Abstract
Behavior of stressed Type 304 steel in H2SO4 solutions with addition of cyanide or thiocyanate has been studied in view of the reported strong adsorption characteristics of the latter spiecies and their tendency to cause embrittlement in carbon steel. Type 304 wire annealed was examined at 353 K in 1 to 4 kmol/m3 H2SO4 solutions with additions of different quantities of KCN, NH4SCN, or NaN3(pseudohalides) mainly under open circuit conditions at a stress of 275 MPa.
With increased additions of KCN or NH4SCN the attack morphology changed from heavy general corrosion to cracking or localized attack and the time-to-failure was prolonged. This is similar to a previously reported behavior of Type 304 in H2SO4 solutions with halide. KCN was a cathodic and anodic inhibitor and NH4SCN was a cathodic inhibitor. The latter was also an anodic inhibitor at and near the open circuit potential. H2S gas evolution from the solution containing NH4SCN was detected suggesting the role of hydrogen in cracking mechanism, as in the case of KCN. In the solutions containing NaN3 Type 304 did not fail due to passivation resulting from the cathodic reaction stimulated by NaN3 or failed by general corrosion at the small additions of NaN3.
