Strain-rate-dependent compressive behaviour and constitutive modelling of circular WAAM ER70S-6 steel walls

Circular collars and wall-type components fabricated using wire-arc additive manufacturing (WAAM) are increasingly being considered for load-bearing steel applications. However, detailed compressive properties and constitutive models are limited. In this study, a circular ER70S-6 steel wall of five layers deposited on the SS400 substrate by WAAM was explored to understand the microstructure-property relationship under compressive loading. The as-deposited wall had a microstructure consisting primarily of ferrite and pearlite. It also showed qualitatively observed scattered gas pores and a high proportion of high-angle grain boundaries (approximately 72%) in the load-bearing region. In contrast, the fusion zone at the wall-substrate interface had coarser grains. The hardness distribution in the wall showed a uniform value (200–235 HV), with a localized minimum in the fusion zone, followed by a recovery in the heat-affected zone and substrate. Quasi-static compression tests were performed at strain rates of 10⁻⁴ to 10⁻¹ s⁻¹ using cylindrical specimens. Under quasi-static compression, the circular wall showed 0.2% yield strengths of 368.3 ± 20.2 to 397.0 ± 2.6 MPa and ultimate compressive strengths of 729.0 ± 31.2 to 801.7 ± 56.2 MPa across the strain rates, with mild strain-rate sensitivity and work-hardening capacities of 0.93–1.15. The flow curves of the wall material analyzed using the Hollomon, Ludwik, Swift, and Afrin models confirmed the high work-hardening capacity and stable constitutive equation values over the strain rates, dominated by a high-angle grain boundary microstructure.