DISSOLUTION,COARSENING AND PRECIPITATION OF TiN PARTICLE IN Ti MICROALLOYED STEEL DURING WELDING THERMAL CYCLE

Carbon extraction replica analysis were carried out on the specimen in Ti microalloyed steel which is subjected to different stage of the 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.It is concluded that at the low heating temperature stage (lower than 1200℃) of thermal cycle, the dissolution was characterized by shrinkage of particles and the number of particles did not decrease noticeably, which shows that particle coarsening was very weak.At the high heating temperature stage (1200~1350℃) of thermal cycle, a large number of small particles disappeared with the mean particle size increment.It is found that TiN particles dissolution still occurred due to lag effect.At high temperature zone of cooling stage, the particles are dissolved continuously.At lower temperature zone of cooling stage, free Ti and N were combined and TiN 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.