Characterisation of TCP precipitation sequences of superaustenitic stainless steel and correlation with electrochemical and mechanical properties

Abstract

This study investigates the influence of precipitation sequences formed at critical high-temperature range for various ageing time of super austenitic stainless steel 654SMO against the evolution of its corrosive resistance performance through the microstructural characterization, hardness and electrochemical corrosion testing. The specific type of stainless-steel alloy is one of the most corrosion resistant along with exceptional mechanical properties, tailor-made for pressurized and erosive systems handling chlorinated sea water, plate heat exchangers, and fuel gas cleaning applications and an excellent case study of in-depth phase transformations-electrochemical properties characterization phenomena. The microstructure evolution is characterized by scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), hardness testing and potentiodynamic polarization curves. The corresponding precipitation characteristics and sequences of secondary phases are discussed and correlated with electrochemical properties. The results demonstrate σ phase with various morphologies formed during isothermal aging and the formation of three more secondary topologically close pack (TCP) phases, such as chi phase (χ), laves phase (A2B), and Cr2N against corrosive resistance and mechanical performance, which are of primary importance for understanding electrochemical phenomena of different phases and useful for optimizing such alloys for various applications.