Evolution of microstructure and mechanical properties of medium Mn steels during double annealing

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2012-04, Vol.542, p.31-39
• Main Authors: Arlazarov, A., Gouné, M., Bouaziz, O., Hazotte, A., Petitgand, G., Barges, P.
• Format: Article
• Language: English
• Subjects: Annealing; Applied sciences; Chemical Sciences; Elasticity. Plasticity; Exact sciences and technology; Heat treatment; Martensite recrystallization; Material chemistry; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Medium Mn steel; Metals. Metallurgy; Phase transformation; Production techniques; Retained austenite; Transformation induced plasticity (TRIP)
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2012.02.024

► Ultrafine microstructure of ferrite, retained austenite and/or martensite. ► Double morphology of microstructural features: lath-like and polygonal. ► Mn redistribution seems to be controlled by diffusivity similar to those in ferrite. ► Austenite stabilization controlled by two factors: chemical enrichment and its size. ► Improved TRIP effect due to the presence of important retained austenite fraction. A double annealing process was applied to cold rolled medium Mn steel. The evolution of both microstructure and mechanical properties during the second annealing were analysed. Austenite reverted transformation (ART) was observed during intercritical annealing. It was shown that a complex ultra-fine microstructure composed of three phases (retained austenite/martensite/ferrite) was formed and two types of morphologies were detected (lath-like and polygonal). Furthermore, a high volume fraction of retained austenite (22%), which was stabilized at room temperature, was the origin of a TRIP effect. A good balance between strength and ductility can be achieved by optimizing the heat treatment. The various results are discussed and some mechanisms are proposed to explain the observations.