Special aspects of localized corrosion processes on austenitic steel at elevated temperatures

As widely known austenitic stainless steels are very sensitive against local corrosion processes especially in environments containing chloride ions and at elevated temperatures. For the understanding of the mechanisms and the kinetics os such local damage processes the complex correlation between the bulk and surface state of the steel, the properties of the environmental medium, the temperature, and the conditions of mechanical loading has to be taken into account. In this contribution results concerning the activation-passivation behaviour of type AISI 321 steel for temperatures below 270 deg. C are presented in relation to the appearing corrosion modes. Depending on temperature three different modes of localized corrosion are observed in 1.10-2 m NaCl solution. The dependence of these modes on mechanical loading conditions and on present copper ions is investigated. These conditions are important in stationary phases of operation of steam generators in pressurized water reactors. In addition, the temperature-dependent mechanisms of crack propagation and their kinetics are considered. 13 refs, 16 figs, 1 tab