Mujun Long

Hydraulics and Mathematics Simulation on the Weir and Gas Curtain in Tundish of Ultrathick Slab Continuous Casting

The molten steel flow pattern in continuous casting tundish could be improved if the flow control devices were properly used. With reasonable application of weir and air curtain, the disturbance at injection zone of the tundish was reduced. The flow path of the molten steel was changed, and the short-circuit flow was eliminated. Therefore, the residence time was lengthened. An air curtain with bubbles floating could promote the surface flow and improve inclusions removal. The application of weir and air curtain in an ultrathick slab continuous casting tundish was investigated with hydraulics and mathematics simulation. The residence time and dead volume fraction were studied through orthogonal experiments with different positions of the flow control devices. The efficiency of three factors was analyzed, and the optimum positions of the weir and air curtain were obtained. Besides, the discrete phase model was suitable for simulation of the interaction between gas bubbles and molten steel, and the mathematics results shown the optimum one got larger inclusion flotation rate.

Two-dimensional heat transfer model for secondary cooling of continuously cast beam blanks

Abstract A two-dimensional heat transfer model was developed for the secondary cooling system during beam blank continuous casting. The finite element method was used to calculate the heat transfer. Accurate cooling boundary conditions in the secondary cooling zone are involved, including spray water cooling, water evaporation cooling, radiation cooling and roll contact cooling in the casting direction and non-uniform distribution of spray water flow density in the cross-section. The causes of longitudinal crack at the fillet during Q235 steel continuous casting were analysed on the basis of the simulation of the developed model, and then the spray water flow and the transverse nozzle layout were optimised. Practical results show that the surface quality of the beam blank improved after optimisations. Numerical results from the present model were validated using previous experimental measurements, which show good agreement.

Mathematical Modeling of Heat Transfer in Mold Copper Coupled with Cooling Water During the Slab Continuous Casting Process

The heat transfer in mold copper plays an important role in the solidification behavior of steel. In this study, a three-dimensional heat transfer model coupled with flow behavior of the cooling water was established to analyze the temperature field of the copper and water slots. And this model was verified by the measured temperature rise of cooling water at the inlet and outlet of slots. The advantages of this model were obtained by comparing it with Dittus–Boelter model and the Sleicher–Rouse model, which did not consider the flow of water. The results show that the Dittus–Boelter model has the highest temperature and that the coupled model has the lowest temperature. Moreover, the coupled model includes calculation of the temperature and velocity field of the cooling water inside the slots. This temperature information is very helpful for predicting the water boiling in the slots. In addition, the coupled model shows that the temperature, heat flux, and heat transfer coefficient around the water slot wall are different from the conventional models.

Effects of Partition Coefficients, Diffusion Coefficients, and Solidification Paths on Microsegregation in Fe-Based Multinary Alloy

To quantitatively study the effects of partition coefficients, diffusion coefficients, and solidification paths on solute microsegregation, an analytical model was developed combined with the calculation of thermodynamic software FactSage. This model, applied with variational partition coefficients and temperature-dependent diffusion coefficients, is based on the Voller–Beckermann model and is extended to take into account the effects of multiple components and the peritectic phase transformation using FactSage. The predictions agree well with a range of measured data and the results of other numerical solutions. As the results indicate, the partition coefficients of solutes are functions of temperature and phase fraction during the solidification process, and the solute microsegregation increases significantly with decreasing partition coefficients. The calculations of solute microsegregation ratio (CL/C0) in the interdendritic region are related to solidification paths. The microsegregation ratios of P and S increase as the initial C concentration increases, while they reduce with increasing initial C contents for solutes C and Si. Parameter sensitivity analysis was performed, and the results indicate that the solute microsegregation shows larger variation with partition coefficients and solidification paths than diffusion coefficients.

Study on Mathematical Model of Temperature and Stress for Thin Slab in Continuous Casting

The heat transfer and stress state of thin slab have a significant impact on quality of slab in the solidification process of continuous casting. A two-dimensional mathematical model of heat transfer, which has considered the characteristics of solidification and heat transfer and the influence of secondary cooling system and equipment on solidification process, has been established to analysis temperature distribution of cross-section and main factors impacting on temperature distribution. A two-dimensional thermal-elastic-plastic stress model has been established to analysis the stress and strain distribution of thin slab in the continuous casting, and it uses the two-dimensional slicing method in a moving coordinate and finite element method for solving the model. The simulation results can provide a theoretical guide for the optimization of continuous casting process parameters and improvement of quality of thin slab. Keywords-continuous casting;thin slab; heat transfer; stress; mathematical model I. INTRODUCTION Continuous casting process is a cooling and solidification process of molten steel and it takes away the superheat, latent heat of solidification and residual heat of molten steel to make it to be solidified slab. It always uses cooling method of spraying water to take the heat away. Its very complex for the internal solidification, heat transfer and stress state of slab in the process of solidification, and the heat transfer density has a significant impact on solidification rate, the formation of slab profile, uniform shell of slab and stress state of slab. Under the complex stress state of molten steel static pressure, slab drawing force, straightening force and thermal stress, it will lead to complex deformation for the slab shell, and the crack and shape defect may appear when excessive deformation. Compared with traditional continuous casting, thin slab more easily bring crack for its high speed, thin slab shell and high cooling intensity. Therefore, its of great significance to understand and master the heat transfer characteristic and state of stress and strain for technical parameters design and optimization of continuous casting and improvement of slab quality.

Simulation and Investigation on Physical Properties of Continuous Casting Slab AH36 at High Temperature

During the continuous casting process, physical properties of slab for continuous casting at high temperature have an important effect on the slab quality in different part and the curve establishment of external target temperature for slab. It has significance to simulate and investigate the physical behaviors of slab at high temperature during the continuous casting process. Investigation existent in this field is scarce around the world. Continuous casting process is a complicated cooling process in unsteady state that sometimes the external temperature of slab will rise. In allusion to temperature rise and temperature drop, the paper simulated and investigated the physical properties of slab AH36 at high temperature under conditions of different temperatures and different temperature variation velocities, such as thermal expansion property, differential thermal analysis curve (DSC), isobaric thermal capacity (CP) and so on. Results of the investigation have provided a scientific data base for a further study on continuous casting technology and quality control for steel AH36.

Computation of Phase Fractions in Austenite Transformation with the Dilation Curve for Various Cooling Regimens in Continuous Casting

A concise model is applied to compute the microstructure evolution of austenite transformation by using the dilation curve of continuously cast steels. The model is verified by thermodynamic calculations and microstructure examinations. When applying the model, the phase fractions and the corresponding transforming rates during austenite transformation are investigated at various cooling rates and chemical compositions. In addition, ab initio calculations are performed for paramagnetic body-centered-cubic Fe to understand the thermal expansion behavior of steels at an atomic scale. Results indicate that by increasing the cooling rate, the final volume fraction of ferrite/pearlite will gradually increase/decrease with a greater transforming rate of ferrite. The ferrite fraction increases after austenite transformation with lowering of the carbon content and increasing of the substitutional alloying fractions. In the austenite transformation, the thermal expansion coefficient is sequentially determined by the forming rate of ferrite and pearlite. According to the ab initio theoretical calculations for the single phase of ferrite, thermal expansion emerges from magnetic evolution and lattice vibration, the latter playing the dominant role. The theoretical predictions for volume and thermal expansion coefficient are in good agreement with the experimental data.

Thermo-Physical Properties of Petroleum Coke during Calcining Graphitization Process

The relationship between thermo-physical properties of petroleum coke and temperature is of importance for determining of the operating parameters during the calcining graphitization process. In this paper, the variations of thermo-physical properties of petroleum coke versus temperature were investigated, such as the DSC-Tg curve, the specific heat capacity, the thermal diffusion coefficient, the thermal conductivity, and so on. The thermal analysis curve of petroleum coke showed synchronous thermal hysteresis at higher heating rates, indicating that a larger heating rate will cause delay of thermal effects. The thermal diffusivity of petroleum coke decreased during the calcining process. With increasing temperature, coefficient of heat conductivity and specific volume heat of the petroleum coke increased with a decreasing variation rate. The research provides a database for the calcining graphitization process of petroleum coke.

Thermal Simulation on Mechanical Properties of Steel Q345 for Continuous Casting Slab

The modeling of solidification in Continuous Casting demands the mechanical properties of steels at high temperature. These mechanical properties parameters provide the design data for the target surface temperature curve and dynamic control modeling of secondary cooling system, and are used to research hot delivery and crack mechanisms of cast slab. The properties parameters of steels can be obtained by physics simulation experiment. Following processing parameters in Continuous Casting, the stress-strain curves and mechanical properties of steel Q345 were tested and analyzed. Then the curves of relationships between the yield strength, tensile strength, reduction of area, Young’s modulus, plastic modulus of steel Q345 and temperature were obtained. We found the strength of steel Q345 cast slab felled down basically; the ductility was decreased below 700°C, in the range of 725°C-900°C and 1275°C-melting point. The plastic modulus was analyzed with the different temperatures and the different strains in detail. The parameters of mechanical properties for steel Q345 were obtained for using in elastic-plasticity stress model.

Hot Ductility of X70 Pipeline Steel in Continuous Casting

Transverse cracks in continuous cast steel may easily form if the hot ductility of the continuous cast steel is poor at the straightening stage. In this paper, the hot ductility of X70 pipeline steel was studied at various temperature from 600 to 1300 °C. The results show that the steel has a good hot ductility (RA above 70%) at 800–1000 and 600–650 °C. And the steel exhibits a hot ductility trough (RA below 80%) at 650–800 °C, which is mainly contributed to the austenite–ferrite transformation. For further understanding the low ductility, the fracture surface was examined by scanning electron microscope, and the second phase particles was examined by energy spectrum analysis. The results indicate that the low ductility of the steel is affected by the equiaxed (Fe, Mn)S precipitate as well as austenite transformation at the third brittle zone.