Effect of the scanning strategy on the SLM produced 18Ni300 maraging steel

The aim of the thesis has been to investigate the effect of the scanning strategy and the main process parameters on the final parts produced through Selective Laser Melting. Selective laser melting (SLM) is the most common Powder Bed Fusion technology and it uses high energy laser to selectively melt pre-deposited powders. The printed material is the 18Ni300 maraging steel, a low-carbon ultra-high strength steel whose properties derive from the presence of nickel-based intermetallic compounds. Thanks to their good weldability and the resistance to quench cracking, the maraging steels are good candidate materials to be produced through the SLM process. Interestingly, the microstructure of the SLM produced parts is completely different from the one of the traditionally produced ones, depending not just on the material but also on the values of the process parameters used to print. So, it is necessary to study in-depth the characteristics of the printed parts. Four prints have been carried out, keeping constant the volumetric energy density, the laser power and the layer thickness. The scan speed, the hatch spacing, the rotation between adjacent layers and the scan strategy have been changed. In particular, the “stripes”, the “chessboard” and the “hexagonal” strategies have been considered. It has been found out that the hexagonal strategy always led to the biggest external diameter, to the lowest density and almost always to the highest roughness of the final parts. All these negative results were probably related to the longer time elapsing between the scan of two adjacent tracks compared to the other two strategies. The results of the nano-hardness tests are not clearly showing which strategy performs better, probably because a too small portion of specimen has been considered for those tests. Moreover, ANOVA analysis has been performed and it confirmed the primary importance of the scan strategy as process parameter.