Liquidus temperatures, obtained by the quenching technique, were studied for mixtures in the system CaO-SiO₂-Al₂O₃-Fe₃O₄ in 10^-7atm of PO₂ atmosphere. Analysis by EPMA of final silicate slag of sinter revealed that chemical compositions lay in the field near the pseudo wollastonite-dicalcium silicate eutectic line between 1250°C and 1300°C of the diagram.
N₂ quenching of sintering pot during operation and sintering simulation experiments of raw mix showed that there were two types of primary melt, which were liquid silicate and liquid calcium ferrite. Liquid caclium ferrite generated two types of structure, one o f which was consisted of quarternary calcium ferrite and silicate slag, the other was mainly composed of dicalcium silicate and dicalcium ferrite or magnetite.
With increasing temperature, primary silicate melt of low basicity dissolved dicalcium silicate to final slag of higher basicity.

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The photographing system with an ultrahigh speed shutter camera has been developed at Kimitsu No. 3 blast furnace. In this system, the shutter speed can be raised up to about 1μs, and the actual raceway can be observed over a long time with high accuracy in on-line real time.
The raceway images obtained with this system contain two sorts of the basic information, i.e., brightness and particle size of coke. By using these two informations, the two phenomena occurring near the raceway were elucidated; melting down behavior of the root of cohesive zone and change in coke properties. As a result, the mechanism for the periodical change of raceway brightness has been considered, and the degradation mechanism of coke in the furnace has been elucidated by analyzing the results of test operations using coke with various high temperature properties. Besides, this system has been used effectively in the blowing-out operation of blast furnace by lowering the burden level to the tuyere level.
Based on the observation results obtained with this system, change in coke properties in the furnace has been investigated by using the model experiments and mathematical calculations. As a result, the following facts were guessed to be occurred.
(1) Coke has already been deteriorated before running into the raceway.
(2) Impact energy working on coke circulating in the raceway was not so great.
(3) There was few cases where coke was degraded in the raceway by the thermal stress generated in coke particle when it came into the raceway.

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A method of determining the steady state temperature distribution in blast furnace hearth and bottom is given. Various cooling and lining systems were considered. A method of solutions coupling is applied. A fairly good agreement of computed and measured results is obtained.

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Experimental measurements are reported on the behavior of a laboratory scale ESR unit, operated both in the presence and the absence of an externally imposed electromagnetic field.
The main findings were the following:
-The imposition of an external magnetic field resulted in quite vigorous stirring, which was manifested by a rapid rotational motion of both the slag and the metal phases.
-The apparent metal pool depth was found to increase with increased stirring intensity.
-The formation of hydrogen blow holes could be suppressed by vigorous stirring, but the formation o f CO blowholes was not materially effected.
-The externally imposed stirring strongly promoted the formation of equiaxed solidification structures.
-A mathematical representation has been developed to interpret these results.

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Rifled boiler tube has high heat-transfer efficiency, and therefore is used for the furnace wall tube in the large power plant boilers.
The manufacturing technique which can ensure high dimensional accuracy of rifled tube were developed through experiments to clarify the rifle forming mechanism and develop the dimensional control method in manufacturing process. As a result, mass production of rifled tubes of good dimensional accuracy has now been made possible by cold drawing process.
Furthermore, it was made clear that the use of the ERW (Electric Resistance Welded) tube whose dimensional accuracy is excellent is advantageous because the dimensional accuracy of the rifled tube is influenced by that of the base tube (the tube before drawing).
The quality characteristics of ER W rifled boiler tube was also studied to find that the high temperature strength including creep rupture strength of the rifled tube under internal pressure depends on the dimensional accuracy of the wall thichness of the rifled tube at the groove.

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Carbidic precipitation and structural changes at elevated temperatures that markedly affect the susceptibility of austenitic CrNi welded stainless steels to intercrystalline corrosion, knife line attack, fissure attack and others in the fusion line zones, are considered. The areas of occurrence of intercrystalline attacks are connected to the potentiodynamic polarization curves for studied stainless steels. Special attention is given to the temperature conditions near the welded metal with regard to the corrosion failures of various areas of the welded joints. The generally encountered phenomena are the formation of chromium carbides after the dissolution of stabilizer carbides in a solid solution or the formation of nitric acid soluble dendritic titanium carbides. There is also the possibility of fusion line corrosion not associated with carbides but with either delta ferrite, segregation effects in austenite or existence of significant internal stresses.

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The corrosion behavior of nickel base heat resisting alloys is investigated in steam at 800°C and 40atm, simulating the superheated steam of the nuclear steelmaking system. The alloys tested are five new alloys developed for the nuclear steelmaking system and one commercial alloy Inconel 617.
A protective surface oxide scale, consisting of Cr₂O₃ mainly and of MnCr₂O₄, forms on the alloys except Inconel 617. Internal oxides, consisting of Al and Ti oxides, also form in the alloys containing Al. For Inconel 617, nodular oxides, consisting of NiO in the outer region and Cr internal oxides in the inner region, form in addition to Cr₂O₃ and MnCr₂O₄ after 1000h. No decarburization occurs in each alloy.
The effect of alloy compositions on the corrosion behavior is discussed. The rate of Cr depletion resulting from the formation of Cr₂O₃-rich scale is found to be influenced by the presence of MnCr₂O₄ layer outside the Cr₂O₃ scale, and is described by a parabolic rate law for the alloys with thin MnCr₂O₄ layer and by a cubic rate law for the alloys with thick MnCr₂O₄ layer. Al and Ti, which are reactive more than Cr, are found to improve a resistance to spalling of the Cr₂O₃-rich scale, through a key-on eject by the internal oxides and by the enrichment of Ti oxides at the Cr₂O₃ scale/alloy interface.

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Morphologies, chemical compositions and distribution of sulfide inclusions in steel have been examined on uni-directionally solidified iron alloy containing about 0.1% sulfur and one of sulfide forming elements; Mn about 1%, Ti about 0.5 or 1%, and Zr about 0.1 or 0.3%.
The results obtained are summarized as follows;
(1) Almost all of titanium and zirconium sulfides are observed in an interdendritic space in the morphology of Type II. The number density and mean diameter of these sulfides are approximately same as those for MnS.
(2) In titanium added alloys many sulfide colonies consisting of rod- and/or plate-like TiS are observed, whose area fraction amounts to 0.2.
(3) Rod- and plate-like inclusions observed in zirconium dded alloys make solid solution with manganese sulfide to form (Zr, Mn)3S4(Zr/Mn molar ratio: 0.4-3.5) and approach to a spherical form in the existence of manganese with about 1%.
(4) The supersaturation for these sulfides to precipitate in the solidification sequence has been evaluated by use of phosphorus content in the steel matrix adjacent to a given sulfide precipitate. The supersaturation for sulfide precipitation is evaluated as follows;
MnS : 1.0-1.7, TiS : 1.0-1.7, Zr3S4: 3.0-10 where the equilibrium relations between sulfur and sulfide forming elements determined by authors, and solute enrichment during solidification are taken into account.

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