等温淬火球墨铸铁（ADI）作为一种性能优良的新型工程材料，已在曲轴、齿轮和铁路车轮等机械结构中得到应用。目前，研究者对其抗磨损性能研究较多，但是对其疲劳性能特别是超高周疲劳性能的研究尚显不足。本研究选用化学成分相同而石墨球尺寸不同的两种球墨铸铁坯料，经过不同的等温淬火工艺处理，分别获得三种强度等级的ADI材料，然后使用常规频率疲劳试验机开展10^4-10^9周次的超高周疲劳试验，明确ADI材料的超高周疲劳破坏行为和S-N曲线特性，研究微观组织和石墨球尺寸对ADI材料超高周疲劳行为和性能的影响，仿真分析内部裂纹萌生和扩展过程，最终揭示ADI材料的超高周疲劳破坏机理。本研究不仅为新型ADI材料的研发和性能优化提供理论指导、为ADI构件的选材和设计提供依据，还可为符合我国国情的ADI材料标准的制定奠定基础。

The austempered ductile iron (ADI) is a new kind of engineering material with good properties and it has been applied to such machine components as crankshafts, gears and railway wheels. Now, the study on the anti-wear properties of it has been carried out a lot, while the research on the fatigue property, especially the gigacycle fatigue perperty, has not been conducted in detail.In this study, two kinds of ductile cast iron blanks with the same chemical compositions and different graphite nodule sizes are to be treated by the austempering treatments to obtain ADI with three strength grades, respectivly. The gigacycle fatigue tests (10^4-10^9 cycles) are to be conducted by conventional fatigue machine. The fatigue fracture behaviors, the characteristics of S-N curve including gigacycle regime and the influence of microstructure and graphite nodule size on fatigue behaviors and properties will be investigated. The internal crack initiation and porpagation progress are to be simulated and the fracture mechanism of ADI in gigacycle regime will be revealed.This study can supply information for new ADI development and optimization of ADI property, material selecting and design for ADI components. Besides, it can lay a foundation for establishment of the ADI standard satisfying the situation in China.