Experiments were conducted on pure Fe₂O₃ fines (–250 mesh) which were mixed with 1, 2.5, 5 and 10% by weight of pure NiO of the same size. The powder mixtures were pressed into compacts and fired at 1473 K for 20 h. The fired compacts were isothermally reduced at 1173-1473 K with hydrogen. The reduction course was followed up by means of weight loss technique. Porosity measurements, reflected light microscope and X-ray diffraction analysis were used to elucidate the reduction kinetics. NiO was found to have a significant effect on the reduction of iron oxide. The rate of reduction at both the initial and final stages increased with the increases of dopant content at all reduction temperatures and this was attributed to the formation of mickel ferrite (NiFe₂O₄) phase and the consequent increase in the total porosity of compacts. Ni_x, Fe_y solid solution (ferronickel alloy) was produced during reduction at all tempetatures studied. The values of apparent activation energy calculated from the experimental results, the structure of partially reduced compacts and the application of gas-solid reaction model were used to elucidate the reduction mechanism.

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Iron oxide-lignite mixed pellets with minor addition of CaO and Na₂CO₃ were reduced isothermally at 900, 950 and 1000°C under constant flow rate of nitrogen gas. The variable parameters studied are the amount of carbon, reduction temperature and the amount of additive. The experiments were statistically planned in order to quantitatively assess the effect of each variable and the interactional effect of different variables.
It was found that under the nitrogen gas atmosphere, the amount of carbon, reduction temperature and the amount of Na₂CO₃ substantially influence the degree of reduction.

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IMEXSA steel has a four electric arc furnaces (EAF) steelmaking shop which was originally designed to melt a DRI/scrap ratio of 80/20 for producing steel slab, but logistical and economical circumstances led to a change in this ratio to 98.2/1.8. This decision brought about increases on specific consumptions of energy, electrodes, refractories and a loss of metallic yield among other items. In order to improve melting performance a study involving industrial measurements and thermodynamic-kinetic aspects of slag foaming was carried out. Implementation of a slag foaming practice gave very encouraging results in the main process variables; energy consumption decreased from 730 to 640 kWh/t of steel while electrode consumption decreased from 2.25 kg/t of steel to 1.81 kg/t of steel. With regard to iron oxidation, iron oxide contents in slag decreased from previous 36-40 wt% values to 23-25 wt% increasing substantially metallic yield. Overall process performance was improved and consequences of this program can be directly seen during seconday refining process of steel in LF.

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Determination of solubility and activity of calcium in liquid Fe+Ca+O alloys in equilibrium with lime at 1823 K were carried out by means of the distribution equilibrium of calcium via gas phase in a closed tantalum vessel between iron melts and Ag+Ca Alloys.
Solubility of calcium in equilibrium with lime increases with increase of calcium potential of the system. Within the concentration range from 3 to 270 mass ppm Ca, the activity coefficient of calcium referred to the hypothetical pure liquid calcium does not change apparently and its value is 7.8±0.7. Solubility of calcium in iron under the condition of both CaO and Ca+O alloy saturation was found to be 270±15 mass ppm. The partial pressure of calcium at this three phases equilibria is 1.2×10⁵ Pa.
Based on the results and the literature data, ditermination procedure of interaction parameter between calcium and oxygen in molten iron was discussed.

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The mechanism by which cracks occur in the immersion nozzle with silicaless inner porous refractory developed to stabilize the injection of argon gas into molten steel, and the prevention of nozzle cracking were investigated. The results obtained were as follows.
(1) Models for estimating the crack formation pressure and hot argon gas inlet pressure for the immersion nozzle were proposed. Using those models, a theory for preventing nozzle cracking according to casting conditions was worked out.
(2) With the immersion nozzle with silicaless inner porous refractory, the hot argon gas inlet pressure does not drop. Therefore, when the initial gas inlet pressure is substantially high, a longitudinal crack tends to occur easily in the powder line which deteriorates in strength due to in the latter half of casting operation.
(3) By increasing the immersion nozzle wall thickness to improve its strength and controlling the hot argon gas inlet pressure below the crack formation pressure, it is possible to prevent cracks in the immersion nozzle with silicaless inner porous refractory.

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A waste-free steelmaking process, in which slags are recycled inside the steelmaking process itself by using a so-called slag regenerator, has been proposed, and its possibility was investigated by means of computer simulations.
There are two kinds of discharged slags from the proposed process. One from the desiliconization furnace and another from the final dephosphorization furnace. The former slag would have no problem to be returned to a blast furnace or to a sintering process due to its low phosphorus content, while the latter could be used as fertilizer materials for its high phosphorus content such as 10 mass%.
In a case that the blast furnace hot metal was of a composition of 5.04%C-0.12%P-0.50%Si-0.30%Mn on mass% base and half of the regenerated slag was recycled to the desiliconization furnace, the [P] level in the steel could be as low as 0.0087 and the total lime consumption for the whole process was approximately 20 kg/t HM. This lime consumption was about 1/2 of that in some conventional converter refining processes.

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The calculation method of loads on the new beam rolling mill "Skew Roll Mill (SKM)" is proposed in order to select adequate rolling conditions for the web expansion of H-beams by SKM. Firstly, the equation of the mean compression stress in the direction perpendicular to the roll axes during the thickness reduction at both ends of the web is introduced by both the equilibrium equation of lateral stresses in the plane strain state and yield criterion. Secondly, an experimental equation of the boundary stress at both the rolling start point and tha rolling end point is established from plasticine-model and hot-rolling-model experiments. Moreover, an equation of the mean roll pressure is given by combining the equation of the mean compression stress with the experimental equation of the boundary stress. As a result, equations of the radial force are introduced by use of the mean roll pressure. Then equations of the thrust force depending on the radial force, the strain stress and shear stresses are introduced. The rolling torque can be calculated by use of the radial force and the thrust force. Calculated reuslts by this model in various rolling conditions have agreed well with hot-rolling-model experimental data.

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In order to predict the deformation process of a liquid droplet impacting on a solid surface at room temperature, the mathematical model has been built up including the effects of surface tension as well as slip mechanism of contact line working in accordance with the degree of wettability on the solid/liquid interface. The numerical droplet deformation process has been compared with the experimental data for some Weber number cases and has been found to be in fairly good agreement not only in the spreading process, but also in the subsequent reducing process. It has been proved that the present model is enough to predict the droplet deformation process. Also, it has been clarified that the droplet deformation process on the solid surface is strongly influenced by the effects of the surface tension as well as the slip phenomenon to keep a proper contact angle.

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The forming conditions strongly influence the product quality. The integrated simulation model "Rod and Wire", which was specially developed, tested and adapted for the rolling of rods and wire, allows the preliminary calculation of important local microstructural and forming parameters. The simulation model "Rod and Wire" comprises several modules: deformation and speed fields, temperature distribution in the deformation zone and the delay time, microstructural parameters (grain size recrystallized fration) and transformation structure, strength of selected steel grades. The results of simulation can be used as a basis for the material evaluation of plants and processes. By examples, it was shown how the effect of process-related influences on product quality can be accurately determined and quantified.

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Our previous works show that S promotes the spalling of Al₂O₃ coating film, and that Y₂O₃ dispersion, as well as rare earth metal (REM) addition, suppresses the spalling through trapping S. In this work comparison was made between dispersion effect of Y₂O₃ and other oxides. Surface segregation of S was measured in an Auger electron spectroscopy system on several alloys. Then they were coated with Al₂O₃ and cyclically heated at 1100 K. The spalling promotion effect of S was little on Fe-20Cr ferritic alloys with any oxide dispersion because of small difference in expansion coefficient between Al₂O₃ and the alloy. In accord with previous works the S effect was very extensive on type 316 austenitic stainless steel by casting without oxide dispersion. But the spalling was moderate on mechanically alloyed 316 steels with Y₂O₃ or Al₂O₃ dispersion although any oxide could not trap S. This result suggests that mechanical alloying method gives the steels some effect to suppress the spalling. Thus the difference between Y₂O₃ and other oxides dispersion was scarcely observed on these 2 series of alloys. On the other hand, the defference between Y₂O₃ and REM was very clear. Y₂O₃ suppressed surface segregation of P but REM did not. The S trapping effect by REM was reconfirmed.

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The age hardening behavior and microstructural characteristics of a 53Ni-20Co-5Mo-4.9Al-1.3Ti alloy has been investigated by micro-Vickers hardness test and transmission electron microscopy. The shape of γ' precipitates was spherical at the early stage of aging and was cuboidal at the later stage. The aged hardness of the alloy closely related to the size and the quantity of γ' precipitates. The γ' precipitation cannot be suppressed by water quenching after solution treatment. It is necessary to cool the specimen at rates of higher than 10⁴ K/s for restraining the precipitation of γ' phase. The growth kinetics of γ' precipitates in the alloy followed the prediction of Lifshitz-Slyozov-Wagner (LSW) theory for growth under volume diffusion control at all aging temperatures examined. The activation energy for the growth was estimated to be 266 kJ/mol which was close to those of diffusion of solute atoms such as Al, Ti and so on in Ni and Ni-base alloys. The actual particle size sidtribution of γ' precipitates was somewhat different from distributions predicted by the LSW and Brailsford-Wynblatt encounter modified (BWEM) theories.

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Mechanical properties of a 0.14%C-1.9%Si-1.7%Mn TRIP steel have been studied especially from the aspect of the plastic stability of retained austenite which was varied by changing bainite transformation time at 400°C. The plastic stability of retained austenite and the strength-ductility balance at room temperature are improved with the increase in C content in retained austenite after opimizing the bainite transformation time in the continuous annealing process. Martensitic transformation can occur from the plastically unstable retained austenite with low C content. The kinetics model for deformation-induced martensitic transformation explains the experimentally obtained change in volume fraction of retained austenite with plastic strain in terms of the C content in retained austenite.

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Mechanism of the formation of intragranular ferrite plates in medium-carbon steels for hot-forging were investigated and the toughness of the steels with the microstructure consisting of intragranular ferrite plates were evaluated. The formation of intragranular ferrite plates was clarified to be enhanced by the addition of both vanadium and nitrogen in the steels continuously cooled after heated at 1250°C. It was observed that the vanadium nitrides precipitating on manganese sulfide particles acted as nucleation sites of intragranular ferrite plates. It is well known that vanadium carbide precipitates in ferrite matrix holding the Baker-Nutting orientation relationship with respect to ferrite matrix in the steels with low nitrogen content and that the lattice mismatch of the interface between vanadium carbide and ferrite matrix is small. In the case of steels with high vanadium and high nitrogen, vanadium nitrides precipitating in austenite matrix during cooling are thought to act as nucleation sites of intragranular ferrite plates. It may, therefore, be concluded that the factor governing the formation of intragranular ferrite plates is the presence of precipitates which can develop coherent, low energy interphase boundaries with ferrite in austenite. The toughness of medium-carbon steels with tensile strength higher than 1000 MPa were shown to be improved through the formation of intragranular ferrite plates.

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There are three controversies regarding the formation of bainite. One concerns the mechanism by which lattice atoms leave the fcc lattice and form the new bcc lattice. The second one concerns the question of local equilibrium and the role of carbon diffusion. The third one concerns the question whether each little region transforms in two steps or not. These questions are examined in the light of experimental information, including information from very rapid cooling experiments.
The information seems to indicate that the lattice atoms move by a diffusive mechanism and there is carbon diffusion under local equilibrium for carbon at the fcc/bcc interface, but not for the lattice atoms.

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A new cell model of slag is proposed in which complex interaction between oxygen cells is considered. Results obtrained for CaO-FeO, FeO-SiO₂ and CaO-SiO₂ systems agree well with published experimental data.

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