Influence of Heat Treatment on Microstructure Stability and Mechanical Properties of a Carbide‐Free Bainitic Steel

Carbide‐free bainitic steels represent attractive candidates for the automotive industry to meet the conflicting requirements of increasing safety and decreasing vehicle weight. Their fine‐grained multi‐phase microstructure enables a well‐balanced combination of high strength and ductility. To identify and characterize all phases in dependence of the isothermal transformation temperature, metallographic and high‐resolution techniques are applied. The stability of the individual phases is evaluated based on their C concentration determined by atom probe tomography and, subsequently, linked to the mechanical properties. Carbide‐free bainitic steels enable a well‐balanced combination of high strength and ductility. In this study, their complex multi‐phase microstructure is investigated by mechanical, metallographic, and high‐resolution methods using correlative microscopy, such as the novel approach of combining transmission Kikuchi diffraction and focused ion beam microscopy.