Microstructural and Mechanical Properties Evolution of Bimetallic Cr-Ni and Cr-Mn-Ni Stainless Steel Joints

In the present work, the replacement feasibility of AISI 304 (Cr-Ni) with low nickel AISI 201 (Cr-Mn-N-Ni) stainless steel has been studied by employing dissimilar welding. Three different welding speeds were selected for gas tungsten arc welding process. The solidification mode and delta-ferrite content were predicted using WRC-1992 diagram, and conventional ferritescope was also used to calculate delta-ferrite. The microstructural analysis of weldments revealed the presence of lathy ferrite morphology dominated by vermicular ferrite for high and medium welding speed specimens, whereas low welding speed specimen depicts only vermicular morphology of ferrite in the weldments. Further, SEM–EDS analysis of weldments was carried out on weldments and indicated for the precipitation at fusion boundary. The tensile strength and microhardness was evaluated to establish structure–property correlation. It was observed that the weldments with higher welding speed depicted better mechanical properties. Failure of the tensile specimens took place in the fusion zone of AISI 201 side (adjacent to fusion boundary) in all three weldments. XRD analysis of fractured surfaces confirmed the formation of intermetallic compounds as Cr₂₃C6 and martensite (small amount), which were responsible for deterioration of mechanical properties and failure of weld joints in fusion zone. Fractographic investigation of fractured surfaces revealed the presence of dimple-like morphology which leads to ductile fracture.