Heat Treatment Optimisation of Electron Beam Welded Reactor Pressure Vessel Steels (Advanced Metallic Systems CDT)

Electron beam welding (EBW) is a promising method for joining together massive steel forgings to create nuclear pressure vessels. EBW is an autogeneous welding process, in that it does not use a filler metal, instead involving the melting of the two parent materials themselves to create the joint. This means that it should be possible, in theory, to make the weld ‘disappear’ given a suitable heat treatment schedule after welding – the composition of the steel across the weld region should be the same as anywhere else in the forging, so re-austenitising and quenching the welded vessel should result in a homogeneous microstructure. ‘Removal’ of the weld in this way is highly advantageous for manufacturers, since it no longer becomes necessary to inspect the joints (or this can be done far less frequently).

Nevertheless, the capability to make the weld ‘disappear’ needs to be demonstrated in practice and there are phenomena that could prove problematic. For instance, it is unclear whether there is preferential evaporation of particular alloying elements during the welding, which would change the composition of material in the weld region leading to inhomogeneous microstructure and properties. It is also unclear whether the austenite grain size achieved during post-weld austenitisation will be the same in the parent and the weld regions, due to the difference in starting microstructure.

The PhD project will aim to determine whether ‘disappearing’ the weld is possible using post-weld heat treatments. It will utilise a combination of advanced characterisation techniques (dilatometry, X-ray diffraction, scanning electron microscopy, electron-probe microanalysis), alongside thermodynamic and kinetic modelling of phase transformation behaviour, to investigate the effects of heat treatment on parent and weld material. It will involve close collaboration with Rolls-Royce plc (the industrial sponsor).

Advanced Metallic Systems Centre for Doctoral Training
The Advanced Metallic Systems CDT is a 4 year programme hosted jointly by the universities of Manchester and Sheffield building on their complimentary expertise and international reputations in materials science and engineering research. In year 1, students from a range of disciplinary backgrounds undertake taught courses in core materials topics. PhD research begins after 6 months. Our transferable skills and personal development programme leads to a Diploma in Professional Skills. Visit our website for more information www.metallicsCDT.co.uk.