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螺栓是机械领域广泛应用的机械零件。采用20 k Hz超声波疲劳振动试验机对高强度大螺栓钢(U20S i2钢)进行疲劳测试,并观察其试样的疲劳断口形貌,分析其疲劳失效机理。结果表明,U20S i2钢在超高周(≥107)阶段的疲劳起裂以内部非夹杂起裂为主。非夹杂起裂主要发生在粗大的软相组织(贝氏体)处。提出应从控制夹杂物和改善内部组织两方面着手,避免高强度大螺栓钢的超高周疲劳失效。
Bolts are widely used mechanical parts in the mechanical field. The fatigue test of the high strength large bolt steel (U20S i2 steel) was carried out with a 20 k Hz ultrasonic fatigue vibration tester. The fatigue fracture appearance of the sample was observed and the fatigue failure mechanism was analyzed. The results show that the fatigue initiation of U20S i2 steel during the ultrahigh-cycle (≥107) stage is dominated by internal non-inclusion fracture. Unincorporated rupture occurs mainly in the coarse soft tissue (bainite). It is proposed that the control of inclusions and internal organization should be improved from both the high strength large bolt steel to avoid ultra-high cycle fatigue failure.