STRESS-CORROSION CRACKING OF INCONEL-600 IN AQUEOUS-SOLUTIONS AT ELEVATED-TEMPERATURE .2. EFFECT OF CHLORIDE AND SULFATE-IONS ON THE ELECTROCHEMICAL-BEHAVIOR OF INCONEL-600

The influencing effects of temperature, potential and electrolyte comp osition on the electrochemical behaviour of Inconel 600 in aqueous sol utions are presented. Considering these effects the connection between the data have been obtained from chemo-mechanical fracture investigat ion on CT-samples in Part I of this paper and pitting corrosion are di scussed. The results have shown that chloride ions depassivate the sur faces of cracks locally and hinder the formation of a new protective o xide layer on the fracture surfaces. Furthermore, chloride promotes th e dissolution of metal and initiates the cracking, respectively. The r esulting crevice corrosion promotes an increase of hydrogen absorption by the metal. The increase of the hydrogen content of the metal influ ences the mechanical fracture behaviour. Contrary, sulphate ions inhib it the initiation of corrosion mainly due to a hinderance of chloride ions adsorption on active sites of the fracture surfaces. The initiati on of localized corrosion in the crevice region may be stimulated by c hromate ions formed by oxidation of chromium from the oxide layer or t he base metal in oxygen containing solutions.