Research On Welding And Performance Of Austenitic Stainless Steel Used In Harsh Environment

In order to solve the global energy crisis,mitigate the greenhouse effect and environmental degradation,reducing the use of fossil fuels and increasing the diversity of clean energy supplies have become the main solutions.Nuclear energy and wind energy are important components of clean energy.800H austenitic stainless steel and 304LN austenitic stainless steel play a vital role in nuclear and wind power generation,respectively.In order to solve the problem of intergranular corrosion of the steam generator heat transfer tube of the PWR nuclear power plant,the sensitivity of intergranular corrosion of 800H austenitic stainless steel welded joints is mainly achieved by improving the welding method and post-weld treatment,which provides a new direction for the problem of intergranular corrosion.The wind power developed in China is mainly offshore wind power and wind power generation in the northwest and northeast regions.These regions have harsh climates and require wind turbines to serve in extremely cold environments.According to the requirements for the use of certain structural components in wind turbines,they are mainly targeted at 304LN Austria Research on the selection of welding wire,the best post-weld stress-relief annealing process,post-weld cryogenic treatment process and shot peening process in the welding process of austenitic stainless steel,determine the optimal wire,the best shot peening process,and different stress-relief annealing Effect of Process and Cryogenic Treatment Process on the Performance of304LN Welded Joints.By comparing the performance of 800H after welding with various laser welding parameters,the optimal laser welding process parameters for 3 mm thick 800H austenitic stainless steel are determined as follows:laser power 2.9 k W,welding speed 25 mm/s,Ar gas shielding gas,air flow 1.5 m~3/h,laser forward 8°,defocus amount 0,without wire butt welding,single pass double-sided welding through;With the increase of the holding temperature and the holding time,the resistance of 800H welded joints to intergranular corrosion first increases,then decreases,and finally stabilizes;The weakest area in the800H laser welded joint is the heat affected zone,and the weld zone has the strongest resistance to intergranular corrosion,followed by the base metal zone.Among them,the heat-affected zone is mainly due to the influence of welding heat sources.It is in the sensitization temperature range for a long time and has the weakest resistance to intergranular corrosion.For the welding of 304LN austenitic stainless steel,the differences in post-weld performance of two types of welding wire ER309L and X series welding wire.The normal temperature and-196?low-temperature impact energy of the improved X series welding wires are significantly higher than those of the first batch of ER309L welding wires.The main reasons are:the phase composition of the weld zone after welding of ER309L wire is austenite+martensite structure,the phase composition of the weld zone of X series wire after welding is pure austenite structure,and martensite is hard phase and has cold brittleness.Aiming at the stress-relief annealing process of 304LN welded joints,the test was carried out with ER309L welding wire welded samples.The effects of stress-relief annealing temperature on the degree of residual stress reduction,normal temperature and low temperature impact energy at-196?,tensile strength at normal temperature and Vickers hardness were investigated.The effect of stress-relief annealing holding time on the degree of stress reduction,normal temperature and low-temperature impact energy at-196?.The study found that there are two types of initial stress states after welding:tensile stress and compressive stress.Both stresses are reduced,and the degree of reduction increases with increasing temperature.,The initial stress is compressive stress,the stress increases after annealing,and the increase degree gradually decreases with increasing temperature;The section is the ground surface after wire cutting,and its residual stress is post-weld stress+grinding stress.The initial stress state is compressive stress.After annealing,the residual stress in all three regions is reduced.The degree of stress reduction in the cross-section heat affected zone and the cross-section base metal zone showed an increasing trend.After annealing at different temperatures,the impact energy at-196?in the weld zone is lower than that at normal temperature,and the change law of impact energy with temperature is not obvious.The fundamental factor that determines the impact energy is the welding wire composition and welding quality;After annealing at different temperatures,the tensile fracture area of the sample is in the base material area.Using X series welding wire after welding,the stress state basically shows the state of compressive stress before and after annealing treatment at different holding time;After the annealing treatment,the residual stress in the heat-affected zone of the cross section showed an increased state,and the residual stress in the heat-affected zone of the surface showed a decreasing state;With the extension of the holding time,the degree of stress reduction in the surface heat-affected zone increases continuously;The increase of the stress in the heat affected zone of the section increases with the extension of the holding time.With the extension of the holding time,the impact energy at room temperature shows a trend of decreasing first,then increasing,and then decreasing,and the low-temperature impact energy at-196?shows a rising state.In order to investigate the effect of the cryogenic treatment process on 304LN welded joints,the residual stress reduction degree,normal temperature and low temperature impact energy of-196?,normal temperature tensile,Vickers hardness,and intergranular corrosion properties of the ER309L welding wire were studied.The results show that:after cryogenic treatment,the residual stresses on the surface and cross-section weld zone,heat affected zone,and base metal area of 304LN welded joints are all slightly reduced after cryogenic treatment;Cryogenic treatment makes the impact energy of 304LN welded joints increase slightly at room temperature and low temperature of-196?;The 304LN welded joints before and after the cryogenic treatment showed strong comprehensive plastic properties,and the elongation increased slightly after the cryogenic treatment;The area with the weakest resistance to intergranular corrosion in 304LN welded joints is the weld zone,and the heat-affected zone and base metal zone have strong resistance to corrosion.After cryogenic treatment,the resistance to intergranular corrosion is improved in the three areas of the welded joint.The best shot peening parameters for the 304LN welded joint after welding with ER309L wire are:shot peening distance is 200 mm,shot peening angle is 90°,shot diameter is 0.71 mm,shot peening pressure is 1.5 MPa,repeat4 cycles,shot shot flow 1.5 kg/min.