Carbon extraction replica analysis is employed to measure number and size distribution of
particles in Ti micro-alloyed steel
specimens which are subjected to different welding thermal cycle so as to study the
dissolution,
coarsening and precipitation of TiN particle in Ti microalloyed steel during different stage of welding thermal cycle. The results showed that the coarsening and re-precipitation lag behind dissolution seriously, and the coarsening mechanisms in different stage of the welding thermal cycle is different. At the low temperature stage (lower than 1 200 ℃) of heating leg of welding thermal cycle, the dissolution is characterized by shrinkage of particles, the number of particles did not decrease noticeably, indicating that particle coarsening is very weak. At the high temperature stage (1 200 - 1 350℃) of heating leg of welding thermal cycle, the mean particle size increase strikingly through disappearance of a large number of small particles. In the cooling stage from 1 300 ℃ to 1 350℃, particle coarsening and dissolution still occurred due to lag effect. In the cooling stage from 1 300℃to room temperature, solute Ti and N are combined to reprecipatated onto the survived particles, thus the mean size increase remarkably. The austenite grains coarsening mainly occurred in the cooling stage of the welding thermal cycle.