超超临界锅炉再热器12Cr1MoVG管焊缝失效研究-中国材料进展

文章信息/Info

Title:: Failure Mechanism of 12Cr1MoVG Tubes from Reheater in an Ultra-Supercritical Boiler

作者:: 范志东1; 都劲松1; 张志博1; 田进2; 马翼超1; 牛坤1; 郭卫铨1; 刘承鑫1; 1，西安热工研究院有限公司 2，西安交通大学金属材料强度国家重点实验室

Author(s):: FAN Zhidong1; DU Jingsong1; ZHANG Zhibo1; TIAN Jin2; MA Yichao1; NIU Kun1; GUO Weiquan1; LIU Chengxin1; (1Xian Thermal Power Research Institute Co., Ltd., (2State Key Laboratory for Mechanical Behavior of Materials, Xian Jiaotong University,

摘要:: 通过显微组织分析、化学成分分析、裂纹形貌观察和焊接工艺分析，对某超超临界锅炉再热器小径厚壁管12Cr1MoVG钢焊缝接头裂纹进行了失效分析。结果表明：裂纹沿周向分布，起始于焊缝的热影响区粗晶区，向细晶区扩展，并呈沿晶扩展特征；在裂纹区域可见宏观裂纹、微裂纹和孔洞。根据裂纹产生的位置和形貌、焊缝显微组织等特征，确定该裂纹为焊接再热裂纹。失效原因为焊缝焊接质量差：焊缝各区域硬度值均超过标准规范范围上限值，表明焊缝内有较大的残余应力；焊缝晶粒粗大，导致晶粒间变形协调性大幅降低。

Abstract:: For any plant, it is very important to generate electricity without forced outages. Failure of boiler tubes is the major concern of forced outages at the coalfired thermal power plant, especially at ultra-supercritical units. 12Cr1MoV steel has been widely used as tubes in the ultra-supercritical boiler. Cause of the failed reheater tube joint of 12Cr1MoVG steel was studied by chemical composition test, microstructure analysis, crack morphology observation，joint structure, hardness, and welding qualities analysis. The results show that the crack initiated from coarse grain heat affect zone (HAZ) along with the circumferential distribution, and propagated along grain boundaries. There are macrocracks，microcracks and voids in the cracking region．According to the microstructure，position，process and fractography analyses of the cracks，it is concluded to be the weld reheat cracking. The failure of the tube is mainly due to bad welding quality, characterized by high residual stress, coarsened grain size, and so on. Formation of intergranular cavity and microcrack is shortened by high residual stress and is easier due to plastic-deformation disharmony between coarse grains.