Oxide Formation on Steels: Improving the Magnetic Performance of Electrical Steels
Lead Research Organisation:
University of Warwick
Department Name: The Warwick Manufacturing Group
Abstract
Electrical steels for transformers and motors form a class of steels that contain silicon and aluminium.
To obtain the magnetic performance required, and minimise core losses, they undergo complex processing.
Processing steps control the microstructure: for example, the grains can be randomly oriented or processed to produce a specific crystallographic texture depending on the application. To improve the performance and to provide insulation, a glassy coating is applied in the final stages. The complex heat treatments required to produce the final microstructure affect the surface and sub-surface of the steel strip, and this can result in significant degradation to the final performance.
The goal of this project is to evaluate and understand the microstructural and surface changes to the steel as it undergoes heating at different temperatures in a range of gas environments together with cycles of cooling and deformation. This is important, as the nature of the oxides formed during these treatments can be external oxide scales along with significant internal oxidation. With the electrical steel strip thickness, approximately 0.5mm, compositional changes to the surface impact the underlying microstructure, while the nature of the oxide formed on the surface affects how easily it is removed and the adhesion of the glassy insulation layer.
Insight into the fundamental oxidation of silicon and aluminium containing steels will be gained through a combined approach of experimental and modelling work to determine the key factors influencing the kinetics and development of oxides. This work will be hugely important in developing alternative beneficial routes for controlling oxidation of electrical steels.
To obtain the magnetic performance required, and minimise core losses, they undergo complex processing.
Processing steps control the microstructure: for example, the grains can be randomly oriented or processed to produce a specific crystallographic texture depending on the application. To improve the performance and to provide insulation, a glassy coating is applied in the final stages. The complex heat treatments required to produce the final microstructure affect the surface and sub-surface of the steel strip, and this can result in significant degradation to the final performance.
The goal of this project is to evaluate and understand the microstructural and surface changes to the steel as it undergoes heating at different temperatures in a range of gas environments together with cycles of cooling and deformation. This is important, as the nature of the oxides formed during these treatments can be external oxide scales along with significant internal oxidation. With the electrical steel strip thickness, approximately 0.5mm, compositional changes to the surface impact the underlying microstructure, while the nature of the oxide formed on the surface affects how easily it is removed and the adhesion of the glassy insulation layer.
Insight into the fundamental oxidation of silicon and aluminium containing steels will be gained through a combined approach of experimental and modelling work to determine the key factors influencing the kinetics and development of oxides. This work will be hugely important in developing alternative beneficial routes for controlling oxidation of electrical steels.
People |
ORCID iD |
| Barbara Shollock (Primary Supervisor) | |
| Martin Olowe (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509401/1 | 01/10/2015 | 25/02/2022 | |||
| 1792011 | Studentship | EP/N509401/1 | 30/09/2016 | 31/03/2021 | Martin Olowe |
| Description | My PhD is focused on the analysis of scale formation arising from primary high temperature reheating for a selected range of a new range of steels for the power industry which are difficult to descale and roll; We have been mapping the range of defects and mechanisms arising at the interface between the parent steel grade and the oxide with the view to develop a detailed understanding which pre-existing defects and newly developed steel-metal interface may impede good descalability. Advanced techniques for characterisation and analysis of surfaces have been developed and coupled together to encompass the range of physical length scale encountered. A new fractal technique has been developed based on image analysis of the developed interface. The work is progressing to fully quantify all mechanisms involved during oxidation and descaling. |
| Exploitation Route | The current findings of this project will be used to optimise the reheating process avoiding formation of deleterious mechanisms/defects/elements contributing to bad descalability. This will be exploited when the full tracking of these mechanisms and interface elements have been completed coupling chemical, geometrical and mechanical properties which will affect what the high-pressure descaler can impact under given production conditions. Analytical and mechanical techniques for surface oxides are being developed resulting in a fundamental understanding of oxide growth mechanisms and failure upon impact. |
| Sectors | Manufacturing, including Industrial Biotechology |
| Description | This project has under 1 year to go and so final findings are still being summarised. However, a potential benefit has already manifested itself in the area of surface oxide analysis and the implementation of the methodology to identify where the steel has been obtained from during the steel manufacturing process. This is due to a more thorough understanding of the oxide morphology from a macro to nanoscale before and after reheating, giving now much more enriched boundary conditions to the process of reheating and descaling at the right physical length scale. Moreover, there has been a greater understanding on the chemical development of the scale/metal interface as a result of reheat pilot plant test which feeds well into the next stage which will look at the geometry of the interface and the ability for the defects formed to fracture/deform; Data from various furnace/reheating regimes have provided a more practical contribution to plant operations. This project is supported by Tata Steel with results and findings reported and where possible used. |
| First Year Of Impact | 2016 |
| Sector | Manufacturing, including Industrial Biotechology |
| Impact Types | Economic |
| Description | The current research is a collaboration with TATA Steel studying the high-temperature oxidation of electrical steels used in the energy, automotive and transport sectors. |
| Organisation | TATA Steel |
| Country | India |
| Sector | Private |
| PI Contribution | The team at Warwick University have provided space for the installation of the equipment provided by TATA steel and results obtained using the characterisation equipment within the Warwick manufacturing group. |
| Collaborator Contribution | TATA steel has contributed economically and physical (equipment and material) towards my project. They have also contributed in providing advice and documentation which have aided in the progression of the project. |
| Impact | Equipment and materials -TATA has provided me with a Thermogravimetric analyser (TGA) which has been the main equipment needed to obtain results on the oxidation rate of steels. They have also provided the alloy which my project is based on and test are performed on. Documentation -The documentation provided have information on experiments that have been previously performed, parameters used for experiments and financial/scientific information surrounding the manufacturing process of the alloy I'm studying. Supervisory -Regular meeting to ensure progress is being made and advice are provided where necessary. |
| Start Year | 2015 |