AlN precipitation during steel solidification using CA model

Based on the principles of metal solidification and cellular automaton(CA),as well as AlN precipitation thermodynamics and kinetics,a CA model of interdendritic AlN precipitation was established by coupling a large-size mesh describing the dendrite growth of Fe-C-Al-N alloys and a small-size mesh representing AlN precipitation based on transient chemical equilibrium.The results of single dendrite growth stimulated by this model were compared with the Lipton-Glicksman-Kurz solution to verify the correctness of the matrix dendrite growth simulation.The AlN morphology and dimensions obtained from the CA model simulations are following the experimental results.The presence of equiaxed dendrite in the computational domain results in a significant coarsening of the columnar dendrite and a uniform solute distribution around them,and the AlN solid phase fraction decreases.Simulations of AlN precipitation at different wetting angles were also performed,and it was found that the solid phase fraction of AlN decreased with the increase in wetting angle.Thus,it is confirmed that the established model is an effective method to simulate interdendritic AlN precipitation.

A CA-LBM model for simulating dendrite growth with forced convection

A two-dimensional coupled model of the cellular automaton(CA)and the lattice Boltzmann method(LBM)was developed to simulate the solute dendrite growth of Fe-C-Mn-S alloy in the presence of forced convection.The model describes the transport phenomenon by the evolution of moving pseudo-particles distribution functions and utilizes the LBM to solve fluid flow and solute transport under forced convection numerically.Based on the solute field calculated by the CA technique,the dynamics of dendrite growth were determined by the previously proposed local solute balance method.The accuracy of the forced convection dendrite growth model was verified by comparing the CA-LBM model with Lipton-Glicksman-Kurz analytical model.It is revealed that the dendrite symmetry structure is destroyed compared to free diffusion,and the upstream arm is more developed than the downstream arm of the dendrite.The enriched solute segregates more at the downstream side than at the upstream side of the dendrite.The length of the upstream dendrite arm increases firstly and then becomes stable with the increase in the flow velocity,the dendrite necking is restrained,and the vertical dendrite arm becomes longer.

Analysis on Initial Defects Based on Mechanical State of Meniscus Shell

The meniscus shell plays an important role in slab quality and process operation for continuously cast steel. One decisive reason is initial solidifying shell and growing dendrite under the mechanical stress caused by mold oscil- lation and liquid steel flow to generate disturbance of casting. The mechanical state of meniscus shell was analyzed using mathematical models in combination with thermo-physical properties and flow rate of steel to shed light on the formation of initial defects. The results show that the mold oscillation is a critical factor on the initial crack formation because the periodic stress makes the shell bending. The formed crack may also expand and propagate due to the fol- lowing secondary cooling and straightening behavior. The primary dendrite has high possibility to be broken by fluid flow in the solidification front to lead to the non-uniform thickness of solidifying shell. The inter-dendrite bridging is also likely to be formed to produce other internal defects, such as air hole and solute enrichment in the residual mol- ten steel located in the bridging area.