Research On Arc Stability And Welding Processes Of Underwater Wet Welding Of Ship Steels

Underwater welding is a key technology for underwater repairs in marine engineering.Research on the key technology and application of underwater welding of marine high-strength steel can lay a technical foundation for improving the level of marine mobile repairs for ships,which has important research significance and practical application value.In this paper,a set of underwater wet welding test platform was established.It mainly included underwater wet manual arc welding equipment based on ZX7-400 dual-module manual arc welding machine and special SH-68 underwater welding torch,and underwater electrical signal acquisition system based on Hall voltage and current sensors and Lab VIEW software.For 907 A steel and Q235 B steel,self-made wet resin welding rod,TS203 A underwater wet welding rod and HS-490 underwater high strength steel welding rod were used to the underwater welding tests with different welding parameters..According to the experiment plan,the electrical signal parameters of the underwater welding process were collected,and the low-pass filtering method suitable for this experiment was selected.The underwater welding current waveform and voltage waveform with better filtering effect were obtained.The U-I curve,voltage probability density distribution diagram and current probability density distribution diagram of underwater welding with different electrodes and different parameters were drawn.The reciprocal of the coefficient of variation of the underwater welding voltage and current under different electrodes and different parameters were counted,and they are used to characterize the stability of the underwater welding arc.The TS203 A and resin electrodes with better arc stability were screened out,and the optimal welding parameters were determined.The welding current is 160 A and the welding speed is 3.5mm/s.For 907 A steel and Q235 B steel,12 groups of underwater wet plate welding under different welding current were carried out.After wire cutting,grinding,polishing and corrosion,metallographic specimens were obtained.Then the metallographic structure was observed under optical microscope,and the microhardness was measured by Vickers microhardness tester.It was found that the microstructure of base metal zone(BM)was mainly white ferrite and black pearlite.According to the different heat inputs,there are two kinds of microstructures: fine grain ferrite and martensite.Due to the formation of fine lath martensite and high quenching hardness,the heat-affected zone(HAZ)has the highest microhardness value in Vickers microhardness tests.In the welded joint of 907 A steel,the lowest microhardness value appeared in the weld cover layer.In the welded joint of Q235 B steel,the lowest microhardness value appearred in the lower deposited layer area.With 160 A welding current and 3.5mm/s welding speed,TS203 A wet welding rod and self-made resin welding rod were used for underwater butt welding of 907 A steel and Q235 B steel.The tensile strength of the welding seam of the two kinds of welding rods met the requirements.The cooling speed of underwater wet welding is fast.The microstructure of the welding seam was mainly ferrite and pearlite.The columnar crystal structure was more obvious,and the toughness of the joint decreased obviously.