Overlap Percentage Effects on Microstructure and Microhardness in Wire Arc Additive Manufacturing of AISI 308L Stainless Steel

ABSTRACT This study investigates the influence of overlap percentage on the microstructure, dilution behavior, and microhardness evolution of AISI 308L stainless steel fabricated by robotic Cold Metal Transfer Wire Arc Additive Manufacturing (CMT‐WAAM). Although previous WAAM studies on AISI 308L have primarily addressed single‐track deposition and process parameter optimization, the effect of overlap percentage, a parameter unique to multitrack deposition that governs the metallurgical bonding between adjacent beads, has remained largely unexplored. Two overlap conditions, 25% and 50%, were investigated, with the aim of achieving defect‐free deposition beads while clarifying how overlap governs thermal interaction between tracks. Optical and scanning electron microscopy revealed that a lower center‐to‐center track spacing at 25% overlap concentrated the heat input toward the substrate, producing a deeper dilution area (2374 μm) and HAZ (1345 μm) but a narrower transition zone (7642 μm), whereas the greater spacing at 50% overlap distributed heat more broadly, widening the transition zone (9737 μm) while reducing the dilution area (2148 μm) and HAZ depth (1215 μm). Microhardness measurements, reported with standard deviations and validated statistically, showed a progressive increase from the base metal (∼278 HV) to the overlap and fusion regions, reaching a maximum of ∼343 HV, attributed to combined grain refinement, δ‐ferrite redistribution, and an elevated local cooling rate. These findings indicate that higher overlap is preferable for wider, more productive builds with stronger intertrack continuity, whereas lower overlap is better suited to applications requiring dimensional accuracy and localized repair, providing practical guidance for overlap strategy selection in industrial CMT‐WAAM applications.