High hardness-toughness and wear resistance of white cast iron treated by a multicycle quenching-partitioning-tempering process

Based on a multicycle quenching-partitioning-tempering process, a novel process is proposed to treat Fe–2.4C–12.0Cr (mass %) white cast iron balls. It is a destabilizing heat treatment following multicycle quenching and sub-critical treatment (De-MQ-Sct) process. Such a complex process may be simply performed by alternate water quenching and air cooling. For comparison, the white cast iron balls also were treated by conventional normalization (NOR) process and oil-quenching process. The partitioning of carbon from martensite to retained austenite during the De-MQ-Sct process promotes the interaction between carbide precipitation and martensitic transformation. While this interaction is a unique effect only produced by multicycle quenching linking destabilizing and sub-critical treatments, which leads to more, and finer, secondary carbides and more carbon-enriched austenite in De-MQ-Sct sample than those in a NOR or oil-quenching sample. The average hardness of 60 HRC and impact toughness of 12.6 J/cm2 are obtained in De-MQ-Sct white cast iron balls, which are much higher than those in a NOR and oil-quenching ones. The wear behavior measured by pin-on-disk wear tests indicate that the weight loss of De-MQ-Sct sample is only about one-third of the NOR sample and one half of the oil-quenching sample. Microstructural characterization reveals that high hardness-toughness and wear resistance of the De-MQ-Sct balls are mainly attributed to the large quantities of fine secondary carbides and stable carbon-enriched retained austenite.