Materials and Molecular Research Division, Scripta Metallurgica, Further Discussion of Orientation Relationships, Surface Reliefs and FCC-BCC Transformations in Steels.

摘要

In a recent communication, Bhadeshia gives an explanation of the tent-shaped surface relief effects observed in association with Widmanstatten ferrite and lower bainite. Based on his proposed explanation he concludes that the diffusional fcc(yields)bcc transformation tn steel takes place by a displacive mechanism. This conclusion is disputed by Aaronson in a letter following that of Bhadeshia by showing that the experimentally observed orientation relationships are different from the one (Nishyama-Wassermann (N-W)), necessary for Bhadeshia's mechanism. He therefore holds that the transformation is purely diffusional and that 'any attempts to understand diffusional phase transformations in terms of a shear mechanism are counterproductive.' The purpose of the present note is (l) to show that Bhadeshia's mechanism seems to be based on a misinterpretation of the lattice symmetries resulting from the fcc (yields) bcc transformation and cannot explain a tent-shaped surface relief even if the N-W orientation relationship is followed, and (2) to suggest that attempts to formally understand diffusional phase transformations in terms of shear may not always be counterproductive.