Microstructure And Property In Simulated Heat-affected Zone Of New High Nitrogen High Manganese Low Nickel Austenite Stainless Steel

Welding is an important processing mean of austenitic stainless steel plate and profiles.High nitrogen austenitic stainless steel is a kind of steel,in which nickel is partially or completely substituted with nitrogen to obtain single austenite,which can save a lot of nickel,reduce the cost and has excellent mechanical properties and corrosion resistance,so it is widely used.However,there are a lot of problems such as the loss of nitrogen,nitride precipitation and other issues during the welding of the high nitrogen austenitic stainless steel.All of them have a detrimental effect on the mechanical properties of joint.Therefore,it is meaningful to study the welding performance of high nitrogen austenitic stainless steel.In this paper,HAZ simulation tests were carried out on a new type of high nitrogen,high manganese and low nickel austenitic stainless steel after solution treatment by the Gleeble-3500thermal/mechanical simulation testing machine.In the thermal simulation experiment,the peak temperature was 1050?~1300?,the line energy was 5~12kJ/cm.Then the actual welding were based on thermal simulation results.The microstructure of simulated HAZ and welded joints were analyzed by metallographic microscope.The further analysis were conducted by X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The tensile tests,impact tests and hardness tests were carried out to study the mechanical properties of simulated welding HAZ of experimental steels and actual welded joints.After the thermal simulation experiments at different peak temperature,the grain sixe of experimental steels increase and the tensile strength and hardness decrease with the peak temperature increased.However all of them are higher than the tensile strength of base metal799 MPa and hardness 239.26 HV respectively.The plasticity of experimental steels are lower than base metal,and the peak temperature has little effect on it.When the peak temperature is1150 oC,the experimental steel shows a different law of change.After the thermal simulation experiments on experimental steels with different line energy,the microstructure of welding HAZ is austenite and twin crystal,and(Cr,Mn,Fe)23C6 appear in the grain of welding HAZ,the carbide precipitation disappear and the grain also grow with the line energy increased gradually,the plasticity of experimental steels are slightly lower than that of base metal,but the change of line energy has little effect on its plasticity,the hardness of experimental steels is higher thanbase metal,so there was no softening area,when the line energy is 10kJ/cm,the experimental steels have the best mechanical properties,the tensile strength reaches 826 MPa,the elongation is 54.6%,the impact absorption work is 306.1J,the hardness is 319.03 HV.The experimental steels was subjected to TIG welding with optimized experimental parameters,the microstructure of welded joint heat affected zone is uniform,the hardness is higher than base metal and the tensile fracture appears in the welds.