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

Highlights: • Ti affected precipitation behavior and austenite stability of low C medium Mn steel. • Amount of nano-scale TiC precipitates increased with increasing Ti content. • Increasing Ti content refined both prior austenite grains and laminar structure. • Medium Ti addition led to a high combination of strength, ductility and toughness. • High Ti decreased the ductility and toughness due to reduced austenite stability. -- Abstract: Controlled rolling and direct quenching followed by intercritical annealing was adopted to process Ti microalloyed 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 °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 °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.