In order to develop a process of both recovering the heat retained in molten blast furnace slag and producing aggregate for concrete making, characteristics of molten slag in granulation and solidification were investigated.
The newly developed method of dry granulation, consisted in making the molten slag collide with a hard surface that was insulated with a thin coat of oil or water, was found to have several advantages, such as (1) low power consumption for granulation, (2) low heat loss during granulation, and (3) relatively short range of dispersion of the slag granules.
In the solidification study, slag granules of 5mm diameter were subjected to air blast of various velocity. It was found that such a granule was cooled at a rate of about 100°C/sec in the high temperature range, solidifying at about 850°C. As this meant that it took some 5sec to solidify a molten slag granule of 1 350°C, acceleration of cooling was deemed necessary. Thereupon, it was shown that the use of air-fluidised bed of slag powder was effective to cool and solidify the slag granules individually as well as to extract the heat both while molten and after solidified.

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Long-term creep rupture properties and microstructure of 12% Cr heat resisting steels were investigated. It has been found that solid solution hardening by an addition of Mo is very effective on long-term creep rupture strength, but precipitation or dispersion hardening by an individual addition of V or Nb is little effective. Especially, the presence of excessive amounts of undissolved NbC leads to the coarsening of MX precipitates, and a marked drop in long-term creep rupture strength. The combined addition of V+Nb with Mo and B leads to superior 30 000h creep rupture strength. Microstructural differences between long-term crept specimens at 600°C and short-term crept specimens at 650°C were discussed by considering the parameter, T(C+log t). Long-term specimens at 600°C exhibit higher dislocation density substructure caused by intensive precipitation reactions which include both fresh precipitation within lath and agglomeration at boundaries, and exhibit intergranular fracture probably caused by stress concentration around the agglomerates, whereas short-term specimens at 650°C exhibit intragranular fracture. It is considered that the deviation of long-term creep rupture strength from the extrapolated value is caused by differences in precipitation hardening level and fracture mode.

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The mechanism of degradation of agglomerates during reduction is studied with pellets made from powdery ingredients of chemical reagent grade, and the changes in mineral phases due to certain oxides leading to degradation, are examined quantitatively.
The results obtained are summarized as follows:
(1) Microscopic observations suggest that cracking occurs in the skeletal hematite and the calcium ferrite phases. Analysis by line-broadening measurements of X-ray diffraction reveals no strain both in the bulky and in the skeletal hematites regardless of the amount of alumina held in solid solution. Micropores are generated in magnetite as it is reduced from hematite to give rise to a stress when reduced at a low temperature, and stress concentration occurs around inclusions of small radius of curvature to cause cracking of skeletal hematite grains.
(2) The quaternary calcium ferrite is expected to be reduced to metallic iron in the blast furnace through dicalcium ferrite or wustite. Nonferrous oxides form gehlenite and β-dicalcium silicate. Calcium ferrite is not only fragile but its amount to increase with the basicity under existence of Al₂O₃.
(3) The amount of skeletal hematite depends mainly on the degree of supersaturation of iron ions in slag and on the dissociation temperature of hematite. The addition of TiO₂ in sinters enhanced greatly the crystal growth of skeletal hematite in the case of induration at above T_HM, whereas bulky hematite at below T_HM.

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Resistivity change during isothermal aging and the associated tensile properties have been investigated on Fe-10Ni-1.8Ti, Fe-15Ni-1.8Ti and Fe-20Ni-1.8Ti maraging steels. In order to investigate the effect of strain rate on ductility, a crosshead speed was varied from 0.005 to 10mm/min.
Embrittlement caused by the decrease in strain rate is found in the maraging steels containing fine and coherent precipitates, formed in the first precipitation process. Brittleness independent of strain rate is also found in the Fe-10Ni-1.8Ti and Fe-15Ni-1.8Ti maraging steels strengthened fully by the first process at lower temperatures. Both cases result from the slip character that intense slip bands tend to be formed during deforming. Tensile properties which are ductile and insensitive to strain rate are obtained after subjecting to the second process. Aging structures in which intense slip bands are difflcult to be formed during deforming are concluded to be suitable for the improvement of ductility.

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The isothermal and continuous cooling transformation kinetics of bainite were studied using an automatic quench dilatometer. It was found that the overall isothermal bainite transformation kinetics were well expressed by Johnson-Mehl type equation and that the transformation rate decreased with increase in the austenite grain size. The analysis of transformation kinetics and the optical microscope observations suggested that the nucleation site of bainite was both on the grain boundaries and inside the austenite grain. This effect of austenite grain size on the rate of isothermal transformation to bainite was found to be smaller than that to pearlite. Comparison of the observed cooling transformation kinetics with that predicted from the isothermal kinetic data showed that the transformed fractions were additive in bainite transformation. This result might be understood if it were assumed that the bainite transformation proceeds with repeated nucleation and growth of basic subunits, each attaining the limit size rapidly.

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Effect of applied stress on the temper embrittlement was studied using aboratory heats of normalized and tempered 2_1/4Cr-1Mo steel. Charpy impact tests and tensile tests were performed to assess the embrittlement and scanning electron microscopy and Auger electron spectroscopy were conducted for the analysis of fracture surface. Applied stress and ageing time dependences of the embrittlement at 450°C were investigated. The results showed that applied stress enhanced the embrittlement when the material contained a substantial amount of residual phosphorus which was believed to cause the temper embrittlement.

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Experiments have been made to study the phosphorus distribution between liquid iron and MgO saturated CaO-MgO-FeO_x-SiO₂ slags containing 1 to 4% CaF₂ in the temperature range 1550 to 1650°C. The effect of CaF₂ on the equilibrium quotient k_p(=(%P₂O₅)/{[%P]²(%FeO)⁵}) was found to be nearly equal to that of CaO on the weight percentage base. The equilibrium quotient k_p is expressed as logk_p=8.22log[(%CaO)+(%CaF₂)+0.3(%MgO) -0.05(%FeO)]+21460/T-27.02 or logk_p=0.156[(%CaO)+(%CaF₂)+0.3(%MgO)] +20730/T-19.48
The effect of CaF₂ on the activity coefficient of P₂O₅ was also studied by the Turkdogan and Pearson's treatment. The following expression for the activity coefficient of P₂O₅ is given for the slags containing CaF₂. logγ_P2O5=-1.01(23N_CaO+21N_CaF2+17N_MgO+8N_FeO) -26300/T+11.24
It was found from the plot of the activity coefficient of FeO vs. the mole fraction of SiO₂ that the activity of FeO increases with the addition of CaF₂.

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Quantitative evaluation of stress intensity factors a steel experienced during propagation and on arrest of a brittle crack was made by applying the X-ray fractography technique to the fracture surface of the compact specimens of a pressure vessel steel SA533B C1. 1. The stress intensity factor, which was determined along the crack path using the half value breadth of X-ray diffraction intensity curve obtained on the fracture surface, was found to decrease monotonically as the crack propagated, but to become undulating before arrest. It was shown, contrary to the general belief, the stress intensity factor for crack arrest was not necessarily the smallest, not even a minimum, of all those obtained for the crack propagation. The stress intensity factor for crack arrest was in good agreement with the crack arrest toughness K_Ia determined by the static analysis, while it was smaller than K_ID determined by the dynamic analysis.

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This paper deals with two-dimensional gas flow in the blast furnace which has a complicated bed structure by the application of the finite element method. Besides this, simultaneous analysis on the gas flow and heat transfer is also carried out for the simplified conditions in which solid flow is approximated reasonably to potential flow.
As for the gas flow, multi-dimensional Ergun's equation is solved together with the equation of continuity by using the variational principle. However, heat balance equation for gas and solid is solved on the basis of the Galerkin method. In order to consider the layered structure and also the properties of cohesive and raceway zones in the blast, furnace, the finite elements for the numerical computation are corresponded to the ore and coke layers.
Computed results indicate that the drastic changes in gas flow occur around the cohesive and raceway zones which have extremely different properties of gas flow. Zig-zag flow of gas appears in the lumpy region which is caused by the different permeability of ore and coke layers and also by the inclination of the layers. Computed results for the simultaneous analysis on gas flow and heat transfer show that the bed structure principally governs not only gas flow pattern but also temperature distribution.

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The effect of addition of 5 Co, 1 Ti or 1-2 Mo (percent by weight) to Fe-17Ni-15Co-4Mo-2Ti steel has been studied in order to produce higher strength maraging steels. Grain refinement through α'_??_γ cyclic heat treatment was applied and the microstructures and mechanical properties were investigated in comparison with the results of conventional solution heat treatment. Initial grain size prior to cyclic treatment was coarse (0.6mm) because of complete solution treatment at high temperature. The addition of each alloying element increased strength level for base steel from 2550 to 2750MPa and lowered fracture toughness irrespective of the kind of alloying elements and the heat treatment. The results of conventional solution treatment showed that there existed little effect of alloying elements on grain size, and the ductility decreased monotonously according to the increase in strength level. In the case of cyclic treatment, the addition of Co promoted grain refinement (7μm) and thus yielded the same ductility as that of the base steel even at higher strength level, whereas the addition of Ti and Mo suppressed refinement (11-20μm) leading to marked decrease in ductility. The cyclic treatment was thus found to be more useful in obtaining good combination of strength, ductility and toughness than the conventional solution treatment, particularly, in the steel with high Co.

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The quality and operation data generated in the Kakogawa iron and steel works have been rapidly increasing each year. Effective use of the date greatly influences quality improvement and cost reduction. The sooner the data can be utilized, the more profit can be obtained. What is essentially required for such a data processing system in easy and quick retrieval and more flexible data processing.
Kobe Steel, Ltd. (KSL) established the integrated quality information system called “KSL: Kakogawa Information System” in April, 1981. It is the first system connecting Data Base with APL in Japan.

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