The influence of Laves phase in the microstructure on the creep strength of a modified 9Cr-1Mo tempered ferritic steel, F91, is investigated in this research. Through additional aging heat treatment up to 5000 h, a pronounced increase of Mo-rich Laves phase is found around Cr-rich carbide M23C6, which is pinned on the prior-austenite grain boundaries and martensitic lath boundaries. This secondary precipitation hardening provided by the Laves phase is rapidly offset by its coarsening into large clusters during long-term thermal exposure and under creep conditions, leading to earlier creep rupture than the pristine material. Uniaxial constant-load creep tests are conducted on both aged and non-aged coupons under the same creep conditions. The creep rupture behavior of both materials is rationalized with the assistance of a deformation-mechanism-based true-stress creep model that was developed in the previous work. The effects of Laves phase on the creep strength of F91 are related to its influence on the well-recognized existing deformation mechanisms: dislocation glide, dislocation climb, and grain boundary sliding.

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Keywords Creep, Deformation-mechanism-based model, Heat treatment, Laves phase, Modified 9Cr-1Mo steel
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Journal Materials Science and Engineering A
Zhang, X.Z. (X. Z.), Wu, X.J. (X. J.), Liu, R. (R.), Liu, J, & Yao, M.X. (M. X.). (2017). Influence of Laves phase on creep strength of modified 9Cr-1Mo steel. Materials Science and Engineering A, 706, 279–286. doi:10.1016/j.msea.2017.08.111