A novel heat treatment process,stepping quenching and partitioning(S-Q-P),has been developed to manipulate microstructure and mechanical properties of steels.Based on incomplete partitioning of carbon from martensite to austenite,volume fraction and distribution of the retained austenite resulting from the following quenching of the steels could be effectively controlled,and then the synthesized mechanical properties of the steels would be improved.In this paper,20SiMn2MoVA steel was treated with conventional quenching-tempering(Q-T),currently prevailing quenching-partitioning(Q-P) and S-Q-P processes,respectively.The results indicated that the volume fraction of the retained austenite of the steel treated by Q-P and S-Q-P processes increased significantly that resulted in the increase of ductility and decrease of strength.The product of strength and ductility of the steel treated by S-Q-P process reached 23.7GPa%,that was increased by about 13% and 7% compared with that after Q-T and Q-P processes,respectively.Compared with the great improvement of the synthesized mechanical property obtained by S-Q-P process with another steel 35SiMn,there would be some factors that deteriorated the effect of S-Q-P process on 20SiMn2MoVA steel.It was found by microstructural testing that the carbide forming elements V and Mo in the steel led to precipitation of carbides during partitioning period and lack of carbon in austenite.As a result,less austenite would remain after final quenching and mechanical properties of the steel would be influenced.The results would be beneficial for understanding the principle of S-Q-P process and improving the design of the S-Q-P steel compositions. A novel heat treatment process, stepping quenching and partitioning (SQP), has been developed to manipulate microstructure and mechanical properties of steels. Based on incomplete partitioning of carbon from martensite to austenite, volume fraction and distribution of the retained austenite results from the following quenching of the steels could be effectively controlled, and then the synthesized mechanical properties of the steels would be improved.In this paper, 20SiMn2MoVA steel was treated with conventional quenching-tempering (QT), currently prevailing quenching-partitioning (QP) and SQP processes, respectively. These results indicated that the volume fraction of the retained austenite of the steel treated by QP and SQP processes increased significantly that resulted in the increase of ductility and decrease of strength. The product of strength and ductility of the steel treated by SQP process reached 23.7GPa%, that was increased by about 13% and 7% compared with that after QT and QP processes, respectively. Compared with the great improvement of the synthesized mechanical property obtained by SQP process with another steel 35SiMn, there would be some factors that deteriorated the effect of SQP process on 20SiMn2MoVA steel. It was found by microstructural testing that the carbide forming elements V and Mo in the steel led to precipitation of carbides during partitioning period and lack of carbon in austenite. As a result, less austenite would remain after quenching and mechanical properties of the steel would be influenced. The results would be beneficial for understanding the principle of SQP process and improving the design of the SQP steel compositions.