Effects of ageing conditions on the precipitates evolution, chromium depletion and intergranular corrosion susceptibility of AISI 316L: experimental and modeling results

Chromium carbides and intermetallic phases which form in industrial AISI 316L stainless steel during ageing for up to 80 000 h between 550 and 650 °C were identified by combining transmission electron microscopy (TEM) thin foil imaging and electron diffraction and used to establish the time–temperature–precipitation (TTP) diagram. Following the precipitation phenomena, the chemical changes in the grain boundary region were determined by energy-dispersive X-ray microprobe analysis using a scanning transmission electron microscope (STEM). From the experimentally determined chromium profiles the chromium depleted zones were quantified. The interactions between carbide precipitation involving chromium depletion and intergranular corrosion (IGC) were clearly visible from superposition of TTP diagrams and time–temperature–sensitization (TTS) diagrams obtained from ASTM standardized tests. In addition, an experimental criterion to sensitization–desensitization phenomenon was established. Moreover, an analytical model has been developed in this study and successfully validated to predict the profiles of chromium depleted zones. This model coupled with the previously described criterion provides TTS diagrams in good agreement with experimental results.