# Thermally induced sensitisation of austenitic stainless steel for AGR fuel cladding

Jiang, Siben (2019). Thermally induced sensitisation of austenitic stainless steel for AGR fuel cladding. University of Birmingham. Ph.D.

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## Abstract

In this thesis, the sensitisation behaviour of thermally treated Advanced Gas-cooled Reactor (AGR) fuel cladding, a Nb stabilised 20%Cr/25%Ni austenitic stainless steel containing different silicon concentrations was investigated. Silicon bearing alloys exhibit more severe grain boundary chromium depletion during the sensitisation stage while less chromium depletion during the desensitisation stage than the silicon free alloy, and the addition of silicon decreases the time needed to reach the maximum chromium depletion. This might be because silicon increases the diffusion coefficient of chromium atom in austenitic stainless steel. The DOS values and surface morphology obtained from the DL-EPR test show that the effect of silicon on sensitisation is not evident.

After the DL-EPR test, low angle grain boundaries and coincidence site lattice $$\Sigma$$3 boundaries are found to be mostly free from attack while the majority of the random high angle grain boundaries (HAGBs) are attacked and the extent of attack depended on the magnitude of chromium depletion at the grain boundary. There exists a threshold grain boundary misorientation angle below which grain boundaries are immune to intergranular attack while grain boundaries with a misorientation higher than this angle are subject to attack and the extent of attack varies from grain boundary to grain boundary. At individual random HAGBs, the magnitude of chromium depletion is the key factor affecting sensitisation, rather than the misorientation angle. No obvious relationship is found between the extent of attack and the misorientation angle for random HAGBs.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Supervisor(s):
Supervisor(s)EmailORCID
Chiu, Yu-LungUNSPECIFIEDUNSPECIFIED
Connolly, Brian J.UNSPECIFIEDUNSPECIFIED