Influence of post-treatment on microstructure and mechanical properties of additively manufactured C300 maraging steel

Abstract

The aim of this work is to explore various homogenization solution-aging post- treatments (HAT) related to maraging steel, manufactured by selective laser melting (SLM), in order to achieve high-level mechanical behaviours in the shortest processing time. Different (HAT) post- treatments experiments, combinate from a common homogenization solution treatment (HT) step performed at 1020 °C for 15 min, using aqueous NaCl solutions for cooling, and aging treatment (HT) step on mechanical properties of as-built maraging steel manufactured by selective laser melting (SLM). Three different aging temperatures (485 °C, 585 °C, and 685 °C) and aging times (120 min, 150 min, and 180 min) were used on the parts. In order to characterize the effects of heat treatment on the microstructure and on the mechanical behaviour, various microscopy techniques, such as confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), were used. To quantify the mechanical behaviour of SLM maraging steel (C300), hardness measurements and tensile tests were performed after homogenization solution-aging treatments (HAT). Furthermore, a statistical model was developed using analysis of variance (ANOVA) to predict the mechanical behaviour (hardness) and determine the related significant parameter. The model related the mechanical behaviour to the post-treatment properties in the work region. Compared to the as-built parts, the microhardness and ultimate tensile strengths were significantly improved after homogenization solution-aging treatments (HAT). The effects of heat treatment parameters (cooling solutions, aging temperature and aging time) on mechanical properties depend primarily on the microstructure changes that occur. The results showed that the heat-treated parts had a finer and non-continuous microstructure, leading to higher hardness (∼20–50%) and higher ultimate tensile strength (∼25–55%) properties, as compared to the as-built parts. The microhardness and ultimate strength can go up to ∼56 HRC and 2150 MPa, respectively, at the optimal heat treatment regime (solution treatment at 1020 °C for 15 min + aging treatment at 480 °C for ∼175 min).