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With the object of clarifying the heat resisting mechanism of the dilute Al-Zr alloys, the isothermal and isochronal annealing characteristics of cold drawn pure aluminum and its dilute Al-zr alloys were studied. It was shown that the high degree of thermal stability achieved in this alloys was due to the Cottrell effect produced by the soluted zirconium and the substructure which was formed by the severe plastic deformations at low temperatures. The recovery process of the alloy, which proceeded with the coalescence and growth of subgrains and the dissipation of subboundaries, was depressed by the strong binding energy between zirconium atom and edge dislocation and the low diffusivity of solute Zr in aluminum.

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The plastic deformation and stress relaxation behaviour of Pb-Sn alloys have been investigated for four different compositions including eutectic at various temperatures. The data obtained showed that the differences in deformation and relaxation for each composition were attributed to the amount and distribution of phases presented in the specimens. The differences as well as the unique development of microstructures during deformation cycle could be interpreted on the basis of the modified g.b.s. mechanism at the phase boundaries and dynamic recrystallization process upon deformation.

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Desulfurization of molten steel was carried out in a high frequency induction furnace at 1550℃. Rates of desulfurization by CaO powder were measured with varing the amount of aluminum as a reducing agent, and were investigated and compared under conditions of the powder injection and top powder. Results showed that the desulfurization rate by the powder injection method was considerably faster than that by the top powder method. Also the rate was increased with increasing the amount of aluminum added. It is interesting to note that product CaS as well as unreacted CaO powder floats immediately after the injection, leaving CaS and CaO free melt. Rate equation for desulfurization was developed to be the first order with respect to sulfur activity when dissolved aluminum and oxygen remain constant, and the desulfurization mechanism was proposed.

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The samples of the used direct-bonded magnesia-chrome refractories of a VOD were made into thin sections for the optical and electron microscopic investigations to characterize the failure mechanisms of the lining in the stainless steelmaking conditions. In addition to the extremely hostile conditions imposed on the VOD refractory bricks, the lack of a retardation mechanism of the slag penetration makes them exceptionally more vulnerable compared with those of the carbon-containing MgO-based bricks of LD converters and EAFs. The study on the brick samples using optical microscope, EPMA, X-ray diffraction and EDAX has shown: 1. In the early stage of the process, the matrix of Mag-Chrome brick consisting mainly of MgO fines with M₂ S and CMS bonds is attacked by the low basicity slag and the lime added as a flux, forming low-melting silicates such as CMS and C₃ MS₂ . 2. The alumina foamed as a result of the addition of aluminum to reduce Cr₂ O₃ to Cr is responsible for the formation of no less detrimental low-melting aluminates such as C₄AF, CAS₂, etc. in the later stage.

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The cyclic creep behavior of pure aluminum is investigated for two different types of testing machine, one is the creep testing machine having constant values of peak stress, stress amplitude and frequency, and the other is Instron machine controlling peak load constant. Temperature range of the tests is around 0.33 T_m. Both results from the two different machines show the cyclic creep acceleration for which the constant load condition is more significant. The activation energies for the creep and the measured internal stress are increasing with the strain but the values are always higher for the constant peak stress test. Since the lower internal stress is one of the representatives of softer substructure, it probably accounts For the more accelerated cyclic creep and the lower apparent activation energy for the creep test under constant peak load. It is thought that the significant deviation of the creep behaviors with Instron machine is due to the increasing stress amplitude and peak stress, and the difference in the initial loading rate.

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The effects of aging treatment has been investigated in rapidly quenched Al-3.5Swt% Cr-lwt%X(X=Zr, V, Ti, Ni, Mn, Si) alloys. Specimens are aged from room temperature to 600℃ for 1hr. Vickers microhardness, electrical resistivity, microstructure is examined closely to study the aging phenomena in the alloys. Thermal stability is an important factor in designing alloys. In this respect, Al-Cr alloys containing V, Zr or Ti is better than the others. Al-Cr-Zr and Al-Cr-V is also desirable for age hardening, so Vickers microhardness is 120-126 at 450℃. The TEM results show that Al-Cr-Si alloy isn`t suitable for high temperature property because of high diffusivity and segregation. But the alloy including V or Zr is composed of homogeneous fine precipitates which are spherical-type.

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