Incremental Formulation for the Prediction of Flow Stress and Microstructural Change in Hot Forming

Abstract

In metal forming, the workpieces are formed to the desired shapes or profiles. Especially in hot forming, the microstructure of workpiece changes during plastic deformation. Modern forming technologies allow to control the shape and the microstructure of formed product in a wide range and will gain increasing importance in future in the field of metal forming. In order to develop this forming technology which may be called “macroscopic microscopic materials processing”, theoretical predictions of plastic deformation as well as microstructural changes are indispensable. A new mathematical formulation to predict flow stress and microstructural change in hot forming will be presented in this paper. This model is based on an incremental formulation taking the dislocation density as a representative variable.

Three-dimensional Numerical Analysis of Microstructural Evolution in and after Bar and Shape Rolling Processes.

“…Figure 1 shows the schematic illustration of integrated analysis. Change in distribution of dislocation density and grain size during hot rolling were analyzed by incremental formulations for microstructure evolution, 12,13) temperature transition and strain rate along each stream line was used as 'process oriented' boundary conditions. Material parameters, embedded in recrystallization kinetics, recoveries etc.…”

“…It was the purpose of current research by implying the incremental formulation proposed [12][13][14][15][16] to demonstrate an integrated numerical model of predicting microstructural evolution, three-dimensional plastic deformation and temperature changes applied to the industrial hot bar rolling and Hbeam rolling. Their characteristics of microstructural evolution in industrial rolling processes will be the topic of examination and discussion based on the information obtained from numerical analysis.…”

“…For this reason, authors had proposed the incremental formulation for the prediction of microstructural changes in austenite state and phase transformation state. [12][13][14][15][16] In the model, authors used dislocation density and grain size as representatives to trace the microstructural evolution procedure. By this model, the microstructural changes in austenite state has been evaluated continuously, and the effect of plastic deformation on phase transformation prior to cooling can described by the resid-ual dislocation.…”

Rolling Technology and Theory for the Last 100 Years: The Contribution of Theory to Innovation in Strip Rolling Technology

“…Therefore, the technique to calculate the change of the internal micro structure depending on the history of stain velocity and rolling temperature was necessary and some techniques were suggested in the 1990s. [124][125][126] In addition, the internal micro structure of material after hot rolling changes while cooling down. The model to analyze the incremental phase transformation for the purpose of the nucleation mechanism in the grain boundary was formulated by Yanagimoto and others, based on the models 127,128) targeted at the plain carbon steel for ferrite, pearlite, and bainite transformation.…”

Numerical Analysis for the Prediction of Microstructure after Hot Forming of Structural Metals

“…As finite element analysis can reveal the transient changes in temperature and strain rate at each point of the structural metal during forming, we need a new approach to reflect this transient change in process variables in the evolution of microstructure. This movement promoted the development of an evolutional method by Karhausen and Kopp 11) and an incremental dislocation density and microstructural evolution analysis method by Yanagimoto et al for dynamic events, 12) static events 13) and phase transformation.…”