the flow stress scales with the square root of the dislocation density. This σ-ρ relationship was used in conjunction with an equation characterizing the dislocation evolution with strain to derive a strain-hardening law. The parameters that play a key role in the strain-hardening are the mean dislocation free path and a dislocation annihilation coefficient. The values of these parameters used to describe the strain-hardening law as well as their temperature dependence are found to be consistent with the microstructure.