Four steels containing Si + Al = 2 wt-% were investigated in this study. Three mixed microstructures, namely, bainite + martensite + retained austenite (MB+Ar), martensite + retained austenite (M+Ar) and low-temperature bainite + retained austenite (LB+Ar) were obtained. Wear resistance was determined by dry sliding friction testing under different conditions. Results showed that Al promoted the formation of oxide films during wear process, resulting in the improvement of wear resistance, especially under a high-load condition. Under the same hardness, the wear resistance of MB+Ar was improved by 65 and 100% compared with that of LB+Ar and M+Ar microstructures, respectively. At high temperature, the worn surface was covered by oxide films and the samples exhibited abrasive and adhesive wear mechanisms. However, at low temperature, the oxide films were difficult to generate on the worn surface; the adhesive wear mode was dominant and resulted in severe wear.
The mechanical properties of Mn-Mo-Ni nuclear power forging steel can be affected greatly by tempering processes. In the present paper, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and hardness measurements were employed to correlate property variation with the evolution of microstructure during tempering of an Mn-Mo-Ni steel. Kinetics analysis based on hardness measurements was applied to isothermal tempering at temperatures in the range 600-660uC. The hardness variations during tempering are explained by decomposition of retained austenite and martensite-austenite (M-A), precipitation and coarsening of carbides within bainitic ferrite, and recrystallisation of bainitic ferrite. According to the kinetics analysis, the tempering transformation activation energy has been calculated as about 101?4 kJ mol 21 , which indicates a mechanism of carbon diffusion within ferrite. Finally, the considerable precipitation and coarsening of carbides within bainitic ferrite have been observed only at high isothermal temperatures (generally equal to or above 660uC), indicating a high tempering resistance of the Mn-Mo-Ni steel.
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