Section 9.14 - Mechanical Behavior of Steels during Solid—Solid Phase Transformations

Abstract

The model presented in this chapter involves thermomechanical characteristics of the material. They are not derived from heuristic considerations but from homogenization. It is supposed that the anomalous plastic behavior during phase transformations, and especially the so-called transformation plasticity phenomenon, arise from the sole microscopic mechanism proposed by Greenwood and Johnson, with that suggested by Magee being disregarded. In spite of this limiting assumption, the models proposed are often experimentally found to be sufficient. Purely mechanical parameters are obtained through standard tests at temperatures sufficiently high or low for a single phase to be present. The thermal expansion coefficients of the phases and the difference of specific volume between them can be obtained through dilatometry tests. If one wishes to assess the accuracy of the formulae given previously for the transformation plastic strain rate, one must perform in addition dilatometry tests with some external stress applied, which requires more sophisticated equipment. For the numerical implementation of the models each time step, one should first correct the “elastically computed” stresses to account for the values of the transformation plastic strain increment and the classical plastic.