1989 Volume 75 Issue 4 Pages 626-633
The carbide distribution prior to cold rolling was studied to know its effect on mechanical properties with respect to retained austenite (γR) in 0.2%C-1.4%Si-1.0%Mn-0.05%P steel cold rolled and intercritically annealed and isothermally held at bainitic transformation temperature. The microstructures after final heat-treatment were of ferrite, γR, bainite and/or martensite. In general, the steel with prior ferrite/pearlite structure (FP steel) gave more amount of γR and better mechanical properties such as strength, elongation, etc. than that with prior ferrite/cementite one (FC steel). The excellent mechanical properties in FP steel were based on a large amount of γR which transforms to martensite during deformation, giving rise to a high work hardening rate. The experimental results also showed that an increase in intercritical annealing temperature and/or time brought about a similar amount of γR in FC steel as in FP steel. However, FP steel still exhibited a superior elongation compared with FC steel. The reason for this is that the former contained a relatively large amount of small (about 2 μ, m) γR with stacking fault which would originate from fine cementites prior to cold rolling. It was concluded that the mechanical properties were strongly affected not only by the amount of γR but also by the γR size and configuration.
