Influence of titanium addition on pitting, crevice and intergranular corrosion resistance of type 316 austenitic stainless steel

Pitting crevice and intergranular corrosion resistances of titanium-modified low-carbon austenitic stainless steel with a nominal composition of 15% Cr, 15% Ni, 0.24% Ti and 2.5% Mo were found superior to conventional type 316 SS. Potentiodynamic anodic polarization studies in a neutral chloride medium (0.5M NaCl solution) and the immersion studies in boiling solution containing (by wt%) 11% H2SO4 + 3% HCl + 1% CuCl2 + 1% FeCl3 for 24 h showed higher critical pitting and crevice potentials and lower corrosion rate values respectively. The elemental composition across the pit sites was also determined by EPMA analysis. Sensitization studies carried out by following ASTM A262 practices A and E and electrochemical potentiokinetic reactivation (EPR) tests on this alloy heat treated at 923 K for 1 and 50 h showed a better resistance to intergranular corrosion than that for conventional type 316 SS. From the results available, the most likely reason for the improvement in the localized corrosion resistance of this modified alloy appears to be due to the presence of titanium in solid solution, which could be assisting the formation of a highly stable passive film with resistance against pitting and crevice corrosion attack, and delaying the formation of M23C6 carbide by its higher carbide forming tendency to avoid sensitization. (author). 22 refs., 4 figs., 4 tabs