Increasing Casting Speed in High Carbon and Micro Alloy DIN EN ISO 16120-2: 2011-C66D Steels

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.

The Hazelett continuous casting and rolling process represents a leading-edge production method for cold-rolled aluminum sheet and strip billets in the world. Its solidification microstructure significantly influences the quality of billets produced for cold rolling of aluminum sheets and strips. In this study, employing the CAFE (Cellular Automaton—Finite Element) method, we developed a coupled computational model to simulate the solidification microstructure in the Hazelett continuous casting process. We investigated the impact of nucleation parameters, casting temperature, and continuous casting speed on the microstructural evolution of the continuous casting billet. Through integrated metallographic analyses, we aimed to elucidate the controlling mechanisms underlying the Hazelett continuous casting process and its resultant microstructure. The results demonstrate that the equiaxed rate of grains increases with an increase in nucleation density, and the grain size decreases under constant cooling strength. With other nucleation parameters held constant, the grain size decreases as undercooling increases, and the columnar crystal zone expands. The nucleation density of the Hazelett continuous casting aluminum alloy has been determined to range between 1011 m−3 and 1013 m−3, and the undercooling ranges between 1 °C and 2.5 °C. The solidified grain structure can be controlled between 35 μm and 72 μm. The grain size of the continuous casting billet increases with an increase in pouring temperature and decreases as the casting speed increases. Elevating the pouring temperature positively impacts the fraction of high-angle grain boundaries and promotes the dendritic to equiaxed grain transition. Moreover, there exists potential for further optimization of continuous casting process parameters.

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.

The continuous casting-rolling process is widely used due to the lower energy consumption and its compact process. However, the defect in continuous casting slab severely limits the development of the continuous casting-rolling technology. In this paper, based on big data mining technology, the quality prediction model for hot rolled coils and the corresponding optimization method for continuous casting parameters were proposed. Firstly, the GA (Genetic algorithm)-BP (Backpropagation) neural network prediction model with high accuracy was constructed according to the characteristics of actual production data. Then, the effect of continuous casting parameters on the probability of defects occurrence was investigated with the established model. The results show that the defects occurrence probability decreases firstly and then increases with the casting speed, as well as the temperature of molten steel, which are consistent with metallurgical theory. Meanwhile, the optimum casting speed and mold level are 1.3 m/min and 8200 mm, respectively. When the flow rate of argon blowing for stopper and nozzle are restricted to 8.5 and 8 L/min, the defects occurrence probability will be lower. Furthermore, the optimum critical values of temperature difference of mold cooling water and inlet temperature are 8 °C and 35 °C, respectively. This paper can provide the guidance for narrow range control of continuous casting parameters and contribute to the production of high-quality steel.KeywordsContinuous castingHot rolled coilsSurface defectsData miningParameter optimization

In this study, the relationship between macro segregation and the equiaxed zone in high-carbon grades with continuous casting parameters was investigated and optimized at the İsdemir iron and steel plant. The work was conducted for the 1080 quality of the SAE J403 standard. In this study, some parameters, such as casting speed, secondary cooling, EMS current value and EMS frequency value, were examined. When the results of the experiments are examined, it can be observed that the equiaxed zone in the macrostructure decreases significantly with the reduction of the EMS frequency value. The decrease in casting speed and increase in EMS current value caused an increase in the equiaxed zone. The increment in secondary cooling led to a decline in the equiaxed zone. Once the macro segregation results are examined, it can be seen that it is very important to optimize the continuous casting parameters in order to reduce the macro segregation results of—especially—carbon, sulfur and phosphorus elements. It has also been determined that the macro segregation values of carbon, sulfur and phosphorus elements are low in casting conditions where casting speed is low, and the EMS current value and EMS frequency value are high. In addition, macro segregation measurements of manganese, silicon, chromium and vanadium elements are found to be low under similar casting conditions. It is critical to optimize the continuous casting parameters before production, especially in high-carbon grades to be used for prestressed concrete wire and cord wire applications. As a result of the work conducted using the İsdemir billet continuous casting machine for the 1080-grade SAE J403 standard, aiming to optimize macro segregation and the equiaxed zone, the effective results have been achieved by using process parameters of 2.8 m/min casting speed, 360 A EMS current, 5 Hz EMS frequency and low secondary cooling intensity.

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.

Molten Steel Level Control of Strip Casting Process Monitoring by Using Self-Learning Fuzzy Controller

Effects of casting speed on microstructure and segregation of electro-magnetically stirred Aluminum alloy in continuous casting process

A continuous ingot casting process was developed to improve the productivity of ingot fabrication. A supplemental charge method in which uranium dendrites were additionally added into molten uranium was introduced for the first time, and a tilting system of a melting crucible to mold was developed. The feasibility of these processes was confirmed by a uranium melting test at the laboratory scale, successfully obtaining a uranium ingot in about 4.6 kg. Based on the results, we scaled up the ingot casting processes at the engineering scale. A rotating continuous feeder was installed for the ceaseless feeding of the dendrites into molten uranium. The tilting system and eight mold crucibles on a turn-table were adopted. The operability of the continuous ingot casting process at the engineering scale was successfully confirmed by a melting test of copper. We consider that the engineering scale equipment can cast above a 50 kg U/batch with the continuous casting processes.

Effects of micro-alloying elements and continuous casting parameters on reducing segregation in continuously cast slab

The solidification structure of a thin slab during the continuous casting process at high casting speed was simulated based on the cellular automaton-finite element (CAFE) model. The simulations were consistent with the solidification structures of actual steel samples, and the influence of the continuous casting process parameters and alloy elements were further studied in detail. The optimum process parameters obtained are as follows: the casting speed at 5.2–5.4 m min−1, the superheat at 20–25 °C, and the specific water flow at 1.62–1.64 L kg−1. Meanwhile, the Si content in the thin slab was appropriately increased to refine the grains and improve the production efficiency. This study provides important theoretical data for practical thin slab production, improvement of the continuous casting efficiency, thereby reducing accidents.

While the solidification macrostructure of continuous cast billets is an important factor influencing the final performance and rolling yield of oil casing steel, the continuous casting process parameters have a direct influence on the solidification structure. This study simulated the solidification process of the continuous casting round billets of oil casing steel using a cellular automaton–finite element (CAFE) model. According to the simulation results, at a superheat degree of 20–35 K, a casting speed of 1.9–2.1 m/min, and a secondary cooling specific water flow of 0.34–0.45 L/Kg, the solidification structure had a relatively high equiaxed crystal ratio and small average grain radius. Guided by the simulation results, this paper establishes optimal process schemes for producing 26CrMoVTiB steel round billets, comparatively analyzes the equiaxed crystal ratio and central shrinkage of round billets produced according to these schemes, and defines the optimal continuous casting process conditions, which are: superheat degree = 25 K, casting speed = 2.1 m/min, and specific water flow = 0.35 L/Kg. When adopting these process parameters, the 26CrMoVTiB steel round billets demonstrate a tiny central shrinkage and an equiaxed crystal ratio of 45.2%.

The effect of casting speed on slag-inclusion defects in 1050 × 200 mm ultra-low-carbon automobile steel (UAS) slabs was studied by performing nail plate experiments and by monitoring the liquid level fluctuations during the continuous casting process. The number, location, length, and proportion of slag-inclusion defects in hot-rolled coils produced at different casting speeds were analyzed. The results showed that the defects in the hot-rolled coils were mainly owing to the mold protective slag. For the continuous casting speed of 1.6 m/min, the fraction of slag-inclusion defects was the lowest (at 5.3%), and the number of slag-inclusion defects was lower than for the other casting speeds. The length of slag inclusions was under 900 mm. Furthermore, the number of slag-inclusion defects on the upper and lower surfaces was smaller than those for the other casting speeds. At different casting speeds, slag-inclusion defects mainly existed within 100 mm of the edge on both surfaces of hot-rolled coil plates. The fluctuation within the 0–1 mm range was 98.1% for the casting speed of 1.6 m/min, indicating that the flow rate of molten steel on both sides of the nozzle was relatively stable, which helps to control slag-inclusion defects in hot-rolled coils.

The article presents the results of the chemical composition influence on element segregation and properties of steel strip manufactured by strip casting route. It is shown that in the transition from the slab production with a thickness of 220 mm to slabs with a thickness of 1.2 mm, the thickness of the segregated diffusion layer in the case of the continuous strip casting process is 4.1 - 12.4 times less than in the case of traditional continuous casting. The carbon, nitrogen, copper, tin, phosphorus and sulfur segregation percentage in the continuous strip casting process is 1.7 - 5.1 times less than in traditional continuous casting. A method is proposed for calculating the element segregation based on the equality of the segregation level in traditional and strip continuous casting. It has been established that the content of elements in steels during two-roll continuous casting can be increased for impurities such as S, O, N, P, H from a minimum of 3 for P to a maximum of 497% for S. For residual elements such as Pb, Bi, Sn, Cu, Sb, Zn, As minimum increase from 1.1 for Zn to maximum 401% for Pb. The content of such alloying elements as B, Se, Al, Te, Ca, Mg, Ce, C, La, Nb, Ti, Mn, Ni, Si can be increased from a minimum of 1.1 for Si and Mn to a maximum of 675% for B. The time and rate of cooling of a 20-ton coil of steel strip are calculated, which are, respectively, 13.7 hours and 0.0051 oC/s. Such cooling conditions create the prerequisites for the precipitation of chromium carbides and an increase in the tendency of steel to intergranular corrosion. It was found that for eliminate this problem, it is necessary to increase the cooling time with water after rolling to a strip temperature from 300 to 400 oC.

A supervision algorithm for controlling of continuous casting (CC) process is presented. The control strategy is based on the observation of temperature distribution through the casting strand. The algorithm is composed of two parts, an original 3D transient numerical model of the temperature field and the fuzzy‐regulation model. The numerical model calculates and predicts the temperature distribution while the fuzzy‐regulation model tracks the temperature in specific areas and tunes the casting parameters such as the casting speed, the cooling intensities in the secondary cooling, etc. The main goal is to keep surface and core temperatures in the specific ranges corresponding with the hot ductility of steel and adequately reacts on the variable casting conditions. The results show good and robust control behavior, fast response to dynamic system changes and general applicability for any CC process.