Optimizing the Morphology and Stability of Retained Austenite in a δ-TRIP Steel

delta-TRIP is a low-alloy steel in which ferrite persists at all temperatures in the solid-state, with the remaining microstructure consisting of carbide-free bainite and carbon-enriched retained austenite. The present work explores for the first time, how changes in the intercritical annealing temperature and the transformation conditions associated with bainite influence the morphology and stability of the austenite, and hence the behavior of the microstructure during tensile deformation. It is found that the structure can be optimized to consist of a combination of blocky and film austenite that undergo transformation over a range of plastic strains, thus minimizing the possibility of plastic instabilities, and hence imparting considerable strength and uniform elongation.