Maraging steel 300 processed by SLM (Selective Laser Melting) is widely used for manufacturing inserts and molds with conformal cooling channels. For such applications, high fracture toughness and strength are required in order to withstand thermal fatigue generated in aluminum die casting, especially at high pressure. Any defect like pores, lack of fusion and cracks should be avoided so that durability of the mold is not reduced. In this study, two powder batches were employed and different behavior was observed in parts manufactured with the same processing parameters. The susceptibility of cracking was linked to slight variations in the characteristics of the powder and to the preheating temperature.