The martensitic transition pathway in steel

The martensitic transformation (MT) lays the foundation for microstructure and performance tailoring of many engineering materials, especially steels, which are with > 1.8 billion tons produced per year the most important material class. The atomic-scale migration path is a long-term challenge for MT during quenching in high-carbon (nitrogen) steels. Here, we provide direct evidence of (1(1) over bar 2) body-centred tetragonal (BCT) twinned martensite in carbon steels by transmission electron microscopy (TEM) investigation, and the increase in tetragonality with the C content matches X-ray diffraction (XRD) results. The specific {1(1) over bar 2}(BCT) twin planes which are related to the elongated c axis provide essential structural details to revisit the migration path of the atoms in MT. Therefore, the face-centred cubic (FCC) to BCT twin to body-centred cubic (BCC) twin transition pathway and its underlying mechanisms are revealed through direct experimental observation and atomistic simulations. Our findings shed new light on the nature of the martensitic transition, thus providing new opportunities for the nanostructural control of metals and alloys. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

This study provides new evidence and insights into the martensitic transformation in carbon steels through transmission electron microscopy. The migration pathway and underlying mechanisms of this transformation are revealed, shedding light on nanostructural control of metals and alloys.