Proposition of an Empirical Functional Equation to Predict the Kinetics of Austenite to Ferrite Transformation in a Continuous Cooled IF-Ti-Stabilized Steel

Abstract

The kinetics of phase transformations in isothermal processes is well described by the classic JMAK model. However, it is known that most industrial facilities employ continuous cooling processes and, for this condition, the JMAK model is adapted but, sometimes, without success. Considering the importance to predict critical temperatures, the present work proposes an alternative empirical functional equation to describe the kinetics of steel phase transformation under continuous cooling, being useful when the JMAK use is not successful. In this study, the continuous cooling austenite to ferrite transformation was experimentally characterized by dilatometry for an IF-Ti-stabilized steel. The proposed equation was compared with the classic adapted JMAK model regarding to evaluate its efficacy to fit the dilatometric experimental data. Using the constants obtained by the both model fittings as input parameters, a computational simulation was performed to determine the CCT diagram of the IF-Ti steel. The proposed functional equation was efficient to predict the critical temperatures, the kinetics of austenite decomposition and the CCT diagram of the studied steel. The results predicted by the proposed model greatly met the experimental data measured by dilatometry.

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“…The lever rule was used for calculating the evolution of the transformed fraction from dilation curves. This rule involves extrapolating linear expansion behavior from the temperature regions where no transformation occurs, and subsequently assuming proportionality between the fraction of decomposed austenite and the change in length observed [43][44][45].…”

“…The lever rule was used for calculating the evolution of the transformed fraction from dilation curves. This rule involves extrapolating linear expansion behavior from the temperature regions where no transformation occurs, and subsequently assuming proportionality between the fraction of decomposed austenite and the change in length observed [43][44][45]. Microstructural evolution simulations of the alloy during the rolling process were performed using the MicroSim-SM ® model customized for Steckel mill rolling conditions, with the characteristics of austenitic microstructure evolution for each rolling pass being predicted by the model.…”

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“…Two linear regressions were performed before and after the continuous cooling transformation. With the two straight lines from the regressions, the lever rule was used to determine the percentage of pearlite from austenite during continuous cooling [26,27].…”

Influência da microestrutura antes e depois da soldagem de topo por centelhamento de trilhos ferroviários: uma abordagem de fadiga de contato de rolamento, transformações de fases e simulação por elementos finitos.

“…As outras propriedades físicas e mecânicas dependentes da temperatura utilizadas foram consideradas de acordo com as fases (e/ou microconstituintes) presentes: austenita e perlita. Com a regra de alavanca calculada descrita na Figura 114 e A técnica de alavancagem calculou a cinética da austenita para a decomposição da perlita [141,142]. Duas regressões lineares foram realizadas antes e depois da transformação contínua do resfriamento.…”

“…A cinética da formação da perlita para a austenita foi calculada usando a regra de alavanca [141,142]. Duas regressões lineares foram realizadas antes e depois da transformação contínua do resfriamento.…”