ASAP - Advanced electromagnetic Sensors for Assessing Property scatter in high value steels

The development of new techniques to measure the microstructure of a material in a non-contact non-destructive fashion can lead to a dramatic improvement in the understanding of the material and its behaviour during processing and in-service. This, in turn, can lead to a greater ability to control the material properties and predict the evolution of these properties. At present, the majority of microstructural analysis techniques are destructive and / or require small samples. Consequently, existing techniques are limited in applicability especially if dynamic microstructural control during commercial processing is of interest. Several techniques have been proposed to directly measure microstructures in these situations but, as yet, no single technique offers a full solution. It is well known that the microstructure is directly related to the mechanical properties of steel, therefore if the microstructure can be measured on-line during processing, and the inherent variability in microstructure can be assessed (on-line or off-line), then the mechanical properties (including any scatter) can be inferred. This could provide enormous saving to the manufacturing industry as product quality can be improved through real-time feedback for processing control and / or reduction (or better still elimination) of the off-line destructive mechanical testing for release specifications. In this context, our proposal focuses directly on advanced sensors for measuring the key microstructural parameters that are directly linked to mechanical properties in high value steels.

Our ambition is to exploit novel electromagnetic (EM) techniques to analyse microstructure directly, and therefore to infer mechanical properties, for a range of advanced steel types during and after processing. Typically these EM techniques have included multi-frequency interrogation combined with advanced signal and data processing and modelling. Both the UK and Indian teams have successfully considered the electromagnetic response, using different sensor types, to component phase fractions (such as ferrite), which in the UK has been supported by 3D modelling of both idealised and realistic microstructures. In parallel, the problem of inverting the complex inductance spectra acquired by the sensor systems to yield parameters of metallurgical significance has been addressed, and in India a link between sensor output and mechanical properties for relatively simple steels has been established. In the EU sensor configurations that can be deployed on-line for phase transformation monitoring by measuring the mutual inductance have been successfully tested, in collaboration with Tata Steel Europe, and are now in the process of being commercially exploited via a licensing agreement with an external company. The natural next step in the research is to combine EM sensor techniques to exploit the full electromagnetic characteristics of steel (for example using sensors that measure coercivity, saturation and incremental permeability) to characterise the more complex microstructures, and their spatial inhomogeneity, in advanced steels. This requires collaboration between the leading international groups on sensor design, implementation and microstructure-signal relationships. On-line deployment of these systems will allow greater feedback control during processing to enable these advanced steels to be produced on older as well as new mills. Mechanical property determination, through the microstructure-property relationships, provides the potential to reduce or eliminate the off-line property release tests that are currently performed with a significant saving to the industry.

The potential beneficiaries of this project may be grouped in the following categories:

Society
Environmental
Industrial (steel producers, steel end users, support organisations etc)
Academic and scientific

In the broadest sense, the industrial benefits will stem from an ability to provide reliable inspection technologies, in-service, for high value steels especially with the need for non-destructive measurement of materials properties (including scatter) for release testing and on-line process control. Greater on-line processing control will enable to production of higher strength/formability strip product that can be used to further lightweight car bodies. There is then an environmental and societal benefit in terms of increased efficiency (lower fuel consumption) and reductions in CO2 emissions.

Although this project focuses on steel processing mills, which has very high industrial, environmental and global importance, the research is also highly inter-disciplinary, and involves a variety of areas such as: metallurgy, electromagnetic engineering, magnetism, modelling and simulation, electronics, digital signal processing, inverse algorithms, process and mechanical engineering and applied mathematics. In general, results from the project will be beneficial to a cross-section of scientific workers in these areas and we would reasonably expect spin-off applications to arise in other areas, as we have seen from the previous work we have done.

Academics working on materials characterisation will benefit from the development of a non-destructive sensor that can monitor microstructures. Greater knowledge of EM signal - microstructure relationships will benefit the NDT community.