Microstructure And Properties Of Welded Joints Of 2205 Duplex Stainless Steel With TIG/MIG Welding

2205 duplex stainless steels combine the outstanding properties of austenitic stainless steels and ferritic stainless steels due to its dual microstructure consisting of approximately equal proportions of ferrite and austenite phases.However,welding thermal cycle will change the microstructure badly.The phase ratio will deviate from 1:1;the microstructure of both phases,especially the austenite phase,will change significantly and harmful secondary phase may precipitate on certain conditions.These will lead to a dramatic reduction of mechanical and corrosion properties.Therefore,it's of great importance to study the influence of welding heat input and cooling rate to the welding performance of 2205 DSS.In this paper,ER2209 welding wire has been chosen as the welding filler material.2205 DSS plates are welded by tungsten inert gas arc welding(TIG)and metal inert gas welding(MIG),respectively.The microstructures of the welding joints acquired by these two welding methods are examined under OM,SEM and TEM.The mechanical properties and corrosion resistance of welding joints are tested.The main results are as follows:1.In the welding joints,welding thermal cycle has great influence on the microstructures of HAZ.The peak temperature in HAZ varies depending on location driving the a/y transformation to different levels of completion which lead to the microstructures differ widely within HAZ.The morphology of austenites in different area of the weld zone varied largely.In the center of the weld zone austenites are mainly equiaxed austenites while at the edge of weld zone austenites are mostly Widmanstatten austenites.2.With the increasing of heat input,both the cooling time and high temperature dwell time will be prolonged which will aggravate the degree of grain coarsening.As a result,the equiaxed austenites coarse in length and thickness,the thickness of Widmanstatten austenites increases remarkably.3.The volume fraction of austenite phase rises with the increasing of heat input.For TIG welding,the phase ratio of austenite to ferrite in weld zone is close to 1:1 when heat input increases to 3.4 kJ/mm.For MIG welding,the proportion of austenite increases to approximately 50%when heat input reaches 1.1 kJ/mm.4.The proportion of austenite increases with the increasing of heat input.Therefore,the ductility of weld joints increases with the increasing of heat input while the micro hardness shows the opposite trend.TIG welding,the mechanical properties of weld joints achieve the best when heat input is 3.4 kJ/mm.For MIG welding,the weld joints show the best mechanical properties when heat input reaches 1.1 kJ/mm.5.With the increase of heat input,the width of HAZ increases and the distribution of alloy elements becomes more uniform due to diffusion,which lead to the deterioration of pitting corrosion property in ferrite.Accordingly the pitting corrosion rate increases with the increasing of the heat input.