Influence of Post-processing and Build Direction on the Wear Behaviour of Laser Powder Bed Fused Maraging Steel

Abstract

Present study investigates the effect of post processing (heat treatment: solutionising at 850°C for 2 hr with aging at 490°C for 3 hr and cryogenic treatment at -196°C for 24 hr) and the effect of build direction (along the build direction (BD) and perpendicular to the build direction (PBD)) on the wear behavior of maraging steel fabricated by Laser powder bed fusion (LPBF). The results are also compared with conventional hot-forged samples. The pin on disc equipment was used to conduct the wear experiments with an EN31 steel disk as the counter body. Heat treatment decreased the wear rate of LPBF material by 54.78% and 83.84% in BD and PBD, respectively. This is due to the restriction of grain expansion by the Ni-based precipitants in age hardening treatment. The cryogenic treatment further decreased the wear rate of LPBF material by 87.84% and 90.9% in BD and PBD, respectively. This significant reduction can be attributed to the change of phase to martensite, as confirmed through microstructure and X-ray diffraction (XRD) analysis. Moreover, hot forged material also obtained a reduced wear rate after heat and cryogenic treatments. The highest wear resistance was found with the LPBF cryo-treated BD sample due to increased hardness from 388 HV to 640 HV. The worn surface of test samples was examined by using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), 3D profilometer, and XRD analysis. Oxidation wear, adhesive wear, and abrasive wear are the predominant wear mechanisms identified using SEM.