ASSURE 2 - Advanced Steel Shaping Using Reduced Energy

Steel continues to be the most used material in the world by value and play an essential role in all aspects of society, from construction to transport, energy generation to food production. The UK steel industry is undergoing significant changes with changes in ownership. The long-term sustainability of UK steel making requires lower energy production and the development of high value steel products. Energy constitutes a significant portion of the cost of steel production, between 20% to 40% and, whilst the amount of energy required to produce a tonne of steel has reduced by 50% in the past 30 years through changes in steel making technologies, further improvements are necessary. Heating and reheating steel is responsible for significant energy consumption in the steel supply chain. Therefore the introduction of new processing routes to minimise or eliminate reheating stages will have a dramatic effect on energy use, and, if this is coupled with reduced hot deformation by casting to near net shape, further energy reductions can be realised.
This project is concerned with establishing the process and chemistry windows for production of conventional and advanced high strength strip (AHSS) steel grades using belt casting technology. Belt casting is a near net shape casting process, producing strip that needs minimal hot deformation to achieve the required product thickness. It is a significantly lower energy production route compared to traditional continuous casting to large sections with subsequent hot rolling, for example energy consumption could be reduced by > 3 GJ/tonne steel produced (based on savings of approx. 2 GJ/tonne from reduced hot rolling and approx. 1.25 GJ/tonne from near net shape casting). In addition belt casting allows the production of AHSS steel grades that cannot currently be manufactured using conventional processing: TWIP (twinning induced plasticity) and TRIP (transformation induced plasticity) grades have high work hardening rates meaning they cannot be rolled in current hot rolling strip mills; and low density (high Al) steels have very large grain sizes (millimeters) that result in poor processability (e.g. hot tearing during continuous casting). These steels are extremely attractive commercially, given their vastly superior properties (TWIP and TRIP steels are 2x as strong, with 3x the ductility of conventional steels, and high Al steels have a combination of good strength and lower density), which can contribute to light weighting in the automotive and construction industries.
During the ASSURE feasibility project facilities were established at WMG to allow simulation belt cast microstructures, including dynamic direct observation of the solidifying steel at different cooling rates. It was shown that the microstructures are altered by the higher cooling rate of belt casting, compared to conventional slab casting, and that further beneficial modifications (e.g. reduction in grain size in high Al steels) can be achieved by composition control. In this project (ASSURE2), quantitative relationships between composition, process parameters and microstructure (and hence final product properties) will be established, taking into account the higher cooling rates of belt casting and the reduced hot deformation after casting to final thickness compared to conventional processing. Novel new concepts, such as atmospheric control for composition modification and / or solidification temperature reduction and electromagnetic fields for microstructure refinement will also be considered. The collaboration with Professor Guthrie at McGill University in Canada, the leading expert on belt casting technology and computational modelling of liquid metal processes, will provide significant added value to the scientific studies, with the subcontract to use their pilot plant facilities, at MetSim, allowing us to consider the scale up from laboratory scientific studies to industrially relevant processing.

This project aims to assess the potential for eliminating energy intensive re-heating for hot rolling and instead directly produce strip steels using high productivity belt casting. This requires high, asymmetric cooling rates during solidification affecting the steel structure, but enables the production of novel more highly alloyed steel grades with potentially new microstructures and ways to control them.
Energy and C footprint
The elimination of re-heating will result in a reduction of 2-2.4 GJ and 110-132 kg of CO2 per tonne of steel. Considering that 5 million metric tonnes of strip steel is currently produced in the UK this will have a substantial impact nationally (full elimination of reheating would give approximately 0.15% reduction in the national CO2 emissions).
Energy Savings and Technical Benefits to UK Steel Industry and Society
The chief industrial beneficiaries are the strip steel producers, including Port Talbot (currently owned by Tata Steel UK, but up for sale). Tata Steel employs approximately 5,000 people directly in the strip businesses in Wales and produces steel products in several UK sites using continuous casting, with automotive and electrical grades as sheet steels being key products produced at Port Talbot and Cogent-Orb Steel in Newport respectively. In addition to the energy and CO2 saving noted above, the use of direct strip belt casting rather than continuous casting to thick slab, allows steels more highly alloyed with Al, Mn and Si, such as advanced high strength strip (AHSS) steels, to be produced. These high value grades are not currently commercially produced in the UK and success in this project would increase the range of steel grades offered by the UK manufacturers. It should be noted that the ability to manufacture these value added steels will also increase sales of conventional steel grades, as customers often choose suppliers that can provide complete order coverage. This will provide the UK steel industry with a competitive advantage in the international market. The use of mini-mill steel production using twin roll casting by competitors allows low cost (due to low energy use) manufacture, however the increased capacity of belt casting, and hence suitability for UK production, will give market advantage. The approach of this project would also allow new alloy grades to be designed that optimise the direct casting process parameters to yield unique microstructure and property combinations.
Light Weighting of Steel Products - Benefits to UK's Automotive Industry
A secondary beneficiary of this project will be the automotive industry, which will have access to a UK source for light weight AHSS products. The automotive sector in the UK comprises over 3000 separate companies employing over 180,000 people. The UK has the sector's 4th highest output in Europe and the 12th highest globally. The use of new AHSS in automotive parts is vital to the competitive advantage of UK car manufacturers since the EU has defined legislation to meet the requirements of the Kyoto protocol and beyond.
Educational Impact
Within the project we are training two RFs and an EPSRC case PhD student. We will involve MSc and undergraduate students in the research area through offering related projects. In addition exposure of younger students to the research area will be achieved via outreach activities (e.g. pewter casting experiment for school students) and links with the WMG Academy, which offers places to 640 students aged 14-19 years from the Coventry, Warwickshire and Solihull areas and is coordinated with over 40 employers located in the Midlands.
(http://www2.warwick.ac.uk/fac/sci/wmg/about/capitalprojects/wmgacademy/).