Category | Steel

The science behind the steel

 
We speak to the talented team behind the work that led to ArcelorMittal’s involvement in the scientific breakthrough of the century.

In early July, the scientists at the European Organization for Nuclear Research (CERN) proudly announced that they had made a breakthrough discovery in understanding the origins of the universe.

The team of experts told the world’s media that they believed they had found the subatomic particle, the ‘Higgs boson’ commonly referred to as the ‘God particle’, that confirms our understanding of how the universe works.

For ArcelorMittal this was great news, because 50,000 tonnes of our steel was produced by Flat Carbon Europe to build the Large Hadron Collider (LHC) – the particle accelerator that fires trillions of protons around a 27km tunnel at 99.99% of the speed of light.

The CERN tender, issued in 1998, called for 50,000 tonnes of magnetic steel with strictly identical properties. And thanks to close collaboration between ArcelorMittal’s research and development (R&D), technology and commercial teams, our company won the contract by offering a new, high thickness magnetic steel guaranteeing a weak coercive field. The product was called MagnetilÒ; ArcelorMittal’s Philippe Harlet, part of the R&D team in Liege, led the team that created this new, unique steel.

Initially, MagnetilÒ was provided for the Large Electron-Position (LEP) collider, which was in the CERN tunnel from 1983 to 2000. Then, in 2009 the team was contacted again and supplied MagnetilÒ for the super LHC project, the LEP’s successor.

Now, the CERN team is discussing the possibility of creating an even bigger collider, with an 80km tunnel that would look into physics mysteries such as how gravity works on a particle level.

ArcelorMittal hopes to be involved in any new development at CERN, given its close involvement in this major project. In fact, according to global head of research and development Greg Ludkovsky, only top performance magnetic steel could ever meet the CERN team’s requirements.

“The material used had to have a high initial permeability. And it has to be mechanically strong enough to be used as a structural component to provide rigidity” explains Greg.

The overall goal in the production process for this ground-breaking project was to achieve a very particular crystallographic structure and texture in the magnets’ active part; this in turn would maximise the magnetic strength of the magnets. In fact not a traditional steel, but rather pure iron, would fulfill this job, which was a real challenge to produce in our industrial installations. The basic metallurgical principle is two-fold.

First, for the structure, the key requirement was cleanliness– meaning the team had to develop unique practices to ensure extremely low residual content in the steel used, except for elements that do not interfere with magnetic properties such as limited amounts of manganese and phosphorus. It started by using pre-decarburised steel (decarburisation is the process of removing carbon) and continued by developing specific thermo-mechanical
treatments, to ensure optimal grain size for maximum magnetic performance.

Second, the texture is linked to the iron crystals’ position in the steel sheet, which in turn helps boost the magnetism of the steel. The texture control involved a challenging slab reheating, rolling and annealing schedule, going against all standard production practices.

“We developed a cubic texture, because this gives the best magnetic permeability. Out of this, magnetic material laminations were created: these hot-rolled coils were further annealed, making sure that the oxide layer was retained in order to provide insulation between individual laminations” said Greg.

Traditional ways of insulating the metal using organic coating could not be used in the Hadron Collider because of the very low temperatures that the metal is exposed to and the risk of degradation of organic compounds when exposed to radiation. The low temperatures in the HLC are linked to the use of superconductivity in the magnets, which requires cryogenic circumstances.

For the cold rolled version of the MagnetilÒ, an inorganic insulation was created, using a blue-ing step at the end of the production process to provide a layer of insulation.

ArcelorMittal’s work to develop this product for CERN means that a unique magnetic steel has been created that is now available to any other project in atomic physics. With accelerator projects being developed all over the world – ArcelorMittal has also provided steel to such projects in Canada and Russia – the chances of our company providing the steel for another landmark scientific discovery are greater thanks to the work done by Long Carbon Europe, the research and development and commercial teams.