残留オーステナイトを含む複合組織鋼板の変形と変態過程

抄録

The deformation and transformation processes of an Fe-0.28%C-1. 41%Si-1.50%Mn steel subjected to various annealing conditions were investigated using in-situ TEM and SEM straining techniques. The retained austenite(γ_R) was observed in three distinctly different morphological forms, i. e., a film type located between bainite laths, an island type isolated in relatively large ferrite grains, and a granular type located at grain boundaries especially triple junction points. When stress was applied on the steel, the ferrite matrix was found to deform first piling-up dislocations at ferrite-γ_R boundaries. The internal stress fields generated by these piled-up dislocations seem to act as the driving force for the deformation induced transformation of γ_R. As the plastic deformation proceeded, fracture began with void formation at ferrite-second phase interfaces leading into subsequent void growth and coalescence until a final failure. The in-situ TEM observation showed that the transformation of γ_R is accomplished in the two different paths, i. e., γ_R→twin→α' and γ_R→α'. The orientation change resulting from a γ_R→α' transformation can be described by the Kurdjumov-Sachs relationship.