Microstructure and mechanical property variations within inertia friction-welded joints of stainless steel to steel

Abstract

Inertia friction (IF) welding was used to fabricate butt joints between AISI type 304L stainless steel and AISI 1018 steel for proof of concept work directed toward novel corrosion-resistant cladding applications. Microstructure and mechanical property trends were identified within each joint in the radial and axial directions. Rotation speed and axial force (pressure) were varied to determine the effects of processing on joint morphology, microstructure, and mechanical properties. Light optical microscopy (LOM) was used to correlate processing parameters with microstructural characteristics. Microhardness mapping revealed the effects of processing conditions through the various weld zones. Tensile testing was performed using digital image correlation (DIC) with the tensile axis normal to the weld interface. Causal relationships were revealed between the processing parameters and microstructure and mechanical property variations in radial and axial directions. IF welding with low axial pressure resulted in an enlarged softened zone near the centerline, whereas high axial pressure resulted in an enlarged softened zone near the periphery. High rotation speed caused an enlarged heat-affected zone (HAZ), and low rotation speed resulted in bond line fracture for the tensile test near the periphery. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) examinations were performed on the bond line fracture surface. The presence of voids at the bond line, near the periphery, detrimental to joint mechanical properties corresponded with inadequate energy input for the low-rotation-speed joint.