A team of researchers from ICAMS, the Institute for Materials at Ruhr-Universität Bochum, and the Max-Plack Institut für Eisenforschung has shed new light on the mechanism of martensite formation in Fe–C-based alloys. In a recent Nature Materials publication, the authors show the unexpected effects of two correlated phenomena on the collective ordering mechanism: anharmonicity and segregation. The improved description of the mechanism enriches the theory of phase transitions in materials and constitutes a crucial step in the design of ultra-high-performance alloys.