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Description
The microstructure of laser powder bed fusion (L-PBF) processed 18Ni300 differs from that of manufactured using conventional processing routes. The L-PBF steel, due to the non-equilibrium solidification, comprises a cellular/dendritic solidification structure with the presence of intercellular austenite as a result of heavy micro-segregation of alloying elements. On the other hand, the conventionally manufactured counterpart shows a fully martensitic microstructure in solution annealed condition. This difference appears to be insignificant in view of the static mechanical properties (e.g., tensile properties) after ageing heat treatment. Therefore, it is suggested that the L-PBF 18Ni300 can be directly aged from the as-built condition without a need for prior microstructural homogenization. However, the influence of the initial microstructure on the dynamic mechanical properties of the age hardened parts such as impact toughness, and fatigue resistance has not been systematically studied. In this work, the effect of homogenization and solution annealing treatment prior to ageing on mechanical properties and fatigue resistance of an 18Ni300 maraging steel is investigated. The results show an improvement of fatigue resistance by application of proper homogenization heat treatments.