Controlling microstructure and mechanical properties of directed energy deposition-arc fabricated 18Ni-350 maraging steel through inter-layer temperature adjustment

Abstract

Directed energy deposition-arc (DED-arc) enables the fabrication of large maraging steel components, yet its high heat input often results in suboptimal mechanical properties. This study investigates the effect of inter-layer temperature—150 °C and 200 °C—on the microstructure and mechanical properties of DED-arc-fabricated 18Ni350 maraging steel. Thin walls were deposited under the two temperature regimes, followed by comprehensive characterization of thermal history, microstructure, and mechanical properties. Results indicate that the lower inter-layer temperature of 150 °C promotes faster cooling, leading to a finer grain structure, higher martensite content, and reduced retained austenite compared to 200 °C. These microstructural refinements contribute directly to enhanced mechanical properties, including higher average microhardness (369 HV vs. 341 HV) and superior tensile performance. The 150 °C condition achieves a vertical tensile strength of 1267 MPa with 14.2% elongation and a horizontal strength of 1200 MPa with 14.9% elongation, outperforming the 200 °C condition (1229 MPa, 7.9% vertically; 1076 MPa, 11.9% horizontally). The work demonstrates that controlling inter-layer temperature near the martensite start temperature effectively optimizes microstructure and achieves an excellent strength–ductility balance in DED-arc produced maraging steel.