Microstructure and Properties of T91/HR3C Dissimilar Joint in an Ultra-supercritical Unit

LI Junliang; LIU Fuguang; WANG Dongzhen; SONG Hai; YANG Mingchang; CHANG Zhe; SHI Zhenli; CHU Qiaoling

doi:10.3969/j.issn.1674-6457.2026.07.003

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Journal of Netshape Forming Engineering ›› 2026, Vol. 18 ›› Issue (7) : 30-40. DOI: 10.3969/j.issn.1674-6457.2026.07.003

Key Technologies for Precision Forming of High-end Energy and Aerospace Equipment Components

Microstructure and Properties of T91/HR3C Dissimilar Joint in an Ultra-supercritical Unit

LI Junliang^1,*, LIU Fuguang¹, WANG Dongzhen², SONG Hai³, YANG Mingchang³, CHANG Zhe¹, SHI Zhenli¹, CHU Qiaoling⁴

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Abstract

The work aims to systematically evaluate the safe service capability of a T91/HR3C dissimilar welded joint after approximately 101 592 h of cumulative operation in an ultra-supercritical unit, and to provide a basis for maintenance and replacement decisions. Through means such as chemical composition testing, microstructure observation, energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), and micro-Vickers hardness testing, the chemical composition, microstructure distribution, and mechanical properties of the as-serviced T91/HR3C dissimilar joint were systematically investigated. Meanwhile, numerical simulation was employed to calculate the residual stresses during the welding and post-weld heat treatment processes of the dissimilar joint. The compositions of the T91/HR3C dissimilar joint met the standard requirement. A significant difference in microstructure was observed on both sides of the dissimilar joint. Chain-like M₂₃C₆ carbides existed along the fusion line on the T91 side, FeCr phases and M₂₃C₆ carbides precipitated at grain boundaries on the HR3C side, and the nickel-based weld metal exhibited a typical cellular dendritic structure. The microhardness distribution of the dissimilar joint was rather uneven, with the highest hardness (290HV0.3-330HV0.3) in the T91 heat-affected zone (HAZ) and the lowest (170HV0.3-200HV0.3) in the HR3C HAZ. Numerical simulation of the dissimilar joint showed that the peak circumferential residual tensile stress in the as-welded joint was 790 MPa, concentrated at the interface between the HR3C HAZ and the outer wall fusion line of the T91 side; after post-weld heat treatment, the peak stress decreased to 496 MPa, but the stress concentration tendency did not fundamentally change. After approximately 101 592 h of long-term service, the T91/HR3C dissimilar joint exhibits multiple degradation features, including chain-like aggregation and coarsening of carbides, hardness fluctuation in the HAZ. It is recommended that future inspection efforts be strengthened on the T91 side of such dissimilar joints, and that manufacturing process control and in-service monitoring be enhanced in similar structures.

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LI Junliang, LIU Fuguang, WANG Dongzhen, SONG Hai, YANG Mingchang, CHANG Zhe, SHI Zhenli, CHU Qiaoling. Microstructure and Properties of T91/HR3C Dissimilar Joint in an Ultra-supercritical Unit[J]. Journal of Netshape Forming Engineering. 2026, 18(7): 30-40 https://doi.org/10.3969/j.issn.1674-6457.2026.07.003

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Funding

China Huaneng Group Science and Technology Project (TN-25-TZK51); Special Plan for Serving Local Development of Shaanxi Provincial Department of Education (24JC064)