Influence of Cr/C ratio on microstructure and corrosion of hypoeutectic high chrome cast irons

Abstract

The paper investigates how the Cr/C ratio influences microstructure and corrosion behaviour of hypoeutectic high-chromium cast irons (HCCIs) in 3.5 wt% NaCl, 0.5 M NaOH and 0.5 M H 2 SO 4 . Three alloys; P1 (Cr/C = 12.13, 26.3% carbides), P2 (8.62, 37.3%) and P3 (8.06, 42.9%) were evaluated based on carbide size, morphology and distribution. Open-circuit potential and potentiodynamic polarisation corrosion tests were performed on the samples. In NaCl, P3 showed the most severe corrosion due to micro-galvanic effects from coarse, interconnected carbides and limited Cr available for passivation. In NaOH, P1 corroded the most due to rapid carbide dissolution and insufficient sustained Cr release for passive film growth. In H 2 SO 4 , P3 suffered the greatest attack, driven by galvanic interactions and unstable film formation. Heat treatment refined carbide distribution and promoted secondary carbide precipitation. These changes improved corrosion resistance in neutral media but increased it in acidic and alkaline. These results show that Cr/C ratio and carbide control are key to optimising HCCI corrosion resistance.