The purpose of this paper is to point out the influence of the mineralogical properties of magnetite on the reducibility of indurated pellets. Magnetite ores of various sources were used for experiment. Conditions for preparing pellets and testing their reducibility have been kept constant. The results obtained are summarized as follows: 1) Fe (II)/Fe (III) ratio of natural magnetite deviates from the theoretical value of 0.50 to some extent. 2) The relation between Fe (II)/Fe (III) ratio and magnetization intensity of natural magnetite is similar to that of artificial one. 3) A positive correlation exists between Fe (II)/Fe (III) ratio of magnetite and the reducibility of indurated pellets. 4) A negative correlation exists between (Fe) II/Fe (III) ratio of magnetite and its oxidation rate.<BR.5) The result of 3) may be caused by the difference of Fe/O ratio in ferric oxide which in turn depends on the difference in Fe (II)/Fe (III) ratio of magnetite.
The experimental work on the equilibrium between molten iron and FeO-MnO, FeO-MnO-SiO2 slags at 1 560°C was carried out in a rotating crucible furnace, thereby avoiding the slag to contact with the refractory. From the molten slag-metal equilibrium data, it is shown that FeO-MnO system behaves ideally in liquid region, and also shown that it extends to 36 mol % MnO, which is in a fair agreement with the phase diagram. When the composition of FeO-MnO slag, which is in equilibrium with molten iron, is in the twophase region, the solubility of oxygen in the molten iron substantially remains constant at 0.125% regardless of slag composition. Combining those results on slag-metal equilibria with the data on heat of fusion of FeO, the heat of fusion of MnO was estimated, by assuming an ideal FeO-MnO solid solution behavior. This was found to be 12700 cal/mol. The value of Kl′Mn (=NMnO/NFeo/[%Mn]) is fairly constant at 4.45, when the slag consists of FeO and MnO, while in the slag of FeO-MnO-SiO2, Kl′Mn varies with silica content according to the equation. Log Kl′Mn=1.056 NS102+Log 4.45 It is shown that the similar equation can be derived by a simple regular solution equation with the interaction parameter; FeO-MnO: O, FeO-SiO:-6 700 cal/mol, and MnO-SiO: 15 600 cal/mol. To check the values of interaction parameters thus obtained, the composition-activity relation for each end system, or along the silica liquidus are derived also according to the regular solution formula with the same interaction parameter, and are compared with the experimental data. The agreement with experimetal data is reasonably good, except for the calculated silica activity referred to solid silica, of which the absolute level is much lower than experimental data. In order to make the calculated silica activity, referred to solid silica, be fitted to the experimental result, the free energy for the fusion of silica should be assessed as follows; ΔFSiO2f=8 800-2·0T Iso-activity diagram for the Fe0-MnO-Si02 melts and iso-consentration diagram for the molten iron in equilibrium with those slags are constructed, based on both the calculation according to the regular solution formula and the experimental data.
The effects of convection on the separation of floating oxide inclusions in liquid steel in mold were discussed theoretically, and the following results were obtained. 1. The pattern of convection, characterized by the cross section and the velocity of downward flow, has an extensive influence on the separation of inclusions. The effect of convection is remarkable for inclusion whose rising velocity is comparable with the velocity of the downward flow, and it is small for inclusions whose rising velocity is considerably higher or lower than the velocity of downward flow. 2. For such a convection with a small cross section of downward flow as that in killed steel in mold, large inclusions separate more rapidly than in tranquil bath in early period, but some large inclusions can not separate even after the time which is enough for separation in tranquil bath. 3. In such a convection having a large cross section of downward flow as that in rimming steel in mold, the separation of large inclusions is hindered remarkably.
The dependence of the yield stress of mild steel at low temperatures on grain size, strain rate and temperature was studied mainly by compressive deformation test. (1) The following equation relating strain rate (ε), temprature (T) and frictional stress (σt) of Petch equation was obtained; This is applicable when at is in the range of 8.7 to 28.2 kg/mm2. Strain rate exponent n and activation energy E are constant, both being independent on temperature, strain rate or stress. Above this stress level, n becomes larger but E is substantially invariable. (2) According to the study on BCC metals, it can be said that they behave in a similar manner to mild steel. That is, is is in the range of 7 to 9, being constant and specific to BCC metals, and in addition, E is approximately proportional to an energy of μb3, where μ is the shear modulus and b the Burgers vector. (3) The relations between strain rate, grain size and ductile-brittle transition temperature were studied by using the above equation, and the calculated temperatures are generally in accordance with the measured values.
Recrystallizaticn textures of Al-killed steel sheets cold-rolled to 60, 70 and 80% reductions in thickness and finally heat-treated by various combinations of 1st-stage and 2nd-stage annealings were examined by X-ray diffraction method and optical microscopy. The time of the 1st-stage annealing was kept to 40 min, and the pole densities of (222), (110) and (200) parallel to the sheet plane after the 2nd-stage annealing were measured as functions of the 1 st-stage annealing temperature. The maximum densities of (222) after the 2nd-stage annealing.at 650°C for 1 hr could be obtained in the 70% rolled sheet by the 1 st-stage annealing at about 480°C and 575°C. These two maxima were termed as 1st-peak and 2nd-peak respectively. The 1st-peak temperature (480°C) was independent on the cold-rolling reduction in the range between 60 and 80%, but shifted to a higher temperature when a higher 2nd-stage annealing temperature was adopted. The maximum elongation ratio of the recrystallized grains after final annealing could be related to the maximum density of (222), whereas the maximum size of the recrystallized grains was found to correspond to the minimum in the (222) pole density. These results were discussed by relating the recrystallization process with the process of clustering of Al and N which inhibits the nucleation of recrystallized grains with some ranges of orientation.