2024 Volume 64 Issue 2 Pages 338-344
A crystallographic analysis was conducted on the lower bainite formed at the austenite grain boundary in Fe-0.6C-0.8Mn-1.8Si (in mass%) steel at the initial stage of transformation. The variant selection and the effect of the character of the austenite grain boundary on the formation of lower bainite were investigated from several perspectives: the character of the prior austenite grain boundary (PAGB), the crystal orientation relationship between the bainitic ferrite (BF) and the adjacent prior austenite grain (PAG) across the PAGB, and the geometrical relationship between the BF and PAGB plane. BFs do not form at twin boundaries but form at high-angle grain boundaries. The effect of the orientation of the adjacent PAG across the PAGB is not dominant in the case of lower bainite formation, while the PAGB plane strongly affects the formation and the variant selection of BF. BF tends to form when its habit plane or shape deformation direction is nearly parallel to the PAGB plane. It is suggested that the formation of BF, whose HP is parallel to the PAGB, is favored from the perspectives of the interfacial energy, the elastic strain energy, and the plastic accommodation.
