Near-Net Shape Manufacture of Ultra-High Strength Maraging Steel Using Flow Forming and Inertia Friction Welding: Experimental and Microstructural Characterization

Flow forming and inertia friction welding (IFW) have been widely used as manufacturing processes that produce high-value engineering components. Combining these two advanced processes facilitates the fabrication of near-net shape components leading to optimized designs. This study introduces the joining of flow-formed seamless tubes of MLX^®19 maraging steel using the IFW process to fabricate a near-net shape component used in landing gears and missile parts. The as-received material was initially provided ≈30% reduction in thickness from the flow forming trials and then welded at four varying weld energies while maintaining constant friction and forge pressures. The mechanical behavior of the weldments was characterized, and the optimized weld parameters were determined. The concomitant microstructural evolution of the optimized weld was also examined to comprehend the underlying deformation mechanisms. The weld strength, axial shortening, and width of dynamic recrystallization (DRX) displayed an increasing trend with an increase in the weld energy. The weld-zone (WZ) and thermomechanical affected zone (TMAZ) showed the presence of martensite, whereas in the HAZ presence of intermetallic precipitates and reverted austenite was confirmed along with tempered martensite. Based on microstructural evidence, it was concluded that the peak temperature attained in the WZ was above Ac₃, whereas in the TMAZ it was in-between Ac₁ and Ac₃. The evolution of crystallographic texture implied that WZ was subjected to pure shear deformation during the welding whereas the TMAZ experienced a combined shear and compressive deformation.