屏式过热器异种钢焊接接头失效分析  

Failure Analysis of Dissimilar Steel Welding Joints of Platen Superheater

作　　者：刘东明 宁玉恒 张书媛 蒋涛 LIU Dongming;NING Yuheng;ZHANG Liyuan;JIANG Tao(Datang Northeast Electric Power Test ＆ Research Institute, Changchun 130012, China;Guodian Jilin Longhua Changchun Thermal Power Plant, Changchun 130012, China)

机构地区：[1]大唐东北电力试验研究所有限公司,吉林长春130012 [2]国电吉林龙华长春热电一厂,吉林长春130012

出　　处：《热加工工艺》2018年第19期258-262,共5页Hot Working Technology

摘　　要：某电厂前屏过热器管与限位块的异种钢焊接接头在运行期间发生泄露失效,利用电子探针、光学显微镜、显微硬度计及扫描电镜等手段对过热器管、限位块以及接头熔合区进行化学成分、显微组织、显微硬度、断口形貌分析。结果表明：过热器管侧熔合区出现增碳层,熔合区组织为类马氏体,且出现σ相脆化,导致熔合区显微硬度高,脆性大,且熔合区为结构上的应力集中点,在热应力长期作用下导致熔合区起裂;随着锅炉的起停以及管内介质温度、压力的变化使得裂纹进一步向管内扩展,其断口特征呈现似河滩条带;当管道承载能力低于管内介质压强时管道则泄漏失效。The leaking appeared at the dissimilar steel welding joints between the pre-screen superheater tube and limited block during running in a power plant. The chemical composition, microstructure, microhardness, fracture morphology of the superheater tube, limited block and fusion zone of the welded joint were studied by means of electron probe microscope analysis（EPMA）, optical microscope（OM）, microhardness tester and scanning electron microscope. The results show that the carburized zone appears at the fusion zone near the superheater tube, and the microstructure of the fusion zone is martensite-like and the brittleness of σ phase appears, which causes the high microhardness and brittleness of the fusion zone.Meanwile, the fusion zone is stress concentration zone in the structure, and the crarcks initiate under thermal stress in long time. The start and stop of the boiler and the change of temperature and pressure of the medium in pipe makes crack extend to the inside of the pipeline. And it＇s fracture characteristics are similar to the beach belt. Finally, the leaking appears when the pipeline carrying capacity is lower than the tube medium pressure.

关 键 词：过热器 限位块 异种钢 焊接接头 失效分析 

分 类 号：TG404[金属学及工艺—焊接]