Abstract
This investigation was conducted because the development of new alloys with increased resistance to pitting corrosion appears to be largely dependent on an understanding of the effects of various concentrations of alloying elements on the initiation and steady operation of localized pitting sites on the metal surface.
Corrosion tests in 0.5N FeCl3 and determinations of passivity breakdown potentials in 0.1 N NaCl were employed to study the pitting tendencies of 18 Cr-14Ni stainless steels to which alloying elements in various concentrations had been added. The alloying elements, chosen for their stability in solutions containing chloride ions and their solubility in austenite, were: Mo, Si, V, W, Ti, Ce, Nb, Ta, Zr and Re.
Mo, Si and V, respectively, at 5 percent concentration, had the most marked effect in increasing resistance to pitting. Re, even in concentrations below 1 percent, was also very effective. The other elements tested had either a negative influence or no effect.
Heat treatment in the dangerous temperature zone (650 C for 2 hours) greatly impaired the resistance of steel alloyed with 5 percent Mo, Si or V, which is not susceptible to pitting corrosion in the quenched state.
