The corrosion of NiCrMoV steel welded joints is performed in an aqueous solution of 3.5 wt% NaCl at 180 °C in a container at a pressure of 0.8 MPa. The specimens in the shape of cylindrical tensile rods are immersed in the aqueous solution under the action of tensile stress in a range of 0 to 0.9 of the yield stress of the base metal. The experimental results suggest that there is macro-galvanic corrosion in the welded joint with the coarse-grained heat affected zone (CGHAZ) as anode due to the highest corrosion susceptibility of the CGHAZ. The CGHAZ has the highest positive current density in the welded joints as measured by the scanning vibrating electrode technique. The two-parameter Weibull distribution function, which is represented by the Weibull modulus and characteristic strength, is used to analyze the distribution of the depth of pits at different immersion times. Both the Weibull modulus and characteristic strength are calculated, and found to be dependent on the applied tensile stress. The values of the characteristic pit depth and the average pit depth reveal that there are two mechanisms controlling the corrosion of the NiCrMoV steel welded joints; one is galvanic corrosion, and the other is stress-assisted corrosion.

中文翻译：

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由电偶和应力辅助耦合腐蚀引起的 NiCrMoV 钢焊接接头熔合线周围的坑演变

NiCrMoV钢焊接接头的腐蚀是在压力为0.8 MPa的容器中于180°C的3.5 wt% NaCl水溶液中进行的。将圆柱形拉伸棒形状的试样浸入水溶液中，在拉伸应力的作用下，拉伸应力为母材屈服应力的 0～0.9。实验结果表明，粗晶热影响区（CGHAZ）作为阳极的焊接接头存在宏观电偶腐蚀，因为CGHAZ的腐蚀敏感性最高。通过扫描振动电极技术测量，CGHAZ 在焊接接头中具有最高的正电流密度。由 Weibull 模量和特征强度表示的二参数 Weibull 分布函数，用于分析不同浸泡时间下凹坑深度的分布。计算了威布尔模量和特征强度，发现它们取决于施加的拉伸应力。特征凹坑深度和平均凹坑深度值揭示了NiCrMoV钢焊接接头腐蚀的控制机制有两种；一种是电偶腐蚀，另一种是应力辅助腐蚀。