The science and “alchemy” behind making durable steel

by time news

alchemy

‘What we do in the lab is actually a kind of alchemy,’ Santofimia laughs as she describes how she and her team are working on the design of a new type of steel. ‘We ensure that a certain microstructure is created by choosing a specific chemical composition and heat treatment. That level of control was impossible in the past.”

Microstructure

Steel is an alloy of iron and carbon with other elements. Santofimia: ‘If you look at steel under a microscope, you don’t see a continuum, but a microstructure. That microstructure is formed by aggregates that we call “grains”. Those granules look a bit like cells in natural tissues, but they are actually crystals and precipitates with different atomic structures and shapes, for example round or ellipsoidal. They also differ in size, composition and orientation. Based on both the chemical composition of the steel and the type of heat treatment, we can change the microstructure and produce different types of steel with different properties.’

This is very useful, because steel is used on everything, while the steel used for knives is completely different from that used for keys, cars or buildings. After all, each type of steel has its own physical properties. ‘If you look at the microstructure of all those materials under the microscope, they are all completely different. And yet we all call it steel.’

Forging sword in the forge

Even before people knew about the existence of microstructures, they already realized that the process of making steel, especially the heating and cooling, is just as important as the composition of the alloy: ‘If you see someone in a movie holding a sword they heat the steel, punch it into a mold and then put it in cold water – magic! But of course that’s not magic at all. We now know that these steps are necessary to create the microstructures that give the sword its specific properties.’ Microstructural changes are controlled by physical, thermodynamic and kinetic laws. That is, temperature changes and specific rates of heating and cooling affect the behavior of atoms, creating certain microstructures. ‘Once we have insight into these microstructural changes, we can therefore make different types of steel with specific properties.

From Applied Physics in Andalusia to Metallurgy in Madrid

Santofimia grew up in Cordoba, in the south of Spain. She also studied physics there and planned to obtain her doctorate in optics. ‘But I also applied for grants for other universities. There is a lot of potential in Andalusia, but there were few places for a scholarship in the south of Spain.’
In the end, she opted for a PhD in Metallurgy at the Centro Nacional de Investigaciones Metalurgicas (National Center for Metallurgy Research) in Madrid. Santofimia, laughing: ‘You may wonder why. But I wanted to work on a European project and collaborate with the industry. I wanted to be in a field of research where I could see the direct application of physical principles to materials. I hadn’t seen that during my earlier studies.’

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