Study On CMT+P Welding Process Of P92 Steel

P92 steel is a kind of martensitic steel with a variety of alloy elements.P92 steel has the advantages of high temperature strength,good thermal conductivity,low thermal expansion coefficient and good creep performance.It is widely used in high temperature and high pressure main steam pipeline of supercritical unit.In engineering,the commonly used welding method of P92 steel is TIG welding as backing welding and SMAW welding or SAW welding as filling or covering welding.TIG welding is a welding process with excellent welding joint microstructure and performance,but the welding efficiency is low.SMAW and SAW welding process have the same feature that welding current is larger,which can achieve higher welding efficiency,but the big welding line energy and high heat input will contribute to the coarse grains of weld microstructure,broadening of joint heat affected area—relate to the ? type crack.CMT welding process is a low heat input welding process through wire withdrawing,and the droplet transitions to the molten pool in the period of the welding current near to zero.But the depth of the weld beam by this welding process is so small that it can't be used to thick plate.CMT + P is a new welding process that is a mix of CMT and pulse welding.The new welding process can integrate the low welding heat input of CMT and large molten depth of pulse welding.CMT+P can be used for the welding of thick plate.So,the application of CMT+P in the welding of P92 steel might reduce the heat input,improve the weld microstructure,reduce the width of the weld heat affected zone and improve the joint performance.Thereby a new welding process for P92 steel is proposed,which can promote the further application of P92 steel in industry.In this paper,the effect of protective gas and gas flow velocity,welding wire elongation,wire feed speed,welding speed and CMT/P ratio parameters on weld formation are explored through flat welding;And the effect of groove gap on backing weld forming of the CMT+P backing welding is also explored;Besides,the impact of arc plate,arc extinguish plate,welding gun angle and the welding torch swing on weld quality are explored in multilayer welding.Then,the suitable welding parameters are got through experiment above and the butt joints of 15 mm thick P92 steel plate are got with the CMT+P welding process and welding parameters above.Finally,the microstructure of CMT+P welded joints of P92 steel are observed and the mechanical properties of the welded joints are tested.And the conclusion that the microstructure of CMT+P weld joint of P92 steel is better than that of TIG+SMAW can be gained.Besides,the mechanical properties of CMT+P weld joint of P92 steel can meet the standard requirements.It is shown that the CMT+P welding process is feasible in the welding of P92 steel.