Abstract
As part of an ongoing development of third-generation advanced high-strength steels with acceptable cost, austenite reversion treatment of medium Mn steels becomes attractive because it can give rise to a microstructure of fine mixture of ferrite and austenite, leading to both high strength and large elongation. The growth of austenite during intercritical annealing is crucial for the final properties, primarily because it determines the fraction, composition, and phase stability of austenite. In the present work, the growth of austenite from as-quenched lath martensite in medium Mn steels has been simulated using the DICTRA software package. Cementite is added into the simulations based on experimental observations. Two types of systems (cells) are used, representing, respectively, (1) austenite and cementite forming apart from each other, and (2) austenite forming on the cementite/martensite interface. An interfacial dissipation energy has also been added to take into account a finite interface mobility. The simulations using the first type of setup with an addition of interfacial dissipation energy are able to reproduce the observed austenite growth in medium Mn steels reasonably well.
Highlights
THE austenite reversion treatment of medium Mn steels (3 to 10 mass pct Mn) has gained much attention recently, since the reverted austenite gives rise to both high strength and high elongation.[1]
Austenite is mainly stabilized by C and Mn partitioning from martensite, martensite gradually becomes ferrite due to C depletion and dislocation annihilation.[2,5,14]
In the simulation with the largest cementite fraction, 2.5 vol pct, no plateau corresponding to the non-partitioning local equilibrium (NPLE) growth is observed, since in this case martensite has such a low C content and is in the partitioning local equilibrium (PLE) region from the beginning
Summary
THE austenite reversion treatment of medium Mn steels (3 to 10 mass pct Mn) has gained much attention recently, since the reverted austenite gives rise to both high strength and high elongation.[1].
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