Rapid Austenite Restoration through Non-Partitioning Transformation

Steel microstructures that contain retained austenite exhibit unique mechanical flow behavior which renders them applicable to high-strength forming, and energy absorbing applications. During deformation, meta-stable austenite transforms to martensite and induces dramatic work hardening which increases the strength, ductility, and toughness. After the deformation induced transformation of austenite, these steels have limited remaining ductility. Restoration of austenite through rapid thermal treatments, after it is expended through deformation, can enable retained austenite to be leveraged during additional deformation.

Metallurgical design of these steels includes substitutional solutes such as manganese and/or nickel which enable austenite retention to room temperature. During longer, initial thermal processing, the solute is concentrated in austenite through a partitioning ferrite-to-austenite transformation. After deformation induced transformation of austenite to martensite, austenite may be rapidly restored by leveraging non-partitioning transformations through judicious thermal processing. Here, rapid austenite restoration heat treatment following deformation induced martensite formation is presented along with the corresponding effects of this treatment on mechanical flow behavior. Experimental characterization and MICRESS® simulations are discussed to elucidate microstructural evolution during thermal processing.