Microstructural evolution of a low-carbon steel fabricated via wire-arc additive manufacturing: the effect of interpass time and number of layers

Abstract Wire-arc additive manufacturing (WAAM) provides advantages in deposition rate and design complexity compared to conventional fabrication processes. However, despite its advantages, studies on the influence of processing parameters on the microstructural evolution of WAAM components remain limited. To address the gap, this work examines the effects of interpass time and build height on microstructural development and microhardness across different regions of WAAM single-bead structures. Specifically, mild steel samples were fabricated following a two-factor, three-level, single-replicate design of experiments. Their microstructures were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques, while phase transformation histories were correlated with different printing configurations through parent austenite grain reconstruction. The findings reveal that single-layer deposits exhibit a dual-phase microstructure consisting of ferrite and martensite. Furthermore, the addition of subsequent layers increases the ferrite phase fraction in the first layer, leading to a reduction in microhardness measurements. Interpass time and build height were found to influence the local morphology of parent grains, phase distribution, and grain topology. These results provide insights into the effects of thermal cycling and deposition strategies on solidification and grain growth associated with fabrication of mild steels. A deeper understanding of these relationships could enable process optimization for modifying microstructure and mechanical properties in WAAM-fabricated components, resulting to improved performance in structural and engineering applications.