Modeling Of Metal Hot Deformation And Weld Solidification Process Using Cellular Automaton Method

The microstructure exerts a strong influence on the properties of metallic materials. Therefore,microstructural control during thermo-mechanical and subsequent process is an important and support factor in theoretical development and technology optimization.In the past decades,the studies of microstructural evolution are mainly based on a number of experiments and semi-empirical formulations.It can cause great expense of time and costs, and can not provide a direct view of microstructural development.Recently,with the advent of powerful computers and new simulated techniques,computer simulation has been playing an increasing important role in the studies on microstructural evolution during thermo-mechanical process.Cellular automaton(CA) is one of meso-scale simulated methods widely used in materials science.Compared with the traditional numerical methods,CA is relatively flexible in simulating different physical systems.It combines the utilities of both deterministic and stochastic transitional rules.Theoretical models of materials process can be readily incorporated into the CA simulation through appropriate transformation function to model nucleation and grain growth.In this paper,microstructural evolution of metal hot deformation and weld solidification are simulated by using CA method.The main contents are as follows:(1) Based on dynamic recrystallization(DRX) metallurgical principles,a dynamic recrystallization in pure metal two-dimensional(2-D) CA model is developed.The evolution of dislocation density,DRX nucleation and grain growth are under consideration.Then,a modified DRX 2-D CA model for particle-containing alloy is constructed.Particle stimulated nucleation(PSN) is incorporated into the CA model to determine the influence of second-phase particles on the nucleation of DRX.It is considered that dispersed second-phase particles enhance the accumulation of dislocation density and resist the movement of grain boundary.The models are applied to model single hit compression tests of pure copper and GCr15 bearing steel.It is observed that DRX kinetics depends on both thermo-mechanical parameters and initial grain sizes.The simulated results are compared with the experimental results and are found to be in good agreement.(2) A 2-D CA model is developed to predict the microstructural evolution during two-stage hot deformation of metallic materials.The physically-based model has integrated the effects of the individual metallurgical phenomena related with the hot deformation, including DRX,static recovery,static recrystallization(SRX),metadyanmic recrystallization (MDRX) and grain growth,etc.The model is validated by simulating double hit compression tests of pure copper and GCr15 beating steel.The effects of the interval and pre-strain on microstructural evoutions,stress-strain curves and recrystallization kinetics are investigated. The simulated results agree well with the experimental results and theoretical models.(3) The 2-D DRX CA model is extended to a three-dimensional(3=D) one.The simulation domain is subdivided into a regular lattice of cubic cells and the modified Moore's neighbour rule is introduced.The 3=D model is applied to simulate the microstructural evolution of pure copper and GCr15 bearing steel single hit compression tests.The effects of intial grain size and thermo-mechanical parameters on stress-strain curves and kinetics of DRX are discussed.(4) A quasi=synchronous integration model is constructed by coupling a CA model with a grain deformation model.The uniform topology deformation technique is introduced by changing the size of CA grid so as to keep the volume constant.The model is applied to simulate single hit compression process for pure copper and GCr15 bearing steel.The influences of grain deformation on microstructural evolution and the kinetics of recrystallization are investigated.(5) A 2-D welding solidification model is developed by coupling CA with monte carlo (MC) method.The finite difference(FD) method is introduced to calculate heat transfer and solute diffusion.The CA/MC model is used to construct the evolution rule of nucleation and growth of solid.The key problems of combination between CA/MC and FD method are solidification latent heat and solid/liquid interface solute partitioning.The model is introduced to simulate welding solidification process in 17Cr-Ti-N stainless steel.Based on the experimental results that titanium nitride(TiN) works as an inoculant of equiaxed grain formation,given number of TiN is allocated to CA cells randomly.The columnar-to-equiaxed transition of welding solidification microstructure is predicted.The simulated results agree well with experimental results.