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Load-controlled tensile tests were conducted at 76 and 4 K on high strength austenitic steels. The loading rate was varied from 5 to 5000 N/s. The effects of loading rate and testing temperature on tensile properties of high strength austenitic steels were observed and the results were correlated to the temperature rise of the specimens due to internal specimen heating effects during tensile tests. The change of loading rate also affected the onset of discontinuous yielding and, in turn, the fracture characteristics of the steels at 4K. The role of discontinuous yielding in affecting the dependence of ultimate strength on loading rate was discussed.

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This work was carried out in order to investigate the effects of the grain size and vacancy on the Ms temperature of an austenitic Fe- 33%Ni alloy. The Ms temperature was raised with increasing the austenitizing temperature within the range from 850℃ to 1150℃, owing to the grain growth and the vacancy concentration. It was observed that the larger was the austenite grain the higher was the Ms temperature. The influence of the austenite grain size was similar to that of the austenitizing temperature. With regard to the effect of vacancy, the Ms temperature was increased with increment of quenching temperature below 900℃, but was lowered above 1000℃. Meanwhile, the specimen which was quenched at 900℃ contained the straight dislocations and the sample which was heat-treated at 1150℃ included the curved dislocations with the coalesced vacancies. From the above results, it was concluded that the Ms temperature was mainly dependent upon the austenite grain size and the dislocation pinning with vacancy arrangements.

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Chemically induced recrystallization occurs when Fe atoms are added to Mo-Ni grains in liquid phase sintered Mo-Ni alloys. Alloy specimens of 90Mo-10Ni by wt have been heat-treated at 1400℃ after replacing their liquid matrix by Cu-Fe melts of varying Fe concentration. When the Fe concentration in the Cu-Fe melt is 3 wt%, chemically induced grain boundary migration(CIGM) occurs. When the Fe concentrations are 5 and 10 wt%, chemically induced recrystallization(CIR) occurs at the grain surface with the recrystallized grain density increasing with the Fe content. The recrystallized grains contain Fe with the average amount increasing wigh the Fe content in the matrix, but the Ni concentration is reduced to 0 because of Ni depletion into the Cu-rich matrix. With advance of the recrystallization front, the Fe concentration in the recrystallized region decreases because of Fe depletion in the matrix. The density of misfit dislocations produced by diffusion of Fe atoms at the critical concentration required to nucleate CIR is estimated to be close to that for the recrystallization in cold worked solids. The result thus appears to be consistent with the theory that the nucleation of CIR is induced by solute diffusion producing misfit dislocations upon coherency breaking. When the specimen is sintered at 1540℃ and heat-treated at 1540℃ with Cu-10wt% Fe matrix, the recrystallization front stops when the Fe concentration decreases to such a level that the coherency strain is reduced to 0 due to simultaneous decrease of Ni concentration. The grain boundaries formed by recrystallization then move back to the specimen surface and disappear, leaving behind regions enriched with Fe and depleted of Ni. This behavior is consistent with the theory that the diffusional coherency strain energy acts as the driving force for the growth of grain nuclei formed in the recrystallization process.

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Initial yield conditions and elastic-plastic response of sintered porous iron are investigated under combined tension and torsion. By using tubular specimens of initial relative densities 0.8 - 0.9, initial yield conditions were compared with several yield functions in the literature. Kim`s yield function agreed well with experimental data from combined tension and torsion of sintered porous iron. Gurson`s and Richmond and Smelser`s yield functions did not agree well with data for initial densities lower than 0.9. Shima and Oyane`s yield function showed reasonably good agreement in tension, but not so good in torsion. Other characteristic behaviors of porous metals are also investigated.

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The preferred orientations and microstructures of the cold rolled 0.004%C and 0.022%C steel were studied. The crystallographic deformation theory was applied to analyse the results of the x -ray measurements and TEM observations. It was found that the rolling texture of the steels could be described by a {111}//ND fiber and a $lt;110$gt;//ND fiber. The equiaxed cells developed by homogeneous slip might be a major deformation mechanism of the steels at low rolling reductions. At medium to high rolling reductions, however, the major deformation mechanism was changed to the formation of the microbands, which was developed by a localized inhomogeneous slip. As further increasing reduction, the deformation mechanism was changed consecutively as clustering of microbands, decreasing microband thickness, a rotation of microbands to the rolling direction and a development of shear bands in the hard grains.

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To study the effect of Al on the superplasticity of the ultra-high carbon steel (UHCS), 3-5%Al were added to the UHCS, and superplastic behavior has been measured at 700-800℃. To produce the fine and superplastic microstructure, an isothermal rolling at 700℃ was used, and the grain size of ferrite was less than about 2㎛ in diameter after the process. Significant improvement in superplasticity was observed ; the strain-rate sensitivity was high upto strain-rate of 1 × 10^(-2)s^(-1), and 535% elongation was measured at 750℃ when the engineering strain-rate was 500%/min(i.e., 8 × 10^(-2)s^(-1)). It has been analysed that the Al-addition lead to finer grain size, which, in turn, improved the superplastic properties of the ultra--high carbon steels.

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The tensile strength of squeeze cast 20% Al₂O₃, whisker reinforced Al-12% Si matrix composite was investigated in temperature range from room temperature to 500℃. The interfacial reaction and the variation of tensile strength in Al₂O₃,/Al- Si composite with the exposure time up to 192 hours at 300℃ and 500℃ were also investigated. The tensile strength of Al₂O₃/Al-Si composite decreases rapidly with increasing temperature above 200℃, however, the composite maintains 2∼3times higher tensile strength compared with the matrix above 300℃. The tensile strength of the composite decreases with increasing exposure time at 300℃ due to the decrease in tensile strength of Al-Si matrix. The tensile strength of the composite decreases with increasing exposure time at 500℃ due to the interfacial reaction in addition to the decrease in tensile strength of the matrix. When the composite is exposed at 500℃, the interfacial reaction is found to be proceeded at whisker/matrix interface and the reaction compounds of Mg(Al, Fe)₂O₄, MgAl₂O₄and Mg₃Al₂SiO₃O_(12) have been identified.

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Localized neck in a sheet is assumed to occur by localized shear deformation on the plane where pure shear condition is attained. The three dimensional stress state of the incipient shear plane is determined from the stress transformation. The stress transformation gives the geometry of the slip plane and therefore approximates the shape of the localized neck.

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The thickness dependence of the thermal emf and thermoelectric power of thin film Cu/Constantan thermocouples showed nearly bulklike behavior when the thickness of each element film comprising the thermocouples was greater than∼3300Å. The changes in electron transport properties(resisitivity, Hall coefficient, carrier concentration, and mobility) of the $quot;as-deposited$quot; and the $quot;vacuum-annnealed$quot; Cu element films showed three different regions of thickness dependence ; region - I (t≥1500Å), - II (1500≥t≥3300Å), and - III (t≥3300Å). Each region was attributed to the differences in the size-, grain boundary-effect and the effect of the saturated structural defects. In Constantan film, only two such regions(t≥1000Å and t≥1000Å) were observed, and the main reason of it was believed to be the alloying effect of evaporants(Cu and Ni) as well as the rapid deposition rate. The increased or decreased thermoelectric power of thin film thermocouples with the thickness or the annealing treatment was directly related to the facts that the electron transport properties of both element films were subjected to change by the above mentioned effects.

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The effect of type, size and quantity of non-metalic inclusions on the fatigue behavior of high C-Cr bearing steel during thrust-type rolling contact fatigue have been investigated. It was observed that elongated MnS inclusions, fragmented stringers of angular Al₂O₃inclusions and AI₂O₃-MnS duplex inclusions were distributed along the direction of working. ASTM A 295-84 SAM method was more suitable for assessing non- metallic inclusions to estimate fatigue life of high C-Cr bearing steel than Fairey method. Fatigue life decreased with the content of Al₂O₃inclusions. It was also observed in the region below flaking that fatigue crack was initiated by debonding of large AI₂O₃inclusion from matrix whereas void formed around small Al₂O₃inclusion

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