Swirl motions of a bubbling jet in a cylindrical bath with centric bottom gas injection were investigated. The swirl motions were classified into two kinds. One was observed when the bath depth H_L was nearly equal to the bath diameter D or less than that, while the other occurred for H_L/D≥2. These two kinds of swirl motions were named the first kind and the second kind, respectively. For the first kind of swirl motion, which was caused by internal forced oscillation due to quasi-periodical bubble formation, empirical correlations describing its initiation and cessation were proposed. The swirl period almost agreed with the period of rotary sloshing. On the other hand, the second kind of swirl motion was caused by the instability of a large scale ring vortex enclosing the bubbling jet. Empirical correlations for the initiation of swirl motion and the swirl period were derived.

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The activity of carbon in a Mn-C alloy has been measured at 1628 K by equilibrating solid MnO with molten Mn-C alloys in an Ar-CO atmosphere according to the following reaction.
[C]_Mn+MnO(s)=[Mn]+CO(g)
The activity coefficients of manganese and carbon relative to pure liquid manganese and solid carbon, respectively, obtained from the carbon content of the Mn-C alloy at different CO partial pressures are expressed as follows:
ln γ_Mn=5.47X_C²–46.8X_C³
ln γ_C=–0.291–10.9X_C+75.6X_C²–46.8X_C³

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In order to understand the behavior of manganese oxide in smelting reduction process, the manganese equilibrium between ironmaking slag containing FeO and silver melt was investigated over the temperature range of 1400-1500°C. The oxygen partial pressure was controlled by CO/CO₂ ratio. Test results on Mn content in silver have been thermodynamically converted into those in supercooled or carbon-saturated iron melts and the activity coefficient of MnO in slag was determined experimentally. The activity of MnO decreased with increasing FeO content in slag. Higher FeO content as well as lower slag basicity resulted in larger equilibrium manganese distribution ratio between slag and iron. The temperature dependence of equilibrium manganese distribution was determined in the temperature range of 1400-1500°C. The relative partial molar heats of solution of MnO and Mn were also experimentally determined.

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The present work is a fundamental study of reduction in mixtures of iron ore concentrate and pulverized coal by indirect heating. Cylindrical steel crucibles, 118 mm i.d. and 150 mm height, with full-load of mixtures were placed in a muffle furnace which was controlled to be at a constant temperature of 1200°C for predetermined times of reaction. The profile of temperature and degree of reduction, and distribution of residual carbon were measured by embedded tiny thermocouples during the course of reaction and sampling and chemical analysis of reacted solids. It has been found that reducing gas generated in higher temperature regions by devolatilization and Boudouard reaction plays a role in convective heat transfer and indirect reduction for benefits of interior regions. The likely rate-controlling step of the overall reaction is considered to be heat transfer.

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In order to avoid iron ore agglomerat in and cokemaking in blast furnace ironmaking processes, direct reduction of iron ore concentrate with pulverized coal is desired for its potential environmental and cost advantages. A non-isothermal mathematical model has been developed based on experimental results.¹⁾ This model includes chemical kinetic expressions for heterogeneous reactions and equations of heat and mass transfer in porous medium. It has been found that heat transfer within the mixture is the dominant rate limiting step for overall reactions, and that the flow of gaseous products plays a significant role in convective heat and mass transfer.

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The burden distribution simulation model was indispensable so as to ensure smooth blow-in and stable operation with high productivity of Keihin No. 1 blast furnace, which is one of the largest blast furnace with bell-less top. For this purpose, basic factors governing the burden distribution in the bell-less top for a large blast furnace were examined through the 1/10 scale model experiment on the basis of the burden distribution simulation model formerly developed for Fukuyama No. 2 blast furnace. By incorporating these results and considering the particle size change during discharge, a burden distribution simulation model suitable for Keihin No. 1 blast furnace was newly constructed. It has been applied for the operation of Keihin No. 1 blast furnace. As a result, a productivity of 1.9 t/d·m³ was achieved in only two weeks after blow-in. Further use of this burden distribution simulation model has permitted stable continuation of high-productivity of 11000 t/d for a period of about a year.

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In order to avoid sticking during a fluidized bed reduction of iron ores and elucidate its mechanism, their reduction tests using two types of easily sticked ores coated by a water-slurry consisting of each submicron reagen of gangue species were carried out at 900°C by N₂-H₂ mixtures having sulfur activities incapable of forming FeS, where fibrous irons are known to be predominated from the authors' previous researches.
Without coating, ores sticked mostly due to fibrous morphology and/or high surface energy of iron. With coating, ores kept fluidizing mainly due to the physical spacer effect among ore surface. Al₂O₃ and MgO were effective agents, while CaO was ineffective due to nonuniform coating and preferential upward growth of irons. Particularly, the conditions near a_s=0.1 in a bed (a_s: sulfur activity in gas phase relative to Fe/FeS equilibrium) increased fairly the coating amount necessary to improve fluidization, because such conditions promote most fibrous irons. It was found that the coating amounts required to improve fluidization increase with fibrous iron morphology, active iron surface, and less original gangue coverage. Coating traces of ore tail rich in Al₂O₃ and SiO₂ species was also effective for fluidization.

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Theoretical and experimental studies were carried out to quantitatively understand the effect of fluid flow on the decarburization reaction rate in an RH degasser. Hydrodynamic calculations on fluid flow in the ladle were proved reasonable by a cold model experiment. The decarburization model in conjunction with the fluid flow by hydrodynamic calculations in the ladle made it clear that the decarburization rate obtained from this model was faster than that for perfectly mixed flow, and slower than that for plug flow when the same parameters were used for the calculations. The decarburization model enabled us to predict the concentration distribution of carbon in the ladle during an RH treatment. The maximum carbon content, which was found in the recirculating zone in the ladle, reached about twice the minimum value obtained in the region just below the down-leg. No dead zone existed which would disturb the decarburization rate in the process, and it was also made clear that the shape of ladle had little effect on the decarburization rate.

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A study was conducted to examine the influence on the Charpy impact properties of various sizes and distributions of precipitates in microalloyed steels and also of the combined effects of precipitation and dislocation strengthening. Most of the work was done using vanadium steels but two niobium containing steels and a C-Mn steel were also included for comparison. Isothermal and continuous cooling treatments were used to obtain a range of sizes and distributions of precipitate particles while three different rolling schedules were used to obtain variations in the amount and type of dislocation substructure.
It was found that continuous transformation gave greater precipitation strengthening than isothermal transformation and was also less detrimental to impact properties. The embrittlement vector was not constant but varied over the range 0.3-0.8°C/N/mm² and increased as the level of precipitation strengthening increased and as the transformation temperature decreased. The combined effects of precipitation and dislocation strengthening led to much greater strengths in the vanadium steels than in the niobium steels and also tended to be less embrittling. The optimum microstructure in the vanadium steels consisted of fine ferrite grains with a well recovered substructure containing row precipitates formed at a relatively high transformation temperature.

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