应用显微硬度计对高周疲劳不同循环周次下正火45钢光滑圆试样进行了表面显微硬度测量。使用数理统计的方法对显微硬度测试值进行了处理。研究结果表明，不同疲劳阶段，试样表面显微硬度测试值呈正态分布，显微硬度方差在整个疲劳过程中始终呈现较大的离散性。在三级应力水平下显微硬度统计均值随循环周数的不同变化规律基本相同，表现出明显的阶段性，即显微硬度先升高，后下降，再上升并逐渐趋于稳定，其中在寿命的20%~30%阶段是一个活跃时期。随着应力水平的提高，表面硬度达到稳定状态所需时间有缩短趋势。疲劳后期，随着应力水平的提高，试样表面显微硬度有明显降低。

The microhardness on the surface of normalized 45 steel smooth sample was measured using micro Vickers under different cycle number during high cycle fatigue. The measured values of microhardness were calculated using mathematical statistic method. The results showed that in different fatigue stages the measured values of microhardness obey normal probability distribution and the variances of microhardness present certain degree dispersivity. Under different stress level the statistical means of microhardness appear to increase, then decreasing and slowly increasing, the 20%~30% stage of fatigue life is an active time. In the later fatigue life, along with the stress level enhancement, the surface microhardness of sample reduce obviously.