Influence of pore defects on the mechanical property and corrosion behavior of SLM 18Ni300 maraging steel

Pore evolution in the surface of SLM 18Ni300 maraging steel during the heat treatment process was studied by in-situ observation and the pore size is sensitive to high temperatures. The overall equivalent average pore sizes of macropores (unmelted powder and lack of fusion pores) increased since stress around the pores changed during phase transformation occurred in the solid solution process at 820 °C. When the original average equivalent diameters of the lack of fusion pores were greater than the critical size of 15 μm, the sizes of pores increased after solid solution treatment. When aged 5 h after solid solution, the overall average size of manufacturing pores decreased from around 11.82 μm to around 7.82 μm since the grain distortion which shrunk or split of pores came from the formation and coarsening of Ni3Mo during aging treatments. The corrosion resistance of SLM 18Ni300 was negatively correlated with the size of pores. After solution treatment, the depth of pits increased from 95.472 μm to 138.977 μm. The depth of pits decreased to 124.756 μm and 117.945 μm after heat treatment for 2 h and 5 h, respectively. In addition, secondary cracks penetrated the pores to accelerate the fracture process and reduce the elongation.