Precipitation Behavior and Mechanical Properties of Ti-Mo Medium-Carbon Steel During Austenite to Bainite Transformation

The precipitation behavior and evolution of mechanical properties of Ti-Mo-bearing microalloyed medium-carbon steel during austenite to bainite transformation were studied, and two different cooling rates including ultrafast cooling (similar to 80 A degrees C/s) and accelerated cooling (similar to 15 A degrees C/s) during transformation were also investigated. The results suggest that Ti-Mo-bearing medium-carbon steel yield finer microstructure and nano-precipitates during austenite to bainite transformation during both ultrafast cooling and accelerated cooling processes. Yield strength and tensile strength obtained by ultrafast cooling process were higher than the accelerated cooling process, while the elongation was slightly reduced. Microstructural characterization indicated that grain refinement and precipitation hardening were the primary reasons for the increase in strength. Ultrafast cooling increased the density of dislocations and refined the grain size. Average size of precipitates containing Ti and Mo was 3-6 nm by ultrafast cooling process, while average precipitate size obtained by accelerated cooling process was 6-9 nm.