Heat Treatment Behavior of the 18Ni300 Maraging Steel Additively Manufactured by Selective Laser Melting

The steel 18Ni300 is widely used for tooling of injection moulding and die casting industries. Additive manufacturing (AM) technology is applicable to manufacture dies with " ideal" design without construction of manufacturing reality. Selective laser melting (SLM) processed materials have finer microstructure due to steeper temperature gradient and more rapid cooling conditions than conventional casting process during solidification. This difference may make different heat treatment behavior in obtaining optimal properties of the 18Ni300 maraging steel manufactured by SLM. Heat treatment is one of the most processes to improve microstructure, mechanical properties and performance of tooling dies. This work studies evolution of microstructure and properties during heat treatment, by X-ray diffraction, optical and scanning electron microscopy (SEM). The results show that the SLMed materials with only aging treatment have comparable strengths and hardness to those of conventionally cast materials with both solution and aging treatment. For the SLMed materials, with increase of aging time and/or temperature, the formed reverted austenite (.-Fe) fraction increases, while aging precipitation hardening decreases. This is more apparent at aging temperatures of higher than 540 degrees C. The combined effects of softening by formation of reverted austenite (.-Fe) and age hardening induced by precipitation are discussed.