Abstract: Large residual stress and delayed crack would be produced after assembly and welding of largediameter cutterhead, hence, the scheme of improving the surfacing welding quality by controlling preheating temperature is put forward. The selfprotecting flux cored wire is used to weld the shield tool plate by material Q345R, and the variations of surfacing welding structure and performance at the preheating temperature of 50, 100, 150 and 200 ℃ are studied respectively. The results show that after preheating by 100 ℃, the residual stress is the least, the impact toughness is the best, the microhardness gradient variation is the least, and the comprehensive mechanical property is the best. The conclusions obtained by the test are used to guide the selection of preheating temperature for surfacing welding of the cutterhead. It has been proved in practice that by selecting the appropriate preheating temperature, the onetime pass rate of UT flaw detection results after welding of the cutterhead reaches 100%, and good results have been achieved in practical application.

Key words: shield cutterhead, surfacing welding, repair of cutterhead, preheating temperature, residual stress, delayed crack