Caustic stress corrosion cracking of low alloy iron base materials

This paper report a study of stress corrosion cracking of Fe-3Ni, Fe-3Ni-0.5Mo, and Fe-3Ni-0.06P alloys in 9M NaOH. The samples were tested at 980C and at -400 mV /sub Dhg/Hgo/ under constant load. The results show that Fe-3Ni is very resistant to caustic stress corrosion and that additions of 0.5Mo degrade this resistance only slightly. However, phosphorus segregation to grain boundaries significantly impairs caustic cracking resistance. Possible mechanisms for the effect of phosphorus and molybdenum on caustic stress corrosion cracking are considered. It will also be demonstrated by comparison of these data with those obtained on low alloy steels that the presence of carbon or carbides degrades the caustic cracking resistance of iron base alloys but that small additions of vanadium and chromium have little effect. Segregated sulfur also has no effect on the cracking process