High-speed Casting Research Articles

Characteristics of subsurface inclusions in deep-drawing steel slabs at high casting speed

Deep-drawing steels are widely used in the automobile industry and macro-inclusions in continuous casting slabs should be strictly controlled because they cause surface defects in the final products. In this paper, industrial tests with different casting speeds from 1.0 m.min-1 to 2.5 m.min-1 and different tundish superheats were carried out, then subsurface inclusions in high-speed casting slabs were investigated with a large detection area by the ASPEX automatic inclusion analysis system, and the effect of the casting speed and tundish superheat was studied. The results show that there are six different types of macro-inclusions found beneath the slab surface, named cluster alumina, bubble plus cluster alumina, lump alumina, cluster TiOx-Al2O3, entrapped mold powder and CaO-Al2O3-MgO, respectively. The above first three types account for about 98% of total inclusions in the slabs cast with the mold fluctuation within ±3 mm. The size of more than 80% of such inclusions ranges from 20 to 50 μm. The number density of inclusions larger than 50 μm decreases with the increase in the casting speed and tundish superheat. The subsurface macro-inclusions in deep-drawing steel slabs are closely related to the hook structure. Increasing the casting speed and superheat is effective for reducing the hook depth and large-sized inclusions on the subsurface of slabs.

Reduction of slivers by the use of an electromagnetic actuator

The submeniscus velocity has a big influence on the surface quality of slabs. Slabs casted with a low casting speed result in a low submeniscus velocity and suffer more from Al-inclusions, while slabs casted with a higher casting speed have a higher submeniscus velocity and suffer more from mould powder inclusions. If the submeniscus velocity can be controlled, the amount of slivers has to be reduced. ArcelorMittal Ghent decided to install an ElectroMagnetic Actuator (EMA) to control this submeniscus velocity. This topic shows what the impact of the EMA can be on slivers.

The Overview on Sticking Breakout Behavior for Thin Slab Continuous Casting

Breakout is the most detrimental event associated with the continuous casting process, with the overview of the sticking breakout behavior, a lot of valuable things had been acquired. For the mechanism of the sticking breakout forming, the key for the breakout prevention is decreasing the probability of the hot spot; the content of the carbon or alloy element, the wear and tear of the mould corner, the mould flux, the fluctuation of the casting speed and the fluctuation of the meniscus are easy to cause the sticking; and with high casting speed and the funnel mould, the thin slab continuous casting is more easier to lead to sticking breakout than the normal strand.

Application of High Speed Continuous Casting on Low Carbon Conventional Slab in SGJT

Based on the achievement of high speed continuous casting in SGJT, fluid flow, heat transfer, and lubrication behavior were analyzed elaborately. The results indicated that well-bottom SEN with the angle of −20° together with FC mold could reduce the level fluctuation effectively. When FC mold was applied at 1.9 m min−1, there was an increase of average heat flux about 0.06–0.1 MW m−2. During heat transfer analysis, the empirical equation of heat flux was proposed and solidification crater end was validated by pin shooting method. Furthermore, a kind of mold powder employed in high speed casting was described and a new criterion of the consumption rate for high speed casting was put forward.

Effect of casting process on mould friction during wide, thick slab continuous casting

Real time detection of the complex friction behaviour and reasonable regulation of lubrication between mould and initial solidified shell are key factors in quality improvement, steady operation and efficient production in continuous casting. In the present work, mould/slab friction was detected based on an online mould friction monitoring system on a wide, thick slab continuous caster equipped with hydraulic oscillators. The influence of the main casting parameters on mould friction is discussed including the casting temperature, slab dimensions and mould level. The response and sensitivity of friction to the changes of steel grade and powder were analysed, as well as the effects of different oscillation modes and oscillation parameters on friction. The results show that the friction is sensitive to variations of casting parameters, and steel grades and powder have significant effect on mould/slab friction behaviour. A reasonable match of oscillation modes and oscillation parameters can significantly optimise the friction behaviour at high casting speed, which also has an important role in improving the slab surface quality. These experimental results provided foundations for further understanding and controlling on the mould/slab friction behaviour.

Main Trends in the Development of Technology for Casting Steel into Ingots

This article discusses promising technological measures that can be used to cast ingots. It also examines such issues as multi-ladle casting, optimization of ingot geometry and the chemical composition of the metal being cast, mastery of the production of hollow ingots, stream vacuum-degassing, aspects of the bottom-pouring of large ingots, materials for warming the hot-top part of ingots, protection from secondary oxidation, and high-speed casting. Recommendations are given to improve the technological regimes that are used to cast steel into ingots at Russian plants.

Thermal fluid mathematical modelling of twin roll casting (TRC) process for AZ31 magnesium alloy

A two-dimensional computational fluid dynamics (CFD) thermal fluid model has been developed and validated for twin roll casting (TRC) of AZ31 magnesium alloy using the commercial package ANSYS CFX. The model was developed to represent the steady state part of the TRC process. The thermal history of the strip was studied in terms of the temperature gradient through the strip thickness at the exit of the caster, the sump depth and mushy zone thickness at the centreline for different casting speeds, final strip thicknesses and heat transfer coefficients between the rolls and the surface of the strip. Moreover, the effect of these parameters on the average solidification cooling rate and secondary dendrite arm spacing in the solidified structure was investigated. Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing (SDAS) through the thickness of the sheet to those measured using the Natural Resources Canada Government Materials Laboratory, CanmetMATERIALS located in Hamilton, Ontario, Canada. Analysis of the effect of TRC conditions on the SDAS showed that more uniform SDAS through the thickness is obtained when casting thinner strips at higher casting speeds.

Research and Application of Dynamic Secondary Cooling Control Method for Slab Caster of CISDI

After analyzing the characteristics of each type of dynamic secondary cooling control methods, the combination use of on-line thermal model control and effective casting speed computer dynamic control method was adopted in CISDI dynamic secondary cooling control. On the basis, the transient heat-transfer mathematic model was developed, the determination methods of strand target surface temperature and real time cooling water were proposed, and the design idea of effective casting speed computer dynamic control method was introduced. Considering the probably unreliability of heat transfer difference calculation and inadaptability of heat transfer boundary conditions when too low, too high casting speed or speed variation rate, the on-line thermal model control method was used when the casting speed between 0.8m/min and 1.4 m/min and casting speed variation rate within 0.1m/(min·s), in other cases, effective casting speed computer dynamic control method was adopted.

High Speed Twin Roll Casting of Aluminum-Copper Strips with Layered Structure

Mathematical modeling of the solidification behavior of Al-33 wt% Cu strips in a twin roll caster at speeds varying between 0.079 m/s to 3.98 m/s predicted that at high casting speed strips will have layered structure with distinct morphology. The model was validated by production of Al-33 wt% copper strips in a laboratory twin roll caster. As per the prediction from the model the high speed cast strips had layered structure with zones near the roll surface showing higher hardness as compared to the interior.

Water Modeling of Self-Braking Submerged Entry Nozzle Used for Steel Continuous Casting Mold

Slag entrainment in a continuous casting mold is one of the major causes of macro nonmetallic inclusions in continuous casting steel products. Stabilizing the level fluctuation is an important factor to improve steel quality. A new type of submerged entry nozzle (SEN) named self-braking SEN was designed. In the current study, water modeling experiments were performed to study the effect of self-braking SEN on level fluctuation in a continuous casting slab mold. The level position and the root mean square value of level fluctuation were analyzed through the online detection data. The results showed that the flow in the mold was more symmetrical and the tracer dispersion was more uniform. Moreover, the meniscus was also more uniform than the conventional nozzle with the self-braking SEN, especially at high casting speed.

Determination of CC slab solidification using nail shooting technique

The technology of nail shooting was improved and used to study the transverse shape of the solidified shell during steel continuous casting. Three locations across the slab width (1/2, 1/4 and 1/8) were measured by nail shooting and which indicated a larger solidification coefficient and longer liquid core in the slab at higher casting speeds. The solidified shell across the slab width direction was non-uniform due to uneven secondary spray cooling. The point of final solidification at locations 1/8 and 1/4 was much longer than the position between the slab centre and location 1/4, leading to a long solidification end of >2 m, which is poor for the application of dynamic soft reduction. A mathematical model was developed to simulate the growth of the solidified shell and which was in good agreement with the measurements measured by nail shooting. Based on the measurements and simulations, the water spray pattern was improved, making the solidified shell more uniform. Dynamic soft reduction was then optimised resulting in reduced centreline segregation.

Investigation of the Influence of the Roll Surface on the Cast Strip at the Casting Using a Vertical Type High Speed Twin Roll Caster

A vertical type high speed twin roll caster can be cast an aluminum alloy strip directly from a melt at high casting speed. However defects of the cast strip occurred at faster roll speed, which includes small cracks on the cast strip and unsoundness thickness distribution. They are related to contact condition of roll surface and melt. In the present study, a grooved roll was used to eliminate the defects and adopted in terms of the cost saving. We experimented using several grooved rolls with different patterns. When the groove width was 0.45mm; depth 0.2mm; pitch 0.1mm and 1.0mm, stable casting was possible. The shape of bulge was formed on the cast strip surface by the grooved roll. As a result of color check, we found that the grooved roll eliminate the small cracks. We stopped the rotated roll during the casting to observe the contact condition between the melt and the roll, and confirmed how the bulge was formed. The as-cast strip with the bulge was able to cold rolling.

Control of Carbides and Graphite in Cast Irons Type Alloy’s Microstructures for Hot Strip Mills

The carbide and graphite formation and redistribution of alloy elements during solidification were investigated on high-speed steel (HS) and Ni-hard type cast irons with Nb and V. The crystallization of hypereutectic HSS proceeds in the order of primary MC, γ + MC, γ + M6C, γ + M7C3, and γ + graphite eutectic, in hypoeutectic alloys proceeds in the order of primary γ, γ + MC, γ + graphite, γ + M6C, and γ + M7C3 eutectic, and in Ni-hard proceeds in the order of primary γ, γ + MC, γ + M3C, and γ + graphite eutectic. The γ + graphite eutectic solidifies with the decrease of V, Nb, and Cr and the increase of Si and C contents in residual liquid during solidification. The behavior in graphite forming tendency in the residual liquid is estimated by the parameter ∑CLimi′. The eutectic graphite crystallizes at the solid fraction when ∑CLimi′ takes a minimum value. The amount of graphite increases with the decrease in ∑CLimi′ of initial alloy content in both specimens. Inoculation with ferrosilicon effectively increases the graphite content in both specimens.

Mathematical modeling of the shape of the cavity of a thin-slab continuous-casting mold

A method is proposed for constructing the profile of the expanded upper working cavity of the mold to allow it to accommodate the pouring nozzle in the casting of thin slabs. A relation is presented to determine the angle of inclination of the narrow faces of the mold. The main function of the mold in the continuous casting of steel is to form an ingot having the required cross sec- tion. The main requirements which the mold must satisfy are that it ensure that the necessary amount of heat is removed from the solidifying steel and that the skin formed on the ingot by the time it leaves the mold has a quality surface and is strong enough to withstand the heat of the liquid phase and the ferrostatic pressure exerted on it. High casting speeds are needed in order to be able to combine the operations of the casting of thin slabs and the hot- rolling of plates. The need for high casting speeds in turn makes it necessary to optimize the thermal performance of the mold and the strength of the forming ingot skin. The shape of the cavity of the mold is determined with allowance for the specific features of the casting operation. The technology used to cast steel on a continuous caster entails introducing the molten steel into the mold of the caster through a submersible refractory nozzle that is positioned below the meniscus of the liquid metal. In order to be able to position the nozzle inside the mold during the casting of thin slabs, the top section of the mold is formed with an expand- ed working cavity (funnel), while the bottom part of the funnel transitions smoothly into a planar section that shapes the stream so as to form a thin rectangular slab. A mold of this design is shown in Fig. 1. The cross section of the funnel-shaped part is determined by the geometry of its boundary in the XY plane (Fig. 2) at the level of the meniscus, as well as by the change in the depth of the funnel a along the Z axis over the height of the mold (see Fig. 1). To provide for intensive heat removal and a rapid increase in the thickness of the ingot's skin, it is necessary to min- imize the rate at which it is deformed as it passes over the surface that forms the funnel. Minimizing this rate appreciably lessens the danger of having internal and external cracks form in the ingot. This situation can be realized when the rate at which the curvature of the mold's cooling surface changes is minimal. The profile of the funnel should be a smooth shallow symmetrical curve with the largest deviation in its middle sec- tion. The largest deviation on the top end of the mold can be referred to as the amplitude. The amplitude should smoothly decrease to zero approaching the bottom end of the mold, where the broad face of the mold straightens out and becomes flat. It is best if the amplitude changes in accordance with a linear law

Solidification and the δ/γ phase transformation of steels in relation to casting defects

Many advanced steels fall within the peritectic composition range, which are notoriously difficult to cast due to cracking and breakout problems in the continuous casting process especially at high casting speeds. In this study an attempt was made to obtain practical understanding of the solidification and the δ→γ phase transformation of various commercial steels using high-temperature laser-scanning confocal microscopy. Under rapid cooling conditions the transformation morphology showed a massive-type of transition rather than a classical diffusion-controlled transformation.

Simulation of the Temperature, Stress, Strain Field in Aluminum Thin-Gauge High-Speed Casting

Based on the analyses of aluminum melt solidification and heat transfer during the process of twin-roll casting, a coupling mathematical model of thin-gauge high-speed casting was developed, which included the casting roller shell. At the same time, FEM was adopted to solve the coupling model. The temperature field, thermal stress field and strain field of aluminum melt in casting zone were simulated by this model. When the casting velocity is 7m/min, and the thickness of strip is 2 mm, in the melt zone, the temperature of melt decreases rapidly as it approaches the rollers; the surface stress of strip is larger than the central stress; In the liquid zone and mushy zone, thermal stress is relatively small; in rolling zone, thermal stress is much larger than in the former two zones, and gradually increases along exports, then gradually decreases after the peak; the outsurface strain of the casting strip is larger than the inner strain, and the thermal stress gradually increases along exports.

Researches on the Behavior of Carbon and Sulfur Segregations of 82B Billet

The behavior of carbon and sulfur segregations of 82B hard wire steel produced under different continuous casting conditions has been systematically studied by the combination of field trial and laboratory analysis. The results showed three factors such as superheat degree, casting speed and F-EMS which influenced the segregation of billet worked differently with the variations of inner positions of the billet and segregation elements. For the central segregations of carbon and sulfur, the dominant factor was casting speed. Under high casting speed, proper increase of secondary cooling intensity could effectively decrease carbon and sulfur segregations of billet, especially for the central position of billet. The hydraulic simulation of the tundish showed the optimal casting speed should be 1.8m/min.

Research on Thermocouple Embedded Theory for Thermal State of CC Mould Copper Plate with High Casting Speed

High casting speed would change the thermal state of the mould copper plate, The coupled visco-elasto-plastic FEM models have been presented for thermal process analysis of steel shell and the mould copper plates. With the understanding to the mould thermal state for different casting speed, the characters of mould copper plate thermal flux is obtained. It is shown that, the highest thermal flux zone is getting downward with casting speed increasing, and it would also make harder for breakout signals catching.

Research on Hot State of Mould Copper Plate with High Casting Speed

High casting speed has a great influence to thermal state and strain/stress field of the mould copper plate. The coupled visco-elasto-plastic FEM models have been presented for thermal process analysis of steel shell and the mould copper plates. It is shown that, when the casting speed is increasing, the turning point of the temperature distribution curve is getting further to the meniscus; and the increasing casting speed has no influence to the equivalent strain distribution along the thickness direction of the mould.

Effect of Laser Surface Modification and Tempering Process on Microstructure and Hardness Profiles of Roll Materials

Laser surface modification, using a continuous wave CO2 crosscurrent laser with generated beam power of 1 kW, was performed on the adamite steel, indefinite chilled cast iron and high speed steel rolls which were applied to the industries. Optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and micro Vickers hardness test were applied to reveal the microstructural details and hardness profiles of the laser treated zone. The results indicate that, laser treated zones of three roll samples consist of melting zone, phase transformation zone and heat affected zone. After laser treatment, the melting zone have low hardness compared to the phase transformation zone, but after tempering at 540°C for 1 hr, the hardness at the melting zone dramatically increases, because of the formation of the fresh martensite from retained austenite. In contrast, the hardness at the phase transformation zone sharply decreases as fresh martensite changed to tempered martensite. There are many small and well distributed FeS and MnS inclusions in the melting zone at the three roll samples.