Effect Of Welding Process And Specimen Thickness On Weldability Of 2205 Duplex Stainless Steel

Duplex stainless steel is a kind of single steel and has various excellent properties of metal materials,in the petroleum,chemical and other fields have been widely used.The microstructure of dual-phase stainless steel is ferrite+austenite two-phase structure.When the ratio of dual-phase is balanced,the performance of dual-phase stainless steel reaches the best.At present,the research on the weldability of 2205 duplex stainless steel is more and more extensive.Different welding process and plate thickness have great influence on the microstructure and properties of welded joints.In this paper,three welding methods of SMAW,GTAW,GTAW+SMAW are used to conduct multi-layer and multi-pass flat butt welding tests on test plates with three thickness of 8 mm,30 mm and 55 mm,through the experimental comparison of different process with the same plate thickness(8 mm)and different plate thicknesses with the same process(GTAW+SMAW),the weldability of welded joints was studied by means of microstructure analysis,mechanical property test and finite element simulation,which provided theoretical basis for engineering practice.The following research results were obtained:(1)The XRD analysis of the joint shows that there are only two phases?and?in the joint welds of the three welding processes,and there is no harmful secondary phase precipitation;The microstructure analysis of welded joints under different welding process conditions shows that the ferrite content of SMAW joint is higher,and the austenite content of GTAW joint is higher,GTAW joint has higher austenite content and finer grain size.The ferrite phase content of GTAW+SMAW weld microstructure is moderate,due to the maximum heat input and the fastest cooling rate,the welding seam cover layer of the three processes has large grain size and higher ferrite content than other welding layers,the filling layer is obviously refined by thermal cycling;The average ferrite content(%Fe)of the weld of the three processes is F_SMAW>F_GTAW>F_GTAW+SMAW,indicating that SMAW has poor corrosion resistance;In general,the microstructure distribution of GTAW+SMAW joints is the best.(2)The joint tensile strength of the three welding processes is Rm _GTAW>Rm _GTAW+SMAW>Rm _SMAW,there are no cracks in the joints of the bending samples,which meet the requirements of material properties;The joint welds and impact toughness of heat-affected zone of the three welding processes all show ak _GTAW>ak _GTAW+SMAW>ak _SMAW,indicating that GTAW has better impact toughness;SMAW and GTAW tensile fracture properties are ductile fracture,and GTAW+SMAW is ductile-brittle mixed fracture;The impact fracture of the weld of the three processes is ductile fracture,the impact fracture of the heat-affected zone is quasi cleavage fracture and ductile-brittle mixed fracture;Vickers hardness test was carried out on the different welding layers of the joints of the three welding processes,and the weld hardness showed HV_SMAW>HV_GTAW+SMAW>HV_GTAW,in which,the filling layer has the highest hardness,and the hardness value will decrease as the heat input increases;The pitting corrosion resistance of the joints with three welding processes was tested,and the corrosion rate was CR_GTAW>CR_SMAW>CR_GTAW+SMAW,indicating that the corrosion resistance of GTAW joint is poor;In general,the mechanical properties of GTAW joints are the best.(3)The three plate thicknesses all adopt multi-layer and multi-pass welding.The heat input and cooling rate of different welding layers are different,and the austenite microstructure content is different;The XRD test results show that the welds of the three plate thicknesses have only two phases?and?,and no harmful phase precipitates;As the thickness of the plate increases,the number of welding layers increases,and the welding heat input increases,the weld filling layer is subjected to more thermal cycle,leading to finer grains;The ferrite content of the weld cover layer is higher and the grains are coarser,and the grains of the bottom layer of the weld are finer;The average ferrite content(%Fe)of the weld of the three plate thicknesses is F_{8 mm}>F_{55 mm}>F_{30 mm};In general,the microstructure grain distribution of the 55 mm plate thick joint is better.(4)The average tensile strength of the joints decreases gradually with the increase of the thickness of the three plates,and no cracks appear at the joints of the bending samples,which meets the requirements of the performance of the materials;With the increase of plate thickness,the impact toughness of joint weld and heat-affected zone decreases gradually,and the 8 mm plate thickness joint has better plastic toughness;The failure mechanism of the three kinds of plate thickness tensile fracture is basically the same,the fracture is ductile brittle mixed fracture,the impact of the weld filling layer is all ductile fracture,and the impact of the heat-affected zone is all quasi cleavage fracture;In general,the mechanical properties of 8 mm plate thick joints are the best.The hardness of different welding layers of the three kinds of plate thickness joints was tested.With the increase of the plate thickness,the weld hardness gradually increased,and the weld hardness and the heat-affected zone hardness were the highest.The pitting corrosion resistance of the three kinds of plate thickness joints was tested.The average corrosion rate increased with the increase of plate thickness,indicating that the corrosion resistance of the joints was worse.(5)Finite element simulation was carried out on the changes of temperature field and stress field in the welding process of three plate thicknesses;With the increase of plate thickness,the gradient range of temperature field gradually increases.The heat dissipation of55 mm plate thickness is slower and the temperature is the highest,while the heat dissipation range of 8 mm plate thickness is the largest and the heat dissipation speed is the fastest.During multi-layer and multi-pass welding,the thermal cycle curve has many peaks.The temperature of the three plate thicknesses increases rapidly in the heating stage,but decreases slowly in the cooling process.With the increase of the thickness of the plate,the equivalent stress decreases gradually.The more the number of welding layers,the greater the range of stress release.The stress peak value of the three kinds of plate thick joints almost appears in the same position and the longitudinal residual stress is greater than the transverse residual stress.