DISSOLUTION, COARSENING AND RE-PRECIPITATION OF SECOND-PHASE PARTICLE IN TI MICROALLOYED

STEEL DURING WELDING
THERMAL CYCLE

Chen Maoai  Wu Chuansong

(Shandong University)

Lian Rong

(Shandong Science and Technology Bureau)

Tang Yimin

(Shanghai Jiaotong University)

Abstract: Carbon extraction replica analysis is employed to measure number and size distribution of particles in Ti microalloyed 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 1200 °C) 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 (1200 ~ 1350°C) 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   1300 °C to 1350 °C, particle coarsening and dissolution still occurred due to lag effect. In the cooling stage from 1 300 °C 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.

Key words: TiN particle  Welding thermal cycle  Dissolution  Re-precipitation

CLC No: TG142.33