A study on the corrosion properties of a novel precipitation-hardening stainless steel fabricated by laser powder bed fusion
University of New Brunswick
The purpose of this study is to achieve an understanding of the microstructural features and the relationship with the resultant corrosion performance of the CX stainless steel (CX SS) components fabricated using the laser powder bed fusion (L-PBF) technique. The first part of this research is focused on the microstructural features developed on CX SS parts after applying different heat-treatment processes. The mechanism of austenite reversion as well as the precipitation reactions were found to be controlled by a diffusion mechanism. In addition, it was observed that the grain refinement occurred within the austenite reversion of the continuously heated samples, and the microstructure showed a coarser grain size after isothermal heating. The effect of anisotropy and heterogeneities developed during the L-PBF process on the corrosion behavior of the two different sections of the as-printed samples was also investigated. Results suggested that grain size and grain boundary density have a close correlation with corrosion resistance. In addition, the effect of the post-heat-treatment processes was studied on the variations in the microstructure and the corrosion behavior of the asprinted CX SS parts. Partial recovery of the L-PBF solidification structure, annihilation of the cellular/ fine sub-grains, and the absence of high stored energy regions adjacent to the martensite-retained austenite interface and Cr-depleted zones in the L-PBF CX SS were attributed to a superior corrosion response of the heat-treated CX SS samples. The final part of this research targets on the corrosion behavior of hybrid components of CX SS and AISI 420 in both as-built and heat-treated conditions. The possible galvanic corrosion and pitting resistance at the interface area of the hybrid components were also investigated using the electrochemical noise (EN) technique. The statistical analysis of the EN results accompanied with the results of conventional electrochemical tests showed that the interface area in the as-built condition has a poorer ability of pit growth than after the heat-treatment process.