Billet Continuous Casting Research Articles

Inducing columnar-to-equiaxed transition by gradient impediment-flow optimization mechanism: The inheritance chain of solidification

Optimization of the metal solidification microstructure is a long-standing topic. It is the initial and critical guarantee of fabricating high performance metal materials, especially in the context of external field control, for example, for electromagnetic fields. However, tailoring the final solidification microstructure is extremely difficult because its mechanism is a long process inheritance chain which can be hardly observed by experiments. In this study, systematically simulations of the continuous casting using an electromagnetic swirling flow nozzle (EMSFN) was made to clarify this inheritance chain. It was newly found that a relatively uniform flow field inherited from a magnetic field generates a gradient impediment-flow optimization mechanism (GIFO), which is beneficial for both columnar-to-equiaxed transition (CET) and grain refinement. Specifically, 600 A increases the superheat dissipation, and the temperatures of the solidification front at 200 mm and 400 mm below the meniscus are increased by 15.47 K and 12.27 K, respectively, and the temperature gradient is decreased by 17.3 % and 22.8 %. The concentration gradient at the solidification front decreased by 89.9 %, 31.1 %, and 51.3 % at 200 mm, 400 mm, and 650 mm below the meniscus, respectively. Coupled changes in the temperature and concentration gradients impede dendritic growth and promote equiaxed grain nucleation. In addition, more equiaxed grain nuclei are transported to the forefront of the growing dendrite when the molten steel rotates and is transported from the inner to the outer regions. According to the simulation, the experimental validation proved that electromagnetic swirling flow nozzle was a convenient method for promoting this mechanism. It can optimize the solidification structure of Grade 70 carbon spring steel continuous casting billets with an increase of 21.26 % in the equiaxed grain ratio extremely low carbon segregation, and improved mechanical properties. This newly found mechanism can be considered as a generic theory for optimizing the solidification microstructure of alloys, which can guide the process design of various external field control technology.

Selection of internal design of crystallizer sleeves for continuous casting of 200 mm billets

The crystallizer is the most critical and most important functional unit of a continuous casting machine (hereinafter referred to as CCM). It is the main technological unit of the CCM, an assembly for removing heat during the solidification of the solidifying metal and the formation of the ingot. The main requirement for the crystallizer is to provide maximum heat removal from the solidifying steel to the cooling water, and to obtain a strong ingot shell with a good surface at the outlet of the crystallizer, which would not be destroyed by the heat of the liquid phase and the ferrostatic pressure. During the reconstruction of the CCM by the contractor company, drawings of crystallizers and crystallizer sleeves with a double‑cone internal geometry for casting 200 mm continuous cast billets were developed. The 200 mm continuous cast billet is a billet for the production of hot‑rolled seamless steel pipes. During the operation of the crystallizer sleeves with a double‑cone internal geometry, an accelerated wear of the protective coating in the lower part of the sleeve was noted, as well as an increased rejection of hot‑rolled pipes due to defects on the outer surface of the pipes. In order to identify the cause of the defect formation, complex metallographic studies of the outer surface of the pipes were carried out. As a result of the metallographic study, surface defects classified as steel mill scale on the outer surface of the pipes were identified. To minimize the “steel mill scale” defect and reduce the wear of the protective coating of the crystallizer sleeves, work was carried out to select the optimal conditions for the crystallization of the continuous cast billet: the use of crystallizer sleeves with a three‑cone internal geometry compared to a double‑cone was investigated; maintaining the temperature difference of the water at the inlet and outlet of the crystallizer within specified limits (ΔT) was tested. It was found that the use of a crystallizer sleeve with a three‑cone internal geometry for casting 200 mm billets and the stable behavior of the ΔT parameter made it possible to ensure the required quality of the surface of seamless pipes, reduce the wear of the protective coating of the crystallizer sleeves and increase the productivity of the CCM.

Investigation on the microstructure and mechanical properties of large-tube forging manufactured by additive forging

Large-tube forgings were formed using nine layers of continuous-casting billet made from 15CrNi3MoV alloy steel via additive forging. The interfacial microstructural evolution under different hot-compression bonding temperatures and strains was investigated using optical microscopy, scanning electron microscopy, and electron backscatter diffraction. The tensile properties of the hot-compression-bonded and tube-forged samples were also evaluated. The results showed that as the hot-compression bonding temperature and strain increased, the bonding interface gradually disappeared and the voids at the bonding interface closed. Finally, the interface was replaced with recrystallised grains. The tensile properties of the hot-compression-bonded samples at different temperatures and strains were identical. The tensile properties of the interface and base samples of the tube forging were comparable, and the fracture morphologies were consistent. The fracture position of the large tensile sample with a length of 1000 mm containing three original interfaces is the base, indicating the complete metallurgical bonding of the forging.

Growth and transition of dendrites in steel strands under different electromagnetic stirring methods

In the industrial continuous casting process, some central defects such as shrinkage cavity, porosity, segregation and crack are generated especially at the final solidification zone of steel strands because of the poor fluidity and feeding ability of molten steel in the center of strand, especially for the special steel strand. In this paper, a new type of vertical linear electromagnetic stirring (V-LEMS) was proposed to apply in the casting of Incoloy 825 alloy ingot and investigate the growth and transition of dendrites, distribution of Ti in the special steel, and compare its effect with the generally conventional industrial rotary electromagnetic stirring (R-EMS). The results shown that the growth direction of primary dendrite under R-EMS is perpendicular to the mold wall, but the primary dendrite growth under V-LEMS have present an upstream dendrite growth state. It proves that the V-LEMS can generate a longitudinal circulation convection in the height direction of ingot, which can strengthen the temperature and composition mixing of the upper and lower melts of the ingot and promote the homogenization of the overall melt temperature and composition. The radial macrosegregation of Ti under V-LEMS is slightly higher than that of R-EMS, but R-EMS tends to increase the longitudinal macrosegregation of Ti element. The longitudinal macrosegregation degree of Ti element under V-LEMS is less than that without EMS and with R-EMS. V-LEMS makes the longitudinal distribution of Ti element in Incoloy 825 alloy ingot more uniform. The research results give some beneficial suggestions for improving the central quality of special steel continuous casting billet.

Quality prediction and process parameter importance analysis of cord steel during continuous casting

Continuous casting process control is crucial for enhancing the quality of steel. Center segregation, a key indicator of quality, plays a significant role in ensuring the quality of cord steel. However, the complexities of the continuous casting process, such as data silos, delayed inspections, uneven sampling and non-linearity, pose challenges to making timely improvements in quality. This study introduces an ensemble learning algorithm called LOF-KPCA-XGBoost, which combines Local Outlier Factor (LOF) sample weight, Kernel Principal Component Analysis (KPCA) and eXtreme Gradient Boosting (XGBoost) for online prediction of the center segregation coefficient of continuous casting billets. The algorithm achieves an accuracy of 90% and 98% within ±3% and ±5% relative error, respectively, with an average relative error of 1.6%. A sensitivity analysis method that leverages multivariable feature fluctuations is proposed to identify the process parameters that affect billet quality. The proposed method assists steel enterprises in improving the quality of cord steel billets.

Homogenization Path Based on 250 mm × 280 mm Bloom under Mixed Light and Heavy Presses: Simulation and Industrial Studies

This study proposed a new method for homogenizing continuous casting blooms based on solidification simulation calculations and industrial tests. The text describes a theoretical analysis of the solidification route of a cast billet of high-carbon alloy steel (B300A) under different process conditions. It summarizes the changing law of different under-pressure process parameters and under-pressure efficiency. The text also presents a solution to the seriousness of center shrinkage defects in the continuous casting of a large square billet of high-carbon alloy steel with the synergistic control technology of mixed light and heavy mixing under pressure. The study indicates that the center carbon segregation index of a high carbon steel continuous casting billet is 1.05, with a carbon extreme difference of not more than 0.08% and a proportion of 98.4%. Additionally, the center shrinkage is not more than a 0.5 level with a proportion of 99.5%. Meanwhile, the internal quality of cast billets has been improved, allowing for the rolling of large-size bars with a low consolidation ratio. The pass rate for internal ultrasonic flaw detection using the GB/T4162A grade is now higher than 99.95%, significantly reducing process costs and improving production efficiency for continuous casting and rolling.

A new hybrid local radial basis function collocation method for 2.5D thermo-mechanical modelling of continuous casting of steel

This study presents a new strong-form meshless method to solve the thermo-mechanical problem of the solidification process in the continuous casting of steel. A two-dimensional slice that travels in the casting direction is modelled in the Lagrangian system. The newly developed mechanical model is one-way coupled to the thermal model, where the heat flux due to the mould, sprays, rolls and radiation are imposed to solve heat transfer in the strand. The resulting temperature and metallostatic pressure govern the Norton-Hoff visco-plastic model used for computing shrinkage of the solid shell and induced residual stresses. The results are used to estimate critical areas susceptible to hot-tearing formation. The mechanical model uses a generalised plane strain assumption that includes linear strains perpendicular to the slice and enables the computation of the straightening of the strand. The thermo-mechanical model is spatially discretised with a local radial basis function collocation method (LRBFCM). The mechanical part includes a new hybrid method that combines LRBFCM with finite differences for increased stability. The presented work shows how the developed model is used to assess the impact of casting velocity on the solid shell shrinkage and the probability of hot-tearing occurrence in the continuous casting of square billets.

Numerical modelling of continuous casting of round billets with turbulence in the melt

The present work aims to solve the continuous casting benchmark problem in axisymmetry with turbulence in the melt by the meshless method. The physical model of the liquid-solid system that involves mass, momentum and energy conservation is formulated in the mixture continuum approximation. The melt is assumed Newtonian and incompressible. A k-epsilon Reynolds averaged Navier-Stokes turbulence model is implemented with Abe-Kondoh-Nagano closures. The mushy region is modelled as a Darcy porous media with the Kozeny-Carman permeability model. The solution of partial differential equations is implemented locally using collocation with radial basis functions and explicit time-stepping. The velocity pressure coupling is performed using the fractional step method. The validation of the model is assessed by comparing its outcomes with the results of the finite volume method. A sensitivity study of the varying casting speed and temperature on the velocity, temperature, and solid fraction fields is shown.

Simulation and Study of Influencing Factors on the Solidification Microstructure of Hazelett Continuous Casting Slabs Using CAFE Model.

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.

Estimating Non-Linear Heat Flux in Continuous Billet Casting Process With Limited Sensors

In a continuous billet caster, the heat transfer from the pool of molten steel to the cooling water via the copper mold depends non-linearly upon several casting parameters. A reliable and accurate methodology based on the principle of inverse heat transfer technique has been proposed in this work to obtain the nonlinear heat flux of a continuous billet casting mold. Differential evolution optimization technique has been used, in conjunction with the 2-D and 3-D steady state conduction heat transfer equations to develop the complete algorithm. It has been observed that both the 2-D and 3-D models are able to accurately predict the heat flux for different numbers and locations of temperature sensors. While the 2-D model estimates the 1-D heat flux profile varying along casting direction within a very short time period, the 3-D model offers the advantage of estimating a more accurate 2-D heat flux profile varying along both the mold length and width. The 2-D model has also been used to estimate the heat flux for an industrial continuous casting mold using measured plant data. It is observed that the present methodology accurately estimates the boundary heat flux in the continuous billet caster mold.

Examination of industrial safety of structures of the continuous casting Department of the open-hearth shop of the Taganrog Metallurgical Plant

The working draft of the main building of the department of continuous casting of billets (ONLZ) of the open-hearth shop of JSC Tagmet at the stage of "KM" was developed by the DKO of JSC UkrNIIPSK in 2000. Taking into account the design decisions taken and the need to ensure high reliability of structures arising from the specifics of metallurgical production (when installing a heavy duty crane (7K) with a lifting capacity of 225+63/20t at a significant height of the crane rail head – 27 m) in 2001, the customer (JSC Tagmet) decided to carry out an expert examination of design solutions for the main structures of the building frame and engaged the Central Research Institute of Building Structures named after V.A. Kucherenko, who, since 1995, has already conducted surveys of other workshops of the plant, built back in the XIX century, for this work. Then the correctness of the choice of sections and lengths of the elements of the main load-bearing structures was checked and the load-bearing capacity of these elements was assessed. The forces in the elements obtained as a result of carrying out a verification calculation on a computer with the refinement of the design scheme, the applied loads and the quality of steel used in the elements were used. The article presents the reasons for the conduct and results of the industrial safety examination carried out in 2011, a new department was put into operation by 2005, attached to the open-hearth shop.

Numerical Simulation of Fluid Flow, Solidification, and Solute Distribution in Billets under Combined Mold and Final Electromagnetic Stirring.

In this study, a three-dimensional segmented coupled model for continuous casting billets under combined mold and final electromagnetic stirring (M-EMS, F-EMS) was developed. The model was verified by comparing carbon segregation in billets with and without EMS through plant experiments. The findings revealed that both M-EMS and F-EMS induce tangential flow in molten steel, impacting solidification and solute distribution processes within the billet. For M-EMS, with operating parameters of 250A-2Hz, the maximum tangential velocity (velocity projected onto the cross-section) was observed at the liquid phase's edge. For F-EMS, with operating parameters of 250A-6Hz, the maximum tangential velocity occurred at fl=0.7. Furthermore, F-EMS accelerated heat transfer in the liquid phase, reducing the central liquid fraction from 0.93 to 0.85. M-EMS intensified the washing effect of molten steel on the solidification front, resulting in the formation of negative segregation within the mold. F-EMS significantly improved the centerline segregation issue, reducing carbon segregation from 1.15 to 1.02. Experimental and simulation results, with and without EMS, were in good agreement, indicating that M+F-EMS leads to a more uniform solute distribution within the billet, with a pronounced improvement in centerline segregation.

On issue of stress and curvature of shell of continuous cast billet

On issue of stress and curvature of shell of continuous cast billet

Simulation of BB-2 beam billet conti-nuous casting for production of large-sized I-beams

In connection with expansion of construction sector, it is planned to develop 80‒90‒100 I-beams. For these I-beams, universal section of continuously cast billet BB-2 (1050×450×120) was developed. The purpose of this work was to check casting parameters of given billet in a simulation model, using LVMFlow software, to confirm analytical calculations. Following parameters were chosen as parameters to be evaluated: geometric shape of the cast billet, temperature and dynamic parameters of casting. For maximum reliability, boundary conditions were set similar to real parameters of the CCM-3 at EVRAZ NTMK JSC, however, as assumptions, the calculation was carried out only in zone of direct contact with mold sleeve, and plane deformation condition was set along casting. Simulation results showed possibility of using LVMFlow to simulate the beam blanks casting processes with high degree of convergence. Casting BB-2 billet is technically possible in the conditions of continuous caster No. 3 at JSC EVRAZ NTMK, when the mold is replaced. Hydrodynamic pressure is created only on walls of crystallizer; there is vacuum on remaining surfaces due to lack of crystallizer walls narrowing sleeve towards cooling. Crystallization occurs most slowly along the interface between the wall and the BB flanges, however, there are no defects in the form of splashes, due to the low hydrodynamic pressure in these zones

Simulation of BB-2 beam billet conti-nuous casting for production of large-sized I-beams

In connection with expansion of construction sector, it is planned to develop 80‒90‒100 I-beams. For these I-beams, universal section of continuously cast billet BB-2 (1050×450×120) was developed. The purpose of this work was to check casting parameters of given billet in a simulation model, using LVMFlow software, to confirm analytical calculations. Following parameters were chosen as parameters to be evaluated: geometric shape of the cast billet, temperature and dynamic parameters of casting. For maximum reliability, boundary conditions were set similar to real parameters of the CCM-3 at EVRAZ NTMK JSC, however, as assumptions, the calculation was carried out only in zone of direct contact with mold sleeve, and plane deformation condition was set along casting. Simulation results showed possibility of using LVMFlow to simulate the beam blanks casting processes with high degree of convergence. Casting BB-2 billet is technically possible in the conditions of continuous caster No. 3 at JSC EVRAZ NTMK, when the mold is replaced. Hydrodynamic pressure is created only on walls of crystallizer; there is vacuum on remaining surfaces due to lack of crystallizer walls narrowing sleeve towards cooling. Crystallization occurs most slowly along the interface between the wall and the BB flanges, however, there are no defects in the form of splashes, due to the low hydrodynamic pressure in these zones

Flow and Heat Transfer on the Surface of Molten Steel Slag Layer in Continuous Casting Mold

Protective slag is coated on the surface of molten steel during continuous casting, the flow and heat transfer state of the protective slag is a decisive factor affecting the inflow and consumption of liquid slag and is also an important prerequisite for stabilizing and improving the quality of continuous casting billets. Based on the Navier Stokes fluid momentum conservation equation and energy equation, a two-dimensional longitudinal numerical model describing the flow/heat transfer of liquid protective slag on the surface of steel is established. The data comes from the equipment parameters and casting process of an arc shaped slab continuous casting machine in a domestic steel plant. The flow field and temperature field distribution of protective slag are calculated and analyzed, and the effects of factors such as slag layer thickness and shear speed on the flow and heat transfer status of the liquid slag layer are discussed. When the bottom shear velocity increases from 0.005 m/s to 0.2 m/s, the maximum flow velocity of liquid slag from the nozzle to the narrow surface in the center area of the model increases from 0.0012 m/s to 0.0617 m/s, and the average longitudinal flow velocity of liquid slag near the nozzle increases from 0.0012 m/s to 0.0627 m/s. The research results provide reference for investigating the complex metallurgical behavior of protective slag.

Identification of the nature of defects arising in the production of continuously cast pipe billets for the oil and gas industry

The paper presents the results of studies of defects that occur in the production of continuously cast pipe blanks for the oil and gas industry. It is shown that the use of the technology of continuous casting of pipe billets in comparison with the traditional methods of pouring liquid steel into a mold has a number of advantages, among which is the high productivity of the technological process. However, it was noted that in many cases, an abnormally high degree of contamination with non-metallic inclusions is observed in the structure of the steel of continuously cast pipe billets. It was revealed that the largest inclusions are oxides of silicon and manganese. On the surface of the pipes, there are defects in the form of oxide spots, near which there are large non-metallic inclusions. On the surface of the oxide spot, the presence of iron oxides in the form of scale is found, which is a consequence of the secondary oxidation of the metal by air oxygen. A mechanism for the development of oxide spots and decarburized strips in pipe billets has been determined, which consists in the formation of defects in the form of scratches and cracks on the surface before rolling. These defects during heating for rolling lead to the oxidation of the metal and the formation of scale on the surface of the pipe blanks. The results of experimental studies on the development of recommendations for improving the quality of the initial metal of seamless pipes for the oil and gas industry are presented. The study of the microstructure of steel and the assessment of its contamination with non-metallic inclusions were carried out on optical and electron microscopes, and the mechanical properties of pipe blanks were studied by standard methods

Optimization of Macro Segregation and Equiaxed Zone in High-Carbon Steel Use in Prestressed Concrete Wire and Cord Wire Application

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.

Microstructure evolution of lean duplex stainless steel produced by a short process

A short process of direct cold rolling of continuous casting billets following solution treatment is proposed, and the effect of cold-rolled reduction on the microstructure evolution and corrosion resistance of lean duplex stainless steel (LDSS) 2101 is investigated. The results show that when the cold-rolled reduction increased to 50%, the strain-induced martensite (SIM) engulfed the austenite along the annealing twin boundaries (TBs). Furthermore, the galvanic corrosion of the martensite and matrix combined with the decreasing fraction of the low-Σ CSL boundaries results in a significant reduction in corrosion resistance at 50% cold-rolled reduction. Additionally, the majority of metastable pits were generated within the ferrite grains and at the α/γ phase boundaries.

Adjustment of the Coarse Grain Problem of the Horizontal Continuous Casting Slab by Optimizing the Crystallizer Structure

This paper mainly focuses on the problem of coarse grain on the bottom surface of the red copper horizontal continuous casting billet, and tries to thicken the bottom end of the crystallizer by combining numerical simulation and industrial experiment, and indirectly improves the cooling strength of the bottom surface of the casting billet to solve the problem of grain coarseness. The results show that the optimum diameter of the lower inlet of the copper sleeve was 14.2 mm, when the diameter of the inlet increased from 11 mm to 14.2 mm, the cooling intensity of the lower part of the casting billet gradually increased, and the grain on the lower surface was significantly refined; and with the increase of the diameter of the water inlet, the average width of the columnar grain decreased from 1.94 mm to 1.64 mm, the grain size decreased, and the number of grains increased.