Effect of Martensite–Bainite Duplex Microstructure on Carbide Precipitation and Mechanical Properties of M50 Steel

By means of microstructure observation, phase analysis, and mechanical‐property tests, the effect of martensite–bainite (M–B) duplex microstructure on carbide precipitation and mechanical properties of M50 steel is studied. In that results, it is shown that the distribution of secondary carbides in specimens with M–B duplex microstructure is more uniform and finer, and the stability of retained austenite (RA) in the steel is also improved, so that the content of RA in specimens with M–B duplex microstructure is 2.34%, which is higher than the 0.94% of the specimens with full martensite microstructure. The M–B duplex microstructure leads to the reduction of tempering hardness of M50 steel to 60.9 unit of Rockwell hardness (HRC), compared to the 61.6 HRC of the specimens with full martensite microstructure, but the wear resistance is slightly enhanced. Moreover, the M–B duplex microstructure effectively improves the impact toughness and fatigue properties by refining the microstructure and carbides in the steel, and the increase amplitude is 47.4% and 41.0%, respectively.