Effect of aging of 2507 super duplex stainless steel on sliding tribocorrosion in chloride solution

The tribocorrosion behavior of SAF 2507 (UNS S32750) superduplex stainless steel exposed to heat treatments at 800 °C was examined in 0.6 M NaCl and in deionized water. Heat treatment induced the growth of secondary phases including sigma phase, secondary austenite, and chi phase. Potentiostatic and potentiodynamic polarization revealed no significant effect of the presence of these secondary phases on the electrochemical behavior in the absence of sliding contact. Reciprocating sliding experiments revealed that material loss rates were inversely proportional to the sample hardness in deionized water as well as at 100 mVSCE in the chloride solution under potentiostatic conditions. Worn surfaces readily repassivated during experiments at 100 mVSCE, but at 600 mVSCE, with longer heat treatments, current transients increased over time and pitting was observed in and near wear tracks. Pitting was preferentially associated with secondary austenite, and material loss calculated from the current transients during pitting was much greater than that measured through surface profiling of wear tracks.