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对SCM440和SUJ2钢进行了高达109次循环的千兆周期疲劳试验。千兆周期疲劳性能试验结果被分成两组:由SCM440和二次熔炼SUJ2钢构成的一组显现出其疲劳强度高于由一次熔炼SUJ2钢构成的另一组。高疲劳强度组中的鱼眼状裂纹基本上起源于一种小的Al2O3夹杂物,而在低疲劳强度组中则完全起源于大的(Cr、Fe)3C夹杂。当夹杂物尺寸小于约10μm时,大体上暗光区尺寸随夹杂物尺寸下降而增加。当夹杂物尺寸超过10μm时,暗光区尺寸呈稳定状态。由于这种关系,当夹杂物尺寸非常小时,109次循环时疲劳极限与夹杂物尺寸无关。估计夹杂物尺寸在10 -20μm之间时疲劳极限便失去与夹杂物尺寸的依存性。另一方面,当夹杂物尺寸超过上述尺寸时,疲劳极限取决于夹杂物尺寸及暗光区尺寸。暗光区和大夹杂物与小夹杂物相似,其△Kth取决于裂纹尺寸的1／3次方,这意味着疲劳极限取决于暗光区尺寸和大夹杂物尺寸的-1／6次方。
Up to 109 cycles of giga cycle fatigue tests were performed on SCM440 and SUJ2 steels. The giga cycle fatigue performance test results were divided into two groups: a group consisting of SCM440 and a second-remelted SUJ2 steel showed a higher fatigue strength than the other group consisting of the first-smelled SUJ2 steel. Fish-eye fissures in the high fatigue strength group originated essentially from a small Al2O3 inclusion, whereas in the low fatigue strength group it completely originated from large (Cr, Fe) 3C inclusions. When the inclusion size is less than about 10 μm, the size of the substantially dark region increases as the size of the inclusions decreases. When the inclusion size exceeds 10μm, the dark area size is stable. Due to this relationship, the fatigue limit at 109 cycles is independent of inclusion size when the inclusion size is very small. It is estimated that the fatigue limit at inclusions between 10 and 20 μm loses dependency on the inclusion size. On the other hand, when the inclusion size exceeds the above size, the fatigue limit depends on the inclusion size and the dark area size. Dark areas and large inclusions are similar to small inclusions, and their ΔKth depends on the 1/3th power of the crack size, which means that the fatigue limit depends on the / / 6th power of the dark area size and the size of the large inclusions .