In this study, the effect of microstructure on crack nucleation and microstructurally short fatigue crack growth is investigated for a metastable austenitic stainless steel. Fatigue tests were conducted at an intermediate fatigue life regime between 10⁴ and 10⁶ cycles such that martensitic phase transformation occurs given sufficient localized deformation. Through the use of scanning electron microscopy, along with electron backscatter diffraction, several micro-cracks were analyzed and compared. The influence of microstructural features such as twin boundaries, slip band intrusions/extrusions, grain boundaries, inclusions, and martensitic transformed areas on the crack initiation life is discussed. The initiation stages of crack nucleation and the subsequent microstructurally short crack growth for each microstructural feature are compared revealing that twin boundaries and slip bands are the most dominant initiation features. However, the initiation mechanism governing crack nucleation for each feature was different. Additionally, the phase transformation behavior showed only minor effects on the microstructurally short crack growth leading up to an engineering crack. It was found that while the cracks that propagated more quickly had larger transformed martensitic zones around the crack tip, this was due mostly to the size of the crack. Interestingly, the initiation life in the transitional fatigue regime was observed to be more sensitive to crack initiation feature than the martensitic transformation.

在这项研究中，研究了亚稳奥氏体不锈钢的微观结构对裂纹形核和微观结构短时疲劳裂纹扩展的影响。疲劳测试是在10 ⁴到10 ⁶的中等疲劳寿命范围内进行的在足够的局部变形的情况下发生马氏体相变的循环。通过使用扫描电子显微镜以及电子反向散射衍射，对几个微裂纹进行了分析和比较。讨论了微观结构特征，如孪晶边界，滑带侵入/挤压，晶粒边界，夹杂物和马氏体相变区，对裂纹萌生寿命的影响。比较了每个成微结构特征的裂纹成核起始阶段和随后的微结构短裂纹扩展，发现孪晶边界和滑移带是最主要的起始特征。但是，控制每个特征的裂纹成核的引发机制是不同的。此外，相变行为仅对微观结构的短裂纹扩展产生微小影响，最终导致工程裂纹。结果发现，虽然裂纹扩展得更快，但裂纹尖端周围的马氏体相变区更大，这主要是由于裂纹的大小所致。有趣的是，与马氏体相变相比，在过渡疲劳状态下的萌生寿命对裂纹萌生特征更敏感。