The evolution of microstructure and toughness in multipass welds that contain acicular ferrite.

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This project involves a fundamental study on the toughness of multipass steel welds. Weld toughness is of vital importance to structures and components across a wide range of industries, including the construction sector, the wind energy sector, thermal power generation, and in petrochemical industries. The term "toughness" refers to the ability of a material to absorb energy prior to fracture. Toughness is particularly important in resisting the propagation of cracks and avoiding sudden failures. In safety-critical applications such as those that arise in the nuclear industry, the safe operation of components such as the reactor pressure vessel or a steam generator strongly depends on the toughness of welded joints. The successful candidate for this post will be involved in the manufacture of weld test pieces, the coordination of mechanical testing on the welds, and detailed microstructural characterisation through electron microscopy. At least two different weld filler materials will be chosen for investigation on the basis that they are under consideration for industrial application. As part of the research, some microstructural analysis may also be carried out on steel test pieces for which the chemical composition (i.e. the concentrations of C, Mn, Cr, Mo, Ni, Cu, Ti, O) has been carefully and systematically varied, in order to gain insights and understanding that could lead to the design of a new filler material. The focus of the microscopy and the overall research project will be to develop a deep understanding of the following:- The factors that control the formation of acicular ferrite during a single weld pass, since the presence of acicular ferrite is associated with excellent weld toughness;- The phases that form when acicular ferrite is reheated by subsequent thermal cycles;- The factors that influence the apparent toughness of acicular ferrite after it has transformed into other microphases (due to subsequent thermal cycles in a multipass weld).- The influence of heat input and welding conditions on the weld metal microstructureThe work will involve both optical and scanning electron microscopy (OM/SEM), as well electron probe micro-analysis (EPMA), and both energy- and wavelength-dispersive spectroscopy (EDS/WDS). The successful candidate can expect to emerge as an expert in the welding metallurgy of steels, and as an expert electron microscopist. The combination of skills that will be developed in this project will provide an ideal platform for a number of different career options after the PhD programme.