Effects of Austempering and Martempering Processes on Amount of Retained Austenite in Cr-Mo Steels (FMU-226) Used in Mill Liner

The presence of retained austenite gives rise to deterioration of the wear resistance and fracture strength of Cr-Mo steels in many cases. Thus, the effects of heat treatments including direct quenching, martempering, and austempering on the retained austenite existing in the microstructure of these steels were investigated. Specimens were austenized at 950 °C followed by direct quenching using compressed and still air. The specimens were also isothermally quenched in salt bath at 200 and 300 °C for 2, 8, 30, and 120 min. Microstructures of the specimens were studied using optical microscope (traditional black and white etching as well as color etching), scanning electron microscope (SEM), microhardness tester, and X-ray diffraction (XRD). The results showed that the lowest amount of retained austenite in the microstructure was obtained in the specimens quenched isothermally at 300 °C for 120 min.