Low-cycle fatigue behaviour of AM46 carbon steel produced by wire arc additive manufacturing

AM46 is a novel steel wire developed for wire arc additive manufacturing (WAAM) with potential for fatigue-sensitive applications. However, its low-cycle fatigue behaviour and fracture characteristics remain unexplored. This paper investigates the cyclic plastic response of WAAM-produced AM46 specimens, considering as-built and machined-polished surface conditions, as well as vertical and horizontal build orientations. Process stability and material integrity were assessed through thermal monitoring during deposition, complemented by microstructural analysis, X-ray microtomography, microhardness and monotonic tensile testing. Low-cycle fatigue strain-controlled tests were followed by scanning electron microscopy of fracture surfaces to identify dominant fracture mechanisms. The material exhibited a homogeneous ferritic-pearlitic microstructure with reduced anisotropy and low porosity. The cyclic response was strain-amplitude dependent, showing cyclic softening at lower strain amplitudes and cyclic hardening at higher strain amplitudes. Vertically oriented specimens performed better at lower strain amplitudes, while horizontally oriented specimens showed longer fatigue lives at higher strain amplitudes. This transition occurred earlier in the as-built condition. Fatigue crack initiation was governed by internal porosity and surface defects, while crack propagation involved fatigue striations, microvoids and secondary cracking. WAAM-produced AM46 carbon steel demonstrated improved low-cycle fatigue performance compared to WAAM-produced ER70S-6 carbon steel and in the machined-polished vertical orientation approached the strain-life response of conventional S355 steel.