Effect of Cr:Fe ratio on the mechanical properties of (Cr,Fe)7C3 ternary carbides in abrasion-resistant white cast irons

• Published in: Journal of materials science 2023-05, Vol.58 (17), p.7504-7521
• Main Authors: Jokari-Sheshdeh, Maziar, Ali, Yahia, Gallo, Santiago Corujeira, Lin, Weikang, Gates, J. D.
• Format: Article
• Language: English
• Subjects: Abrasion resistant alloys; Alloys; Anisotropy; Bulk modulus; Carbides; Cast iron; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chromium; Classical Mechanics; Composition; Crystal structure; Crystallography and Scattering Methods; Deformation; Density functional theory; Ductility; Fracture toughness; Hardness; Materials Science; Mechanical properties; Metals & Corrosion; Modulus of elasticity; Morphology; Nanoindentation; Polymer Sciences; Solid Mechanics; Strain hardening
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-023-08461-z

(Cr,Fe) 7 C 3 ternary carbides constitute the majority of eutectic carbides in abrasion-resistant white cast irons. Density functional theory models have predicted these carbides to have a combination of metallic, covalent and ionic bonding, in proportions depending on the carbide’s Cr:Fe ratio. However, experimental research to validate these predictions has been lacking. This study investigates the characteristics of the carbides as a function of Cr:Fe ratio, which was manipulated from Fe-rich to Cr-rich by varying the Cr:C ratio of the bulk alloy. The carbides’ crystalline structure, hardness, Young’s modulus, fracture toughness and abrasion performance have been assessed through techniques including nano-indentation, HR-TEM and the inner circumference abrasion test (ICAT). Fe-rich M 3 C formed at very low bulk Cr:C ratio was found to have an orthorhombic crystal structure. In all other alloys, with Cr:C ratios above 2.7, M 7 C 3 was formed and found to have a hexagonal structure. Hardness, Young’s modulus and calculated fracture toughness of M 7 C 3 all increase with Cr:Fe ratio, from (Fe 5 ,Cr 2 )C 3 up to a maximum for (Cr 4 ,Fe 3 )C 3 (in 18Cr–6.8Cr:C WCI). This gave the highest hardness (22.9 GPa) and Young’s modulus (315 GPa), but also the highest fracture toughness (4.5 MPa.m0.5). The peak fracture toughness at carbide composition of (Cr 4 ,Fe 3 )C 3 in this study is consistent with the prediction of DFT models in the literature; while the peak hardness at the same carbide composition shows a marginal deviation from the predictions. Abrasion performance generally increased with carbide hardness and fracture toughness, with one exception: (Cr 4.3 ,Fe 2.7 )C 3 . Although (Cr 4.3 ,Fe 2.7 )C 3 showed marginally lower inherent fracture toughness than (Cr 4.0 ,Fe 3.0 )C 3 , the higher Cr:Fe carbides imparted the highest abrasion performance, associated with modified eutectic morphology.