The reduction behavior of constituent minerals of iron ore sinter has been investigated microscopically by using two kinds of commercial sinter having different basicity and FeO content. The results are summarized as follows:
(1) There is a difference in reducibility between hematite and magnetite, and hematite is reduced faster than magnetite.
(i) Both hematite and magnetite are reduced rapidly to wustite, but there is a difference in the rate of reduction from wustite to iron.
(ii) The reduction of wustite reduced from hematite does not proceed topochemically but homogeneously. Although the reduction of the wustite is comparatively fast in the almost whole period of reduction, part of the wustite becomes surrounded by dense iron and left unreduced in the final stage of reduction.
(iii) In the reduction of wustite reduced from magnetite, almost all grains of wustite are surrounded by dense iron from the early stage of reduction, which causes the retardation of reduction.
(2) Calcium ferrite is reduced much faster than the wustites mentioned above, which is shown by the fact that many grains of wustite are left unreduced even after calcium ferrite is reduced completely.
(i) The reduction of calcium ferrite proceeds topochemically.
(ii) Iron produced by the reduction of calcium ferrite is very porous and not sintered, which does not cause the retardation of reduction.
(3) In many cases, reduction begins with the surface of mineral grains facing a macro-pore, which serves as a passage of reducing gas to each mineral grain to be reduced.

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A sample sphere of hematite, 3.3cm in diameter, was reduced by H₂ and the variations of pressure and temperature within the sphere were continuously measured. At a reduction temperature 1168K, the pressure and the temperature at the center of the sphere became 116mmHg higher and 23K lower, respectively, than those in the ambience. The variations of the pressure increase and the temperature fall were simulated according to the unreacted-core shrinking model with 3 reaction interfaces by use of the dynamic effective diffusivity. The calculated results were well consistent with the experimental results and the following conclusions were obtained.
(1) The variations in pressure and temperature within the sphere reflected the progress of the reduction steps of Fe₂O₃ and gave useful information for analysing the consecutive reaction proceeding with multiple reaction interfaces.
(2) The effect of the pressure increase on the overall reduction rate was remarkable, because the rate calculated under the isobaric assumption was much faster than the experimental one.
(3) The difference in temperature between the center and the ambience of the sphere was not so large that the calculated results for isothermal and non-isothermal conditions gave almost the same overall reduction rate.

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Dense Wustite micropellets having different sizes (W.1-W.4) were isothermally reduced at 900-1100°C with H₂, CO and H₂-CO mixtures. The reduction was conducted with a microforce balance and the weight changes during reduction was recorded. Surface area measurements light and scanning electron microscopy and X-ray and carbon analyses were used to elucidate the kinetics and mechanisms of reduction.
The influence of micropellets size, reducing gas composition at different temperatures were extensively studied. At 900-950°C a reaction rate minimum was only detected in H₂ and H₂-rich gas mixtures which was attributed to α-γ-transformation of the formed metallic iron.

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A formula has been derived which predicts the degree of negative segregation due to bulk liquidfow during solidification of alloys. The formula includes the alloy composition, the primary dendrite-arm spacing and the width o f the mushy zone as well as the solidification condition and the bulk flow rate. It is ascertained that the formula can be applied both to aluminum-copper alloys solidified unidirectionally from a copper chill face under flow conditions and to continuously cast high carbon steels electromagnetically stirred during their solidification.

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To decide on the condition where injected particles penetrate into liquid through the gas-liquid interface and disperse in liquid, the water model experiments have been done. The penetration distance of a particle is closely related to the parameter defined as the ratio of the kinetic energy of a particle to the drag force of liquid on a particle. The dispersion behaviour of penetrated particle is influenced by the gas flow rate and the density and diameter of the penetrated particle, and can be expressed by the parameter defined as the ratio of buoyancy force to the drag force of liquid on a particle. The dispersion behaviour of penetrated particle also depends upon the physico-chemical properties such as wettability. Moreover, this result has been confirmed by the hot model experiment.

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The unidirectionally solidified large scale (USL) ingots, which have low height and large expanse, were developed based on the results of the simulation experiments with the ammonium chloride solution. The USL ingots were found to be free from V segregates, the loose structure and the accumulation of non-metallic inclusions. The intensity of top segregation of USL ingot closely related to that of the negative segregation in the region which solidified from the mold wall. Both segregations, however, can be minimized by optimizing the mold wall design and they can be completely removed by conditioning to obtain the highly homogeneous and sound ingot. It was found that the wider the ingot, the milder the top segregation. It was realized that the USL ingot was suitable for production of high grade heavy gauge plates of the large unit weight. The manufacturing process of high grade heavy gauge plates was completed by the combination of USL ingots and the low-speed heavy-reduction plate rolling technique. The qualities of the plates produced by the process were found to show superior mechanical properties, homogeneity, cleanliness and workabilities for manufacturing pressure vessels. The maximum thickness and the size of the plate were both substantially expanded.
The formation mechanisms of the sedimental crystal zone and the top segregation in the ingot were also suggested in the course of development of the USL ingots.

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The processes of recrystallization and annealing-texture formation in rapid heating and isothermal annealing have been observed in cold rolled sheets of a low-carbon titanium-added steel which were subjected to three types of heat treatments prior to cold rolling: quenching from 1250°C (Q₀) and the subsequent annealing for 0.5hr (Q_0.5) or 100 hr (Q₁₀₀) at 700°C. In the 850°C-recrystallization, the relative intensity of (111) reflection was lower, while that of (110) reflection was higher, in specimen Q₀ than in specimens Q_0.5 or Q₁₀₀. On the other hand, in the same specimen (Q₀) annealed in two stages, the 1st at 700°C and the 2ndstage at 850°C, the {111} recrystallization texture developed markedly. In the early stage of annealing of the specimen Q₀ the recovery was suppressed probably by the effects of interaction of titanium or Ti-C dipoles with dislocations. From the thermoelectric power vs, conductivity diagram and the transmission electron micrographs, the amount of recovery before commencement of recrystallization was estimated to be larger in specimen Q₁₀₀ than in specimen Q₀. In addition to the changes of deformation structure and texture that arise from the scavenging of interstitial solute atoms, the increased amount of recovery before nucleation of recrystallized grains was pointed out as one of the important factors which develop the recrystallization texture characteristic to the low-carbon titanium-added sheet steels.

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The use of air-atomizing mist nozzle for the secondary cooling of continuous casting machine results in the following advantages over the conventional water spray nozzle: less longitudinal surface cracks and higher temperature of cast slabs, wide control range of cooling, and prevention of nozzle clogging. The air injection to the water spray nozzle is also good for preventing nozzle clogging.
The authors have developed a few types of air-atomizing nozzles and their application techniques, including methods of injection, for the secondary cooling system of the slab casters.
Discussed here are structural and fluidic features of the newly developed mist nozzles and the air-injection type spray nozzle with reference to some technical points concerning the new cooling system and the operational results.

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A dual phase steel has been developed for which grain refining treatment subsequent to vacuum carburizing treatment at high temperature above 1000°C is not necessary. This 2wt% Si steel, which contains 0.3 wt% V and 0.04 wt% Nb, has a fine structure in both the core and case, sufficient surface hardness and excellent mechanical properties equivalent to those of SCr 420 steel, even without grain refining treatment subsequent to vacuum carburizing at 1050°C.

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A grain growth simulation model consistent with the commonly observed phenomena has been derived from the grain growth theory for a pure metal. We have then simulated the process of the grain growth and discussed the grain morphologies.
We have been able to obtain a qualitative agreement between the simulation and laboratory experiment in that at low temperatures, the growth rate is slow, while at higher temperatures, the grain growth is more promoted. Again, in our simulation model, the growth does not indefinitely continue toward the single crystal. Rather, the grains tend to cease to grow in the long run, and the system of the grains is left in a state such that moderate local competitions remain at the grain boundaries. We have also investigated the process of the grain growth as well as the grain morphologies using α-iron, and compared the experimental results with the computational ones obtained by the simulation model. The agreement between the two has been found fairly satisfactory.

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A simple test method “Lateral Compression Bend Test” was developed to evaluate crack arrestability of steel plate and line pipe. In the test, a V-press notch is introduced at crack initiation site after the lateral compression has been processed. The lateral compression bend test was applied to several kinds of steel plate and line pipe, and the industrial utility of the test was verified.

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