Description
This project aims to develop a mechanistic understanding of the oxidation and simultaneous carburisation in type 316H austenitic stainless steel under Advanced Gas- cooled Reactor (AGR) service conditions, and subsequently their impact on the creep mechanics at 550 °C of pre-carburised creep specimens. Sections of the boiler pipework in the AGRs are fabricated from type 316H austenitic stainless steel and are exposed to high temperatures (480-650 °C) and pressurised (4.14 MPa) gaseous primary coolant mixture of CO2/CO. The remaining life of these boiler components is restricted by their tolerance to creep and resistance to environmental degradation mechanisms i.e. oxidation and carburisation. In this project, two 316H austenitic stainless steel casts, differing in the Mn content, were first exposed to simulated AGR service conditions at 550 or 600 °C, inducing the simultaneous formation of oxide and carburised layers. The results revealed a limited amount of atomic carbon in solid solution within the austenite lattice, whereas the excess carbon precipitates as M23C6 carbides. The local diffusion of substitutional solutes (i.e. Cr) is the rate-controlling step for carburisation. Furthermore, the creep behaviour at 550 °C of the pre-carburised specimens was influenced by the cracking of embrittled, carburised grain boundaries and by the modified local material properties of the near-surface carburised layer. The formation of ferrite grains in the carburised layer was also detected, with the ferrite fraction increasing with creep strain, indicative of a strain relief mechanism locally. This work contributes to further the understanding of environment-creep interactions required for structural assessment procedures for AGRs and future Gen IV fission reactors.| Period | 1 Aug 2023 |
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| Examinee | Jack Eaton-Mckay |
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| Degree of Recognition | International |