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

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 microstructure
The 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.

The EPSRC Centre for Doctoral Training in Advanced Metallic Systems was established to address the metallurgical skills
gap, highlighted in several reports [1-3] as a threat to the competitiveness of UK industry, by training non-materials
graduates from chemistry, physics and engineering in a multidisciplinary environment. Although we will have supplied ~140
highly capable metallurgical scientists and engineers into industry and academia by the end of our existing programme,
there remains a demonstrable need for doctoral-level training to continue and evolve to meet future industry needs. We
therefore propose to train a further 14 UK based PhD and EngD students per cohort as well as 5 Irish students per
cohort through I-Form.

Manufacturing contributes over 10% of UK GVA with the metals sector contributing 12% of this (£10.7BN [4,5]) and
employing ~230,000 people directly and 750,000 indirectly. It is estimated that ~2300 graduates are required annually to
meet present and future growth [5]. A sizeable portion of these graduates will require metallurgical expertise and current
numbers fall far short. From UK-wide HESA data, we estimate there are ~330 home UG/PGT qualifiers in materials and
~35 home doctoral graduates in metallurgy annually, including existing AMSCDT graduates, so it is unsurprising that
industry continues to report difficulties in recruiting staff with the required specialist metallurgical knowledge and
professional competencies.

As well as addressing this shortfall, the CDT will also impact directly on the companies with which it collaborates, on the
wider high value manufacturing sector and on the UK economy as a whole, as follows:

1. Collaborating companies, across a wide range of businesses in the supply chain including SMEs and research
organisations will benefit directly from the CDT through:

- Targeted projects in direct support of their business and its future development and competitiveness.
- Access to the expertise and facilities of the host institutions.
- Involvement in the training of the next generation of potential employees with advanced technical and leadership skills
who can add value to their organisations.

2. The UK High-Value Manufacturing Community will benefit as the CDT will:

- Develop the underpinning science and advanced-level knowledge base required by future high technology areas, where
there is high expectation of gross added value.
- Provide an enhanced route to exploitation, by covering the full spectrum of technology readiness levels.
- Ensure dissemination of knowledge to the sector, through student-led SME consultancy projects, the National Student
Conference in Metallic Materials and industry events.

3. The wider UK economy will benefit as the CDT will:

- Promote materials science and engineering and encourage future generations to enter the field, through outreach
activities developed by the students that will increase public awareness of the discipline and its contribution to modern
life, and highlight its importance to future innovation and technologies.
- Develop and exploit new technologies and products which will help to maintain a competitive UK advanced
manufacturing sector, ensure an internationally competitive and balanced UK economy for future generations and
contribute to technical challenges in key societal issues such as energy and sustainability.

References:
1. Materials UK Structural Materials Report 2009
2. EPSRC Materials International Review 2008
3. EPSRC Materially Better Call 2013
4. The state of engineering, Engineering UK 2017
5. Vision 2030: The UK Metals Industry's New Strategic Approach, Metals Forum