采用常规疲劳试验方法分别对400 MPa级和500 MPa级两种热轧态超细晶粒钢进行了疲劳试验，分析了这两种超细晶粒钢的疲劳性能，并研究了超细晶粒钢疲劳裂纹萌生的机制。结果表明：由于500 MPa级超细晶粒钢的晶粒尺寸相比400 MPa级钢的更细小，因此其疲劳性能优于400 MPa级钢的;在应力比R=-1、正弦波加载、循环周次基数N=5×106次的条件下，500 MPa级和400 MPa级超细晶粒钢的条件疲劳强度分别为270 MPa和220 MPa;两种超细晶粒钢的疲劳裂纹均在试样表面形核，且呈单源特征。

The fatigue tests of 400 MPa grade and 500 MPa grade two kinds of ultra-fine grained steels were carried out,and fatigue performances of these two kinds of ultra-fine grained steels,as well as mechanism of fatigue crack initiation were investigated. The results show that fatigue properties for 500 MPa grade steel were better than those of 400 MPa grade steel due to its smaller grain size. Under the conditions of stress ratio of -1,loading way of sine wave,and life cycles of 5×106,the conditional fatigue strength for 500 MPa grade and 400 MPa grade steels were 270 MPa and 220 MPa,respectively. The cracks were initiated from the surfaces of the smooth fatigue specimens which had single-fatigue origin.