N. De Wispelaere

Corrosion properties of nickel free austenitic stainless steels in 0.5M H2SO4 and 0.5M H2SO4 plus 0.4M NaCl

Abstract The corrosion behaviour of four nickel free austenitic stainless steels were investigated in 0·5M H2SO4 and 0·5M H2SO4 plus 0·4M NaCl solutions by means of potentiodynamic and potentiostatic anodic polarisation testing. The performances of the nickel free alloys are compared to those of an experimental intermediate nickel alloy (4%Ni) and a standard AISI 304 steel grade. Once passivity was reached all alloys displayed similar current densities i p in 0·5M H2SO4, independent from alloying. Mo and Cu were shown to be beneficial in decreasing the active dissolution currents and i crit values. The commercial AISI 304 steel displayed superior resistance to pit initiation during potentiodynamic testing, and AISI 304 steel displayed the highest E pit value of all alloys tested. When tested potentiostatically the N and Mo alloyed nickel free alloys showed excellent resistance to pit initiation and growth. The dominant effect of N was associated with repassivation of incipient pits, while Mo appeared to act at an earlier stage, suppressing initiation.