Abstract
The aim of this study was to determine optimum conditions of the DL EPR test in order to evaluate the highest values of the degree of sensitization (DOS) of a forged austenitic stainless steel type 316L, evaluated by the ratio Ir/Ia or Qr/Qa in %. The criteria of sensitization to the IGC corresponds to Ir/Ia >1% and Qr/Qa >1%. A model using a full factorial design has been established and the selected factors were the sweep rate (dE/dt), sulphuric acid concentration (H2SO4), ammonium thiocyanate concentration (NH4SCN) and temperature in °C. A first order model is obtained by using 24 full factorial design. An experimental test carried out using a factorial design 24 indicated that all the factors and their interactions have a positive effect on the response Ir/Ia. Furthermore, the highest value detected of Ir/Ia was found to be 65,6 %. On the other hand, a microstructural study based on optical microscope and Scanning Transmission Electron Microscope (STEM), have been carried out for annealed and aged samples (550°C-80 000 h). The profiles of chromium, nickel and molybdenum concentration established by X-ray microanalysis in STEM, confirm a decrease of content of these elements leading to the formation of Cr-depleted zones responsible of the sensitization to the IGC.