Correlation between micro-to-macro mechanical properties and processing parameters on additive manufactured 18Ni-300 maraging steels

Abstract

The 18-Ni 300 maraging steels with bulk cuboidal shape were fabricated by selective laser melting (SLM) to understand correlation between micro-to-macro mechanical properties and processing parameters. The as-built specimens fabricated under various laser power and scanning rate conditions were composed of α martensite phase with cellular arm spacing of 0.2 – 0.5 µm. The relative density of as-built specimens increased from 89.14% to 99.86%, depending on volume metric energy density (VED), laser power, and scanning rate, but it is more affected by the VED and laser power than the scanning rate. For porous specimens fabricated under lower VED than 73 J/mm3, the laser power had a greater impact on relative density than VED, whereas relative density of specimens had a positive correlation with VED in the range of 75 − 93 J/mm3 and reached full density. Micro Vickers hardness tended to decrease with increasing VED and relative density in porous specimens, whereas in the full dense specimens, micro Vickers hardness gradually increased with increasing VED. The contrast in micro hardness between porous and dense specimens was attributed to nanoprecipitation affected by intrinsic heat treatment during SLM. Compression test demonstrated that yield strength strongly correlated with relative density, gradually increasing to 1.13 GPa as the specimens reached full density. From the investigation, this study provided an optimized SLM processing condition for high strength as-built 18Ni-300 maraging steel.