Investigation On TIG Welding Of Nonmagnetic-magnetic Dissimilar Metals

Dissimilar metal welding plays an important role in industrial production.It can make full use of the advantages of the two materials,avoid their shortcomings,and reduce production costs.However,the welding of dissimilar metals is affected by the chemical composition,metalurgical properties and physical properties of the two materials,and the electromagnetic properties of the materials are an important factor.In view of the difficulty of welding between magnetic and non-magnetic dissimilar metals,304 austenitic stainless steel(non-magnetic)and 430 ferritic stainless steel(magnetic)were selected for TIG welding.By changing the tungsten electrode offset to adjust the fusion ratio of welds,the microstructures and solidification modes of dissimilar joints with different fusion ratios were analyzed,and the similar 304 and 430 joints were also studied for comparison.The strain distribution in uniaxial tension of different joints was calculated by digital image correlation method,and the local mechanical behavior was calculated to analyze the fracture behavior of dissimilar joints.The results show that the dissimilar joints with different offsets are well formed and no welding defects such as cracks and inclusions are found.But different offsets affect the width of weld and the melting width of two materials.When tungsten electrode offset is 0,because of that 430 is magnetic and 304 is non-magnetic,the welding arc deflects to 430 side during the welding process,which results in the welding seam to 430 side.The melting width of the two base metal is approximately the same when the tungsten electrode offset is 0.5 mm to the 304 side.The dissimilar 304/430 joints are divided into four parts: fusion zone,304 side heat affected zone,430 side high temperature heat affected zone and 430 side low temperature heat affected zone.The structure of the fusion zone is a mixture of ferrite and austenite,and the ferrite content and the morphology of the two phases in the fusion zone vary with the offsets.When the offset is smal,the content of ferrite in the fusion zone is high,and the two-phase morphology is the network austenite structure distributed on the ferrite matrix.When the offset is large,the ferrite content in the fusion zone is very low,and the fusion zone is almost all austenite.Different offsets also affect the solidification mode of 304/430 dissimilar joints.When the offset is smal,the solidification mode is F mode,and when the offset is large,the solidification mode is FA mode.The difference of solidification modes also leads to differences in microstructure near the 430 side fusion lines.In the F solidification mode,the associated crystalization can be observed between the high temperature heat affected zone on 430 side and the fusion zone,but not in the FA solidification mode.The fracture modes of dissimilar 304/430 joints can be divided into two types.When the offset is smal,the mechanical properties of the joints are better,and the fracture occurs at 430 base metal,which is ductile fracture;when the offset is large,the fracture occurs at fusion line on 430 side,and the tensile strength and elongation are relatively low,which is brittle fracture.The strain field distribution during uniaxial tension is calculated and analyzed by using digital image correlation method.The tensile process of dissimilar joints with small offset can be divided into four stages,which show different strain distributions.The tensile process of dissimilar joints with large offset can be divided into three stages.The strain distribution of the first two stages is almost the same as that of the joints with small offset.The work hardening exponent(n)and intensity factor(K)of different joints were calculated.The difference of n and K values between heat-affected zone at 430 side and fusion zone under small offset is much smaler than that at large offset.That is to say,under large offset,there is more obvious difference of performance at the interface of heat-affected zone and fusion zone at 430 side,and the huge change of performance at this interface results in fracture during uniaxial tension.