Huabiao Chen

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 transport phenomena in the beam blank continuous casting mould coupling copper mould with molten steel

The copper mould and molten steel were modelled simultaneously by a three-dimensional (3D) model, which couples fluid flow, heat transfer and solidification. Thermal boundary conditions (e.g. air gap distribution, slag resistance, contact resistance) along casting direction and circumference direction were discussed and applied. The results of solid shell thickness distribution were compared with reference experimental data and reasonable agreements were found. The calculations indicate that, the shell thickness distribution along circumference in web was affected by the cross-section sizes. The uniform shell thickness distributions at narrow face and R corner were caused by the scouring of fluid flow. The heat transfer fluxes at hot face of mould were various at different locations.

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.

Manganese Influence on Equilibrium Partition Coefficient and Phase Transformation in Peritectic Steel

The equilibrium partition coefficient (k) affected by chemical component, phase constitution and temperature is a critical parameter related to solutes distribution during steel solidification. In this study, the effect of Mn on equilibrium partition coefficient and phase transformation was quantitatively analysed. A technique according to the relative amount of δ-Fe and γ-Fe to determine the equilibrium partition coefficients of solutes in L, δ-Fe, and γ-Fe three-phases coexistence zone was proposed. Results showed that Mn promotes the generation of γ-Fe and its effect on peritectic reaction zone is significant. The equilibrium partition coefficients were determined based on the phase change and relative amount of δ-Fe and γ-Fe according to the solidification paths which undergo difference phase coexistence zone. All of \( k_{C}^{\delta } \), \( k_{Si}^{\delta } \), \( k_{Si}^{\delta + \gamma } \), \( k_{P}^{\delta } \), \( k_{P}^{\delta + \gamma } \), \( k_{S}^{\delta } \), and \( k_{S}^{\delta + \gamma } \) decrease with Mn increasing, while \( k_{C}^{\delta + \gamma } \) increases due to solute Mn promote the generation of γ-Fe forming from peritectic reaction.

Stress and Friction Distribution around Slab Corner in Continuous Casting Mold with Different Corner Structures

The non-uniform friction and thermal stress in the mold are important as causes of the transverse cracks around strand corner. To analyze the stress distribution features around strand corner, a three-dimensional thermo-elastoplastic finite-element mold model with different corner structures (right-angle, big-chamfer, multi-chamfer, and fillet) was established. The temperature field in the mold was indirectly coupled through a three-dimensional fluid flow and heat transfer model. In addition, the non-uniform mold friction stress loaded on the strand surface was calculated through a friction model. The results show that the stress distribution on the shell is similar to the temperature distribution. The stress concentration appears in the strand corner and the lower part of wide face. The friction stress enhances the corner stress around the edge of the air-gap. For chamfered molds, the stress around the corner between the wide face and chamfer face is larger than that between the narrow face and chamfer face. Around the corner region, both the stress peak and the area of the large stress zone of the right-angle strand are the largest, while those of big-chamfered, multi-chamfered, and fillet strands decrease in that order. The stress peak position of the chamfered strands is closer to the mold exit than that of the right-angle strand. Compared with the use of the right-angle mold, the application of chamfered molds is able to reduce the stress concentration around the strand corner.

Fluid flow and heat transfer behavior of liquid steel in slab mold with different corner structures. Part 2: Fluid flow, heat transfer, and solidification characteristics

ABSTRACT In this article, the complex transmission behavior was discussed in the slab mold with different corner structures. Results show that the up backflow is stronger than the down backflow. The cooling water temperature rise and heat flux through the wide face in the right-angle mold are the largest, while those through the narrow face in the multichamfered mold are larger than those in the big-chamfered mold. The corner temperature at mold exit of the right-angle, big-chamfered, and multichamfered strand increases. The shell thickness at the narrow face center in the chamfered mold is thinner than that in the right-angle mold.

Fluid flow and heat transfer behavior of liquid steel in slab mold with different corner structures. Part 1: Mathematical model and verification

ABSTRACT A three-dimensional model considering the fluid and temperature field of the liquid steel and cooling water, along with the copper plate temperature was established to study the fluid flow and heat transfer behavior of liquid steel in slab mold with different corner structures. Then, a two-dimensional stress–strain model was established to calculate the strand shrinkage. The two-dimensional stress and three-dimensional temperature were connected through the thermal resistance. The model was validated by the measured solidification shell, copper plate temperature, and cooling water temperature rise. Results show that this model is suitable to study the complex transmission behavior in slab mold.

Numerical Simulation of the Coupled Turbulent Flow, Heat and Solute Transport in the Turbulent Flow Region of Slab Continuous Casting

In the current work, a three-dimensional model coupling turbulent flow, heat and solute transport was developed to investigate the solute transport and redistribution in the mold of slab continuous casting where the Reynolds number is very high and the molten steel flows strongly. The conservation equations of momentum, energy and species for a multicomponent system which includes solute element C, Si, Mn, P, S were solved with the commercial software ANSYS Fluent. The parameters used in the model are based on the actual continuous casting. The fluid flow, temperature distribution and solute elements distribution were analyzed. Results showed that negative segregation occurred near the strand surface, and the species concentration reached a peak value at the solidification front during solidification. The segregation degree of solute element S is higher than the other solute elements because of its lower equilibrium partition coefficient. The species concentration in the liquid pool is homogeneous because of the turbulent flow effect.