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The influence of cooling method of continuous-cast slabs on the grain growth behavior of Ti-microalloyed steel during reheating to the austenite region has been studied using optical microscope and transmission electron microscope. The reheated structure of air-cooled continuous-cast slabs exhibits the austenite grain sizes ranging from 30 to 40㎛ and a fine uniform distribution of TiN particles from 10 to 20 ㎚. The grain coarsening temperature(GCT) ranges from 1250℃ at the slab center to 1300℃ at inbetween the surface and center. The values of GCT are in good agreement with the prediction of Gladman model. On the other hand, the reheated structure of water-cooled continuous-cast slabs shows a rather low GCT(1150℃∼1250℃). This is because this structure consists of bimodal TiN particle size distribution of coarse particles(30∼45 ㎚) and fine particles(5∼20 ㎚). The reason for this is believed to be owing to the fact that the water cooling of the continuous-cast slab effectively suppresses the occurrence of continuous particle nucleation during cooling and only enhances the growth rate of particles formed prior to the water cooling stage.

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The intermetallic compound formation, growth reaction and microstructural changes as functions of aging time and temperatures were studied in the electrodeposited SnPb/Cu and SnPb/Ni/Cu system. Diffusivities in the SnPb/Cu were about one order less than those in the Sn/Cu system. Activation energies for the growth of the η phase(Cu_6Sn_5) were 10.44 and 15.97 ㎉/㏖ for the Sn80Pb20/Cu and the Sn60Pb40/Cu system, respectively. Those of the ε phase(Cu₃Sn) were 15.47 and 15.20 ㎉/㏖ respectively. Mostly, the T/T_m(homologous temperature) of the SnPb layer affected the growth rate of the η phase when the aging temperature was near to the melting temperature(T_m) of the SnPb alloy(>0.9T_m). Therefore the growth rate of the η phase depended on the composition of the SnPb. However, the ε phase which grows consuming the η phase did not depend on the composition. In the SnPb/Ni/Cu system, an unknown phase(name it as χ phase) was formed in addition to the stable Ni₃Sn₄phase. The χ phase grew fast toward the SnPb layer at the SnPb/Ni interface and developed as plate like shape. From the EDS analysis, the composition of χ phase was approximately Cu_7(NiSn₃)_(83).

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Flow stress of a material, usually measured by compression test, is obtained for a strain rate and an environmental temperature. During the compression test, however, temperature of the material increases due to the deformation heat. Especially, the flow stresses of Inconel 718 and Ti-6Al-4V are quite sensitive to temperature, the deformation heat should be taken into account to obtain flow stresses of such materials. In the present study, a series of compression tests were performed for the two materials under various temperatures and strain rates, and temperature increases were calculated under the assumption that 90% of the deformation work was converted to heat. Using inter/extrapolation schemes, flow stresses at certain temperatures and strain rates were obtained and they were fitted into the Holloman equation of σ￣=Cε￣^m, where C and m varied with strain, strain rate and temperature. To show the influence of the deformation heat onto the estimation of flow stress, flow stresses of the materials when the deformation was considered were compared with those when it was not. It was worthwhile to note that the influence became more significant as the strain rate increased.

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The effect of heat treatment on the residual stress, the sheet resistance, and the solderability of SnPb/Cu and SnPb/Ni/Cu system were studied. The sheet resistance in the Sn80-Pb20/Cu system increased steeply aged at 170℃. The residual stress and the texture of the SnPb layer were the prime factors to affect the sheet resistance change. Higher the heating temperature, thicker the SnPb layer, and higher the Sn content, the residual stress increased faster and changed more. The variation of residual stress was directly related to the intermetallic compound formation. Degradation of the solderabilities in SnPb/Cu system during the aging was affected by the intermetallic compound thickness, the residual stress changes, and the composition changes of the SnPb layer. In the SnPb/Ni/Cu system, the sheet resistances and the solderabilities did not change much in contrast to the SnPb/Cu system. The relative stability of the electrical and the solderability property of SnPb/Ni/Cu system might be due mainly to the coarse plate-like χ phase formation in the SnPb/Ni interface.

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Effects of the amounts of SiC coating on the properties of WC-SiC-Ni cemented carbide were investigated. A highly condensed sintered material with a theoretical density higher than 98% was obtained for SiC with 0.8w/o when W powders coated with SiO2 were carburized at 1450℃ and SiC coated WC was sintered with Ni. The particle size of W C powders in this sintered material was about 0.9 ㎛ and very uniform. The Vickers hardness was measured to be as high as 1760 ㎏/㎟. Transeverse Rupture Strength (TRS) to be 338 ㎏/㎟. These good properties of the cemented carbide were able to be obtained by forming a condensed SiC layer for SiC of 0.8w/o which enhanced the interface reaction of the carbide with Ni and thus by inhibiting WC particle growth, making the particle size uniform, and making the sintered material condensed.

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Variations in thickness and microstructure of ribbons produced by planar flow casting have been investigated as functions of various process parameters. Continuous polycrystalline ribbons of Al-Cu alloy with a thickness range of 50 to 180 ㎛ and a width of 12 ㎜ were fabricated. The ribbon thickness was closely related to wheel velocity, ejection pressure, slot/wheel gap distance, and superheat of molten metal. Microstructural transitions from segregation free zone to cellular/dendritic regions were observed. The thickness ratio of the columnar layer to the entire ribbon thickness and the average inclination angle of the columnar layer increased with increasing the wheel velocity and the superheat of molten metal. X-ray diffraction spectra indicated an increasing tendency towards a ｛200} preferred orientation on the wheel-side surface of the ribbon with increasing the superheat of molten metal. On the air-side surface of the ribbon,｛111｝planes predominated over the entire range of the superheat, and the variation of peak intensity ratios with the superheat was rather negligable.

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AISI 430 stainless steel strip was fabricated by laboratory scale twin-roll strip caster. Microstructure of ascast strip consists of ferritic α matrix, (Fe,Cr)_(23)C_6 carbides and lath martensite at grain boundary, observed in transmission electron microscopy. Martensite was transformed from retained austenite at grain boundary due to rapid cooling of strip casting. The martensitic formation can be suppressed by the slow cooling after roll nip point. The lower value of hardness at the strip surface was obtained because primary ferrite remained due to higher cooling rate. As it goes from center region to edge region, the solidification end point is located above average height and the white band zone at the central layer become wide. The zone of negative segregation results from squeezing out near the central layer of the liquid which has high phosphorus and sulfur content.

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The shape variation of billet was investigated by numerical and experimental spray forming with various average substrate withdrawal velocity V￣, withdrawal velocity change interval △t and velocity deviation from average velocity V_(dev). The shape and diameter of billet which is manufactured at the condition of large V￣, △t, vary largely. When V￣, △t and V_(dev) are small, the shape of billet is similar to that of the billet with constant withdrawal velocity. The average diameter of billet is determined by V￣ independent of △t, V_(dev). With V￣ of 0.2 ㎜/sec, △t of 200 sec and V_(dev) of 0.2 ㎜/sec. billet of which diameter 230 ㎜ and height 1000 ㎜ was manufactured.

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Behaviors of solute elements segregation and primary carbides in the solidification structure of rare earth metals(REM) treated 0.35C-0.45Si-0.33Mn-4.9Cr-1.2Mo-0.8V ingots have been investigated. The important results are summarized as follows. 1) REM addition brought about a remarkable reduction of center-segregation, center-blow hole, and enlargement of equiaxed zone and fine solidification structure. 2) REM addition brought about a remarkable reduction of solute elements segregation area in ingots, so that it resulted in refinement of primary carbides. 3) Crystallized carbides in solute elements segregation area of 5Cr and REM treated ingots were MC of dendrite type and M₂C of skeleton type. Dendrite crystal, solute elements segregation area, and M₂C changed into γ-Fe, MC, M_7C₃, M_(23)C_6 and M_6C by 845℃ soaking treatment. REM addition did not influence on the carbide composition at the same heat treatment.

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We have synthesized α-Fe2O3 particles directly from ferric salt solution by hydrothermal reaction. The effect of citric acid concentration and hydrothermal reaction temperature on the formation of α-Fe2O3 particles, formation process of α-Fe2O3 particles were investigated. Also, we proposed a formation model of needle-like α-Fe2O3 particles in this reaction system. The length and aspect ratio of α-Fe2O3, particles were decreased gradually with increasing of citric acid concentration. The crystallization of needle-like α-Fe2O3 particles was inhibited beyond citric acid concentration of 1.5 × 10(-4) mol. We can synthesized α-Fe2O3 particles with the most superior acicularity at 140℃. Aspect ratio of α-Fe2O3 particles was decreased with increasing reaction temperature. α-Fe2O3 particles formed above 220℃ exhibited sphere-like particles. The crystallization to α-Fe2O3 particles from ferric salt was accomplished at 140℃ in 10 minutes. Citric acid was adsorbed with the form of citrate anion(R-COO(-)) on the ferric hydroxide and exerted important role on the formation to the needle-like α-Fe2O3, particles in this reaction system.

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