An overview is made on recent research and development in rapid solidification technologies in Japan. It includes basic researches on such as metastable phase diagrams, structure and properties of rapidly solidified materials, and various types of processing to produce powders, ribbons, wires, and sheets thinner than 10mm. The promise of the processings and problems to be solved are also discussed.

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To understand the formation of rapidly solidified metal wire directly from the molten state by the In-Rotating-Water Spinning Method, some experiments have been done by the use of Pb-Sb alloy. In the experiments, the behavior of molten metal jet in rotating water was directly observed to reveal that the jet orbit closely relates with the cross-sectional shape, longitudinal shape and continuity of wires obtained.
Under the experimental conditions adopted in this study, it has been confirmed that the apparent properties of the wire are influenced mainly by both the jet velocity and the water-drum velocity. With increasing ratio of the jet velocity to the water velocity, molten metal jet penetrates deeper into rotating water. The range showing the optimum conditions for the production of long-continued straight wire has also been determined.
Furthermore, the theoretical methods to estimate the jet velocity at the nozzle outlet and the jet orbit in water have been developed. The jet velocity of molten metal can well be predicted by the use of the equivalent nozzle orifice diameter obtained from the water experiment on the characteristics of nozzle. The calculated jet orbit agrees well with the observed results.

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A new technique has been developed to obtain large supercooling for Fe-C alloys. A mother alloy was prepared by the addition of rare earth metal (REM) of 0.75mass% to molten Fe-C alloy of 2kg. A specimen weighing 0.08kg was taken out o f the mother alloy and charged into an alumina crucible. The procedure of melting and freezing of the specimen was repeated in a Tammann furnace. The surface layer of the solidified ingot was removed after being repeated the procedure of melting and freezing for several times, and then the procedure was further repeated. By this procedure the supercooling of 100K was obtained. Furthermore the non-dendritic structure and uniform concentration of carbon were obtained by supercooling.

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Spherical particles having the diameter of 0.5 to 1.4mm have been produced by the ejection of Fe-Ni-C-B liquid alloy into circulating cold water containing 1vol% of surface active agent. The rapidly quenched structures are the supersaturated γ phase in the entire composition range of nickel for the Fe-Ni-5C-5B, and γ+M₂₃(B, C)₆+M₃(B, C) in the range below 0.40Ni/(Fe+Ni) and γ+M₂₃(B, C)₆ in the higher Ni concentration range for the Fe-Ni-C-B alloys above 10%C and 10%B. The sphericity of particles defined by the ratio of the minimum diameter to the maximum diameter is above 97%. The diameter of particle (D) is about three times as large as that of orifice (2r) of the quartz nozzle. The size ratio is interpreted under the assumption that the fragmentation of ejected molten metal stream takes place in the progress of the oscillation leading to the increase and decrease in diameter at a localized position under the appropriate balance between the surface tension and the internal pressure f liquid. From the result that spherical particles are not formed in the cold water without the addition of surface active agent, a significant decrease in the surface tension of coolant by the addition of surface active agent is found to be essential factor for the formation of spherical liquid particles from the ejected melt stream. The iron-based particles with the diameter below about 1.0mm have the hardness ranging from 230DPN for the γ Phase to 1240 DPN for the γ+M₂₃(B, C)₆+M₃(B, C) phases. It is thus found that the iron-based spherical particles with high hardness and good sphericity are directly produced by the simple process in which the jet stream of molten metal is ejected into circulating cooled water.

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Experiments have been conducted to study the niobium, phosphorus and manganese distribution between MgO_sat.-Fe_tO-MnO-SiO₂ NbO_x slaps and liquid iron at 1600°C. It is shown that the niobium distribution ratio increases with the iron oxide content in slag, whereas the phosphorus and manganese distribution ratios remain almost constant. Also, the thermodynamic criteria governing the selective oxidation of niobium, phosphorus and manganese in the extractive process of niobium from hot metal have been discussed.

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For the endpoint control of the top and bottom blowing process in BOF, a simplified mathematical model which is suitable for the online application has been established by the following procedure.
(1)The basic equations for the rates of oxygen consumption and temperature increase, which have the comprehensive characteristics in both the ranges of low and carbon high carbon contents, have been derived in the current work.
(2) On the basis of the basic equations, the fundamental curves of oxygen consumption and temperature increase, which show the progress of blowing, have been determined by the analysis of the actual operational data. The fundamental curve of dephosphorization has also been determined in the same way.
(3) A control model for the endpoint carbon content and the endpoint temperature of metal has been established by the use of the fundamental curves.
At No. 2 BOF shop in Kashima Steel Works, Sumitomo Metal Industries, Ltd., the model is now being used for the automatic blowing and contributes to the reduction of reblow ratio and furnace refractories.

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The hot ductility of a C-Mn-Nb-AI steel, as measured by reduction of area in a tensile test, has been obtained after a variety of different cooling patterns to the test temperature. Samples were first solution treated at 1330°C and then cooled to test temperatures in the range 800 to 1100°C. One cooling pattern involved cooling at constant rate of 60°C min^-1 to the test temperature whilst the others involved temperature oscillations of constant amplitude. It was found that introducing cyclic temperature oscillations widened and deepened the ductility trough and this was further aggravated by increasing the amplitude of the oscillations. Replica examinations indicated enhanced NbCN precipitation during the temperature oscillations. It is concluded that temperature oscillations should be kept as small as possible during continuous casting to obtain optimum hot ductility.

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The relationship between the sharpness of secondary recrystallization texture and the morphology of AlN during secondary recrystallization was investigated through changing the dew point of primary annealing and the dew point and the N₂ partial pressure of secondary annealing atmosphere. The main conclusion is summarized in the following.
(1) The secondary recrystallization initiates near the surface layer of primary matrix when a gradient of the intensity of the inhibitor along the thickness direction is formed and reaches to a certain level at the specific temperature while the matrix grains are inhibited to grow because of the higher intensity of inhibitor. Here the intensity of inhibitor is defined as f/r (f: volume fraction of AlN or MnS, r: mean radius of AlN or MnS). The intensity gradient of AlN along the thickness direction is formed by the selective oxidation of Al during secondary recrystallization annealing.
(2) A critical temperature (T_cr) is required for the initiation of secondary recrystallization. The annealing temperature above T_cr weakens the sharpness of Goss oriented secondary. The results of secondary recrystallization behavior are explained in terms of the distribution of coincidence boundaries and their migration characteristics controlled by the intensity of the inhibitor.

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