汽车用高强度弹簧钢54SiCrV6和54SiCr6 的超高周疲劳行为

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，两种弹簧钢的疲劳破坏均起源于表面基体；而在低应力幅长寿命区，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10^9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聚集引起的，而在54SiCr6钢中则起源于碳化物的偏聚．临界夹杂物尺寸的估算表明，当高强弹簧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．

VERY HIGH CYCLE FATIGUE BEHAVIOR OF 1800MPa CLASS AUTOMOTIVE SPRING STEEL

Ultra high cycle fatigue behaviors of 54SiCrV6 and 54SiCr6 clear high strength spring steels were investigated and their fractographs were observed by means of field emission scanning electron microscope (FESEM) and electron probe microanalyzer (EPMA). Experimental results show that for the two steels, the fatigue failures originated from the matrix of sample surface 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 the fatigue limit eliminated in 109 cyc regime, however, the fatigue limit of 54SiCr6 steel still existed. Analysis of fractographs shows that the internal failure initiated at clusters of small inclusions for 54SiCrV6 steel or at carbides for 54SiCr6 steel. An estimation of critical inclusion size shows that in 109 cycles regime, the fatigue limit eliminated when inclusion (or inclusion clusters) size is greater than a critical size in high strength steel.