No. 6 Blast Furnace at Chiba Works of Kawasaki Steel Corporation, Japan's first large blast furnace equipped with Bell-less charging equipment, started its operation. The Bell-less top charging techniques have been completed with fundamental experiments and operational experience in this blast furnace. In July, 1979, test operation using burden composed fully of agglomerated ore (sinter and pellets) was performed for further operational stabilization. As a result, No. 6 Blast Furnace set the record of 429kg/t in low fuel rate operation of the large blast furnace with Bell-less top.

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Regarding the reduction under load test for measuring high temperature properties of blast furnace burdens, the test conditions, i.e. the load, gas flow rate, particle size and bed height were examined through tests and calculations based on a reduction model for fixed bed. Examinations covered also evaluation criteria of test results for high temperature properties.
The results obtained are summarized as follows:
(1)Test results are influenced by each of the load, gas flow rate, particle size and bed height conditions.
(2) It is desirable to minimize the longitudinal difference of degree of reduction and the dependence on load of test results. The optimal test conditions (Fig. 2) were decided from such a point of view.
(3) The following evaluation criteria of test results for high temperature properties were proposed: (i) the temperatures at the beginning of softening and melt-down are high, with a small temperature difference; (ii) the integral and average values of index of permeability resistance between softening and melt-down are small; and (iii) the degree of reduction achieved at 1000 to 1200°C is high.

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An investigation has been made on the effects of the annealing conditions and cooling rates on the Charpy impact value and the other mechanical properties of Ti and Nb stabilized low C, N-19%Cr-2%Mo stainless steel sheets. The precipitation of Laves phase has a great influence upon the mechanical properties of the steel. Therefore its precipitation behavior has been investigated in connection with the manufacturing process. On the basis of these studies, the best process has been proposed.

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The effect of Nb content in HSLA steels on hot ductility was investigated under various thermal cycles. The increase of Nb content was found to deteriorate hot ductility in all the thermal cycles investigated. The change in hot ductility with temperature gave rise to only one trough in the temperature region from 700 to 900°C, which covered the lower temperature region of the austenite (I), and the γ-α region (II). The strain concentration in the ferrite primarily reduced hot ductility in the region II, and the increase of Nb content reduced hot ductility remarkably in region I, where grain boundary precipitates such as Nb(CN) primarily controlled hot ductility. The latter fact was confirmed through the studies of fractography and reversibility of hot ductility behavior. The improvement of hot ductility in the Nb-bearing steels was shown to be attained by adoption of the thermal cycle corresponding to hot charging process of the ingot or the slab, and also by the decrease of N content or the addition of the small amount of Ti. Relation between hot ductility and hot deformation mechanism, such as dynamic recrystallization or grain boundary sliding, is discussed.

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Concerning the formation of macrosegregation in ingots, it is well known that the channels are smooth on the side facing the outside of ingot and rough on the side facing the inside of ingot.
In this work, these phenomena were reproduced by the model experiments using NH₄Cl-H₂O system and the progression of channel formation was precisely visualized. The experiment indicated that the channels were melted on the side facing the outside of ingot and solidified on the other side, and that the interdendritic liquid flowed into the channels through the wall facing the inside of ingot and a part of the liquid flowed out the channels through the other wall. The difference in the roughness between both walls is theoretically explained on the basis of transport phenomena in this paper.

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The softening and melting characteristics off some pellets and sinter during the reduction and the heating were examined by using an X-ray TV apparatus. The structure of the samples after the experiment were also examined by a microscope and an electron microprobe analyzer.
For the runs without load, the melt-down temperatures varied from 1250°C to the melting point of iron according to the reducing conditions and rose with the increasing reduction degree.
An application of load lowered the melt-down temperature of each sample, which strongly depended upon the properties of the formed slag.
The EPMA analysis shows that the slag containing a small amount of iron oxide is formed in Hirohata P. of high melt-down temperature, but much iron oxide, about 50%, is contained in the slag formed in Robe River P., which melts at a low temperature.

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To cope with rapid increase of oil prices in recent years, this project started in the fall of 1978 with the object of COM injection into commercial blast furnaces to achieve a reduction in heavy fuel oil consumption. The project is being carried out in partnership with the Coal Mining Research Center under the sponsorship of Ministry of International Trade and Industry. The COM flow tests indicate that the pressure drop of COM in the pipe can be precisely estimated by a pseudo plastic fluid model using the viscosity measured by a cone and plate viscometer.
On the other hand, through the COM combustion tests by the experimental blast furnace it was found that 60 to 85% of injected fine coal was combustible in the raceway and that there was little difference in the gas permeability between COM and oil alone. It is expected that the COM injection rate can be maintained higher than that of heavy fuel oil to keep the theoretical flame temperature at the same level.

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The effect of hot rolling condition and chemistry of steels on the onset temperature of γ-α transformation after hot rolling was investigated using a thermal analyzer developed for the measurement of A_r3 temperature after hot rolling. The changes of A_r3 temperature and austenitic microstructure in connection with reheating temperature, rolling temperature and reduction rate were investigated in a Si-Mn and a Nb-bearing steels. The results were analyzed based on the changes of the effective interfacial area per unit volume (S_v) that included both of the recrystallized and unrecrystallized grain boundaries and deformation band as nucleation sites for ferrite. Although the S_v value increased with the refinement of recrystallized γ grain or the increase of rolling reduction below recrystallization temperature of austenite, the latter resulted in a much greater change of A_r3 temperature in the Nb steel. This was considered to be due to a reduced amount of dissolved Nb atoms around the grain boundary or deformation band through the strain induced precipitation of Nb(CN).
The effect of chemistry and plate thickness on the A_r3 temperature after controlled rolling was studied in a large number of steels with different chemistry, and the relation between the A_r3 and chemistry was quantitatively established based on the multiple regression analysis.

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Refining of the solidification structure of Type 430 stainless steel by the electromagnetic stirring was studied. By the preliminary tests for small ingots, it was made clear that the following conditions must be satisfied for a preferably equiaxed solidification:
1) the formation of sufficient fragments of solidified steel which act as nuclei, and
2) the stability of nuclei in the molten pool.
A pair of linear-motor type stirrers was set in the slab machine and Type 430 steels were treated by the electromagnetic stirring under various conditions of stirring powers, stirring modes and superheats of liquid steels. By controlling these conditions, the formation of equiaxed structure having the thickness more than 50% of slab was realized and the ridging of cold sheet was improved.

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