Mathematical Formulation of Cooling Water Flow Rates for High Speed Continuous Slab Caster

The usage of units with high reduction in the casting and rolling module would allow to improve the quality of the mill products due to intensive processing of bulk continuous cast slabs along the section and obtainment of homogeneous fine-grained metal structure, as well as to increase the cross-section of the continuous cast slab. The analysis of the formation causes of nonmetallic inclusions and liquates in the axial zone of thick-plate steel was carried out. The analysis of the deformation unevenness along the slab height during the reduction of large continuous cast slabs was performed at mill 5000 of JSC “Magnitogorsk Metallurgical Plant”. The design is described and the technological possibilities for definition of the cyclical deformation are presented for the preliminary deformation of continuous cast slabs. The technology is described and the parameters of the strikers for pre liminary deformation of large continuous slabs were determined. The experimental study results of the deformation process of continuous cast slabs of steel 45 and steel 12Cr18Ni10Ti are given. The evaluation of the structure of continuous cast metal in the process of reduction of continuous cast billets at a cyclic deformation facility was carried out. The main parameters of the installation for preliminary deformation of large continuous cast slabs were determined. The technological possibilities of the installation for cyclic deformation were stated in terms of the essential improvement of the quality of sheet blanks. Based on the analysis of technological possibilities, it was proposed to use the cyclic deformation installation in the continuous casting line for preliminary reduction of large continuous cast slabs in order to fully adjust the speed of continuous casting and cyclic deformation and provision of the one-pass reduction with the degree of deformation 45 – 90 % to obtain a good casting structure along the slab cross-section. It was suggested, when using the installation in the line of a continuous casting machine, to perform reduction of continuous cast slabs using the heat of the cast metal, thereby substantially reducing the energy consumption in the technological process of producing the sheet blanks. The use of a cyclic deformation installation in the lines of thick-plate and wide-band mills for preliminary deformation of heated slabs in one pass is proposed, which will improve the quality of sheet blanks and reduce the number of passes in rolling mills. © 2017, National University of Science and Technology MISIS. All rights reserved.

In order to improve design efficiency and reduce design cost, a new method combining numerical simulation with experimental verification was proposed in this study. Firstly, controllable process parameters such as continuous casting speed and cooling water flow rate, are robustly designed according to the numerical simulation results of flow field, process experiments were subsequently done on a newly developed continuous casting machine of lead slice, then the robust optimal design for the continuous casting process were gained. The results show that the cooling water flow significantly affects axial thickness of the lead slice, while the casting speed determines mainly its circumferential thickness. When the casting speed is between 280L/min and 320L/min, and the cooling water flow rate is between 950r/min and 1100r/min at the same time, the axial thickness and circumferential thickness can been kept respectively in1.0±0.03mm and 1.0±0.1mm, which meet the robust design requirements.

The dendrite arm spacing in the continuous casting slab of Mn13 steel under different casting speeds was measured using the metallographic microscope. Meanwhile, a heat transfer model was established by the Pro-cast software. The relationship between the dendrite arm spacing and casting speed in continuous casting slab of Mn13 steel was studied and described by a function expression. The results provide an important theoretical basis for the development and optimization of continuous casting production process of high-manganese steel and help to improve the quality of continuous casting slab of high-manganese steel. Under the experimental conditions, the suitable casting speed is about 0.9 m/min. The secondary dendrite spacing maintains a relatively stable low-amplitude increase trend, and it is beneficial to obtain a higher proportion of equiaxed crystals.

A cellular automaton finite‐element coupling model is developed to investigate the influences of the solidification structure of a continuous casting slab by the state of the cooling spray and process conditions. The model is validated. The solidification structure is simulated for different cooling spray schemes, superheat degrees, and casting speeds. The grain growth and distribution of the continuous casting slab near the corner area are sensitive to the cooling spray. As the distance of the nozzle from the surface of the continuous casting slab increases, the radii of the columnar and equiaxed grains tend to increase near the corners. The distribution of a columnar‐to‐equiaxed grain transition near the corner area gradually moves toward the core of the slab as the distance of the nozzle from the continuous casting slab decreases. At a casting speed of 1.2 m min−1 and superheat degree of 20 °C, the best nozzle height from the surface of the continuous casting billet is 234.5 mm. The casting speed and superheat significantly affect the grain radius. With the increase in the casting speed and decrease in the degree of superheat, the average grain radius decreases, while the equiaxed grain area increases.

Herein, multiphase flow patterns in a continuous casting slab strand are studied using a 3D numerical model and nail board measurement. The motion and turbulence of the argon gas and molten steel are simulated using the Euler–Euler approach and the realizable κ–ϵ turbulence model, respectively. Casting parameters for a 1435 mm × 200 mm mold are optimized by both the simulation and the capillary number. The capillary number is calculated by the measured velocity and used to evaluate the capability of the slag entrainment by the turbulent flow. The optimized values of the casting speed and the gas flow under the current specific continuous casting condition are 1.4 m min−1 and 8 NL min−1, respectively. Slag entrainment might occur near the narrow face under a casting speed of 1.6 m min−1 and near the SEN under a gas flow rate of 15 NL min−1. Meanwhile, effects of casting speed and argon flow rate on the transformation of flow patterns inside the mold with different dimensions are analyzed. A software incorporated by a Graphical User Interface is developed to predict the flow pattern inside the mold for a given steel grade and casting parameters.

A control model of the steel casting process will be proposed using fractional order differential equations (FDE) and the orthogonal distance fitting (ODF). These two mathematical approaches will be used for creating a relationship between the speed of steel casting and the measured temperature of the steel strand in a critical place of the continuous steel casting machine. To obtain the required physical properties of the slab of individual sort of casted steel, a given interval of temperature should be reached in concrete parts of the steel strand. The proposed control model uses the speed of steel casting as the primary parameter (control parameter) influencing the temperature of steel in a critical place of the continuous steel casting machine (controlled parameter). This way we neglect the influence of other parameters, which are dependent on the steel casting speed anyway. A system of two fractional order differential equations is considered to describe the relation between the steel casting speed and the measured temperature. Experimental data containing information about the casting speed and the temperature of the strand are taken and an approximation (defined by optimal parameters) is sought. To find parameters of the proposed control model, the orthogonal distance fitting is used in the formulation of the fitting criterion. With the help of the created control model, it is possible to set the value of the steel casting speed based on the casted sort of the steel, to keep the measured temperature in the corresponding interval.

Deep-drawing steels are widely used in the automobile industry and macro-inclusions in continuous casting slabs should be strictly controlled because they cause surface defects in the final products. In this paper, industrial tests with different casting speeds from 1.0 m.min-1 to 2.5 m.min-1 and different tundish superheats were carried out, then subsurface inclusions in high-speed casting slabs were investigated with a large detection area by the ASPEX automatic inclusion analysis system, and the effect of the casting speed and tundish superheat was studied. The results show that there are six different types of macro-inclusions found beneath the slab surface, named cluster alumina, bubble plus cluster alumina, lump alumina, cluster TiOx-Al2O3, entrapped mold powder and CaO-Al2O3-MgO, respectively. The above first three types account for about 98% of total inclusions in the slabs cast with the mold fluctuation within ±3 mm. The size of more than 80% of such inclusions ranges from 20 to 50 μm. The number density of inclusions larger than 50 μm decreases with the increase in the casting speed and tundish superheat. The subsurface macro-inclusions in deep-drawing steel slabs are closely related to the hook structure. Increasing the casting speed and superheat is effective for reducing the hook depth and large-sized inclusions on the subsurface of slabs.

A two-dimensional heat-transfer model for transient simulation and control of a continuous steel slab caster is presented. Slab temperature and solidification are computed by the model as a function of time-varying casting speed, secondary spray cooling water flow rates and temperature, slab thickness, steel chemistry, and pouring and ambient temperatures. Typically, the solidification path, temperature-solid fraction relationship, is prescribed. However, if these data are not available, a microsegregation solidification model that approximates the effects of steel chemistry and cooling rate is incorporated in the caster model. Measured slab surface temperatures recorded from an operating caster are compared with predictions from the transient model. These demonstrate that the model typically can predict the temperature response at the slab surface within 30 °C. Results of several simulations are given to demonstrate the effects of changing casting conditions on the slab thermal profile, end of liquid pool, and solidification end point. A control methodology and algorithm suitable for online control of a continuous casting machine is described, and the ability to control the surface temperature profile by dynamically adjusting secondary spray cooling flow rates is demonstrated by simulation. Results from a preliminary version of the model that is capable of running in real time are presented and are compared with the slower, but more realistic, version of the model.

Copper mould is an important and integral component of any Conventional Slab Caster for steel to take care of the initial solidification. In case of SMS-I, Rourkela Steel Plant, the slab caster was a “Brown field project” and was commissioned in 1996. This project was having severe space constraints, as it was built in the old SMS which was commissioned during late fifties. In this slab caster the copper mould is a “Constant cooling water volume” design and water flow could not be altered, as per the casting speed. Therefore, the strand shell formed in the mould is thicker in case of lower casting speed and thinner in case of higher casting speed. As per the DPR, the designed sequence size of slab casting was only 2 (Two), with a total production capacity of 0.305 MT per annum. Further, Ladle Heating Furnace was not envisaged during commissioning of slab caster. Though, several attempts were made to cast more than 2 heats in the caster, it was not possible, primarily due to logistic issues, in absence of LHF. Subsequently, the Ladle Heating Furnace (LHF) was commissioned, adjacent to the slab caster in 1998. However, even after LHF was commissioned, the maximum sequence that could be cast was only 5 (Five), with a heat size of 66 Tons. Due to higher production demand, for increasing the sequence size, it was found that the major constraint was “Inlet water temperature to the Copper Mould”, which was crossing the threshold limit of 42 °C. In the present study, an in depth analysis of mould inlet water temperature was carried out and the problem was eradicated, so as to cast more than 5 (Five) heat sequence to increase the productivity.

In order to predict the dendritic evolution during the continuous steel casting process, a simple mechanism to connect the heat transfer at the macroscopic scale and the dendritic growth at the microscopic scale was proposed in the present work. As the core of the across-scale simulation, a two-dimensional cell automaton (CA) model with a decentered square algorithm was developed and parallelized. Apart from nucleation undercooling and probability, a temperature gradient was introduced to deal with the columnar-to-equiaxed transition (CET) by considering its variation during continuous casting. Based on the thermal history, the dendritic evolution in a 4 mm × 40 mm region near the centerline of a SWRH82B steel billet was predicted. The influences of the secondary cooling intensity, superheat, and casting speed on the dendritic structure of the billet were investigated in detail. The results show that the predicted equiaxed dendritic solidification of Fe-5.3Si alloy and columnar dendritic solidification of Fe-0.45C alloy are consistent with in situ experimental results [Yasuda et al. Int J Cast Metals Res 22:15–21 (2009); Yasuda et al. ISIJ Int 51:402–408 (2011)]. Moreover, the predicted dendritic arm spacing and CET location agree well with the actual results in the billet. The primary dendrite arm spacing of columnar dendrites decreases with increasing secondary cooling intensity, or decreasing superheat and casting speed. Meanwhile, the CET is promoted as the secondary cooling intensity and superheat decrease. However, the CET is not influenced by the casting speed, owing to the adjusting of the flow rate of secondary spray water. Compared with the superheat and casting speed, the secondary cooling intensity can influence the cooling rate and temperature gradient in deeper locations, and accordingly exerts a more significant influence on the equiaxed dendritic structure.

This chapter contains sections titled: Introduction Model Description Model Validation Parametric study of TC sensitivity to level fluctuations Inverse Heat Conduction Model Conclusions Acknowledgements

Upward continuous casting is the key process in the production of contact wire for electric railway. The stability of the process and the quality of the produced billet are directly related to the performance of the contact wire and ultimately the safety of the railway operation. To ensure the quality of continuous-casting billet, the optimal process conditions need to be experimentally determined, which is not only costly but also time-consuming. To facilitate this optimisation process, the simulation of the solidification process of Cu-0.45%Sn alloy in upward continuous casting is described in this paper to assess the influence of casting temperature, upward continuous casting speed, the time of stop-pull, and primary cooling water flow rate on the liquid core length. The results show that the speed of upward continuous casting exhibits a great influence on the liquid core length, while the casting temperature has only little influence. In a certain range of the ratio of stopping time to pulling time, the quality of updraft Cu-0.45%Sn alloy billet is improved; exceeding a certain ratio results in a decrease of the surface quality and an increase in internal and external defects. The liquid core length of the continuous casting rod decreases with the increase of the cold water flow rate, and properties are stable when the flow rate reaches 0.45 m3·h−1. For a billet with a diameter of 20 mm, the appropriate upward continuous casting process parameters are determined as a casting temperature of 1175 °C, an upward continuous casting speed not exceeding 25 cm·min−1, a ratio of stopping time to pulling time not exceeding 2.13, and a cooling water flow rate of 0.45 m3·h−1.

In continuous casting of steel, a number of parameters have to be set, such as the casting speed and cooling water flowrate, in which the secondary cooling has a considerable influence on cracks and other defects of the billets. The aim of this paper is to develop a optimization algorithm used for solving the optimal secondary cooling water flowrate under different casting speeds with respect to multiple objectives. For this purpose, an optimization algorithm based on multi-objective ant colony system(MOACS) algorithm is developed for solving an optimal control of secondary cooling water distribution according to certain metallurgical criteria and some technological constraints. The optimization method consists of the simulator of continuous casting process, MOACS algorithms linked with two cost function. The use of the developed optimization algorithm for determining optimal setting of cooling parameters demonstrate that better results can be attained in improving the surface temperature distribution.

To investigate superheat dissipation in a continuous slab casting machine, mathematical models have been developed to compute fluid flow velocities, temperature distribution within the liquid pool, heat transfer to the inside of the solidifying shell, and its effect on growth of the shell. Three-dimensional (3-D) velocity and heat-transfer predictions compare reasonably with pre-vious experimental measurements and two-dimensional (2-D) calculations. The results indicate that the maximum heat input to the shell occurs near the impingement point on the narrow face and confirm that most of the superheat is dissipated in or just below the mold. Superheat tem-perature and casting speed have the most important and direct influence on heat flux. The effects of other variables, including mold width, nozzle jet angle, and submergence depth, are also investigated. Calculated heat flux profiles are then input to a one-dimensional (1-D) solidifi-cation model to calculate growth of the shell. Shell thickness profiles down the wide and narrow faces are compared with the predictions of conventional heat conduction models and available measurements.

In this paper, for the first time, using a three-dimensional (3D) thermo-elastoplastic model, the effects of cooling rate and casting speed on the continuous casting (CC) process are studied. Some significant parameters such as solidified shell thickness, mushy zone thickness, metallurgical length, and residual stress in the CC process under different cooling rates and casting speeds are investigated. All analyses are performed using the meshless local Petrov–Galerkin (MLPG) method. The effective heat capacity method is employed to simulate the phase change process. The von Mises yield function with isotropic hardening is used to simulate the stress state, and material parameters are assumed as temperature dependent. To demonstrate the accuracy and efficiency of the present 3D MLPG method in thermo-mechanical analysis of highly nonlinear solidification problems, the obtained results are compared with an exact analytical solution. Several numerical examples for different cooling rates and casting speeds are provided to investigate their effects on the CC process parameters, as well as on the stress, displacement, and temperature fields induced in the cast material. The results from the analyses can be very useful for the optimal design of CC processes.