Microstructure and corrosion behaviour aging at 750 °C in 25% Cr duplex stainless steel

Abstract

This work concerns the effect of solution temperature on the microstructure and corrosion property aged at 750 °C in 25% Cr duplex stainless steel (DDS). The evolution of microstructure and phase compositions were studied by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Precipitation of sigma phase initially occurred rapidly aging for 80 min, subsequently became slower with further aging for 330 min corresponding to the decomposition of δ-ferrite. The precipitation of sigma phase was suppressed by increasing solution temperature from 1060 to 1230 °C. The EDS analysis combined with microstructure evolution indicates an increase of sigma phase precipitation is attributed to the decrease of δ/γ interfaces and Cr concentration in the ferrite. The potentiodynamic anodic polarization test confirms that the transition from metastable pitting to stable pitting occurs easily for aging at 750 °C due to more precipitation of sigma phase, the better resistance to pitting corrosion was attributed to higher solution temperature in initial high temperature aging.