Assessment of AM70 high-strength steel processed via wire arc additive manufacturing for pressure vessel applications: Role of spray and pulsed arc

Abstract

Achieving optimal mechanical performance in wire arc additive manufacturing (WAAM) of high-strength low-alloy (HSLA) steels is critical for the structural integrity of load-bearing and pressure-retaining components. This study compares the effects of high-capacity Spray Arc and voltage-controlled Pulsed Arc gas metal arc welding (GMAW) modes on the microstructure, residual stress distribution, and mechanical behavior of AM70 HSLA steel, an alloy formulated for enhanced arc stability and deoxidation. Comprehensive characterization using optical/electron microscopy, X-ray diffraction, mechanical testing, and fractography reveals distinct process–structure–property relationships. Pulsed Arc mode produces a refined acicular ferrite matrix with more uniform crystallite size and elemental homogeneity, leading to superior hardness (236–246 HV₅ vs. 223–235 HV₅), tensile strength (743–793 MPa vs. 687–710 MPa), and Charpy impact toughness (78.5–103 J vs. 59.3–78.2 J) compared to Spray Arc. Additionally, compressive residual stresses are more uniformly distributed under Pulsed Arc (−134 to −288 MPa), whereas Spray Arc introduces steeper gradients (−66 to −311 MPa), which could affect long-term structural performance. Although Spray Arc yields higher ductility (34.7–36.4 % vs. 29.1–32.9 %), Pulsed Arc offers a better balance of strength and toughness. Fractographic analysis confirms ductile failure modes in both cases, with finer dimple morphology observed in Pulsed Arc samples. These findings demonstrate the potential of Pulsed Arc WAAM with AM70 steel for manufacturing pressure-resilient and structurally reliable HSLA steel components.