Cyclic deformation and fracture behavior of a type 316 LN austenitic stainless steel (SS) weld joint (WJ) were investigated under thermomechanical fatigue (TMF) and isothermal low cycle fatigue (IF) cycling at the maximum temperature (T_max) of TMF. A higher cyclic stress response (CSR) and reduced cyclic softening were observed under TMF compared with IF tests. In-phase (IP) TMF resulted in lower lives compared with IF cycling at the T_max and out-of-phase (OP) TMF, which was attributed to the more pronounced creep-induced intergranular damage. Characterization of microstructural features and microhardness variations revealed that the accumulation of damage and associated failure depends on the strength and microstructural gradient, together with the deformation incompatibility. The crack propagation is found to depend on the individual and synergistic interactions of the microstructural transformations, creep, and oxidation, depending on the type of fatigue cycle (IF and IP/OP TMF), strain amplitude, and thermal cycling effects.

中文翻译：

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对 AISI 316 型 LN SS 焊接接头热机械疲劳行为的新见解

在热机械疲劳 (TMF) 和等温低周疲劳 (IF) 循环下，在TMF的最高温度 ( T _max ) 下研究了 316 LN 型奥氏体不锈钢 (SS) 焊接接头 (WJ) 的循环变形和断裂行为。与 IF 测试相比，在 TMF 下观察到更高的循环应力响应 (CSR) 和减少的循环软化。与T _max下的 IF 循环相比，同相 (IP) TMF 导致更低的寿命和异相 (OP) TMF，这归因于更明显的蠕变引起的晶间损伤。微观结构特征和显微硬度变化的表征表明，损伤的积累和相关失效取决于强度和微观结构梯度，以及变形不相容性。发现裂纹扩展取决于微观结构转变、蠕变和氧化的单独和协同相互作用，取决于疲劳循环的类型（IF 和 IP/OP TMF）、应变幅度和热循环效应。