Abstract
The corrosion behaviour of the austenitic alloy Fe-24Mn-7Cr-3Al in various aqueous solutions with pH between −0·8 and 15·3 and the corrosion protection mechanism imparted by the presence of chromium and aluminium were investigated using electrochemical measurements, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The anodic passivity of Fe-24Mn-7Cr-3Al in 1M Na2S04. 10–50%HNO3 and 10–50%NaOH aqueous solutions was, in each case, superior to that of Fe-25Mn-3Al, Fe-30Mn-9Al, and 9%Ni cryogenic steel and approximated to that for 1Cr13 (0·1%C) stainless steel. None of the alloys showed passivation in either 3·5%NaCl or 10%HCl solution. The passive film formed on the surface of Fe-24Mn-7Cr-3Al alloy in 1M Na2SO4 consisted of hydroxide, Cr2O3, Al2O3, and oxides of iron and manganese and the subsurface of the passive film formed in 50%HNO3 was enriched in chromium and aluminium. Consequently, it is reasonable to state that the corrosion resistance of Fe-24Mn-7Cr-3Al is provided mainly by a thin barrier film of Cr2O3. Al2O3, and Fe2O3.
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