Nitrogen solubility and aluminum nitride precipitation in liquid iron alloys containing nickel and aluminum

The solubility of nitrogen in liquid iron-base Fe-Ni-Al alloys has been measured up to the solubility limit for formation of aluminum nitride using the Sieverts’ method. Measurements were conducted over the temperature range from 1843 to 2023 K and aluminum concentration range from 1.5 to 3.0 wt pct Al. The effect of nickel additions was determined at 2, 5 and 10 wt pct Ni. The cross interaction parameter describing the effect of nickel and aluminum on the activity coefficient of nitrogen in iron was determined. The first and second order effects of nickel on the activity coefficient of aluminum also were determined. The solubility product of aluminum nitride increases with increasing aluminum content and increasing temperature. Addition of nickel decreases the solubility products of aluminum nitride in lower aluminum content alloys. However, the effect of the cross interaction terme _Al ^NiAl becomes significant with increasing aluminum content and compensates for the effects of the first and second order nickel-nitrogen and nickelaluminum interaction terms. Therefore the effect of nickel additions show little effect on the solubility products of aluminum nitride in higher aluminum alloys.     

Dissolution of boron nitride in liquid iron

The rate of dissolution of boron nitride in liquid iron and Fe-B alloys has been measured using a volumetric technique. The solution process was found to be diffusion controlled and directly related to the concentration of boron in the liquid metal. Diffusion control was substantiated further by experiments utilizing boron nitride rods which were rotated in liquid iron. Formerly Research Associate, Department of Chemical and Metallurgical Engineering, The University of Michigan, Ann Arbor, Mich.     

Equilibria in reactions of CO and CO2 with dissolved oxygen and carbon in liquid iron

Carbon and oxygen activities have been established in molten iron using CO-CO₂ mixtures in the temperature range 1550 to 1750°C. Pressures of up to 70 atm were used to establish the required carbon activities up to carbon saturation at 1550°C in gas mixtures with CO₂ contents between 0.76 and 8.21 pct. The levitation technique was used to avoid any possible contamination and the effect of thermal diffusion in the gas mixture was measured and corrected for. The data obtained on carbon activities fall between those of previous workers at low carbon but measurements have been extended to the much higher carbon concentrations which had not been investigated previously. By using the same CO-CO₂ mixture and varying the total pressure it was possible to measure the effect of carbon on oxygen concentration at fixed oxygen activity and it was found that carbonincreases the activity coefficient of oxygen.     

Equilibria in reactions of Co and Co2 with dissolved oxygen and carbon in liquid iron

Carbon and oxygen activities have been established in molten iron using CO-CO₂ mixtures in the temperature range 1550 to 1750°C. Pressures of up to 70 atm were used to establish the required carbon activities up to carbon saturation at 1550°C in gas mixtures with CO₂ contents between 0.76 and 8.21 pct. The lévitation technique was used to avoid any possible contamination and the effect of thermal diffusion in the gas mixture was measured and corrected for. The data obtained on carbon activities fall between those of previous workers at low carbon but measurements have been extended to the much higher carbon concentrations which had not been investigated previously. By using the same CO-CO₂ mixture and varying the total pressure it was possible to measure the effect of carbon on oxygen concentration at fixed oxygen activity and it was found that carbonincreases the activity coefficient of oxygen.     

Nitrogen solubility and aluminum nitride precipitation in liquid iron,Fe-Cr,Fe-Cr-Ni,and Fe-Cr-Ni-Mo alloys

The nitrogen solubility and aluminum nitride formation in liquid Fe-Al, Fe-Cr-Al, Fe-18 pct Cr-8 pct Ni-Al and Fe-18 pct Cr-8 pct Ni-Mo-Al alloys were measured by the Sieverts' method. The temperature range extended from 1823 to 2073 K, and the aluminum contents from 1.01 to 3.85 wt pct Al. Increasing aluminum content increases the nitrogen solubility. The effect of molybdenum additions was determined for 2, 4 and 8 wt pct Mo levels. The first and second order effects of chromium, nickel, molybdenum and aluminum on the activity coefficient of nitrogen in iron were determined. The first and second order effects of chromium, nickel and molybdenum on the activity coefficient of aluminum also were determined. The nitride precipitates were identified as stoichiometric aluminum nitride, AIN, by X-ray diffraction analysis. The lattice spacing was in good agreement with the ASTM standard patterns for AIN in both higher and lower Al content solutions. The solubility product of AIN increases with increasing aluminum concentration and with temperature in liquid iron and the iron alloys studied. However, the magnitudes of the solubility products of AIN in those alloys are different because of the effects of chromium and nickel additions. Additions of molybdenum show little effect on the solubility product of AIN. The standard free energy of formation of AIN in liquid iron is: δG? = -245,990 + 107.59 \T J/g-molAIN, based on the standard state of the infinitely dilute solution in liquid iron for aluminum and nitrogen, referred to a hypothetical one wt pct solution, and on the pure compound for A1N.     

Nitrogen solubility and aluminum nitride precipitation in liquid iron, Fe-Cr, Fe-Cr-Ni, and Fe-Cr-Ni-Mo alloys

The nitrogen solubility and aluminum nitride formation in liquid Fe-Al, Fe-Cr-Al, Fe-18 pct Cr-8 pct Ni-Al and Fe-18 pct Cr-8 pct Ni-Mo-Al alloys were measured by the Sieverts' method. The temperature range extended from 1823 to 2073 K, and the aluminum contents from 1.01 to 3.85 wt pct Al. Increasing aluminum content increases the nitrogen solubility. The effect of molybdenum additions was determined for 2, 4 and 8 wt pct Mo levels. The first and second order effects of chromium, nickel, molybdenum and aluminum on the activity coefficient of nitrogen in iron were determined. The first and second order effects of chromium, nickel and molybdenum on the activity coefficient of aluminum also were determined. The nitride precipitates were identified as stoichiometric aluminum nitride, AIN, by X-ray diffraction analysis. The lattice spacing was in good agreement with the ASTM standard patterns for AIN in both higher and lower Al content solutions. The solubility product of AIN increases with increasing aluminum concentration and with temperature in liquid iron and the iron alloys studied. However, the magnitudes of the solubility products of AIN in those alloys are different because of the effects of chromium and nickel additions. Additions of molybdenum show little effect on the solubility product of AIN. The standard free energy of formation of AIN in liquid iron is: δG‡ = -245,990 + 107.59 \T J/g-molAIN, based on the standard state of the infinitely dilute solution in liquid iron for aluminum and nitrogen, referred to a hypothetical one wt pct solution, and on the pure compound for A1N.     

Titanium deoxidation reactions in liquid iron

Abstract

An experimental study has been made of the equilibrium between titanium and oxygen in liquid iron at 1625° and 1700°C. Equilibrium was established between liquid Fe-Ti-O alloys held in Ti₃O₅ or Al₂O₃ crucibles and water vapor-hydrogen gas mixtures which were used to control the oxygen potential of the melt. The gas mixture was bubbled through the melt to give good gas-metal contact and to avoid thermal diffusion effects. In the reaction

Ti₃O₅(s) + 5H₂(g) ? 3 Ti + 5H₂O(g)

equilibrium was attained both by reduction of the solid oxide crucible and by oxidation of titanium in the alloy. Quenched samples obtained by suction into SiO₂ tubes were analyzed chemically for titanium and by vacuum fusion for oxygen. X-ray diffraction techniques were used to identify the products of deoxidation. Thermodynamic data for Fe-Ti-O alloys are presented and the use of SiO₂ sampling tubes at low oxygen potentials is discussed. Results are compared with published data and it is suggested that titanium decreases appreciably the activity coefficient of oxygen in liquid iron and that the deoxidizing power of titanium is closer to that of aluminum than that of silicon or vanadium.

Résumé

Les auteurs ont étudié l'équilibre entre le tatane et l'oxygène dans le fer liquide à 1625 et 1700°C. Des mélanges vaporeux d'eau-hydrogène ont servi à contrô1er le potentiel d'oxygène dans les alliages liquides Fe-Ti-O dans des creusets de Ti₃O₅ ou de Al₂O₃. Le mélange gazeux circulait à travers le bain liquide pour favoriser les échanges gaz-métal et éviter des effets de diffusion thermique.

Le point d'équilibre de la réaction:

Ti₃O₅(s) + 5H₂(g) ? 3 Ti + 5H₂O(g)

a été atteint par réduction du creuset d'oxyde solide et par oxydation du titane de l'alliage. Le titane a été dosé par voie chimique et l'oxygéne par fusion sous vide. Les échantillons pour le dosage ont été prélevés par aspiration de l'alliage dans des tubes de silice. Les produits de désoxydation ont été identifiés par diffraction des rayons-X. Les auteurs présentent des données thermodynamiques et discutent de l'utilisation des tubes de silice pour l'echantillonnage.

Ils comparent leurs résultats aux données de la littérature: ils rapportent que le titane abaisse le coefficient d'activité de l'oxygéne dans le fer liquide et que le pouvoir désoxydant du titane se rapproche plus de celui de l'aluminiumque de celui du silicium ou du vanadium.     

Equilibria between liquid Mn-Si alloys and MnO-SiO2-CaO-MgO slags

The activity of silicon in manganese-silicon melts was determined at 1500°C. The results are in general agreement with the thermodynamic data of the iron-silicon system. Equilibria between manganese-silicon melts and slags containing MnO, SiO₂, CaO, and MgO were studied at 1400 and 1500°C in silica and magnesia crucibles. An empirical relationship easy to use in practice was derived, expressing the manganese and silicon distribution ratio between slag and metal as a function of the slag basicity. This relationship describes equilibria pertinent to the silicothermic reduction of manganese oxide and the production of silicomanganese. The present knowledge of the activities in the slag and metal phase is adequate to explain the experimental results. The presence of up to about 10 pct CaF₂ in the slag makes it possible to maintain a higher slag basicity and therefore a lower activity of silica, resulting in lower silicon contents in the metal. Iron contents of up to about 20 pct in the metal cause a slight increase in the silicon content of the metal under otherwise similar conditions. The effect of 1 to 2 pct carbon in the metal on the equilibrium was roughly estimated and found to be almost negligible.     

The diffusion of hydrogen in liquid iron alloys

Rates of absorption of hydrogen in stagnant liquid iron and ten (Fe-X) binary iron alloy systems were studied by an unsteady-state gas-liquid metal diffusion cell technique. These rates were found to be controlled by diffusion of hydrogen in the liquid phase. Chemical diffusion coefficients (D _h) were measured in pure iron and Fe-X alloys in the following (at. pct) composition ranges: Mn (0 to 5), Cr (0 to 25), V (0 to 25), Nb (0 to 10), Mo (0 to 25), W (0 to 5), Ni (0 to 75), Co (0 to 75), Sn (0 to 10), and Cu (0 to 25). All measuredD _H values at 1600°C lie between 7 × 10^-4 and 16 × 10^-4 sq cm per sec. The diffusion coefficients found for pure iron can be represented by D_H ^Fe = 4.37 × 10⁻³ exp (−4134 ± 1012)/RT cm²/sec where the uncertainty in the activation energy, Q, in cal per mole, corresponds to the 90 pct confidence level. A linear relationship was found between the logarithm of the hydrogen diffusion coefficient D_H ^Fe-X and the interaction parameter ε_H ^X for low and medium concentrations of alloying elementX, when applied to a fixed concentration ofX(5 or 25 at. pct) and to individual periods in the periodic table. A useful linear correlation also appears to exist between logD_H ^Fe-X and hydrogen solubility for fixed concentration ofX and with respect to the period in whichX is found. Formerly Research Assistant, Department of Mineral Engineering, Stanford University, Stanford, Calif. This paper is based upon a thesis submitted by P. J. DEPUYDT in partial fulfillment of the requirements of the degree of Doctor of Philosophy at Stanford University and part of a presentation made at the 1970 Annual AIME Meeting.     

Nitrogen solution and titanium nitride precipitation in liquid Fe-Cr-Ni alloys

The solubility of nitrogen in liquid Fe-Cr, Fe-Ni, Ni-Cr, and Fe-Cr-Ni alloys up to 20 wt pct Ni and 40 wt pct Cr was measured by the Sieverts’ method. The first and second order interactions in iron between nitrogen and chromium, and nitrogen and nickel were determined. Chromium increases the nitrogen solubility at lower chromium concentrations but the second order interaction term which is of the opposite sign becomes significant at higher chromium levels and compensates partly for the effect of the first order interaction term. Nickel decreases the nitrogen solubility in iron. Titanium nitride formation in liquid Fe-Cr, Fe-Ni, and Fe-Cr-Ni alloys also was investigated. The first and second order interactions between titanium and chromium or nickel were determined at 1600°C. Chromium increases the solubility product of TiN, principally by decreasing the activity of nitrogen in the melt. Nickel decreases the solubility product of TiN by increasing the activities of nitrogen and titanium.     

Kinetics of reactions between gases and molten alloys of iron

Abstract

Under conditions where transport in the gas phase is rate determiiling, a unified concept of reactions between gases and solutes dissolved in liquid metals may be based on the equilibrium constant for the reaction. Examples are given for reactions between the gases hydrogen or oxygen and the solutes carbon, sulphur and oxygen dissolved in liquid iron.

Résumé

Quand le transport en phase gazeuse détermine le taux de réaction, un concept unifié de réactions entre des gaz et des solutés dissouts dans un métal liquide peut être basé sur les constants d'équilibre de la réaction. Nous présentons des exemples pour la réaction de l'oxygène ou de l'hydrogène gazeux avec du carbone, du soufre ou de l'oxygène dissouts dans du fer liquide.     

Activity of carbon in liquid iron alloys at 1550°C

The effect of chromium, cobalt, molybdenum, nickel, and vanadium on the activity of carbon in liquid iron alloys at 1550°C was investigated by equilibrating Fe-C binary alloys with Fe-C-_i ternary alloys in an isothermal closed chamber through transport in the gas phase. From the equilibrium distribution of carbon among the charges, free energy interaction coefficients have been deduced. The first order coefficients ∈ⁱ _C fori = Cr, Co, Mo, Ni, and V were found to be equal to -5.4, 1.8, -4.0, 2.4, and -6.2, respectively. Extrapolation of the data through the “Central Atoms” statistical model shows good agreement with data reported in the literature on the effect of the solutesi on the solubility of graphite. Formerly Graduate Student at Carnegie-Mellon University, Pittsburgh, Pa.     

Enhancing rate of slag-metal reactions involving carbon in liquid iron

Abstract

A series of experiments on decarburisation and iron oxide reduction have been conducted over the past 10 years. Experiments have been recently conducted to demonstrate that the slag-metal reaction between iron oxide and solute carbon is electrochemical, and that the rate of this reaction can be increased by applying a dc voltage across the slag layer. Analysis of this phenomenon has resulted in a deeper understanding of the rate limiting processes. Current research on iron oxide reduction and decarburisation is aimed at studying the effect of reduced pressure and the effect of applied potential on the reaction rate, and the relationship between applied potential and current efficiency. Future research will focus on other oxide reduction reactions, and other reducing agents.     

Modeling and experimental study of gaseous oxidation of liquid iron alloys

On the basis of the experimental results and thermodynamic and kinetic theories, a system reaction model was developed for liquid iron reacting with O₂/CO₂/CO/N₂ gases. For verification of the model, laboratory-scale experiments using a levitation melting technique were carried out on the kinetics of simultaneous oxidation of carbon, silicon, and manganese in a liquid metal droplet by oxygen and/or carbon dioxide in nitrogen gas. Both reaction model predictions and experiments show that for medium- or high-carbon (1.64 and 3.38 pct carbon, respectively) liquid iron, oxidation of silicon and manganese occurs at 1873 K only after cessation of the vigorous decarburization reaction, but that they proceed from the beginning in a low-carbon (0.4 pct carbon) run. The oxidation of silicon was accompanied by oxidation of manganese because of the reduction of the activity of manganese oxide once an oxide formed on the surface of the metal droplet. In a low-temperature run (< 1633 K), the metal surface was covered by a solid or very viscous oxide layer and the reaction proceeds far more slowly. The reaction model does not interpret reaction behavior at lower temperature because diffusion in the oxide layer may be the rate-controlling step, and this mechanism has not been included in the model.     

A study of the reaction of CO on liquid iron alloys

In all previous studies of the CO reaction on liquid iron the rate was controlled by liquid phase mass transfer. In this study an isotope exchange technique was used to eliminate liquid phase mass transfer as a possible rate-controlling mechanism. The rate in the present work is over an order of magnitude faster than previously measured. The isotope exchange rate for C¹³O¹⁸ in normal CO on liquid iron was not a function of temperature or sulfur content up to 0.43 pct S, but was a function of gas flow rate, indicating that the rate is controlled by gas phase mass transfer. the mass transfer parameter for the specific experimental condition was determined and the calculated rate for gas phase mass transfer of C¹³O¹⁸ in CO controlling the rate is in agreement with the experimental results. At low temperatures (1523 K) and sulfur contents greater than 0.015 pct the rate may be controlled by mixed control, gas phase mass transfer, and chemical kinetics in series. The chemical rate constant is estimated to be 1.5×10⁻⁵ moles/cm² sec atm for these conditions. S. ANTOLIN, formerly Granduate Student at Carnegie Mellon University     

Rates of dissolution of rotating iron cylinders in liquid copper and cu-fe alloys

Iron cylinders with molybdenum capped ends are rotated at speeds of 260, 570, and 835 rpm in liquid copper and Cu-Fe alloys maintained at 1220°, 1300°C, and 1370°C under argon at 1 atm pressure. The dependence of the dissolution rate of the cylinders on the concentration of iron in the bulk liquid is observed. The solution-rate constants defined by an approximate form of the Berthoud equation vary from 7 × 10^-3 to 30 × 10^-3 cm.s^-1. There is a linear relation between the logarithm of the rate constant and the reciprocal of absolute temperature for each rotational speed. The rate constant is found to vary with the 0.85 to the 0.96 power of the Reynolds number in the range 6500 〈 Re 〈 22000. This suggests that the dissolution process is diffusion controlled. The dependence of the dissolution rate on the activity of iron in the bulk liquid is observed. Oxygen increases markedly the dissolution rate, whereas sulfur does not.     

Effect of dendrite coarsening on the solidification of interdendritic liquid in iron alloys

The solidification of the interdendritic liquid in austenitic 110G13L steel and white cast iron is studied. In the absence of dendrite coarsening, the solidification mechanism of the interdendritic liquid in the manganese steel is shown to change and solidification occurs in the form of polycrystalline aggregates around dendrites from different centers. The relation between the standard solidification of the interdendritic liquid and the dendrite coarsening in iron alloys is grounded.     

Equilibria of Ce-Al-O and Nd-Al-O in molten iron

Equilibrium of Ce-Al-O or Nd-Al-O system in molten iron was studied by separately melting radioactive isotope ¹⁴¹Ce or ¹⁴⁷Nd in an Al₂O₃ crucible filled with pure iron to form ¹⁴¹CeAlO₃ or ¹⁴⁷NdAlO₃ around its inner wall. The content of dissolved Ce or Nd in iron was determined by means of electrolysis in anhydrous electrolyte and radioassay. The concentration of dissolved Al in iron was obtained by photometry and followed by calculation. Activity of oxygen in liquid iron was directly measured by solid electrolyte sensors made of ZrO₂(MgO) tube. By extrapolation of data obtained, the temperature dependence of the equilibrium constant of RE-Al-O in molten iron, , or of interaction coefficient, may be described as:      

Measurement of hydrogen solubility in liquid iron alloys employing a constant volume technique

The solubility of hydrogen in liquid pure iron and in several liquid binary iron alloys at steelmaking temperatures has been determined by measuring changes in hydrogen pressure in a constant volume system. The solubility of hydrogen corrected to one atmosphere pressure was found to be 27.70 ± 1.28 cc (STP)/100 grams in liquid pure iron at 1600°C with a temperature coefficient of solubility of 2.9 x 10^-2 cc (STP)/°C. This solubility decreases with increasing concentrations of aluminum, boron, or silicon; slightly increases with increasing concentrations of chromium, nickel, and niobium; and is almost independent of the concentrations of copper or sulfur. The data are compared with those of previous investigators who employed the more conventional Sieverts’ or sampling techniques.