Continuous Casting Of Steel Research Articles

Effect of TiO2 content on structure of BaO-CaO-Al2O3-TiO2-Li2O slags by molecular dynamics simulation

During the continuous casting of high-titanium steel, traditional CaO-SiO2-based mold slag undergoes severe slag-metal reactions. Therefore, BaO-CaO-Al2O3-TiO2-Li2O slag system, which has low reactivity, has become a potential new slag system for the continuous casting of high-titanium steel. In this study, a melt of BaO-CaO-Al2O3-TiO2-Li2O is used as the research object. The effects of component changes on the microstructure of the quinary slag system and the evolution of amphoteric oxides are examined by molecular dynamics (MD). The results reveal that the amphoteric behavior of TiO2 is affected by Al2O3 when the content of TiO2 is less than 3 wt%. Whereas the amphoteric behavior of Al2O3 is affected by TiO2 when TiO2 content is more than 3 wt%. NBO/T increases continuously in the low TiO2 system ranging from 1 to 6 wt%. However, in the high TiO2 system ranging from 7 to 12 wt%, NBO/T first increases and then decreases.

Study on high temperature mechanical properties of niobium microalloyed cold heading steel

In recent years, high-strength micro-alloyed cold heading steel has developed rapidly, mainly by adding Nb, V, Ti and other micro-alloying elements to the steel for grain refinement and precipitation strengthening, it is widely used in automobiles, bridges, construction machinery and other fields due to its excellent strength and toughness, fatigue resistance and corrosion resistance. However, the common quality defects in the process of continuous casting and hot rolling of such steels - transverse cracks on the surface and corners, are still one of the technical difficulties in the production of the world’s iron and steel enterprises. Therefore, it is of great scientific and engineering significance to deeply explore the evolution law of high temperature mechanical properties of niobium microalloyed cold heading steel, to analyze the common generation mechanism of surface transverse cracks and to propose general improvement measures. In this work, the high temperature thermoplastic properties of niobium microalloyed cold heading steel was studied by using Gleeble-3500 thermal simulator, combined with optical microscope (OM) and scanning electron microscope (SEM), the tensile fracture morphology and nearby microstructure were observed, and its high temperature plasticity mechanism was analyzed. The results show that the niobium microalloyed cold heading steel has two brittle temperature ranges: the first brittle zone is from the melting point to 1200°C, the temperature range of the third brittle zone is below 700°C, and the optimum plasticity zone is 700-1200°C. At 650°C, the fracture mode is ductile fracture and cleavage fracture; at 800°C, it is a typical cleavage-brittle fracture type; at 950°C, the fracture mode is dimple fracture, with good plasticity; at 1100°C, the particles become finer and the plastic deformation is more uniform. In order to avoid the occurrence of cracks in the continuous casting billet, the straightening temperature of the continuous casting billet should be higher than 700°C, it should be heated slowly in the early stage of heating, and the hot rolling temperature should be controlled at 700-1100°C.

Effect of electropulsing intensity on nucleation of TiN in 321 stainless steel

ABSTRACT In the process of titanium microalloyed steel continuous casting, tiny TiN can refine solidification structures, while thick TiN will affect casting. In this paper, the experimental results showed that electropulsing could refine the size of TiN precipitates and improve the nucleation rate of the TiN precipitates. The larger electropulsing intensity resulted in a better effect. The modelling results showed that electropulsing could reduce the nucleation barrier of TiN in the molten steel and the two-phase region. In addition, the larger the electropulsing intensity and the higher the temperature, the better the promotion effect is. This research is of great significance for solving the problem of nozzle clogging and solidification microstructure refinement of titanium microalloyed steel.

Characteristics of SEN clogging and adhesive behavior of oxide inclusion during continuous casting of Ti-stabilized ultra-pure ferritic stainless steels

Characteristics of SEN clogging and adhesive behavior of oxide inclusion during continuous casting of Ti-stabilized ultra-pure ferritic stainless steels

Nanoindentation of alumina and multiphase inclusions in 42CrMo4 steel

Cleaning filter systems for metal melt filtration combine reactive filtration by functionalized filter surfaces for chemical reaction with the steel melt and active (mechanical) filtration. In the present work, a combined cleaning filter system was applied to 42CrMo4 steel melt containing nonmetallic inclusions, which were generated artificially before filtration. The nonmetallic inclusions in the solidified steel were investigated by an automated scanning electron microscope (ASPEX), nanoindentation, atomic force microscopy (AFM), focused ion beam technique (FIB) and confocal laser scanning microscopy (CLSM). The combined filter system was found to reduce the amount of aluminum in the steel and to form novel multiphase inclusions. These multiphase inclusions consist of TiO 2-x and Al 2 O 3 in a low-melting spessartine matrix and were characterized by nanoindentation. Compared to pure Al 2 O 3 inclusions, the spessartine inclusions are softer and have a lower Young's modulus, fitting much better to the mechanical properties of the steel. The area below the indents was investigated by focused ion beam technique and transmission scanning electron microscopy revealing cracks and dislocations. Furthermore, the low-melting character of the spessartine matrix was proven by means of a confocal laser scanning microscope. Accordingly, the low-melting spessartine inclusions appear as liquid inclusions during steel melt processing and could contribute to clogging prevention in continuous steel casting. • Combined steel melt filtration system caused formation of multiphase inclusions. • Multiphase inclusions entrapped TiO2-x and Al2O3 in a matrix of soft spessartine. • During nanoindentation of Al2O3, pop-in events marked elastic-plastic transition. • Analysis of EBSD data by MTEX suggest activation of pyramidal slip system in Al2O3. • Beneath the indents, plastic zone based on dislocations was observed by t-SEM.

Research on solidification behavior of a high Mn steel during continuous casting based on solidification characteristic unit analysis

A novel research route combining numerical simulation and physical simulation was used to study the solidification behavior of high Mn steel continuous casting billet under different superheats in this work. The results indicated that higher super heat degree will lead to lower equiaxed crystals content and severer element segregation. Moreover, the Mn element segregation was lighter than that of the C element, and it was caused by the higher value of solute partition coefficient of Mn. Finally, the superheat degree suitable for continuous casting of high Mn steel was modified to be 10 ℃.

Clogging on submerged nozzle in Al killed continuous casting

Nozzle clogging is a common problem in Al deoxidized continuous casting steel production. Clogging occurs when impurities in liquid steel and deposit build up on the wall of the submersible nozzle (SEN). The results of the study on the change of elements Al, Ca, O, N,… in the process of Ca addition continuous casting, the impurity composition in liquid steel and the composition of the deposit layer on the SEN wall can indicate the evolution of SEN clogging through the Ca/Al ratio and predict well the occurrence of calcium aluminate phases affecting the clogging process.

Hydraulic Jump Behavior during Filling Process of Cast Start II

This paper presents a 0.25-scale quasi-three-dimensional hydraulic model experiment of transient fluid flow phenomena during continuous casting of steel under solidification. Water cooling is performed at the bottom of the mold, and saturated sodium acetate solution is covered on the spring and particle arrangement at the bottom of the mold/on the dummy bar to simulate the solidification phenomenon in the actual continuous casting process. The results show that the solidification on the dummy bar surface is very important to the early stage of the filling process and cannot be ignored. Its influence gradually decreases with the rise of the liquid level, and basically disappears when the liquid level rises to a certain height (steady liquid level, SLL). In SLL, the interface morphology of the solidified layer is more affected by the flow, while the interface morphology of the solidified layer has no significant effect on the liquid surface velocity.

Controlling the Thermal and Rheological Properties of Silicate Glasses for Development of Advanced Mold Flux Systems

Development of the advanced mold flux is always mandatory to enhance both the quality and productivity of continuous casting of steels. Especially, the increasing demands for high alloy steels production and high speed casting reveals serious contradiction between two principal functions of mold flux: lubrication and controlling heat transfer. In order to overcome this problematic needs, some innovative research activities are being carried out. MAE (Mixed Alkali Effect) has been examined in alumino-borosilicate-based mold system to stabilize alkali cation and aluminum association, which enables chemically stable glassy mold flux film during casting of high alloy steels. Non-Newtonian mold fluxes could be developed by addition of Si3N4 or SiC due to the increase of stiffness of polymeric structure, which would be beneficial to satisfy the contradictory requirements of viscosity at mold top surface and mold wall. Some innovative ideas for controlling mold heat transfer without deteriorating the lubrication have been examined by dispersion of nano-size metallic particles and by modification of prenucleation motif. All these trials are closely related with glass science and engineering. Therefore, it should be highly beneficial to enhance the collaborative research activities between glass and metallurgy society for further development of advanced functional mold flux systems.

TRADITIONS AND INNOVATIONS IN THE TECHNOLOGICAL HISTORY OF DONETSK METALLURGICAL PLANT

The paper considers the general historical outline of the Donetsk Metallurgical Plant (DMZ) development, which began 150 years ago with mass production of metal, as well as the process of introducing and mastering innovations, primarily within the framework of the blast furnace and steelmaking industries. The presented data considers implementations which at that time were of a pioneering nature within the framework of the Soviet, and in some cases the world metallurgy. The contribution to the development of DMZ by such metallurgists and scientists as M.K. Kurako, I.P. Bardin, A.N. Tsaritsyn, N.S. Shchirenko, V.F. Basantsov, I.M. Ektov, S.L. Yaroshevsky, V.I. Machikin, A.M. Zborshchik, E.N. Skladanovsky, D.A. Dyudkin, K.V. Baranov, P.G. Glazkov is mentioned. The particular attention is focused on the technologies of steel continuous casting and injection of pulverized coal into the hearth of a blast furnace, which were first introduced at industrial scale at the DMZ. At present, these technologies, the impetus for the development of which was given at the DMZ, are an integral part of the set of advanced modern technologies of ferrous metals production. The issues of introducing the new technologies and equipment in the post-Soviet period up to 2014 are also considered. Some examples are also provided, which illustratie the effective and practically trouble-free use of equipment created more than a hundred years ago. The role of the Donetsk National Technical University (DonNTU) in the history of the DMZ is considered. For more than a century it consists in preparing highly qualified engineering personnel and scientific support of all innovations.

Hydraulic Jump Behavior during Filling Process of Cast Start I

This paper presents a 0.25 scale quasi-three-dimensional hydraulic model experiment of transient fluid flow phenomena during continuous casting of steel. The relationship between the continuous casting process and the hydraulic jump phenomenon is established. The casting process in the mold is divided into four stages (I–IV) from the beginning to the end of continuous casting. The filling process involves stages I–II and is investigated by high-speed camera. The filling process is part of the cast start. In this paper, the hydraulic jump behavior varies and is controlled by different spring and iron chips arrangement on the dummy bar during the filling process. A filling coefficient is proposed to judge the best filling conditions and apply them to the whole filling process. There is an optimal spring and iron chip arrangement, which can adjust the hydraulic jump to optimize the initial flow field during the filling process, even the whole continuous casting process.

Thermal optimization of secondary cooling systems in the continuous steel casting process

A new process design methodology for the cooling system in the continuous steel casting process is introduced. It is based on a semi-empirical approach for choosing the primary cooling zone design parameters and using an optimization-based method to decide on the design parameters corresponding to the secondary cooling zone. The heat flux through the secondary cooling zone is the design parameter in the latter case. Unlike former studies that considered a misfit temperature function as the objective function, it is defined here as the square of the temperature field penalized with the Niyama’s criterion infeasibility to ensure the production of microporosity-free strands. This way, no information about the target temperature field is required in advance. The corresponding heat transfer problem is coupled to CALPHAD to consider commercial steel grades straightforwardly. An efficient gradient-based optimization algorithm is employed to find the optimal values of design parameters. Then, this algorithm is employed in an actual process design problem corresponding to the continuous slab casting of a commercial steel grade. A post-processing approach is suggested to convert the results of numerical optimization to industrially relevant machine parameters, and then they are exploited in practice in the foundry plant. While the optimization problem is only constrained to avoid solidification-induced defects, it produces sound and crack-free strands. Moreover, comparing numerical results to actual surface temperature measurements reveals more petite than a six percent discrepancy between the simulation and experiment. These observations illustrate the feasibility of the presented design methodology as the initial step in deciding on the cooling system parameters in this process.

Examining the reliability of the data analysis system for continuous steel casting

The application of industry 4.0 guidelines is also an integral part of the life of ISD Dunaferr Zrt. Working closely with technology professionals, we have created a data analysis system that processes data from continuous steel casting. The life cycle of slabs can be traced in a complex way from raw steel production to the end of hot rolling. In an industrial environment, the program provides an opportunity to study the effects on slabs (e.g. change in casting speed, change in mould level, change in the position of tundish stopper rod (TSR), etc.). The results provided by the system are suitable for both qualifications made by experts and automatic one during the visual inspection using the web display system. In this paper, we examined the correlation between the slabs burdened with known significant changes in casting parameters in the cast sequence and the slabs with significant changes classified by the data processing system to verify the reliability of the data analysis system. The results confirmed the reliability of the data analysis system and pointed to the greater reliability of the study of cast length-based changes versus time-based changes.

Thermo-mechanical behaviour analysis of slab corner during special steel continuous casting

ABSTRACT The corner crack is an important issue during special steel continuous casting. To comprehensively investigate the heat transfer, stress, and shrinkage behaviours of slab corner, a full-scale thermo-mechanical model of a slab and its mould was developed, the inverse algorithm was applied to the model. The model was validated by comparing the calculated data with the measured data in the plant trials. The results showed that the thermo-mechanical behaviours of the slab corner showed a similar tendency but were not the same, which reflected the necessity of building a full-scale model. There exists ‘hot spots’ at the slab off-corner region, and its position moved away from the corner along the casting direction, which affects the temperature and stress distributions. The maximum stress value reached approximately 16 MPa at the mould exit. The model provides an in-depth understanding of slab corner during special steel continuous casting.

Modeling of Multiphase Flow, Superheat Dissipation, Particle Transport, and Capture in a Vertical and Bending Continuous Caster

A new model of particle entrapment during continuous casting of steel is presented, which includes the effects of multiphase flow from argon gas injection and thermal buoyancy from superheat in the strand. The model simulates three different capture mechanisms, including capture by solidified hooks at the meniscus, entrapment between dendrites, and engulfment by the surrounding of large particles. The fluid flow and bubble capture results are validated with plant measurements, including nail board dipping tests and ultrasonic tests, respectively, and good agreement is seen. Results suggest that the superheat has a negligible effect on the flow in the mold region. However, higher (30 K) superheat causes a more complex flow in the lower strand by creating multiple recirculation zones due to the thermal buoyancy effects. This causes less penetration deep into the strand, which leads to fewer and shallower particle captures. Lower (10 K) superheat may enable significant top surface freezing, leading to very large internal defect clusters. Lower superheat also leads to deeper meniscus hooks, which sometimes (0.003%) capture large (1 mm) bubbles. Capture bands occur near the transition line from vertical to curved, due to the downward fluid velocity balancing the particle terminal velocity, enabling capture in the relative stagnation region beneath the longitudinal recirculation zone. These findings agree with plant observations.

Effects of the Cooling Rate and Recovery Temperature on the Growth of AlN Precipitates in Gear Steel

During the continuous casting and rolling process of gear steel, AlN precipitation often causes surface cracks on the cast slab. Rapid cooling of the slab surface is a new concept to inhibit AlN and improve the cracking resistance, but it requires further investigation for practical application. Here, the effects of the cooling rate and recovery temperature on AlN growth behavior in gear steel are investigated by designing five cooling conditions. A mathematical model to describe the growth characteristics is constructed based on Ostwald ripening theory. The experimental results show that the cooling rate significantly influences the size and quantity of AlN. When the cooling rate increases from 3.0 to 5.0 °C s−1, the average diameter of AlN decreases from 133.6 to 75.8 nm and the number density of AlN decreases from 6.8 × 105 to 2.1 × 105 cm−2. The calculated results show that AlN has maximum size, which significantly decreases with decreasing temperature. When AlN reaches the maximum size, it stops growing. AlN growth during the cooling process mainly occurs above 800 °C. Therefore, a high cooling rate and a recovery temperature lower than 800 °C are key to inhibiting AlN precipitation and improving the cracking resistance.

A faster than real-time heat transfer model for continuous steel casting

In this paper, a three-dimensional faster than real-time heat transfer model is presented for the continuous casting process. The model features a high computational capability required for real-time prediction, optimization, and control of the casting process. The computational model is implemented with a multi-level acceleration method on GPUs to ultimately shrink the computational time cost. This acceleration method helps to build a proper mapping from numerical models to GPU hardware features and provides two acceleration strategies with slight accuracy loss. With the multi-level acceleration method, a 117× speedup with a max 1.74% relative error compared to a 14-threaded CPU implementation is achieved. Moreover, the accuracy of the model has been verified with the Stefan problem and validated with industry measurement. The relative computational time, which is required to be less than 1 in real-time simulations and significantly far less than 1 in dynamic optimization of the casting process, is adopted to evaluate the real-time ability of the model. The proposed model achieves a relative computational time between 0.0003 for a coarse mesh and 0.015 for a very fine mesh. Our demonstrated high-performance modeling tool herein is envisioned to dominate among the applications of advanced process control and optimization in continuous casting.

Вплив швидкості охолодження та перегріву вище лінії ліквідусу на формування структурних складових

In the paper, the comparative analysis of the process of forming a cast structure of carbon steel after termination of its crystallization in continuous cast steel billet with diameter of 450 mm and overheating of steel to 50° C and 150° C above the liquidus line, and further pouring into wedge-shaped molds, is performed. The microstructure of the skin zone after continuous casting of steel with maximum cooling rate of 106 °С/min consists of dendrites, which have branches of the first and second order, indicating their formation from the melt. When etching the surface of the specimens with solution of nitric acid, the microstructure of the skin zone was represented by ferrite, perlite with separate areas of martensite. The formation of ferrite, perlite and bainite areas was observed at a distance of 0.5 ingot radius and in the central part of the samples, and separate areas of bainite and perlite were observed in the central part of the ingot. Upon further cooling of steels below the temperature of Ar3, the formation of excess ferrite along the boundaries of austenitic grains occurs. Overheating of steels to 50° C and 150° C above the liquidus line gives rise to the formation of a more homogeneous structure. Non-metallic inclusions formed in steel do not exceed 1 point according to DSTU 4967:2015and are not the centres of crystallization – they are observed in perlite grains. There is the formation of separate inclusions of phases located in the perlite grain, which contributes to the finely dispersed hardening of steel. Increasing the overheating temperature leads to the formation of more finely divided inclusions and to the formation of a more homogeneous structure. After overheating to 50° C in the middle part of the wedge (cooling rate of 102-103 ° C/min) no ferrite formation is observed. At all overheating temperatures, perlite has a fine differentiation, but increasing in the overheating temperature above the liquidus line enhances the dispersion of both individual inclusions and perlite. Keywords: carbon steel, continuous cast steel billet, hardening, cooling rate, overheating of steels above the liquidus line.

Transport in turbulent, recurrent flows: Time-extrapolation and statistical symmetrization

We investigate bubble dynamics in a submerged double-jet as an example of weakly coupled, Lagrangian transport. The setup resembles continuous casting of steel at Reynolds numbers Re=136000 to Re=272000. Using short time series of flow fields obtained from large-eddy simulations (LES) with a discrete bubble model, we calculate a database of transport patterns and time-extrapolate them to long durations in the framework of recurrence CFD (rCFD). A dedicated averaging procedure along bubble trajectories allows us to study their transport with large steps at little numerical costs and monitor their spatial distribution. Besides time-extrapolation for fixed Re with a single database, we demonstrate how several time series can be combined to (i) enforce symmetries and (ii) approximately model conditions in between. We compare bubble volume fraction fields and total hold-up obtained from LES and from rCFD and find very good to satisfying agreement with speed up factors of more than 500.

The Effects of Nozzle Inclination, Area Ratio, and Side-Hole Aspect Ratio on the Flow Behavior in Mold

During the steel continuous casting, the submerged entry nozzle (SEN) plays a crucial role in the fluid characteristic of fluid steel, which further affects the slab quality. In this paper, a nozzle model is developed to study the influences of nozzle inclination, nozzle area ratio, and side hole aspect ratio on the fluid characteristic of fluid steel. The results show that when the nozzle angle increased from 10° to 20°, the impact points of the narrow surface were 0.402 m, 0.476 m, and 0.554 m away from the meniscus, respectively. In addition, when the nozzle area ratio increased from 0.96 to 1.16, it resulted in a significant decrease of the speed of high-temperature liquid steel flowing out of the nozzle. Moreover, when the side-hole aspect ratio was 1.47, the maximum turbulent kinetic energy of the free surface reached 0.00141 m2 s−2. Furthermore, when the aspect ratio was 1.67 and 1.84, a slight difference existed, and the maximum turbulent kinetic energy was almost 0.00095 m2 s−2. The proposed model can provide theoretical basis and guidance for nozzle optimization.