Influence of arc duration on microstructure and tensile behavior of magnetically impelled arc butt welded AISI 409 ferritic stainless steel tubes

Magnetically impelled arc butt (MIAB) welding has been the focus of several industries to weld metals in tubular form. 4 mm thick AISI 409 ferritic stainless steel tubes were joined effectively using MIAB welding. The arc duration was varied (4s–8s with an increment of 1s) during welding and all other process parameters such as arc rotation current, upset current, upset time, upset pressure and initial gap were maintained at a constant value. Several microscopic techniques were used to study the microstructure evolution in the joint region. The increase in arc duration pumped more heat energy during joining and increased the size of the weld zone and the axial shortening. The weld zone exhibited a typical forged structure which was affected by heat and mechanical force and is known as TMAZ. The grain size was continuously refined from base metal towards the weld center. The changes in grain size allowed dividing TMAZ into three regions. The welding cycle did not cause any grain growth to produce a heat affected zone (HAZ) similar to fusion welding processes. The increase in arc duration increased the grain size at the weld center. The ferritic structure did not transform into other structures during welding. There was a remarkable increase in the hardness of TMAZ compared to base metal. The strengthening was ascribed to the formation of strain fields in large quantities due to upsetting. Variation in arc duration remarkably influenced the tensile strength and the fracture location. The choice of the arc duration is important to produce sound joints.