A low-carbon Nb-microalloyed Fe–Mn–Si-based steel was treated by a novel quenching–partitioning–tempering(Q–P–T) process as a modified quenching and partitioning(Q&P) process. After processed by Q–P–T treatment,this steel exhibits excellent mechanical properties such as high product of strength and elongation. The addition of Nb markedly raises both the yield strength and tensile strength of Q–P–T martensitic steel, especially the yield strength, which can be attributed to the strong grain refinement strengthening and precipitation strengthening of Nb. The Nb addition can also lead to a little increase in ductility. The Nb-microalloyed steel treated by Q–P–T process displays much higher ductility than that treated by traditional quenching and tempering(Q&T) process. The mechanisms of Q–P–T process on ductility enhancement were fully analyzed and can be attributed to high quenching temperature and considerable amount of retained austenite. A low-carbon Nb-microalloyed Fe-Mn-Si-based steel was treated by a novel quenching-partitioning-tempering (Q-P-T) process as a modified quenching and partitioning -T treatment, this steel exhibits excellent mechanical properties such as high product of strength and elongation. The addition of Nb markedly raises both the yield strength and tensile strength of Q-P-T martensitic steel, especially the yield strength, which can be attributed The Nb-microalloyed steel treated by Q-P-T process displays much higher ductility than that treated by traditional quenching and tempering The mechanisms of Q-P-T process on ductility enhancement were fully analyzed and can be attributed to high quenching temperature and considerable amount of retained austenite.