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

Abstract

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 V_{Silver 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.