Stress-corrosion cracking of low-alloyed chromium steels in nitrate media

The stress-corrosion cracking (SCC) behaviour of a low-alloy (0.07% C-2.0% Cr) steel in nitrate media (5M NH4NO3) has been studied using the slow strain rate method in combination with potential sweep measurements, metallographic microscopy and SEM observations. It is found that the steel undergoes intergranular SCC in ammonium nitrate media with pH 1 to 7 and temperature above 50 °C in a wide potential range (-1,0 up to +0.8 V, SCE). The highest susceptibility to SCC, however, occurs at potentials in the region of active to passive transition of the steel. The low alloying with Cr, although with a favourable effect on SCC resistance, does not change significantly the SCC behaviour of low-carbon steels in hot nitrate environments.