Effect of Micro‐Alloying Elements on Microstructure and Mechanical Properties in C–Mn–Si Quenching and Partitioning (Q&P) Steels. Issue 1 (10th October 2018) - Yan, Shu
Abstract : The authors design two kinds of Mo–Nb and Ni–Mo–Ti microalloyed steels based on C–Mn–Si steel using quenching and partitioning (Q&P) processing. The results indicate that the addition of microalloying elements increases retained austenite fraction, however, the average carbon concentration in retained austenite is reduced. Nano‐sized NbC and TiC precipitates are separately observed in the Mo–Nb and Ni–Mo–Ti microalloyed steel. Both precipitates can refine prior austenite grains as well as martensite packets and laths. The yield strength of Mo–Nb microalloyed steel treated by Q&P processes is about 87–155 MPa higher than that of the typical C–Mn–Si steel due to precipitation strengthening of NbC and refinement of martensitic structure. However, in the Ni–Mo–Ti microalloyed steel, the increment of yield strength based on precipitation strengthening of TiC is offset by the decrease of solution strengthening due to carbon dilution of the martensitic matrix, and finally the yield strength is not improved. Additionally, although the addition of alloying elements is not associated with strengthening, the product of tensile strength and total elongation (PSE) for both Mo–Nb and Ni–Mo–Ti microalloyed steels approach or exceed 20 GPa%, which indicates a superior comprehensive performance. Abstract : NbC and TiC particles are, respectively, confirmed in Mo–Nb and Ni–Mo–Ti microalloyed steel, but the yield strength increase based on precipitation strengthening is partially offset by decrease of solution strengthening due to carbon dilution within martensitic matrix. Addition of alloy elements reduces the sensitivity of mechanical performance depending on partitioning parameters, which is beneficial to broaden the process window during manufacturing.