Effects of Ti addition and reheating quenching on grain refinement and mechanical properties in low carbon medium manganese martensitic steel

The grain refinement and mechanical properties improvement resulted from Ti addition and reheating quenching were demonstrated in this study. The direct quenched medium manganese steel with low carbon content (0.05C) was treated by reheating quenching process. The yield strength and Charpy impact energy were measured. The microstructures and the second precipitated particles were examined by optical microscopy (OM), scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM), X-rays diffraction and phase analysis method. It was found that reheating quenching at 900–1000 °C resulted in significant grain refinement, especially the refinement of effective grain size (EGS), which was attributed to the large amount nano-sized precipitation of TiC. In addition, high elastic modulus was also obtained from the large amount TiC precipitated from the matrix. It is concluded that reheating quenching process is a useful method to refine the grain size and improve the combined mechanical properties of the martensitic steel through Ti addition.

► TiC precipitation can induce the grain refinement after reheating–quenching process.
► EGS refinement is more effective to explain the improvement of toughness.
► The experimental results of precipitation agree with the theoretical calculations.
► Excellent mechanical properties with high strength and high toughness can be gained.