研究了54SiCrV6和54SiCr6两种洁净高强弹簧钢的超高周疲劳行为，并利用FESEM和EPMA对疲劳断口进行了观察。实验结果表明，在高应力幅区，两种钢的疲劳破坏均起源于表面基体，而在低应力幅区，疲劳开裂均发生在试样内部。54SiCrV6钢的S-N曲线为典型的台阶式曲线，在109循环周次内，其疲劳极限消失，而54SiCr6钢存在疲劳极限。疲劳断口分析表明，54SiCrV6钢内部破坏是由钢中小夹杂物的聚集引起的，而54SiCr6钢则起源于碳化物的偏聚。临界夹杂物尺寸的估算表明，当高强钢中的夹杂物尺寸大于临界夹杂物尺寸时，其疲劳极限消失；反之，则疲劳极限存在。
Very high cycle fatigue behaviors of 54SiCrV6 and 54SiCr6 clear high strength spring steels and the fractography observed by means of field emission scanning electron microscope (FESEM) and electron probe microanalyzer (EPMA) are investigated. Experimental results show that for two steels, fatigue failure originates from sample surface matrix at high stress amplitude and from sample interior at low stress amplitude. The S-N curve of 54SiCrV6 spring steel is a typical step-wise curve, and elimination of fatigue limit in 109 cycles regime, however, fatigue limit of 54SiCr6 steel exists. Analysis of fractography shows that internal failure initiates clusters of little inclusions in 54SiCrV6 steel and localized carbide in 54SiCr6 steel. Evaluation of critical inclusion size shows that, in 109 cycles regime, fatigue limit eliminates when inclusion size is greater than critical inclusion size in high strength steel. Contrary, fatigue limit exists.
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