车轮作为高铁列车的关键零部件，在高速行驶过程中，承受循环载荷作用，其疲劳性能直接影响列车服役寿命和整车行驶安全。同时，为了满足高速铁路经济高效运行，需要在确保安全的前提下延长维修间隔、优减维修范围。为了实现该目标，首先需要对车轮钢材料的高周和超高周疲劳性能进行测试，以这些数据作为依据，实现车轮修程修制的优化。
基于以上背景，本文针对高铁车轮钢轮辋、辐板的疲劳强度，超声疲劳实验温升引起的微结构演化，疲劳裂纹萌生方式以及竞争关系，疲劳裂纹萌生机理几个方面展开研究。主要关注两个关键科学问题：短间歇加载导致的温升对高铁车轮钢微结构演化的影响；基体起裂的超高周疲劳裂纹萌生机理。
针对高铁车轮钢超高周疲劳性能研究不充分的问题，通过对轮辋、辐板试样进行一系列超声疲劳实验，确定了轮辋、辐板的疲劳强度，并从显微结构层面解释了两者疲劳强度不同的原因；其次，通过对高周和超高周疲劳断口的观察，对高铁车轮钢疲劳裂纹萌生方式进行了分类，并分别对轮辋、辐板裂纹萌生倾向性进行了统计分析；另外，对裂纹萌生特征区尺寸进行了统计分析。
通过对短间歇（50 ms）加载的疲劳失效试样的EBSD表征，对比分析了从断口表面沿剖面深度的微结构差异，从晶粒尺寸、晶粒取向、晶界角度、几何必须位错密度和织构强度等角度分析了温升带来的微结构演化，并测量了显微硬度，分析了不连续动态再结晶的发生。
针对基体起裂这一超高周疲劳裂纹萌生方式，计算了裂纹萌生区刻面处铁素体各晶粒中各滑移系的Schmid因子，从此角度分析各滑移系滑移难易程度，从而得出了基于滑移的裂纹萌生机理；另外，分析了片状珠光体中铁素体发生塑性变形程度大的原因，得出了刻面的形成与片层珠光体中铁素体-渗碳体的排列方向密切相关。
本文研究了高铁车轮典型部位（轮辋与辐板）的疲劳行为，包括室温与温升下的疲劳强度变化以及微结构演化；从应力强度因子幅值的角度分析了夹杂物起裂、基体起裂两种裂纹萌生方式之间的竞争关系；还重点讨论了基体起裂这一严重威胁高铁车轮疲劳性能的裂纹萌生方式，为优化高铁车轮、延长维修周期提供指导。

As a key part of high-speed train, the wheel bears cyclic loading in the process of high-speed driving. Therefore, the fatigue property of wheel steel directly affects the safety and service life of the train. Furthermore, in order to meet the economic and efficient operation of high-speed railway, the maintenance interval of wheels should be extended while ensuring its safety. In order to achieve this goal, it is necessary to conduct fatigue test to obtain the high-cycle and very-high-cycle fatigue strength of wheel steel first, and then realize the optimization of wheel repair program based on these fatigue data.
In this thesis, the researches on the fatigue strength of rim and web plate, self-heating induced microstructure evolution during ultrasonic fatigue test, different fatigue crack initiation modes and competition relationship between them, and mechanism of fatigue crack initiation were conducted. It mainly focuses on two key academic issues: the effect of self-heating as a result of short-time loading intermittence on microstructure evolution; the mechanism of matrix induced fatigue crack initiation.
With regard to insufficient research on very-high-cycle fatigue performance of high-speed rail wheel steel, ultrasonic fatigue tests were carried out on the rim and web plate samples to determine the fatigue strength of them. The reasons for the different fatigue strength were explained from the microstructure level. Then, the initiation modes of fatigue cracks were classified through the fractographic analysis, and the respective crack initiation tendencies of rim and web plate were statistically analyzed. In addition, the size of the characteristic area of crack initiation was also analyzed statistically.
Microstructure of the sample failing under 50 ms loading intermittence was characterized by EBSD. The microstructural difference of different depths of longitudinal section was analyzed, from the perspective of grain size, grain orientation, grain boundary, geometrically necessary dislocation density and intensity of texture. Besides, microhardness along the section was also measured. Finally, the occurrence of discontinuous dynamic recrystallization was demonstrated.
To investigate the mechanism of matrix induced crack initiation, Schmid Factors of all slip systems of ferrite grains beneath the facet were calculated, which is helpful to decide slip system activation. Besides, the reason why ferrite within lamellar pearlite experiences more significant plastic deformation than the block one was analyzed. The relationship between facet formation and ferrite-cementite alignment was also determined.
In this thesis, the fatigue performance of rim and web plate was studied, including different fatigue strength under ambient and self-heating temperature. The competing relationship between inclusion and matrix induced crack initiation was discussed from the angle of the amplitude of stress intensity factor. The mechanism of matrix induced crack initiation was proposed, which will provide beneficial effects on optimizing of wheel steel and extending of maintenance interval.