选用40Cr结构钢,分别在空气、水和3.5%NaCl水溶液中进行旋转弯曲疲劳实验,研究环境介质对该结构钢高周和超高周疲劳特性的影响.结果表明,40Cr钢在水环境中的疲劳强度比在空气中明显降低;在3.5%NaCl水溶液环境中的疲劳强度比在水中低.断面观察显示,在水和3.5%NaCl水溶液中,疲劳裂纹多源萌生;在稳态扩展阶段,裂纹沿晶界扩展并存在广泛分布的沿晶二次裂纹.
Very-high cycle fatigue of metallic materials is commonly regarded as fatigue failure occurs at stress levels below conventional fatigue limit and the relevant fatigue lives are above 10^7 cyc. Rotary bending fatigue tests for a structural steel 40Cr were performed in laboratory air, fresh water and 3.5%NaCl aqueous solution, respectively, to investigate the influence of environmental media on fatigue behaviors of the steel in high cycle and very-high-cycle fatigue regimes. The results show that the fatigue strength of the steel in water is remarkably degraded compared with that in air, and the fatigue strength in 3.5%NaCl solution is even lower than that in water. The fracture surface observations show that for the specimens tested in water and 3.5%NaCl solution, multiple crack originations exist and cracks propagate along grain boundary with widespread secondary cracks in their steady propagation period.