700℃超超临界机组锅炉候选材料异种焊接头服役组织研究

Study on microstructure of dissimilar welded joint of candidate alloys for 700℃ ultra supercritical unit boiler in service

对700℃超超临界燃煤发电机组关键部件验证试验平台运行1万h的TG700A和HT700T的锅炉合金管异种焊接头进行取样品分析,研究了服役态焊接接头微观组织和硬度的演化。结果表明:服役后,焊缝中富Mo、Ti元素的一次碳化物稳定存在于枝晶间,熔合线两侧合金元素未发生明显的互扩散;焊接热影响区晶界碳化物发生轻微粗化,且硬度与母材相当;内壁蒸汽氧化层以氧化铬为主,热影响区与母材氧化层形貌均无差别,平均厚度约为7μm,在服役工况下属于完全抗氧化级;经过1万h服役后焊接接头的组织稳定性良好。

The weld joint of TG700A and HT700T which is used in superheater of ultra supercritical power plant boiler was studied after 10000 h service on 700℃ ultra supercritical coal-fired power unit key component verification test platform.The evolution of microstructure and microhardness of the in-service weld joint was investigated.The results show that,after being put intoservice,the Mo/Ti-rich primary carbides distributed in interdendrite,and there was no obvious inter diffusion on both sides of the fusion line.Coarsening of grain boundary carbides occurred in the heat affected zone(HAZ),and microhardness of the HAZ was consistent with the base metal.The steam oxide layer on inner wall was mainly chromium oxide,and the morphology of the HAZ was the same as that of the oxide layer of the basematerial.The average thickness of the oxide layer was about 7μm,which was excellent oxidation resistance under the service conditions.The microstructure stability of the welded joint was good after 10000 h service.