The high and very high cycle fatigue (VHCF) properties of ultrahigh-strength Ck45M steel processed by thermomechanical rolling integrated direct quenching were investigated. S–N tests with smooth and small drilled holes containing specimens as well as near-threshold fatigue crack growth measurements were performed up to 2 × 10¹⁰ cycles using ultrasonic-fatigue testing technique. The fatigue strength of smooth specimens is mainly determined by the size of nonmetallic inclusions. For surface defects larger than 80 μm, the fatigue limit can be correlated with a constant threshold-stress intensity factor. The -parameter model adequately predicts the fatigue limit for internal defects and for surface defects with sizes between 30 and 80 μm. VHCF failures from smaller surface defects occur at stress amplitudes below the predicted fatigue limit. The long-crack threshold in ambient air is close to the effective threshold stress intensity factor. In optically dark areas at interior inclusions, cracks grow at mean propagation rates of 10⁻¹⁵ m/cycles.

中文翻译：

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细小缺陷和非金属夹杂物对超高强钢高周疲劳强度和超高周疲劳强度的影响

研究了热机械轧制整体直接淬火处理的超高强度Ck45M钢的高周疲劳和甚高周疲劳(VHCF)性能。 使用超声波疲劳测试技术对包含试样的光滑和小孔进行S-N测试以及近阈值疲劳裂纹扩展测量，最多可进行 2 × 10 ¹⁰次循环。光滑试样的疲劳强度主要由非金属夹杂物的大小决定。对于大于 80 μm 的表面缺陷，疲劳极限可以与恒定的阈值应力强度因子相关联。这-参数模型充分预测了内部缺陷和尺寸在 30 到 80 μm 之间的表面缺陷的疲劳极限。由较小表面缺陷引起的 VHCF 失效发生在低于预测疲劳极限的应力幅度下。环境空气中的长裂纹阈值接近有效阈值应力强度因子。在内部夹杂物的光学暗区，裂纹以10 ^-15  m/周期的平均传播速率增长。