Materials Science Forum Vols. 575-578

Abstract: The finite element model of coupling the thermal field with structural analysis is proposed in order to analyze the thermo-stress of casting ladle structure. The thermal fields of casting ladle with refractory lining structure are computed according to the thermal properties of materials and boundary conditions. Numerical simulation shows that that computed outer temperatures of casting ladle agree with measured ones. The thermo-stress of casting ladle structure is simulated by taking thermal loadings as the loading conditions of the steel shell structure. Material behaviors were described by the Drucker–Prager plasticity model and Von Mises yield criterion. Calculation results of thermo-stress fields shows the outer shell structure is safety under the action of thermal loadings.

Abstract: In the process of the continuous straightening during continuous casting, elevated temperature creep and stress relaxation are remarkable. During continuous straightening, temperature of steel billet is very high, where the characteristic of deformation is low strain and low strain rate. Experiments of elevated temperature creep, stress relaxation and elevated tension under the conditions of continuous straightening were carried on Gleeble3500 thermal-mechanical simulation machine and the results indicate that both the creep speed and the stress relaxation speed are very fast in the conditions of continuous straightening. Then metallurgical structures were observed. A lead plate was used to simulate the billet during continuous straightening and then straightening forces were measured. An elasto-viscoplastic model and an elasto-plastic model were built according to the experiment to calculate the straightening forces. The contrast between the calculation results and the measured data shows that ignoring the creep and stress relaxation will result in great errors when calculating the straightening forces in continuous straightening. Carrying researches on elevated temperature creep and stress relaxation and using their characteristics in design has great importance to improve the quality and quantity of billets in the process of continuous casting.

Abstract: The heat transfer during the casting solidification process includes: the heat radiation of the high temperature casting and the mold, the heat convection between the casting and the mold, and the heat conduction in the casting and the casting to the mold. In this paper, a formula of time step in simulation of solidification is derived, considering the heat radiation, convection and conduction based on the conservation of energy. The different heat transfer condition between the ordinary sand casting and the permanent mold casting is taken into account in this formula. The characteristic of heat transfer in the interior and surface of the casting is also considered. The numerical experiments show that this formula can avoid radiation of the computation, and can improve the computational efficiency about 20% in the simulation of solidification process.

Abstract: The numerical solidification simulation for oceangoing freighter rudder horn steel casting has been made and the location and reasons forming casting defects have been predicted by HUAZHU CAE software. Simulating result shows that the casting perfects can be realized by means of the technological optimization and rationally assembling gating system, risers and iron chill. After magnetic particle detection and ultrasonic inspection, the properties and microstructure of the oceangoing freighter rudder horn steel casting are in accord with the standard of USA, Germany and Japan.

Abstract: In the present work, rapidly solidified alloys strips with Al-0.24Ti and Al-21Si-0.24Ti(in wt.%) were prepared by single roller melt-spinning method. The microstructures, phase and morphology characteristics of the resultant strips were characterized by means of scanning electron microscopy (SEM),transmission electric microscopy (TEM) and XRD technique. The results show that the grains have been refined after rapid solidification processing, and the micro-nanocrystalline grain are formed. The morphology characteristics can be changed. The microstructures of Al-0.24Ti alloys strip are micro-nanostructure α-Al solid solutions which are similar with granular or nodular, the corresponding SAD pattern is rings, it presents characteristic of polycrystal; Compared with equilibrium solidification, the microstructures of hypereutectic Al-Si alloy are changed obviously. They are composed of primary micro-nanostructure α-Al supersaturated solid solution and nanocrystal granular (α+Si) eutectic which set in the supersaturated solid solution. The nucleation and growth of primary silicon are suppressed and primary silicon can not precipitate, meanwhile, α-Al phase is nucleated which prior to eutectic, therefore the microstructures become into the metastable state. The mechanism of the formation for microstructures of melt-spinning alloys has also been discussed.

Abstract: Base on the coupled three-dimensional model of flow temperature and apparent viscosity on semisolid materials, the mould filling processes of liquid and semisolid magnesium alloys have been analyzed. The simulation results showed that the semisolid mould filling with the characteristic of pseudo-plasticity and Bingham type is steady and the air entrapment is much smaller than that of liquid die casting. Therefore, the semisolid die casting can prevent from those defects produced by the traditional die casting, which offer a new technology for lower interior defects and better quality.

Abstract: Compared with traditional blazing furnace, the Continuous Casting-Direct Rolling is an advanced manufacturing steel technology, which can reduce energy waste, decrease pollution and enhance efficiency. The characteristics of steels during induction heating are complex, the change of material properties with temperature makes exact analysis methods very difficult to implement. Therefore, a powerful computer aided numerical tool (i.e., finite difference analysis) is selected to numerically model the induction heating process in this paper. The mathematic model coupling with electromagnetic field and thermal field was established, and it was solved by finite difference method (FDM), thus the slab temperature distribution and its variation with time were obtained, and the characteristics in whole induction heating process were studied. To validate the program feasible, the results were evaluated and compared with experiment results, which showed that the simulation results are reliable and effective. The skin effect in heating process from the two results was studied and demonstrated, the temperature change caused by different parameters such as the induced power intensity and the corner radian were also presented, which indicate that the slab temperature can be heated uniformly through adjusting these parameters, thus the continuous casting slab can meet the rolling requirement.

Abstract: Level Set Method is an appropriate mathematical tool for solving two-phase flow problems. The main advantage of Level Set Method is its efficiency to deal with complex interfaces, even if topology changes. In this paper, the liquid-gas two-phase flow is simulated using a combination of Level Set Method and SOLA method. SOLA is used to compute the Navier-Stokes equation, and Level Set Method is used to track the interfaces between the liquid and the gas during mold filling process. The difficulty in the simulation of two-phase flow comes from great change of physical parameters (e.g., density and viscosity) across the interfaces. Level Set Method allows for large density ratio and jump in viscosity without reconstructing the numerical grid. In this work, the forming and moving of the gas bubbles in liquid were numerically simulated by Level Set approach. The numerical simulation results and experiments suggest that Level Set Method is quite reliable and effective for the simulation of liquid-gas two-phase flow during mold filling.