Microstructure Evolution of Cold Rolled Hot Dip Galvanized Dual-Phase Steel during Continuous Heating Process

The annealing process of 800MPa grade hot dip galvanized DP steel was simulated on Gleeble-1500 thermo-mechanical simulator. The recovery and recrystallization of ferrite and the formation of austenite during the continuous heating process were studied in this paper. The results show that the fine equiaxed recrystallized nucleus started emerging nearby grain boundaries of deformed ferrites when the heating temperature was 630°C. With the increase of temperature, the recrystallized grain began to grow up, some new crystallized nucleus formed in other places with high stored energy of deformation. when the heating temperature was 690°C, the recrystallization process was basically finished, the deformed microstructure had been replaced by equiaxed ferrite grains. When the heating temperature was 730°C, the austenite nucleated on the carbide particles of the ferrite grain boundaries in the original pearlite area mainly. Some austenite also nucleated on the ferrite grain boundaries or the carbide particles within the ferrite grain. When the temperature was 750°C, the austenite began to grow along and parallel to ferrite grain boundaries.

Coupled Simulation of the Static Recrystallization in Hot Deformed Austenite on Mesoscale

The kinetics and microstructure evolution during static recrystallization (SRX) of hot-deformed austenite in a low carbon steel are simulated by coupling a cellular automaton (CA) model with a crystal plasticity finite element model (CPFEM). The initial deformed characteristics, which include the stored energy of deformation and the crystallographic orientation induced by a plane strain hot compression are simulated using a crystal plasticity finite element model. These data are mapped onto the CA regular lattices as the initial parameters for SRX simulation. The coupled simulation results reveal that the heterogeneous distribution of the stored energy of deformation results in non-uniform nucleation and a slower kinetics. The influence of non-uniform distribution in stored energy on the SRX kinetics and microstructure evolution is discussed based on a microstructural path (MP) analysis.

Atomic-Scale Simulation of Grain Boundary Kinetics during Recrystallization

We present two-dimensional molecular dynamics (MD) simulations of symmetric tilt grain boundary kinetics, driven by stored energy of deformation. The latter is introduced by prescribing a well-defined gradient in dislocation density across a flat grain boundary. Bicrystals simulations reveal that the boundary motion, albeit jerky, increases linearly with simulation time. We also employ a control simulation to extract the driving force for motion, which then yields a unique boundary mobility. Preliminary comparisons with curvature driven boundary migration for misorientations 30° and 22.78° suggest that misorientation dependence of boundary migration is significantly less anisotropic, in turn implying that the mechanism of motion itself is different.