Microstructure and Failure Analysis of TP347H/T91 Dissimilar Steel Welded Piping

• Published in: Journal of failure analysis and prevention Vol. 22; no. 2; pp. 578 - 586
• Main Authors: Miao, Keji, Liu, Jianfeng, Yin, Yangyang, Wang, Ting, Sun, Ge, Liu, Chuanhuai, Shen, Li, Ji, Dongmei, Pan, Weiguo
• Format: Journal Article
• Language: English
• Published: Materials Park Springer Nature B.V 01.04.2022
• Subjects: Creep (materials); Delta ferrite; Dissimilar material joining; Dissimilar metals; Failure analysis; Filler metals; Grain growth; Heat affected zone; Heat resistant steels; Holes; Martensitic stainless steels; Microstructure; Weld metal; Welded joints
• ISSN: 1547-7029; 1864-1245
• DOI: 10.1007/s11668-022-01349-1

This paper investigated the microstructure and failure reason of the TP347H/T91 dissimilar steel welded joints using Ni-based filler metal under ultra-supercritical condition. There was a large amount of carbide precipitation and δ-ferrite phase around the microstructure of T91 heat-affected zone. Carbon elements migrated from T91 to the weld and TP347H side during operation. Columnar grain growth was observed in the weld metal near the interface and extends across the interface to the TP347H side. With the extension of operation time, the microstructure of T91 gradually degenerated, and the deposition around the tissue increased. The creep cavity was formed due to the inconsistent deformation between the secondary particles and the matrix under the action of load. The average temperature of T91 was 6 °C higher than that of TP347H, and the peak stress was located in the fine-grain heat influence zone of T91. The cavities were easier to nucleate and expand in the T91 fine-grain heat-affected zone, which led to the formation of a type IV crack making welding joint happened early failure.