Intergranular Corrosion and Anodic Polarization at Grain Boundary Groove in Fe-28%Cr Alloy

Abstract

The intergranular corrosion of Fe-28%Cr alloy was studied by the corrosion test (boiling solution of 50%H₂SO₄ containing 25 g of Fe₂(SO₄)₃) and by “local” anodic polarization measurements in which only the local region near a grain boundary groove is involved in the polarization process.
On an anodic polarization curve of the grain boundary groove in the sensitized alloy, a current “halt” in the transition region from the active to the passive state was observed, which could not be observed in the anodic polarization curves in the non-sensitized alloy. The alloy was sensitized by solution heat treatment at 1100°C followed by air cooling or rapid cooling and reheating at 600°C for 10 min.
The current “halt” was shifted to a more noble potential as the corrosion resistance of the alloy became lower. The current “halt” is ascribed to the existence of a chromium depleted zone or the α and α′ two phase formation due to spinodal decomposition.
In the alloy reheated at 475°C the anodic current “halt” was always observed at −0.33 V regardless the corrosion resistance of the alloy.