Effect of carbon on corrosion and passivation of iron in hot concentrated NaOH solution in relation to caustic stress corrosion cracking

Quenched Fe-C materials with up to 0.875 wt.% C were examined in 8.5 M NaOH at 100 degrees C to better understand the effect of carbon on caustic stress corrosion cracking (SCC) of plain steels. Carbon at contents up to about 0.23 wt.% C accelerated anodic dissolution of iron, whereas at high contents it hindered corrosion and promoted the formation of magnetite. It is suggested that carbon particles on the corroding surface form confined regions with an increased concentration of H(+) and HFeO(2)(-), thereby favouring the formation of Fe(3)O(4). Intergranular SCC can be explained by preferred anodic dissolution of grain boundary material enriched in carbon. (C) 2009 Elsevier Ltd. All rights reserved.