Application and Study on Heat Transfer Model for Continuous 82B Billet Casting
The centerline segregation in the 82B steel billet reduces seriously the final product quality; it is closely related to the unreasonable secondary cooling water system. This paper has established a two-dimensional non-steady-state heat transfer model for the continuous 82B billet casting process, and optimized the existing secondary cooling water scheme, The results show that: the strand surface temperature falling rate is lower than the center temperature falling rate in the original cooling water scheme; it is necessary to add an additional cooling subzone after the fourth subzone for decreasing centerline segregation; the optimal cooling water scheme is that cooling intensity of the fifth subzone is increased by 150% compared with the original fourth subzone.
Improvement of inner quality of continuously cast billets using electromagnetic stirring and thermal soft reduction
Centreline segregation in continuously cast billets has been decreased using thermal soft reduction (TSR) at the end of solidification in the caster. Full scale experiments have shown that it is possible to decrease the segregation ratio in steel with 0.51%C from 1.23 to 1.10. The segregation ratio is calculated as the mean value plus two standard deviations from 30 samples divided by the ladle composition. Multivariate data analysis (MDA) has been used to find the relationship between observed segregation and registered process variables. The MDA model's ability for explanation is sufficiently high to be used as a model for segregation prediction. The influence of different variables according to the MDA model agrees well with that determined by traditional methods of evaluation. The short range variation of segregation along the centreline can not be explained by the variables in the MDA model. Electromagnetic stirring in the mould alters the best position of the TSR cooling zone in the caster.
Magnetohydrodynamic calculation for electromagnetic stirring of molten metal
To get the fundamental characteristics of magnetohydrodynamics is extremely important, because in-mold electromagnetic stirring is required to get high quality steel. We have researched magnetohydrodynamic calculations to estimate the experimental data. At first, we compared the calculation velocity and measurement velocity in a pot mold. There is good agreement, though the calculation data depend upon the procedure after now dynamic calculation. Next, we compared molten metals such as molten steel, mercury and fused metal. Since molten steel provides difficulties for measurements, we often estimate the magnetohydrodynamic characteristics through measurement data from mercury or fused metal. The calculation data show that molten steel has the highest speed, though the fused metal has the lowest speed. Lastly, we compare the fluid dynamic characteristics between a pot mold and an endless mold. Though an endless mold is already used in practice, the experimental mold is a pot one. After we get measurement data from the pot mold, we must estimate the characteristics of the endless mold. The calculated data show that the velocity of the pot mold near the meniscus level is larger than that of the endless mold, because the endless mold has the turned over now from the fixed bottom in the pot mold.