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The changes in the microstructure, mechanical properties and Fracture mode were investigated for Fe-38at.%Al alloys when Cr, Mo, Nb and B were added. As the amount of B or Nb addition was increased, the grain size became smaller. The effects of Mo and Cr were not significant. Hardness and yield strength of Fe-38at.%Al alloy were decreased by adding 6%Cr. However Mo, Nb and B additions were increased. The fracture mode of Fe-38at.%A1 binary alloy was the typical intergranular fracture, but it was changed into the quasi-cleavage fracture mode by adding 6%Cr. In Fe-38Al-6Cr+Mo alloy, the fracture mode was changed into cleavage. The typical intergranular mode was observed in Nb added alloys where cracks propagated along the grain boundary precipitates. However, the fracture mode in B added alloys was the quasi-cleavage mode due to strengthening of grain boundaries.

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Hot restoration and strain rate sensitivity of SiC_p(15Vol.%)/AA2024 composites reinforced with different sizes of SiC_p reinforcements (1, 8, 15, 36. and 44 ㎛) were investigated by hot torsion tests. For the composites reinforced with SiC_P of 8, 15, 36, and 44 ㎛ sizes, dynamic recrystallization (DRX) was responsible for the hot-restoration at 320-480℃. Also, for the composite reinforced with SiC_p of 1 ㎛ size, dynamic recrystallization (DRX) was responsible for the hotrestoration at 320-430℃, and dynamic recovery (DRV) was responsible for the hot-restoration at 480℃. The composite reinforced with SiC_p of 1 ㎛ showed the highest strain rate sensitivity (0.361) at 480℃, even though the failure strain (2.36) of the composite reinforced with 1 ㎛ SiC_p was lower than that (3.65) of the composite reinforced with 8 ㎛ SiC_p. These results were discussed in relation to dislocation density and stacking fault in the matrix grain of the composites by transmission electron microscopy (TEM).

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Strand bulging is presumed to play a major role in the formation of internal cracks and centerline segregation in continuous casting. During the solidification process, the shell is subjected to cyclic mechanical and thermal loads which can cause various defects when the strains exceed critical value. In the present study, multi roll pitch and dynamic creep model has been developed for bulging analysis. Bulging strain was reasonably predicted to increase by repetitative bulging when considering creep damage accumulation by the model. Also cumulative creep bulging strain could be calculated by the regressive equation which has been derived based on the present model. Bulging increase was measured during strand stoppage and compared with the calculated results. Finally we considered the effect of roll misalignment on bulging strain. The model can be used for the caster design and optimum operation for soft reduction, high speed casting, etc.

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In equilibrium, 304 stainless steel has only γ-austenite phase below about 1170℃ and solutes are uniformly distributed in γ-austenite. Due to incomplete solid-state diffusion, it has retained δ-ferrite as well as γ-austenite and the solute distribution becomes inhomogeneous in each phase. To further understand the solidification behavior of 304 stainless steel, the variation of δ-ferrite amount with temperature and the solute concentration in each phase across the phase boundary are calculated in this study. The calculated solute contents at the interface are in good agreement with experimental data available. It is shown that the equilibrium calculation using 304 steel composition itself produces better results than using equivalent composition. The calculated amounts of retained δ-ferrite using 304 equivalent composition are somewhat higher than experimentally observed values. Much better agreement between calculation results and experimental data is expected if more reliable experimental data can be obtained.

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The fluid flow and heat transfer in the melt puddle of Fe_(78)B_(13)Si_9 amorphous strip on Planar Flow Casting process were analyzed by numerical method based on the Body Fitted Coordinates and Finite Volume Method. The necessary conditions for the existence of the solidification layer were that the thickness of solidified layer in the puddle should be less than that of strip, and the minimum temperature of puddle should be higher than that of solidified layer. The range and magnitude of heat transfer coefficient satisfying the necessary condition were decreased with increasing contact length. The magnitude of heat transfer coefficient was increased with increasing the size of gap between nozzle and roll. By the analysis of fluid flow characteristics, melt recirculation in downstream was found to be existed.

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Thermoelectric properties of p-type polycrystalline (Bi_(1-x)Sb_x)₂Te₃ (0.75 ≤ x ≤ 0.85), fabricated by mechanical alloying and hot pressing, were investigated as a function of the Sb₂Te₃ content and the amount of excess Te addition. The effect of a reduction treatment in Hz atmosphere on thermoelectric properties of (Bi_(1-x)Sb_x)₂Te₃ was also studied. Among (Bi_(1-x)Sb_x)₂Te₃ fabricated by mechanical alloying. (Bi_(0.2)Sb_(0.8))₂Te₃ exhibited the highest figure-of-merit of 2.98×10³/K. When (Bi_(1-x)Sb_x)₂Te₃ powders were reduction-treated in H₂ atmosphere, the Seebeck coefficient and electrical resistivity decreased due to the removal of the oxide layer on the powder surface. With the reduction treatment, the figure-of-merits of (Bi_(0.25)Sb_(0.75))₂Te₃ (Bi_(0.2)Sb_(0.8))₂Te₃, (Bi_(0.15)Sb_(0.85))₂Te₃ were changed from 2.76×10^(-3)/K to 2.79×10^(-3)/K, from 2.98×10^(-3)/K to 2.80×10^-3/K, and from 2.78×10^(-3)/K to 1.81×10^(-3)/K, respectively. When 1.0 wt% excess Te-doped (Bi_(0.2)Sb_(0.8))₂Te₃ powders were reduction-treated, a Figure-of-merit of 3.33×10^(-3)/K was obtained.

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The mechanism of oxide formation in a weld line of high-frequency induction welding was studied through the microstructural observation and the oxide characterization. A decarburized weld line was produced by the reaction between wustite, which was formed in a heating stage, and carbon in steels. At welding temperature, 1400℃, however, wustite melted down and dissolved oxygen to the decarburized zone to form complex oxides, SiO₂-MnO-FeO-Al₂O₃. Therefore, the formation of a weld line is basically consisted with two processes: the simultaneous oxidation and decarburization process in a heating stage. and the oxygen dissolution and internal oxidation process in a welding stage. The composition of complex oxides, especially the content of MnO and SiO₂, showed a good relationship with the manganese-to-silicon ratio of steels.

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The metal oxides contained in electric arc furnace(EAF) dust are reduced by solid carbon at the various temperatures and basicities to investigate their effects on the reduction reaction and rate. A thermogravimetric analysis(TGA) was also carried out for franklinite to show that the zinc oxides could effectively be reduced and evaporated completely at the temperatures above 1100℃. The X-Ray diffraction study of reduced EAF dust revealed that the slag was a mixtures of Merwinite[Ca₃Mg(SiO₄)₂]. apparentely crystallized first and Akermanite [Ca₂MgSiO_7] as the second crystallization product. The reaction rate constants evaluated for zinc removal reaction and also the reduction reaction of metal oxides are found to be expressed as a classical Arrhenius type relation with the temperature.

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The distribution of waste gas temperature along the sinter strand is affected mainly by the permeability of raw material mixture and by the combustion efficiency of coke breeze in sintering reaction. Therefore, the analysis and control of waste gas flow play a important role to control for sinter quality management. In this study, numerical characterizing indices were provided from the temperature distribution of waste gas. For the more, relations between sinter qualities and these indices were estimated by simple regression analysis. From the relationship between both factors, it was confirmed that the sinter productivity was lineally increased by increase of the burn rising rate of waste gas at wind box. Also, from the result of multi-regression analysis between sinter qualities and characterizing indices of the temperature distribution, the sinter quality prediction program was developed. With this program, the productivity, yield and shatter index of sinter ore could be estimated directly when the temperatures of twelve wind box are input as a data file.

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The experiments have been carried out to understand the thermodynamic dissolving behaviors of carbon into slags at high temperature. Carbon is dissolved as carbide under highly reducing atmosphere in CaO-SiO₂ as well as CaO-SiO₂-CaF₂ slags. Carbide solubility in CaO-SiO₂-CaF₂ slag decreased with the oxygen potential with theoretical relationship of (-½), which implied a reaction mechanism of ion exchange between carbon and oxygen ion. The dependence of carbide solubility in slag on slag basicity, measured far various slag systems appeared to confirm this mechanism. This reaction mechanism is feasible if carbide dissolution proceeded by reaction between solid carbon and oxygen ion supplied from (CaO) in slag which would be influenced by slag components and temperature as shown in capacity concepts. Substitution of CaO by MgO decreased the solubility of carbide in CaO-SiO₂-MgO slag due to the relatively low electronegativity of (MgO).

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