Continuous Casting Of Steel Research Articles

Improvement of Technology for Producing Rolled Sheet from Continuously Cast Steel Slabs. Part 1. Experimental Study of Casting Using a Pressure Submersible Nozzle

It is proposed to use a new submersible nozzle with eccentric apertures in order to improve continuously-cast slab quality. Calculations show that up to 38% of the heat of steel overheating is removed in the upper part of the crystallizer. The number of equiaxed crystals increases by several factors with an increase in crystallization rate. Pilot plant approval of advanced continuous casting of low-carbon and low-alloy steels makes it possible to improve hot rolled metal strength and toughness. Forecasting low-carbon steel sheet ultimate strength and relative elongation is conducted using known experimental equations. Rolled steel quality is evaluated from slabs selected from eight melts. The slab sulfur content obtained using a nozzle with eccentric apertures is somewhat higher than in slabs cast through existing nozzles.

Effect of Exit Shape of Submerged Entry Nozzle on Flow Field and Slag Entrainment in Continuous Casting Mold

In steel continuous casting with submerged entry nozzles at a domestic steel plant, nozzle clogging was largely alleviated and defect rates of hot-rolled and cold-rolled sheets relating to slag entrainment were reduced for a nozzle with an approximately oval exit relative to a nozzle with a rectangular exit. Numerical and physical models were built to investigate the above phenomena. A turbulent model was applied in large eddy simulation to obtain the evolution of turbulent features within the nozzle and mold, while particle image velocimetry was adopted to monitor fluid flow beneath the slag–steel interface. Main results were that the flow speed of the main stream from the approximately oval exit was higher than that from the rectangular exit, while the zone of a velocity magnitude below 0.2 m/s within the approximately oval exit was smaller than that within the rectangular exit, indicating that inclusions tended to reside for longer in the latter. At the same casting speed, that slag entrainment occurred more frequently for the nozzle with a rectangular exit was found to have no direct relationship with the velocity magnitude and vorticity at 1/4 mold width on the top surface. Meanwhile, slag entrainment always occurred at the moment that vorticity changed most rapidly. The current study thus provided new insight into the structural parameter optimization of the submerged entry nozzle.

A 1D Analytical Model for Slag Infiltration during Continuous Casting of Steel under Non-Sinusoidal Mold Oscillation

A 1D analytical model for slag infiltration during continuous casting of steel is developed to investigate the slag behavior in the mold–strand gap. The superposition principle and Fourier expansion are applied to obtain the analytical solution for transient slag flow under arbitrary mold oscillation including non-sinusoidal oscillation mode. The validated model using literature data partially explains several controversies such as slope of slag film channel, mechanism of non-sinusoidal mold oscillation, and timing of slag infiltration. The model shows that a converging slag film into the casting direction is required to open the mold–strand gap if compression is applied in between. Also, model calculations imply that higher slag consumption is achievable from non-sinusoidal mold oscillation by means of the increase of film thickness through longer positive pressure with higher peak pressure. The model demonstrates a time difference between slag flow and pressure near the meniscus and the discrepancy in timing of infiltration between previous works is attributed to the mismatch. The model provides a concise but reliable tool to understand slag infiltration behavior and design mold oscillation settings.

Domestic developments of equipment and technologies of steel in-linne degassing in the process of continuous casting

Apart from traditional methods of steel ladle treatment, degassing in the process of continuous casting (in-line degassing) is a perspective one. In the world a line of process flowsheets have been elaborated, but in practice the only one process has been implemented, which was developed by Professor G.A. Sokolov based on theoretical elaborations. The experience of its application in the BOF shop No. 2 of NLMK confirmed the efficiency of degassing in the process of continuous casting and expediency of further work on perfection of the technology and facilities structure for in-line degassing. Accounting the experience gained at AKHK “VNIIMETMASH”, a modified variant of in-line degassing facility was elaborated based on technological specifications of CNIIchermet. It was noted, that thanks to additional bunker-accumulator, fixed at the vacuum chamber, a possibility appeared to change steel ladles without disruption of continuous casting series. It enables to increase the share of degassed steel. At the designing of BOF shop of “Zaporozhstal” steel-works, planned for construction, specialists of AKHK “VNIIMETMASH”, CNIIchermet and YUMZ elaborated a design of two-position facility of increased efficiency for steel in-line degassing. Detailed description of the facility design presented as well as description of its basic units, elaborated at the level in invention. Taking into account that the facility height with the accumulator will make it difficult to place it in the existing shops, a modified in-line degassed elaborated without accumulator, which makes it possible continuous degassing of several heats. Such a degasser can be applied at both continuous casting of steel and casting of large ingots from several heats. The backlog, created by domestic scientists and specialists enables to solve technical problems, arising at elaboration and running of modern facilities of in-line degassing.

Kinetic Modeling of Nonmetallic Inclusions Behavior in Molten Steel: A Review

The kinetic modeling for the nucleation, size growth, and compositional evolution of nonmetallic inclusions in steel was extensively reviewed in the present article. The nucleation and initial growth of inclusion in molten steel during deoxidation as well as the collision growth, motion, removal, and entrapment of inclusions in the molten steel in continuous casting (CC) tundish and strand were discussed. Moreover, the recent studies on the prediction of inclusion composition in CC semiproducts were introduced. Since the 1990s, the development of thermodynamic model and relevant databases for inclusion engineering has been initiated by the steel industry. Later, the commercial software FACTSAGE employing the FACT database was widely used to predict the gas (atmosphere/bubble)–liquid (steel/slag/inclusion)–solid (refractory/slag/steel/inclusion) multiphase equilibria. With the help of the comprehensive thermodynamic database and solution models in conjunction with the development of user-friendly computing packages, the kinetics of inclusion evolution in molten steel can be successfully predicted based on several kinetic models such as the coupled reaction (CR) model, reaction zone model, and tank series recirculation (TSR) model. However, some parameters are needed to represent the real processes according to the model employed at different operational or experimental conditions. The effect of reoxidation on the evolution of inclusions in the ladle and tundish, which was experimentally confirmed, can be simulated by the effective equilibrium reaction zone (EERZ) model. The complex slag–steel interfacial reaction phenomena have been successfully explained by the interfacial kinetic model based on the dynamic interfacial tension and oxygen adsorption/desorption characteristics at the slag-steel interface.

Thermal analysis techniques applied to study corrosion mechanisms of SEN used in the steel continuous casting process

Recent advances in the technology of black refractories for steel continuous casting promote the development of materials that operate at extreme conditions. The effects of different damage mechanisms are critical, and it is necessary to provide detailed information about the thermal behaviour of the nozzle–mould flux system, at steel continuous casting process condition. Mould fluxes present a chemical composition that includes a complex mix of oxides, fluorite (CaF2) and carbonaceous materials (coke, graphite, etc.). Their physical properties [viscosity (η) and surface tension (γ)] are strongly dependent on chemical composition and temperature evolution at process conditions. For this reason, a complete characterization and deep knowledge of the thermal behaviour of the mould flux is the key to understand in detail the interaction phenomena present in the system (insert nozzle–mould flux), in order to identify the corrosion mechanisms. In these circumstances, the use of thermal analysis techniques (DTA-TG and dilatometry) can provide relevant information about nozzles and mould fluxes such as phase transformations, mass changes and volumetric variations, which occur in the system of study. In this paper, these results are correlated with a microstructural study of two samples: S1 (as received) and S2 (post-mortem) applying different microscopy techniques, X-ray diffraction and thermal simulation of the nozzle corrosion by FactSage 7.2 in order to identify the wear mechanisms and to obtain relevant information for the refractory and steelmaking industry.

Selection of refractory concrete for batching nozzles of an intermediate ladle of continuous casting machine

The paper presents experimental research on selection of refractory concrete for the glass dosing promove in continuous casting of steel. In the experiments we consider three types of refractory concrete determined by their basic thermal properties using standard methods and the selected refractory concrete with the best performance. The batcher glass was manufactured and tested in production conditions, which showed good results in continuous casting of steel.

Reactivity and thermo-physical properties of MnO-modified CaO-Al2O3-based mold fluxes for advanced high-strength steels

Advanced high-strength steels (AHSS) with superior strength, formability and ductility meet the new demand for balancing vehicle performance and passenger safety in the automotive industry. AHSSs are typically alloyed with substantial amounts of Al and Mn. However, during continuous casting, the alloying elements may react with the conventional CaO-SiO2-based mold fluxes and cause significant compositional changes, leading to deterioration of mold fluxes and surface defects of steel plates. In this study, the CaO-Al2O3-MnO-based mold fluxes were investigated based on CALPHAD-type thermodynamic calculations and kinetic modeling based on the local equilibrium model as well as high-temperature in situ interfacial reactions at 1600 °C. Furthermore, viscosity measurements and thermal analyses were performed to evaluate the thermo-physical properties of the CaO-Al2O3-MnO-based mold fluxes. The simulations agreed closely with experiments, suggesting the interfacial reactions were diffusion-controlled. While MnO in the mold fluxes participated in the redox reactions with Al in molten steels, its addition could lower the break temperature, viscosity, and liquidus temperature of mold flux without too severe reactions at the initial stage. The CaO-Al2O3-MnO-based mold fluxes are promising for continuous casting of high-Mn high-Al steels.

Microstructure, mechanical and ballistic property evaluation of a high strength low alloy steel produced through continuous casting route

ABSTRACT 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.

Electromagnetic Effects on Solidification Defect Formation in Continuous Steel Casting

Understanding and reducing defects formed during continuous casting of steel are challenging because of the many inter-related, multiscale phenomena and process parameters involved in this complex process. Solidification occurs in the presence of turbulent multiphase flow, transport and capture of particles, superheat transport, and thermal–mechanical behavior. The application of electromagnetic fields provides an additional parameter to control these phenomena to reduce solidification defects. It is especially attractive because the field has the potential to be easily adjusted during casting to accommodate different casting conditions. This article briefly reviews how electromagnetic forces affect solidification defects, including subsurface hooks, particle capture, deep oscillation marks, depressions, cracks, breakouts, segregation, and shrinkage. This includes the related effects on superheat transport, initial solidification, surface quality, grain structure, internal quality, and steel composition distribution. Finally, some practical strategies regarding how to apply electromagnetics to improve steel quality are evaluated.

Prospects of small capacity ca sting ladles transfer to stopperless casting of steel

Despite encouraging results, obtained at pilot tests, attempts to substitute the stopper facilities by sliding gates at casting ladles of small capacity, used at foundries of machine-building plants, did not result in their implementation in industry. The problems of transferring casting ladles with a capacity of up to 10 tons to continuous casting of steel, due to the peculiarities of their operation under conditions of obtaining low-weight castings, were considered. Priority problems were noted, the successful solution of which will confirm the prospects of using slide gates in foundry. The main requirements for a steel tapping gate system of a casting ladle of small tonnage are as follows: autonomy of the power supply of the shutter drive, eliminating the need to move flexible hoses over a long distance along the working platform; guaranteed start of casting in normal mode without burning the channel with oxygen; the stability of the node pressing the refractory plates of the slide gate to high temperatures in the absence of forced air cooling; the possibility of an active influence on reducing the intensity of the process of overgrowing of the steel outlet of the ladle in the course of filling molds. As a constructive solution aimed at fulfilling the indicated conditions, it was proposed to use a balancer-type cartridge valve equipped with a modernized electromechanical actuator and auxiliary devices for starting casting in normal mode due to mechanical destruction of the crust at the entrance to the steel outlet channel, as well as heating its walls in the closed state when moving the ladle from one form to another. It was recognized that participation on a parity basis in the creation of a promising sliding gate system for foundry ladles with a capacity of up to 10 tons of several development organizations with practical experience in this technical field is worthwhile.

Root cause analysis of metallurgical defects in continuous cast steel slabs at ISD DUNAFERR Zrt.

As market demands tighten, ISD Dunaferr Zrt. is placing increasing emphasis on improving the quality of its products. Line Scanner equipment used in rolling mills can identify most surface defects, but the majority of metallurgical faults are located beneath the surface (e.g. inclusions, cavity, gas bubbles, etc.). There is no standardized device for detecting them, only ultrasonic and microscopic testing is possible. In addition, it should be noted that some of the defects detected on the surface (e.g. surface cracks) can only be determined by microscopic testing, whether they are metallurgical or due to the parameters of the rolling process. Several pilot programs have been implemented to explore the causes. In this theme, the most significant pilot programs, as well as the evaluation of their results will be presented.

Role of Solidification in Submerged Entry Nozzle Clogging During Continuous Casting of Steel

Metallurgists are embroiled in a debate on the role of solidification in submerged entry nozzle (SEN) clogging during continuous casting of steel: does clogging originate from solidification, or does clogging cause the solidification? This study tries to clarify this debate. An enthalpy‐based mixture continuum model is used to simulate solidification in a clog structure. The 3D structure of the clog is reconstructed using X‐ray tomography images of an as‐clogged piece in an SEN, and is directly used in the numerical model. The flow and solidification in the open pores/channels of the clog structure are then calculated. The modeling results demonstrate that although solidification does occur deep in the clog structure as the melt flow is stopped, a gap remains between the solidification and clog fronts. This gap signifies an open‐channel clog region, and the clog structure in this region needs to be mechanically strong to withstand the impact of the melt flow; otherwise, fragmentation occurs. The study verifies that the solidification cannot occur before clogging if the molten steel has sufficient superheat and the SEN is properly preheated. A SEN made of an isolating refractory material can postpone the clogging, thereby extending its service life.

Investigation on Mold Flux Melting and Consumption During Continuous Casting of Liquid Steel

Mold powders play an integral role in maintaining the stability and efficiency of the continuous casting process as they (1) provide lubrication, (2) control heat transfer, (3) absorb nonmetallic inclusions, and (4) prevent reoxidation of liquid steel during continuous casting of liquid steels. Much of the previous investigations are focused on the characterization of mold powders to understand the physicochemical aspects of the continuous casting process. However, limited attention has been given to analyzing the melting behavior of mold powder, which is necessitated for the proper functioning of the caster. An experimental technique akin to the industrial practice has been adopted in this investigation to study the melting behavior of the mold powder. A realistic nondimensional correlation is proposed considering the various casting parameters (casting speed, mold oscillation frequency, and stroke, negative strip time, and cross-sectional area of mold), the mold powder melting, and the consumption rate based on the adopted experimental and theoretical methods for real-time application.

Microstructures and Formation of Tundish Clogging Deposits in Ti-Alloyed Al-Killed Steel

The continuous casting of Ti-alloyed Al-killed steels traditionally experiences clogging in the tundish, impeding stable operation. We studied the microstructures and mode of formation of such clogging deposits in tundish skulls recovered after long cast series. We sampled the steel skull along the whole tundish bottom from under the ladle shroud (impact zone) up to the tundish well and nozzle. The microstructures imply that the steel solidifies to the refractory (gunning mass) and remains partially solid through the entire cast. Thus, a “mushy zone” of steel loaded with solid delta ferrites is present along the margins of the steel during casting. In this mushy zone, the widely observed clusters of variably sintered alumina (NMI) accumulate, along with a substantial amount of gas bubbles acting as inclusion scavengers. The clustered alumina particles show a lognormal particle size distribution (PSD) in all locations, which becomes more pronounced if correcting for the observable sintering. Sintering of alumina size distributions linearizes a PSD, and further evolution, once the deposit is locked in place, occurs by Ostwald ripening, introducing skewness to the distributions. The observed PSDs contrast with the established log-linearity of PSDs of individual floating alumina NMI in the bulk steel, and suggest that the source of the alumina in the clogging deposits is not the passing bulk steel. However, ubiquitous sedimentary features show that the alumina particles are also not grown by reoxidation in situ. An upstream source separate from the bulk stream must be inferred, which is also required by the consistent sporadic presence of oxidic materials which cannot be derived from local sidewall reaction. In summary, the development of clogging deposits in this type of steel is an example of “slurry casting” of partially solidifying steel over thermal loss surfaces of refractories in the nozzle area.

Development of steel continuous casting at the Nizhny Tagil steel-works

Steel continuous casting is one of fundamentals of modern steel industry. Specialists of Nizhny Tagil steel-works (NTMK) made an important contribution to the process perfection. The one-strand slab CCM of curvilinear type with radial mold and slab straightening by multipoint curve, designed and manufactured at Uralmashzavod, became a prototype for many machines, which were later manufactured at domestic and foreign steel-works in the end of 60th of the previous century. In the process of mastering of CCMs, which were put into operation within the programs of the plant modernization and transferring to BOF production with steel continuous casting, the CCMs were significantly modernized and technology of casting was perfected. To bring down the impact on the solidifying billet peel and decrease a billet swell, the scheme of the supporting rollers location was changed, which enabled to increase the length of the supported zone. A principally new scheme of billets cooling was implemented, which ensured a softer and uniform secondary cooling due to water-air “fog”. To create optimal conditions of axis zone forming during production of round billets of 430 mm diameter, a technology of protective heat screens application was used. The protective screens were installed in the end of ingot solidification zone. A large work was done on determination of optimal technological casting parameters – temperature and speed modes, types of slag forming mixtures, types of heat-insulating mixtures, methods of metal protection in the process of casting. As a result of the work done, at EVRAZ NTMK a complex of steel continuous casting was created, which enables to be flexible depending on the varying situation at the market and to produce continuously casted billets of various dimensions and wide range of steel grades.

Modern status and ways of development of round billet production technology by steel continuous casting

Production of round billets by steel continuous casting, widely used for manufacturing seamless pipes, railway wheels and tyres, quality long rolled products etc., is widely spread in the world steel industry. Constant search for improved design of CCM takes place, separate parts of existing machines are being perfected. An analysis of collected in the world practice experience of solving problems, related to production of round continuously casted billets, enables to choose proper technical solutions for each particular situation, to determine rational parameters of technology. History of development of round continuously casted billets production technology considered. Data on their modern producers presented. Peculiarities of steel continuous casting technology, as well as reasons of defects of round continuously casted billets have been discussed. Classification of basic kinds of cracks of round continuously casted billet presented. Basic problems during production of round continuously casted billets relate to ovality formation, mainly because of unevenness of heat-away in the mold. The increased ovality can lead to formation of internal and external cracks. Ways of solving problems of defects formation and ways of round continuously casted billet technology perfection summarized. Application of methods of mathematical simulation for a technology, which enables to produce defectless billets considered. It was shown, that basic measures to decrease number of billet defects, relate to setting rational parameters of temperature-speed mode, transfer to internal mold profile, corresponding to the billet shrinkage. Another measure is elimination of uneven impact of the liquid metal stream on the solidifying shell in the area of small and big radius. A perspective direction of round continuously casted billets production technology perfection is application of soft reduction methods and electromagnetic stirring of the liquid metal.

Modification of tundish design to improve quality of slabs, casted at CCM No. 4 of EVRAZ NTMK

A technology of continuous casting of steel has a large effect on its contamination. In particular, proper organization of metal flows in tundish and mold is very important. After completion a series of casting through a tundish and drop of metal level in it, it possible, that the slag flows from the surface layers of the tundish to capture the metal. An analysis of results of ultrasonic control of finished strip showed, that the basic number of the revealed defects was obtained during strip rolling out of the last slabs of the last heat in a series for a tundish. Metallographic studies determined, that the defects were located in the slab axis zone and filled by macro-inclusions of complex composition. To determine the actual distribution of metal flows, a water simulation of them was accomplished for the existing design of the EVRAZ NTMK tundish. It was determined, that at the drop of metal level in a tundish, a capture of slag from the metal reservoir and its transfer into the main bath of the tundish takes place due to whirligig flows. Following the weight metal consumption, the zone of slag inclusions distribution enlarges. Besides, denudation of the metal mirror in the metal reservoir takes place, resulted in metal secondary oxidation. Based on the results of the simulation, it was proposed to modify the design of the “turbostop”, which is installed in the metal reservoir of the tundish. Besides, it was proposed to remove the dividers installation in the tundish. It was noted, that the proposed steps enable to ensure a minimal level of rejections.

Dry cooling as a way toward minimisation of water consumption in the steel industry: A case study for continuous steel casting

The steel industry represents a chain of technological processes, which consume a vast amount of energy and water, and produce a large quantity of emissions. A number of restrictions and regulations have therefore been recently imposed on the steel industry and involved processes aiming at the improvement of the use of resources, reduction of footprint in the natural environment as well as at the enhancement of overall efficiency of the steel production. In contrast to other research papers, the paper focuses on water use in a particular steelmaking process - continuous steel casting, which is used to cast more than 95% of the worldwide steel production. Approaches allowing the minimisation of water consumption are first identified and analysed. Spray cooling using once-through water and its substitution with dry cooling coupled with internally-cooled rollers by means of closed-loop water is computationally investigated. A 3D heat transfer and solidification model for continuous steel casting, which was validated with data from an actual steel plant, was used for this purpose. The results indicate that partial substitution of water spray cooling with dry cooling can provide a 48% lower once-through water use, which represents approximately a 1.5 m3/min reduction in water consumption. The annual potential for water savings at a steel plant operating three casters at 24/7 is about 2.4 Mm3.

Investigation of rheological behavior for commercial mold slags

Rheological behaviors of several commercial mold slags, which were designed for continuous casting of high-carbon steel, peritectic steel, and high-Al steel were studied using rotational viscometer with various rotating speeds. The crystallization rates, which were correlated with rheological behaviors, were detected by in-situ observation. The effect of steel-slag interface reaction between high-Al steel and CaO–Al2O3-based slag on the non-Newtonian fluid behaviors was also discussed. The main results demonstrated that these mold slags all belonged to pseudoplastic fluid and exhibited shear thinning characteristics. The index of flow characteristics in high temperature zone was less than 1 and fluctuated around 0.9, while in low temperature zone, n rapidly decreased from 0.9 to 0.3. The results show that the low temperature zone is more obvious than the high temperature zone for the shear thinning characteristics of the mold fluxes below the break temperature. The shear thinning was closely related to the crystallization rate and grain size of crystals precipitated within melts. Steel-slag interface reaction decreased the content of glass formers, such as SiO2 and B2O3. The crystallization capacity was enhanced, followed by a reduction of lubrication ability. It is found non-Newtonian behaviors of commercial mold slag are closely associated with their crystallization capacity, and the discussion range of viscosity temperature is more in line with the actual temperature drop range of molten flux during continuous casting, which is of great significance to understand the mechanism of shear thinning and optimize the comprehensive performances of commercial mold slags.