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The behavior of Al₂O₃ based inclusion was studied during the production of ultra low carbon steel under RH degasser of 250 ton. The optimum condition to improve the cleanliness of ultra low carbon steel, the effect of decarburization type and ladle slag composition on the total oxygen content in ladle treatment are as follows. The optimum slag composition after RH treatment to achieve the total oxygen content less than 0.0012% should be 48% CaO, 45% Al₂O₃ and 7 % SiO₂ in slag composition. More than 1.9 watt/ton in stirring power and 6 in slag basicity were required. The main types of inclusion in slab were SiO₂ and Al₂O₃ mixed with TiO₂. It was revealed that titanium in molten steel reacted with inclusions containing FeO or MnO and the content of TiO₂ in inclusions gradually increased during the process transfer.

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The room temperature strengths of chromite solid carbon mixing pellets were investigated experimentally and theoretically by varying the reaction temperatures from 1200 to 1400℃ and reaction times from 1hr, to 2hrs. The following results were obtained. 1) The strength of firing pellets was found to increase with temperature but decrease with firing time. This is thought due to the gasified reaction of carbon. 2) From the break down pattern of fired pellets the strength of pellets appears to originate mainly from the slag banding of particles in pellets at an early stage of reduction process, while the strength at the later stage is caused by metal banding. 3) The coke mixing pellets showed the highest room temperature strength among the three pellets tested in this study.

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No single test can accurately predict the press shop formability of sheet metal and provide reproducibility of measured data. However a Limiting Dome Height(LDH) test was developed to specifically rank sheet metals for forming operations. The dome height at plane-strain state, which is the typical failure condition in many automotive stamping process is used as the criterion for sheet metal formability. Moreover, the strain state at failure in the test can duplicate the various strain state at failure in actual stamping operations by oaring the sample width and lubrication condition. In this study the difference between the FLD and the LDH tests was investigated and the LDH curves of various low carbon steel sheets were compared to yield a ranking of materials used in press shop. It was found that lubrication(or friction) was no less important than material itself in LDH values and no significant differences in punch speed and blank holder force(BHF) during the test were observed. A high LDH value is therefore, resulted at low interface friction allowing uniform distribution of strains. The relevance of the plane-strain LDH values with real stamping was checked by material control limit obtained from statistical deformation control chart for wheel house inner blanks.

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The mechanism of sulphur transport from steel bath into slag droplets produced during slag injection processes has been investigated by simulation experiments using the slags of different compositions. Powdered slags were introduced onto the surface of small steel melts in alumina crucibles at 1550℃ and the ensuing sulphur profiles in the steel and slag were determined by microprobe analysis. The results are as follows : 1) The desulphurization ability of molten steel appears to be best when the slag basicity is high. 2) The concentration and transport rate of sulphur within a slag is increased with high slag basicity; the mode of sulphur distribution is stepwise in basic slags while parabolic in acid. 3) Sulphur in the molten steel moved to the slag during the reaction and in the sulphur content in the steel at the interface was reached at the quasi-equilibrium state in a short reaction time. 4) The mechanism of sulphur transport seems to be controlled by a diffusion procsss in the slag side, which is in turn related to the viscosity of the slag.

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Isothermal and cyclic oxidation behavior of W-Mo-Cr alloys with and without Al addition(5 weight %) has been studied in air at 1000, 1100 and 1200℃. During isothermal oxidation, the rapid weight loss of W-30Mo-35Cr alloy after 10hrs at 1200℃ was considered to be due to the evaporation of W and Mo oxides through the porous oxide layers. W-24Mo-36Cr-5Al alloy formed the internal oxidation zone of Al₂O₃ particles and the outer protective Cr₂O₃ layer and thus revealed good oxidation resistance, During cyclic oxidation, W-24Mo-36Cr-5Al alloy showed better oxidation resistance than W-30Mo-35Cr alloy. W-30Mo-35Cr alloy showed a significant spallation after 30 cycles while W-24Mo-36Cr-5Al alloy revealed Cr₂O₃ layer still remaining as a protective layer after 100 cycles at 1100℃. It is suggested that the Al internal oxidation zone formed by addition of Al performs an important role in formation and stabilization of the outer protective Cr₂O₃ layer.

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With a specially designed water-cooled mold, casting thickness could be varied between 40 and 80㎜. With the decrease of casting thickness the secondary dendrite arm spacing was reduced and the ferrite grain size, after γ->α phase transformation, was reduced. In addition, the casting thickness has no influence on mechanical properties and ferrite grain size after hot rolling with the different total reduction in the range of 0.7∼1.4 in the process of roughing mill. So it is possible, in contrast to conventional casting and rolling, the strand thickness could be reduced during the casting stage instead of hot rolling process without the inferiority in mechanical properties.

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In order to develop protective coatings on the Fe-based equipments used in a continuous hotdip galvanizing process, sol-gel silica(SiO₂) coatings are formed on steel substrate and their durability in molten zinc has been investigated. The structure of silica coating was glassy and did not change during immersion test. Although many cracks were formed in the coating layers during immersion test, the silica coating was not separated from the substrate and effectively protected steel base from molten zinc attack. It is suggested that such a excellent durability of sol-gel silica coatings in molten zinc is due to the unwettability of silica coatings against molten zinc and high bonding strength between silica coatings and steel. Consequently, it is believed that sol-gel SiO₂ coatings could be used as a protective coating for Fe-based equipments used in a continuous hot-dip galvanizing process.

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Basic research has shown that ion plating has its advantage in producing highly adhesive film which can be controlled by gas pressure and discharge conditions like current-voltage characteristics, electrode geometry, assisting magnetic field. In this study, an ion energy analyzer is computer-aided designed to fit to a quadrupole mass spectrometer so as to give energy and mass spectra of ions. Energy distributions for ions and neutrals were simulated using Monte Carlo method in axi-symmetric 3D electrostatic field model. Charge exchange collisions and elastic collisions are incorporated. In the range of gas pressures between 0.8mTorr and 10mTorr, the average energy of positive ions is equivalent to 25% of substrate bias and that of charge-exchanged fast neutrals is equivalent to 13% of it. In comparison of measured energy distribution of Ti^+ and simulated result shows agreement well over the entire range except high energy tail.

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The Purpose of this study is to investigate the rolling deformation and preferred orientation for Ni₃Al intermetallic compounds. The chemical compositions of the alloys used in this study are 75.7Ni-24Al-0.3B(Al alloy) and 78.8Ni-21Al-0.2B(A2 alloy). The preferred orientation has been characterized by plotting inverse pole figures and pole figures. The preferred orientations of Al alloy after cold rolling, are {110} $lt;111$gt; and {110} $lt;211$gt;, whereas A2 alloy has brass type orientation of {110} $lt;211$gt;. This alloy could be cold rolled soundly to 80% reduction without intermediate annealing. The microstructure of A2 alloy consists of the ordered γ´cells surrounded by disordered γ phases. Also dislocations were concentrated in the γ phase near the of γ´/γ interface. The improved workability of this alloy may be due to the γ phase located at Ni₃Al interface, which alleviates the grain boundary embrittlement.

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In this study, Al-1%Si alloy for bonding wire was fabricated by the upward directional continuous casting process employing a heating mold above melt temperature. Effects of cold drawing and softening heat treatment on microstructure and properties of Al-1%Si alloy were investigated. The macrosegregation of Si particle in the directionally solidified Al-Si alloy significantly reduced comparing with the conventionally solidified alloy. As the cold drawing ratio increased, tensile strength increased and elongation decreased up to the drawing ratio of 99%, partially due to strain hardening and partially due to refinement of Si particles. The tensile fracture mode of the drawn specimen up to 95% was ductile fracture. The softening heat treatment below 200℃ did not affect the tensile properties. It was found, however, that the tensile strength decreased and elongation increased with increasing the softening heat treatment temperature above the recrystallization temperature between 200℃ and 350℃. The electrical resistivity showed increasing tendency with cold drawing and decreasing tendency with softening heat treatment.

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