Mathematic Model of SEN Clogging During Continuous Casting of Steel

The aim of this paper is to present an application of the input variable significance analysis to finding probable causes of product defects occurring in continuous casting (CC) of steel. The research was carried out using production data routinely recorded in one of Polish steel plants and basically referred to defective fraction of billets per heat as the process output. The data did not include the cases with zero defects which made the analysis difficult. The process inputs included eight parameters of different nature (physical, organizational and human). For determining which of the process input parameters are crucial for the output and which of them can be easily eliminated in further analyses two different approaches were applied and compared. The basic tool was an MLP-type Artificial Neural Network in which the relative significance was defined as the sum of the absolute weights of the connections from the given input node to all the nodes in the first hidden layer. As a complementary method the one-way analysis of variance (ANOVA) was utilized in which the value of the F-statistics is used as a measure of the input significance. It was found that the both methods indicate that the start-time of the CC process is the factor highly influencing the fraction of defective products. The process physical parameters which are expected to have a large influence on the billet quality, i.e. deviations from nominal casting temperature and deviation from nominal casting speed also appeared to be significant, moreover their variations also highly depend on the start-time of the CC process. The final conclusion is that the direct cause of the defective products are incorrect adjustments of the casting speed occurring mainly in the morning hours, however not correlated with particular operators. This finding can considerably facilitate the identification of the root cause of the defects by the plant engineers. Some recommendations concerning the future work are also given.

The paper analyses the effect of the nozzle arrangement on the continuous steel casting, depending on its shape and dimensions. At the same time, the work analyses the effect of cooling water pressure on the contact with the cast in order to improve the heat transfer coefficient at boiling. The present research in that, more specifically, disposed cooling water injection nozzle during the continuous casting method for arranging the nozzle for spraying cooling water to the cast surface to cool the play cast steel during the continuous casting of a continuous cooling water jetting nozzle alignment during casting It relates. An injection nozzle arrangement method during continuous casting is provided to evenly inject cooling water onto the surface of a continuous cast steel slab in a secondary cooling zone during the continuous casting.

In high speed continuous steel slab castings machine, the partially solidified strand emerging out from the bottomless mold is cooled to complete solidification by means of water sprays arranged through its metallurgical length. The cooling water flow rates are dependent on slab size, grade of steel cast, working length of mold, casting speed, water pressure, spray nozzles and their location in the strand support system of the caster. In this paper an analytical method to predict the spray cooling water flow rates is presented. A least square polynomial is found which best describes extensive data of cooling flow rates obtained from high speed continuous steel slab caster at Linz, Austria. Polynomial curves for various slab sizes, grades of steel cast and casting speeds have been determined using the actual water flow rates data and the developed least square technique. The technique developed in this paper is general and can be used for determination of cooling flow rates of any type of continuous steel casting machine.

In the present study, a coupled 3-D model of flow, solidification, and heat transfer was established to apply to gain new insights into the effects of casting speed and nozzle diameter on the remelting of continuous casting billets. The effects of nozzle diameters and casting speeds on the remelting of continuous casting billet were analyzed separately. Nozzle diameters vary from 20 mm to 50 mm, and casting speed varies from 1 m/min to 4 m/min. The flow behavior and velocity distribution, which are at different casting speeds, were calculated, and the reasons for shell remelting at high casting speeds were analyzed. The remelting of the billet shell, which is at different combinations of different nozzle diameters and casting speeds, was calculated. Then, the comprehensive effects of nozzle diameters and casting speeds on the remelting of the billet shell are analyzed. Finally, the remelting degree maps of different continuous casting process parameters were presented. By the simulation, it is found that the casting speed has more obvious effects on whether the remelting phenomenon occurs, while the diameter of the nozzle has more obvious effects on the degree of remelting. When the casting speed is lower than 2 m/min, remelting does not appear. When the casting speed is higher than 3 m/min, remelting will occur. When the casting speed is 3 m/min, as the nozzle diameter increases, the remelting degree continues to decrease, and the range of remelting first remains stable, then gradually decreases. It can be observed that when the casting speed is increased to 3–4 m/min, the nozzle diameter should be in the range of 30–40 mm.

To estimate the quality condition in continuously cast steel slabs, simple but accurate macrosegregation criteria have been proposed. The formation of macrosegregation phenomena in continuous casting of peritectic carbon steels has been investigated by metallographic study of collected slab samples. The metallographic study involved plant trails to collect the slab samples and to prepare them for chemical macrosegregation analysis. The experimental results show a fluctuation of carbon between positive and negative segregation with distance from slab surface based on the cooling conditions experienced by the slab. Via mathematical analysis, formulae of average macrosegregation level ASL, its fluctuation level FSL and its segregation quality number SQN have been developed. The results calculated by these formulae show good agreement with the description of the formation mechanisms of different continuous casting defects and their locations. Therefore, these calculations illustrated that macrosegregation criteria and their distributions can be considered by experimental, simple and vital tools to evaluate the conditions of surface and inner qualities in continuously cast steel slabs. The mechanisms of these criteria with some mechanisms of continuous casting defects have been explained and discussed.

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

In continuous casting (CC) of steel, the water spray cooling system installed in the secondary cooling (SC) zone plays a critical role in controlling its productivity and product quality. In this paper, recent developments in spray cooling applied to the SC are reviewed and evaluated. After introducing the importance of CC in the metal industry and the significance of spray cooling in CC, the development of nozzles and cooling facilities as well as the fundamentals of spray cooling used in the SC zone are presented and discussed. The quantification of heat transfer performance of spray cooling in CC is then studied and the leading correlations developed for the heat transfer coefficient HTC related to major spray cooling parameters are selected and compared. The development of techniques for measuring the essential spray cooling parameters and HTC are also described and assessed. Finally, recommendations on future efforts for developing a better spray cooling system or correlation are provided.

After investigation in many continuous casting shop of steel, a dynamic water distribution model is proposed for flexible control on secondary cooling in continuous casting. In this model, the water cooling intensity is determined by the model casting speed instead of the real casting speed. When the casting speed is steady, the model casting speed is equal to the real casting speed. When the real casting speed is changing, the model casting speed according to calculating algorithm to adjust and approaches to the real one, but there is a time delay between them, so it can avoid the slab surface temperature fluctuated due to casting speed changes. The secondary cooling can be dynamically controlled by monitoring the model casting speed. The compare of the simulation results and the measured results reveals that the temperature field and thickness of slab shell in simulations agree very well with the real production situations.

This paper presents the commercial production of a high strength low alloy steel with 8 different thicknesses through continuous casting route. All the plates exhibit tempered martensite structure after heat treatment. Mechanical properties of different thickness plates are obtained from tensile testing. Charpy impact properties of the steel plates are evaluated at room temperature and at −40°C. From the tensile and impact tests, it is noticed that the continuous cast steel displays a good combination of strength and impact toughness. Ballistic performance of the steel is carried out by impacting against 7.62-mm-high hardness armour piercing (AP) steel projectiles and 125 mm FSAPDS ammunition. A comparison of microstructure, mechanical and ballistic propertiesof the continuous cast steel and conventional ingot cast steel has been carried out. It is observed that the continuous cast steel displays marginal improvement in ballistic performance in comparison to the ingot cast steel.The ballistic behaviour of the continuous cast steel is also compared with that of the rolled homogeneous armour steel.

This paper presents the results of research based on real data taken from the installation process at Arcelor Mittal Hunedoara. Using Matlab Simulink an intelligent system is made that takes in data from the process and makes real time adjustments in the rate of flow of the cooling water and the speed of casting that eliminates fissures in the poured material from the secondary cooling of steel. Using Matlab Simulink simulation environment allowed for qualitative analysis for various real world situations. Thus, compared to the old method of approach for the problem of cracks forming in the crust of the steel in the continuous casting, this new method, proposed and developed, brings safety and precision in this complex process, thus removing any doubt on the existence or non-existence of cracks and takes the necessary steps to prevent and correct them.

Modelling of the strand and mold temperature in the continuous steel caster

The movements of the driven rolls were measured during the continuous casting of steel and their fluctuations were compared with other signals such as the casting speed and the mold level. From the observation of large fluctuations in the movements of the driven rolls and the unevenness in the thickness of the solid shell, it is proposed that the unevenness in the thickness of the solid shell is the main reason for unsteady bulging during the casting of medium carbon steel. A two-dimensional model over the successive rolls was used to calculate the bulging profile and its changes with time, during the fluctuations in the casting speed, with the finite element method. As a result, the calculations were in good agreement with the experimental results, and, it could be concluded that the period of unsteady bulging is greatly influenced by the roll pitch, therefore, depends on the locations where different roll pitches occur, and is somewhat affected by casting speed variations. Finally, based on the calculations and the experimental results, the effect of the unsteady bulging on the mold level was discussed.

Non-metallic inclusions are present in small volume fractions in steel products. A significant portion of them is associated to the deoxidation process. The type and form of inclusions is, in general, directly connected to the deoxidation practice and to eventual reoxidation during processing. Besides influencing the steel properties, non-metallic inclusions can have an important effect on their processability. In this work, we review the processability questions associated with inclusions in the continuous casting of steel, with emphasis on long products. When solid inclusions are present during the casting of steel they may agglomerate and clog the valves used in the continuous casting equipment, limiting the number of sequential heats that can be casted and reducing casting speeds. Additionally, in some conditions, solid non-metallic inclusions may agglomerate and form surface defects in the continuous casting products, sometimes referred to as scum. As productivity and quality are essential to the profitability of steelmaking, avoiding these conditions is of paramount importance. Thus, we review the main thermodynamic conditions that may lead to the clogging of continuous casting valves, and discuss, from the thermodynamic point of view, the measures that can be taken to avoid the occurrence of these various conditions. Furthermore, we discuss the conditions that might cause to the formation of scum and the thermodynamics of its formation and elimination. It is concluded that the analysis of steelmaking conditions via computational thermodynamics can have an important role in avoiding problems in continuous casting and helping ensure productivity and quality in the process.

In the continuous casting of steel, mold level fluctuation caused by unsteady bulging of the solidifying shell affects the surface quality of the product and stable operation of the continuous casting process. To clarify this problem, inter-roll bulging and unsteady bulging in experimental casting machines and commercial continuous casting machines have been measured by various methods in a number of studies. In this study, the fluctuation of inter-roll bulging with time in a commercial continuous casting machine was measured by an ultrasonic range finder using a water column. In these measurements, the fluctuation of the segment was also considered. The validity of the measured data was estimated by comparison with the mold level. The results showed that both inter-roll bulging and the mold level fluctuated with the cycle calculated from the roll pitch and casting speed, and the amplitude of the mold level fluctuation converted from the amount of fluctuation of inter-roll bulging corresponded to the actual mold level fluctuation. Therefore, the cycle and absolute amount of inter-roll bulging fluctuation measured in this study were considered reasonable. These results also revealed that the value measured in this study corresponded directly to the fluctuation of inter-roll bulging as such.

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.