Comparing the abrasion performance of NiHard-4 and high-Cr-Mo white cast irons: The effects of chemical composition and microstructure

NiHard-4 and high-Cr-Mo white cast irons are two classes of abrasion-resistant cast irons extensively utilized in mining and related industries. Despite widespread usage, systematic performance comparisons between the two classes are lacking. Using four exemplar NiHard-4 and four exemplar high-Cr-Mo WCIs, this study compares the abrasive wear performance of the two alloy classes under a variety of conditions. The wear tests were the dry sand rubber wheel abrasion test (DS-RWAT), inner circumference abrasion test (ICAT) with quartzite, and ICAT with basalt. The resulting quantitative trends were interpreted and explained using bulk hardness, microhardness and nanohardness measurements, coupled with SEM of microstructures and worn surfaces. In all three abrasion tests the average wear life of high-Cr-Mo WCI was superior to NiHard-4. Average life improvements were 20% in DS-RWAT, 77% in ICAT-quartzite and 124% in ICAT-basalt. In the DS-RWAT there was overlap in the data and the difference between the two alloy classes was not statistically significant, but in the ICAT, for both rock types the two classes were strongly differentiated. Of various hypotheses considered to explain the results, the experimental evidence required that differences in carbide volume fraction or matrix hardness must be rejected. Instead it was shown that the superior performance of high-Cr-Mo WCIs was due primarily to their higher Cr:C ratio, resulting in higher Cr:Fe ratio and therefore elevated hardness and fracture toughness of the eutectic carbides.