Medium Manganese Steel and Mechanism of Austenite Formation during Reversion Annealing

Alloy chemistry and process conditions are studied for a steel having a tempered martensite matrix providing an indicated tensile strength of >900 MPa and containing >20% austenite for enhanced ductility and formability. Conditions equivalent to industrial annealing are simulated in laboratory tests. In the initial quenched state, the steel has a martensitic matrix and contains around 2.5% retained austenite which is maintained throughout the subsequent heating stage and then increases significantly in volume during isothermal reversion annealing above the A(1)temperature. There is evidence to support the conclusion that this increase in the austenite content takes place by growth of the pre-existing fragments of retained austenite in the initial martensitic microstructure, rather than by new independent nucleation events.

Automated summary

Study focused on alloy chemistry and process conditions to achieve a steel with a tempered martensite matrix, providing a tensile strength >900 MPa and containing >20% austenite for improved ductility and formability. Laboratory tests simulated industrial annealing conditions. The increase in austenite content during isothermal reversion annealing primarily occurs by growth of pre-existing fragments of retained austenite in the initial martensitic microstructure.