Effect of layer-wise deposition and post-annealing heat-treatment on the microstructure and mechanical properties of wire laser additive manufactured ER70S-6 steel

Steel is widely used in structural applications, and wire laser additive manufacturing (WLAM) provides a promising approach for fabricating structural steel components. Understanding the relationship between microstructure and mechanical response is essential for optimizing the performance of WLAM-fabricated steels. In this study, ER70S-6 steel wall was fabricated using WLAM and examined in the as-printed condition and after post-annealing heat treatment at 600 °C and 700 °C. Microscopic analysis revealed a ferrite–pearlite microstructure in the as-printed sample. Following heat treatment, the pearlite fraction progressively decreased, the as-printed sample exhibited an average pearlite fraction of ∼6.5%, which reduced to 3.8% and 3.4% after annealing. Concurrently, the average grain size increased from 0.98 µm to 1.50 µm and 1.85 µm, confirming grain coarsening during heat treatment. SEM-EDS revealed a ferritic matrix containing pearlite along grain boundaries and EDS point analysis revealed minor variations in the concentration of Mo and Mn at analyzed locations. Moreover, XRD analysis confirmed α-Fe as the dominant phase. Mechanical testing demonstrated a clear trade-off between strength and ductility, with hardness and strength decreasing after heat treatment, whereas elongation increased. The as-printed wall exhibited a UTS of 447 MPa and 18.3% elongation, after annealing at 600 °C, UTS decreased by 2.4% and elongation increased by 11.9%, whereas at 700 °C, UTS decreased by 7% and elongation increased by 29%. These results demonstrate that ER70S-6 steel produced via WLAM, combined with post-annealing, allows tailoring of microstructure and mechanical properties, providing a pathway for designing high-performance structural components.