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.     

Mixing phenomena inside the ladle during RH decarburization of steel melts

The RH (Rheinstahl-Heraeus) process is in widespread use to produce ultra-low carbon steel by vacuum treatment. Among other factors, the decarburization rate is effected by mixing phenomena inside the ladle. Thus, supervisory control of the RH treatment requires an adequate and precise representation of the mixing conditions. In this work, mixing is characterised by concepts of chemical reaction engineering. Different sizes and geometries of RH installations are taken into account using similarity criteria. A simple model is derived from the experimental results and detailed numerical flow computations. For this model, a mathematical function of mixing is developed which can be incorporated into supervisory control systems.     

Rate of decarburization of iron-carbon melts: Part II. a mixed-control model

The observed retarding effect of sulfur on the decarburization of Fe-C melts has been interpreted by means of a mixed-control mechanism involving gas-phase mass transfer and dissociative adsorption of CO₂. A mathematical model formulated on the basis of the proposed mechanism gave an excellent fit to the experimental data. The application of the model to the data provided a value of 4.42 x 10⁻³ mole · cm⁻² · s⁻¹ · atm⁻¹ for the dissociative adsorption rate constant for CO₂ on liquid iron at 1973 K; the fraction of surface sites that cannot be occupied by sulfur, even at apparent surface-saturation, was found to be 0.085. The model predicts a residual rate of decarburization at high sulfur concentrations; this prediction is borne out by the experiment. The effect of convective motion within the levitated melt on the rate of decarburization below a characteristic carbon concentration was quantified. The liquid-phase mass transfer was greatly enhanced by the stirring effect of the electromagnetic field. The effective diffusivity of carbon in Fe-C melts under levitation conditions has been found to be 3.24 x 10⁻³ cm² · s⁻¹, a value ten times as large as that under stationary conditions.     

Properties of iron powders obtained from high-carbon melts by air atomization with subsequent decarburization

Conclusion The article examines the physical and processing characteristics of iron powders obtained by atomization and subsequent decementation. Experimental data, obtained by x-ray diffraction investigation, are presented on the influence of compaction pressure on the fine structure (second-type microdistortions, dislocation density, and mosaic-block size) of the powder particles.Translated from Poroshkovaya Metallurgiya, No. 10 (70), pp. 11–14, October, 1968.     

弱氧化环境下褐煤氧化产物的定性分析

以双氧水作为氧化剂,在1.2 mol/L NaOH溶液中,经程序升温至200℃对褐煤进行氧化反应,反应产物经盐酸酸化处理后,以氯仿、乙酸乙酯(10∶1,V/V)混合溶剂作为萃取剂,进行索氏抽提。对抽提所分离的有机物组分采用红外光谱和气相色谱/质谱联用的方法进行定性分析。红外谱图中:3400 cm-1,1500~1600 cm-1,1700 cm-1,1200 cm-1等处有吸收,表明组分结构中分别含有-OH、苯环、-C=O、酚羟基。而质谱分析表明:氧化产物中除含有9~18个碳的脂肪羧酸外,还有酚酸,总离子流色谱图中No.4的质谱与邻羟基苯甲酸标准样品谱图的相似度达97%,可以确定其为邻羟基苯甲酸(即水扬酸)。     

Rate of decarburization of Fe-Csat melts by H2O at 1523 and 1873 K

The rate of decarburization of carbon-saturated iron by H₂O gas at 1523 and 1873 K was measured as a function of sulfur content. The measurements were made under conditions for which the gas phase mass transfer is negligible or a reasonable correction for its effect can be made. The measured rates are consistent, with the rate-controlling reaction being the dissociation of H₂O on the surface. Sulfur was found to significantly decrease the rate. The rate constant for the dissociation of H₂O on iron is considerably higher than those for the dissociation of CO₂ and N₂ on liquid iron; about 2 to 3 times higher than CO₂ and 300 to 600 times higher than for N₂ at 1873 K. The practical significance of the present results relevant to steel ladle processing and iron bath smelting is briefly discussed.     

Kinetics and mechanism of the reaction of iron-chromium and iron-chromium-molybdenum alloys with chlorine gas

This report deals with the kinetics and mechanism of the reaction of iron-chromium and iron-chromium-molybdenum alloys (containing 1.25 pct Cr-0.5 pct Mo, 5 pct Cr-0.5 pct Mo, and 12 pct Cr) with low partial pressure chlorine gas in the temperature range 270 to 550 °C. The rate of reaction generally decreases with exposure time and, in the case of alloys containing five pct Cr and higher chromium content, the kinetics follows a parabolic rate law. The reaction kinetics is influenced by surface films containing FeCl₂ and CrCl₃ which have very low vapor pressure in the temperature range studied. The effect of molybdenum on the reaction is negligible. In the case of alloys containing five pct Cr-0.5 pct Mo and 12 pct Cr, the reaction product film consists essentially of CrCl₃ (outer layer) and much smaller concentration of FeCl₂ (inner layer). For these alloys, the observed parabolic kinetics is attributed to kinetic control of the overall reaction by solid-state diffusion through the reaction product surface film. In the case of the 1.25 pct Cr-0.5 pct Mo alloy, the film consists essentially of a mixture of FeCl₂ and CrCl₃. In this case, an outer CrCl₃ film layer is not formed and the overall kinetics is influenced by the rate of formation of volatile FeCl₃ speciesvia the reaction 2 FeCl₂ + Cl₂ (FeCl₃)₂.     

Kinetics of the dissolution of zinc sulfide in an oxidizing slag

A new concept has been developed for the production of zinc from zinc and complex zinc concentrates. It is a two-stage process involving oxidation of zinc sulfide to oxide and dissolution into slag and the fuming of zinc from the slag by injecting carbonaceous materials into it to produce zinc vapors which can be subsequently condensed in a lead-splash condenser such as those used in the Imperial Smelting Process (ISP). In this paper, the effects of the quantity of air, temperature, and concentrate feed rate have been discussed on the production of zinc-rich slag, which is the first stage of the proposed process.     

The CO2 solubilities of highly basic melts

The CO₂ solubilities of highly basic melts have been measured by equilibrating samples with a gas phase. According to the results, the investigated oxides can be arranged as follows in order of decreasing basicity; K₂O>Na₂O>Li₂O, BaO > CaO, SO₃ ? CrO₃ > BO_1.5 > SiO₂ > PO_2.5. By comparing the solubility data with optical theoretical basicity value, sulfide capacity, phosphate capacity and activity of CaO, it has been found that the carbonate capacity is a good measure of slag basicity.     

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.     

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An experiment simulating the heating environment of CSP furnace was performed to study the effects of heating temperature, holding time and heating atmosphere on the decarburization of 50CrV4 spring steel. The results show that the decarburization layer depth of 50CrV4 steel increases with increasing the holding time. With holding time of 30 and 60min, the decarburization layer depth increases with increasing the heating temperature below 1050?? and decreases when the temperature is over 1050??. The decarburization layer depth reaches the peak at 1050??. The mixed atmosphere of O2+CO2+H2O+N2 can effectively reduce the decarburization layer depth more than that of O2+CO2+N2 and H2O+N2. Combined with the oxidation model and Fick??s Second Law, the decarburization calculation model is established and corrected with experimental data.     

Kinetics of the carburization of iron alloys in methane-hydrogen mixtures and of the decarburization in hydrogen

The surface reaction kinetics have been investigated for the reaction CH₄ (gas) = C (dissolved) + 2H₂ (gas) on Fe and Fe-M foils (M = Mn, Cr, Co, Ni, Sn) at temperatures between 800 and 1000°C. The resistance relaxation method was applied in a flow apparatus. The following rate equation was observed for the rate of carbon uptake where is the carbon concentration and k and k′ are the rate constants for carburization and decarburization respectively. For Fe, Fe-10 Ni and Fe-10 Co the value of v = 3, for the alloys with > 20% Ni as well as for all Fe-Mn and Fe-Cr alloys the value v = 4 results from the measurements, which indicates differences in the rate determining step. With increasing Cr, Mn, Ni, Co content the rate constants k and k′ increase. The decrease of the equilibrium carbon concentration with increasing Ni content in Fe-Ni alloys is correlated to a fast increase of k′ and a slow increase of k with increasing Ni content. Beyond the minimum of at about 70 wt.% Ni both rate constants show a strong increase. By holding Ni at high carbon activities (a_C > 0.7 at 1000°C) segregation of carbon induces a surface reconstruction which is characterized by formation of (111) planes and which reduces the reaction rates. The increase of the equilibrium carbon concentration in the systems Fe–Mn and Fe–Cr with increasing content of alloying element is correlated to a slow increase of k′ and a fast increase of k with increasing Mn or Cr content. Sn segregates to the surface and retards the reaction rate by blocking the reaction sites for the surface reaction, similar to the effects of P and S.     

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.     

Kinetics of external dissolution of metals in metallic melts. (Review)

Conclusions Dissolution rate under diffusion conditions is usually controlled by three parameters, D, , and c_m. Since the dependence of D and values on the individual properties of metals (D 10^–5 cm²/sec, 10^–3 cm) is slight,dissolution rate under diffusion conditions is determined chiefly by cm, which thus constitutes the principal criterion governing the choice of a metal compatible with any given melt. Dissolution under kinetic conditions does not appear to be typical of metals, since even tungsten, which has the highest crystal lattice energy of all metals [62], dissolves under diffusion conditions [19, 20, 63–66].It thus follows that detailed researches into the dissolution kinetics of metals in metallic melts are hardly likely to reveal any new corrosion-resistant metallic materials. The existing liquid-metal corrosion inhibitors are refractory compounds such as nitrides or carbides [67]. This does not mean, of course, that investigations into the dissolution kinetics of solid metals in metallic melts serve no useful purpose, since they are concerned not only with corrosion, but also with a number of other processes referred to in the introduction to this survey.Translated from Poroshkovaya Metallurgiya, No. 8 (92), pp. 39–54, August, 1970.     

Dendrite growth processes of silicon and germanium from highly undercooled melts

The crystal growth behavior of a semiconductor from a very highly undercooled melt is expected to be different from that of a metal. In the present experiment, highly pure undoped Si and Ge were undercooled by an electromagnetic levitation method, and their crystal growth velocities (V) were measured as a function of undercooling (ΔT). The value of V increased with ΔT, and V=26 m/s was observed at ΔT=260 K for Si. This result corresponds well with the predicted value based on the dendrite growth theory. The growth behaviors of Si and Ge were found to be thermally controlled in the measured range of undercooling. The microstructures of samples solidified from undercooled liquid were investigated, and the amount of dendrites immediately after recalescence increased with undercooling. The dendrite growth was also observed by a high-speed camera.     

CO2和H2O气氛下Fe-C合金薄带脱碳对比

 为了对CO₂和H₂O两种气氛的脱碳效果进行对比,将碳质量分数约为4.2%的Fe-C合金薄带分别在两种气氛中进行脱碳处理。通过热力学分析结合试验保证碳被脱除且铁不氧化的气氛条件分别为:Ar-CO-CO₂(气体流量为850 mL/min,CO的体积分数为25%,$P_{CO_2}$/(P_CO+$P_{CO_2}$)为0.26),Ar-H₂-H₂O(气体流量为500 mL/min,H₂体积分数为15%,水浴温度为313 K)。当脱碳温度为1 413 K时,Ar-H₂-H₂O气氛下,脱碳时间为50 min时,脱碳后的平均碳质量分数为0.6%,Ar-CO-CO₂气氛下,脱碳时间为70 min时,脱碳后的平均碳质量分数为0.92%。当脱碳时间相同时,Ar-H₂-H₂O的脱碳效果优于Ar-CO-CO₂的脱碳效果,由于随着脱碳反应的进行薄带表面与氧化气体反应达到平衡,Ar-H₂-H₂O反应平衡时薄带的碳活度要低于Ar-CO-CO₂气氛条件的碳活度,导致Ar-H₂-H₂O气氛条件下薄带的碳浓度梯度高于Ar-CO-CO₂气氛条件,进而导致Ar-H₂-H₂O气氛条件的扩散通量大,脱碳效果好。