Browsing by Subject "stochastic model"

Now showing 1 - 2 of 2

Access status: Open Access ,
Accounting for the random character of nucleation in the modelling of phase transformations in steels
(Wydawnictwa AGH, 2023) Poloczek, Łukasz; Kuziak, Roman; Foryś, Jakub; Szeliga, Danuta; Pietrzyk, Maciej
In our earlier work, a stochastic model of multi-stage deformation at elevated temperatures was developed. The model was applied to calculate histograms of dislocation density and grain size at the onset of phase transformation. The histograms were used as input data for the simulation of phase transitions using the traditional deterministic model. Following this approach, microstructural inhomogeneity was predicted for different cooling conditions. The results obtained, showing the effect of dislocation density and inhomogeneity of austenite grain size on the microstructural inhomogeneity of the final product, can be considered reliable as they are based on material models determined in previous publications and validated experimentally. The aim of the present work was to extend the model by taking into account the stochastic nature of nucleation during phase transitions. The analysis of existing stochastic models of nucleation was performed, and a model for ferritic transformation in steels was proposed. Simulations for constant cooling rates as well as for industrial cooling processes of steel rods were performed. In the latter case, uncertainties in defining the boundary conditions and segregation of elements were also considered. The reduction of the computing costs is an important advantage of the model, which is much faster when compared to full field models with explicit microstructure representation.
Access status: Open Access ,
Thermal-mechanical finite element simulation of flat bar rolling coupled with a stochastic model of microstructure evolution
(Wydawnictwa AGH, 2022) Szeliga, Danuta; Czyżewska, Natalia; Kusiak, Jan; Kuziak, Roman; Morkisz, Paweł M.; Oprocha, Piotr; Pietrzyk, Maciej; Piwowarczyk, Michał; Poloczek, Łukasz; Przybyłowicz, Paweł; Rauch, Łukasz; Wolańska, Natalia
It is generally recognized that the kinetics of phase transformations during the cooling of steel products depends to a large extent on the state of the austenite after rolling. Austenite deformation (when recrystallization is not complete) and grain size have a strong influence on the nucleation and growth of low-temperature phases. Thus, the general objective of the present work was the formulation of a numerical model which simulates thermal, mechanical and microstructural phenomena during multipass hot rolling of flat bars. The simulation of flat bar rolling accounting for the evolution of a heterogeneous microstructure was the objective of the work. A conventional finite-element program was used to calculate the distribution of strains, stresses, and temperatures in the flat bar during rolling and during interpass times. The FE program was coupled with the stochastic model describing austenite microstructure evolution. In this model, the random character of the recrystallization was accounted for. Simulations supplied information about the distributions of the dislocation density and the grain size at various locations through the thickness of the bars.