Study On The Forming Process Optimization Of 921a Steel Underwater Laser Filler Wire Welding

With the progress of industrial production technology and the improvement of the ability of ships to carry out tasks in the far sea,the technology of ocean-going ship manufacturing and underwater hull field maintenance is in urgent need of improvement.921A steel has been widely used in the production and manufacture of naval ships due to its excellent performance in the aspects of pressure resistance and corrosion resistance.Underwater laser welding,as a new type of automatic underwater welding maintenance technology,has attracted much attention due to its high welding quality and low environmental impact.Build underwater laser welding test system.Underwater wet laser welding technology was used to conduct welding tests in different water depths.The test results showed that the weld surface formed well when the water depth was 1mm.When the water depth increases gradually,the uneven surface of the weld appears gradually.When the water depth reaches 4 mm,the welds is difficult to form and cannot forming a stable weld pool.Aiming at the problems of bad surface forming and narrow water depth adaptability of underwater wet laser welding,the local dry laser wire filler welding technology was proposed to improve the weld quality.Three kinds of drainage devices with different structures were designed and manufactured by ourselves,and one of them was selected to conduct underwater local dry laser wire filler welding test.Comparing and analyzing the quality and characteristics of onshore and underwater local dry laser welding joints,and verifying the feasibility of local dry underwater welding process.The experimental results show that the local dry method can effectively improve the welding quality,and the main mechanical properties of underwater welding seams are similar to those of onshore welding.Using 8mm thick 921A steel as a base metal for local dry method underwater laser wire filler welding experiment research.Focuse on study the technological parameters and different environmental factors impact on the local dry method underwater welding welds.The results show that with the increase of defocusing amount,the weld width decrease firstly,and then has gradually steady trend,while the weld depth decrease gradually.With the increase of welding speed,the forming continuity of weld surface decrease.With the increase of environmental pressure,both the weld width and weld depth decrease gradually.When the wire feeding speed is slowly,the formation of the weld surface of local dry welding is uneven.With the increase of wire feeding speed,the formation of the welds becomes continuous and uniform.The mechanical properties and microstructure of underwater local dry laser filler wire welding seams were tested and observed.With the increase of the environmental pressure,the hardness of the weld seam did not change obviously,while the hardness of the heat-affected zone increased gradually.Metallographic analysis showed that with the increase of pressure,the massive ferrite structures became thicker.