The in-situ observation of the phase transformation processes of weld metal during high-heat input welding were carried out by a high temperature laser confocal microscope. The influences of Ti content on the phase transformation process were investigated. It was found that the Ti inclusions could act as the nucleation sites for α→γ transformation during the heating stage of welding thermo cycle and inhibit the growth of austenite grains. The number of inclusions was increased with increasing Ti content. During the cooling stage of welding thermo cycle, the inclusions could induce the nucleation of acicular ferrites when the Ti content was below 0.078%. With increasing Ti content, more acicular ferrites collided with each other and restricted their further growth. When the Ti content was increased up to 0.115%, a proportion of Ti atoms were dissolved in the matrix, which increased the hardenability and thus generated the lath bainite microstructure instead of acicular ferrite.

利用高温激光共聚焦显微镜对高热输入焊接过程中焊缝金属的相变过程进行了现场观察。研究了Ti含量对相变过程的影响。发现在焊接热循环的加热阶段，Ti夹杂物可以作为α→γ相的成核部位，并抑制奥氏体晶粒的生长。随着Ti含量的增加，夹杂物的数量增加。在焊接热循环的冷却阶段，当Ti含量低于0.078％时，夹杂物会引起针状铁素体的形核。随着Ti含量的增加，更多的针状铁素体相互碰撞并限制了它们的进一步生长。当Ti含量增加到0.115％时，