Decreasing surface roughness improves the fatigue strengths of SLM steels. The degree of this improvement depends on the type of the steel and surface processing technique. Various types of surface machining processes can be used to serve this purpose. However, machining has two effects on the surface of an SLM steel which has conflicting outcomes. Firstly, it smoothens surface roughness which results in the improvement of fatigue life. Secondly, it releases substrate compressive residual stresses, which are very common in AM parts. Lower compressive residual stresses near the surface result in easier crack initiation and faster fatigue crack growth. Hence, further study is necessary to distinguish the effects of these two phenomena and consider them simultaneously to have a better understanding of the fatigue crack initiation and propagation in SLM steels.