为保障核电管路系统安全服役，针对20钢/316不锈钢异种焊接接头，结合微区电化学测试、电子背散射衍射（EBSD）表征、扫描电子显微镜（SEM）、激光共聚焦显微镜观测及应力腐蚀开裂（SCC）试验等手段，系统研究其在110℃高温腐蚀介质中的腐蚀行为与点蚀演化规律，并探究蚀坑特性对SCC敏感性的影响。结果表明：接头20钢侧为电偶腐蚀阳极，点蚀为主要腐蚀形式，且接头腐蚀演化过程为经一次“点蚀-均匀腐蚀”腐蚀形式转变后，呈现出点蚀定向生长的腐蚀特性；各浸泡周期内点蚀坑可分为窄深型、垂直型、宽浅型三类，其纵横比是调控应力集中与临界裂纹尺寸的核心参数；378~390MPa应力工况下，高纵横比蚀坑更易诱发SCC，纵横比为0.393、0.337、0.3的蚀坑对应的临界裂纹尺寸分别为73.025μm、90.425μm、107.84μm，诱发应力腐蚀开裂的安全运行周期分别为363.5天、411天、450.5天。

To ensure the safe service of nuclear power pipeline systems, this study systematically investigates the corrosion behavior and pitting evolution mechanism of 20 steel/316 stainless steel dissimilar welded joints in a high-temperature corrosive medium at 110℃, while exploring the influence of pit characteristics on stress corrosion cracking (SCC) susceptibility. A comprehensive experimental approach was employed, including microarea electrochemical tests, EBSD characterization, SEM observation, laser scanning confocal microscopy analysis, and SCC testing. Results indicate: The 20 steel side of the joint acts as the anode in galvanic corrosion, with pitting being the dominant corrosion form. The corrosion evolution process undergoes an initial uniform corrosion stage, followed by directional growth of pitting. Pits can be classified into three types (narrow-deep, vertical, and wide-shallow) across all immersion periods. The aspect ratio of pits is identified as the core parameter regulating stress concentration and critical crack size, with pits of higher aspect ratio being more prone to inducing SCC. Under a stress condition of 378~390 MPa, the critical crack sizes corresponding to pits with aspect ratios of 0.393 (narrow-deep), 0.337 (vertical), and 0.3 (wide-shallow) are 73.025μm, 90.425μm, and 107.84μm, respectively. The safe service cycles before inducing stress corrosion cracking are 363.5 days, 411 days, and 450.5 days, respectively.