Effect of the parametric optimization and heat-treatment on the 18Ni-300 maraging steel microstructural properties manufactured by directed energy deposition

Maraging steels (MS) are widely used materials for heavy-duty applications and are considered an alternative to carbon hardened steels when high strength and good toughness is needed. Their processing through additive manufacturing (AM) technologies offers additional high-value opportunities, for instance, in the rapid prototyping or fabrication of tooling and inserts, and in the repair of molds and dies as well as in maintenance applications. This work studied the maraging 300 steel (18Ni-300) deposited by the laser cladding (LC) process. The experimental design was based on a 2³-full factorial design used to determine the optimum processing windows, using a constant powder feed rate. After that, samples with optimal process parameters were manufactured to determine the influence of deposition strategy and aging heat treatments on structural and mechanical properties (i.e., macrohardness). Results indicated the influence of crucial process parameters (i.e., laser power, velocity, and laser spot size) on the track’s geometrical characteristics. The processing windows also revealed that particular combinations of these parameters’ values produced LC tracks with the minimum dilution with either maximum height or maximum width, which is desirable for manufacturing and repair applications. Although the as-built samples did not show significant differences in their hardness, they showed a considerable difference in their austenitic phase content due to a combined effect between the sample’s geometry and deposition pattern. Aging heat treatments between 460 and 490 °C (4–8 h) resulted in the maximum hardness value (~55HCR) with an austenite content below 6 wt% calculated by Rietveld analysis. Finally, SEM and EDS analysis were carried out; it was found that the austenite located in the boundaries of the solidification structures is rich in Mo, Ti, and Ni for the samples in the as-built condition, while for the samples with aging, the highest content of austenite rich in Ni and Mo was obtained with aging at 530 °C.