Effect of Graded Microstructure on Magnetic Properties of Rotary Friction Welded Cobalt–Iron–Vanadium Alloy with SS 321 Alloy

SS 321 steels are used in aerospace applications due to high corrosion resistance. They are used in combination with soft magnetic materials (CoFeV alloys) for solenoid valves and other aerospace applications. In such applications, the welding of dissimilar materials (SS 321 and CoFeV alloys) needs to be performed. There is no reported literature on the welded joint behavior. Hence, there is a need to establish welding parameters and study the joint behavior in terms of changes in microstructure and magnetic and mechanical properties. The magnetic properties of CoFeV alloy are sensitive to mechanical working and welding operations. SS 321 and CoFeV alloys (as rolled and annealed) are joined using a rotary friction welding process and subjected to post-weld heat treatment. The welded samples are characterized by XRD, SEM (EDS), VSM, hardness and tensile tests. XRD analysis revealed no phase transformations or intermetallic compound formation in the welded joints. The magnetic properties have reduced in the weld central region (20-30 microns width) by about 50% of the original values. A pre-annealing treatment followed by welding has resulted in better magnetic properties and uniform hardness values in the welded regions of the joint compared to post-weld heat treatment operations.