Characterization of the Factors Influencing Retained Austenite Stability in Q&P Steels via In Situ EBSD

The current work studies the correlations between microstructure and retained austenite (RA) transformation, in a single-quenched and partitioned (Q&P) 1180 steel microstructure, through in situ tensile tests combined with electron backscatter diffraction (EBSD) analysis. This allows the study of RA stability across a limited range of morphological characteristics to be studied in the absence of confounding factors introduced by varying the entire steel microstructure. Among the microstructural attributes of interest, RA grain aspect ratio is found to have the largest influence on transformation rate, where globular-shaped grains transform more slowly than those with a more lenticular shape. Furthermore, by tracking individual grains during deformation, it is apparent that larger grains transformed more slowly than smaller grains; a purely statistical study of grain size vs strain might conclude that smaller grains are more stable, but in reality, the smaller grains transform faster and are simply statistically replaced by partially transformed larger grains. These conclusions are in contrast to relationships that might be inferred from previous studies where the entire steel microstructure was varied, along with the morphology of the RA.