A Physically based Microstructure Model for Predicting the Microstructural Evolution of a C-Mn Steel during and after Hot Deformation

Abstract

A physically based model for predicting microstructural evolution has been developed. The model is based on a physical description of dislocation density evolution, where the generation and recovery of dislocations determine the flow stress and also the driving force for recrystallization. In the model, abnormally growing subgrains are assumed to be nuclei of recrystallized grains and recrystallization starts when the subgrains reach a critical size and configuration. To verify that the model is able to describe dynamic, static and metadynamic recrystallization of C‐Mn steels, hot compression tests combined with relaxation were performed at various temperatures, strains and strain rates. The model showed reasonable agreement with the experimental data for the compression tests performed at temperatures ranging from 850°C to 1200°C and strain rates ranging from 0.1 to 10 s−1. Similarly, the calculations of the stress relaxation tests were in accordance with experimental data. A validation of the model was done by calculating a multi‐step test where good agreement with both flow‐stress values and grain sizes was obtained. The main purpose of the model is to predict the microstructural evolution during hot rolling and this investigation presents very promising results.

Modeling the Effect of Solute Drag on Recovery and Recrystallization during Hot Deformation of Nb Microalloyed Steels

“…Compared to the measured grain size for a C-Mn steel, 11) with more volume fraction of MnS, heated at the same temperature, the grain size of the Nb1 steel is smaller, see Fig. 3.…”

“…4 to Fig. 6 flow stress curves from compression tests of the two Nb steels and a C-Mn steel 11) are shown.…”

“…This investigation is a continuation of the work by Engberg and Lissel 11) where a physically-based model for describing the microstructural evolution of austenite during hot deformation was validated for a plain C-Mn steel. In the present paper, the solute drag effect of Nb on recovery and recrystallization is investigated using the microstructure model.…”

“…When more dislocations are generated, the subgrain size, R sub , is reduced. In the model it is assumed that the subgrain size is proportional to the mean free distance of dislocation slip and the subgrain development is described by 11) ...................... (4) where the parameter k s is a constant.…”

“…The growth rate of recrystallizing grains are dependent on the mean value of the vacancy concentration on both sides of the moving boundary and is described by 11) ........ (11) where k r (ϳ1) is a constant, M g is the grain boundary mobility and c v,def and c v,rec , are the vacancy concentration in the deformed and recrystallized material, respectively.…”