Strain-Induced Precipitation Behavior and Microstructure Evolution of Ti-V-Mo Complex Microalloyed Steel

The austenitic strain-induced precipitation behavior of Ti-V-Mo complex microalloyed steel was investigated by using the stress relaxation method. The changes in precipitation phase, microstructure and hardness of the Ti-V-Mo complex microalloyed steel with varying relaxation temperatures were studied by using an optical microscope, a transmission electron microscope and a Vickers hardness tester. The results revealed that the precipitation-time-temperature diagram of Ti-V-Mo complex microalloyed steel exhibited a characteristic "C" shape, with the nose point temperature being close to 1000 degrees C, and the corresponding precipitation start and end times were 4.1 and 472.4 s. The strain-induced precipitation phase is identified as (Ti, V, Mo)C particles and nucleates primarily at dislocations and subgrain boundaries. With the temperature rising from 950 to 1050 degrees C, the average size of precipitation increased from 10.8 to 33.7 nm. Appropriately lowering the austenite strain temperature can refine the austenite precipitation phase, which is conducive to the (Ti, V, Mo)C from ferrite, thus improving the precipitation strengthening effect. Furthermore, the average grain size of prior austenite increased from 60 to 70 mu m with temperature increasing from 920 to 1080 degrees C under holding 2000 s, and the high-density (Ti, V, Mo)C particles of the strain-induced precipitation played a crucial role in preventing significant coarsening of prior austenite grains. The austenitic deformation temperature has almost no effect on the hardness of experimental steels.