冷延鋼板の残留オーステナイト形成および機械的性質に及ぼす熱延組織の影響

抄録

The carbide distribution prior to cold rolling was studied to know its effect on mechanical properties with respect to retained austenite (γ_R) 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, γ_R, bainite and/or martensite. In general, the steel with prior ferrite/pearlite structure (FP steel) gave more amount of γ_R 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 γ_R 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 γ_R 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) γ_R 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 γ_R but also by the γ_R size and configuration.