The structure after welding commonly needs special postweld heat treatment in practice,like normalizing + one or one more times temper heat treatment. In this way the strength of weld metal decreases sharply and cannot meet the requirement of structure in service. The selection of welding materials is proposed based on the solid-state phase transformation principle. When the phase transformation temperature of selected weld metal is lower than the heat treatment temperature,During the postweld heat treatment,the austenite nucleates again on the columnar grain boundary in the austenite reverse transformation,so that the weld metal is refined and the strength of weld metal improves. Thus,it is ensured that the strength of weld metal matches base metal after special postweld heat treatment.