Post-Heat Treatment Analysis of High-Strength Low-Alloy Steel Hollow Tubes Fabricated by Wire-Arc Directed Energy Deposition Process

Wire-arc directed energy deposition (DED) versatility in processing a wide range of materials, including high-strength low-alloy (HSLA) steel, positions it as an ideal method for producing customized, lightweight, high-performance components for industries such as automotive, maritime, and aerospace. Building on this capability, this study investigates the impact of post-processing on wire-arc DED fabricated HSLA steel, focusing on the resulting changes in microstructure and mechanical properties in comparison to its as-build (AB) part. During the post-processing, the samples underwent austenization at 950 degrees C (Aus), cyclic re-austenization (Aus-2C), and tempering (Aus-2C-T). Microstructural analysis revealed a shift in phase composition, with the Aus sample predominantly consisting of martensite (77 pct) and bainite (23 pct). Cyclic re-austenization (Aus-2C) reduced martensite to 66.3 pct and increased bainite to 33.7 pct, indicating phase stabilization. Tempering (Aus-2C-T) enhanced atomic diffusion, expanding the lattice along the c-axis and mitigating contraction observed in previous samples. Texture analysis showed reduced intensity from the AB to post-processed samples, indicating improved grain randomness due to rapid cooling and thermal cycling. Mechanical testing demonstrated significant improvements in ultimate tensile strength (UTS) (1233 MPa), yield strength (YS) (1062 MPa), and hardness (330.5 HV) in the Aus sample, with reduced elongation. The Aus-2C treatment achieved a balance between strength and ductility. Overall, post-processing led to enhanced mechanical properties and microstructural homogeneity, evidenced by reduced texture intensity and corresponding less variation in mechanical properties.