Maria Santofimia Navarro is world famous for her work on advanced high strength steels. Together with her team, Santofimia combines fundamental theoretical research, advanced simulation techniques and high-resolution experiments to explain how the structure of steel at the microscopic level has a huge influence on the physical properties of the material. With this new knowledge about the microstructure of materials, Santofimia is designing “greener”, more sustainable types of steel.
‘Actually what we do in the lab is a sort of alchemy,’ laughs Santofimia describing how her team approaches the design a new type of steel. ‘We control the formation of a particular microstructure by choosing a specific chemical composition and heat treatment – a level of control that was not possible in the past.’
Steel is an alloy of iron and carbon, together with other elements. Santofimia: ‘When you look at steel through the microscope, you don’t see a continuum - what you see is a microstructure and this microstructure is formed by aggregates that we call “grains”. These grains look a bit like cells in natural tissues but they are actually crystals and precipitates that have different atomic structures and different shapes - for instance rounded or elongated - and also different sizes, compositions or orientations. By altering both the steel’s chemical composition and the type of heat treatments, we can modify the microstructure to produce different types of steel with different properties.’
This is extremely useful because steel is used everywhere: however, the steel you use to make a knife is completely different from the steel you use to make a key or a car or a building because each type of steel has different physical properties. ‘If you look through a microscope at the microstructure of each material, they are all completely different – yet they are all called steel.’
Sword forging at the blacksmith
Even before people knew about microstructures, they realised that the process of making steel - particularly the heating and cooling processes - is as important as the composition of the alloy: ‘In the movies, when you see people making a sword, they heat it to make it very hot, then shape it, and then they plunge it into cold water - and magic! But of course, it’s not magic. We know now that these steps were needed in order to create the right microstructure to give the sword its particular properties.’ As microstructural changes are controlled by physical, thermodynamic and kinetic laws, so changes in temperature, and specific cooling and heating rates, affect the atomic behaviour leading to the creation of a specific microstructure. ‘So understanding these microstructural changes allow us to create different types of steel with specific properties.’
If you look through a microscope at the microstructure of each material, they are all completely different – yet they are all called steel.
From Applied Physics in Andalusia to Metallurgy in Madrid
Santofimia grew up in Cordoba in southern Spain, where she studied physics and considered doing a PhD in optics: ‘But I also applied for scholarships in other places because, although there’s lots of potential in Andalusia, there were very few opportunities to get a grant to study for a PhD in southern Spain.’
Eventually Santofimia opted for doing for a PhD in Metallurgy at the National Centre for Metallurgical Research in Madrid: ‘You may ask why?’ laughs Santofimia, ‘but I decided to work on a European Project with industries because I wanted to explore a field in which I could see a direct application of physics in materials, something that I had not explored in my previous studies.’
On getting her PhD, Santofimia was initially unsure whether to continue in academia. However, an opportunity to do post-doctoral research at TU Delft’s Department of Materials Science Engineering, in collaboration with TATA Steel in the Netherlands, made up her mind: ‘There was an opportunity to work here in Delft on a topic related to my PhD - namely the development of new steels with novel microstructures and improved mechanical properties using a different approach in terms of heat treatment and its influence on the microstructure.’
And that was not the only thing that was different: ‘When I started my post-doc research, the research dynamics were very different from what I was used to,’ remembers Santofimia. ‘I was always asking “Shall I investigate this or shall I do that?” but Professor Jilt Sietsma, my supervisor at the time, just gave me a lot of freedom to follow my own questions.’
Santofimia also remembers an occasion when one of her experiments did not quite go as she had expected: ‘I went to Jilt and said “I’ve got this result, I don’t know what it is so I’m going to change the material.” But he said “Oh no! You’re going to figure out what this is!” – and that was an eye-opener moment for me!’
What Santofimia had found in fact was a new microstructural constituent growing in the material during the cooling process. ‘We were not expecting this because, in principle, the growth of this phase is associated with the redistribution of alloying elements that move very slowly. However, in this case we observed that the growing mechanism only involved the redistribution of carbon atoms, which are small and diffuse quickly, while the rest of alloying elements remained frozen. Investigating this unexpected phenomenon worked out really well for us because it led to the publication of several articles!’
Professor of Physical Metallurgy
After a brief period working at the Madrid Institute for Advanced Studies of Materials (IMDEA-Materials), Santofimia decided to go back to the Netherlands: ‘That was a very big decision but I came back from Madrid to Delft after nine months and started as a post-doc again. And while doing that, I applied for an ERC starting grant, a Fellowship grant and a Vidi grant - and eventually, I got all of them. And then in 2017, I was appointed Professor of Physical Metallurgy.
Sustainability and the life cycle of steel
One of the biggest challenges for the steel industry right now is to make the whole production process much “greener” and to this end, Santofimia has been working with several steel companies to help them become more sustainable: ‘In my opinion, it is now very important to look at the whole life cycle of steel - the production process, use and recycling possibilities - and to work with industry on making steel more sustainable at every stage. That’s what I want to focus on more in the future; till now I’ve been looking at individual aspects of sustainability within processing and use, but now I would like to pursue a more holistic approach.’
It is now very important to look at the whole life cycle of steel, and to work with industry on making steel more sustainable at every stage.
Recycling scrap for new steel
Along with the development of new technologies for “green steel” production using renewable hydrogen sources, there is a drive to maximise the use of scrap metal in making new steel: ‘Recycling technologies using greater amounts of scrap metal need to be included in steel production plants. Over the last 20 years, there’s been a massive increase in steel production globally so there will be a lot more steel around to be used for recycling in the future - and ideally we would like to use all of it!’
A great idea, of course, but not without its challenges. For instance scrap metal is often contaminated with other elements like copper which is used in cables and coatings, explains Santofimia: ‘So instead of trying to extract these elements in the initial production processes, I want to look into how we could make use of these “impurity” elements in the material: for example, how can we incorporate them within the microstructures, or how can we minimise any detrimental effects on properties and performance – and that will be a huge challenge.’
Combination of experimental and theoretical research
Santofimia’s drive to produce better sorts of steels is motivated as much by curiosity as sustainability: ‘I’m keen to learn new things, to try to understand what we observe under different conditions, and to explore new fields within steel production.’ This sort of knowledge would have a direct application in terms of sustainability: ‘For example, we could make specific steels using less energy, or make steels with better mechanical properties so that we can use them as thinner parts, and therefore use less material; or how can we make steels with very good properties but using fewer of the elements that are scarce or strategic, such as nickel.’
The future of steel?
Santofimia’s research combines high-resolution experiments with fundamental theoretical research and advanced simulation techniques: ‘Simulations are needed because we are dealing with processes that take place within the bulk of the material and at the atomic scale, meaning that they cannot often be observed experimentally. And my big scientific dream would be to use only modelling to predict how the microstructure changes during processing and how that microstructure controls the properties, so completely eliminating the experimental stage, which takes a lot of time and energy.’
Meanwhile how does Santofimia envisage steel production in the future? ‘I would like it if our children and grandchildren didn’t have to worry about sustainability, and that measures and technologies were already in place so we that we don’t have to pass on the sustainability issues that we have now - issues that we should have tackled when we first knew about them 50 years ago - and that’s what we’re working on now!’
Professor Santofimia will be taking part in the forthcoming “Steel for Sustainability” symposium to be held at the Prinsenhof in Delft on the 31st March 2023, where ‘we want to show and explain the impact of our research on steel to all audiences.’