Sintering technology that lowers the SiO₂ content from 5.6% down to 4.9% has been achieved at Kobe Works on the basis of the following concept: the desirable structure of quasi-particles for low-SiO₂ sinter consists of limonite ores as the nucleus and fine ores with low SiO₂ and Al₂O₃ contents as adhering particles. In addition, the basicity and MgO content of sinter should be increased. As a result, the reducibility and high-temperature properties of sinter have been improved, though the RDI value of sinter increased. The use of low-SiO₂ sinter in the Kobe No. 3 Blast Furnace has brought about the increase in overall permeability due to an increase in permeability at the lower part of the furnace, in spite of a decrease in the upper part. This increase has contributed to an appreciable increase in the ore/coke ratio and rate of pulverized coal injection.

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Free surface fluctuations of molten steel in the mold of a continuous caster are considered to have a significant effect on the surface quality of the cast. To find out the relationship between the surface wave motion of molten steel near the mold wall during casting and mold oscillation, the meniscus of molten steel in the mold was directly observed through a quartz glass window mounted on the mold wall. As a result, it was confirmed that the meniscus fluctuates at the same period and phase as those of the mold oscillation.

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To quantify the solute redistribution during solidification, an approximate solution of the Brody-Flemings model of dendritic solidification has been derived on the assumption of parabolic solidification and a constant partition ratio, and compared with an exact solution of the model. It has been shown that the approximate solution has good accuracy. Further, on the basis of the derived equation, an extended mathematical model is proposed, incorporating a thermal model of solidification into the analysis without assumption on the solidification rate. The extended model includes the treatment of multi-component alloy and δ/γ transformation, the temperature dependence of diffusion coefficients and the estimation of the diffusion path. The extended model provides the results consistent with the available data.

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A mathematical method is presented to quantify solute redistribution during solidification with δ/γ transformation; new methods to solve the equation of diffusion numerically and to estimate the equilibrium phase diagram of multi-component low alloyed steel are described. Thermal analyses of low alloyed steels were made to verify the mathematical method described. It has been shown that the unequilibrium phase diagram of low alloyed steel for a given cooling rate can be predicted by this method.

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In order to study fundamental technologies required for thin slab casting, the solidification mechanism in a mold has been investigated by the use of thin slab of 30mm×100mm cast at withdrawal speed of 3.8 to 5.1m/min with a laboratory scale twin-belt caster. In the caster, a movable steel belt is used as the wide face and a stationary copper plate as the narrow face. From the observation of thin slab cast, it has been concluded that the solidified shell is formed continuously at the wide faces and intermittently at the narrow faces. The occurrence frequency of ripple marks observed on the narrow face is related to the connecting condition between the nozzle and the stationary plate, the tensile strength of the shell and the friction force in the mold. Countermeasures against the occurrence of corner and transverse cracks are discussed in connection with the ripple mark and the brittleness of the γ grain boundary in coiling practice of thin slab cast.

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In present work, molten Sn and Sn-Cu have been pulverized by an impact atomizer which has a bladed rotator. The powder properties, especially mean particle size, specific surface area and particle shape, have been related with the operating conditions for atomization. The relations give the informations for the size and shape controls of the powder particles on the atomizing method.

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An improved tint etching method was developed to obtain a quantitative measure of the microstructure of high strength steel sheets with a mixed structure. The procedures of etching are presented with typical examples. The present method reveals ferrite in blue, martensite and retained austenite in light yellow, and bainite in brown. Each constituent is identified by electron microscopic observations of the same area on etched microstructure. The different colors are analyzed to be a result of difference in the thickness of etched films by means of Auger spectroscopy. The new method is combined with image analysis to determine quantitatively the fraction and morphology of microconstituents.

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Sulfide stress cracking (SSC) in AISI 4130 type steel containing small amounts of Ni up to 1% is investigated. A Shell-bent-beam test shows a significant detrimental effect of Ni, whereas no effect of Ni is observed in a slow strain rate tensile (SSRT) test.
These results suggest the importance of plastic deformation introduced at the stress-concentrated portion in a Shell type specimen. It is revealed that cold work remarkably deteriorates the SSC resistance of Ni bearing steel through an acceleration of pitting corrosion, even though its Ni content is as low as 0.1%.

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Rusts in the crevice areas on vehicle used in Quebec State in Canada and Okinawa island in Japan were collected and studied through a quantitative analysis of their composition. From these results, the corrosive environments of automotive body in each salt pollution region are revealed as follows:
(1)The crevice areas on vehicle are surrounded by the corrosive environment of a low pH and concentrated Cl^-.
(2) In Okinawa, they are surrounded by the high humid environment at high temperature in addition to the corrosive environment as described above.

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