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By J. E. Stukel, J. Cocubinsky

A CONSIDERABLE amount of information is available on the equilibrium distribution of manganese between slag and metal under oxidizing conditions. These data have increased our knowledge of the manganese reactions in the open hearth, ladle, and ingot mold. In contrast, there is a paucity of data on the slag-metal distribution of manganese under reducing conditions. The purpose of the present investigation was to study the equilibrium distribution of manganese between blast-furnace type slags and iron saturated with carbon. Experimental Method Furnace: The induction furnace used for the experiments is shown in Fig. 1. A 1 in. pipe, attached to the transite cover, was fitted with a window through which the charge could be observed. Material could be introduced into the furnace through a tee and plug without removing the cover. A graph-it cylinder (3 in. ID and 10'/2 in. long), centered within the induction coil, was used as a heating element. During a test, a zircon plug kept the top of the furnace from becoming too hot from heat radiation. At the bottom, a graphite block on the vertical center line of the furnace and extending 1 1/2 in. into the coil, was used as a support for the graphite crucibles containing the melt. The graphite crucibles, machined from regular carbon electrode stock, had a 2% in. OD with 3/16 in. walls and were 5% in. long. The fumes present in the furnace during the early part of a run made optical readings uncertain. A noble metal thermocouple was, therefore, adopted to measure the temperatures. The arrangement used, shown in Fig. 1, allowed the silmanite protection tube to be replaced with a minimum effort. The thermocouple was calibrated against a standard Pt-Pt-Rh thermocouple in a fused quartz protection tube. The latter was inserted in the molten iron by removing the glass window on the cover. The lower couple was found to be very sensitive to temperature changes. To insure accurate temperature readings, the graphite crucibles were made to fit tightly against the silmanite protection tube. Further, to avoid contamination of the thermocouple by carbon, the silmanite tube was changed and the calibration procedure was repeated at frequent intervals. By using this temperature measuring technique, the furnace was easily held within *1O°C of the desired temperature. Because of the small free space in the furnace, no attempt was made to control the atmosphere. It

Jan 1, 1955

By C. A. Hope, H. B. Wishart

THE number and severity of surface imperfections on rolled slabs, assuming the reception of uniformly good quality heats from the open hearths, depend upon a number of conditions associated with heating and rolling of steel in the primary mills. While there are other elements that have an effect on surface quality, rather than make this paper too lengthy the discussion of mill processing variables will be limited to three factors in order to illustrate their effect on slab surface quality: 1—amount of reduction between ingot and slab, 2—slab finishing temperatures, and 3—influence of roll changes. Measurement of the percentage of surface removed by scarfing on the flat surfaces of the slabs was used for evaluating quality in this study. A study of this nature must be made on slabs that are inspected and conditioned under uniform conditions and standards. In order to be certain that steel of the best possible steelmaking quality was received at the rolling mills, a low carbon deep drawing grade of rimmed steel, made for sheet mill application and manufactured under carefully controlled open hearth practices, was selected. Use of this particular steel thereby reduced the steel quality factor as a possible source of variation. The measure of slab surface quality is the amount of surface removed by scarfing during yard conditioning and is expressed as percentage of surface removal. This percentage was estimated by experienced personnel to uniform standards and it should be noted that these percentage figures are representative only for the grade selected and under the rigid inspection standards to which the slabs were subjected. Surface removal is a matter of concern because the imperfections, if undetected, often are the cause of poor surface quality in the finished product and their removal, by conditioning, add to the total plant costs. The data was collected at various times over a period of six months and, with normal weekly fluctuation in the level of quality, it is to be expected that for any period of sampling there will be some variation in the plotted results. The type of defect that is responsible for most slab conditioning at Gary Steel Works is a light angular surface break. This defect is usually interconnected to form large defective areas and occurs mainly on the bottom half of the slab on both sides. This type of defect is illustrated in Fig. 1, showing a bottom portion of a slab; while a close-up of an area of the same slab where the surface breaks were found is given in Fig. 2. The large dark areas are heat patterns, results of hot stacking and cooling. Independent of these light breaks, but sometimes associated with them, are larger and deeper isolated breaks. However, most of the surface removal occurs from conditioning the large areas of small breaks. There are also occasional scabs of varying degrees of severity but these are relatively infrequent. The slabs are generally free of rolled-in scale. Ingot to Slab Reduction vs Quality Some ten years ago at Gary Steel Works, the minimum slab ingot thickness was 30 in. Subsequent operating and other quality features indicated the desirability of using an ingot of reduced thickness with the result that a series of molds that would produce a 22 in. thick ingot with various widths was adopted as standard. A minimum number of the thicker mold sets are still used. From the standpoint of quality difficulties from pipe and segregation, the smaller ingots are an improvement. From a quality surface viewpoint, the slab product from the thin molds requires approximately twice the surface removal as the slab product from the thick molds. This is shown in Fig. 3 where the percentage of surface removal is plotted against slab product rolled from

Jan 1, 1956

By W. O. Philbrook, K. M. Goldman, G. Derge

THIS is the third in a series of papers from the Metals Research Laboratory dealing with the transfer of sulphur across the iron-slag interface in a carbon-saturated system. The first paper' showed that the transfer obeyed first-order kinetics. The second' presented detailed evidence in support of the three-stage mechanism: FeS(Fe) FeS(slag) FeS(slag) + CaO(sing) ? CaS(slag) + FeO(slag) FeO(slag) + C ? Fe + CO. This emphasized the role of an iron-sulphur complex as the transfer agent across the interface and as an essential intermediate in the overall process. The present paper shows the influence on the process of the individual elements, carbon, silicon, manganese, and phosphorus, the alloying elements normally present and of interest in commercial blast furnace operations, aluminum, which has a pronounced accelerating influence, and nickel and copper, which are common minor impurities in the raw materials. The experimental methods and procedures for interpretation of data are the same as described earlier.1,2 Induction heated, graphite crucibles were used, and sulphur-free slag was added to the molten iron containing sulphur and the selected alloy. Slag samples were taken at regular time intervals and analyzed for sulphur and other components of interest. The authors wish to state specifically that these experiments were not intended to simulate industrial blast furnace operations. However, they do represent a study of the kinetics and mechanism of sulphur transfer at the slag-metal interface under specified laboratory control of the major variables in the system. It is believed that the results can be usefully applied to the blast furnace if consideration is given to the differences which are known to exist between the two conditions. A rigorous evaluation of the accuracy of rate studies is difficult. Recognized sources of error include sampling and analysis of both slag and metal, temperature measurement and control, selection of zero time, composition of the gaseous atmosphere over the reaction system, and extraneous sources of sulphur from the graphite crucible and reagent materials. In this study carefully standardized procedures were followed consistently in order to minimize the errors. It is believed that the reproducibil-ity of duplicate runs indicates that errors have been rendered negligible relative to the observed effects from intentional variables. For example, original experimental points for duplicate runs are shown in Figs. 1, 2, 7, etc. In most cases in this paper the drawn curves represent an average of at least two heats. The spread in sulphur values at a given time ranges from 0.02 to 0.08 pct, which is a small frac-tioi of the total values ranging up to 2 pct S in slag. In the systematic study of the influence of alloy additions, each element was added over a range of concentrations. The two slags used in this study were designated as "acid" or 1530 and "basic" or 1545. They had the nominal compositions given in Table I. Rates were measured in the temperature range 1500" to 1650°C. Data will now be presented to illustrate the various features of the study. Silicon The first alloying element examined was silicon, because its presence is unavoidable in any silicate slag system through the reaction y/2SiO2(slag) + xM?y/2Si(liq.Fe) + MxOy where M is any reducing agent such as iron or carbon. It is known that the attainment of equilibrium by this reaction is extremely slow and probably not reached in the blast furnace." The influence of silicon on the final stages of the sulphur reaction has also been studied.' It has been shown5 hat silicon increases the activity of sulphur in iron. For such reasons silicon may also be expected to influence the kinetics of the reaction. The observed effects will now be described. The general procedure was to melt 530 grams of ingot iron in a graphite crucible, 3 in. OD, 2 1/4 in.

Jan 1, 1955

By F. R. Cattoir, R. W. Kimball, C. T. Anderson

ONE of the principal impurities in all steels is sulphur. Sulphur-bearing, manganese-free steels exhibit hot shortness. Manganese is added to steel to improve the hot-working properties. If no sulphur were present in steel, it is probable that hot shortness would be nonexistent. This paper is the first of a series to be issued by this Laboratory reporting the measurements of hot forgeability tests and the physical properties of Fe-C alloys to which additions of various alloying elements have been made. The present paper describes the results- obtained by the addition of varying amounts of sulphur to Fe-C alloys. To obtain control over residual elements in the various charges melted in the arc furnace, it was considered advantageous to use sponge iron from one source as the melting stock rather than scrap metal having an unknown history. Small amounts of unwanted alloying elements might be introduced into the charge when scrap was used, thereby influencing the results of the various heats. A sponge iron having a high silica-lime ratio was used. Ore from Sunrise, Wyo., had been reduced to sponge iron and briquetted at the Bureau of Mines sponge-iron plant at Laramie, Wyo. The briquettes were 5 in. in diam and 2 to 3 in. in thickness, and weighed about 10 lb each. The chemical analysis of the sponge iron is as follows: C, 0.67 pct; Mn, 0.10; SiO2, 4.75; CaO, 1.4; P, 0.044; S, 0.72; MgO, 0.4; A12O3, 1.1; total Fe, 87.5; Fe metallic, 79.2; and reduction, 90.5 pct. Where a reducing agent was required, crushed graphite electrodes usually were used. The charcoal available contained 0.20 pct S. An analysis of the available coke showed it to contain 0.70 pct S. Where high sulphur heats were required, elemental sulphur additions were made to the ladle. Limestone of good quality was obtained locally and had the following analysis: CaO, 53.7 pct; MgO, 0.8; ignition loss, 42.4; R2O3, 0.2; SiO2, 3.0; and P2O5, 0.014. Melting Procedure Sponge iron was melted to produce metal stock for the experimental alloys in a silica-lined, three-phase, direct-arc, size ST, Moore Rapid Lectromelt furnace with a 500 kva rating. Fig. 1 shows this furnace installation. About 25 tons of sponge iron was melted in 75 heats, averaging 927 lb of sponge iron to the heat. An addition of carbon was required to complete the reduction of a portion of the iron oxide remaining in the sponge to prevent high losses of iron oxide in the slag and a low carbon content in the resulting metal. As reducing agents in preparing the melting stock, charcoal, coke, and a carbon product resulting from the thermal decomposition of natural gas were used. The quantity varied from 20 to 60 Ib per furnace charge, with an average of 38 lb. An average analysis of the metal obtained gave 0.52 pct C, about 0.01 pct Mn, 0.070 pct P, and 0.092 pct S. The average yield of metal was 647 lb with 241 1b of slag, the sponge-iron recovery being 70 pct. The metal obtained in melting the sponge iron was cast into pigs weighing about 20 lb each to facilitate recharging into the furnace for further refining. The pouring of the pigs is shown in Fig. 2. The average power consumption for the production of the 24 tons of metal obtained was 1704 kw-hr per ton.

Jan 1, 1954

By Donald B. Evans, Robert D. Pehlke

The solubility of nilrogen in liquid binary alloys of iron with Litanium. zivconium, columbium, vanndiurn, and tantalum was measured for alloy composiLions up to the solalbility limils of lhe alloy nitrides. All five alloying agents were found to decrease markedly the activity coefficient of nitrogen in liquid ivon. The metal/nitvogen mole ralios in the alloy nitrides formed were generally .found to be slighlly greater than 1.0, but in no case greater than 1.5. From the experimental data, the standard free energies of fortmation of titanium and zir-conium nitrides have been calculated for the Lemperaluve range 1550° to 1750 C. The solublily Products for columbium, tantalum, and vanadium nitrides are also reported. A number of research investigations have examined the effect of refractory metals on the solubility of nitrogen in liquid iron. Although data on zirconium are not available, investigators are in agreement that titanium, vanadium, columbium, and tantalum markedly increase the solubility of nitrogen in liquid iron. This fact alone makes desirable the acquisition of thermodynamic data for these elements in liquid iron. Since refractory metals are known to be stable nitride formers, they have been suggested as steel denitrifying agents, and some of their nitrides have recently been considered as containment materials for liquid iron and iron alloys. Most available thermodynamic data for these metals relate to their dilute concentrations, but effective thermodynamic treatment of these applications requires data at concentrations near the solubility limit of the alloy nitride. Although some work has been done at relatively high alloy concentrations in liquid iron (particularly for vanadium 2,3 and titanium 2,4), the results have been somewhat contradictory. Disagreement may be partly attributed to the fact that the compositions of most refractory metal nitrides have been shown to be nonstoichiometric, and to vary 2,5-8 depending on the temperature and nitrogen gas pressure with which the solid nitride phase is in equilibrium. One purpose of this study consequently has been to determine the compositions of the refractory metal nitrides precipitated from a liquid iron solution. EXPERIMENTAL PROCEDURE Rao and Parlee2 and Evans and Pehlke 9 have discussed the technique for measuring the solubility product of an alloy nitride phase in liquid iron by finding the point of departure of the nitrogen solubility from Sieverts' law. The method consists of measuring the solubility of nitrogen in a melt of iron containing a known concentration of a second metal as a function of the nitrogen gas pressure over the melt. In this study the second metal was one of the refractory metals titanium, zirconium, columbium, vanadium, or tantalum. When the nitrogen pressure at which the refractory nitride forms is reached, a deviation of the measured solubility of nitrogen in the melt from Sieverts' law is observed in the form of a "pressure halt." The concentration of nitrogen in the melt associated with this breakpoint in the nitrogen-absorption curve is then used to calculate the nitride solubility. The Sieverts method was used to measure nitrogen solubility as a function of nitrogen pressure and temperature. The experimental equipment for this technique has been previously described in detail. 1,9 Charge materials used were vacuum-melted high-purity iron (Ferrovac-E) and the best commercial grades of the refractory metals obtainable (in all cases at least 99.8+ pct pure). Recrystallized alumina crucibles were used to hold all melts except those containing zirconium, for which zirconia crucibles were necessary. Temperatures were measured by a disappearing-filament type optical pyrometer sighted vertically downward on the melt surface through a 1/4-in.-diameter sight hole in the crucible lid. By means of a technique previously described, 9 in which the refractory-metal nitride was precipitated at one temperature then redis-solved by raising the temperature 50°C and precipitated again at a higher temperature, it was possible to obtain data over a temperature range of up to 200°C on a single melt. It was found that this technique could not be used with melts containing zir-

Jan 1, 1965

By J. Chipman, N. J. Grant, H. L. Bishop, H. N. Lander

Data of several studies on the equilibrium between molten iron and open hearth-type slags have been combined to determine some of the chemical reactions involved in steel-making. Effects of slag composition and temperature on the iron oxide activity, distribution of sulfur between slag and metal, and the carbon content of the metal are discussed. Also, an overall reaction for the equilibrium between sulfur and oxygen is presented. DURING the past 15 years, a number of significant equilibrium studies have been carried out between liquid iron and simple basic and acid slags in an effort to throw light on the chemical reactions involved in steelmaking. This paper is a summary of the experimental reports on investigations which have been conducted at the Massachusetts Institute of Technology, and of related work in other laboratories. The investigations summarized in this paper include the works of Fetters and Chipman1 and Taylor and Chipman,' which dealt with simple slags that are similar to those found in the open hearth. The sulfur determinations of the slag-metal tests of Fetters and Chipman as reported by Grant and Chip-man" are included. Also, the investigations by Win-kler and Chipman' and Grant and ChipmanQ f more complex slag systems are included in this summary. The experimental procedure is described in detail in each of these papers and will not be discussed. Since the previous reports have been somewhat independent, it is desirable to review and combine the data of the various investigations to determine, as accurately as possible, the reactions in the slag-metal systems of the open hearth. It is the object of this report to present the combined data in such a way as to enhance their utility and applicability. Oxidizing Power of Slags of the System (CaO+MgO)-Si0,-FeO in Equilibrium with Carbon-Free lron The slags selected to determine the iron oxide activity in equilibrium with pure liquid iron were those containing less than 2 pct each of P,O,, MnO, or A1,0, on a weight percentage basis. The method used to calculate activities of iron oxide in liquid slags was that developed by Taylor and Chipman.' The solubility of oxygen in molten carbon-free iron under pure iron oxide slags can be expressed by the following eauation —6320 log (pctO)-------------— + 2.734 [1] where T is the absolute temperature. The oxygen solubility values as determined from Eq. 1 were used throughout this study to calculate the iron oxide activity. The iron oxide activities of slags of various iron oxide contents are plotted in Fig. 1 as a function of the basicity, which is defined as the ratio (pct CaO + pct MgO)/pct SiO,, and are based on molecular percentage values of the components. The percent (FeO), is the total iron content in the slag calculated to FeO. Fig. 1 shows that as the basicity increases at constant mol pct (FeO),, the iron oxide activity increases rapidly and reaches a plateau which extends on the basicity scale from about 1.3 to 2.3; the iron oxide activity then decreases rapidly until a basicity of about 3.0 is reached, where it tends to level off. The solid portions of the curves represent the experimental data of Fetters and Chipman and Win-kler and Chipman. Their experimental heats were made in magnesia crucibles, and hence the slags were saturated with magnesia. The broken lines on the left represent the experimental data of Taylor and Chipman, who used a rotating crucible. In general, these slags contained less than 3 pct MgO. The absence of data for slags containing less than about 40 mol pct (FeO), and basicity ratios greater than about 2.5 made it necessary to calculate curves using ionic concepts of slags. The broken lines on the right, which disregard the solubility limits of di and tricalcium silicate and lime, were obtained by following the treatment of Flood and Grjotheim,"

Jan 1, 1957

By R. L. Hadley, G. Derge

The amounts of oxygen in liquid iron-titanium alloys up to 50 pct Ti were measured and the oxide phases in equilibrium with these alloys were determined by using TiO² crucibles. A minimum of about 0.003 pct 0 occurs at less than 1 pct Ti. The various liquid and solid oxide phases can be arranged on a ternary isotherm. THREE characteristics of titanium contribute to the interesting aspects of its reaction with oxygen in liquid iron: 1—It forms a number of stable oxides. 2—All oxides have large negative free energies of formation. 3—The pure metal exhibits high solubility for oxygen. In addition, the use of titanium as a stabilizing and strengthening element in alloys suggests a need for investigation of its reactions in amounts greater than those normally required for deoxidation. These higher compositions are also of interest because they occur during the addition of ferroalloys and produce deoxidation products before dilution is achieved. Titanium Deoxidation in the Literature While the use of titanium as an alloying element and deoxidizer has been common for several decades, the first detailed study of its deoxidizing characteristics was carried out by Wentrup and Hieber' in 1939. These authors determined the extent of deoxidation possible with titanium and identified, by microscopic examination, the products formed. They found that titanium in excess of 0.2 pct did not reduce the oxygen content of iron below 0.004 pct at 1600°C. They identified the spinel FeO-TiO² at low titanium concentrations and Ti2O³ in melts containing more than 0.2 pct Ti. A portion of the area surveyed by Wentrup and Hieber has been investigated recently by Evans and Sloman² using X-ray diffraction for inclusion identification. They concurred in general with the findings of Wentrup and Hieber, but reported the existence of Ti³O5 as a deoxidation product in the range near 0.1 pct Ti. Comstock, Urban, and Cohen³ discussed the deoxidation of iron with titanium, correlating the data of Wentrup and Hieber with free-energy data for the titanium oxides. Scatter at high titanium values was considered attributable either to the formation of an oxide exhibiting high solubility in liquid iron or to the entrainment of solid oxide particles leading to high apparent solubility. Chipman' has calculated the deoxidation curves for titanium based on free-energy data for titanium oxides. These calculations (Fig. 1) and those of Comstock, Urban, and Cohen involve assumptions as to the activity coefficients of oxygen and titanium in liquid iron, since such data have not been determined. Investigation of the deoxidizing characteristics of chromium" and vanadium0 have shown that these elements decrease the activity coefficient of oxygen in liquid iron, leading to a tendency toward relatively high oxygen values and experimental scatter in highly alloyed melts. Experimental This investigation involved two major objectives: 1—determination of the composition of the oxide phases in equilibrium with liquid Fe-Ti alloys, and 2—establishing the pattern of oxygen solubility in liquid Fe-Ti alloys at titanium concentrations in excess of that required for attainment of minimum oxygen content. Raw Materials Ingot iron was used having the following composition: 0.02 pct C, 0.017 pct Mn, 0.01 pct Si, 0.02 pct S, 0.006 pct P, and 0.03 pct 0. The titanium used

Jan 1, 1956

By S. Ramachandran, R. A. Walsh

Many investigations have shown that the manganese enhances the deoxidation power of silicon. Here it is suggested that this phenomenon could be explained in terms of the formation of impure silica. Data of Hilty and Crafts on the Fe-Mn-Si-O System has been evaluated on the basis of the reaction S_i + 20 = (SiO2) where (SiO2) denotes silica of variable activity. The activity of silica in this system is a function of aMn/aSi and the temperature, and can be described by the equation 12700 l°gaSiOz = -6.85+ - - 0.5 log aMn /asi PRACTICAL melting experience has shown that it is helpful to maintain a certain range of Mn/Si ratio in deoxidizing quality alloy steels. Herty,1 as early as 1932, reported a strong association between manganese and silicon as did schenck2 and Korber and Oelsen3 in later work. More recently, Hilty and crafts4 have studied the solubility of oxygen in the Fe-Si-O system, both with and without manganese. Their study confirmed the marked ability of manganese to increase the deoxidizing power of silicon. This phenomenon has remained unexplained in the liter,ature5 since it has been shown that manganese has virtually no influence on the activity coefficients of silicon or oxygen.= In this paper, an explanation for the role of manganese is suggested and equations are devised for quantitatively describing this influence. DISCUSSION Hilty and crafts4 equilibrated their melts under an argon atmosphere and the system established equilibrium with a self-generated slag which was not always the oxide of lowest free energy. Drawing on the early work of Korber and Oelsen,3 it was reasoned that the formation of complex Fe-Mn-silicates

Jan 1, 1963

By J. Chipman, M. N. Dastur

The importance of dissolved oxygen as a principal reagent in the refining of liquid steel and the necessity for its removal in the finishing of many grades have stimulated numerous studies of its chemical behavior in the steel bath. From the thermodynaniic viewpoint the essential data are those which determine the free energy of oxygen in solution as a function of temperature and composition of the molten metal. A number of experimental studies have been reported in recent years from which the free energy of oxygen in iron-oxygen melts can be obtained with a fair degree of accuracy for temperatures not too far from the melting point. Certain discrepancies remain, however, which imply considerable uncertainty at higher temperatures; also several sources of error were recognized in the earlier studies. It has been the object of the experimental work reported in this paper to reexamine these sources of uncertainty and to redetermine the equilibrium condition in the reaction of hydrogen with oxygen dissolved in liquid iron. The reaction and its equilibrium constant are: H2 (g) + Q = H2O (g); K1 _ PH2O / [1] Ph2 X % O Here the underlined symbol Q designates oxygen dissolved in liquid iron. The activity of this dissolved oxygen is known to be directly proportional to its concentrationl,2 and is taken as equal to its weight percent. The closely related reaction of dissolved oxygen with carbon monoxide has also been investigated:3,4,5 co (g) +O = CO?(g); K _ Pco2___ [2] K2= pco X % O [2] The two reactions are related through the wat,er-gas equilibriuni: H2 (g) + CO2 (g) = CO (g) + H2O (g); K2 = PCO X PH2O [3] PH2 X PCO2 and with the aid of the accurately known equilibrium constant of this reaction, it has been shown5 that the experimental data on reactions [1] and 121 are in fairly good, though not exact, agreement. Experimental Method Great care was taken to avoid the principal sources of error of previous studies, namely, gaseous thermal diffusion and temperature measurement. The apparatus was designed to provide controlled preheating of the inlet gases and to permit the addition of an inert gas (argon) in controlled amounts, two measures found to be essential for elimination of thermal diffusion. A known mixture of water vapor and hydrogen was obtained by saturating purified hydrogen with water vapor at controlled temperature. This mixture, with the addition of purified argon, was passed over the surface of a small melt (approximately 70 g) of electrolytic iron in a closed induction furnace. After sufficient time at constant temperature for attainment of equilibrium the melt was cooled and analyzed for oxygen. GAS SYSTEM A schematic diagram of the apparatus is shown in Fig 1. Commercial hydrogen is led through the safety trap T and the flowmeter F. The catalytic chamber C, held at 450°C, was used to convert any oxygen into water-vapor. A by-pass B with stopcocks was provided so that the hydrogen could be introduced directly from the tank to the furnace when desired. From the catalytic chamber the gas passed through a water bath W, kept at the desired temperature by an auxiliary heating unit, so that the gas was burdened with approximately the proper amount of water vapor before it was introdvced into the saturator S. All connections beyond the catalytic chamber were of all-glass construction. Those connections beyond the water bath were heated to above 80°C to prevent the condensation of water vapor. After the saturator, purified argon was led into the steam-hydrogen line at J, and finally the ternary mixture was introduced into the furnace. THE SATURATOR The saturator unit comprised three glass chambers, as shown in Fig 1, the first two chambers packed with glass beads and partially filed with water and the third empty. Each tower had a glass tube with a stopper attached for the purpose of adjusting the amount of water in it. The unit was immersed in a large oil bath, which was automatically controlled with the help of a thermostat relay to constant temperature, ± 0.05ºC, using thermometers which had been calibrated against a standard platinum resistance thermometer. The performance of the saturator over the range of experimental conditions was checked by weighing the water absorbed from a measured volume of hydrogen; the observed ratio was always within 0.5 pct of theoretical.

Jan 1, 1950

By C. W. Sherman, N. J. Grant

The correlation of the high temperature chemical properties of slag-metal systems with some easily measured property of either slag or metal at room temperature has been the goal of both process metallurgists and melting operators for many years. There are several rapid methods for estimating various constituents in steel in addition to the conventional chemical methods which are quite fast, but these do not reveal the nature of the slag as a refining agent, which is of primary interest to the steelmaker. Furthermore, there are several methods for examining slag, the three principal ones being slag pancake, petrographic examination, and the previously mentioned chemical analysis. The main objection to the last two is the lime required to make a satisfactory estimate of the mineralogical or chemical components. The objection to the first is the inadequacy of the information obtained. A new technique has been developed by Philbrook, Jolly and Henry1 whereby the properties of slags are evaluated from an aqueous solution leached from a finely divided sample of slag. It is known that the pH or hydrogen ion concentration (of saturated solutions that have dissolved certain basic oxides, notably calcium oxide) will indicate a pronounced basicity. Philbrook, Jolly and Henry devised the pH measurement technique in order to supply open hearth operators with a fast, reasonably accurate method of estimating slag basicity. They offered the method as an empirical observation and made no claims as to its theoretical justification. The results were presented as an experi-metally observed relationship which applied over an important range of basic open hearth slags. They found that, in plotting the measured pH against the basicity, the best relationship existed between the pH and the log of the simple V ratio, CaO/SiO2. Extensive investigation also showed that there were several variables in the experimental technique that influenced the results and necessitated following a standard procedure to obtain reproducible pH readings. These variables were: 1. Particle size of the slag powder used. 2. Weight of sample used per given volume of water. 3. Time of shaking and standing allowed before the pH was measured. 4. Exclusion of free access of atmospheric carbon dioxide to the suspension. 5. Temperature of the extract at the time the pH was measured. In subsequent investigations of the pH method by Tenenbaum and Brown2 and by Smith, Monaghan and Hay3 the general conclusions of Philbrook's work were reaffirmed. It was the object of the present investigation to extend the technique to a point where it could be used to evaluate slags of all types. Experimental Results PARTICLE SIZK OF SLAG POWDER A large sample of commercial blast furnace slag of intermediate basicity (V-ratio 1.15) was selected for the study. The slag had been put through a jaw crusher until all of it passed through a 20 mesh screen. Five fractions of this crushed material were separated, -20 to +40, -40 to +60, -60 to +100, -100 to +200, and -200 mesh. A representative sample of 0.5 g was removed from each fraction and the pH determined using the method of Philbrook. Check pH analyses on the sample fractions varied due to the different amounts of shaking. To eliminate this variable, a mechanical shaker was employed. In order to know the exact time of contact between the slag and water, it was found necessary to filter the extract at the end of the shaking period. Using the mechanical shaker and a filtering apparatus, similar runs were made on the five fractions for contact times of 5, 10, 20, and 40 min. Random checks gave reproducible results within 0.02 pH. The data are plotted in Fig 1. It can be seen from the plot that each slag fraction is hydrolyzed to an extent that is roughly proportional to the surface area exposed to the water. The (—100 to +200) mesh material changed very little in pH after 10 min. shaking time. The curves are symmetrical and lie in proper relation to one another. The —200 mesh curve appears to be somewhat flatter than the others, but this can be attributed to the portion of very fine material that is not present in the other fractions. The closeness of the (-100 to +200) mesh curve to the —200 mesh curve and the fact that a —100 mesh sample would contain amounts of slag down to 1 or 2 microns in diam were considered sufficient reasons for selecting a —100 mesh sample as representative of the whole sample of slag for the purposes of this investigation.

Jan 1, 1950

By P. D. S. St. Pierre

IN recent years the use of high sulphur fuels and charges in steelmaking has necessitated rapid methods of slag control in order to insure the production of high quality steel. Several systems of control have been discussed in the literature, and of these the method described by Philbrook, Jolly, and Henry' has received the most attention recently. In their process the hydrogen ion concentration of an aqueous slag suspension is determined under controlled, but arbitrary conditions. The basicity of the slag may then be derived from a previously established pH-V ratio curve. Thus, by measuring the pH, some indication of the V ratio is gained, from which significant properties of the slag may be deduced. Philbrook et al. made no claims as to the theoretical justification of their treatment, but simply offered it as a rapid means of slag control. Encouraging results caused others to study the method and publish their findings.2-5 Although there was fair agreement on the efficacy of the method, no common parameter was evolved against which pH readings could be plotted. The results of the various determinations were related to such V ratios as CaO/SiO2 and CaO/ SiO2 + P2O5 by some,'-3 while others" plotted against "excess lime." Rivet,' however, found a simple proportionality between the hydrogen ion concentration and the sulphur content of the molten steel beneath the slag. Since slag control in North American practice is largely directed toward the efficient removal of sulphur from steel, Rivet's approach to the problem had the advantage of connecting directly a property of the slag with the impurity being removed. In view of the diversity of parameters used it seemed probable that some fundamental point was being overlooked in seeking a relationship. Examination of the literature revealed that much emphasis had been laid on experimental detail but scant attention paid to the fundamental aspects of the hydrolysis of the aqueous slag suspension. Consequently the present investigation was undertaken with the object of rectifying this deficiency and deriving, if possible, a parameter of general application. Petrographic studies on several matured Canadian open-hearth steel slags have shown that their major constituents are dicalcium and tricalcium silicates set in a complex matrix of iron oxides and ferrites. These phases are shown in Figs. 1 and 2. Free lime is frequently encountered in slags, but is not an equilibrium phase since on continued heating it dissolves forming silicates or ferrites. Thus, it appeared that a study of the hydrolysis of the major phases in steel slags would be profitable. The experimental technique used in the present work was a modification of that described by the other workers.'- Electrical conductivity measurements were also made on the suspensions, since Smith et al." had claimed advantages for this method in their paper on slag control. Experimental Procedure The compounds studied in this investigation were prepared in the laboratory by heating purified oxides

Jan 1, 1954

By D. J. Carney, E. C. Rudolphy

IT has been demonstrated that inclusion size, distribution, and composition affect the machin-ability of resulphurized steels. Merchant and Zlatinl concluded that large sulphide inclusions aided machining by forming a (lubricating) coating on the tool face. Boulger et al.² and Van Vlack³ noted that the size, distribution, and composition of the inclusions in the steel affected the machinability. Steel specimens containing large globular sulphide inclusions usually exhibited excellent cutting properties, while machinability was adversely affected by the presence of numbers of oxide-type inclusions. Consequently a thorough knowledge of all the factors which affect the inclusions in the final product is desirable. Since almost all the inclusions have their origin in liquid steel, it was necessary to begin a study of inclusions in free-machining steels by studying the inclusions and chemical segregation in the as-cast ingot. Very little information is available on the size, distribution, shape, and composition of inclusions in large, capped, free-machining steel ingots, particularly the B1113 grade. Gregory and Whiteley4 made a general study of the inclusions in a small, high sulphur, free-machining steel ingot. Also, numerous authors have described the solidification and segregation characteristics of the four basic types of steel ingots, namely, rimmed, capped,7 semikilled,7,8 and killed7,9,10 ingots. Most of these studies were made with plain carbon or low alloy, low sulphur steel. It was desirable to study not only the ingot but also the change in size, shape, and number of inclusions on rolling an ingot to a bloom and thence to a billet. This procedure was followed and it is hoped that this study may serve the dual purpose of adding to the general knowledge of ingot solidification as well as contributing to the knowledge of the size, shape, distribution, and composition of inclusions from the ingot to the billet in a high sulphur, free-machining steel. Procedure A 12.000-lb 23x35x75 in. slab ingot of the B1113 grade was cast, sectioned, and studied both macro-scopically and microscopically. An adjacent ingot from the same heat and of the same size was rolled to a 77/8x77/8 in. bloom and thence to a 21/2x21/2 in. billet. These various bloom and billet sections were also sectioned and studied macroscopically and microscopically. Sectioning the Ingot: The ingot herein described was obtained from the United States Steel Corp.'s South Works Bessemer Blow No. 0193, a B1113 mechanically capped heat. The 23x35 in. ingot (No. 2) was teemed according to normal procedures and after stripping and transportation to the rolling mill was not placed in the soaking pit but allowed to air cool in an upright position. When completely solidified, the ingot was cut into sections by means of a powder scarfing torch and further sectioned by saw cutting as indicated in Fig. 1. Cut No. 2 (1x10x12 in.) from sections A through H was cleaned thoroughly, macroetched in a solution of 50-50 water and hot muriatic acid and used to obtain a macrograph of a horizontal section from the surface to slightly beyond the center of the 23-in. ingot dimension. Cuts No. 5 and 3 (lx81/2xl0 in. each) from sections A through H were treated in a similar manner to obtain a macrograph of a horizontal section from the surface to slightly beyond the center of the 35-in. ingot dimension. The composite macrograph of these horizontal ingot sections, which shows a vertical section of the ingot from top to bottom, is shown in Fig. 2. It should be noted that sections No. 2 are normal to sections 5 and 3 in the composite. Drillings for chemical analyses were obtained from selected positions within the above-mentioned ingot sections as noted in Fig. 3. The oxygen content was determined by the vacuum-fusion method. Samples for microscopic examination were cut from

Jan 1, 1954

By Claude H. P. Lupis, John F. Elliott

WAGNERL described the thermodynamic behavior of a metallic solution consisting of the solute components 2, 3,... at very dilute concentrations in the solvent, 1, in terms of the excess partial molar free energy, or alternatively the logarithm of the activity coefficient. In the Taylor expansion of FiE, by neglecting the second- and higher-order differential terms, he obtained the excess partial molar free energy as a linear function of the composition:

Jan 1, 1965

By W. W. Mullins

The development, by the mechanism of volume diffusion, of a grain boundary groove on an interface separating a solid phase and a saturated fluid phase is calculated under the following assumptions: 1) isotropy of the interfacial free energy 's, 2) applicability of the Gibbs-Thompson formula relating curvature and chemical potential, 3) a nearly planar groove surface. The groove profile is found to have a .fixed shape and linear dimensions that are proportional to (time)1/3. The constant of proportionality is evaluated and involves ?s in such a way that the latter my be evaluated from grooving kinetics. A grain boundary that intersects an interphase interface will tend to produce a groove along the line of intersection (Fig. 1). The ultimate motivation for the formation of the groove is the reduction in interfacial free energ that occurs as the grain boundary contracts. Smith has discussed the way in which the free energy of the interfaces determines their dihedral angles at the groove root and has given a detailed analysis of the effect of the dihedral angles upon the nature the microstructures developed in polyphase alloys. Herring2 has extended the considerations to the case in which the free energy of an interface depends on its orientation and has thus added torque terms to the condition for interface equilibrium. Although the grain boundary and the interphase interface may quickly achieve the proper equilibrium angles where they intersect, as determined by the balance of equivalent tensions and torques,"2 the groove will generally continue to grow (though with decreasing speed). Thermodynamically, this continued growth reflects the fact that the lowest free energy cannot be achieved until the entire grain boundary has been eliminated; mechanistically, the growth occurs in response to inhomogeneities of chemical potential that are caused by the constraint of fixed dihedral angles at the groove root. The latter point is illustrated in Fig. 1, which shows that atoms* near the groove are on the convex side of a cylindrically curved surface and therefore have a higher chemical potential than atoms on the flat interface beyond. Thus atoms tend to leave the curved groove shoulders and force the groove to deepen. When both phases are solid additional chemical potential gradient may arise from whatever strain fields are necessary to insure continuity of material across the interface. In the discussion that follows, this complication due to strain will not occur since we always assume one phase to be a fluid and the other a solid. The transport processes that may operate to permit growth of the groove are surface (interface)* diffusion, volume diffusion in the phase on either side of the interface, and evaporation-condensation when one phase is gaseous. (Also a melting-freezing process is responsible for groove enlargement on a solid-melt interface as discussed in Sec. VI). The theory of grain boundary grooving has been discussed in detail for the processes of surface diffusion and of one type of evaporation-condensation.3'4 The theoretical predictions for the mechanism of surface diffusion have been confirmed in an experimental study of grooving kinetics in copper.5 In this paper, the theory of groove development by volume diffusion will be presented. Volume diffusion can occur either by atomic migration in the solid S or by diffusion of S atoms in the fluid phase, or solvent, adjacent to the groove surface. As discussed in Sec. V, volume diffusion in the solid should be less important than surface diffusion in forming a groove. Apart from verifying this statement then, the main interest of the present analysis centers on diffusion in an external solvent. The solvent may be either a liquid (e.g., water, or-

Jan 1, 1961

By D. J. Rose, W. M. Armstrong, A. C. D. Chaklader

The wetiability of single crystals of MgO by specimens of vacuum-cast iron was studied using the sessile drop technique in vacuo at 1550ºC. Formation of FeO at the liquid-vapor interface caused the contact angle (6) to decrease from 117 to 65 deg during the first minute. After cooling, all specimens possessed a peculiar annular interfacial deposit of Fe,O,. Within the annulus the interface showed no sign of chemical attack. Chemical reaction occurred where the iron was alloyed with Ti, V, Cr, Nb(Cb), Ta, cmd Zr. Vnriation of 6 with alloy concentration was studied. Although vanadium md chromium improved the wettability of MgO by iron, the effect of Zr, Ti, Nb, and Ta was indeterminable because the 8 derived from sessile drop considerations was that of the metal against a restrictive peripheral volume of liquid oxide wetting the substrate. INTEREST in the nature of metal-ceramic interactions has been stimulated by progressive development of metal-ceramic combinations. One of the more valuable methods used for bond investigation is the sessile drop technique. Recent attempts to improve wettability through solute additions to the drop have revealed that the solute may a) react with the oxide creating new compounds at the solid-liquid interface, b) adsorb at the interface in a monolayer formation, or c) distribute throughout the drop uniformly causing no wettability variation. This work, part m in a series1,2 of investigations of interface reactions between metals and ceramics, embraces a study of the Fe-MgO system. MgO possesses a large negative free energy of formation (-173 kcal per g mole 0, at 1550ºC) compared to FeO at this temperature (-73 kcal per g mole 02). Hence the electronegativity difference between the drop and substrate allows selection from an extensive group of metal solutes with intermediate electronegativity differences that would, in the absence of chemical reactions, be expected to adsorb pre- ferentially at the solid-liquid interface. However, the high oxygen pressure of MgO in vacuo creates an oxidation environment which influences the solute behavior. Recent studies of the Fe-MgO systemJ74 have been restricted by chemical reactions that obscured observations. In view of the current interest in liquid-phase sintering of metal-ceramic combinations under partial oxidizing conditions,5 a more comprehensive study of the Fe-MgO system seemed beneficial. EXPERIMENTAL PROCEDURE 1) Specimen Preparation. Optical-grade MgO single crystals and Ferrovac vacuum-cast iron were used in all experiments. A spectrographic analysis of the iron indicated 0.008 C, 0.05 V, 0.005 Mo, 0.01 Ti, 0.002 S, 0.01 Cr, 0.001 Mg, 0.01 Si, 0.003 A1 (wt pct). The MgO crystals were cleaved along (100) planes into plates approximately 20 by 20 by 1 mm. Following annealing in vactto at 1100°C for 3 hr, surface irregularities were removed by a chemical etch in phosphoric acid at 100°C. The iron rod was machined into small cylinders approximately 0.250 in. in diam and length and these were carefully cleaned in organic and acidic solutions to remove surface impurities. All specimens were weighed to the nearest 0.1 mg. 2) Apparatus. The apparatus described in detail by previous authors1,2 was modified for this work. A Polaroid Land Camera was incorporated into the optical system so that drop measurements at ten-second intervals after melting were possible with ultra-high-speed self-develop ing film. 3) Procedure. The iron cylinders were placed upright on the MgO plates and positioned in the molybdenum susceptor. After furnace assembly the system was pumped down to a vacuum of 1 µ and flushed with H2 at 800°C. The system was again evacuated to 5 x 10-5 mm of mercury and the temperature raised to 1550°C within 2 min. The molten drops were photographed at appropriate time intervals. TWO min after melting the iron vapor pressure caused gas discharge, or corona, within the tube. The specimens were then slowly cooled to room temperature, sectioned and examined metallographi-cally. X-ray identification of interfacial reaction products was attempted by the powder diffraction technique. Alloying elements (Ti, V, Cr, Zr, Ta, Nb) were added to the iron in various concentrations up

Jan 1, 1963

By A. E. Jenkins, L. A. Baker, N. A. Warner

The electromagnetic levitation technique has been successfully applied to rate studies of the de-carburization of liquid Fe-C alloys from 5.5 to zero pct C at 1660°C using gas mixtures containing 1 to 100 pct CO2 with CO or helium as diluents. The rate was shown to be independent of carbon concen -tration in the melt and only slightly affected by total pressure. The results were shown to be consistent with control either wholly or predominantly by gaseous diffusion. As well as avoiding side reactions with the crucible, levitation allowed precise calculation of reaction rates since the geometry of the system was accurately known. It also enabled interpretation using the established mass-transfer correlations for a gas flowing past a single sphere, The existence of gaseous-diffusion control and the extremely high rates of reaction reported for gas flowing past small spheres are of great practical significance in relation to current investigations into the use of spray-refining techniques in continzcous steelmaking. PREVIOUS work on the kinetics of carbon removal from liquid iron has generally involved the use of oxygen as the gaseous oxidant. Investigations have been made on commercial steelmaking furnaces and in addition laboratory-scale experiments have been attempted with a slag phase present. The general lack of agreement and the obvious difficulty in interpreting the results is at least partly due to the complexity of the systems used. This work has been reviewed by carter1 and more recently by Bods-worth2 and ward.3 The gas-liquid metal reactions have also been studied with slag-free melts by the conventional technique of blowing oxygen onto the melt contained in a crucible. The reaction between the oxidant and carbon could be followed by sampling either the melt or the gas phase. Side reactions with the crucible material have precluded direct interpretation of the results. Fujii, 5-7 using O-A mixtures, attempted to correct for the crucible reaction and reported that the reaction between carban and oxygen occurred at the melt surface and was controlled by gaseous diffusion for carbon contents greater than a critical value and by carbon-diffusion control in the metal for carbon contents less than the critical. The critical value was given as approximately 0.15 pct C. However, whereas this was the case for oxygen contents in the gas stream up to 10 pct, between 10 and 20 pct the rate was found to be approximately independent of oxygen content, and Fujii attempted to explain this observation by postulating the presence of an oxide "film".7 Turkdogan et a1.' have studied iron fuming during decarburizing and suggested gaseous-diffusion control of the reaction above a critical carbon concentration, given as approximately 2 pct C. Filippov9-12 reports in a similar manner to Fujii but makes no mention of the crucible reaction with the carbon in the melt, even though this would be expected with the temperature, crucible material (MgO), and carbon contents used. Both CO2 and O2 were used as oxidant gases. In the present work the decarburization of liquid Fe-C alloys was studied using an adaptation of the electromagnetic levitation technique, and thus the complexities introduced by crucible side reactions were eliminated. In this technique a single sphere of the Fe-C alloy is freely suspended and heated by electromagnetic induction in a flowing stream containing the oxidant gas. The full range of carbon levels up to saturation was studied, the temperature of the melts in this instance being held constant at 1660°C. The oxidant was CO2 which was used either pure or in association with a diluent gas, the total gas pressure being maintained either at 1 atm or at a reduced pressure. Thus the reaction under study was:

Jan 1, 1964

By R. D. Pehlke, P. D. Goodell, R. W. Dunlap

The rate of dissolution of steel bars in molten pig iron has been measured experimentally in the temperature range 2300° to 2650° F. The rate of solution is shown to be a .function of bath composition, temperature, and stirring. A kinetic model based on carbon diffusion in the liquid phase has been derived to fit the experimental results. THE rate of scrap melting has long been an important variable in steelmaking operations. With the advent of the oxygen steelmaking process and the accompanying shorter heat times, the rate of scrap melting has now become one of the rate-limiting factors in steel production. As observed in commercial practice, the solution rate is influenced by the compositions of liquid and solid, the temperature, agitation, and time. However, no definitive work has been done on the Fe-C system, and there is very little information in the literature regarding the relative effects of these variables in steelmaking systems. A number of questions have been raised in regard to scrap utilization in basic oxygen steelmaking operations. Consideration has been given to the optimum size and shape of scrap, and to the use of preheated scrap as a means for decreasing the pig-iron requirement in oxygen blowing. The determination of an optimum scrap practice for a specific installation depends to a large extent upon the economics of the scrap market and also upon the behavior of scrap in the vessel. The present research was undertaken as a preliminary study in evaluating the behavior of steel in a pig-iron bath under various conditions of temperature, composition, and agitation, as might be encountered in oxygen converter operations or in any steelmaking operation where scrap behavior is an important process variable. Related studies have been carried out on non-ferrous systems. The solution rate of solid aluminum in a molten A1-Si alloy has been studied.' Furthermore, the increasing use of liquid metals has created considerable interest in studies related to dissolution of a solid in a liquid, or mass transfer taking place between a solid interface and a liquid metallic phase.2-10 In an effort to clarify the relative importance of factors influencing the dissolution of scrap in Fe-C alloys, this paper presents the results of a study of the rate of dissolution of a low-carbon steel cylinder in a molten Fe-C bath at various bath compositions, temperatures, and conditions of agitation. An attempt has been made to determine the mechanism of solution, and a model has been derived to fit the experimental results. The rate of heat transfer between the molten pig-iron bath and the solid-steel cylinder has also been studied. EXPERIMENTAL PROCEDURE A molten bath of pig iron (nominal composition 4.2 pct C, 0.5 pct Mn, 0.8 pct Si)* was held in a 200- *In view of the fact that the composition of the pig-iron bath was slowly changing with time because of steel dissolution and reaction with the surrounding atmosphere, intermittent samples of the liquid bath were taken throughout each experiment, Table 1. lb induction melting unit. The internal diameter of the furnace was 8-1/2 in. and the bath depth approximately 14 in. Cold-finished 1020 steel cylinders of 1/2-, 3/4-, 1-, 1-1/2-, and 2-in. diameters were cut into 1 -ft lengths for use as test specimens. One end of each bar was machined to fit a hand-driven, mechanical stirring device which rested on top of the furnace. This fixture permitted 7 to 8 in. of the bar to be immersed in the melt. The steel cylinders were cleaned to free the surface of grease and oxide. The rods, at ambient temperature, were immersed into the molten pig-iron bath. The melt temperatures studied in this investigation were 2300°, 2500°, and 2650°F. Different agitation conditions were achieved by operating with a) the power to the furnace, giving induction stirring; b) induction stirring plus mechanical stirring, using hand rotation with a chain and sprocket assembly at approximately 200 rpm; c) mechanical stirring alone with the power off; and d) the power off and no mechanical stirring resulting in minimum agitation, i.e., only that caused by natural convection currents in the bath. The samples were immersed in the melt for prescribed times ranging from 30 sec up to 6 min. Immersion times were measured with a stopwatch and temperature control of the melt was achieved by power adjustment following temperature measurement with an optical pyrometer. The measurements with the calibrated pyrometer were checked out to within less than 10°F with simultaneous thermocouple measurements. Following immersion, the bars were water-quenched and the diameters were measured with a micrometer at several positions on the reduced area, and by volumetric displacement. The dissolution rates calculated from the

Jan 1, 1965

By N. A. Gokcen, M. N. Dastur

In metallurgical process industries a knowledge of true melting and casting temperatures is very essential for increasing the operating efficiency as well as improving the quality of the finished product. Optical pyrometers are widely used for the purpose because of their cheapness and ease of operation. It is an unfortunate fact, however, that this mode of measuring temperature entails a source of severe error inasmuch as with all non-black bodies, the temperature observed is always below the true temperature owing to deficient emissive power. Hence, the need for emissivity correction arises. In 1913 Bidwell1 obtained emissivity values of 0.36-0.48 for a temperature range of 1520-1800°C. He measured the true temperature of molten iron by sighting into a carbon cavity immersed in the iron under an atmosphere of hydrogen. In 1914 Burgess2 determined the emissivity of a smooth surface of liquid iron free from oxide to be 0.37 under an atmosphere of hydrogen. He claimed to have attained an accuracy of within 5°C at 1500°C with an optical pyrometer using monochromatic light. He reported that no difference appeared to exist between the emissivities of pure iron and of steels containing considerable percentages of carbon, nickel or manganese; nor was there any appreciable variation of emissivity with temperature from 1530 to 1571°C. Wensel and Roeser3 found an elnissivity value of 0.4 for temperatures above 1375°C for cast iron. The average emissivity value for carbon steels reported by Leiber,4 odd,5 Hase6 and Umino7 range from 0.4 to 0.45. Knowles and Sarjant8 made an extensive study of emissivity of molten iron and steel over a wide range of workshop and laboratory conditions. Observations of true temperature were made with immersion thermocouples, and correlated with apparent temperatures indicated by optical pyrorneter readings taken on the pouring stream as it passed over the lip of the crucible. The emissivity of Armco iron was shown to be of the order of 0.4, rising slightly with increasing temperature. But for plain carbon steels containing up to 1.0 pct carbon the emissivity was shown to fall slightly with increasing temperatures. The results of their investigation are in agreement with those of Guthmann.9 Naeser,10 Spencer," Todd5 and Hase6 in regard to the relation between emissivity and temperature for plain carbon steels. However, Goller12 has found a rise of emissivity with increasing temperature for the same steels. Results of several investigations are given in Fig 1. Measurement of True and Apparent Temperatures The necessity for an accurate optical temperature scale for liquid iron in studies of gas-metal equilibria led to this investigation. Experimental measurements were carried out in the induction furnace used by Dastur and Chipman13 in their studies of the reaction of hydrogen with oxygen in liquid iron. The furnace as modified for this work is shown in Fig 2. The atmosphere of the furnace was a mixture of purified argon with hydrogen containing a small controlled amount of water vapor. Gases were preheated by means of a platinum-10 pct rhodium resistance coil. The stream of hydrogen sweeping across the surface of niolten iron vir-

Jan 1, 1950

By B. M. Larsen, T. E. Brower, J. W. Bain

A mass of circumstantial evidence is presented to indicate that the main source of alloy losses in open-hearth tapping is oxidation by air, with the steel apparently reacting with an amount of oxygen equivalent to about 30 times its own volume of air. The effect is erratic from heat to heat, depending largely on turbulence and distance of free fall of the stream of liquid metal. THIS paper reports another phase in a general study of oxidation in the open-hearth, various aspects of which have already been discussed in previous papers.1,2,3 It is based on experiments conducted on commercial, basic open-hearth furnaces at various times when opportunity offered, beginning about 1938, in an attempt to determine the mechanism and measure the amount of air oxidation during the flow of the tapping stream through the air into a ladle. This effect is closely connected, not only with alloy losses and control of chemical analysis, but possibly with various questions regarding inclusion content and steel quality and with a true picture of the deoxidation of steel in general. Thus it is believed that discussion of a large part of the results to date may be of assistance to others who are studying problems related to deoxidation or to steel cleanliness and quality. The literature reveals that strangely little attention has been devoted specifically to the effect of pouring steel through open air. Bardenheuer and Henke4 in 1939, in a paper devoted largely to overall losses of manganese in the basic open-hearth, reported that for a number of heats tapped into a tilted ladle held just beneath the runner so that the maximum distance of drop of the stream through the air was held to less than about 30 in., there was in most cases almost no loss of manganese from furnace to ladle. Hultgren,5 in 1945, showed that in high-carbon basic electric steel deoxidized in the furnace and containing no large inclusions as it left the furnace, large silicate inclusions, often rich in manganese oxide, were present in samples dipped from the pool in the ladle; also that the rise in content of large inclusions (above 0.01 mm dim) was greater when the metal stream was made to spray or flow in a turbulent manner. Our interest in this phase of oxidation in the open-hearth was first aroused by a study of alloy efficiencies on ladle additions. The frequency curves of manganese efficiency (net recovery of metal added in ladle) given in fig. 1 are of interest in this connection. Lowest, and also most variable (47 to 95 pct), recovery was in low-carbon heats having no coal additions to the ladle, progressing upward to a maximum average and least variable (82 to 97 pct) recovery in high-carbon heats killed with aluminum and silicon. Both coal additions and higher carbon contents in the tap stream, as well as additions of silicon and aluminum, help to lower the amount of manganese loss. But the most interesting point is the amount of manganese oxidized in many heats tapped at 0.50 to 1.06 pct carbon. It has been shown in a previous paper3 that the amount of oxygen in the tap stream in such heats is very small, usually below 0.01 pct, too small to oxidize any appreciable amount of manganese. Also, the fact that manganese should be oxidized at all in a metal solution containing such more stable oxide-forming elements as aluminum and silicon is an indication of some rather intense oxidizing effect such as could be caused by reaction with the air during ladle filling. Oxygen Balances from Tap Stream to Teeming Stream: Data in the form of alloy efficiencies, such as those shown in fig. 1, are not a proper measure of such a general oxidation effect. Having available

Jan 1, 1951

By W. M. McKewan

Magnetite pellets were reduced in flowing hydrogen at pressures up to 40 atm over a temperature range of 350° to 500°C. The rate of weight loss of oxygen per unit area of the reaction surface was found to be constant with time at each temperature and pressure. The reaction rate was found to be directly proportional to hydrogen pressure up to 1 atm and to approach a maximum rate at high pressures. The results can be explained by considering the reaction surface to be sparsely occupied by adsorbed hydrogen at low pressures and saturated at high pressures. PREVIOUS investigation1,2 have shown that the reduction of iron oxides in hydrogen is controlled at the reaction interface. Under fixed conditions of temperature, hydrogen pressure, and gas composition, the reduction rate is constant with time, per unit surface area of residual oxide, and is directly proportional to the hydrogen pressure up to one atmosphere. The reduction rate of a sphere of iron oxide can be described3 by the following equation which takes into account the changing reaction surface area: where ro and do are the initial radius and density of the sphere; t is time; R is the fractional reduction; and R, is the reduction rate constant with units mass per area per time. The quantityis actually the fractional thickness of the reduced layer in terms of fractional reduction R. It was found in a previous investigation2 of the reduction of magnetite pellets in H2-H,O-N, mixtures, that the reaction rate was directly proportional to the hydrogen partial pressure up to 1 atm at a constant ratio of water vapor to hydrogen. Water vapor poisoned the oxide surface by an oxidizing reaction and markedly slowed the reduction. The enthalpy of activation was found to be + 13,600 cal per mole. It was also found that the magnetite reduced to meta-stable wüstite before proceeding to iron metal. The following equation was derived from absolute reaction-rate theory4,8 to expfain the experimental data: where Ro is the reduction rate in mg cm-2 min-'; KO contains the conversion units; Ph2 and PH2O are the hydrogen and water vapor partial pressures in atmospheres; Ke is the equilibrium constant for the Fe,O,/FeO equilibrium; Kp is the equilibrium constant for the poisoning reaction of water vapor; L is the total number of active sites; k and h are Boltzmann's and Planck's constants; and AF is the free energy of activation. Tenenbaum zind Joseph5 studied the reduction of iron ore by hydrogen at pressures over 1 atm. They showed that increasing the hydrogen pressure materially increased the rate of reduction. This is in accordance with the work of Diepschlag,6 who found that the rate of reduction of iron ores by either carbon monoxide or hydrogen was much greater at higher pressures. He used pressures as high as 7 atm. In order to further understand the mechanism of the reduction of iron oxide by hydrogen it was decided to study the effect of increasing the hydrogen pressure on rebduction rates of magnetite pellets. EXPERIMENTAL PROCEDURE The dense magnetite pellets used in these experiments were made in the following manner. Reagent-grade ferric oxide was moistened with water and hand-rolled into spherical pellets. The pellets were heated slowly to 550°C in an atmosphere of 10 pct H2-90 pct CO, and held for 1 hr. They were then heated slowly to 1370°C in an atmosphere of 2 pct H2-98 pct CO, then cooled slowly in the same atmosphere. The sintered pellets were crystalline magnetite with an apparent density of about 4.9 gm per cm3. They were about 0.9 cm in diam. The porosity of the pellets, which was discontinuous in nature, was akrout 6 pct. The pellets were suspended from a quartz spring balance in a vertical tube furnace. The equipment is shown in Fig. 1. Essentially the furnace consists of a 12-in. OD stainless steel outer shell and a 3-in. ID inconel inner shell. The kanthal wound 22 in. long, 1 1/2, in. ID alumina reaction tube is inside the inconel inner shell. Prepurified hydrogen sweeps the reaction tube to remove the water vapor formed during the reaction. The hydrogen is static in the rest of the furnace. The sample is placed at the bottom of the furnace in a nickel wire mesh basket suspended by nickel wire from the quartz spring. The furnace is then sealed, evacuated, and refilled with argon several times to remove all traces of oxygen. It is then evacuated, filled with

Jan 1, 1962