Rate of nitrogen desorption from liquid iron-carbon and iron-chromium alloys with argon

The rate of nitrogen desorption from inductively stirred liquid iron, iron-carbon, and iron-chromium alloys with argon carrier gas has been measured by the sampling method for a wide range of nitrogen, carbon, and chromium contents mainly at 1600 °C. The results obtained by the present work and other data of previous investigators are used to clarify the reaction mechanism of nitrogen desorption from liquid iron. The rate of nitrogen desorption from liquid iron and iron alloys is second order with respect to nitrogen content in the metal under the present condition, and mutual relationships among interfacial chemical reaction, liquid-phase mass transfer, and gas-phase mass transfer are elucidated. The effects of oxygen and sulfur on the rate of nitrogen desorption are given byk _' ^{c ’} = 3.15?_N ² [1/(1 + 300a₀ + 130a_s)]. Carbon dissolved in iron increases the rate of nitrogen desorption, and chromium decreases it. The effects of these alloying elements can be explained by the change of the nitrogen activity in the metal.     

Rate of nitrogen desorption from liquid iron-carbon and iron-chromium alloys with argon

The rate of nitrogen desorption from inductively stirred liquid iron, iron-carbon, and iron-chromium alloys with argon carrier gas has been measured by the sampling method for a wide range of nitrogen, carbon, and chromium contents mainly at 1600 °C. The results obtained by the present work and other data of previous investigators are used to clarify the reaction mechanism of nitrogen desorption from liquid iron. The rate of nitrogen desorption from liquid iron and iron alloys is second order with respect to nitrogen content in the metal under the present condition, and mutual relationships among interfacial chemical reaction, liquid-phase mass transfer, and gas-phase mass transfer are elucidated. The effects of oxygen and sulfur on the rate of nitrogen desorption are given byk _' ^{c ’} = 3.15ƒ_N ² [1/(1 + 300a₀ + 130a_s)]. Carbon dissolved in iron increases the rate of nitrogen desorption, and chromium decreases it. The effects of these alloying elements can be explained by the change of the nitrogen activity in the metal. This paper is based on a presentation made at the G. R. Fitterer Symposium on Nitrogen in Metals and Alloys held at the 114th annual AIME meeting in New York, February 24–28, 1985, under the auspices of the ASM-MSD Thermodynamic Activity Committee.     

The rate of absorption of hydrogen into iron and of nitrogen into Fe-Cr and Fe-Ni-Cr alloys containing sulfur

The rate of absorption of hydrogen into liquid iron and of nitrogen into liquid Fe-Cr alloys containing various levels of sulfur was measured by using a constant-volume Sieverts apparatus employing a sensitive pressure transducer. The rate for the absorption of hydrogen was measured by using H2 containing a small amount of H₂S(<0.2 pct) such that the activity of sulfur on the surface of the melt was the same as in the bulk metal. The hydrogen-absorption rate for Fe-S melts containing up to 0.72 pet sulfur was virtually independent of sulfur content and controlled by liquid-phase mass transfer. The liquidphase mass-transfer coefficient for hydrogen in liquid iron, calculated from the results, was comparable to that for nitrogen transfer in liquid iron. The rate of absorption of nitrogen into Fe-Cr melts with low-sulfur contents was controlled by liquid-phase mass transfer. For melts containing significant amounts of sulfur it was controlled by both mass transfer and the chemical rate of the dissociation of nitrogen on the surface in series. Equations were developed to calculate the chemical rate from the measured rate, correcting for mass transfer. The chemical rate decreased with increasing sulfur content as expected, because sulfur is strongly adsorbed on the surface and increased with chromium content at constant sulfur activity, possibly because available Cr sites promote nitrogen dissociation. Formerly with United States Steel Corporation, Monroeville, PA     

钢液真空脱氮动力学研究

研究了真空度对钢液脱氮动力学的影响。结果表明,真空度为６７Ｐａ及１１０Ｐａ进,脱氮的限制性环节为氮在钢液液相边界层中的传质,真空度为２０００Ｐａ时,脱氮的限制性环节为氮在气液界面的化学反应。真空下的碳氧反应对脱氧效果有明显的影响,当有碳氧反应时,钢液脱氮速度常数增大,同时钢液内生或外来固态粒会作为气泡形核核心,加速脱氮过程。     

现代电弧炉炼钢过程物理化学行为及应用

本文研究了现代电弧炉炼钢过程的冶金物理化学变化。研究表明钢水中铁、磷、碳与氧枪吹入的氧气发生直接氧化反应,而钢水中的溶解氧无氧化能力、渣中氧化铁无脱磷能力;钢水中碳与氧气的反应最为剧烈,可通过调整配碳量与吹氧强度可对其它各反应进行控制。在实际生产熔炼过程中,通过及时加入碳粉、焦炭或石墨块,还原渣中氧化铁,可以提高钢水收得率。冶炼过程化清后,通过强化吹氧至接近终点氧,减缓升温速度,流渣换渣,可以深度脱磷,并有效抑制“回磷”。     

含铬镍铁水脱磷保铬的机理与试验

 为了解决铬镍生铁因磷质量分数高用做不锈钢原料受限的问题,开展了关于含铬镍铁水脱磷保铬的理论计算和工业试验研究。采用竖炉工艺回收不锈钢粉尘,冶炼出的含铬镍铁水磷质量分数高,导致铁水利用量受限。通过计算铬、镍、铁氧化物还原热力学条件和磷、铬、碳氧化的临界氧势,提出了采用碱性CaO渣系、控制炉渣氧势和出铁温度实现脱磷保铬的措施。在理论计算基础上,进行了竖炉冶炼含铬镍铁水的脱磷保铬工业试验。试验共冶炼出含铬镍铁水32 t,当炉渣碱度为1.15、炉渣[w(FeO)]为4.98%、出铁温度为1 673～1 684 K时,脱磷率可达36%以上,铁水中磷质量分数可降至0.023%,铬收得率为88%以上,本研究达到了脱磷保铬的目的,并且解决了含铬镍铁水磷质量分数高的问题。     

The kinetics of the nitrogen reaction with liquid iron-chromium alloys

The isotope exchange technique was employed to study the interfacial reaction kinetics of nitrogen with liquid iron-chromium and iron-chromium-sulfur solutions. Chromium was found to increase the rate of the nitrogen exchange reaction. The increase in the rate occurs, at least in part, through promotion of N₂ dissociation on the chromium surface sites. Although mass transport effects in the liquid are eliminated through the use of the isotope exchange technique, it was found that a correction for gas phase mass transfer was required for the determination of the interfacial reaction rate constant due to the faster exchange rates encountered in liquid iron solutions containing chromium. Formerly with the Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, Pittsburgh, PA     

Kinetics of simultaneous reactions between liquid iron-carbon alloys and slags containing MnO

The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction rate of MnO from slag were examined at 1450 °C to 1550 °C by using high carbon iron alloys and CaO-SiO₂-CaF₂ slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface, and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization. The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of experimental results, were found to increase with increasing the (MnO + CaO)/SiO₂ ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the aid of the kinetic model.     

The rate of absorption of nitrogen into liquid iron containing oxygen and sulfur

The rate of nitrogen absorption into and desorption from liquid iron containing sulfur and/or oxygen was measured by employing a constant-volume technique with a highly sensitive pressure transducer. Critical evaluation of the results demonstrated conclusively that the chemical rate at high oxygen or sulfur contents is second order with respect to nitrogen content in the metal and probably controlled by the dissociation of the nitrogen molecule on the surface. The effect of sulfur on the rate is complex because of the influence of 1) liquid-phase mass transfer at low sulfur contents, 2) the chemical rate on vacant iron sites at intermediate sulfur contents, and 3) the rate on the adsorbed sulfur layer or the limiting rate at high sulfur contents. However, at intermediate concentrations the limiting case for the adsorption isotherm for sulfur is adhered to and the rate is inversely proportional to the sulfur concentration. For Fe-O melts the rate is inversely proportional to the oxygen content except at low oxygen levels where mass transfer affects the rate. The rate for Fe-S-O melts can be calculated reasonably well from the results for the Fe-S and Fe-0 alloys, assuming that oxygen does not effect the adsorption of sulfur andvice versa and that there is nearly complete coverage of the surface with oxygen and sulfur atoms.     

The effect of absorbed oxygen on the kinetics of chemical reactions on metal surfaces

The effects of adsorbed impurities on the kinetics of reactions on metal surfaces are discussed, in particular the reactions of water vapor and carbon dioxide with iron surfaces are analyzed. The critical oxygen potentials for the onset of ‘poisoning’ of the reactions appear to correspond with the onset of facetting of iron and the formation of surface phases on the iron. The maximum chemical reaction rate constants for the reactions of water vapor and of carbon dioxide on iron surfaces at a given temperature are shown to correspond closely to the chemical reaction rate constants determined from the reduction of iron oxides in their respective systems. The phenomena observed on the reaction of gases with iron and iron oxide surfaces are reported in other metal systems thus the analysis used for the present reactions appears to be applicable to other systems involving metal/gas reactions.     

Formation of TiN/TiC-Fe composites from ilmenite (FeTiO3) concentrate

The production of a ceramic hard material-metal composite directly from a mineral concentrate has great potential application. An homogenizing pretreatment of a mixture of ilmenite (FeTiO₃) and graphite, followed by annealing under an argon ambient, showed the formation of titanium carbide and elemental iron. Annealing of the same powder in nitrogen resulted in the formation of a composite of elemental iron and titanium nitride. The nitride was formed at a lower temperature than the carbide with almost complete conversion after 1 hour at 1000 °C. The rate of carbide formation was controlled by carbon diffusion, whereas the nitridation reaction was controlled by either oxygen or nitrogen diffusion. The TiC was found to form via TiC_0.5, which slowly increased its carbon content until near stoichiometric TiC was formed; stoichiometric TiN formed directly with no intermediate phases. Titanium carbide showed the presence of a second phase with a slightly smaller unit cell size; this was due to interdiffusion between the iron and TiC. The titanium carbide composite was found to be composed of 3 to 4 μm anhedral iron grains dispersed in the titanium-rich matrix. There was no segregation in the iron/titanium nitride composite with apparently submicron distribution.     

Kinetics of the reaction of SiO(g) with carbon saturated iron

The reaction of SiO(g) with carbon saturated iron plays an important role in silicon transfer in the iron blast furnace. In the tuyere zone SiO(g) is generated from the reaction of coke with its ash, and the SiO(g) reacts with carbon saturated iron droplets as they pass through the furnace. This reaction may also play a role as a gaseous intermediate reaction for the reduction of SiO₂ from slags by carbon dissolved in iron. The rate and controlling mechanism for the SiO reaction with carbon dissolved in liquid iron was determined in the temperature range 1823 to 1923 K. A constant pressure of SiO(g) was generated by the reaction of CO with SiO₂; the reaction of carbon with SiO₂ gave higher but decreasing pressures of SiO with time. The SiO(g) generated was then reacted with carbon saturated iron under conditions for which the gas phase mass transfer conditions are clearly defined. By a systematic variation of the appropriate variables it was demonstrated that the rate was controlled by gas phase transfer of SiO to the gas-metal interface. The rate changed with gas diffusional distance but was not a strong function of temperature or of melt composition. The rate calculated for gas phase mass transfer was in good agreement with the experimental results. An erratum to this article is available at .     

Reduction of iron and chromium from oxides by carbon

The reaction of iron and chromium oxides with carbon is considered. The decomposition of carbon monoxide is an important source of carbon at the surface of the iron oxides. In the reaction of Cr₂O₃ with carbon, the first stage includes dissociation of the oxides, with the liberation of atomic and molecular oxygen, and the formation of carbon oxides. Rapid reduction of chromium is ensured by the reaction of Cr₂O₃ with C₃O₂ and elementary carbon, which is produced from oxides.     

The kinetics of the nitrogen reaction with liquid iron-Sulfur alloys

An experimental apparatus was designed and constructed which permits utilization of both the modified Sieverts' technique and the isotope exchange technique for study of the kinetics of ni-trogen reaction with liquid iron alloys. Experimental results from the two techniques are used in con-junction with the current knowledge in the field to readdress several persisting questions dealing with the nitrogen reaction. Results from this study have confirmed that N₂ dissociation is the rate lim-iting step in the intrinsic chemical reaction mechanism of nitrogen absorption. In addition, the ex-istence of a residual nitrogen absorption rate at high sulfur concentrations has been reaffirmed and possible reasons for the phenomenon are discussed. Lastly, results of an investigation into the in-fluence of carbon on the nitrogen reaction rate in liquid Fe-C-S alloys indicate that carbon has a negligible effect on the rate. Formerly with the Department of Metallurgical Engineer-ing and Materials Science, Carnegie-Mellon University, Pittsburgh, PA     

Kinetics of the reactions between silica and alumino-silicate refractories and molten iron

The rate of corrosion of silica and alumlno-silicate refractories in Armco iron melts at 1600°C was measured. A standard “immersion” technique was used under both static and dynamic conditions. It was found that the corrosion of the refractories in Armco iron melts was initially controlled by a chemical reaction process but changed rapidly to a steadystate, diffusion-controlled process. A liquid silicate product layer built up at the interface during the induction period. The steady-state rate of corrosion was independent of the oxygen content of the melt and was also found to be a linear function of the peripheral velocity of the refractory specimen. The rate of corrosion for the various refractories was measured and found to be controlled by diffusion of iron and oxygen in the silicate layer.     

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.     

不锈钢渣熔融还原中铬在铁浴和熔渣间的分配行为研究

通过正交试验考察不锈钢渣铁浴熔融还原中反应温度、炉渣碱度、渣中Al2O3含量及铁水初始铬含量对铬在铁浴和碱性炉渣间分配行为的影响。试验在石墨坩埚内进行,还原剂为碳饱和铁水中的碳。试验结果表明,对影响渣中铬还原因素的显著性顺序依次为:炉渣碱度>渣中Al2O3含量>铁水初始铬含量>反应温度。此外采用模式识别方法对试验样本进行聚类分析和优化,以获得对渣中氧化铬还原的最佳参数。     

Investigations on the carbothermic reduction of chromite ores

Experimental studies were carried out on the reducibility of two different chromite ores using different reducing carbonaceous reducing agents in the temperature range 1173 to 1573 K. “Friable lumpy” ores and “hard lumpy” ores were used in the experiments. Petroleum coke, devolatilized coke, (DVC) and graphite were used as reducing agents. It was found that iron was practically completely reduced before the commencement of the reduction of chromium in the ore. The reduction of iron was controlled by diffusion. The activation energy for this process was estimated to be 130 kJ/mole. The reduction of chromium was controlled by either chemical reaction or nucleation. Rate of reduction was highest when raw petroleum coke was used as the reducing agent. The DVC was less effective compared to raw coke, whereas the rate of reduction was lowest when graphite was used as the reducing agent.     

还原碳化法制备超细碳化铬粉末

以纳米Cr_2O_3和乙炔黑为原料,经高温还原碳化制备超细Cr_3C_2粉末,研究反应温度、反应时间以及配碳量对Cr_3C_2粉末的粒度与游离碳含量的影响。通过热力学计算,只有当温度高于1 350 K时还原碳化反应才有可能进行,采用纳米Cr_2O_3可显著降低反应温度,在1 573 K下焙烧6 h碳化率即达到98.20%;Cr_3C_2粉末的游离碳含量随配碳量增加而显著提高,配碳量(质量分数)为理论配碳量的1.05倍时制得游离碳含量为0.23%、氧含量为0.91%(均为质量分数)、平均粒度为1μm的Cr_3C_2粉末,该粉末达到硬质合金及热喷涂应用的要求。     

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.