A constitutive model for transformation superplasticity under external stress during phase transformation of steels

Abstract

Most models of superplastic deformation behavior under external stress during phase transformation have been derived under the assumption of plastic deformation in the weaker phase. In the present paper, we suggested a constitutive model for the transformation induced superplastic deformation of steels based on a concept of Migration of Transformation Interface induced Plasticity (MITIP) including the phase transformation kinetics. The concept is that the migration of atoms in the transformation interface is a principal mechanism of superplastic deformation under stresses during phase transformation. The model could well describe the effect of the cooling rate, the transformed phase and the transformation temperature on the amount of the transformation induced superplastic strain. In order to calculate the deformation behavior under stresses during phase transformation of steels, the elastic strain, the volumetric strain due to thermal and phase transformation, the viscoplastic strain, and the transformation induced superplastic strain were taken into account. The calculated results were found to be in good agreement with the experimental data obtained from literature. © 2002 ISIJ.