低合金TRIP鋼板の機械的特性に及ぼすSiおよびAlの影響

概要

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Effects of Si and Al on the mechanical properties of low alloy TRIP-assisted steels were investigated especially focusing on characteristics of retained austenite and work hardening behavior of ferrite. 0.17%C–1.5%Si–Mn and 0.17%C–1.5%Al–Mn steels, of which the microstructures consist of a ferrite matrix with dispersed bainite, retained austenite and martensite, were used in the study. Higher elongation was obtained with increase in carbon content of retained austenite between the steels of the same chemical compositions. However, the change in ductility can not be explained only by the stability of retained austenite. The 1.5% Si added steel exhibits higher ductility than the 1.5% Al added steel in spite that the stability and the volume fraction of retained austenite are almost the same. The ferrite matrix was highly work-hardened in the 1.5% Si steel than in the 1.5% Al steel. Considering the fact that Si addition lowers stacking fault energy and depresses cross slip, high work-hardening rate of ferrite phase may be caused by suppressing dynamic recovery of dislocations during tensile straining in the Si added steels. The results strongly suggest that not only the characteristics of retained austenite but also the work-hardening behavior of ferrite phase affects the ductility of low alloy TRIP-assisted steels.