Unraveling the synergistic influence of Nb, V, and Ce on corrosion and high temperature performance of austenitic alloys

Abstract

The influence of the synergistic effect of the addition of Ce–Nb–V and Ce–V–Nb on the microstructural behavior and oxidation resistance at 800 °C to produce new austenitic steels (ASS) was investigated. Thermodynamic modeling (Thermo-Calc) was employed to optimize the composition, and their production was carried out from stainless steel scrap and ferroalloys in the open atmosphere induction melting process to contribute to the circular economy. The morphology, evolution, and mechanisms of the microstructure of the zone affected by oxidation were determined by applying various characterization techniques such as X-ray diffraction, electron spectroscopy, Raman spectroscopy, scanning electron microscopy (XRD, XPS, RAMAN, and SEM) and thermodynamic calculations. The oxidation kinetics indicated that adding Ce–Nb–V synergistically promotes a decrease in the oxidation rate and more adherent oxides. However, in the Ce–V–Nb system, a higher oxidation rate was presented, attributed to a high V content, which reduces the anticorrosive behavior of the alloy. In general, there is a high resistance to oxidation in the ASS produced, which is improved by the formation of oxide layers enhanced by the presence of a stable and complete spinel structure. In this sense, the addition of Ce improves grain refinement, contributes to the formation of Ce-rich inclusions with good oxide anchoring properties, and allows selective segregation in Mo and Cr diffusion, allowing a decrease in intermetallic secondary phases.