轻水堆焊接接头的应力腐蚀开裂(SCC)是在裂纹尖端局部微观区域材料、力学和水 化学环境交互作用下的一种裂纹缓慢扩展形式，它给核电结构长期安全服役带来重大安 全隐患。以安全端异种金属焊接接头为代表的核电关键焊接结构环境致裂已成为影响压 水堆电站长期安全运行的关键问题。这种焊接接头通常是在低合金钢管嘴堆焊镍基合金 形成隔离层后，再用镍基合金焊材将安全端喷嘴与不锈钢安全端焊接在一起。异种金属 焊接接头组织和力学性能的不均匀性、几何结构的不连续性、焊接缺陷以及残余应力的 影响，给直接利用实验室数据定量预测核电异种金属焊接接头的在役寿命带来困难。为 准确分析异种金属焊接接头环境致裂裂纹尖端局部力学特征，本文完成的主要工作如下：通过国内外研究现状综述，详细探究了异种金属焊接工艺与应力腐蚀开裂机理。阐 述了异种金属焊接历史以及焊接工艺及过程；分析了常见焊接接头类型以及常见的冶金 缺陷；阐述了焊接接头中存在的应力类型以及分析应力腐蚀开裂的扩展机理。

     通过对异种金属焊接过程中碳迁移的介绍，详细阐述了核电站安全端异种金属焊接 接头中应力腐蚀开裂损伤机理，并从材料层面分析轻水反应堆中应力腐蚀开裂速率。实验和数值模拟相结合，获取了异种金属焊接接头材料的力学性能。通过疲劳拉伸 试验机和应变仪相结合，利用板状拉伸试样获取了材料力学性能，并通过有限元软件 ABAQUS 进行数值模拟建模。详细分析了不同焊接填充材料(镍基合金 625/52 等)对界面裂纹尖端力学场的影响。 重点研究在材料力学性能失配条件下，界面裂纹尖端应力应变场的分布状态，以及不同 材料力学性能对应力应变场和力学行为的影响。

本研究成果为进一步精确预测裂纹启裂和裂纹扩展速率提供理论基础。

Stress corrosion cracking (SCC) of light water reactor welded joints is a form of slow crack expansion under the interaction of material, mechanical, water and chemical environments in the local microscopic region of the crack tip, which poses a major safety hazard to the long-term safe service of nuclear power structures. Environmental cracking of critical nuclear power welding structures represented by safety end dissimilar metal welded joints has become a key issue affecting the long-term safe operation of pressurized water reactor power plants. This type of welded joint is usually formed by overlaying a nickel-based alloy on the low-alloy steel nozzle to form an isolation layer, and then welding the safety end nozzle to the stainless steel safety end with nickel-based alloy welding material. The inhomogeneity of the organization and mechanical properties of the dissimilar metal welded joint, the discontinuity of the geometric structure, welding defects, and the influence of residual stresses make it difficult to directly predict the in-service life of nuclear dissimilar metal welded joints quantitatively using laboratory data. To accurately analyze the local mechanical characteristics of the environmental cracking tip of the dissimilar metal welded joint, the main work accomplished in this thesis is as follows: Through a review of the current state of research at home and abroad, a detailed exploration of the dissimilar metal welding process and stress corrosion cracking mechanism. Explained the history of dissimilar metal welding and the welding process and process; analysis of the common types of welded joints and common metallurgical defects; description of the type of stress present in the welder's joint; and analysis of the expansion mechanism of stress corrosion cracking. Through the introduction of carbon migration during the welding of dissimilar metals, the stress corrosion cracking damage mechanism in dissimilar metal welded joints at the safety end of nuclear power plants is elaborated, and the stress corrosion cracking rate in light water reactors is analyzed from the material level.

A combination of experiments and numerical simulations to obtain the mechanical properties of the material of the heterogeneous metal welded joints. The mechanical properties of the material were obtained through a combination of a fatigue tensile testing machine and strain gauge using a plate tensile specimen and modeled by numerical simulation with the finite element software ABAQUS. Detailed analysis of the effect of different weld filler materials (nickel-based alloy 625/52, etc.) on the mechanical field of the interface crack tip. Focus on the study of the state of distribution of the stress-strain field at the tip of the interface crack under the conditions of material mechanical properties mismatch, as well as the influence of different material mechanical properties on the stress-strain field and mechanical behavior. The study results provide a theoretical basis for accurately predicting the crack initiation and crack propagation rate.

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