Numerical simulation on the multiphase flow and reoxidation of the molten steel in a two-strand tundish during ladle change

A 3D mathematical model was proposed to investigate the molten steel–slag–air multiphase flow in a two-strand slab continuous casting(CC)tundish during ladle change.The study focused on the exposure of the molten steel and the subsequent reoxidation occurrence.The exposure of the molten steel was calculated using the coupled realizable k–εmodel and volume of fluid(VOF)model.The diffusion of dissolved oxygen was determined by solving the user-defined scalar(UDS)equation.Moreover,the user-defined function(UDF)was used to describe the source term in the UDS equation and determine the oxidation rate and oxidation position.The effect of the refilling speed on the molten steel exposure and dissolved oxygen content was also discussed.Increasing the refilling speed during ladle change reduced the refilling time and the exposure duration of the molten steel.However,the elevated refilling speed enlarged the slag eyes and increased the average dissolved oxygen content within the tundish,thereby exacerbating the reoxidation phenomenon.In addition,the time required for the molten steel with a high dissolved oxygen content to exit the tundish varied with the refilling speed.When the inlet speed was 3.0 m·s^(-1)during ladle change,the molten steel with a high dissolved oxygen content exited the outlet in a short period,reaching a maximum dissolved oxygen content of 0.000525wt%.Conversely,when the inlet speed was 1.8 m·s^(-1),the maximum dissolved oxygen content was 0.000382wt%.The refilling speed during the ladle change process must be appropriately decreased to minimize reoxidation effects and enhance the steel product quality.

Reduction and Reoxidation of Silicon in Blast Furnace Hearth

This paper introduces both laboratory experi- ment and equilibrium calculations concerned with the Si reduction and reoxidation.The results give evidence that the Si transport in different directions just exists in the furnace hearth synchronistically, by which the desulphurization is also affected.The problems noticed for smelting tow Si pig iron are given.

Reoxidation of liquid steel and evolution of inclusions during protective atmosphere electroslag remelting of Ce-containing heat-resistant stainless steel

The evolution of Ce-containing inclusions and its correlation with the reoxidation of liquid steel during protective atmosphere electroslag remelting(ESR)of heat-resistant steel were studied.The reoxidation of liquid steel took place during the ESR,resulting in the oxygen pickup from 0.0014 to 0.0053 wt.%.The inclusions in the consumable electrode,liquid metal pool and remelted ingot are Ce_(2)O_(2)S and Ce_(2)O,inclusions invariably.The inclusions in the remelted ingot are originated from three ways:(I)the original inclusions from the electrode;(Il)the newly formed Ce_(2)O_(2)S and Ce_(2)O_(3) inclusions in the liquid metal pool by reoxidation remaining still in remelted ingot;(IlI)the newly generated Ce2O2S and Ce_(2)O_(3) inclusions during cooling and solidification of liquid steel.The relative proportions of Ce_(2)O_(3) inclusions in liquid metal pool and remelted ingot are 41% and 76.5%,respectively.The inclusions ranging from 2 to 5μm in the remelted ingot take up 55%,followed by the inclusions smaller than 2μm(43%of total inclusions).The number proportion of the Ce_(2)0,inclusions in the liquid metal pool which were removed by floating up into slag is 1.96×10-5%.

Modeling reoxidation behavior of Al-Ti-containing steels by CaO-Al2O3-MgO-SiO2 slag

A kinetic model was developed using FactSage Macro Processing to simulate the reoxidation of Al-Ti-containing steels by CaO-Al2O3-SiO2-MgO slags. The calculated results show a good agreement with the experimental data. Thus, the developed kinetic model can be used to predict changes in slag, steel, and inclusion compositions during the reaction process. During the slag reoxidation process, the reactions occurring at slag-steel interface and in the bulk steel were confirmed to be the reduction of SiO2 by [All and [Til and the self-dissociation of SiO2 into [Si] and [O]. Increasing the ratio of CaO to SiO2 in the slag can significantly suppress the self-dissociation of SiO2 in the slag and lower the amount of inclusions produced during reoxidation. The formed inclusions changed from solid Al2O3 to Al2O3-TiOx inclusions, which was mainly dependent on the w（[Al]） and w（[Ti]）. The amount of inclusions was obviously influenced by the composition of the top slag.

Soil Aeration Variability as Affected by Reoxidation

The interplay between soil physical parameters during the recovery from anoxic stresses （reoxidation） is largely unrecognized. This study was conducted to chaxacterise the soil aeration status and derive correlations between variable aeration factors during reoxidation. Surface layers （0-30 cm） of three soil types, Haplic Phaeozem, Mollic Gleysol, and Eutric Cambisol （FAO soil group）, were selected for analysis. The moisture content was determined for a range of pF values （0, 1.5, 2.2, 2.7, and 3.2）, corresponding to the available water for microorganisms and plant roots. The variability of a number of soil aeration parameters, such as water potential （pF）, air-filled porosity （Eg）, oxygen diffusion rate （ODR）, and redox potential （Eh）, were investigated. These parameters were found to be interrelated in most cases. There were significant （P 〈 0.001） negative correlations of pF, Eg, and ODR with Eh. A decrease in water content as a consequence of soil reoxidation was manifested by an increase in the values of aeration factors in the soil environment. These results contributed to understanding of soil redox processes during recovery from flooding and might be useful for development of agricultural techniques aiming at soil reoxidation and soil fertility optimisation.

Reoxidation process and corrosion behavior of TA15 alloy by laser ablation

The thermal oxide layer formed of TA15 alloy has poor corrosion resistance.In this paper,the changes of the elements and components on the surface after laser ablation with different energy densities(E) were researched.The formation process and corrosion behavior of laser-generated oxide layer were clarified.As E increases,the oxygen content decreases from 8.52% to 5.43% and then increases to 11.89%.The surface oxide layer changes from TiO_(2)(R)(i.e.,rutile) to Ti_(2) O_(3)+TiO_(2)(R) and finally becomes TiO_(2)(R)+TiO_(2)(A)(i.e.,anatase).The TiO_(2)(R) gasification was confirmed by calculating the surface temperature rise.The surface reoxidation process was illustrated by a thermodynamically calculated ΔGT(i.e.,the Gibbs free energy changes with temperature).When E≥17.5 J·cm^(-2),the oxide layer exhibits an agitated morphology,and oxide falls off at the bottom.As E increases,the corrosion rate decreases first and then increases.With energy density of 8.75 J·cm^(-2),the surface corrosion rate was 20.43 times slower than that of the untreated sample.The impedance spectrum and equivalent resistance results also prove the best corrosion resistance at 8.75 J·cm^(-2).The corrosion behavior of the oxide layer is analyzed from the properties of the oxide layer components and the reaction products with the electrolyte.

Uranium sequestration in sediment at an iron-rich contaminated site at Oak Ridge, Tennessee via.bioreduction followed by reoxidation

This study evaluated uranium sequestration performance in iron-rich (30 g/kg) sediment via bioreduction followed by reoxidation.Field tests (1383 days) at Oak Ridge,Tennessee demonstrated that uranium contents in sediments increased after bioreduced sediments were re-exposed to nitrate and oxygen in contaminated groundwater.Bioreduction of contaminated sediments (1200 mg/kg U) with ethanol in microcosm reduced aqueous U from 0.37 to 0.023 mg/L.Aliquots of the bioreduced sediment were reoxidized with O2,H2O2,and NaNO3,respectively,over 285 days,resulting in aqueous U of 0.024,1.58 and 14.4 mg/L at pH 6.30,6.63 and 7.62,respectively.The source-and the three reoxidized sediments showed different desorption and adsorption behaviors of U,but all fit a Freundlich model.The adsorption capacities increased sharply at pH 4.5 to 5.5,plateaued at pH 5.5 to 7.0,then decreased sharply as pH increased from 7.0 to 8.0.The O2-reoxidized sediment retained a lower desorption efficiency at pH over 6.0.The NO3--reoxidized sediment exhibited higher adsorption capacity at pH 5.5 to 6.0.The pH-dependent adsorption onto Fe(Ⅲ) oxides and formation of U coated particles and precipitates resulted in U sequestration,and bioreduction followed by reoxidation can enhance the U sequestration in sediment.

Laboratory study on the formation of Al2O3 inclusions at the on-set of deoxidation and during reoxidation

The formation of Al2O3 inclusions in liquid iron has been investigated in a resistance heated tube furnace to obtain deoxidation and reoxidation related data. The formation of inclusions during the early stages of deoxidation was simulated by bringing a piece of AI in contact for a short time with liquid Fe containing different dissolved oxygen levels. Reoxidation was studied by exposing AI containing Fe melts to a CO/CO2 atmosphere, Through modeling, an estimate of the local and time-dependent growth conditions for the inclusions can be made and linked to the inclusion characteristics.

Teeming stream protection using an argon shroud during casting of steel ingots

Two kinds of argon shroud protection devices with two different basic structures were designed and investigated. Industrial experiments and numerical simulations were used to examine the protection effect, and the mechanism of air entrapment during the casting of steel ingots was analyzed. The influence of the structure of the argon shroud protection device on the protection effect was investigated. An argon shroud protection device mounted to the nozzle holder on the bottom of the ladle does not provide a good protection effect because air can easily flow into the teeming system and cause reoxidation of molten steel during teeming. By contrast, an argon shroud protection device seated on the top of the central trumpet provides an excellent protection effect, where air has little chance of flowing into the teeming system during casting. The feasibilities of the argon shroud protection devices are discussed.

Effect of Annealing Time on the Dielectric Properties of BaMn₃Ti₄O_14.25Pellets by Spark Plasma Sintering

In this paper, the effects of annealing time on the dielectric properties of the Spark Plasma Sintered (SPS) BaMn3Ti4O14.25 pellets were detail studied by the crystal structure analysis, micro structural observation and electrical properties research. The results showed that long annealing time was beneficial to the recovery of crystal structure damage caused by SPS, the formation of a reoxidation layer at the surface of grains and decreasing of the electrically insulating phase. All of these resulted in an increase in dielectric constant and loss, and a reduction in breakdown voltage.

Population Evolution of Oxide Inclusions in Ti-stabilized Ultra-low Carbon Steels after Deoxidation

Population density function （PDF）, which can eliminate the arbitrariness caused by the choice of the num- ber and the size of bins compared to the well-used histograms, was introduced to analyze the amount of inclusions. The population evolution of oxide inclusions in forms of PDF in Ti-stabilized ultra-low carbon steels after deoxidation during industrial RH refining and continuous casting processes was analyzed using an automated SEM-EDS system. It was found that after deoxidation till the early stage of casting, the alumina inclusions exhibited a lognormal PDF distribution, and three factors including the existence of a large amount of alumina clusters, the generation of alumi- na from the reduction of Al-Ti-O inclusions and the reoxidation of molten steel were estimated as the reasons. The shape parameter σ was high after deoxidation and then decreased after Ti treatment, indicating that in a short period after deoxidation, the size of alumina inclusions was widely distributed. After Ti treatment, the distribution of inclu- sion size was more concentrated. The scale parameter m decreased with time during the whole refining process, indi- cating that the proportion of large inclusions decreased during refining. Contrarily, the Al-Ti-O inclusions presented a fractal PDF distribution except at the end of casting with fractal dimension D of 4.3, and the constant of propor- tionality C decreased with time during RH refining and increased during casting process. The reoxidation of steel by slag entrapped from ladle was considered as the reason for the lognormal PDF behavior of Al-Ti-O inclusions at the end of casting.

Non-metallic inclusions in electroslag remelting:a review

Non-metallic inclusion in electroslag remelting is a constant topic that has been studied for decades.Different results and conclusions are obtained on some of the subjects from these previous investigations.These differences originate in part from different experimental conditions,including original inclusion chemistries in consumable electrode,slag composition,oxygen level,liquid metal compositions,deoxidation schemes,and melting rates of electroslag remelting.The advances in the operating practices of inclusion control in electroslag remelting production are reviewed.Inclusion evolution during the electroslag remelting and related processing parameters are also reviewed and assessed.The role of the reoxidation of liquid steel during electroslag remelting on oxide inclusion composition is discussed.The generation of inclusions in remelted ingot is critically assessed.Perspective and remaining issues are noted.