1993 Volume 79 Issue 6 Pages 665-670
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(γR) 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-γR boundaries. The internal stress fields generated by these piled-up dislocations seem to act as the driving force for the deformation induced transformation of γR. 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 γR is accomplished in the two different paths, i. e., γR→twin→α' and γR→α'. The orientation change resulting from a γR→α' transformation can be described by the Kurdjumov-Sachs relationship.
