Unraveling the Stress Corrosion Cracking Of Strain-induced Martensite in Stainless Steel Reinforcements

Abstract

During the manufacturing process of stainless steel (SS) reinforcements, due to the rolling process, austenitic steels are prone to transform into martensite on the outermost surface, increasing the hardness of the material. The martensite packets show higher susceptibility of SCC than the bulk austenite microstructure, thus acting as crack nucleation sites. In addition, given a tensile stimulus strain induced martensite is formed, which can be a site for the initiation of stress corrosion cracking. AISI 316LN SS reinforcement were exposed to 8 wt.% Cl– contaminated synthetic concrete pore solution. The slow strain rate technique was used in conjunction with electrochemical tests to analyze passivity breakdown over the entire strain region. Electrochemical impedance spectroscopy (EIS), and current transient were monitored while the samples were being strained, in addition cyclic potentiodynamic polarization (CPP) was performed to evaluate dissolution kinetics. Fractographic study was performed, and crack initiation and propagation were studied by metallographic examination and scanning electron microscopy (SEM). A better understanding on the corrosion behavior of the outer martensitic surface of the reinforcement, including the passive film and the crack initiation, helps identify the reason for the premature failure of the reinforcement during their service lifetime. This study elucidates the main factors behind the stress corrosion cracking initiation due to strain induced martensitic transformation, making emphasis on the relation between material properties, such as composition and microstructure; and corrosion properties.