Evaluation of silicon effects on abrasion performance, microstructure and crystalline structure of NiHard-4 white cast iron using synchrotron X-ray diffraction

NiHard-4 is a class of abrasion-resistant white cast iron widely used in mining ore-handling operations. It has a multi-component microstructure consisting of eutectic carbides and metallic matrix, both of which can influence abrasion performance. This work investigates the influence of silicon concentration on abrasion performance, microstructure and crystalline structure. Abrasion was assessed by dry sand rubber wheel abrasion test (DS-RWAT), inner circumference abrasion test (ICAT) with quartzite, and ICAT with basalt. Abrasion performance trends were explained in terms of microstructure and crystallographic evolution, using SEM, macro-hardness, micro-hardness and nano-hardness measurements, cryogenic treatment and synchrotron X-ray diffraction (XRD). As Si content increases, duplex (M3C + M7C3) eutectic carbides are replaced with homogeneous M7C3 carbides, the latter confirmed to have significantly higher hardness. However, contrary to suggestions from literature that Si should enhance abrasion resistance, the tests found that elevated Si in NiHard-4 leads to inferior performance. In the metallic matrix, increased Si results in lower hardness, which synchrotron XRD indicates is due to reduction of dissolved carbon concentration in the austenite. It is demonstrated that the detrimental effects of Si on the matrix outweigh any beneficial effect that it may have on the eutectic carbides, leading to net inferior abrasion performance.