Study On Submerged Arc Welding Technology Of Super-thick Plate

In this paper,the Q345 D thick collage plate with 150 mm thick is butted with the combined process of double wire submerged arc welding and three wire submerged arc welding on the reverse side,and the double-U groove is used after splicing.Before welding,the technology limit of the special thick plate submerged arc welding is solved.After the welding is completed,the mechanical properties of the welded joint are tested,and the macroscopic morphology and microstructure of the welded joints under the two processes are observed.From the mechanical test results,the relationships between microstructure and impact toughness,tensile strength and lamellar tearing resistance of base metal Z direction near weld seam of the special thick plate submerged arc welding are studied.Before welding,the suitable welding material is chosen,reasonable combination for power supply is conducted,and the best wire spacing and angle are designed.After the completion of welding,it is found in macro and metallographic examination of welding joints that,there are no undercut,slag,weld defects such as porosity in the welding seams by two weld processes,and the appearances are bright and clean.By comparing two processes,it is found that the three wire submerged arc welding has wider heat affected zone due to the larger line energy and the obvious columnar crystal is observed in the welding seam of three wire submerged arc.The tensile,side bending and impact tests are carried out on the welded joints of the special thick plate submerged arc welding,and the mechanical properties of the welded joints all reach the requirements.From the hardness test of fracture and welding joint,it is found that the white tissue at the fracture surface is ferrite,the gray tissue is pearlite and the black tissue is bainite.The hardness of weld area is fluctuating in the small range in the vicinity of 180HV~190HV,and the hardness of heat affected zone fluctuates between 230HV~260HV.There is no phenomenon of softening and hardening of welded joints after welding.The tensile test of Z direction is carried out on the base metal near the weld seam after the welding of the special thick plate submerged arc welding.The tensile strength reaches the experimental standard,and the fracture morphology contains a large number of dimples and shear lip characteristics,and fracture is plastic fracture,which shows that after submerged arc welding by two kinds of processes,the anti lamellar tearing performance in the Z direction near the thick plate welds is good.