In conclusion, on the improvement of fatigue behaviour, suitability of a heat treatment depends on the type of SLM steel and the expected properties after its heat treatment. The heat treatment might be chosen according to the type and the strengthening mechanism of the steel. For example, stress relieving had a prominent advantageous influence on the FCG rate and the threshold value of the quench-hardened SLM steel H13; while, it did not show any positive effect on the ductile SLM steel 316L [27,28,58–60,70].