Study on Austenite Transformation Behewior of Fe-C-Mn-Si-Al Dual-phase Steel during Intercritical Annealing
The austenite transformation from ferrite+cementite was investigated by modelling with Dictra software and experimental validation.Especially,the dissolution of cementite as well as austenite transformation kinetics was analyzed.Using field emission electron probe,the morphology of ferrite and martensite and its elements distribution under different heating routes were detected.And the cementite and retained austenite were characterized using transmission electron microscope(TEM).The results show that,compared with the slow heating to 740 ℃ for long isothermal periods and heating to 780 ℃ for a short isothermal time,although the austenite fraction is not very different when the cementite starts to dissolve,but in the process of carbursome dissolution,the austenitic phase transition is different.Under slow heating,austenite preferentially nucleates on ferrite grain boundary.While,under fast heating,austenite can also nucleate on cementite/ferrite boundaries inside ferrite.Combining isothermal treatment at 740 ℃ with fast heating,a special shell-core structure composed of martensite and retained austenite is obtained.
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