Enhancing passivity and corrosion resistance of laser-powder bed fused maraging stainless steel CX through TiC-induced microstructure tailoring

Abstract

Maraging stainless steel Corrax® (also known as SS CX) can be successfully processed using the laser powder bed fusion (L-PBF) technology. However, the fabricated alloy exhibits anisotropic properties due to the formation of columnar grains along the build direction. While heat treatment can partially address this issue, it cannot fully eliminate it and adds an additional post-processing step to the manufacturing cycle. This research explores the strategic addition of TiC particles as an effective inoculant to refine the microstructure of L-PBF SS CX and investigates the influence of these microstructural changes on its corrosion performance—an area yet to be explored in existing literature. TiC particles were incorporated into the initial SS CX powder feedstock at 1 wt% and 2 wt% concentrations, and the results were compared to those of the non-inoculated alloy. The addition of TiC inoculants effectively refined the grain structure and promoted the formation of a duplex microstructure comprising martensite and austenite in the inoculated alloys. Specifically, the proportion of the smallest grains ($\le$2 μm) increased significantly, rising from 24.6 % in the SS CX sample with 1 wt% TiC to 29.3 % in the SS CX sample with 2 wt% TiC. This grain refinement significantly reduced corrosion susceptibility and enhanced the overall corrosion resistance of the alloy. In this context, the charge transfer resistance of 2.8 × 10⁶ Ω·cm² observed for L-PBF SS CX increased by 18 % and 71 % in samples containing 1 wt% and 2 wt% TiC, respectively. Similarly, the corrosion current densities of the L-PBF SS CX samples with 1 wt% and 2 wt% TiC were one and two orders of magnitude lower, respectively, than those of the non-inoculated counterpart. Moreover, the refined microstructure facilitated the formation of a more uniform and defect-free passive film, further improving the corrosion resistance of TiC-inoculated L-PBF SS CX.