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The Ni-base self fluxing alloy was coated on SM45C using High Velocity Oxygen Fuel(H.V.O.F) spray process. The effects of post-treatments such as fusing treatment and aluminizing on the wear and corrosion resistance of the coating were studied. Borides such as Ni₄B₃ and Cr_5B₃ were formed by fusing treatment at 1050℃ for 10∼30min. The borides contributed to the increase in hardness and wear resistance. A dense diffusion layer was formed by aluminizing on the coating at 900℃. As a result of the cyclic hot corrosion test, it came to have the best corrosion resistance when it was performed at 900℃ for 3hrs in the pack composition of 75%Al₂O₃: 20%Al : 5%NH_6Cl. Although the unstable Ni₂Al₃ phase formed in the coating surface was changed to stable NiAl by means of homogeneous treatment, the corrosion resistance was not changed significantly.

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In order to investigate the effect of cooling rate on the formation of δ-ferrite in type 304 stainless steel. Gleeble experiment. TIG welding and laser surface melting were carried out. The transformation mechnism of δ-ferrite to austenite was studied by interrupted quenching experiment of unidirectional solidification. Transformation of δ-ferrite to austenite in the 1400 and 1160℃ range has the profound effect on δ-ferrite content. δ-ferrite content was about 74% at the final solidification, which decreased to about 8% at room temperature. As the cooling rate increased from 0.5 to 9.7×10³C/s, δ-ferrite content increased from 3 to 20%, but the further increase in cooling rate from 9.7×10³ to 3.3×10⁴C/s decreased δ-ferrite content from 20 to 9.7%. With increasing the cooling rate, δ-ferrite morphology changed from vermicular ferrite, lacy ferrite and to euteetic ferrite with concurrent decrease in the δ-ferrite content.

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A technique based on a SHS(Self-propagating High Temperature Synthesis) process is proposed for manufacturing Al₂O₃-B₄C(ΔH_(f298)) system because of a low exothermic potential of the reactants, a chemical furnace technique, which is an indirect combustion ignition using 3TiO₂/4A1/3C, was introduced to this system. The synthesis of Al₂O₃-B₄C composite powder was affected by the mole ratio and the particle size. The synthesized Al₂O₃-B₄C composite powder have an angular shape, and the mean size of produced particle is about 2.17 micron. The Al₂O₃-B₄C composite powder has a higher purity than the reactants. This is because the impurities are volatilized at the high-temperature generated during the rapid exothermic reaction.

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AlNi_x intermetallic compounds have many advantages when it is utilized for high-temperature, it is characteristic of high yield stress reciprocal of the temperature, stress ratio, good oxidation-resistance wear resistance, and high-creep resistance. Currently, a lot of manufacturing skills of direct-sintered materials by HPCS process have been developed. When the direct-sintered material is manufactured by HPCS process, the factors that affect the densfication of it are preheating temperature and pressure. Therefore the higher the preheating temperature and the pressure, the more densified the specimen. It is found that the porosity and specific wear of sample produced were decreased and grain size and micro hardness of sample were increased with increasing preheating temperature.

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For the theoretical discussion of the crack advance phenomena, many models have been suggested. However, most of them could not suggest the exact processes of the crack-tip region in the low cycle fatigue conditions, but only rough approximations in terms of LEFM for the damage of crack-tip region. Recently, Oh and Nam suggested a new model of crack advance and life prediction based on the damage formation in fatigue process zone, where the concentrated degradation of the material occurred with crack advance. In the previous studies a parameter of α₁ which is the term of correcting plastic zone size was suggested to be constant by many researchers in a fixed temperature. But the experimental results for 1Cr-Mo-V steel showed that α₁ is a function of temperature, and the microhardness tests proved that the smaller the value of α₁ in high temperature, the smaller the size of cyclic plastic zone(n).

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The effects of heat treatment on the γ′precipitation and the mechanical properties of a newly developed mechanically alloyed(MA) oxide dispersion strengthened(ODS) Ni-base superalloy were investigated. When the solution treatment temperature of ODS Ni-base superalloy was above 1260℃, the γ′precipitates were completely dissolved and uniform sizes of γ′precipitates were formed during the cooling from the solution treatment temperature. While, when the solution treatment temperature of ODS Ni-base superalloy was below 1260℃, bimodal sizes of γ′consisted of coarse and fine γ′ precipitates were observed after cooling from the solution treatment temperature. During the aging treatment at 954℃, the average size of γ′precipitates increased with increasing the aging time. The ODS Ni-base superalloy with γ′precipitates less than 0.25㎛ was deformed dominantly by shearing the precipitates by pairwise dislocation. While the ODS Ni-base superalloy with γ′precipitates larger than 0.28㎛ was deformed dominantly by the Orowan bypass mechanism. An equation to estimate the yield strength of ODS Ni-base superalloy with bimodal sizes of γ′ precipitates, based on the rule of-mixture was proposed.

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The relationships between the microstructure and the mechanical properties of C-Mn steels were quantitatively analyzed. Specimens with various microstructure of ferrite, pearlite and bainite were manufactured both under isothermal and hot rolling conditions. Quantitative metallorgraphy and tensile test were performed, and the factors which influenced tensile properties were analyzed. The hardness of each phase formed during various thermomechanical conditions was primarily dependent on the chemical composition and the mean transformation temperature. The Hall-fetch type equation combined with the mixture rule were applied to obtain the relations between the microstructure and tensile properties. The tensile properties were formulated as functions of volume fraction and hardness of each phase and ferrite grain size. It was found that the predicted tensile properties were in reasonable agreements with measured ones.

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The results obtained from the reduction-experiment study on the recycling of the waste pickling sludge of stainless steel are follows. 1) From the reduction sintering experiment carried out in an N₂-atmosphere by adding the active carbon to the waste pickling sludge of stainless steel, it was found that the suitable condition for extracting the Fe-Ni-Cr crude alloy from the waste pickling sludge is ; the weight ratio of carbon/sludge should be above 0.32 and the reduction temperature should be above 1200℃. It is necessary that the waste pickling sludge is sintered above 1200℃ to decrease the loss-and-pollution of dust by fine particle powders. 2) The products obtained from the melting process under the conditions of the temperature 1600℃, N₂-atmosphere and the carbon/sludge ratio 0.32 should the recovery fraction of Fe above 96%, Ni above 97% and Cr above 90%. The excessive carbon included in the crude alloy produced in this experiment is necessary to pass by the decarburization progress during the oxidizing period in the steel making process.

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The development of preferred orientations in the annealing texture of the Inconel 690 sheets was studied by the x-ray texture measurements and TEM observations. The pure metal type rolling texture which can be described by preferred orientations near {112}$lt;111$gt;, {123}$lt;634$gt; and {110}$lt;112$gt; was formed in the 60% cold rolled Inconel 690 sheet. The annealing texture of the Inconel 690 sheets was dependent on the annealing temperature. A lower mobility of the moving grain boundaries at 750℃ caused the formation of the annealing texture which was similar to the cold rolling texture. The major preferred orientations of the 950℃ annealed specimens were {112}$lt;110$gt; and {001}$lt;110$gt;. These orientations seemed to have the oriented growth relationship with respect to the rolling texture components. The formation of fine and closely spaced annealing twins in the specimen annealed at 1150℃ led to the randomization of the annealing texture.

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The nitrogen solubility and nitride capacity of the BaO-B₂O₃ and CaO-B₂O₃ slag systems at high temperatures were measured in order to understand the nitrogen solution mechanism of slag by using a chemical equilibration technique. The present slag systems were chosen because they have wide liquid regions at the temperature of interest and were expected to show two different types of nitride dissolution behaviors. The nitride capacities of both systems showed some minimum values with changing composition. This was explained by considering that nitrogen can dissolve into slag as "free nitride" at high basicities and "nitride incorporated" with the network for acidic slags. The change of nitride capacity with optical basicity and the activity of the basic component followed the predicted behavior for the proposed solution mechanism. The nitride capacity of the BaO-B₂O₃ system is considerably greater than that of the CaO-B₂O₃ system because BaO is a more basic oxide than CaO.

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