Fatigue property of an ultraclean 100Cr6 bearing steel was investigated by the high-cycle rotating bending fatigue tests. It was found that the cyclic loading below 1197 MPa led to the frequent cracking initiated from the complex inclusions with the two distinctly different features: the breaking and the debonding of complex inclusions, all of them have a core of oxide agglomerate containing many cavities and a nearly 2 μm-thick sulfide shell. Finite element simulation results reveal that this distinction depends on whether a sufficiently high residual stress (RS), which should be developed near the interface of inclusion and matrix during quenching and accumulated during the cyclic loading, can exceed the yield strength (YS) of steel matrix. Higher interfacial RS than the YS leads to the debonding of inclusion whilst lower one to the breaking of inclusion. A more uniform and thicker sulfide shell could relieve the RS to the greater extent, favoring the breaking of inclusion with longer fatigue life. Finally, we propose that the critical sizes for no fatigue crack initiated at the pure oxide, the complex inclusions with non-uniform and uniform sulfide shell are 11.2 μm, 12.8 μm and 17.0 μm respectively, and the optimum size ratio of oxide core to the entire complex inclusion is 0.56–0.76. Both are of great importance on tailoring the inclusions of ultraclean bearing steel for improving the fatigue life of bearing steel.

中文翻译：

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超洁净100Cr6轴承钢高周疲劳试验中复杂夹杂物诱发断裂机制

通过高周旋转弯曲疲劳试验研究了超洁净100Cr6轴承钢的疲劳性能。结果发现，低于1197 MPa的循环载荷导致复杂夹杂物频繁开裂，具有两种截然不同的特征：复杂夹杂物的破裂和脱粘，它们都具有含有许多空洞的氧化物团聚体的核心和近2μm厚的硫化物壳。有限元模拟结果表明，这种区别取决于足够高的残余应力（RS）是否超过钢的屈服强度（YS），该残余应力在淬火过程中夹杂物与基体界面附近应产生并在循环加载过程中积累。矩阵。界面 RS 高于 YS 会导致夹杂物脱粘，而低于 YS 则导致夹杂物破裂。更均匀、更厚的硫化物壳可以更大程度地缓解RS，有利于夹杂物的破裂，从而延长疲劳寿命。最后提出纯氧化物、不均匀和均匀硫化物壳复合夹杂物不萌生疲劳裂纹的临界尺寸分别为11.2μm、12.8μm和17.0μm，以及氧化物核与氧化物核的最佳尺寸比。整个复合夹杂物为 0.56–0.76。两者对于定制超洁净轴承钢的夹杂物、提高轴承钢的疲劳寿命都具有重要意义。