ZAP // Dall-E-2
New research has discovered the effect of magnetic fields on the movement of carbon, which could allow steel to be made more efficiently and cheaply. The approach can also be applied to other materials.
Researchers at the University of Illinois Urbana-Champaign have identified the first detailed physical mechanism that explains how magnetic fields slow down the movement of carbon atoms within iron.
The discovery, in the journal Physical Review Letters, sheds light on a phenomenon observed for decades but never fully understood, and could lead to a more efficient steel production in energy terms.
Steel, an alloy of iron and carbon, is one of the most used construction materials in the world. Its strength and durability depend largely on its internal grain structure, which is generally controlled through heat treatment processes that require extremely high temperatures and consume large amounts of energy. For years, scientists have known that applying magnetic fields during heat treatment can improve steel’s performance, but the reason remained unclear.
“Previous explanations were phenomenological at best,” said Dallas Trinkle, senior author of the study and Ivan Racheff Professor of Materials Science and Engineering. “There was nothing predictive about themwhich limits its usefulness for the development of new materials.”
To go beyond theories based on observation, the authors proposed to identify a measurable explanationbased on physics. With support from the US Department of Energy, the team focused on how carbon atoms diffuse through iron at the atomic scale when exposed to magnetic fields, explains .
In steel, carbon atoms are inside tiny octahedral “cages” formed by the surrounding iron atoms. The researchers used advanced computer simulations to model how carbon moves between these cages under different magnetic and temperature conditions. The scientists also used a technique known as spin-space averaging, which allowed them to simulate the behavior of the magnetic “spins” of iron atoms.
Iron atoms can be ferromagnetic and have aligned spins or paramagnetic, in which the spins are oriented in a more random way. The simulations revealed that when the magnetic order increases and the spins align, the energy barrier for carbon diffusion also increases. In practice, a stronger magnetic alignment hinders the movement of carbon atoms.
“When the spins are more random, the cage becomes more isotropic and opens up,” explained Trinkle. “This gives the carbon more room to move. The magnetic order does the opposite.”
This discovery provides the first quantitative explanation of how magnetic fields influence the diffusion of carbon into iron. It is important to highlight that the effect is strongest near the Curie temperaturewhere iron transitions between magnetic states and becomes particularly sensitive to external magnetic fields.
The implications could be significant. By using magnetic fields to control the movement of carbon, manufacturers may be able to achieve desired steel properties at lower temperatures, reducing energy consumptioncosts and carbon emissions. Trinkle also believes that the approach can be extended to other alloys and materials.
“Now that we can do real calculations, we can start thinking about alloy engineering more intelligently,” he said. “This could mean optimizing existing steels or even designing chemical compositions of completely new leagues”.
