MEDIUM MANGANESE STEEL: REVEALING THE HIGH SENSITIVITY OF MICROSTRUCTURE AND MECHANICAL PROPERTIES ON INTERCRITICAL ANNEALING TEMPERATURE
Medium manganese (Mn) steel is an important part 3rd generation advanced high strength steels (AHSS). Medium Mn steel grades are famous for overcoming the so-called “strength-ductility trade-off” that was the limitation in previous 1st generation AHSS. Medium Mn steels have high strength-ductility combination due to the ultrafine microstructure consisting of laths of martensite/ferrite along with a significant amount of interlath embedded austenite films. Austenite phase is stabilized in such steels via the austenite reverted transformation (ART) techniques or simply by the intercritical annealing (IA) treatment. In typical IA treatment, the sample with fully martensitic microstructure is held at an intercritical temperature during which partitioning of alloying elements such as carbon, manganese (austenite stabilizers) occurs from the intercritical ferrite to the intercritical austenite phase, thus lower the martensitic start (MS) temperature of the intercritical austenite phase and consequently increasing its thermal stability. Upon subsequent cooling to the room temperature, the microstructure retains sufficient austenite phase, owing to its increased stability
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