Exploration and Practice of Nitrogen Addition Process for LF Refining Ladle Bottom Blowing Nitrogen Steel Liquid

This article discusses and analyzes the law of nitrogen increase in liquid steel and the main factors affect-ing the nitrogen increasing of molten steel,through the way of adding nitrogen to molten steel by bottom blowing nitrogen gas in LF refining process.It is considered that the main factors affecting the nitrogen increasing instability of molten steel are the initial temperature of LF refining,nitrogen relative element,surface active elements[O]and[S]of steel liquid,and bottom blowing rate of ladle.The large-scale production practice shows that T[O]not more than 50×10-6 and[S]is not more than 0.020 in LF refining at the initial temperature of not less than 1570.The liquid steel nitrogen enrichment test is carried out by ladle bottom blowing nitrogen gas after 20 min of refining,the flow rate is set as(6.0~7.0)NL/min per ton,and it is turned to 2 NL/min at 6 min before the end of refining,the nitrogen increasing rate of liquid steel is basically stable at(5~6)×10-6 per minute.

Effect of Refiner Plate Bar Angle and Pulp Properties on the Low Consistency Refining Efficiency in Terms of Power Consumption

Power consumption is the energy source of the impact on fibers or pulp during low-consistency(LC)pulp refining,and the strength of refining affects refining quality and efficiency.The pulp properties,operating parameters,and bar parameters of the refiner plates are important parameters affecting refining efficiency,which can be defined as the ratio of net to total refining power.In this study,LC refining trials for pulps with different consistencies and fiber lengths were conducted using five isometric straightbar plates with different bar angles to explore the influences of the plate bar angle and pulp properties on the no-load power,impact capacity on fibers and refining efficiency.It was found that the no-load power of the LC refining process decreased with an increase in the plate bar angle while increased when pulp with higher consistency was refined under the same refining conditions.However,the effect of pulp consistency on the no-load power can be neglected when refining is conducted using plates with larger bar angles.Meanwhile,a critical bar angle for straight-bar plates in LC refining may exist,which has the strongest impact on the pulp and highest refining efficiency under the same refining conditions.In addition,the impact capacity of the plate on the pulp and refining efficiency in LC refining can be enhanced by appropriately increasing the pulp consistency and average fiber length when the bar angle of the refiner plate with a sector angle of 40°is less than 30°.Therefore,the efficiency and power consumption of the LC refining process can be adjusted by optimizing the pulp consistency and bar parameters of the refining plates.

Effect of gas blowing nozzle angle on multiphase flow and mass transfer during RH refining process

A three-dimensional mathematical model was developed to investigate the effect of gas blowing nozzle angles on multiphase flow,circulation flow rate,and mixing time during Ruhrstahl-Heraeus(RH) refining process.Also,a water model with a geometric scale of 1:4 from an industrial RH furnace of 260 t was built up,and measurements were carried out to validate the mathematical model.The results show that,with a conventional gas blowing nozzle and the total gas flow rate of 40 L·min^(-1),the mixing time predicted by the mathematical model agrees well with the measured values.The deviations between the model predictions and the measured values are in the range of about 1.3%–7.3% at the selected three monitoring locations,where the mixing time was defined as the required time when the dimensionless concentration is within 3% deviation from the bath averaged value.In addition,the circulation flow rate was 9 kg·s^(-1).When the gas blowing nozzle was horizontally rotated by either 30° or 45°,the circulation flow rate was found to be increased by about 15% compared to a conventional nozzle,due to the rotational flow formed in the up-snorkel.Furthermore,the mixing time at the monitoring point 1,2,and 3 was shortened by around 21.3%,28.2%,and 12.3%,respectively.With the nozzle angle of 30° and 45°,the averaged residence time of 128 bubbles in liquid was increased by around 33.3%.

Simultaneously removal of P and B from Si by Sr and Zr co-addition during Al–Si low-temperature solvent refining

To remove the key impurity elements,P and B,from primary Si simultaneously,Sr and Zr co-addition to Al-Si alloy systems during solvent refining has been investigated.Sr reacts with Al,Si,and P in the melt to form a P-containing Al_(2)Si_(2)Sr phase and Zr reacts with B to form a ZrB_(2) phase.In the Al-Si-Sr-Zr system,high removal fractions of P and B in the primary Si,with 84.8%-98.4%and 90.7%-96.7%,respectively,are achieved at the same time,respectively.The best removal effect is obtained in the sample with the addition of Sr-32000+Zr-3000μg·kg^(-1),and the removal fractions of P and B in the purified Si reach 98.4%and 96.1%.Compared with the Sr/Zr single-addition,the removal effects of Sr and Zr co-addition on P and B do not show a significant downward trend,indicating that the nucleation and growth of the B/P-containing impurity phases are mutually independent.Finally,an evolution model is proposed to describe the nucleation and the growth stages of Sr/Zr-containing compound phases,which reveals the interaction between the impurity phases and the primary Si.

Status and Trends of China’s Refining and Petrochemical Industry

China’s refining and petrochemical industry has developed rapidly,with the quality of industry development improving rapidly.The scale of oil refining,ethylene,and PX ranks first in the world,and the quality of refined oil is among the world’s leading levels.However,the industry’s profitability is not strong enough,and there are still technological shortcomings,as well as defects in industry structure and product structure.Under the backdrop of the dual carbon goals,energy transition,electric revolution,and demand differentiation,China’s refining and petrochemical industry will continue to exert efforts in energy conservation and consumption reduction,integrated development with new energy,promotion of oil conversion and the conversion of oil to special products,integration and upgrading of capacity,development of green hydrogen refining and CCUS,diversification of raw materials,circular economy,and other aspects to enhance industrial competitiveness.

An energy saving and fluorine-free electrorefining process for ultrahigh purity lead refining

The present paper reports a new fluoride-free and energy-saving lead electrolytic refining process in order to solve the serious problems of the existing Betts lead electrorefining process, such as low production efficiency,high energy consumption and fluorine pollution. In the process, a mixed solution of perchloric acid and lead perchlorate(HClO4-Pb(ClO4)2) with the additives of gelatin and sodium lignin sulfonate is employed as the new electrolyte. The cathodic polarization curves show that HClO4 is very stable, and there is no any reduction reaction of HClO4 during the electrolytic process. The redox reactions of lead ions in HClO4 solution are very reversible with an ultrahigh capacity efficiency, so the HClO4 acts as a stable support electrolyte with higher ionic conductivity than the traditional H2SiF6 electrolyte. The results of the scale-up experiments show that under the optimal conditions of 2.8 mol·L-1 HClO4, 0.4 mol·L-1 Pb(ClO4)2 and electrolysis temperature of 45 ℃, the energy consumption is as low as 24.5 kW·h·(t Pb)-1 , only about 20% of that by Betts method at the same current density of 20 mA·cm-2, and the purity of the refined lead is up to 99.9992%, much higher than that specified by Chinese national standard(99.994%, GB/T 469-2013) and European standard(99.99%, EN 12659–1999).

Quantifying the Pulp Refining Process

Pulp refining action is commonly described by one or more quantitative parameters to enable comparisons among refiners and optimization of individual refiners. Specific refining energy and refining intensity are the two most commonly used parameters. Both are energy-based,but recent work by this author has shown that additional parameters based on force are of benefit. This paper reviews the background and key aspects of this work.

KINETIC STUDY ON THE REMOVAL OF LEAD AND SILVERFROMCRUDEBISMUTHBYANODEREFINING

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Optimal modifying and refining processes for A356 aluminium alloys

The influence of Ti, B, RE (cerium-rich mixtures of rare earth) and Sr, applied in modification and refining processes, on A356 aluminum alloys has been studied with the aids of OM, etc. The results show that the grain refining efficiency of Grain-Refining Aluminium Ingot (GRAI) and Al-Ti master alloys is similar. But the Tiaddition from GRAI has lower costs than that with Al-Ti master alloys. So A356 aluminum alloys produced with GRAI are feasible in economy. Grain refining with GRAI with 0.01%Ti plus additional 0.03% B offers significant advantages over that from GRAI with 0.1% Ti only in A356 aluminum alloys, which made the dendrite α(Al) grain structure transform into equiaxed α(Al) grain structure, plus a partially modified eutectic silicon structure. RE addition to A356 aluminum alloys with Sr modifier is enable to achieve small DAS, reduced pores, well-refined fibrous silicon, small and dispersive eutectic colonies.

Effect of Ultrasonic Output Power on Refining the Crystal Structures of Ingots and Its Experimental Simulation

In this study, a series of tests were conducted by using aluminum-based alloy to determine the formation of grain refining structure based on the ultrasonic vibration (UV). Furthermore, the simulation test and effect of ultrasonic output power were studied using ammonium chloride. Finally, the mechanism of grain refinement was investigated. The results show that: (1) By applying the UV to aluminum-base alloy, the grain refining rate of ingots tended to increase with the increase of the output value of UV. (2) It was confirmed that time from after the pour to the beginning of crystallization as well as cloudiness tended to decrease with increasing the ultrasonic power value of UV. Moreover, it can be seen from each cooling curve that a uniform temperature gradient existed in the melt as the power of UV increased, that made the melt strongly stirred. (3) It was also considered that the grain refining effect of ingots, which was observed from the simulation tests, resulted from nucleation action and stirring division action by applying the UV.

Top slag refining for inclusion composition transform control in tire cord steel

Controlling conditions for inclusion plasticization were calculated by FactSage, and the steel/slag reaction equilibration time was determined by pre-equilibrium experiments. Laboratory experiments with different top slags were carried out in 90 rain, and industrial tests were performed based on the results of calculation and laboratory experiments. Scanning electron microscopy （SEM） and energy-dispersive spectroscopy （EDS） were used to determine the morphology and composition of inclusions in tire cord steel. It is found that the shape of in- clusions can be controlled well, and the composition of inclusions varies in the industrial test as the following transformation route： MnO-A1EOa-SiO2→CaO-AIEOa-SiO2→MnO-A1203-SiO2. Inclusion plasticization can be achieved by controlling the binary basicity of top slag （CaO/SiO2 by mass） around 1.0 and the （A1203） content in top slag below 10wt%. Under these controlling conditions in the industrial test, almost all of inclusions in the wire rods achieve plastic deformation.

A review:Past,present and future of grain refining of magnesium castings

Magnesium is the lightest constructional metal,which makes it an important material for different applications like automotive,transportation,aviation and aerospace.There are several studies about developing properties of existing Mg alloys and introducing new alloy systems to industrial producers.An important way to improve properties of metallic materials is to decrease grain size that results almost in increasing all kind of properties of the material.This review paper aims to summarize the literature about grain refining of magnesium alloys.The text is consisting of three sections,which focused on the(1)grain refining methods used in the past,which are not used today,(2)grain refining methods currently being used in the industry and(3)novel and newly developed methods that may find usage in the industry in future.Before explaining grain refining methods of magnesium alloys a general summary about grain refinement of metals is also provided.

Refining Effect of a New Al3Ti1B1RE Master Alloy on Al Sheets Used for Can Manufacture and Behavior of Rare Earths in Master Alloy

The refining effect of Al3Ti1B1RE master alloy on Al sheets used for pressure can manufacture and the behavior of mixed rare earths in master alloy were investigated with XRD, OM, SEM and EDAX. It is found that the refining effect of the refiner on the material has superiority over foreign or domestic Al5Ti1B refiner, and the refiner still retains its refining ability for 6 h after adding it to molten Al, thus improving the strength and plasticity of the material remarkably. The excellent refining effect and stability of AlTiBRE refiner result from that RE can lower the surface energy of molten Al and improve the wetting characteristics of molten Al on refinement nuclei such as TiAl 3, TiB 2, etc., thus giving full play to the effect of heterogeneous nucleation and impeding the congregating tendency of TiB 2 phase in molten Al. At the same time, RE gathering in front of solid/liquid interface are also easy to cause composition supercooling in molten Al, thus impeding the growth of α Al grains and promoting α Al nucleation on refinement nuclei. In addition, RE also play certain role in purification and grain refinement, or modification, especially their effect of purification can improve the metallurgical quality of AlTiBRE master alloy.

Physical model of fluid flow characteristics in RH-TOP vacuum refining process

To understand the characteristic of circulation flow rate in 250-t RH-TOP vacuum refining process, the 1：4 water model test was established through the bubble behavior and gas holdup in the up-leg to investigate the effects of different processes and equipment parame- ters on the RH circulation flow rate. With the increases of lifting gas flow rate, liffing bubble travel, and the internal diameter of the up-leg, and the decrease of nozzle diameter, the work done by bubble floatage and the circulation flow rate increase. The expression of circulation flow rate was derived fi＂om the regression analysis of experiment data. Meanwhile, the influences of vacuum chamber pressure and nozzle blockage situation on the circulation flow rate were discussed in detail by the bubble behavior and gas holdup in the up-leg. It is necessary to maintain a certain vacuum chamber liquid level in the molten steel circulation flow. Compared with a nozzle with symmetrical blockage in the up-leg, when a nozzle with non-symmetrical blockage is applied, the lifting gas distribution is non-uniform, causing a great effect on the molten steel circulation flow and making the circulation flow drop largely.

Study on Flow and Mixing Characteristics of Molten Steel in RH and RH-KTB Refining Processes

The flow and mixing characteristics of molten steel during the vacuum circulation refining, including RH(Ruhrstahl Heraeus) and RH KTB(Ruhrstahl Heraeus Kawasaki top blowing) processes, were investigated on a 1/5 linear scale water model of a 90 t multifunction RH degasser. The circulation rate was directly and more accurately determined, using a new method by which the more reliable results can be obtained. The fluid flow pattern and flow field in the ladle were demonstrated, observed and analyzed. The mixing time of liquid in the ladle was measured using electrical conductivity method. The residence time distribution in the RH model was obtained by tracer response technique. The influence of the main technological and geometric factors, including the gas top blowing (KTB) operation, was examined. The results indicated that the circulation rate of molten steel in the RH degasser can be fairly precisely calculated by the formula: Q lp =0.0333 Q 0.26 g D 0.69 u D 0.80 d(t/min), where Q g-the lifting gas flow rate (NL/min); D u and D d-the inner diameters of the up and down snorkels (cm), respectively. The maximum value of circulation rate of molten steel in the case of the 30 cm diameters either of the up and down snorkels for the RH degasser (the “saturated” rate) is approximately 31 t/min. The corresponding gas flow rate is 900 NL/min. Blowing gas into the vacuum chamber through the top lance like KTB operation does not markedly influence the circulatory flow and mixing characteristics of the RH process under the conditions of the present work. There exist a major loop and a large number of small vortices and eddies in the ladle during the RH refining process. A liquid liquid two phase flow is formed between the descending stream from the down snorkel and the liquid around the stream. All of these flow situation and pattern will strongly influence and determine the mixing and mass transfer in the ladle during the refining. The correlation between the mixing time and the stirring energy density is τ m∝ε -0.50 for the RH degasser. The mixing time rapidly shortens with an increase in the lifting gas flowrate. At a same gas flow rate, the mixing times with the up and down snorkel diameters either of 6 and 7 cm are essentially same. The 30 cm diameters either of the up and down snorkels for the RH degasser would be reasonable. The concentration time curve showed that three circulation cycles are at least needed for complete mixing of the liquid steel in the RH degasser.

Decarburization rate of RH refining for ultra low carbon steel

The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing conditions. According to the apparent decarburization rate constant （Kc） calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1-2 min, it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period, which is quite different from the traditional one with three stages. In this study, the average apparent decarburization rate constant during the quick decarburization period is 0.306 min^-1, and that of the stagnant period is 0.072 min^-1. Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period. The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14× 10^-6 after 10 min of decarburization.

Desulfurization ability of refining slag with medium basicity

The desulfurization ability of refining slag with relative lower basicity （B） and Al2O3 content （B = 3.5-5.0; 20wt%-25wt% Al2O3） was studied. Firstly, the component activities and sulfide capacity （Cs） of the slag were calculated. Then slag-metal equilibrium experiments were carried out to measure the equilibrium sulfur distribution （Ls）. Based on the laboratorial experiments, slag composition was optimized for a better desulfurization ability, which was verified by industrial trials in a steel plant. The obtained results indicated that an MgO-saturated CaO-Al2O3-SiO2-MgO system with the basicity of about 3.5-5.0 and the Al2O3 content in the range of 20wt%-25wt% has high activity of CaO （αCaO）, with no deterioration of Cs compared with conventional desulfurization slag. The measured Ls between high-strength low-alloyed （HSLA） steel and slag with a basicity of about 3.5 and an Al2O3 content of about 20wt% and between HSLA steel and slag with a basicity of about 5.0 and an Al2O3 content of about 25wt% is 350 and 275, respectively. The new slag with a basicity of about 3.5-5.0 and an Al2O3 content of about 20wt% has strong desulfurization ability. In particular, the key for high-efficiency desulfurization is to keep oxygen potential in the reaction system as low as possible, which was also verified by industrial trials.

Effect of La on Microstructure and Grain-Refining Performance of Al-Ti-C Grain Refiner

Al-Ti-C grain refiner was prepared by SHS （self-propagating high-temperature synthesis ）-melting technique. The effect of La on the microstructures of grain refiner was studied by OM, TEM, SEM, XRD, and EDS. The experimental results indicate that La can improve the wettability between liquid aluminum and graphite ; the addition of La results in dispersive distribution of TiAl3 and TiC particles in the matrix. An excellent grain refining performance of Al-Ti-C grain refiner on commercially pure Al was obtained.

Development of an improved CBR model for predicting steel temperature in ladle furnace refining

In the prediction of the end-point molten steel temperature of the ladle furnace, the influence of some factors is nonlinear. The prediction accuracy will be affected by directly inputting these nonlinear factors into the data-driven model. To solve this problem, an improved case-based reasoning model based on heat transfer calculation(CBR-HTC) was established through the nonlinear processing of these factors with software Ansys. The results showed that the CBR-HTC model improves the prediction accuracy of end-point molten steel temperature by5.33% and 7.00% compared with the original CBR model and 6.66% and 5.33% compared with the back propagation neural network(BPNN)model in the ranges of [-3, 3] and [-7, 7], respectively. It was found that the mean absolute error(MAE) and root-mean-square error(RMSE)values of the CBR-HTC model are also lower. It was verified that the prediction accuracy of the data-driven model can be improved by combining the mechanism model with the data-driven model.

Hybrid Neural Network Model for RH Vacuum Refining Process Control

A hybrid neural network model,in which RH process(theoretical)model is combined organically with neural network(NN)and case-base reasoning(CBR),was established.The CBR method was used to select the operation mode and the RH operational guide parameters for different steel grades according to the initial conditions of molten steel,and a three-layer BP neural network was adopted to deal with nonlinear factors for improving and compensating the limitations of technological model for RH process control and end-point prediction.It was verified that the hybrid neural network is effective for improving the precision and calculation efficiency of the model.