Three Ultrasonic flaw detection methods, sound check, small angle longitudinal wave method and skew probe lateral wave method, were used for detection of fatigue cracks of wheel axles for DF 4A and DF 4B diesel locomotives during medium maintenance. 中修时东风4A、4B型机车车轴疲劳裂纹的超声波探伤用三种方法:透声检查、小角度纵波探伤和斜探头横波探伤。