Enhancing the Surface Properties of Additively and Conventionally Manufactured 18Ni300 Maraging Steel through Gas Nitriding

The aim of this study was to investigate the differences in microstructure and microhardness between additively manufactured (AM) and conventionally manufactured (CM) 18Ni300 maraging steel, after subjecting samples to a low-temperature gas nitriding treatment in the solution-annealed condition. A microstructural characterization revealed equiaxed grains in CM specimens, whereas AM specimens contained irregular martensitic laths, reflecting their distinct solidification and thermal histories. Nitriding at 360°C resulted in effective case depths of approximately 60 µm for AM and 55 µm for CM specimens, values that were attributed to the enhanced nitrogen diffusivity and reduced competition with intermetallic precipitate formation at this temperature. The surface microhardness reached 1115±15 HV0.01 for AM and 1090±15 HV0.01 for CM, with a gradual decrease toward core hardness values of 560±6 HV0.01 and 548±6 HV0.01, respectively. The superior hardening response for the AM specimens is associated with their columnar grain morphology and higher dislocation density, which facilitate nitrogen trapping and strengthening. These findings demonstrate that when combined with low-temperature nitriding, additive manufacturing offers a promising method of achieving enhanced surface properties in maraging steel components intended for high-performance tool industry applications. KEYWORDS Metal 3D printing, microhardness, microstructure, surface engineering, strength steel, surface properties