Microstructure evolution and mechanical properties during long-term tempering of a low carbon martensitic stainless bearing steel

Abstract

Effect of tempering time on microstructure and tensile properties of a low carbon martensitic stainless bearing steel was studied. Results showed that martensitic blocks became coarser and dislocation annihilation continuously took place during tempering process. It was also found that the number of M2C and M6C was increased firstly and then decreased, while their sizes were increased constantly. Moreover, the austenite content was increased due to the formation of reverted austenite. For tensile properties characterization, there was a transition from a ductile fracture to a quasi-cleavage fracture with increasing tempering time. Yield strength peaked when the steel was tempered for 24 h, followed by a constant decline. The abnormal decrease in elongation after long-term tempering was due to the formation of coarsening M23C6 at grain boundaries.