Abstract: Transformation process associated to Si-Mn,Ti,Ti-B weld metals processed by high-heat input welding process were systematically investigated by in-situ high temperature laser confocal microscope,and influences of Ti and B on transformation process in the weld metal were analyzed and discussed.Results indicate that the transformation can be completely finished in the high temperature region with respect to Si-Mn weld metal,and large amount of equi-axed ferrites are initiated.When Ti is added into weld metal,the transformation temperature region of weld metal is slightly decreased.GBF is firstly initiated at austenite boundary,and the inclusions composed of Ti begin to induce AF nucleation and growth in austenite subsequently.When B is further added into weld metal,the GBF transformation can be effectively prohibited in the austenite,which directly promotes the AF transformation in austenite.