An Assessment of Microstructure and Tensile Behavior of Magnetically Impelled Arc Butt Welded AISI 409 Ferritic Stainless Steel Tubes

Magnetically impelled arc butt (MIAB) welding is being used in industries for joining metallic tubes and pipes. This research work reported MIAB welding of AISI 409 ferritic stainless steel tubes of 4 mm thickness. Joints were obtained by varying arc rotation current and characterized using various microscopic techniques. An increase in arc rotation current enlarged the joint region and increased the axial shortening. The upsetting was improper at higher and lower limits of the current. The joint consisted of deformed structure which was thermally and mechanically affected (TMAZ). The entire TMAZ was further designated into three regions based on the variation in grain size and the degree of deformation experienced. The grains were extremely refined by upsetting. There was no coarsening of grains to form a heated affected zone (HAZ). There was no phase transformation observed in TMAZ. The average grain size showed an increasing trend as the current value was increased. High density of dislocations was observed in TMAZ which caused significant strengthening of the joint region. TMAZ showed multifold increase in hardness due to grain refinement and dislocation fields. The variation in arc rotation current influenced the joint strength remarkably and shifted the fracture location. The choice of arc rotation current is a key factor to obtain sound joints.