Deep decarburization of iron-based melts

The decarburization of liquid iron with preliminary saturation and without saturation of the metal with hydrogen followed by vacuum and aspiration treatments has been studied. A decrease in the gas pressure above the liquid metal is experimentally shown to increase the deoxidizing capacity of carbon only to certain limits. When a steel is subjected to hydrogen treatment with preliminary saturation of the melt with hydrogen, the formation of hydrogen bubbles enhance the effect of the mixing of the metal bath and substantially increase the melt-gas interface area. As a result, the rate and degree of decarburization increase considerably. The aspiration treatment also makes it possible to decrease the carbon content in the metal due to the creation of an additional reaction surface in the volume of the melt under vacuum conditions.     

The rate of decarburization of liquid iron by CO2 and H2

The rate of decarburization of liquid iron in CO-CO₂ mixtures and hydrogen at 1800 K has been investigated. The effect of sulfur on the rate in CO-CO₂ was also determined. Two experimental techniques were employed, one with the gas flow parallel to the surface of the melt, the other with gas flow perpendicular to it. The rate of decarburization in both CO-CO₂ mixtures and hydrogen at high carbon contents is controlled primarily by diffusionsion in the gas film boundary layer near the surface of the liquid. The presence of 0.3 wt pct sulfur reduced the rate of decarburization in CO-CO₂ by about 10 pct indicating that a slow chemical reaction on the surface is effecting the rate slightly when the surface is covered with sulfur atoms. The rate of decarburization at low carbon contents in CO-CO₂ is controlled primarily by carbon diffusion in the metal. The mass transfer relationships for the experimental geometries employed were investigated by measuring the rate of oxidation of graphite in CO-CO₂ mixtures. Previous work in which it was concluded that a chemical reaction was controlling the rate were re-examined and it was concluded that gas phase mass transfer was in fact controlling the rate of the reaction.     

Decarburization of high carbon ferromanganese melts

The effect of oxygen/argon mixing ratio in the bottom blowing gas on the decarburization behaviour of high carbon ferromanganese melt was investigated in the temperature range of 1350 – 1550°C. Thermodynamic analysis indicates that high melt temperature and low P_CO are essential for an effective decarburization. An empirical equation for the utilization ratio of oxygen for decarburization was derived as functions of the melt temperature and the oxygen/argon mixing ratio in the refining gas. The utilization ratio of oxygen for decarburization sharply increases as the melt temperature increases and the oxygen ratio in blowing gas decreases. In oxygen refining of high carbon ferromanganese melt, it is not desirable to inject oxygen through bottom tuyères in an early stage of refining. When the melt temperature is low, the oxygen predominantly oxidizes the manganese in melt in spite of high carbon contents. The injection of oxygen/argon mixture gas is found to be an effective decarburization technique when the melt temperature is higher than 1500°C.     

Mathematical model for nitrogen control in oxygen steelmaking

A mathematical model was developed to quantify the effects of different operational parameters on the nitrogen content of steel produced during oxygen steelmaking. The model predicts nitrogen removal by the CO produced during decarburization and how the final nitrogen content is affected by different process variables. These variables include the type of coolants used (scrap, direct reduced iron (DRI), etc.), the sulfur content of the metal, combined gas blowing practices, and the nitrogen content in the hot metal, scrap and oxygen blown. The model is a mixed control model that incorporates mass transfer and chemical kinetics. It requires a single parameter that reflects the surface area and mass-transfer coefficient that is determined from the rate of decarburization. The model also computes the rate of decarburization and the change in surface active elements, such as sulfur and oxygen, that affect the rate of the nitrogen reaction. Nitrogenization of steel in the converter is also predicted with the model. The computed results are in good agreement with plant data and observations.     

Hot model experiments of the metal bath spraying effect during the decarburization of Fe-C melts through oxygen top blowing

During recent years decarburization has been steadily gaining importance in converter steel metallurgy at the expense of refining reactions for other slag-forming companion elements. Because decarburization is currently a low-slag operation, the phase contact between gas and metal is critical. With the decrease in the amount of slag foam, more attention must be paid to the spraying of iron droplets during oxygen blowing. The experiments were carried out in a hot model reactor with a 50 kg capacity by oxygen top blowing upon Fe-C melts. The resulting spray of iron droplets was collected with the help of a special droplet sampler in the blowing converter. In the metal droplets a pronounced enhanced decarburization was found in comparison to the metal bath. The amount of metal spray was determined with respect to the oxygen blowing pressure, nozzle diameter, and distance between the lance and bath. Depending on the reactor contents, a high circulation rate of the droplets could be observed. At low blowing rates, FeO-slag is formed and sprayed along with the metal.     

底吹氧气,天然气复吹转炉冶金特点的热模研究

为了开发氧气,天然气作底吹气源,在国内建立顶、底吹氧炼钢法,作者在60 kg热模上进行了50多炉吹炼低碳钢的试验。结果为:喷嘴熔损速度≤1mm/炉,喷嘴畅通,可实现100％的复吹;吹炼特性好,过程平静、无喷溅。试验还比较了顶吹与复吹的脱碳速度变化,观察到复吹前期脱碳速度较大,中期比顶吹略低,变化平稳,持续时间较长。此工艺适合冶炼低碳钢。还对不同底吹氧比对终点氢含量的影响进行了研究,在试验条件下得到的增氢量为0.54 ppm。     

70吨高阻抗超高功率电炉强化冶炼技术

攀成钢70吨高阻抗超高功率电炉通过采用热兑铁水工艺、RCB喷枪喷吹氧技术及喷碳粉技术实现强化冶炼。生产实践表明,电炉的冶炼电耗为310.86 kWh/吨钢,冶炼周期为56分钟。     

Reactions of molten Fe,Co, Cu,and Pb sulfides with hydrogen

The kinetics and mechanism of reactions of molten Fe, Co, Cu, and Pb sulfides with hydrogen have been investigated between 1080° and 1340°C. While maintaining high flow rates of hydrogen and argon to ensure chemical control, the rate of reduction of these sulfides was found to be second order in sulfur concentration and half-order in hydrogen pressure. These dependences are similar to those reported earlier for molten nickel sulfide reduction by hydrogen. The kinetics and mechanistic proposal suggest a metal catalyzed step. If the activation energies for the rate determining step of S₂ reacting with hydrogen in the melt for the various sulfides are compared with the values for the hydrogen-liquid sulfur or hydrogen-gaseous sulfur reactions, the order of catalytic activity seems to follow generally the order of the pure metals themselves as found for other processes involving activation of molecular hydrogen.     

Rate of decarburization of iron-carbon melts: Part I. experimental determination of the effect of sulfur

The kinetics of decarburization of iron-carbon melts with CO-CO₂ gas mixtures were investigated at 1700 ° using the levitation technique. The influences of different experimental variables on the decarburization kinetics were determined. It was found that sulfur has a clear and reproducible retarding effect on the decarburization of iron-carbon melts; and this effect is most pronounced at sulfur concentrations in the range of 0 to 0.05 wt pct. The initial carbon concentration has no discernible effect on the decarburization kinetics. Melts containing 2.48 wt pct C and 0.92 wt pct C initially were found to decarburize at virtually identical rates until a substantial portion of the carbon was removed. The decarburization rate of a melt with a specified initial carbon content was found to remain essentially constant until the carbon content fell to a characteristic level below which the rate tended to level off. The partial pressure of CO₂ of the gas mixture has a marked effect on the decarburization kinetics. The flow-rate of the gas mixture has a small but finite effect on the rate of decarburization.     

Interaction of refractory compound nanoparticles with a surfactant in a nickel melt: I. Heterophase interaction

The interaction of nanoparticles of refractory compounds Al₂O₃ and TiN with a model nickel melt containing a surfactant (sulfur) is studied. The choice of the type of nanoparticles for their interaction with the metal at 1873 K and possible versions of sulfur removal from the melt in the form of S₂, SO₂, and H₂S are grounded. A technique for the preparation of an Ni-Al₂O₃ (TiN) compact and its introduction into the melt is developed. The character of the change in the sulfur content in the metal after introducing the compact is determined, and the effect of the isothermal holding time of the melt on sulfur removal is revealed.     

转炉使用低硫铁水冶炼时熔池硫含量变化规律

分析了某厂300t转炉使用低硫铁水冶炼时熔池硫含量的变化规律及影响因素,结果表明：废钢的熔化是熔池硫含量升高的主要原因,钢渣间的脱硫反应主要发生在吹炼的后期,降低废钢比,保持吹炼后期炉渣较高的碱度及较低的氧化铁量有利于得到较低的熔池终点硫含量。     

Kinetics of solution of hydrogen in liquid iron,nickel, and copper containing dissolved oxygen and sulfur

An investigation of the effect of surface active oxygen and sulfur on the rate of hydrogen solution in inductively stirred liquid iron, nickel, and copper was made using a modified constant-volume Sieverts’ method. The overall and initial rates of hydrogen solution in liquid iron and nickel were found to decrease with increasing oxygen content in concentration ranges found in the commercial refining of these metals. The results were consistent with a change in the rate controlling step from mass transport of hydrogen atoms in the metal phase to mixed control of a surface chemical reaction and a diffusion controlled process in the melt. For liquid copper the overall rate of hydrogen solution decreased with increasing oxygen content, but the initial rate could not be determined. It was believed that condensation of water vapor and melt surface turbulence interfered with measurement of the initial rate of hydrogen solution in liquid copper. The addition of sulfur to liquid iron, nickel, and copper lowered the overall rate of hydrogen solution, but the effect was not as pronounced as that for oxygen. Formerly Graduate Student, The University of Michigan, is Research Engineer, Noranda Research Center, Pointe Claire, Quebec, Canada     

Effect of some technical and technological parameters on the efficiency of ladle treatment of steel

The effect of the inert-gas blowing intensity, the arrangement of blowing bottom tuyeres, and the refining-slag thickness on the melt temperature during heating in a ladle-furnace unit is studied by computer simulation and upon full-scale experiments. A shift of the blowing holes from the vertical axis of the ladle and an increase in the slag thickness are found to decrease the rate of metal heating.     

RH生产超低碳钢的脱碳速率及工艺优化

 通过RH超低碳钢脱碳工业试验,对RH精炼过程工艺参数进行全程跟踪。重点对表观脱碳速率常数Kc进行了测定和评价。结果表明,RH脱碳过程分为3个阶段：抽真空阶段、吹氧脱碳阶段和自然脱碳阶段。稳定生产碳含量小于0.002%(质量分数,下同)的超低碳钢的优化工艺参数为：进站碳含量0.05%~0.06%,氧含量0.04%~0.06%;吹氧期的起始真空度12~15kPa,吹氩强度0.015m3·t-1·min-1;自然脱碳时间大于15min,吹氩强度0.015m3·t-1·min-1,终脱氧前的氧含量＜0.035%。     

The Influence of Sulfur on Dephosphorization Kinetics Between Bloated Metal Droplets and Slag Containing FeO

The bloating behavior of metal droplets and the dephosphorization behavior of bloated droplets at 1853 K (1580 °C) were investigated using X-ray fluoroscopy coupled with constant volume pressure change measurements and chemical analysis of quenched samples. The effect of sulfur content on dephosphorization kinetics was studied during the decarburization period. The slag foamed during the reaction forming a foamy layer over a dense layer. After a short incubation period, the droplets became bloated due to internal decarburization. The bloated droplets floated from the dense slag into the foamy slag. The behavioral changes are directly related to the effect of sulfur on the incubation time for swelling. The dephosphorization reaction was very fast; droplets with low sulfur contents experienced phosphorus reversion shortly after entering the foamy slag, while those with higher sulfur content took a longer time to swell and went through reversion before they entered the foam. The dephosphorization rate and maximum phosphorus partition were higher at lower CO evolution rates because the dynamic interfacial oxygen potential increased with the decreasing oxygen consumption rate. The rate controlling step for dephosphorization was initially a combination of mass transport in both the metal and the slag. As the iron oxide in the slag was depleted, the rate control shifted to mass transport in slag.     

Decarburization of high-chromium melts by argon–oxygen plasma

The treatment of Fe–Cr and Fe–Cr–Ni alloys by means of oxygen-bearing plasma is investigated in the laboratory, using a plasma furnace with a tungsten cathode and a water-cooled copper anode. That permits modeling of the processes in the contact spot of the plasma arc and the melt surface. The mathematical model developed describes the melt–plasma interaction. The kinetic parameters of the decarburization of high-chromium melt by argon–oxygen plasma are determined from experimental data. The results show that considerable decarburization of high-chromium melt is possible, with little loss of chromium, by treatment with plasma containing no more than 15–17% oxygen. Comparison shows that the model data and experimental results are in good agreement.     

VOD炉冶炼Cr不锈吹氧脱碳浅析

在采用电弧炉＋VOD＋CC生产Cr不锈连铸坯的生产过程中,VOD精炼的控制对整个生产有着至关重要的作用,而控制Cr不锈VOD精炼过程的关键是吹氧脱碳。在吹氧脱碳过程中,脱碳初期及高碳区、低碳区采用不同的吹氧、吹氩流量及真空度控制,可以提高脱碳速度,同时以氧电势分析仪数据为主,以计算吹氧量、真空度变化、废温变化为辅,能更加准确的控制终点碳,从而提高吹氧脱碳效率。     

Kinetic Model of Decarburization and Denitrogenation in Vacuum Oxygen Decarburization Process for Ferritic Stainless Steel

The characteristics and classification of decarburization and denitrogenation in the vacuum vessel for stainless steel production are analyzed. Based on the analysis of movements of the liquid steel and bubbles, the kinetics of decarburization and denitrogenation in the vacuum oxygen decarburization (VOD) process has been studied. A kinetic model of decarburization and denitrogenation has been developed to simulate the VOD process, considering each reaction zone as oxygen blowing crater, bottom blowing plume, steel/slag interface, and plume eye. As a result, it is possible to quantify the contribution of each reaction zone in decarburization and denitrogenation rate at a different stage in the VOD process. Specific trials at a vacuum induction furnace were performed to refine stainless steel in vacuum carbon deoxidation (VCD) and VOD style, respectively. The trial results are in good agreement with the model calculation. Combining the trials and the model calculation and the influence of temperature control, critical carbon content selection on the terminal total [C] + [N] content can be discussed further to provide a reasonable proposal for high-quality ferritic stainless steel production. This article is based on a presentation given at the International Symposium on Liquid Metal Processing and Casting (LMPC 2007), which occurred in September 2007 in Nancy, France.     

RH快速深脱碳研究

结合理论和实践,对RH脱碳的影响因素进行了分析研究,结果表明:对于250～300t的RH,最佳的初始碳含量为(250～400)×10-6(质量分数,余同);发现吹氧时机对RH脱碳速率的影响很明显,吹氧时间滞后,造成RH前期脱碳速率过低,吹氧时已经进入低碳区域,削弱了吹氧对提高脱碳速率的作用,而且造成RH终点钢水活度氧过...     

Deep decarburization of steel

The process of deep decarburization of steel during argon or hydrogen-argon mixture injection has been studied. Experimental heats show that the gas-mixture injection into a melt is a very effective way to increase the degree and rate of decarburization. Hydrogen diffusion into argon bubbles decreases the partial pressure of CO in bubbles, which also increases the degree of decarburization.