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In line with the mathematical model of the MgO formation in the decarburized zone of the pitchbearing magnesite refractories in the BOF steelmaking, a simultaneous formation of MgO and CaO has been formulated. This computer model has been solved using parameters obtained from thermodynamic data and estimates based on transition rate theory. This study shows that CaO can be formed in parallel with MgO at the steelmaking temperature but its effect is so small that it may be concluded that the beneficial effect of dolomite brick derived from the CaO formation may be of no significance in practice. This result permits inferences to be drawn from the steelmaking practice in relation to the refractories performance in the BOF.

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A study has been made of the aluminization of low carbon steel in packs of powder mixtures composed of aluminum or ferroaluminum, alumina and ammonium chloride. In packs of low aluminum content, in which the weight ratio of Al:Al₂O₃:NH₄Cl was 5:93:2 and that of Fe-50%Al:Al₂O₃:NH₄Cl was 10:88:2, the concentration of aluminum in the surface layer tended to decrease with increasing time at the calorizing temperature of 870 to 1010℃. In packs of higher aluminum content, in which the weight ratio of Fe-50%Al:Al₂O₃:NH₄Cl was 20:78:2, the surface composition was almost time-invariant and a steady state appeared to exist at the pack-coating interface. The apparent activation energy for diffusion in the solid phase (250kJ/mole) calculated on the assumption of constant surface concentration in a solid solution system was comparable with that of the interdiffusion in the Fe-Al system. The hardness of the pack-aluminized steel reached a maximum value of about 300 in the Vickers number on the surface, decreasing with increasing diffusion depth.

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High carbon Cr-V and Cr-Ti alloy steels based on 0.75%-0.76% C were manufactured for trial and their mechanical properties and microstructures were investigated metallographically, and then studied on the fitness of these alloy steels as the rail materials for high speed railroad. According to experimental results, their tensile strength, yield strength, and hardness were 120-130㎏/㎟, 85-90㎏/㎟, 350-370 H_B respectively, and the amount of wear was half as much as normal carbon rail steels`, but their microstructures were largely different from each other. It was concluded that high carbon Cr-V and Cr-Ti alloy steels appear to have mechanical properties suitable for rail materials of high speed railroad, and good properties such as high strength and hardness of the high carbon Cr-V steel will be attributed to its fine pearlite microstructure which were distributed densely.

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In order to develop plates for high-test line pipe of API 5LX-X70, trial production was carried out in several plate rolling patterns of CR 1, 2 and 3. Among them, the CR 3 pattern was turned out to be optimum condition, which could be reached on an average 55㎏/㎟ of yield strength and 10 to 20㎏·m of charpy-V notch impact energy at -20℃. The condition and chemical composition are summerized as follows; 1. Controlled rolling: 75% of reduction given below 900℃ and 720/800℃ of finishing temperature. 2. Chemical composition: 0.70/0.10% C, 1.5/1.6% Mn, 0.03/0.05% Nb, 0.07/0.08% V and 0.02/0.05% Al.

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Delamination behavior in tensile specimen of cold rolled 0.07C-1.4Mn-0.08Nb steel was studied after aging treatment at 600℃. By increasing aging time the degree of delamination increased at first and then decreased gradually. The susceptibility of delamination was strongly related withe the distribution of carbide at the elongated ferrite grain boundaries. Microstructural characteristics of the samples which had been aged to bring about the maximum degree of delamination, were filmy structure of carbides at the elongated ferrite grain boundaries. These filmy structure of carbide was changed into separate spheroidal structure by increasing the aging time further more, and they were distributed at or near grain boundaries. Additionally, recrystallization by the prolonged aging time had helped also decreasing the delamination. By applying tensile stress, many of the micro-cracks had occurred at the interface of ferrite grains and carbides, along ferrite grain boundaries, and then connecting these micro-cracks, delamination crack had propagated.

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Among the mechanism and kinetics of iron oxide reduction and coke gasification reaction reported, only the reactions under isothermal condition or iso-gas compositions are reported. Very few papers are published concerning non-isothermal reactions. In this papers, experiments for the reduction of wustite along with the coke gasification were performed under the simulated conditions of thermal reserve zone of iron blast furnace which is apparently non - isothermal and non iso-gas composition. The main object of this research is to probe the rate and effect of alkaline metal additions on the wustite reduction and coke gasification. Temperature and gas compositions are varied to simulate the running conditions of old type and modern type blast furnace. Gas utilization factor is introduced to explain the abundancy or the shortage of the reducing gases in the blast furnace running conditions.

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