1. The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, Liaoning， China 2. Jinan Iron and Steel Group Co., Ltd., Jinan 250101, Shandong, China 3. Laiwu Iron and Steel Group Co., Ltd., Laiwu 271104, Shandong, China
Abstract：The alloy components of NM400 steel were determined by adding micro-V in Cr-B series wear resistant steel according to the low cost design ideas. Detailed research on different quenching temperatures and tempering temperatures shows the influence of different parameters on the microstructure and mechanical properties of the NM400 steel. The optimal parameters of heat treatment process are obtained, which are suitable for industrial production. Through the observation and analysis by optical microscope, SEM and TEM, the evolution law of fine structure in the lath martensite is obtained after tempering through different temperatures. The results show that the steel has high hardenability. The fine lath martensite which is distributed uniformly can be obtained after quenching at 900-930℃ and tempering at 250℃ for 90 minutes. The results analysed by TEM show that the lath martensite tempered is in width of 0.1-0.2μm and the fine carbides (mainly V(C,N) in size of 10-20nm) are distributed uniformly, which improve the comprehensive mechanical properties of the steel.