A new apparatus to determine the composition of gas in blow-holes in steel has been developed. A steel specimen is pierced in a vacuum vessel by means of a drill which is driven by a motor placed outside the vessel. The vacuum vessel is directly connected with a quadrupole mass spectrometer which analyzes the released gas from blow-holes.
It is demonstrated that analysis of the gas in cavities in steel can be made with this new apparatus and the obtained results may provide the information useful for the assessment to the gas composition at higher temperatures.

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For high-speed continuous rolling, such as in wire rod mill and hot strip mill, behaviors of various carbon steels under high strain-rate hot deformation were investigated. For the purpose, a compression type hot deformation simulator of the following performance was developed; maximum strain rate, 300sec^-1; minimum time interval between each deformation, 15msec; and maximum strain, over 2. A high speed rolling mill was also used, and a strain rate of 800sec^-1 was obtained by this mill. A technique of two-pass rolling was also developed.
Using these experimental devices, steels of 0.05 to 0.81%C were tested in the temperature region between 800°C and 1 100°C. The main results obtained were as follows:
(1) The features of stress-strain curves did not change essentially with the increase in strain rate. It was shown that the dynamic recrystallization of austenite determined the form of the curves.
(2) In the simulator experiments, the maximum stress σ_m, the steady state stress σ_s, and the mean resistance to deformation k_fm, were all found describable satisfactorily well as a function of the Zener-Hollomon Parameter, Z, with an activation energy of 63 800kcal/mol and with an exponent of Z lying between 0.09-0.17. The grain diameter of recrystallized austenite also seemed to be described as a function of Z.
(3) In the rolling experiments, k_fm was also shown to be well described as a function of Z, as k_fm=CZ^r provided that the calculated finishing temperature be taken as the temperature of deformation, k_fm and r both showing a fair agreement with those obtained from the simulator experiment.
(4) The effects of successive deformation on the stress, with a short interval of 0.5sec and below, are nearly the same as those of single deformation, provided the overall strain is the same. Accordingly, the above conclusions (1) and (2) should also apply to the cases of successive deformation as a rough approximation.

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The crushing conditions of coal in a closed circuit with a vertical centrifugal screen and the effect of this closed-circuit crushing were studied, and the CPC process was newly proposed. To commercially apply the CPC process, the vertical centrifugal screen was improved for screening a large amount of wet coal, and test operations with an actual coke oven were conducted to examine the effectiveness of this process by the use of the improved screen. The following practical effects of the CPC process were confirmed.
(1) As coke quality indices, DI¹⁵⁰₁₅and CSR can be respectively improved by 1 to 2 and 1 to 4.
(2) The coke breeze yield can be reduced by 2%.
(3) About 10% American hard-coking coal can be replaced by Australian soft-coking coal.
(4) About 5-10% noncaking and poorly caking coals can be used in the coal blend.
The mechanism for the improvement of coke strength by this process was also investigated. Lastly, it is also mentioned that the CPC process can be assessed as basic coal preparation technique, on the basis of the experimental data in comparison with other technologies and the combination of the CPC process with the other pretreating techniques (coking process with briquette-blend and process with the addition of caking substance).

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Cu-Ni-Cr-Mo-B low alloy steels whose total B content exceeds a certain limit show superior hardenability when they are austenitized at lower temperatures (≤900°C), although their hardenability decreases with higher austenitizing temperatures and longer holding times. As M₂₃(C, B) ₆ in these steels is partly undissolvable at lower austenitizing temperatures, B content in solid solution is not determined uniquely from Fe-B-Al-N equilibrium state but rather regulated by the solubility product of M₂₃(C, B)₆. At lower temperatures (≤900°C) B content in solid solution which balances with M₂₃(C, B)₆ is considered appropriate for hardenability. At higher temperatures (>900°C), B content in solution which equilibrates with M₂₃(C, B)₆ increases and exceeds the limit over which the hardenability of B steels decreases. Heating below Ac₁ for a long period, while M₂₃(C, B)₆ is enriched with C, Mn and Mo atoms, austenitizing condition appropriate for the hardenability is transferred to higher temperatures and longer periods. This is because the solubility product of M₂₃(C, B)₆ is lessened and the particles grow coarser.
Boron content in solid solution which balances with M₂₃(C, B) ₆ is determined approximately from the relation among the decrease of hardenability, quenching temperature, and B content in solution calculated from the Fe-Al-B-N system. The result is as follows: 880°C-3ppm, 900°C-6ppm and 930°C-8ppm.
These values are considered to depend strongly on Cr, Mn and Mo contents and prior heat treating history. In excess-B-containing steels, “Boron Constituents” are observed on the prior austenite grain boundaries at distances longer than 15mm from the quenched end of Jominy end quench test specimens, when they are quenched from 930°C.

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Dynamic recovery and the following static recrystallization process of 1.8% Al steel were investigated by a hot compression machine equipped with a precise control system for quenching after hot deformation. The temperatures and strain rates of deformations were varied in the ranges from 800 to 1 100°C, and from 5×10^-4 to 10.3s^-1, respectively. The subgrain structures developed by dynamic recovery process were observed by interference microscope and transmission electron microscope, and these were correlated with steady state flow stress. The substructural changes in static recovery and recrystallization after dynamic recovery were investigated to understand the nucleation mechanism of static recrystallization after dynamic recovery. Subgrain coarsening at a high rate took place in the recovery stage, and subgrain coalescence along the grain boundary appeared to be the nucleation mechanism of recrystallization. The effects of hot deformation conditions on static recrystallization kinetics were also studied and analyzed based on grain boundary migration rate.

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The pore formation mechanism in water-granulated blast furnace slag and the effect of granulation conditions on the specific gravity of granulated slag are described.
The gases released from molten-slag droplets into cooling water during slag granulation consist of H₂ and N₂ gases. The gases contained in the closed pores of granulated slag are mainly composed of H₂ and N₂ gases, the H₂/N₂ ratio being approximately 1.8. As the nitrogen content of molten slag increases, the amount of pores formed in granulated slag increases. This indicates that the dissolved nitrogen generates the H₂ and N₂ gases. It has been confirmed by an experiment using the heavy water as a tracer that cooling water can dissolve in molten-slag droplets in the extremely short time during solidification of the molten-slag droplets.
From these results, the pore formation mechanism in granulated slag is presumed as follows. Cooling water dissolves in molten-slag droplets, reacts with nitrogen in the molten-slag droplets and evolves H₂ and N₂ gases by the reaction expressed by the following equation; 2N^3-+3H₂O=3H₂+N₂+3O^2- Some of these gases are captured by the molten-slag droplets to form pores in granulated slag.
This work has clarified the effect of granulating conditions (water quantity, water-jet velocity, water temperature and molten-slag temperature) on the specific gravity of granulated slag. The specific gravity increases as the water quantity and water jet velocity increase and the water temperature and molten-slag temperature decrease. These granulating conditions affect the time or temperature of the gas evolution reaction mentioned above.

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Properties of acid pellets with MgO/SiO₂ ratios between 0 and 1.3 and pellets with MgO and CaO/SiO₂ ratios between 0 and 1.3 are presented.
The amount of magnesio-ferrite in the fired pellets with MgO can be evaluated by the value of the magnetic susceptibility of the pellets, since it increases with the MgO contents. This amount varies with the CaO/SiO₂ ratio when CaO is present in the pellets. The MgO density shows stripe-like distribution when Mg⁺⁺ diffuses into hematite at temperatures below 1 395°C, and changes hyperbolicly when the temperature is above 1 395°C. The MgO density changes hyperbolicly at various temperatures when Mg⁺⁺ douses into magnetite in the N₂ gas flow.
The reducibility of magnesio-ferrite is slightly inferior to that of hematite. Therefore, the reducibility of the pellets decreases with the amount of magnesio-ferrite in the pellets. The changes in the volume of magnesio-ferrite during reduction are very slight. Swelling decreases with increasing amounts of it in the pellets.

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There exists a need to improve the high temperature reducibility and lower the softening rate of pellets in order to get high productivity in the blast furnace.
This paper introduces the influence of the MgO/SiO₂ and the CaO/SiO₂ ratios in pellets on the high temperature reduction and softening properties.
The pellets whose MgO/SiO₂ ratio is held at above 0.6, and whose CaO/SiO₂ ratio is held at below 0.05, are proved to have better high temperature properties than those of acid or self-fluxed pellets. There was no deterioration in properties, even if the quantity of SiO₂ is significant.

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A high speed continuous billet caster where casting speed matches the rolling speed has been developed. The mold of the caster consists of a copper wheel with a groove and an endless belt, both strongly cooled by water. There is almost no friction between the mold and a cast billet because of the mold moving simultaneously with a billet. In the course of development two studies were performed to establish the optimum casting and operating conditions. The first was to study the effects of casting conditions on the shell thickness in the mold. The second was on the heat transfer characteristics of the rotating wheel. The results are summarized as follows:
(1) The solid shell thickness of the belt side was smaller than that of the wheel side when the molten steel with large superheat was poured.
(2) Water modeling experiment revealed that flow with high velocity went downward along the belt side, while there was upward flow with low velocity along the wheel side.
(3) The allowable superheat was estimated to be 50°C by the casting experiments and computer calculation taking account of fluid flow.
(4) Good contact between a cast billet and the wheel was obtained by smooth nozzle stream, tension casting where the pinch rollers were driven at a slightly higher rate than the wheel and appropriate guide roller configuration.
(5) The solidification rate constant was 27mm/min^1/2, which was somewhat larger than that of an average conventional caster.
Based upon these results the belt wheel type continuous caster was put into practical use.

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Fluid flow and mixing characteristics in a molten metal bath are analyzed for inert gas injection through a nozzle at the center of the vessel bottom. It is postulated that the bath consists of two zones: bubble plume zone where gas-liquid mixtures flow upward and annular zone where liquid flows downward. The analysis is made by setting up a steady-state energy balance for the liquid phase. The liquid velocity in the plume zone, the liquid circulating flow rate and the mixing time are calculated for various injecting conditions and correlated as simple functions of gas flow rate, liquid depth and cross-sectional areas of both the plume zone and the vessel. It is found that the cross-sectional area of the plume zone has a significant influence on the circulating flow. Large cross-sectional area of the plume zone is favorable for mixing in the bath. The calculated results of circulating flow rate and mixing time agree with the experimental results obtained previously.

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Hardenability increasing effect due to B was studied for low alloy steels treated with Al-B (0.06-0.08%Al-0.0010%B). The quench hardenability was found to be markedly improved by double quench. The mechanism of the increased quench hardenability by the double quench was studied by means of a fission track etching technique. It was shown, in the double quench, that a quenching from 1 000°C for 1hr prior to the 2nd quench gave rise to excellent hardenability which could not be attained by a single quench. The role of the 1st quench is to obtain the optimum amount of soluble B in matrix. A combination of the Al-B treatment and the double quench is a reliable method to maximize the hardenability increasing effect of B in low alloy steels.

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