Selective Laser Melting (SLM) is steadily gaining acceptance across the manufacturing industry. Techniques for manufacturing components with complex geometries layer by layer have proven to be very effective in accelerating product development and hence reducing time to market. To build components by SLM from a nickel based super-alloy requires an understanding of process parameters and how they influence the microstructure, the degree of porosity and the properties. In this work, it was found that the as-fabricated density of parts manufactured from Hastelloy-X by SLM could be increased from 77 to 99% by decreasing the laser scan speed, and that the degree of cracking can be reduced by decreasing the amount of minor alloying additions such as Mn and Si