The effects of carbon content and tempering temperature on the deformation and the strain hardening of martensite in 0.11-0.43 percent carbon-1.4 percent manganese steels were investigated.
(1) The deformation of the martensites as-quenched and tempered at 100°-400°C was composed of two or three kinds of fundamental deformation stages, e.g. the first and the third stages or the first, the third and the fourth stages.
The strain hardening rates in the first stage (at ε=0.01, true plastic strain) and the third stage were raised in proportion to cm' (0.43-0.87) power of the carbon content. Those hardening rates were particularly high in the martensites as-quenched and tempered at 100°-200°C, while very low after tempering at 300°-400°C.
(2) After tempering at 500°-700°C, the second stage appeared. The strain hardening rate in this stage had a linear relationship with f;/(1-f;), where f; represents the volume fraction of spheroidal cementite particles. The strain hardening rate in the third stage showed a little higher values than those after tempering at 300°-400°C.
(3) Relative strain hardening rate 1/σ·dσ/dε of the martensites was affected by tempering temperature. This will influence on toughness of the steels.