Simulation Of Precipitation Of Intergranular Nitride And Evolution Of Dendrite In Flow Field During Solidification Process Of Steel

Microstructure formation is due to a combination of temperature and solute transport,phase change thermodynamics and kinetics,interfacial curvature,and nucleation.Nitride(MN)precipitation can refine the grain and improve the toughness and strength of the steel,while the forced convection process in the molten steel under the influence of external forces is essential for the growth of dendrites and the mass and heat transfer processes.With the development of computer technology,numerical simulation has become an important method to study the microstructure evolution of alloys.Based on the principles of metal solidification and cellular automaton(CA),MN precipitation thermodynamics and kinetics,a CA model of interdendritic MN precipitation was established by coupling a large-size mesh describing the dendrite growth of Fe-C-M-N alloys and a small-size mesh representing AlN precipitation based on transient chemical equilibrium.A nucleation point was set in the center of the computational domain.The dendrite growth of Fe-C-Al-N alloy was simulated using the CA coupling model.The calculated results were compared with the Lipton-Glicksman-Kurz(LGK)solution to verify the correctness of simulating the matrix dendrite growth.The AlN,CrN,and VN precipitation during the solidification of Fe-C-Al-N,Fe-C-Cr-N,and Fe-C-V-N alloys were simulated using the CA coupled model,and the morphology and dimension of the precipitated particles obtained from the simulation were compared with the precipitation experiments at the same solute concentration,and the results were in good agreement to verify the correctness of this model for simulating MN precipitation.The CA-LBM model describing the dendrite growth of Fe-CAl-N alloy under forced convection was developed based on the lattice Boltzmann method(LBM),coupled with the CA model of the same mesh.It is found that the symmetric structure of the dendrite is broken.The length of the dendrite arm on the upstream side is 6.46 times longer than that on the downstream side and 1.88 times longer than that on the vertical side.The simulation results are compared with the linear solvable theory to verify the reasonableness of the CA-LBM model.The AlN precipitation of Fe-C-Al-N alloy at different wetting angles was simulation by the CA coupling model,and it was found that the AlN precipitation was decreasing with the increase of wetting angle;meanwhile,the presence of equiaxed dendrite would destroy the matrix columnar dendrites growth and its surrounding solute field distribution,and the precipitation solid phase fraction was delayed from 0.7052 to 0.7325,while the AlN solid phase fraction was reduced by 18.7%.The CA-LBM model was used to simulate the dendrite growth at different flow velocities.It was found that the dendrite arm length on the upstream side and vertical side tended to increase and decrease on the downstream side when the flow velocity was 0.02～0.10 m·s-1,while the dendrite arm length did not change much with the flow velocity at 0.10～0.20 m·s-1,and the dendrite necking phenomenon is reduced.Therefore,the model developed in this paper is used to simulate MN precipitation and dendrite growth,which can help accurately understand the formation mechanism and dominant factors and is of great significance to optimizing steel solidification organization and properties.