Numerical Simulation and Performance Study of Four-wire Submerged Arc Welding Process for X80 Heavy-wall Steel Linepipe

The temperature field distribution and thermal cycle curve characteristics of the welding process are analyzed via numerical simulation, and then the optimized four-wire submerged arc welding process for the X80 heavy-wall steel linepipe is determined. Then welding tests are carried out to investigate the microstructure and the mechanical properties of the welded joint. The results show that thanks to optimization of the welding process parameters,the impact energy of the coarse-grain heat-affected zone（CGHAZ）at -10 ℃ can be increased to 363 J,and thus the “W-shaped”softening phenomenon of the hardness distribution in the welded joint is obviously improved; the high-temperature holding time T_Hand the cooling time from 800 ℃ to 500 ℃ t_8/5are key parameters leading to microstructure evolution in the HAZ;rapid cooling rate significantly promotes the formation of acicular ferrite,whereas a relatively low cooling rate leads to an increase in the amount of M-A constituents;controlling t_8/5within 40 s can effectively inhibit the formation of brittle phases,and accordingly improve the joint toughness.