발간논문

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The growth rate and the mechanical properties of chemically vapor deposited TiC on WC-6％ Co substrate were investigated by depositing TiC on varying deposition temperatures, total pressure in the reaction chamber, and the partial pressure of CH₄in gas mixtures. TiC is deposited by two different reactions; such as substrate reaction and hydrocarbon reaction. Each activation energy was calculated at 19 ㎉/mole and 70 ㎉/mole, respectively. The growth rate of TiC coating layer was increased with deposition temperatures, the total pressure in the reaction chamber, and the partial pressure of CH₄in gas mixtures. The microhardness of TiC coating layer was increased until the thickness of coating layer was up to 7㎛. The microhardneas of TiC coating layer was increased as the partial pressure of CH₄was increased. When the partial pressure of CH₄in the gas mixtures was increased TiC coating layer was pronounced <100> preferred orientation. It was found that ηcarbide which is formed by substrate reaction is Co_6W_6C.

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This study is to determine the alkali-leaching mechanism by which complex compound by the reaction made between molybdenite (MoS₂) and ferric oxide (Fe₂O₃) in the roasted are when molybdenium trioxide (MoO₃) is formed by the roasting reaction of molybdenite concentrate. The results obtained from this experiment are summarized as follows; 1) The heating reaction analysis shown that the complex compound of iron molybdates (Fe₂O₃·3∼4 MoO₃) is formed by the reaction of molybdenium trioxide and ferric oxide at temperatures of above 500℃. 2) It is shown that at various reaction temperature below 400℃ molybdenium trioxide is almost completely leached by caustic soda irrespective of the mole ratio of two chemical samples used for the experiment, whereas at temperature above 400℃ the leaching rate of molybdenium trioxide decreases except that it varies from 70.77% at a temperature of 900˚at which the mole ratio is 1 to 1 to 84.08% at a temperature of 1000℃. 3) The x-ray diffraction analysis has shown that the complex compound reacted at a temperature of 1000℃ produces a complelex compound with the crystal structure of iron molybdates, and the alkali-leached residues even with 19.0% of molybdenium trioxide, however, contain only α-Fe₂O₃, without showing iron molybdates. 4) The crystalline compound of iron molybdates obtained as a result of heating reaction was leached by using caustic soda, while MoO₃, and Fe₂O₃in the leaching residue was found to contain other compounds unable to be leached by caustic soda.

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Thermal Cycling treatments have been applied to AISI 4330 steel for improving the strength and impact toughness. The constant and alternate cycling have been applied. Experimental results showed that a remarkable grain refinement can be obtained by thermal cycling treatments. The strength and impact value were increased by constant cycling, but the strength tended to decrease with increasing the impact value in alternate cycling. It was found that the best thermal cycling condition was the fourth cycle of constant cycling, and the grain size was reduced from about 15∼20㎛ mean grain diameter to 2∼3㎛, by this treatment. The grain refinement can be attributed to the low austenitizing temperature and short soaking time due to the rapid heating rate and the accumulation of residual stress during repeated thermal cycling. It is believed that the increase in strength is caused by the grain refinement and fine carbide precipitation, and increase in impact value is mainly due to the reduction of plate martensite which deteriorates the toughness.

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The approximate validity of the regular solution model for canons was examined to formulate the thermodynamic properties of steelmaking slags and to express quantitatively the equilibrium reaction between slag and metal. 1) The regular solution model was satisfied for multi-component stags such as Fe_tO-SiO₂-MgO, Fe_tO-SiO₂-CaO-MgO and Fe_tO-SiO₂-CaO-MgO-P₂O_5 systems, and the following values were obtained as interaction energies between cations. α_(15)(Fe^(2+)∼Mg^(2+))=3.070㎈, α_(25)(Fe^(3+)∼Mg^(2+))=-5,620㎈, α_(35)Si^(4+)∼Mg^(2+))=-30,500㎈, α_(45)(Ca^(2+)∼Mg^(2+))=4,500㎈, α_(36)(Si^(4+)∼P^(5+))=11,000㎈, α_(46)(Ca^(2+)∼P^(5+))=-125.000㎈, α_(56)(Mg^(2+)∼P^(5+))=-85,000㎈ 2) It was confirmed that applying the values of interaction energy to the regular solution model had enough certainty to estimate the oxygen content in liquid iron within the accuracy of ±10% over the wide range of slag compositions from basic to acidic stags. 3) Simple regular solution approximation was less favorable to apply for the phosphorus distribution between liquid iron and stags. It was proposed that a further modification of the model considering composition dependence of α_(ij) should be necessary to express the phosphorus equilibrium with a mathematical formula.

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