Due to the coarse grain microstructure and low hardness of ductile cast iron (DCI), this material is unable to meet the performance requirements of bearing structural materials. To obtain ultra-fine-grained and ultra-hardened DCI, the influence of a cyclic quenching treatment on the evolution process and properties of DCI after three cycles of quenching at 860 °C for 30 min was investigated through morphology and grain-size characterization, X-ray diffraction analysis, and mechanical-property determination of DCI. It was found that the microstructure and performance depended strongly on the process of the cyclic quenching. With an increasing number of cycles, the grain size of austenite was significantly refined from 41.2 to 12.3 μm, and the length and width of lath/plate martensite, as well as the lath and twins, are decreased. In the meantime, the morphology of retained austenite changed from blocky to granular, together with the stability increased. The experimental sample obtained a performance with a hardness higher than 60 HRC after cyclic quenching treatment due to the refined grain size and increased dislocation density.

由于球墨铸铁（DCI）的晶粒组织粗大、硬度低，这种材料无法满足轴承结构材料的性能要求。为了获得超细晶超硬化DCI，通过形貌和晶粒尺寸表征，研究了循环淬火处理对DCI在860℃淬火3次循环30 min后演变过程和性能的影响， X 射线衍射分析和 DCI 的机械性能测定。发现显微组织和性能强烈依赖于循环淬火的过程。随着循环次数的增加，奥氏体晶粒尺寸由41.2μm显着细化至12.3μm，板条/板条马氏体的长度和宽度以及板条和孪晶都减小。同时，残余奥氏体的形貌由块状变为粒状，稳定性提高。由于晶粒细化和位错密度增加，实验样品在循环淬火处理后获得了硬度高于60 HRC的性能。