STUDY ON THE CHARACTERISTIC OF THE SURFACE MICROHARDNESS FOR 45 STEEL DURING HIGH CYCLE FATIGUE

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.