Corrosion Properties of Quenching and Partitioning-Processed Martensitic Stainless Steels

Abstract

The increasing demand for lightweight and energy-efficient automobile materials has prompted consideration of the Quenching and Partitioning (Q&P) process for developing martensitic stainless steels with enhanced combinations of strength and ductility. The microstructures of Q&P-processed martensitic stainless steels primarily consist of a matrix of carbon-depleted martensite and films of retained austenite, although some high-carbon fresh martensite may be present.This research aimed to elucidate the influence of chemical composition (manganese content), heat treatment, and phase fractions (martensite and retained austenite) on the corrosion properties of Q&P-processed martensitic stainless steels.The microstructures were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). Corrosion properties were evaluated through electrochemical measurements in a 3.5% NaCl solution, which included open-circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Scanning Kelvin probe force microscopy (SKPFM) measurements were also conducted.Q&P process ideally minimizes carbide formation, as all carbon atoms are partitioned into austenite. Nevertheless, our research demonstrates that this condition is not always met. Depending on the alloy's chemical composition and the partitioning temperature, carbides and inclusions may still form, favoring localized corrosion such as pitting and intergranular corrosion.