Microstructure and microhardness behaviour of L-PBF produced AISI 420 stainless steel

Abstract

This study examines and explores the influence of Laser Powder Bed Fusion processing parameters on the microstructure and density of AISI 420 stainless steel (420SS). The relative density of as-built samples varied significantly with laser power and scanning speed. Samples processed at 90– 125 W exhibited densities of 94.8 – 98.0%, while those at 145–150 W achieved 98.5 – 98.9%, and at 167–200 W reached 98.9 – 99.9%. The interaction of laser power and scanning speed was crucial in achieving near full density, with optimal parameters yielding densities above 99%. Insufficient melting and poor bonding at lower laser power and high scanning speeds caused porosity, while excessive heat input at higher laser power and low speeds resulted in large molten pools and potential cracking. Microhardness varied across samples, with low laser power achieving the highest microhardness of 639 HV at 121 W. Higher laser powers generally produced more homogenous martensitic microstructures, essential for yielding superior mechanical properties. The findings underscore the critical role of finely tuned L-PBF parameters in optimizing the microstructural characteristics and mechanical properties of 420SS, paving the way for its enhanced application in demanding industrial sectors like power generation.