抄録
The morphologies of isothermally transformed Widmanstätten and bainitic ferrites in a low carbon low alloy steel have been investigated by means of optical and electron microscopies. In the steel investigated, the Widmanstätten ferrite grains nucleated from the ferrite grain boundary allotriomorphs in the temperature range between 625 and 600°C, while the bainitic ferrite laths nucleated directly at the austenite grain boundaries below 580°C. The formation of both Widmanstätten and bainitic ferrites accompanies sharp surface reliefs. It was found that both ferrites have the shape of laths formed by the coalescence of parallel needle-like sub-units. The sub-units in both Widmanstätten and bainitic ferrites exhibit exactly the same habits with the ⟨111⟩α growth direction surrounded by two parallel set of {451}α planes. These results suggest that Widmanstätten and bainitic ferrites transformed in a displacive mechanism with respect to substitutional elements, the difference being in the nucleation sites between them.
