Control of the chromium-oxygen reaction in pure iron melts

Oxygen activities in Fe-O-Cr melts, equilibrated with chromium oxide, were determined as a function of chromium content by EMF measurements using ZrO₂(CaO) plug-type sensors with a Cr-Cr₂O₃ reference. Plug-type sensors with or without Cr₂O₃ saturator were used in the experiments. From the experimental results values for the activity coefficient f_O and the interaction parameters and were evaluated. Raoultian chromium activity features a slight positive deviation from ideal solution behaviour in the temperature range from 1550 to 1650°C. Taking into account the calculated interaction parameters, the equilibrium constant K_Cr-O was redetermined at 1550 to 1650°C. In comparison with previous studies a better agreement was obtained with existing thermochemical data.     

Control of the manganese-oxygen reaction in pure iron melts

EMF sensor measurements using ZrO₂(CaO) or ThO₂(Y₂O₃) plug-type sensors with a Cr-Cr₂O₃ reference were performed to redetermine the Mn-O equilibrium reaction. In these experiments a strong effect of deoxidation of manganese was ascertained at saturation with solid deoxidation products. The measuring interval of the sensors at MnO saturation was limited to about 12 min due to chemical corrosion of the used Al₂O₃ sheaths. In the case of double saturation with solid MnO · Al₂O₃ (MA) and Al₂O₃ (A) the sensors could be used as long as desirable. Moreover, the combined deoxidation of the iron melt with Mn and Al was investigated. An auxiliary electrode at the tip of the sensor ensured rapid saturation of the iron melt with solid MnO or MnO · Al₂O₃ + Al₂O₃.     

Nitrogen desorption from pure iron melts under reduced pressure

More recently, lower nitrogen contents of steel are required in view of its workability and applicability. The present study covers basic investigations on the improvement of mass transfer in denitrogenation of steel melts under vacuum. Extensive reduction of the contents of the surface-active elements oxygen and sulfur is a precondition to increase the rate of nitrogen desorption. Kinetics of nitrogen transfer is reliably described by a mixed control model which includes diffusion in the melt, interfacial reaction and diffusion in the gas phase. Particularly at low oxygen and sulfur contents, mass transfer of nitrogen during desorption from steel melts is markedly accelerated. A convincing explanation of this phenomenon has not been found yet.     

Contact reaction of graphite with liquid iron and iron base melts

Conclusions A study was made, by a sessile drop technique involving simultaneous heating of the specimen and the base plate, of the interfacial reactions at the melt/graphite interfaces in the systems iron/graphite, iron-carbon-containing melt/graphite, iron-copper/graphite, iron-tin/graphite, iron-germanium/graphite, iron-gallium/graphite, and iron-aluminum/graphite. It is shown that the strength of the bond between the phase in contact in the systems investigated (except the system iron-aluminum/graphite) is determined by the work of adhesion linked with the departure of the system from a state of equilibrium. A relationship has been found between isotherms of wetting of graphite by the melts investigated and the effects of tin, germanium, gallium, and copper on the solubility of carbon in the relevant ternary systems. It is demonstrated that, for systems characterized by carbide formation (the system iron-aluminum/graphite), an isotherm of wetting of graphite by melts represents a complex dependence on melt composition.Translated from Poroshkovaya Metallurgiya, No. 6 (138), pp. 64–71, June, 1974.     

Settling of undissolved zirconium particles in pure magnesium melts

Zirconium is a remarkable grain refiner for magnesium alloys and is currently introduced into magnesium alloys primarily in the form of a Mg–Zr master alloy (Zirmax^® a Mg–33.3Zr alloy supplied by Magnesium Elektron). Owing to the difficulties of attaining complete dissolution, undissolved zirconium particles are often observed in Zirmax^® alloyed magnesium microstructures in the form of both isolated individual particles varying from submicrometre to greater than 10 μm, and various sizes of clusters that contain a number of zirconium particles. Aimed at improving the alloying efficiency with Zirmax^® and eliminating these undesirable large zirconium inclusions prior to pouring, this paper provides a detailed theoretical and experimental study of the settling behaviour of undissolved zirconium particles in pure magnesium melts. Various characteristics of the settling behaviour of zirconium particles are clarified based on the good agreement achieved between the experimental observations and theoretical predictions. In addition, it is also shown that wet chemical analysis of the total zirconium content in samples taken after different settling times at temperature can be an effective approach for evaluating the settling behaviour of undissolved zirconium particles in pure magnesium melts.     

Deuterium exchange studies of the interfacial rate of reaction of water vapor with silica-saturated iron silicate melts

Measurements have been made of the rate of dissociation of H₂O on silica-saturated iron silicate melts at 1300 °C and 1400 °C by the HDO-H₂ deuterium exchange technique. The general rate equations for the technique are developed, and the available information on the associated isotope equilibria is briefly reviewed. The rate is deduced to be first order with respect to the pressure of water vapor, and the apparent first-order rate constant is found to be essentially inversely proportional to the activity of oxygen in the melt over the range studied;i.e., pH ₂O/ pH₂ − 0.9 to 18 at 1400 °C. Comparison with the rates deduced by Sasaki and Belton from measurements of the steady-state oxygen activity of the melts in flowing H₂O-CO mixtures at 1250 °C leads to the conclusion that interfacial rates of oxidation (or reduction) of the melts in H₂O-H₂ atmospheres are given by the rate lawv = k₁(pH₂O(a′_o) −pH ₂) over the range of conditions covered by the two sets of experiments. The terma’o is the oxygen activity of the melt, defined as the equilibriumpH ₂O/pH₂ ratio, and k₁, in units of mol cm⁻²s⁻² atm⁻¹, is given by the expression: log k¹ = −6700/T − 0.08 to within a factor of about 2 over the temperature range of 1250 °C to 1400 °C. Formerly Postdoctoral Fellow, Department of Metallurgy, University of Newcastle     

Laboratory studies on smelting reduction – a contribution to reaction mechanisms in the production of liquid iron from iron oxide melts

Iron oxide slags are subjected to reduction at 1550 °C with the use of various reducing agents. The experiments with carbon monoxide are subdivided into series of top-blowing, injection or bottom-blowing experiments. Moreover, solid carbon is employed for further experiments. As a result of the necessary addition of Al₂O₃ – because of the corrosivity of FeO_n towards the crucible material during experiments – reaction-inhibiting barrier layers precipitate in the form of spinels during reduction. Foams containing CO_n exert the same effect. From the experimental results, it can be concluded that the reduction of liquid oxides by carbon monoxide or by solid carbon does not consistently obey any law of reaction during the entire process sequence. The essential, decisive parameter for the carbon monoxide blowing experiments is the blowing rate. The experiments performed with the use of solid carbon exhibit the highest reduction rates, on the whole. For the purpose of elucidating the reaction mechanisms, only the experiments conducted by blowing carbon monoxide onto the melt yield clearcut results. After a possible initial steep rise, a reaction of first order is then established, as a first approximation. The further course of the experiment is characterized by covering of the blowing trough. Mass transfer can then proceed only through the spinel layer near the surface, or through the channels between the spinels.     

The prediction of the nitrogen solubility in binary iron melts

Statistical model of nitrogen solubility in iron melts. Equations. Calculation of nitrogen solubility of the systems Fe–Co–N, Fe–Cr–N, Fe–Mn–N and Fe–Ni–N in the liquid state at 0.101 MPa. Comparison between model and experiments.     

Activity of Ti and V in iron melts

Thermodynamic data regarding the formation of the nitrides TiN and VN in iron melts were obtained by Ser’eznov at Moscow Institute of Steel and Alloys on improved Sieverts equipment by a compensation method of measuring the pressure and gas volume using a highly sensitive pressure sensor. The use of this very reliable method to investigate gas–metal interactions was first proposed by Ponomarev and implemented at Chelyabinsk Research Institute. The experimental data obtained in the present work are used to calculate the activity coefficients of Ti and V in dilute solutions based on iron. Refined reference data regarding the Gibbs energy of vanadium-nitride formation from its elements are employed here. The results for the activity coefficients γ _Ti.1873 ^∞ = 0.055 and γ _V.1873 ^∞ = 0.24 are in good agreement with literature values.     

Aluminium nitride probes for application in iron melts

Review on high-temperature properties of aluminium nitride AIN. Investigations on aluminium nitride as a possible solid electrolyte at temperatures around 1600°C. Presentation of available data on the electrical conductivity, the thermal conductivity and the thermal expansion coefficient of AIN at elevated temperatures. Experimental study on the oxidation behaviour of AIN in oxidizing gases and oxygen-containing iron melts. EMF measurements on electrochemical cells of the type iron melt ‖ AIN (Al₂O₃) solid electrolyte ‖ reference representing oxygen and aluminium probes in iron melts under long-term conditions.     

Relaxation of iron melts for the production of amorphous materials

The kinematic viscosity of Fe-B-Si melts from which amorphous materials are produced is studied over time by the torsional-vibration method. Two series of samples of the same chemical composition are produced by different technologies. In isothermal holding, the variation in viscosity over time is oscillatory. By comparing the dependences on the temperature and the time, earlier results on such alloys may be refined. The change in viscosity on relaxation of the melt is established, and an explanation for this behavior is offered. Recommendations are made regarding research on optimization of the production temperature and time for such alloys.     

转炉冶炼纯铁钢种C、Mn元素的控制

通过对生产控制的分析及研究,发现铁水经过 AOD 炉脱锰可满足导电纯铁对低锰铁水的需要;在相同工艺条件下,转炉终点碳含量越低,RH 炉脱碳效果越好。理论分析发现：转炉较低的碳氧积水平有利于终点 C含量的降低;较低的转炉终点温度、避免补吹和良好底吹效果,可保持较低碳氧积水平。利用正规溶液模型计算了碳-铁的选择性氧化临界碳含量范围,并考虑连铸工艺可浇性,控制转炉终点 C 含量,降低中包铝损及二次氧化。分析结果显示,邢钢转炉生产纯铁钢种理想的终点碳质量分数应控制在0·036％~0·045％。     

Degassing of coal particles injected into iron melts

A mathematical model was developed, that describes heating and degassing of coal particles blown into liquid iron. The model combines heat transfer from iron melt to particle surface and heat conduction within particle with the kinetics of the degassing process. The endothermic degassing reaction generates heat sinks within the particle. Local heat consumption per time for degassing is determined simultaneously by heat transfer and by the temperature dependent rate constant of the first order degassing reaction. Model calculations result in temperature distribution within particle, degassing rate, and overall degassing time. Overall degassing time, defined by a degassing rate of 99%, is given by t_g[s] = fd_p^1.5 [mm] for 0.05 ≦ dp ≦ 0.8 mm. The factor f lies between 1.02 and 1.14 for various coals. The exponent 1.5 is nearly independent of coal type. Results obtained are in good agreement with published comparable results for rapid degassing of coal particles.     

Electrode polarization in the DC electroslag melting of pure iron

It is evident from the known ionic properties of the slags used in electroslag melting, that the dc melting process must be accompanied by Faradaic reactions on the slag/ingot and slag/electrode interfaces. The present work has determined the magnitude of the overpotentials resulting from concentration polarization at these interfaces, in the case of pure iron/CaF₂+Al₂O₃, CaF₂+CaO slags using a galvanostatic pulsing technique in an electrolytic cell. The polarization overpotential existing on an electrode in an operating ESR unit has been measured by the same technique. It is found that the potentials observed on the ESR electrode agree well with the results from the electrolytic cell. The primary anodic process is postulated to be the corrosion of iron, leading to an Fe²⁺-saturated layer on the anode surface at sufficiently high current densities. The cathodic process is suggested to be the Faradaic reduction of Al³⁺ or Ca²⁺, to give a concentration of [Al]_Fe or (Ca)_slag in the cathode interface region. This observation is supported by the fact that the cathodic potentials with respect to a C/CO reference electrode are close to those predicted from the reactions: (Al₂O₃)+3C=3CO(g)+2Al(l) or (CaO)+C=CO(g)+Ca(g) At very high current densities both the anodic and cathodic processes may convert to arcs, leading to process instability. The chemical and thermal effects of the overpotentials are briefly discussed and compared with the present results on ESR ingots of pure iron.