温度对动车组车轮钢服役次生疲劳裂纹起裂扩展特性影响

高速动车组车轮材料在严酷服役温度条件下的抗疲劳裂纹起裂与扩展能力是制定车轮合理维修周期和进行服役寿命评估的基础。选用高速动车组用ER8C车轮钢作为研究对象，对其在-60~60 ℃服役温度范围内进行了应力疲劳试验及疲劳失效机制探讨。结果表明：随着测试温度的升高，轮辋、轮辐材料疲劳寿命均呈现出显著缩短趋势；在较高的服役温度条件下，试样出现了半椭圆形的次生疲劳裂纹起裂扩展形貌特征，且由于轮辋与轮辐不同位置材料强度韧性的差异，使得产生次生疲劳裂纹起裂扩展形貌特征所对应的温度条件不同，对于轮辋材料，当试验温度升高到50 ℃时，试样开始产生次生疲劳裂纹，而对于轮辐材料，当试验温度升高到30 ℃时，试样便开始产生次生疲劳裂纹；通过对主次生疲劳裂纹的扩展特性比较分析可知，随着应力强度因子幅值的增大，材料微观薄弱区域由珠光体片层层间转变为珠光体团晶粒边界。

Effects of Temperature on Secondary Fatigue Crack Initiation and Growth Behavior of High-speed Railway Wheel Steels

School of Mechanical Engineering,Southwest Jiaotong University,Chengdu，610031 For high-speed railway wheel steels under severe service temperature conditions, fatigue crack initiation and growth behavior are important for planning maintenance interval and assessing residual lifetime. Fatigue tests were conducted under -60~60 ℃ test conditions for ER8C high-speed railway wheel steels and fracture morphologies were observed. The results show that the fatigue lifetime decreases as the temperature increases for both of wheel rim and web steels. Secondary fatigue crack initiation and growth area with shape of half ellipse exists under high testing temperature conditions. Furthermore, for wheel rim and web, the generation temperatures of secondary fatigue crack initiation and growth areas are different due to the diversity of steel strength and toughness, for wheel rim，this critical temperature is 50 ℃ while it is 30 ℃ for wheel web. Based on the comparison of growth characteristics between the main and secondary cracks, it may be concluded that the weak area changes from pearlite lamella to grain boundary of pearlite colony as the stress intensity factor range increases.