Abstract
The effect of the initial starting microstructures on the austenite reverse transformation kinetics is thoroughly studied in low-carbon steel. The different initial starting microstructures including the ferrite + pearlite, bainite, and martensite are obtained through varied forward transformation. It is found that the bainite phase demonstrates highest reverse transformation rate while the ferrite + pearlite shows the lowest transformation rate. The above observation can be explained through the different grain size of the initial starting microstructures as the grain boundaries could act as the nucleation sites for austenite reverse transformation. The explanation is further substantiated based on the consideration of the reverse transformation kinetics from the martensite microstructure with different grain size.
Highlights
Steels are key structural materials for the improvement of daily life and the increase of economics
We aimed to investigate the effect of different initial starting microstructures initial starting microstructures include ferrite + pearlite, bainite, and martensite, which are obtained on the austenite reverse transformation kinetics in a single chemical composition
Through the detailed dilatometry investigation, the present work shows that the bainite phase demonstrated the highest reverse transformation rate compared to that of martensite bainite phase demonstrated the highest reverse transformation rate compared to that of martensite and ferrite + pearlite
Summary
Steels are key structural materials for the improvement of daily life and the increase of economics. The transformation from austenite to product phases (i.e., martensite, bainite, ferrite) is key for the development of advanced high-strength steels (AHSS), such as the carbide-free bainite (CFB). The forward transformation from austenite to product phases has been intensively investigated [6,7,8,9,10]. It was gradually realized that the reverse transformation from the product phases to the parent austenite is important for the development of AHSS. The dual phase (DP) steel and the medium Mn steel frequently employ the reverse transformation to obtain the reverted austenite grains through the intercritical annealing process [11,12,13]. Note that the reverted austenite grains in DP steel will transform to martensite during the final quenching.
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