Influence of Cr/C Ratio on Cooling Curve Characteristics, Microstructure, Mechanical Properties, and Corrosion Performance of High-Chrome Cast Iron

Abstract

High-chromium cast irons (HCCIs) are widely used in industries requiring superior wear and corrosion resistance, such as mining, petrochemical, and milling operations. The performance of these alloys is primarily dictated by their Cr/C ratio, which influences carbide formation, size, shape, and distribution within the microstructure. Despite extensive research on HCCIs, knowledge gaps remain regarding the combined effects of the Cr/C ratio and heat treatment on microstructure evolution, mechanical properties, wear resistance, and corrosion behaviour. This study investigates the influence of the Cr/C ratio and heat treatment on the microstructural characteristics of Cr24 HCCIs, with a focus on their hardness, toughness, wear resistance, and corrosion performance. Three different compositions were cast with varying C content and subjected to microstructural analysis using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Hardness testing was performed using Vickers and Brinell methods, while wear behaviour was evaluated through pin-on-disc tribometer tests. Corrosion resistance was assessed using potentiodynamic polarisation testing in acidic (0.5M H₂SO₄), neutral chloride (3.5wt.% NaCl), and alkaline (0.5M NaOH) solutions. The findings reveal that a higher Cr/C ratio produces a finer, more uniformly distributed carbide network, while a lower Cr/C ratio results in larger, more interconnected carbides. Hardness and wear resistance increased with higher carbide volume, but excessive carbide coarsening led to higher wear rates due to three-body abrasion. Heat treatment improved fracture toughness but did not significantly enhance wear or corrosion resistance, as expected. The treatment, designed for Cr28 alloys, led to excessive secondary carbide precipitation, which depleted matrix chromium, reducing passive film stability and increasing corrosion susceptibility in aggressive environments. In corrosion testing, chloride and acidic solutions attacked carbide-matrix interfaces, accelerating localised corrosion, whereas alkaline environments led to selective carbide dissolution. A homogeneous carbide distribution improved corrosion resistance by supporting a stable passive film, while large, interconnected carbides promoted material degradation. The study confirms that optimising the Cr/C ratio, carbide morphology, and heat treatment parameters is essential to achieve the best balance between hardness, wear resistance, toughness, and corrosion resistance. These findings provide valuable insights into microstructural tailoring strategies for improving the durability of HCCIs in industrial applications.