발간논문

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Slag foaming phenomena was directly observed by the X-ray fluoroscopy. The BOF slag was a mixture of solid and liquid phases at 1550℃ and easily foamed by CO gas bubbles generated at the slag/metal interface. The iron ore added was decomposed rapidly on the surface of carbon saturated liquid iron. The CO bubbles generated was relatively large in size and hence escaped easily through the slag. However, when sinter ore was added, it was suspended in the slag phase due to its low density and dissolved slowly. The increase of FeO content, in slag caused a rapid generation of small CO bubbles at the slag/metal interface and resulted in an excessive foaming of slag. Anti-foaming agent made of wood sludge was decomposed incidently when dropped into foaming slag, and evolved volatile substances which suppressed the foam. Coke was also effective in suppressing the foam by promoting the coalescence of fine bubbles in contact with the coke surface .

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Electroless copper plating method was employed in copper coating of the (LM)Ni_(4.5)Co_(0.1)Mn_(0.2)Al_(0.2) hydrogen storage alloy powders for the preparation of a hydride electrode by using an acidic bath containing only CuSO₄ and H₂SO₄. The coating characteristics and the electrode properties were examined by SEM, X-ray photoelectron spectroscopy and electrochemical measurements in a half cell. The coating was being performed very fast within 5 min. without any pretreatment at room temperature. It was shown that the maximum discharge capacity was 250mAh/g in all electrodes and was degraded with increasing number of cycles. As the alloy powder used was finer, the electrode reaction was faster. However the degradation of electrode was larger. It can be suggested that this electroless copper plating method could be applied to the preparation of the rare earth-nickel based alloy electrode.

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The sliding wear behavior of the chromium nitride (CrN and a composite CrN+Cr₂N) coated Ti-3Al-2V free machining titanium alloy against heat-treated tool steel was investigated. The wear test was carried out using a ring--on-disc type tester under dry and lubricated conditions. Under the applied stress of 6.5 MPa and dry wear condition the chromium nitride coatings started to be peeled off from the substrate through pitting and micro fragmentation processes. The hard debris of the detached and crushed coatings worked as abrasives, which accelerated the wear even though the coefficient of friction was lowered by them. The effect of precleaning, such as sputtering, on the wear resistance was more significant under the dry wear condition than under the lubricated condition. Under the lubricated condition the wear resistance of the coated specimen increased a lot compared with the dry condition and the variation of the friction load decreased. Good correlation between the wear rates and low coefficient of friction was also observed under the lubricated condition.

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In a specific forming application of kitchen ware, such as a deeper sink, type 304 stainless steel requires good drawability and stretchability. The formability of type 304 stainless steel sheets is decisively influnenced by the alloy composition. This paper describes the alloy design of type 304 stainless steels for the improvement of formability at the lowest cost. With the aid of a regression analysis model, the modified type 304 stainless steel have been developed for the specific forming application. The calculated results from the regression model have a good agreement with the measured results from the commercial forming operation.

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The Influence of cold pre-deformation on the creep properties at 800℃ has been investigated on the Fe-based superalloy INCOLLOY 800H. The material was plastically deformed in tension or compression at room temperature. Then, creep specimens were machined with the axis either transverse or parallel to the direction of cold deformation. The predeformed specimens show significantly lower creep rate and lower creep strain than unpredeformed specimens. This effect was already found after 2% predeformation and became even more pronounced with increasing pre-deformation. At higher creep stresses, recovery is easier and the effect on the creep rate and ductility is reduced. All creep specimens after cold deformation failed by intergranular fracture, in contrast that the undeformed specimens show transgranular fracture mode for creep stresses higher than 70 MPa.

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The finite element method has been used to analyse the deformation behaviour of shadow masks during uniaxial tension. Shadow masks are perforated with a uniform triangular pattern of round holes or slots. The size of hole in the shadow mask varies with depth. In the analysis, the average hole size was used. The average hole size was calculated by averaging the hole sizes changing along the depth. Measured flow curves and apparent lateral strain-longitudinal strain relation were in good agreement with the FEM results calculated based on the plane strain at a larger ratio of thickness to ligament length and on the plane stress at a smaller ratio.

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