The effect of carbide volume fraction on the low stress abrasion resistance of high Cr-Mo white cast irons

High chromium white cast irons display a number of advantages in abrasive wear applications. Their composition may be adjusted so that they contain moderate amounts of chromium yet solidify to produce massive chromium-rich carbides in an austenitic matrix of sufficient hardenability to be transformed to martensite with relatively simple heat treatment. In this study the role of carbide volume fraction (CVF) in developing abrasion resistance was investigated using a series of alloys with varying CVF but with constant matrix and carbide compositions. The low stress abrasion resistance of the alloys against quartz and Al 2O 3 was measured with a dry abrasive rubber wheel abrasion test. The abrasion resistance passed through a maximum at an intermediate CVF, near the eutectic composition, for the softer quartz, while the abrasion resistance increased monotonically with the CVF for tests against the harder Al 2O 3. Scanning electron microscopy showed that for quartz abrasion the reversal in the trend of wear versus CVF which occurred at the eutectic composition was caused by spalling and pitting of the massive primary M 7C 3 carbides in the hypereutectic alloys. This phenomenon did not occur in the Al 2O 3 abrasive tests, in which a monotonic increase in wear resistance with CVF was observed.