Steel In Tundish Research Articles

Study on inclusion removal in two-strand tundish with gas curtain considering bubble-inclusion attachment

ABSTRACT Application of a gas curtain is one of the main means to improve the cleanliness of liquid steel in tundish. In particular, the bubble-inclusion attachment is one of the important ways to remove inclusions, which cannot be ignored. The bubble size and gas flow are the main parameters of the gas curtain. In this paper, the Euler–Lagrange–Lagrange approach is used to study the three-phase interaction behaviour of liquid steel, bubble, and inclusion. The effects of inclusion size, bubble diameter, and gas flow on inclusion removal rate were studied with normal continuous casting conditions. The calculation results show that the cleanliness of molten steel can be improved by replacing the dam with a gas curtain. In the range of gas flow rate from 1.35 to 2.15 Nm3 h−1, the removal rate of bubble-inclusion attachment and total inclusion removal rate increase with the increase of gas flow. In the range of diameter from 4.5 mm to 6.0 mm with the same gas flow, the total removal rate and bubble-inclusion attachment removal rate increase with the bubble size decrease. The results provide a reference for improving the cleanliness of molten steel by properly increasing the gas flow and reducing the bubble size in industrial operations.

The high-efficiency dephosphorization mechanism of steel by a novel porous MgO–CaO based refractories

The interaction between refractories and molten steel in tundish has significant influence on quality of steel. The calcined dolomite and fused magnesia were adopted as raw materials to prepare MgO–CaO based refractories for tundish. Then the reaction behavior between refractories with different contents of calcined dolomite and molten steel was investigated. After reaction with different refractories at 1550 °C for 90 min, the total O and P in steels reduced by 33.9 % and 77 % respectively when increasing calcined dolomite from 0 to 60 wt%, the average size and area proportion of inclusions decreased from 4.92 μm and 9.98 ‰ to 2.47 μm and 4.73 ‰ respectively. Inclusions of FeO wrapped by FeO–P2O5–MnS translated to FeO coated by FeO–MnS. The CaO introduced by calcined dolomite could reduce the increase of oxygen to molten steel owing to better thermodynamic stability compared with MgO. Meanwhile, CaO could absorb [P] to form Ca3(PO4)2 on the surface of calcined dolomite particles, which was beneficial for dephosphorization of molten steel.

Study on the influence of unsteady casting on the flow characteristics and behavior of liquid steel in tundish

Study on the influence of unsteady casting on the flow characteristics and behavior of liquid steel in tundish

Optimal Control of Inclusions to Prevent “Sand-Hole” Surface Defects in Deep Cold-Drawn Battery Cups for Electrical Vehicles

The present work was conducted to elucidate the influence of inclusionson surface quality of deep cold-drawn battery cups for electrical cars. The obtained results revealed that, to prevent the surface defects of sand-holes in battery cups in deep cold-drawing process, attentions should be paid to steelmaking and casting process for optimal control of inclusions. Because sand-holes were often caused by large Al2O3 clusters and CaO-Al2O3 particles. Most important, a worthy finding was that these inclusions were not safe when they were over 100 μm and bigger than 27 μm, respectively, which was important for process optimization. By reducing (FeO) contents in ladle slag and tundish covering flux to about 5% or lower, together with optimal fluid flow of molten steel in tundish, such large inclusions can be well decreased to prevent the occurrences of sand-holes in battery cups in industrial production.

Numerical simulation and application of argon blowing from tundish cover for bloom continuous casting

During the continuous casting process, the remaining oxygen in the tundish can be significantly decreased by argon blowing from the tundish cover(ABTC). As a result, the effect of protective casting can be obviously improved, which helps decrease the reoxidation of molten steel in tundish. In the present work, numerical models for ABTC of a six-strand continuous casting machine were established and verified by the measured oxygen mass fraction in tundish during ABTC. The results indicate that the best conditions of ABTC are installing the argon pipes on either side of the tundish cover holes, sealing the baking holes, and keeping stopper rod holes open. The argon flow rate should be ?120m3/h during the period of empty tundish and ?60m3/h during the period of normal casting. Industrial trials of ABTC based on the calculation results were carried out. The results indicated that the increased nitrogen in steel(?w[N]) from the end of RH to tundish decreased by 21.5% from 8.78?10-6 to 6.89?10-6, and the amount of inclusions except for MnS in bloom (scanned size: 8mm?8mm) decreased by 21.3% from 13.43 to 10.57, and the average size of inclusions decreased by 19.0% from 9.27?m to 7.51?m.

Numerical Simulation and Application of Tundish Cover Argon Blowing for a Two-Strand Slab Continuous Casting Machine

During continuous casting, argon blowing from tundish cover (ABTC) can greatly prevent the flow of the remaining air and decrease the reoxidation of molten steel in tundish. In the current study, a numerical model based on a tundish of a two-strand slab continuous casting machine was established to investigate the feasibility and evaluate the protective casting effect of the ABTC process. The influence of operation parameters, including sealing schemes of tundish cover holes and the argon flow rate of the remaining oxygen content, were studied in tundish. Then, industrial trials based on the operation parameters from the numerical model were carried out to evaluate the protective effect of ABTC. The results indicate that the ABTC process has a great protective effect in avoiding increasing levels of nitrogen and losing titanium and aluminum. With the ABTC process applied, the average increment of nitrogen (△w[N]) in steel from the end of RH to tundish decreases by 90% from 10 × 10−6 to 1 × 10−6, the average loss of titanium (△w[Ti]) by 12.7% from 63 × 10−6 to 55 × 10−6, and the amount of aluminum (△w[Al]) decreases by 7.1% from 70 × 10−6 to 55 × 10−6. The injecting hole and baking holes should be sealed during the period of empty tundish to efficiently discharge the air. In order to ensure that the oxygen volume fraction in tundish is less than 1%, the argon flow rate should be ≥220 Nm3/h during the period of empty tundish and ≥80 Nm3/h during the period of normal casting.

Physical Modelling of Nitrogen Variation in Continuously Cast Blooms Resulting from Atmospheric Exposure of Steel in Tundish during Initial Stages of Teeming

Exposure of liquid steel to air, consequent re-oxidation as well as nitrogen absorption are common in steelmaking and produce unacceptable variations in product chemistry. The phenomena, during continuous casting of the lead or first heat, have been investigated in a full-scale water model of a two-strand, bloom casting shroud-tundish system. Physical modelling results supported by industrial scale measurements have demonstrated that exposure of liquid steel to tundish atmosphere during initial period of ladle teeming and consequent nitrogen absorption, manifest over substantial period, influencing predominantly the first three blooms.

Molten Steel Flow, Heat Transfer and Inclusion Distribution in a Single-Strand Continuous Casting Tundish with Induction Heating

The electrical magnetic field plays an important role in controlling the molten steel flow, heat transfer and migration of inclusions. However, industrial tests for inclusion distribution in a single-strand tundish under the electromagnetic field have never been reported before. The distribution of non-metallic inclusions in steel is still uncertain in an induction-heating (IH) tundish. In the present study, therefore, using numerical simulation methods, we simulate the flow and heat transfer characteristics of molten steel in the channel-type IH tundish, especially in the channel. At the same time, industrial trials were carried out on the channel-type IH tundish, and the temperature distribution of the tundish with or without IH under different pouring ladle furnace was analyzed. The method of scanning electron microscopy was employed to obtain the distribution of inclusions on different channel sections. The flow characteristics of molten steel in the channel change with flow time, and the single vortex and double vortex alternately occur under the electromagnetic field. The heat loss of molten steel can be compensated in a tundish with IH. As heating for 145 s, the temperature of the molten steel in the channel increases by 31.8 K. It demonstrates that the temperature of the molten steel in the tundish can be kept at the target value of around 1813 K, fluctuating up and down 3 K after using electromagnetic IH. In the IH channel, the large inclusions with diameters greater than 9 μm are more concentrated at the edge of the channel, and the effect of IH on the inclusion with diameters less than 9 μm has little effect.

Flow behavior and heat transfer of molten steel in a two-strand tundish heated by plasma

Abstract Tundish plasma heating could achieve constant temperature and low superheat pouring of molten steel, which is conductive for improving the efficiency of continuous casting, enhancing the internal quality of slab. The flow behavior and heat transfer of molten steel in tundish heated by plasma are essential for understanding this process. In the present study, numerical and physical simulation were conducted to investigate the temperature filed and flow characteristics of molten steel in two-strand tundish heated by plasma with different plasma heating powers. Based on the conducted simulation, it was stated that the temperature field of molten steel in tundish was significantly improved by plasma heating. The outlet temperature in 500 kW was increased by 3.05 K compared with non-plasma heating. The physical simulation demonstrated that the dead volume of tundish was reduced by 18.89% in 6 kg/h compared with non-plasma heating. The flow characteristics in the tundish with plasma heating were better than that without plasma heating. With an increase in heating power, the effect of plasma heating was considerably improved.

Evolution of the Numerical Model Describing the Distribution of Non-Metallic Inclusions in the Tundish

Continuous casting is one of the steel production stages, during which the improvement in the metallurgical purity of steel can be additionally affected by removing nonmetallic inclusions (NMIs). This can be achieved by means of various types of flow controllers, installed in the working space of the tundish. The change in the steel flow structure, caused by those flow controllers, should lead to an intensification of NMIs removal from the liquid metal to the slag. Therefore, it is crucial to understand the behavior of nonmetallic inclusions during the flow of liquid steel through the tundish, and particularly during their distribution. The presented paper reports the results of the modeling studies of NMI distribution in liquid steel, flowing through the tundish. CFD modeling methods—using different models and computation variants—were employed in the study. The obtained CFD results were compared with the results of laboratory tests (using a tundish water model). The results of the performed investigations allow us to compare both methods of modeling; the investigated phenomena were microparticle distribution and mass microparticle concentration in the model fluid. The validation of the CFD results verified the analyzed computation variants. The aim of the research was to determine which numerical model is the best for describing the studied phenomenon. This will be used as the first phase of a larger research program which will provide for a comprehensive study of the distribution of NMIs flowing through tundish steel.

A New Method for Sensing Pouring Temperature of Molten Steel in Tundish

Pouring temperature of molten steel at the outlet of the tundish is the key parameter to control the solidification accurately. However, the stopper occupies the top of the outlet, leading to that the existing sensor cannot measure the molten steel temperature at the outlet. To solve the problem, this work develops a new small sensor installed at the bottom of the stopper, which combines the stopper and the temperature sensor into one. Mo-W-ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cermet that has excellent corrosion resistance has been used to make a small sensor with a thin-walled structure of 5 mm thickness. To sense the pouring temperature independently, fast and accurately, the length/radius ratio of the small sensor should reach 13 to form a blackbody cavity approximately. According to the industrial test, the pouring temperature of molten steel is measured for the first time in the field of metallurgy. Meanwhile, a deviation (e.g., 8.2 °C or 1.4 °C) between the pouring temperature and the temperature measured by the existing sensor is found. As a result, based on the temperature measured by the existing sensor, the superheat of molten steel and the cooling water flow usually have enough margin for ensuring the safe operation of continuous casting, reducing the control accuracy of the solidification and increasing the risk of quality problems. Therefore, this work will be helpful to control the solidification more accurately, improving the product quality.

Influence of calcium aluminate flux on reoxidation behaviour of molten steel during continuous casting process

ABSTRACTIt is an important issue to prevent molten steel in tundish from being reoxidized during the continuous casting process for improving the cleanliness of steel products. Rice husk ash (RHA) is an excellent insulation powder to prevent heat loss of the molten steel in the tundish. The addition of RHA increases the silica activity in the molten slag layer, which can cause reoxidation of molten steel. Therefore, the effect of calcium aluminate-based flux (CA-flux) on reoxidation behaviour was investigated with different ratios of CA-flux to RHA + CA-flux (=RCA). The silicon and oxygen pick-up, which is caused by the self-dissociation of silica at the slag/metal interface was suppressed with an increasing RCA, and hence the number of inclusions formed by reoxidation in the molten steel was reduced at high RCA. The evolution of inclusions with different RCA was investigated by comparing experimental results with predictions from a refractory–slag–metal-inclusion (ReSMI) multiphase reaction simulation. Finally, the inclusion formation behaviour in tundish was investigated using a ReSMI simulation with different RCA and including the temperature drop of the steel melts in the ladle during casting.

Characteristics of Nozzle Clogging and Evolution of Oxide Inclusion for Al-Killed Ti-Stabilized 18Cr Stainless Steel

Characteristics of nozzle clogging and evolution of oxide inclusion were studied by sampling the deposits of submerged entry nozzle (SEN) and the molten steel in tundish during Al-killed Ti-stabilized 18Cr stainless steelmaking process. The deposits found in the clogging of SEN were mainly composed of frozen steel and inclusions. The inclusions in the deposits and tundish were both mainly (MgO-Al2O3)rich-CaO-TiOx. The compositions of most inclusions were Liquid+Spinel or Liquid+TiSp phase. The (MgO-Al2O3)rich-CaO inclusions that were not effectively modified by calcium treatment could be a source of clogging. By combining both the experimental results and thermodynamic calculation, (MgO-Al2O3)rich-TiOx inclusions (TiSp inclusions) would be formed with the decreasing temperature in steel during continuous casting, which could be transported and accumulated on the inner wall of the SEN. Increasing the calcium content in the molten steel could decrease the formation of TiSp inclusions. During continuous casting, these inclusions accumulated on the inner wall of the SEN and gradually formed porous network of clog. Molten steel would gradually solidify in the porous space of the clog due to the increased residence time of the molten steel when flowing through it. The clogging gradually increased and caused the shutdown of continuous casting.

Flow Characteristics for Two-Strand Tundish in Continuous Slab Casting Using PIV

With the development of continuous casting technology, there has been an increase in the stringent requirements for the cleanliness and quality of steel being produced. The flow state of molten steel in tundish is the key to: Optimizing the residence time of molten steel in the tundish; homogenizing the temperature of molten steel; and removing inclusions by floatation. Hence, from theoretical and practical aspects, it is imperative to examine and analyze the flow field of molten steel in the tundish in order to ensure the desired molten steel flow. In this study, a two-strand tundish with 650 mm × 180 mm slab casting is considered as the subject for this research. According to the similarity theory, combined with the geometrical shape and dimension of the prototype tundish, a tundish model with a geometric similarity ratio of 2:3 is established in the laboratory. Digital particle image velocimetry (PIV) is employed to measure and examine the flow fields at different casting speeds for a tundish containing different flow control devices. The flow in the tundish is typically turbulent and also consists of a vortex motion; it exhibits both random and ordered characteristics. Results reveal that the presence of baffles with 15° holes can cause an upward-directed flow in the outlet section and give rise to a large circulation. When the casting speed is doubled, the overall velocity of the flow field and turbulent intensity increase, leading to an increase in the molten steel surface velocity.

A Simulation Study on the Flow Behavior of Liquid Steel in Tundish with Annular Argon Blowing in the Upper Nozzle

A three-dimensional mathematical model of gas−liquid two-phase flow has been established to study the flow behavior of liquid steel in the tundish. The effect of the argon flow rate and casting speed on the flow behavior of liquid steel, as well as the migration behavior of argon bubbles, was investigated. The results from the mathematical model were found to be consistent with those from the tundish water model. There were some swirl flows around the stopper when the annular argon blowing process was adopted; the flow of liquid steel near the liquid surface was active around the stopper. With increased argon flow rate, the vortex range and intensity around the stopper gradually increased, and the vertical flow velocity of the liquid steel in the vicinity of the stopper increased; the argon volume flow in the tundish and mold all increased. With increased casting speed, the vortex range and intensity around the stopper gradually decreased, the peak value of vertical flow velocity of liquid steel at the vicinity of the stopper decreased, and the distribution and ratio of argon volume flow between the tundish and the mold decreased. To avoid slag entrapment and purify the liquid steel, the argon flow rate should not be more than 3 L·min−1. These results provide a theoretical basis to optimize the parameters of the annular argon blowing at the upper nozzle and improve the slab quality.

Online tool based on Tundish steel CFD model to monitor and minimise steel intermix in CC slabs

An online tool based on computational fluid dynamics modelling was developed, validated and applied to Colakoglu Metallurji 2-strands slab caster to monitor and manage steel intermixing in tundish at ladle change. The tool allows to reduce the length of the slabs with intermixed steel. Different tundish layout and operating conditions are accounted for as slab size, presence of flow modifiers in tundish, tundish refill time, casting speed (also different from strand to strand), steel grade. The tool was developed by CSM following the suggestions and needs of Colakoglu Metallurji, who provided to a successful validation of such tool, both with slab sampling and support for installation and testing. As a result, the tool has been integrated into the Colakoglu CC2 control system and is currently used offline for optimizing a priori mixed grade production scheduling, and online for slab cutting optimization in order to reduce the downgraded product amount.

Optimization of flow control devices to minimize the grade mixing in steelmaking tundish

The minimization of grade intermixing in a tundish is one of the import concern of steelmakers. Different design and operating parameters of the tundish, as well as flow control devices (FCDs), has been used in last decade by researchers to modify the flow characteristics of melt in the tundish. In the present work, the three-dimensional numerical investigations have been carried out to optimise the design of FCDs in multi-strand tundish by using response surface methodology. The interaction of design parameters i.e., shroud depth, advanced pouring box (APB) wall angle, dam height and dam position has been studied by the response surface plots. An effort has been made to quantify the impact of APB angle and shroud depth. Moreover, these two FCDs have important implications in future for efficient inclusion removal. The quantification of intermixed grade steel in tundish has been made at each strand. Further, average output from all strand has been analyzed and the optimum design of FCDs has been suggested. An important finding from this study is that some FCDs have an adverse impact on mixing in the far zone of the tundish.

Effect of Rice Husk Ash Insulation Powder on the Reoxidation Behavior of Molten Steel in Continuous Casting Tundish

Rice husk ash (RHA) has been widely used as an insulation powder in steel casting tundish. Its effect on the reoxidation of molten steel in tundish as well as on the corrosion of magnesia refractory was investigated. The reoxidation of the steel, indicated by an oxygen pickup, was progressed by increasing the ratio of RHA to the sum of RHA and carryover ladle slag (R ratio) greater than about 0.2. The increase of the silica activity in the slag layer promoted the self-dissociation of SiO2 from the slag layer into the molten steel, resulting in the silicon and oxygen pickup as the R ratio increased. The total number of reoxidation inclusions dramatically increased and the relative fraction of Al2O3-rich inclusions increased by increasing the R ratio. Hence, the reoxidation of molten steel in tundish might become more serious due to the formation of alumina-rich inclusions as the casting sequence increases. MgO in the refractory directly dissolved into the molten slag layer without forming any intermediate compound layer (e.g., spinel), which is a completely different situation from the general slag-refractory interfacial reaction. A flow was possibly induced by the bursting of gas bubbles at the ash-slag (-refractory) interface, since the silica in the RHA powder continuously dissolved into the molten slag pool. Thus, the RHA insulation powder has a negative effect on the corrosion of MgO refractory.

Hydrodynamic effects created by argon stirring liquid steel in a one-strand tundish

ABSTRACTContinuous casting of steel ensures the flexible production of different grades of slabs intended for the Rolling Mill departments. Therefore, it seems justifiable to search new solutions for tundish metallurgy. This study puts forward a new gas-permeable barrier’s design solution with two circular porous plugs, whose purpose is to punctually agitate the liquid steel in tundish. Two argon injection system locations were tested. The results for the hydrodynamic pattern of liquid steel and bubbles’ behaviour in the tundish were obtained from laboratory experiments with water glass model and computer simulations. Within the framework of the investigation, three argon flow rates, i.e. 5, 10 and 15 NL min−1, were considered. The designed gas-permeable barriers effectively stimulate active flow in the tundish for isothermal and non-isothermal conditions, while reducing the stagnant flow share and the transient zone extent.

Magnetohydrodynamic flows and heat transfer in a twin-channel induction heating tundish

Induction heating (IH) electromagnetic field has a significant positive effect on the uniform temperature distribution in tundishes and decreases molten steel superheat to improve the quality of billets in continuous casting. To achieve the effect of electromagnetic force and Joule heating for molten steel in a channel-type IH tundish, a magnetohydrodynamic model is developed and validated by industrial experiment data. The molten steel in the tundish channel has a rotating velocity under the off-centre electromagnetic force. Its flow pattern consists of two contra-rotating vortices close to the outlet zone of the channels. The upper and lower vortices in the tundish channel change with time. The temperature distribution in the cross-sections is almost stable, and the maximum temperature increases by 30.1°C. Molten steel runs upward after flowing past the tundish channel, whose density decreases because of IH. The upward motion changes when the electromagnetic force acts on the molten steel. Results reveal that electromagnetic force has a significant effect on the flow of molten steel in the tundish, and that flow pattern varies in the tundish with or without electromagnetic force under Joule heating.