Effect of austenite deformation temperature on precipitation kinetics, microstructure and hardness of Ti-V complex microalloyed steel

The precipitation-temperature-time curve (PTT curve) of Ti-V complex microalloyed steel at different austenite deformation temperatures was investigated by the stress relaxation method, and the effects of austenite deformation temperature on microstructure, precipitation phase hardness of Ti-V complex microalloyed steel were also investigated by means of OM, SEM and Vickers hardness tester. The results show that the shape of PTT curve of precipitation in austenite is generally a typical C curve. The fastest precipitation nose point temperature is 960~980 ℃, and the corresponding start time and end time of the fastest precipitation of the second phase particles are 2.2 s and 131.4 s, respectively. With the increase of deformation temperature, the original austenite grain size decreases at first and then increases, and the grain size is the smallest (102 μm) at about 1 000 ℃, which is close to the nose point temperature of PTT curve, so deformation near the nose point temperature is conducive to refine the original austenite grain. The precipitated phase gradually increases with the increase in temperature, while the number of particles decreases slightly. Different austenite deformation temperatures have little effect on the hardness, and HV hardness is basically at (360±12).