Computation of Phase Fractions in Austenite Transformation with the Dilation Curve for Various Cooling Regimens in Continuous Casting
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A concise model is applied to compute the microstructure evolution of austenite transformation by using the dilation curve of continuously cast steels. The model is verified by thermodynamic calculations and microstructure examinations. When applying the model, the phase fractions and the corresponding transforming rates during austenite transformation are investigated at various cooling rates and chemical compositions. In addition, ab initio calculations are performed for paramagnetic body-centered-cubic Fe to understand the thermal expansion behavior of steels at an atomic scale. Results indicate that by increasing the cooling rate, the final volume fraction of ferrite/pearlite will gradually increase/decrease with a greater transforming rate of ferrite. The ferrite fraction increases after austenite transformation with lowering of the carbon content and increasing of the substitutional alloying fractions. In the austenite transformation, the thermal expansion coefficient is sequentially determined by the forming rate of ferrite and pearlite. According to the ab initio theoretical calculations for the single phase of ferrite, thermal expansion emerges from magnetic evolution and lattice vibration, the latter playing the dominant role. The theoretical predictions for volume and thermal expansion coefficient are in good agreement with the experimental data.
KeywordsFerrite Austenite Cool Rate Cementite Pearlite
The work was financially supported by the Natural Science Foundation of China (NSFC, Project No. 51374260) and the Natural Science Foundation of Chongqing (Project No. cstc2013jcyjA50005). Part of the work was supported by the Swedish Research Council, the Swedish Foundation for Strategic Research, the Chinese Scholarship Council, and the Hungarian Scientific Research Fund (OTKA 84078 and 109570).
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