Scanning tunnelling microscopy study of surface relief with bainite and martensite transformation

摘要

Although more than half a century has passed since the early work on the morphology of bainite in steel by Robertson in 1929 [1], considerable disagreement [2] still remains as to whether bainite forms by shear or diffusion. Important experimental evidence supporting shear mechanism is the work of Ko and Cottrell [3] in 1952, which showed surface relief during bainite transformation similar to that obtained during martensite transformation, and "found that bainite forms by nucleation and coherent growth". However, Aaronson et al. [4-7] found differences in the two kinds of surface relief, such as the shape of bainite relief is often "tent-like", and of martensite is "N-like", and concluded that bainite formed in a different way from martensite. Bhadeshia [8] gave the difference another explanation, i.e., the "tent-like" bainite surface relief is the result of plastic accommodation of the adjacent austenite by slip, and indeed also of an IPS type. Thus the fine structure of the surface relief is a key point in studying bainite transformation.