Corrosion Resistance of FeCrMnSiB Austenitic Stainless Steels Processed by Plasma Transferred Arc

Boron-containing austenitic stainless steels with low stacking fault have been developed for superior wear and cavitation resistance applications. However, few studies have addressed the corrosion behavior of these steels. This investigation assesses the effect of boron additions (0.2 and 0.5 wt.% B) on the corrosion resistance of FeCrMnSiB coatings deposited by plasma transferred arc (PTA) on AISI 304 stainless steel substrates, benchmarking their performance to those of similar alloys processed by other manufacturing techniques (HVOF, HVAF, Spray forming and melt spinning), as well as to commercial reference materials. The microstructure of the resulting coatings was characterized by optical and scanning electron microscopy, phase analysis by x-ray diffraction, and chemical composition by energy dispersive x-ray spectroscopy. Corrosion resistance was assessed by electrochemical cyclic potentiodynamic polarization in a 3.5 wt.% NaCl solution and the corrosion surface mechanisms were investigated by scanning electron microscopy. Results show that the presence of boron leads to the formation of Cr-rich borides, whose fraction increases with boron additions, depleting the surrounding austenitic matrix in Cr and making it a preferential site for pitting corrosion. Boron increments accounted for a decrease in the corrosion potential of approximately 85 mV and for an increase in the corrosion rate of about three times, but the pitting potential was not significantly affected. Still, FeCrMnSiB coatings processed by PTA developed low corrosion current densities, greatly outperforming coatings processed by HVOF, and having a competitive performance compared to borated stainless steel coatings processed by HVAF and spray forming.