Improved mechanical properties in Ti-bearing martensitic steel by precipitation and grain refinement

The yield strength and impact energy properties for martensitic steel fabricated by vacuum induction melting are investigated. It is found that the addition of Ti can improve the yield strength property of the martensitic steel after reheat quenching process, which can be attributed to increase in precipitation hardening from formation of TiC precipitates in the martensitic matrix and a superfine sized (similar to 8 mu m) grains in the martensitic structure. Moreover, the yield strength can be further enhanced by tempering and reheat quenching process, which can be ascribed to a large amount of freshly nano-sized (1-10 nm) precipitates in the final martensitic structure for martensitic steel-containing Ti. The experimental and theoretical results on the contribution of TiC precipitates to hardening of the martensitic steel are in excellent agreement. In addition, the impact toughness also has been improved along with yield strength followed by the heat treatment, which can be attributed to the high ratio of high-angle grain boundaries after tempering and reheat quenching process.