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2024 aluminum alloy was deformed by extrusion over the temperature range of 300-443℃ and the strain rates between 0.07-2.7/sec. Flow stress and strain rates were calculated from the ram pressure and ram speeds. The stress (σ)-strain rate (ε·)-temperature (T) relationship was found to be similar to that in creep. The experimental data were shown to fit the relationship ε·=A[sinh(ασ)ⁿexp(-ΔH/RT) where A,α, and n are material constants. The activation energy, ΔH, for 2024 aluminum extrusion were determined to be 33.6 Kcal/mole. The dislocation substructures produced during hot extrusion were studied by transmission electron microscopy. The equilibrium subgrain size was found to vary inversely with the logarithm of the Zener-Hollomon parameter, ε·exp(ΔH/RT).

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For the study of strengthened of cast iron, the effect of aluminum on the structure and mechanical property has been investigated with variation of the amount of aluminum addition. It is studied for the addition of aluminum to the effect of addition method, addition amount, variation of composition, and mechanical property. Through this study, following results are obtained. 1) Aluminum addition before inoculation are more effective on microstructure and mechanical property than after inoculation. 2) 0.75% addition of Aluminum is the best of microstructure and mechanical property. 3) In case of same amount of Aluminum addition, separate addition is more effective in mechanical property and due to Aluminum that helps the inoculation effectively. 4) In case of same C.E., the less silicon content the more increase amount of Aluminum required in graphtization.

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For the improvement of sulfidation resistance, several experimental nickel-base superalloys were newly designed by utilizing computer. The corrosion test was carried out using molten salt of 75%Na₂SO₄+25%NaCl at 900℃. Oxide scales of experimental alloys being examined by EPMA and electron diffraction were shown to consist of Cr₂O₃, TiO₂ at the outer side and Al₂O₃ at the innermost which was tightly adherent to the matrix. It is, therefore, proposed that the superior sulfidation resistance of experimental alloys is attributed to the excellent adherent oxide layers. The relationship between corrosion depth and alloying elements was obtained by means of multiple regression analysis. This led to a conclusion that Ti, Al and Cr improve greatly hot corrosion resistance whereas Co and W influence little it.

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Bainitic transformation structure in a low carbon alloy steel, 0.13C-1.8Ni-1.6Cr-0.5Mo-0.07V, has been studied by electron microscopy. Bainitic structure was obtained by isothermal transformation in the salt bath holding at 400℃, 450℃ and 500℃, Bainitic transformation has already begun at the initial cooling stage, from the austenitizing temperature to the respective transformation temperature. In the case of isothermal treatment at 450℃ and 500℃, mixed structure of coarse bainitic ferrite lath and retained austenite was observed in the specimens of short transformation time, for example, 200 sec. As the isothermal transformation time increased, the region of retained austenite was replaced gradually by finer bainitic ferrite lath, and carbide was precipitated in the revious coarse bainitic ferrite lath. Detailed microstructural features of the bainitic structure, produced at the initial cooling stage and at the later isothermal treatment stage, were studied, respectively. At the transformation temperature of 400℃, somewhat different microstructure, so-called granular type bainite, was developed.

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An investigation has been carried out to clarify the effects of final thermomechanical treatments(FTMT) on strengthening phenomena in comparison with isothermal and two-step ageing in Al-6.94%Zn-2.69%Mg alloy. Al-6.94%Zn-2.69%Mg alloy processed by FTMT exhibits higher strength than that of conventionally processed. From these results, the super-hardening effects obtained by final thermomechanical treatment may be explained by the interactions between dislocations induced by deformation and precipitates formed by ageing. Deformation less than 30% and final ageing at lower temperature than the solvus temperature of G.P.zones are desirable in obtaining remarkable improvement in mechanical properties by FTMT. The mechanical properties of Al-6.94%Zn-2.69%Mg alloy processed by FTMT exhibit lower strength than those of isothermal and two-step ageing when the temperature of final ageing is higher than the solvus temperature of G.P.zones. Maximum value of 0.2% proof stress resulted by FTMT is 57㎏/㎟, while that resulted by isothermal ageing is 41㎏/㎟.

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To examine the influences of vibration and the duration of vibration on the grain refinement, gravity segregation of lead, leakage of lead and hardness, the 60 cps vibration was given to the melt of Cu-Pb alloy during solidification. Results obtained from this study can be summarized as follows ; (1) As the content of lead increases from 10% to 20%, 30%, the ratio of the number of grains per unit area decreases from 2.78 to 2.54, 1.36 in the slowly-cooled structure, and the ratio decreases from 24.80 to 4.37, 1.90 in the rapidly-coolded structure, i.e. the vibration has an effect on the grain refinement in case of low Pb alloy, especially in the rapidly-cooled structure. (2) In case of slow-cooling, the vibration can suppress or eliminate the amount of gravity segregation of lead, and can increase the hardness. (3) The influence on the grain refinement occurs only in the period from 1010℃ to 980℃ during which the dendrites begin to form in Cu-20%Pb alloy.

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Correlation between Schmid factor and slip band formation under cyclic and static load was studied with 1.7∼3㎜ coarse grained aluminum(purity:99.999%) and corresponding dislocation structure was also discussed. Back reflection Laue method was used to obtain the orientation and Schmid factor of each grain. Applied creep stress was 240ｇr/㎟ and applied fatigue stresses were between 190∼340ｇr/㎟ and 21.5ｇr/㎟. As the value of Schmid factor of a grain was increased, the number of fatigue cycles, in which slip bands were formed, was decreased generally, but its grain size and orientation of neighbor grain seemed to affect the formation of slip band. In creep such relation did not exist and slip bands were fine and narrowly spaced in comparision with that of fatigue. With increasing the upper stress, slip band broadening became more prominent and under fatigue test between 220ｇr/㎟ and 30ｇr/㎟, cell structure was observed in the particular grain after 6×10⁴cycles.

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Rapid heat treatment has been applied to AISI H13 hot work tool steel for improving the mechanical properties, especially strength and toughness. Experimental result showed that the yield strength was increased by 10.7%, the ultimate tensile strength was increased by 12.6% and fracture toughness (Kc) values were maintained same level to compare with conventional heat treatment. It was found that the best rapid heat treatment condition was that heating rate was 21.8℃/sec, holding time was 60 sec at austenitizing temperature. It is believed that the improvement of mechanical properties, especially strength, was due to the dispersion strengthening of fine carbides precipitates within the lath martensite matrix.

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The magnetic properties of sintered Fe-Si alloys were investigated as function of composition, sintering temperature, and particle size and source of iron powder and silicon powder. Measurements of maximum permeability (μ_(max)) and coercive force (Hc) were performed with hysteresis-graph tracer. The lowest H_c and highest μ_(max) were found in specimen containing 3wt.% Si. It can be explained in terms of the intrinsic parameter K₁/M_5 and sinterability, i.e., the higher the silicon content the lower the value of K₁/M_5 but the lower the sinterability. Prealloyed silicon-iron powder, having lower melting temperature, enhanced sintering but decreased the μ_(max) and increased H_c due to the presence of fine pores in the grain. The μ_(max) and H_c were also affected by the particle size of the iron powder used. Thus the best magnetic properties were found in specimen containing 3wt.% Si prepared from fine carbonyl iron powder and pure silicon powder, sintered at 1450℃ in dry hydrogen.

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The effect of composition on the mechanical and electrical properties of the amorphous Co_(100-)_xB_x in composition range x=19∼x=27 has been investigated systematically. The fracture stress, the Young`s modulus, the toughness, the Vickers hardness and the electrical resistivity of amorphous Co_(100-)_xB_x showed tendency to increase with increasing boron content. The crystallization temperature of amorphous Co_(100-)_xB_x was raised with increasing boron content.

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