VERY HIGH CYCLE FATIGUE BEHAVIOR OF 1800MPa CLASS AUTOMOTIVE SPRING STEEL
汽车用高强度弹簧钢54SiCrV6和54SiCr6 的超高周疲劳行为

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.