The impact of thermo-mechanical controlled processing on structure-property relationship and strain hardening behavior in dual-phase steels

We elucidate here the impact of thermo-mechanical controlled processing (TMCP) in governing nucleation of second phase in Nb-Ti microalloyed dual-phase steels. A wide range of mechanical properties were obtained through change in the microstructure, depending on the TMCP cooling schedule. Polygonal ferrite matrix with martensite as the second phase exhibited highest initial strain hardening rate, lowest yield strength, and highest tensile strength as compared to the situation when bainite or bainite-martensite was the second phase. The Crussard-Jaoul (C-J) strain hardening behavior of granular bainite and granular bainite-martensite as the second phase exhibited one-stage characterized by linear and parabolic behavior, respectively. On the other hand, two stages were observed in steel containing martensite as the second phase, viz., linear stage I and parabolic stage II.