The effects of environment (in air and 3.5 wt% NaCl solution) and artificially-induced surface scratches are investigated on the fatigue properties of railway EA4T (also called 25CrMo4) alloy steel. This steel is found to be markedly sensitive to the chloride-containing environment, with cracking at stresses two thirds of the in-air fatigue limit (+/−326 MPa) under rotating bending (Wöhler) tests. The scratched specimens show even shorter lifetime at stresses below 300 MPa and no fatigue limit is found down to 100 MPa. The fracture surfaces are characterized by the initiation of cracks from multiple sources and intergranular cracking. The fatigue failure of smooth specimens tends to initiate from localized corrosion pitting, while the corrosive environment facilitates crack initiation without pitting for scratched specimens. The fatigue crack growth rate in NaCl solution is slightly higher than that in air. Within the framework of defect-tolerant design, El-Haddad modified Kitagawa-Takahashi (KT) diagrams are constructed to explore the variation in fatigue strength and the defect assessment for both conditions. The modified KT model, which takes the short crack behavior into account, is in better agreement with the experimental results than the original KT diagrams.

研究了环境（在空气和3.5 wt％的NaCl溶液中）和人为引起的表面刮擦对铁路EA4T（也称为25CrMo4）合金钢的疲劳性能的影响。发现该钢对含氯化物环境非常敏感，在旋转弯曲（Wöhler）测试中，应力在空气疲劳极限（+/- 326 MPa）的三分之二时开裂。刮擦的样品在低于300 MPa的应力下显示出更短的使用寿命，并且在100 MPa以下都没有疲劳极限。断裂表面的特征是来自多个来源的裂纹的产生和晶间裂纹。光滑试样的疲劳破坏往往是由局部腐蚀点蚀引起的，而腐蚀环境促进了裂纹的萌生，而没有划痕的试样被腐蚀。NaCl溶液中的疲劳裂纹扩展速率略高于空气中的疲劳裂纹扩展速率。在容错设计的框架内，构造了El-Haddad修改的Kitagawa-Takahashi（KT）图，以探索两种条件下疲劳强度的变化和缺陷评估。修改后的KT模型考虑了短裂纹行为，与原始KT图相比，与实验结果更加吻合。