The kinetics of the oxidation of a cement-bonded pellet made of natural ilmenite was studied with an unsteady nonisothermal kinetic model derived by assuming pseudo-steady state mass transfer through the product layer and unsteady state heat transfer within the pellet. The derived model agreed well with the experiments. It was further found that the amount of the heat accumulated inside the pellet during oxidation was too great to be negligible in comparison with that lost to its surroundings, especially, in the initial period. During the oxidation of an ilmenite pellet with pure oxygen, the overall reaction rate was mainly controlled by the intrapellet diffusion of oxygen and the total heat transfer rate was principally limited by the poor heat conduction through the product shell. In the case of the oxidation of the ilmenite pellet with diluted oxygen, it is reasonable to analyze the reacting pellet as an isothermal system provided the oxygen concentration being less than 10 mol%.

View full abstract

Seven types of iron ores were reduced to iron phase in a laboratory fluidized bed at 900°C by N₂-H₂ mixtures to examine the influence of ore type, reducing potential, and sulfur potential on sticking phenomenon and iron morphology in the bed.
In case without H₂S addition, five types of ores having low Al₂O₃ content sticked by mostly short iron whiskers and/or porous irons, while two types of ores having high Al₂O₃ content fluidized with plain irons on their surface. Increment of the reducing potential did not much change these microstructures besides reaching to higher reduction levels. Addition of H₂S capable of forming FeS into the gas mixtures facilitated the appearance of coarse porous irons to keep fluidized until nearly complete reduction.
The overall metallization process of an ore bed was estimated to proceed under the hydrogen gas supplying control with a high gas utilization.
On the basis of the results obtained for 19 types of ores, including those employed in the previous tests, the sticking tendency is generalized in relation with factors such as iron morphology, surface energy of iron, and external shape of ore.

View full abstract

The travel path of produced gas in a coke oven has always been of interest. However, few studies have been reported on this subject. In the present study, a tracer technique was employed for the determination of the path of gas in a test coke oven with width of 45 cm, and charge height of 85 cm. Three tubes were inserted horizontally from the coke side at 15.6 cm high (L) and at 0, 8 and 16 cm from the center of the width. Two kinds of tracer gas were uniformly introudced along the tubes. Other six tubes were also inserted at 36 (M) and 54 (H) cm high and at 0, 8 and 22 cm from the center, and the gas in the oven was withdrawn from their ends located at the center of the length of the oven. The gas sampling was conducted every two hours through the sampling tubes and from the exit ascension pipe, where the total flow rate of the produced gas was determined from the concentrations of tracers. Ar injected at "L16" was hardly detected inside the charge (0 or 8 cm from the center) at the middle stage of carbonization. The flow rate of produced gas at the vicinity of the wall (22 cm from the center) was determined from mass balance of Ar assuming that all Ar flowed there. Rates of gas cross from the center side to the wall side was evaluated from the concentration profile of He introduced into the coal layer. At the middle stage, most of the produced gas passed upward in the coke layer and no cross flow was found. This phenomena were to be explained by large flow resistance of the plastic zone. At the last stage, both of the tracers were uniformly distributed all over the coke layer.

View full abstract

The travel path of the gases in the coke oven has always been of interest. However, few studies have been reported. In the present investigation, the time variations of flow direction and flow resistance of the produced gas in the coal and coke layers were measured in an experimental one-dimensional carbonization apparatus simulating a commercial coke oven.
The coal packed in a quartz tube was heated from one side simulating the wall side of a commercial coke oven at a constant heating rate and then kept at constant temperature (1274 K). The other side corresponding to the center side of the commercial coke oven entered into the furnace lastly. The first series of runs were conducted by opening both sides of the tube. Most of the produced gas was evolved from the wall side except the last stage of t he carbonization. Small increase in the wall side pressure caused the drastic increase in the evolution rate from the center side at the first and latter middle stages. However, at the earlier middle stage of carbonization, most of the gas was evolved from the wall side even under this condition. In the second series of runs, one side of the tube was closed. The steep increase in the wall side pressure and the interruption of gas evolution were observed at the earlier middle stage of the carbonization, only when the wall side was closed. In the last series of runs, nitrogen was forcedly introduced through a thin layer from one side. Steep pressure increase was randomly observed when the layer was at around 773 K, irrespective of the flow direction of the nitrogen. In conclusion, at the earlier middle stage of the carbonization, a plastic zone at around 773 K existed between the main gas production zone and the end of the center side and the flow resistance of the zone was found to be large.

View full abstract

Atomic models of the series of amorphous and liquid oxides 2MeO·SiO₂ (Me=Mg, Ca, Sr, Ba, Fe) containing approximately 500 ions in the basic cube with periodic boundary conditions were built with the help of continuous static relaxation (CRS) and molecular dynamics (MD) methods. The structural and thermodynamic properties of oxides at T=0 and 2 000 K depending on the Me²⁺ ion radius were analysed. We discovered the structural transformation of the oxide at Mg→Ca transition in the series, which is caused by the Me²⁺ ion radius change. The polymerization constants of the polymer theory of slags were calculated. The MeO oxide activity is not equal to the ion fraction of the "free ions O^2-".

View full abstract

A vertical bubbling jet was generated in a cylindrical mercury bath by injecting air from the bottom through a centric nozzle. Gas holdup α and bubble frequency f_B in the mercury-air vertical bubbling jet were measured by means of an electro-resistivity probe. On the basis of the present and other previously published experimental results, correlations for α, f_B and mean bubble rising velocity [u.gif]_B were derived for bubbling jets with a density ratio ρ_l/ρ_g between 780 and 11 000 as functions of Q_g, d_n, σ and ρ_l/ρ_g, where Q_g is the injected gas flow rate, d_n is the inner diameter of Nozzle, σ is the surface tension of liquid, ρ_l is the density of liquid and ρ_g is the density of gas. These correlations were found to be valid in the vicinity of the nozzle exit where the expansion of gas due to static pressure change was negligible.

View full abstract

A PPC (Plasma Progressive Casting) furnace with a water cooled mold and plural plasma torches was constructed to melt titanium and its alloys. Ingots of titanium and its alloys have been satisfactorily produced and satisfied chemical compositions and mehanical properties required for VAR double melted ingot.
This process has a distinctive advantage of efficient utilization of titanium and titanium alloys scrap.

View full abstract

The formation process of the retained austenite (γ_R) in cold-rolled 0.4C-1.2 to 2.0Si-1.2Mn steel sheets intercritically heated and subsequently austempered is investigated.
It was concluded that granular γ_R grains with less than 2-3 μm dia. in the above steels and the interlath γ_R films in the higher C(≥0.6C)-Si-Mn steel heated at single austenite range and austempered, which have been reported by others, were the same in chemical stability of austenite by C enrichment, in spite of differences in formation site and morphology. Formation of stabilized granular γ_R may be attributed to the smaller granular austenite grain formed during intercritical heating. Addition of Si may cause the suppression of carbide precipitation and the increase in γ_R fraction in steels held isothermally to give the maximum C content in γ_R (C_γmax), whereas the Si addition does not change C_γmax.

View full abstract

Effect of grain size on sulfide stress cracking (SSC) resistance, thought to be an important metallurgical factor, is not clearly understood. There are some conflicting experimental results about grain size effect on SSC resistance. In this paper, effect of austenite grain size of low alloy tempered martensite steel was investigated using a constant load SSC test, considering their correlation with chemical compositions. An Rs value (SSC threshold stress/yield strength) begins to decrease with increase in yield strength at the yield strength equal to σ_c⁸⁵. Fractographic study reveals that σ_c⁸⁵ corresponds to the minimum yield strength for the occurrence of intergranular fracture. σ_c⁸⁵ rises with refinement in austenite grains, Rs is not affected by austenite grain size at yield strengths below σ_c⁸⁵. σ_c⁸⁵ at a constant grain size is influenced also by chemical compositions. When Rs is plotted against its tensile strength, no effect of austenite grain size, however, appears. The proposed model shows that grain refinement strengthening apparently increases σ_c⁸⁵.

View full abstract

Tensile and compressive stresses were applied along the [419] direction of Cu-1.53mass%Fe alloy single crystals to induce they γ→α martensitic transformation in dispersed small iron particles. The magnetic anisotropy of deformed and successively annealed specimens was examined by measuring magnetic torque around (111). The magnetic anisotropy was considered to have two origins: the crystal anisotropy due to the symmetry of the α-iron crystal and the shape anisotropy due to the shape of the α-iron particles. The shape and amplitude of the magnetic torque curves depended strongly on the sense (tension or compression) of the applied stress and on the annealing time. The torque curves were analyzed theoretically by assuming the shape of the α-iron particles as revolution ellipsoids. The preferential formation of particular Kurdjumov-Sachs variants of α-iron particles as well as the shape change of the particles by annealing could be detected easily by the magnetic anisotropy measurement.

View full abstract

The stature of Mr. Masao Yukawa is impressive: a man of knowledge, of action, of culture and of generosity. It is frightening to think that this lecture should ideally be delivered by a man of similar record and I accept this task with great humility. What gives me hope that I might have something in common with Mr. Yukawa is the mention in ISIJ's documents of his "interest and enthusiasm in educational issues". Such issues are as vital as ever, and I propose to offer in this lecture a token of my personal efforts to arouse the student's interest in process metallurgy and to equip him with tools combining rigor and imagination. The minds of students cannot be programmed, they must be trained, and with the highest possible efficiency. Along with research, I tried to make this task my profession. For my lecture today, I chose to present the fruit of my efforts in developing "analogue diagrams" as a pedagogic tool in process metallurgy. For a short half-hour, I hope you will enjoy the feeling that you are back to school!

View full abstract