Austenitic stainless steels used in light water reactor coolant environments are susceptible to environmentally assisted fatigue due to non-monotonic loading conditions, primarily associated with load-follow, thermal transients, or intermittent plant shutdowns and start-ups. This study investigates the effects of a high-temperature pressurized water reactor (PWR) water environment and cyclic loading parameters on the low cycle fatigue behavior of austenitic 304L stainless steel. Prolonged exposure to a PWR environment and cyclic loading conditions such as a lower strain rate or a higher fraction of slow strain rate enhances the initiation and accelerates the crack growth rate of fatigue cracks, resulting in decreased fatigue life. The deformation-induced α'-martensite is observed in proximity to fatigue crack tips primarily in specimens tested in simulated PWR primary water, while cellular dislocation structures are more frequently observed near crack tips in specimens tested in high-temperature air. The deformation-induced martensitic transformation from γ-austenite to α'-martensite, occurring via the precursor ε-martensite phase, contributes to the accelerated fatigue crack growth rate in a PWR environment with hydrogen.

中文翻译：

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压水堆环境和循环加载参数对304L不锈钢低周疲劳行为的影响

用于轻水反应堆冷却剂环境的奥氏体不锈钢由于非单调负载条件（主要与负载跟踪、热瞬变或间歇性工厂关闭和启动相关）而容易受到环境辅助疲劳的影响。本研究研究了高温压水堆 (PWR) 水环境和循环加载参数对奥氏体 304L 不锈钢低周疲劳行为的影响。长时间暴露于压水堆环境和循环载荷条件（例如较低的应变率或较高比例的慢应变率）会增强疲劳裂纹的萌生并加速裂纹扩展速率，从而导致疲劳寿命缩短。变形诱发的 α'-马氏体主要在模拟压水堆原水测试的样品中观察到疲劳裂纹尖端附近，而在高温空气中测试的样品中，在裂纹尖端附近更频繁地观察到细胞位错结构。通过前体 ε-马氏体相发生的变形引起的从 γ-奥氏体到 α'-马氏体的马氏体转变有助于在含氢的压水堆环境中加速疲劳裂纹扩展速率。