Simulation of the Growth of Austenite from As-Quenched Martensite in Medium Mn Steels

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.

Fundamentals and application of solid-state phase transformations for advanced high strength steels containing metastable retained austenite

“…The austenite reversion rate was predicted to be decelerated due to cementite precipitation. It was also found by Huyan et al [367] that the predicted kinetics of austenite reversion can be in good agreement with experiments if a finite mobility of the martensite/austenite interfaces is assumed in the setup A simulations, e. g. Setup A + M. Zhang et al [323] reported that the kinetics of lath-shaped austenite reversion and alloying elements partitioning behaviour in the low Mn steels can also be well predicted based on Setup O + M, assuming the mobility of martensite/austenite interface is much lower than that of ferrite/austenite interface. It should be noted that the effect of cementite precipitation on the kinetics of austenite reversion was not considered in Setup O + M, although cementite precipitation was observed by Zhang et al [323].…”

“…It should be noted that the effect of cementite precipitation on the kinetics of austenite reversion was not considered in Setup O + M, although cementite precipitation was observed by Zhang et al [323]. This could explain why the mobility of martensite/austenite interface adopted by Zhang et al [323] is smaller than that adopted by Huyan et al [367].…”

“…As discussed above, the interaction between carbide precipitationdissolution and austenite reversion during ART depends on many factors and is very complex. In order to better understand this complex phenomenon, many efforts were made to simulate carbide precipitationdissolution and austenite reversion using DICTRA software [341,[367][368][369][370][371][372]. As shown in Fig.…”

“…Huyan et al [367] simulated the kinetics of austenite reversion of an as-quenched Fe-0.2C-5 Mn medium Mn steel annealed at 650 • C using various setups, as shown in Fig. 35d.…”

Current Challenges and Opportunities in Microstructure-Related Properties of Advanced High-Strength Steels

“…Each of these elements contributes differently to the stability of the iron-rich solutions (liquid, ferrite, austenite (c), and epsilon (e)) and the second-phase precipitates. [65][66][67][68][69] The purpose of this section is to present a few key concepts relevant to the thermodynamically guided design of AHSS. The intention is not to present a general review about alloy thermodynamics here.…”