, C. Garcia-Mateo

The carbon supersaturation of bainitic ferrite was investigated by means of atom probe tomography in three steels with different carbon and silicon contents, to elucidate the effect of transformation temperature and the reaction velocity on the mechanisms controlling bainite formation with and without the interference of cementite precipitation. Results indicated no difference in the growth mechanism over the 2 temperature range investigated. These results provide new evidence that the bainite transformation is essentially martensitic in nature. After decades of debate [1] on the mechanism for the formation of bainite, two primary opposing viewpoints have formally evolved. The shear or displacive theory [2,3] states that bainitic ferrite forms by shear and that the transformation is essentially martensitic in nature (i.e., the individual atom movements are less than one interatomic spacing) and proceeds by the formation of sub-units. The ledge-wise or reconstructive theory [4,5] states that bainite is a product of a reconstructive transformation (i.e. the majorit