The structure of the icosahedral phase is still not fully understood, though many works were published. There are researchers who still do not believe in the intrinsic quasi periodic structure of the icosahedral phase. This paper reviews the structure of quasicrystals, which is a general term for phases with aperiodic orientational order of atoms including icosahedral phase.

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The powder of amorphous Fe-16Cr-8Mo-18C-4Si alloy having the size below 25μm has been produced by the ultrasonic helium atomization. A fully dense material with finely and homogeneously mixed structure of α+M₇C₃+M₆C phases can be obtained by hot pressing the amorphous powder at temperatures of 1300 to 1950K. The packing fraction of the hot pressed alloy is about 100%, and the particle size and the interparticle distance of the carbides are as small as 0.6-1.0μm and 1.2-1.9μm, respectively. The hot pressed alloy has high hardness, e.g., 965 DPN at room temperature and 400 DPN at 1073K, as well as good wear resistance which is comparable to the highest value of commercial wear resistant high alloy steel. Since the alloy produced by hot pressing the amorphous high carbon-high alloy steel powder shows high hardness and good wear resistance at temperatures of room temperature to 1073K, it is expected to practically use as a heat-resistant tool material.

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Characteristics of superplasticity in a duplex stainless steel produced by a direct strip casting (DSC) technique have been studied. The thickness of a strip is 1.2mm. The effect of temperature, initial strain rate and cold rolling is investigated. The results are compared with the same type of steel manufactured by the conventional process. An as-cast strip shows superplasticity at 1273K. The superplasticity is enhanced by cold reduction through recrystallization and sigma phase precipitation during heating. An as-cast strip followed by 50% cold reduction without annealing is superplastic at 1173K or higher temperatures. The obtained maximum elongation of cold rolled strip is 1029% when strained for a rate of 8.33×10^-4s^-1 at 1273K. The mechanism of superplasticity in these materials is discussed. The precipitation of fine austenite phases occurs during heating, and the straining at a high temperature causes grain rotation so that the microstructure is equiaxed. Rapid cooling by a pair of drums makes it possible to reduce compositional segregation. The effect of cold reduction is remarkable by acceleration of precipitation of both sigma phase and austenite phase to supply large grain or inter phase boundary area. The superplastic ductility by the sigma phase is enhanced at a relatively higher strain rate range than by austenite phase. This may be explained by that sigma phase precipitation occurs faster than recrystallization of austenite phases at heating and straining stage.

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Experiments on the strip casting of a Type 304 stainless steel have been done by the use of a twin-roll caster with the copper alloy rolls of 400mm diameter and 300mm wide. Cast strips of 120kg with good shape and appearance were obtained with high reproducibility. The casting speed was 17-40m/min, and the length and thickness of the strip were about 30m and O.8-2.3mm, respectively. At an early stage of the casting operation the thickness reduces rapidly, and then approaches a constant value. According to the analysis of heat transfer and thermal expansion of rolls, the early decrease in thickness seems to be caused by the thermal expansion of rolls. The cast strip is not free from defects which should be minimized. The microstructure and segregation of the cast strip have also been inves-tigated. The tensile properties of the cold rolled sheets by this process satisfy those as a Type 304 stainless steel.

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The mechanical properties of low carbon steel sheets produced through the process of rapid solidification casting, cold rolling, and annealing are studied for the purpose of developing sheets with deep drawability by a strip casting method. For a continuously annealed low carbon Al-killed steel sheet, a treatment for grain-refinement of the rapidly-solidif fled plate is favorable to render the r value and tensile properties comparable to the products of conventional continuous casting process. Batch annealed low carbon Al-killed steel sheets produced from the rapidly-solidified plate show good drawability, even though the cast plate has a coarse acicular ferrite structure.

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Classical levitation melting process using conventional conical inductcr can not be used at industrial scale because of the limited size of liquid metal which can be maintained in equilibrium against gravity force. Because of high frequency and axisymmetry of magnetic field distribution, a stagnation point occurs at the bottom of the liquid load, where only surface tension can balance hydrostatic pressure. The use of cold crucibles with particular shape does not suppress the stagnation point but reduces region where magnetic field is deficient. Consequently possible loads of liquid metal which can be levitated are considerably increased. Numerical modeling of cold crucible and of equilibrium shape of levitated liquid metal provides a useful guide for tayloring levitation melting devices.

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Measurements have been done on the rates of nitrogen absorption and desorption of levitated iron droplets. On the assumption that the mass transfer between two phases determines the total reaction rate, the kinetics of this reaction has been studied. The results obtained in the present work are as follows: The rate equation with the same parameter a conformed to both the rates of nitrogen absorption and of desorption. A decrease in influence of oxygen in the melt on the rate constant of the melt phase with increasing temperature was interpreted to be due to the increase infraction of bare surface. In connection with Arrhenius equation, it was suggested that the rate of surface chemical reaction is not possible to be the rate determining factor.

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A bottom-blowing nozzle of a converter, being featured by a wide range of flow rate controllability and a low wearing rate, has been studied with the view of developing a top- and bottom-blowing converter which is capable of producing a wide variety of steel.
(1)When an inert gas is injected into the steel bath through the bottom-blowing nozzle, a so-called mushroom (solidified iron) having extremely small pores is formed atop the nozzle by the cooling effect of gas.
(2) When a stable mushroom is formed atop the nozzle, the flow rate controllability and the wear rate of the nozzle are improved.
(3) In order to form a stable mushroom atop the nozzle, it is most effective to use a nozzle consisting of multiple small-diameter pipes.
(4) There is a proper range for the diameter of individual pipes. On the basis of the heat transfer model it has been established that, for the specified diameter, there is the minimum value both for the distance between neighboring pipes and for the gas flow rate to form a stable mushroom atop the nozzle.
(5) This bottom-blowing nozzle allows to control the bottom gas flow rate over a wide range and ultimately makes it possible to control the iron content in slag (T.Fe) widely. In a low carbon region, the iron content can be reduced by bottom gas injection with the full flow rate. In a high carbon region, the nozzle can be used at a low gas flow rate to increase the iron content and ensure proper dephosphorization of the same level as in a top-blowing converter. Thus, this process is applicable for the production of all grades of plain carbon steel.

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A new mathematical model of which the dynamic equations of material and heat balance are combined with the exhaust gas information obtained by mass-spectrometer has been established for the improvement of the end point control of BOF.
The outline of the model calculation is as follows:
(1) From the amounts of oxygen and submaterials charged into BOF and the composition and flow rate of the gas exhausted from BOF, the amounts of oxygen consumed on the surface of cavity of molten steel and of oxygen consumed by decarburization can be determined.
(2) The transition of composition and temperature of steel bath can be estimated from the amount of oxygen calculated by the above way on the basis of model of reaction theory.
At No. 1 BOF shop in Wakayama Steel Works, the model is now being used as the guide of the operation and contributes to the reduction of reblow ratio.

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Spalling phenomena of the backup rolls used for hot strip mills and their prevention are discussed. The spalling on the surfaces of backup rolls is classified into two categories: excess rolling contact fatigue resulting from the local wear in roll barrel and propagation of the surface cracks generated by thermal shock in the mill accidents such as squeezing and roll slip, and also by incomplete removal of the cracks in roll dressing. Factors for preventing the spalling phenomena are studied from the experiments in both production mills and laboratory. The spalling tendencies are correlated with the carbon and chromium contents, areal fractions of carbides, and fracture toughness values of roll materials. To prevent the spalling, therefore, it is necessary to control and improve both properties of roll materials and procedures of roll maintenance.

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