Microstructure refinement of hypereutectic high Cr cast irons using hard carbide-forming elements for improved wear resistance

Abstract

Hypereutectic high Cr cast irons (HCCIs) possess high resistance to wear, benefiting from their high volume fraction of hard carbides. However, the primary carbides are usually coarse, rendering the materials less tough and thus negatively influencing their resistance to wear, especially when impact force is involved. Refining the microstructure of hypereutectic HCCIs has been demonstrated an effective approach to improve the performance of HCCIs during wear processes. Previously we demonstrated that adding Ti to a hypereutectic HCCI resulted in the formation of fine TiC, which consumed carbon and thus shifted the carbon concentration in the remaining liquid to one corresponding to the eutectic state. As a result, microstructure of the HCCI was refined without the formation of primary carbides while still retaining high volume fraction of carbides. The wear resistance of the modified HCCI was markedly improved. In the present work, we added several other carbide-forming elements, V, Nb, B, and Mo, to a hypereutectic HCCI, respectively, and evaluated the effectiveness of each element in improving the wear resistance of the HCCI. The amount of each added element was adjusted in order to have the HCCI in slightly hypereutectic, eutectic, and hypoeutectic states, respectively. Optimal ranges of the added elements were thus determined based on the degree of microstructure refinement and corresponding wear resistance. Microstructure characterization was carried out using scanning electron microscopy, energy dispersive X-ray spectrometry, and X-ray diffraction technique. Micromechanical properties and wear resistance were evaluated using micro-indenter and pin-on-disc tester, respectively.