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Experiments have been made to demonstrate that when an oxygen-bearing gas is blown on the surface of iron-phosphorus melts, iron and phosphorus vaporize at rates enhanced by vapor-gas phase reactions. These findings are in accord with the theoretical predictions. The reaction mechanism considered is based on the concept of vaporization of phosphorus at the surface of iron as volatile PO and PO2, which then react with iron vapor and oxygen in the gas close to the surface of the melt. If powdered lime were present, as in the Q-BOP, a relatively stable calcium phosphate would form, thus bringing about dephosphrization. From the available thermodynamic data and reaction-equilibrium data, equilibrium constants have been derived for the reaction of PO and PO2 with liquid iron.

The hydrogen-reduction of spheroidal pyrrhotite particles, varying in diameter from about 0.4 to 1.6 cm, was investigated at 600, 800, and 900°C. Microscopic examination of partially reduced samples showed a well-defined interface between unreacted pyrrhotite and a porous iron shell. The rate of reduction is controlled primarily by counter-current diffusion of H2 and H2S in the gas-film boundary layer and in the porous iron layer. The magnitude of the ratio of effective diffusivity to the molecular interdiffusivity for H2-H2S, derrived from the reduction data, suggests that the structure of the porous iron formed is similar to that of an idealized porous material.

The stability of carbon saturated manganese-iron alloys was studied by means of simulated decrepitation tests, and it was found that the product must contain a minimum of about 5 wt pct iron to be stable during storage. By means of several experimental techniques it was shown that the structure of the carbide phase present in carbon saturated ferromanganese determines whether the alloy is stable. Below the critical iron content of about 5 wt pct, the carbide phase is Hāgg carbide (MnFe)5C2, whereas above about 5 wt pct iron the carbide phase is cementite (MnFe)3C. The role of iron is to stabilize the cementite phase. Experiments with the synthetic manganese carbides, Mn5C2 and Mn3C, showed that the former reacts readily with water whereas the latter is stable.

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 thermal decomposition of Mn2O3 was studied at 1000°. The rate of decomposition was inherently fast and dependent on the mass-transfer characteristics of the geometry used. The rate of reduction of Mn3O4 by CO, coconut charcoal, coke, and pure graphite was investigated in the temperature range 900 to 1200°. It was found that the rate of reduction in CO was fast and that the overall rate of reduction by carbon was determined by the oxidation of the carbon by CO2. In general the rate was higher for higher tempera tures and for smaller particle sizes of the oxide and the carbon. Gases such as He, Ar, or N2 were found to decrease the rate because of the dilution effect due to back diffusion into the interparticle pores of the oxide-carbon mixture. It was further found that the oxidation of carbon by CO2 was catalyzed by Mn3O4. This effect was particularly pronounced when the reductant was either graphite or coke.

The effect of additions of fluorspar-and potential substitutes such as borate, manganese ore, and ilmenite—to basic steelmaking slags on the equilibrium phosphorus and sulfur distribution ratio has been studied at 1550δC. From laboratory slag-metal equilibrium studies it was found that the presence of CaF2 in concentrations between 1.5 and 5 wt pct in the slag (equivalent to 2 and 6 kg of fluorspar per ton of steel) lowered the equilibrium phosphorus content in the metal by about a factor of three. The use of B2O3, manganese ore, or ilmenite (the active ingredient in Sorel flux) did not affect the equilibrium phosphorus content of the metal. The effect of CaF2 is ascribed to a lowering of the activity of P2O5 in the slag. Good agreement was found between the metal phosphorus content obtained from open-hearth plant data (no fluorspar added) and the present laboratory data for slags not containing CaF2. None of the fluxes studied in this work, including CaF2, improved the equilibrium sulfur distribution between metal and slag. The present results indicate that the choice of a substitute for fluorspar in an actual steelmaking operation, except when phosphorus presents a problem, should be based primarily on the cost of using the fluorspar substitute, including any change in refractory costs resulting from using the substitute.

Paramagnetic resonance absorption at room temperature in 25 divalent manganous salts is reported. From the shapes of the resonance curves information is obtained with regard to exchange and dipole-dipole interactions.

The solubility of sulfur in wustite in equilibrium with γ iron and liquid oxysulfide was found to be 0.011 wt pct at 1050°C. The sulfur solubility in γ iron in equilibrium with wustite and liquid oxysulfide was also determined at 1050°, 1150°, and 1250°C and found to be 135, 165, and 160 ppm respectively. These values are considerably lower than the sulfur-solubility in y iron in the binary Fe-S system saturated with pyrrhotite. The diffusivity of sulfur in wustite was determined by oxidizing Fe-S alloys in mixtures of CO and CO2, and analyzing the entire sample for sulfur afterwards. From the amount of sulfur diffused through the growing wustite layer into the gas phase, the diffusivity of sulfur in wustite was evaluated, and found to be 4.1 × 10−8 and 9.6 × 10−7 cm2/s at 1050° and 1250°C respectively. These values are of the same order as the self-diffusivity of iron in wustite in equilibrium with iron at the same temperatures.

Experimental results are presented showing that oxidation in air or in mixtures of CO2 and CO of iron alloys, containing Mn (0 to 0.34 pct) and/or S (150 ppm) at temperatures between 900° and 1300°C, results in the formation of a liquid oxysulfide phase at and near the metal/oxide interface. Electron microprobe analysis showed that this liquid consists of Fe (Mn), S and O. Oxidation of Fe−S alloys at rates slower than the rate of diffusion of sulfur in wustite does not cause any precipitation of a liquid oxysulfide at the interface. From indirect evidence, the sulfur diffusivity in wustite is estimated to be of the same order of magnitude as that in iron. The solubility of sulfur in wustite in equilibrium with iron and a liquid oxysulfide at 1250°C is about 140 ppm. It is found that the presence of a thin layer of liquid oxysulfide at the iron/wustite interface does not have a perceptible effect on the parabolic rate of oxidation of the metal.

This is a critical review of available equilibrium data between phases involving Fe, Mn, S, and O. Using the Morey-Williamson theorem, and that modified by Darken, the sulfur and oxygen potential diagrams are constructed for the Fe−S−O system involving nine univariant and three invariant equilibria. The solubility of sulfur in wustite-saturated iron is evaluated; the sulfur content of iron in equilibrium with wustite and liquid oxysulfide reaches a maximum of 143 ppm at 1200°C; this is about one half of that corresponding to the solidus of the Fe−S system. An estimate is made of the phase equilibria in the Fe−Mn−S−O quaternary system involving gamma iron and Mn(Fe)O phases. There is a eutectic invariant at ∼900°C, and the liquid miscibility gap invariant is estimated to be at ∼1225°C. From the expected phase relations and equilibria, it is deduced that if sufficient oxygen and sulfur,i.e. Mn(Fe)O and Mn(Fe)S phases, are present in Fe−Mn alloys, there may be a liquid oxysulfide phase present at temperatures above 900°C, depending on the concentration of manganese in solution. The higher the manganese content in solution, the higher is the temperature above which a liquid phase is present,e.g. for 10 ppm Mn, 900°C and for ∼90 pct Mn, ∼1225°C. A mechanism is suggested for the precipitation of sulfides and oxysulfides near the surface of steel during heating in an oxidizing atmosphere. In the Appendix by Darken and Gurry, results are given of the melting temperatures of mixtures of wustite and pyrrhotite in equilibrium with iron, from an investigation carried out about thirty years ago.

The previous study of the phase relations (Part I) is now extended to the solid-liquid regions of Fe-Mn-S and Fe-Mn-S-O systems. The differential thermal analysis measurements made with 1 to 5 pet Mn-Fe alloys containing sulfur and oxygen substantiated the positions of the univariant curves in pet Mn vsT plots derived from other available data and theoretical considerations. It is found that if sufficient oxygen and sulfur are present in the Fe-Mn alloys, there may be a liquid oxysulfide phase present at temperatures above 900°C, depending on the manganese content. The higher the manganese content in solution, the higher is the temperature below which no liquid phase is present,e.g. for 10 ppm, 900°C and for 10 pet Mn, ∼1200°C. The formation of oxides, sulfides, and liquid oxysulfides in the interdendritic regions during solidification, as predicted from the phase relations in the Fe-Mn-S-O system, was verified by microscopic examination using scanning electron microscopy and metallographic techniques.

The solubility of nitrogen in liquid manganese, in equilibrium with gas containing varying amounts of nitrogen, has been determined at 1300, 1400, and 1500°C. At one atm pressure of nitrogen, the solubility is 2.6 wt pct at 1300°C and decreases to 1.7 wt pct at 1500°C. Dissolution of nitrogen in manganese does not follow Sievert’s law. The activity coefficient of nitrogen in manganese increases with increasing nitrogen concentration. At one atm nitrogen pressure, the value of the activity coefficient, relative to the infinitely dilute solution, is 1.55 between 1300 and 1500°C.

Additions of elements of the rare-earth group to steel, mostly in the form of “mischmetal”, are generally made to improve on the deoxidation and desulfurization. Spring1 was the first to carry out experiments with the addition of mischmetal to certain types of steel as far back as 1918. A comprehensive review of the effects of lanthanum and cerium additions to steel was given by Richerd.2