Internal Variable and Cellular Automata-Finite Element Models of Heat Treatment
Heat treatment is one of the most important process es in advanced steel products manufacturing. While production processes are still being optimised, numerical modelling of heat treatment is very useful. Finite Elements Method (FEM) is widely used in these cases, due to its proved potential fo r modelling of continuous, macroscopic phenomena. However, its capability to simulate microscale and noncontinuous processes is very limited. Introducing e mpirical model of phase changes into FEM, usually based on Internal Variable Method (IVM) is useful when the information about volume fraction of the phases in the domain a nd stresses due to phase change satisfies the requirements. Notwithstanding, it is difficult to obtain information in-depth about microstructure during heat treatment, because it requires more sophisticated description of phase change process. Those problems can be resolved with multiscale modelling. One of the current approaches in this fi eld employs FEM for computing of temperature, stress and strain fields, while non-co ntinuous, microscale model is based on Cellular Automata (CA) method [1]. Recently, several CA models concerning phase transformation have been proposed, e.g. [2]. In th is paper Cellular Automata ‐ Finite Elements (CAFE) is applied for modelling of both macroscopic and microscopic influence of heat treatment. It also takes into acc ount a stochastic character of processes, which is hard to obtain in typical FEM or IVM solut ion. The advantage of CAFE model ensues from direct representation of microstructure. Although the current microstructural CA model is two-dimensional, it reproduces topological and morphological relations between components of microstructure. The state of CA cells is updated synchronically in cons ecutive time steps. Every cell includes state vector representing fractions of all phases. Thermodynamics of phase transition is a base for a rule-based knowledge rep resentation in the CA model. However, the nondeterministic definition of neighbo urhood and probabilistic energy
Mesoscale simulation of ferrite transformation from deformed austenite during continuous cooling in a C-Mn steel using a cellular automaton method
A two dimensional cellular automaton (CA) method is adopted to investigate the growth kinetics of deformed austenite to ferrite transformation during continuous cooling in a C-Mn steel. During thermomechanical processing, part of the energy of deformation is stored in the austenite as the increase in the dislocation density within steels. This stored energy is incorporated into the present CA method as an additional driving force for the ferrite transformation. The modeled ferrite growth kinetics and grain size are compared with the experiments in the literature. (C) 2004 Elsevier B.V. All rights reserved.
Importance of deformation induced ferrite and factors which control its formation
AbstractThe influence of strain, strain rate, temperature, and grain size on the formation of deformation induced ferrite has been examined. Deformation induced ferrite forms very readily in both fine and coarse grained steels and much more rapidly than the ferrite from strain free austenite. Very small strains are sufficient to induce the production of such ferrite and the temperature range over which it appears spans from just below the Ae3 temperature down to the undeformed Ar3 temperature. Although it forms readily in both coarse and fine grained steels, the volume fraction produced is sensitive to the austenite grain size. In coarse grained steels, deformation at low strain rates is concentrated along the grain faces; extensive dynamic recovery occurs, which is why the ferrite remains soft, so that only thin ferrite films are able to form. At higher strain rates, work hardening takes place so that the strength of the ferrite at high strains approaches that of the austenite. Under these conditions, th...