超超临界锅炉高温再热器T91/HR3C异种钢接头失效分析

在超超临界火电机组锅炉受热面管的高温段有许多异种钢接头,其焊接质量及性能直接影响机组的安全运行.对某3 033 t/h超超临界锅炉高温再热器T91/HR3C异种钢接头的失效试样进行了宏/微观分析.研究表明,失效部位在T91侧热影响区,裂纹沿管子周向分布,从外壁粗晶粒热影响区启裂,终止于细晶粒热影响区.焊后热处理不充分,T91侧热影响区组织不稳定和硬度高是异种钢接头失效的主要原因,建议再次进行焊后热处理以改善接头性能和消除焊接应力.此外,研究发现T91侧熔合线附近形成白亮的低硬度δ-铁素体,其对接头失效虽无直接影响,但对接头长期性能的影响需要进一步评估.

Failure Analysis of T91/HR3C Dissimilar Steel Welded Joints in High-Temperature Reheater of USC Boilers

Many dissimilar steel joints are used in the high-temperature section of boiler heating surface tubes of uhra-supereritical （USC） thermal power units and their welding quality and performance directly determines the operation security of the units. Macroscopic and microscopic examinations on the failure specimen of T91/HR3C dissimilar steel welded joints are conducted for the high-temperature reheater in a 3 033-t/h USC boiler. The results show that the failure part is located in the heat affected zone of T91 side with the cracks spreading along the circumferential direction of the tubes, starting from the CGHAZ and ending at the FGHAZ of the outer wall. The insufficient post-welding heat treatment, unstable microstrueture in the HAZ and high hardness are the major causes leading to the cracking failure. Post-welding heat treatment （PWHT） is suggested to improve the ductility and reduce the residual stress for the welded joints. Furthermore, the delta ferritc of lower hardness white and bright is observed near the fusion line of T91 side, It is not directly related to the failure, but further study is required to evaluate its influence on the long-term peffmnanee of the welded joints.