Axially loaded cyclic tests of a precipitation-hardened martensitic steel at different stress ratios in 3% NaCl solution and steam environment were conducted up to very high cycle fatigue regime. In-depth fracture surface observation, quantitative characterization of microstructural damage, and theoretical modeling were carried out to illustrate the physics and mechanics of micro-defect induced interior cracking. Results showed apparent environmental effect on fatigue strength and crack initiation morphology. The fine granular area was observed for the first time in environmental media, heterogeneously distributed around micro-defect, and was found dependent on local fracture mode with a less probability in the case of faceted failure. The formation of fine granular area was confirmed as a result of microstructural damage with significant contribution from cyclic stress amplitude, and could be assisted by hydrogen speeding up lath martensites breakdown. A chemo-mechanical model of interior cracking was finally established based on the concept of interaction of inclusion, matrix, and environment induced plasticity. All these underpin a general fatigue damage law in micro-defects assessment for long-life structural integrity.

在 3% NaCl 溶液和蒸汽环境中以不同应力比对沉淀硬化马氏体钢进行轴向载荷循环试验，直至达到非常高的循环疲劳状态。进行了深入的断口观察、微观结构损伤的定量表征和理论建模，以说明微缺陷引起的内部裂纹的物理和力学。结果表明，环境对疲劳强度和裂纹萌生形态有明显的影响。首次在环境介质中观察到细颗粒区域，在微缺陷周围不均匀分布，并且在小面失效的情况下发现依赖于局部断裂模式，概率较小。基于夹杂物、基体和环境诱导塑性相互作用的概念，最终建立了内部开裂的化学力学模型。所有这些都为长寿命结构完整性的微缺陷评估中的一般疲劳损伤规律奠定了基础。