The Influence of Layer Remelting on Microstructure, Porosity, Hardness, and Tensile Properties of M300 Steel Parts Produced by Laser Powder Bed Fusion

In this paper, the influence of additional heat treatment of additively manufactured (AM) M300 steel is discussed, implemented by means of remelting each layer of the material using a laser beam from the AM machine directly during the process. The proposed heat treatment was used for the improvement of the AM process in situ. Research results revealed that using a small laser exposure velocity, it is possible to obtain parts with low porosity both after a single exposure (0.03%) and multiple exposures, including double (0.04%) and triple (0.04%) exposures. Furthermore, a stable increase in hardness with subsequent exposures. The hardness increased from 365.67 ± 3.92 HV after a single exposure to 385.17 ± 4.91 HV, after a triple exposure of each layer. The hardening effect of the remelted area was only registered in the case of exposure of the whole layers, and further improvements by selective hardening were not possible in a part of the layers.