Effect of N, Mo, and Si on Local Corrosion Resistance of Unstabilized Cr–Ni and Cr–Mn–Ni Austenitic Steels

Features of the effect of both individual and combined alloying with nitrogen, molybdenum and silicon of unstabilized cold-worked and heat-treated austenitic Cr–Ni and Cr–Mn–Ni steels on pitting and intercrystalline corrosion (ICC) resistance in weakly oxidizing media are studied. On the basis of corrosion and electrochemical test results (electrochemical method), an ambiguous effect of alloying cold worked Cr–Mn–Ni steels with nitrogen and molybdenum on pitting corrosion resistance is revealed. It is established that a necessary condition for intergranular corrosion resistance of chromium-nickel steels after prolonged tempering at 550–750°C is the presence of silicon in addition to nitrogen and molybdenum, which participates in improving the passivity of chromium-depleted boundary zones. Silicon added to nitrogen-containing steel alloyed with molybdenum and 0.03 wt.% carbon with a balanced content of Cr, N, Mo and Si facilitates an improvement of passivity for boundary zones impoverished in chromium. Introduction of silicon into nitrogen-containing chromium-nickel steel (0.03% C) alloyed with molybdenum with a balanced content of Cr, Ni, Mo, and Si makes its ICC resistance equal to specially low-alloy stainless steel containing 0.003% C.