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An investigation was carried out on the effect of high temperature thermomechanical treatment (HTMT) on the strength and toughness of AISI 4340 steel. HTMT was carried out at 850℃ which is in the lower temperature range of the stable austenized region, and the degree of working was between 0% and 58%. The tempering temperature was between 250℃ and 650℃ including room temperature and microstructures of specimens were observed by optical microscope, transmission electron microscope(TEM), and scanning electron microscope (SEM). The results showed that HTMT increased the strength and toughness of steel compared to conventional heat-treatment and produced the subgrain structures which become finer with increasing degree of working and tempering temperature. It seems that the improvement in strength and toughness of this steel resulting from HTMT is attributed to the formation of subgrain structure, and the refinement of structure is the predominent factor contributing to improved strength and toughness of the steels tempered at 550℃.

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A study on the oxidation of stibnite has been carried out using a vertical reactor with N₂-O₂ mixtures of 5 to 20 volumes% at the temperature between 320℃ and 420℃. Possible oxidation mechanism for the reaction has been discussed with the experimental kinetic data obtained in this investigation. To evaluate a rate equation satisfying the data of the reaction, various oxidation kinetic models have been discussed. The results obtained in this work can be summarized as follows; 1) The rate for the oxidation process of stibnite at the temperature between 320℃ are 340℃ was found being controlled by the reaction of O₂with Sb₂S₃at the reaction surface. But the rate, at the temperature between 350℃ and 420℃, was found being controlled predominantly by O₂diffusion through the product layer. 2) The effect of O₂concentration in N₂-O₂mixtures on the oxidation of stibnite decreased as the roasting temperature increased. And also more the O₂concentration in N₂O₂mixtures, less the roasting temperature was effective on the oxidation of stibnite. 3) The rate equation for the oxidation of stibnite showed a good agreement with experimental data.

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After solidification Ni-hard, the effects of cooling rate on abrasive wear resistance are investigated. When most of retained austenite is transformed to bainite by tempering, the change of abrasive wear resistance is also investigated. The heardess of Ni-hard increases with increasing the temperature from which slow cooling begins. But the hardness remains at the maximum value even though the temperature gets over about 650℃. This may mean that when the temperature is about 650℃ or above, the carbon concentration of austenite comes to be near equilibrium. By tempering, retained austenite is transformed to bainite and hardness is increased. But the wear resistance of this transformed Ni-hard is lower than that of original one. It may be because of the fact that the transformed Ni-hard has much less retained austenite to be transformed to martensite by wear at abrading surface than original one. Using scratch test, the effect of grain size to wear resistance was investigated. As a result, the existing abrasive formula may be modified as follow: V= (K"W·L/H)·1/N^¼ N : numoer of carbide or aggregate grains in a unit area of wear surface.

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Tensile properties and hardness of ordinary cast iron with additions of copper have been studied in relation to its microstructure. The results obtained are as follows: (a) Small additions of copper up to a certain level significantly increases tensile strength and hardness of the cast iron. (b) Increased tensile strength may be due to an enhanced peralitization of matrix by copper addition. (c) With increase in silicon content, an ever-increasing copper addition is required to improve these mechanical properties, with carbon remaining constant.

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Residual stress and fatigue of welded 0.22%C carbon steel were studied by X-ray diffraction method. The macroscopic and the microscopic rediual stresses were measured by shift of diffraction peak, and broadening of integral breadth, respectively. The distribution of residual stresses, tensile on welding zone and compressive near the side end of welding zone, were found. The effect of residual stresses on fatigue were not so significant. These residual stresses and integral breadth during the fatigue process were changed in three stages by cyclic stressing as follows. On the first stage compressive residual stress and rapid increase in integral breadth were found, on the second stage the compressive stress which found in the first stage was decreased rapidly and the integral breadth was increased slightly, on the third stage the gradual increase in compressive residual stress and the rapid increase in integral breadth were noticed.

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The oxidation of 200/270 mesh and 150/200 mesh stibnite was carried out at the temperature range of 340℃-440℃. The results obtained in this study are as follows; 1) The rate for the oxidation process of 200/270 mesh Sb₂S₃at the temperature between 340℃ and 370℃ is controlled by the chemical reaction at the reaction surface, while, in the region 380℃-440℃, the rate is controlled by the oxygen diffusion through the product layer. 2) The reaction of the oxidation of 150/200 mesh Sb₂S₃is chemically controlled at the temperature range of 340℃-380℃, while in the region 400℃-440℃ the rate is controlled by the diffusion. 3) The effect of oxygen concentration on the oxidation decreases as the temperature increases. 4) The effect of the size on the reaction decreases as increasing the temperature.

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The growth kinetics of intermediate aluminide compound was studied by applying process at temperature range of 700℃-800℃. The intermediate phase observed was confirmed to be Fe₂Al_5 (η) phase whose growth obeyed a parabolic rate law. Growth of intermeditate phase depends on interdiffusion of iron and aluminum. And chemical diffusion coefficients of Al and Fe in η phase are obtained through the consideration of flux and compound stoichiometry in association of alloy layer growth rate. The addition of silicon to aluminum bath results in decreasing growth rate of the intermediate phase. This effect found to be due to the drastic. reduction of frequency factor. The activation energy for the growth of Fe₂Al_5 (η) was found to be 31㎉/㏖, when specimen was dipped in pure aluminum bath, but activation energy was found to be 24.4㎉/㏖, 16.9㎉/㏖, 18.4㎉/㏖ respectively when dipped in 4%, 8%, 12% Si alloyed aluminum bath. A diffusion study of Fe-Al binary system yielded the interdiffusion coefficients and the activation energy for interdiffusion in the intermediate aluminide, η phase. The growth rate of this phase was retarded by the silicon addition. The silicon addition lowers the activation energy for interdiffusion, but decreases the frequency factor drastically.

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Effects of the composition, sintering temperature and heat treating temperature on magnetic properties of sintered SmCo_5 permanent magnets were investigated. SmCo_5 magnets heat treated at 900℃ and quenched exhibited the highest coercive force. This is believed to be due to the difficulty in nucleation of reverse domains without the Sm₂Co_(17) phase in the microstructure of the magnets and strong pinning of domain walls at grain boundaries where oxygen is segregated. The coercive force of the magnets decreased as the heat treating temperature was raised to higher temperatures (>900℃). This is attributed to the weaker pinning of domain walls at grain boundaries. The SmCo_5 magnets heat treated at lower temperatures (<900℃) exhibited lower coercive Force values than those exhibited by the magnets heat treated at 900℃. This lower coercive values are due to easier nucleation of reverse domains at the Sm₂Co_(17) phase that is formed as an eutectoid decomposition product below 800℃. SmCo_5 magnets whose total Sm content was 36wt.% exhibited the highest coercive force and also the greatest shrinkage. The SmCo_5 magnets with 36wt.% Sm content are of a hyperstoichiometric composition at which Co vacancy concentration is the maximum. The highest coercive force exhibited by the magnets containing 36wt.% Sm is attributed to the fact that the more the Co vacancy exists, the more the segregation of oxygen occurs at grain boundaries and the stronger the domain wall pinning is. The coercive force decreased as the sintering temperature was raised to higher temperatures. This decrease of the coercive force is attributed to the grain growth and ripening of inclusions and pores, since domain wall pinning at new grain boundaries become weaker.

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A study has been made of the effects of a free surface on recrystallization and grain growth of super-purity aluminum. Aluminum was cold rolled to the reduction of 75 percent and isothermally annealed in a salt bath. The cold worked surface layer was removed by electropolishing prior to annealing to avoid complications due to inhomogeneous deformation in the surface layer. The free surfaces of polycrystal specimens were found not to be a specially preferred site for the nucleation of recrystallization, and fractions of recrystallized part and grain size in the surface layer differed little from those in the bulk. However when specimens were annealed for long at higher temperatures, the grain size near the surface was slightly finer than that in the bulk. The isothermal grain growth kinetics satisfied the expression of D=ktⁿ where n was found to vary from 0.07 to 0.14 with increasing temperature. The secondary recrystallization or exaggerated grain growth occurred near the surface layer in spite of the superpurity of aluminum. The exaggerated grain growth seemed to be associated with an inhibition of grain growth by surface grooves and sudden growth of some grains.

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A method is given for the determination of the surface orientation of polycrystalline face centered cubic metals from slip traces produced by the microhardness. At the same time, a new graphical method using a loci net of the ｛111｝ poles is proposed. An example of the use of the microhardness is presented on a Cu-6% Al specimen, where relevant matters such as the locating of the microhardness indentations, the kind and processing of informations obtainable from the slip traces, the minimum surface area of a crystal required and the accuracy of results are described. It is seen that when slip traces by the microhardness are concerned, the orientation of a crystal can be determined unambiguously even if there are only three slip trace directions. Observation of a considerable twin imperfection and of a correlation between the bright-dark separation of crystals on the etched surface and the crystal orientations is made as result of the determination of the orientation in this example.

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