Temperature dependence of pitting potentials for austenitic stainless steels above their critical pitting temperature

Fitting potentials of austenitic stainless steels decrease slowly with increasing temperature above the critical pitting temperature. Fitting potentials have been measured in 1 M NaCl for 304, 316 and 904L stainless steels between 20 and 90 degrees C, and narrow diameter artificial pit electrodes of 302 stainless steel have been used to study dissolution kinetics over the same temperature range. The transition potential, E-T, between activation/ohmic control and diffusion control of the dissolution has been mapped as functions of limiting current density and temperature, and the results interpreted using a simple model of dissolution kinetics within the pit. The dependence of E-T on temperature is strikingly similar to the dependence of the pitting potential, and the model has been used to differentiate between the contributions of activation and solution resistance overpotentials; the observed effects are due mostly to a decrease in the activation overpotential with increasing temperature. (C) 1998 Elsevier Science Ltd. All rights reserved.