Preferential dissolution behaviour of the austenite phase in Fe-27Cr-xC high chromium cast iron.

Preferential dissolution behaviour of the austenite (γ) phase in Fe-27Cr-xC high chromium cast irons (HCCIs) immersed in 0.1 mol dm-3 H2SO4 + 0.05 mol dm-3 HCl was investigated. Potentiodynamic and potentiostatic polarisation revealed that the primary and eutectic γ phases dissolved preferentially at -0.35 and 0.00 VSilver Silverchloride Electrode potential in sat. KCl (SSE), respectively. The immersion of the HCCIs in the solution showed that the dissolution of the primary γ phase dominated for ca. 1 h, while the primary and eutectic γ phases dissolved after ca. 1 h. However, the carbide phases remained undissolved during the dissolution of the γ phases. Furthermore, the corrosion rate of the HCCIs increased with the increasing C content owing to the increase in the contact potential difference values of the γ and carbide phases. The change in electromotive force due to C addition was related to the accelerated corrosion rate of the γ phases.