Reduction of iron ore fines by coal fines in a bed fluidized by air has been studied. The investigation includes study of the kinetic aspect of reduction and effect of major process variables. The variables used are time, temperature, coal/ore ratio and air flow rate. The kinetic data of reduction fit the first order reaction model. Within the range of variables studied, an increase in reaction temperature and coal/ore ratio of the reduction mixture result in higher reduction rate, whereas, increase in air flow rate adversely affects the reduction rate. The activation energy for the reduction reaction is found to be about 155 kJ/mol.
Permeation tests and structural analysis of voids were carried out on the sinter cakes prepared by varying the admixing ratio of coke in the raw mixture. The relationship between permeation characteristics and structural parameters were examined. Void networks in the cake were observed using a void replica made of silicon rubber. Void fraction and specific surface area of the cake estimated by substituting the permeation test results into Ergun's equation did not agree with those measured by a water imbibition method and image analysis. The structure of the replica suggests that the permeability of a well-sintered cakes, in which large voids developed, is governed by the permeability of relatively thin gas flow paths connecting among large voids. The permeation test results were reasonably consistent with such structural features of the void networks in the cake. A permeation anisotropy of the cake, between the vertical and horizontal directions, was found and it seems to increase with an increase in the admixing ratio of coke in the raw mixture.
Phase equilibria of Fe-S-C ternary melt has been studied to establish fundamental knowledge on the copper removal from iron melt by sulfide fluxes. Measurements were made to clarify the solubility of carbon and the miscibility gap between iron and FeS melts in Fe-S-C system at the temperature range from 1 473 to 1 873 K. Thermodynamic analysis was tried by applying interstitial solution model. Activity of iron in liquid Fe-C binary alloy was determined by distributing iron between liquid iron and silver phases to determine the interaction parameter between iron and carbon in Fe-C melt. It was concluded that interstitial solution model was applicable to express thermodynamic relation in this system. Phase diagram and activity contours of constituents in Fe-S-C ternary melt were calculated by the model.
Copper distribution between FeS-NaS0.5 flux and carbon saturated liquid iron has been studied at 1 673 K. Copper distribution ratio, LCu=(mass%Cu) flux/[mass%Cu]iron, was about 9 when FeS only was used as sulfide flux. The addition of NaS0.5 to FeS increased the copper distribution ratio. The LCu showed the maximum value of about 24, at around XNaS0.5=0.4, and became nearly constant at the range of higher NaS0.5 content than 0.4 of NaS0.5. The addition of NaS0.5 also lowered sulfur content in liquid iron from 1.9 Mass% at XNaS0.5=0 to 0.04 mass% at XNaS0.5=0.8. CuS0.5 dissolved in flux decreased LCu at high concentration range of NaS0.5. In order to discuss the effect of NaS0.5 and CuS0.5 on the copper distribution ratio, the activity coefficient of CuS0.5 in flux was evaluated. It was found that NaS0.5 decreased the activity coefficient of CuS0.5 in flux, so that the LCu increased in spite of the significant decrease of sulfur potential in the system by the addition of NaS0.5.
Measurements have been made to study the effect of the addition of alkaline or alkaline earth metal sulfide such as Li2S, K2S, MgS, CaS, SrS or BaS to FeS on the copper distribution ratio between FeS flux and carbon saturated liquid iron at 1 673 K. Since each solubility of MgS and CaS in liquid FeS was limited, no apparent effect of MgS or CaS on the copper distribution ratio was observed. Similar to the effect of Na2S studied in our previous work, the addition of Li2S, K2S, SrS or BaS to FeS increased the copper distribution ratio, LCu=(mass%Cu) flux/[mass%Cu] Fe, and LCureached maximum value at certain content of these additives in each flux. The maximum values of LCu measured in each flux were 30, 20, 22 and 19 in FeS-LiS0.5, -KS0.5, -SrS and -BaS fluxes, respectively. The sulfur content in liquid iron also decreased by the addition of these sulfides to FeS.
The nitride capacities (CN3-=(%N)·PO23/4/PN21/2) in CaO-Al2O3 melts were measured by a gas-slag equilibration technique, using CaO, Al2O3, and Mo crucibles in the temperature range of 1723 to 1923 K. The oxygen partial pressures measured by a solid electrolyte cell were controlled by N2-H2-H2O gas mixtures. It was found that the nitride capacities increased with increasing temperature and Al2O3 content in the slag. Activity coefficients of AlN calculated from the reported activities of Al2O3 increased with a decrease of Al2O3 content and temperature.
In order to extend the applicability of a coupled reaction model to the hot metal dephosphorization process, evaluation method for unknown parameters was investigated. The following points were clarified. (1) Mass transfer coefficient in metal phase was increased in proportion to ε1/2 and its activation energy was about 125 kJ/mol. (2) Ratio of mass transfer coefficient in metal phase to slag phase did not clearly depend on stirring energy, temperature, or flux composition. (3) Phenomenological rate parameter for CO evolution also did not clearly depend on stirring energy or flux composition but decreased with an increase in temperature. (4) Activity coefficients of FeO and P2O5 in CaF2 and CaCl2 containing oxide slag were able to be estimated by a regular solution model in which the interaction energy was expressed as a function of the CaF2, CaCl2 content. By the application of these results to the coupled reaction model, the change of concentration during the hot metal dephosphorization experiments was calculated without using a parameter fitting method.
In order to apply a coupled reaction model to the simulation of industrial scale hot metal pretreatment process, a new computer program of MACSIM (Mathematical Analysis Codes for Slag-metal Reaction and Injection Metallurgy) has been developed. In this program, the reactions by injected flux, slag on bath surface and top blown oxygen gas can be calculated and most of the parameters were determined based on the experimental results of the previous paper. The following phenomena were clarified by this program and the control of the hot metal dephosphorization process became possible. (1) In the case of hot metal pretreatment by torpedo car, about 50% of top blown oxygen gas had the same effectiveness as Fe oxide for dephosphorization reaction. The remaining oxygen contributed to the heat supply through decarburization and post combustion reactions. (2) When [P] concentration before treatment was high, the efficiency of oxygen and that of lime for dephosphorization were high but a clear dependence on temperature was not found. (3) The efficiency of oxygen and that of lime for dephosphorization mainly depended on CaO/O and hot metal composition ([P], [Si]) although dephosphorization treatment time and flux supply rate differed widely.
The activities of tin and antimony in liquid Fe-S alloy saturated with carbon were determined at 1673 to 1873 K by the distribution method using liquid silver. The concentration range of tin and antimony measured in the iron melt was less than 2 mass% and that of sulfur was up to FeS saturation (about 1.9 mass% at 1 673 K). The activity coefficients of tin and antimony, γSnFe−Csat. and γSbFe−Csat., and the solubility of carbon, [C]sat. in iron melt measured could be empirically expressed as the function of tin, antimony and sulfur contents in liquid iron saturated with carbon and temperature as follows: log γSnFe−Csat.=485/T+0.777-28.33 XSn-4.20 XS, log γSbFe−Csat.=-1000/T+0.314-18.34 XSb-2.17 XS. [C]sat.=2.54×10-3T+0.65-0.33[mass%S]+βM[mass%M] (mass%) βSn=-0.11, βSb=-0.12 (1 673-1 873 K, Sn≤1.5 mass%, Sb≤1.9 mass%, S<1.9 mass% (FeSsat.)) The activity coefficients of SnS and SbS1.5 in FeS-Na2S flux were estimated to explain the distribution behavior of tin and antimony between the flux and liquid Fe-Csat. by combining the results of the present work with the distribution ratios of tin and antimony between FeS-Na2S flux and Fe-Csat. melt determined in our previous work. Equilibrium partial pressure of SnS in Fe-C-S-Sn melt was also estimated by using the activities of tin and sulfur and free energy of formation of SnS, and the possibility of tin removal from iron melt as SnS gas was quantitatively evaluated.
The phosphate capacities of CaO-CaF2-SiO2 melts saturated with CaO were reexamined by measuring the phosphorus partition ratio between the slag and carbon saturated iron at 1300°C, because the previous data were not compatible with their sulfide capacity values which have been recently measured. New results show a good correlation between the two capacities as the theory predicts. The influence of replacement of CaF2 by CaCl2 on the phosphate capacity of the CaO saturated CaO-CaF2 melts was also studied by equilibrating the slag and silver at 1400°C. It was confirmed that thermodynamically CaF2 is more effective for dephosphorization than CaCl2.
In order to evaluate the influence of C content and annealing temperature on the mechanical properties of steels containing retained austenite, cold-rolled sheets containing 0.12 to 0.4 C, 1.2 Si, and 1.5 Mn have been intercritically annealed and isothermally transformed at 400°C. Annealing near AC1 temperature followed by the 400°C isothermal transformation for 100 to 300 sec results in the best combination of strength and ductility. The ultimate tensile strength ranges from 590 Mpa in the 0.12 C steel to 980 Mpa in the 0.4 C steel. The total elongation varies 39 to 33%, and is ranked well above that of conventional ferrite-martensite dual-phase steels at the comparable strength. Amounts of retained austenite in these specimens are 7 to 20% and linearly related to the C contents of the steel. Mechanical stability of the retained austenite is fairly improved compared to that found in conventional dual-phase steels, and enhances the ductility at high strength. Better combinations of strength and ductility are maintained even in the lower C steels due to the contribution of an increased amount of highly ductile ferrite.
Single-pass rolling in the (γ+α) two-phase region has been carried out to investigate the effect of Ti and Ti-Nb additions on the γ→α transformation and the restoration characteristics of deformed α in a 0.13%C-1.45%Mn base steel. The microalloyed steels consisted of 0.016%Ti, and 0.019%Ti plus 0.024%Nb. Experimental results showed that rolling in the (γ+α) two-phase region accelerated the γ→α transformation, and the presence of Ti or Ti plus Nb enhanced this accelerative effect. In undeformed and lightly deformed samples, α grains nucleated mainly at γ grain boundaries during and/or after rolling. In samples rolled with reductions higher than a critical value, α grains nucleated at γ grain boundaries as well as interiors, mainly at the boundaries of deformation bands and deformed annealing twins. Depending on the rolling reductions, holding time and alloy composition, deformed α grains developed into cell and/or subgrains, or recrystallization occurred resulting in equiaxed grains. Recovery and recrystallization of deformed α proceeded rapidly in the C-Mn steel, but was sluggish in the Ti and Ti-Nb steels. The incubation time for recrystallization of deformed α was retarded by 1-2 orders of magnitude in the Ti and Ti-Nb steels compared with the base C-Mn steel, because of the presence of alloy carbide/nitride precipitate particles. Ti and Ti-Nb additions also produced finer initial γ grains after reheating before rolling, and stabilized the dislocation substructures during and after rolling. The substructures resulted in increased nucleation sites for the γ→α transformation. These effects led to finer α grains and a higher hardness (and strength) in the microalloyed steels than in the C-Mn steel after the same rolling and holding treatments.
The anomalous X-ray scattering (AXS) technique has been applied to obtain the environmental radial distribution function (RDF) around a zirconium in amorphous ZrO2 prepared by hydrolytic condensation of zirconium alkoxide. The environmental RDF was determined from the intensities measured at the Zr K absorption edge using synchrotron radiation and compared with the ordinary RDF. By combining the environmental and ordinary RDFs of amorphous ZrO2, zirconium is quantitatively confirmed to be surrounded by six oxygens at a distance of 0.214 nm and a considerably distorted ZrO6 octahedron is likely to exist as a fundamental local ordering unit structure. A possible structural model of amorphous ZrO2 in near neighbour region has also been proposed.