Effect of Ti variation on microstructure evolution and mechanical properties of low carbon medium Mn heavy plate steel

Controlled rolling and direct quenching followed by intercritical annealing was adopted to process Ti micro-alloyed low-C medium Mn heavy steel plates. Furthermore, the effect of Ti content on the microstructure evolution and mechanical properties was elucidated. The submicro-laminar microstructure of reverted austenite and lath-shaped ferrite was obtained after intercritical annealing at 630 degrees C. Increase in Ti content from 0.014% to 0.032% increased the amount of nano-scale TiC precipitates, leading to refinement of both the prior austenite grains and the subsequent laminar structure. Ultra-high yield strength of 790 MPa, elongation of 27.4%, and high toughness of 158 J at 0 degrees C was obtained. Further increase of Ti content to 0.053%, the mechanical stability of reverted austenite was significantly decreased, and the work-hardening behavior was changed to three-stage because a large amount of reverted austenite transformed to martensite prematurely. As a result, the elongation and impact energy were decreased due to the insufficient TRIP effect. Ti remarkably influenced the precipitation behavior, transformation process, and the mechanical properties of low C medium Mn steel in terms of structural refinement and austenite stability.