발간논문

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The effects of the holding temperature, heating rate and nickel content on the formation of the send phase were investigated for the ductile cast iron having ferrite matrix. In order to vary the heating rate, specimens were prepared from 1 to l0㎜ in thickness and nickel was added up to 1% to study the effect of nickel content. The main results obtained from this study were as follows; 1. Austenitizing velocity increased with high holding temperature and rapid heating rate but decreased with nickel amount. 2. Incubation period decreased with high holding temperature, rapid heating rate, and high nickel content. 3. Radius of the second phase formed by the graphite diffusion into ferrite matrix increased by the rapid heating but decreased by addition of nickel. 4. Uniform spheroidal second phase was formed when the specimen were held at high temperature and heated rapidly to the high temperature. 5. The discrepancies between Paxton-Judd model and this study were mainly arised from the condition of the holding temperature, the carbon, and the impurities. 6. After rapid increase of the hardness in early stage, the hardness increased slowly with the amount of the second phase.

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Creep test was carried out to percieve actual stress change due to pore formation in Inconel 617. The number and size of pores was increased as strain increased, the influence of pores on actual true stress was insignificant up to 20% strain and the influence to the stress near rupture was 1-2%.

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The dissolution of gold and silver in acidic solutions of thiourea containing Fe^(++) ions as an oxidant was studied. It was found using a rotating pure metal disk experiment that gold and silver can respectively be dissolved at much greater rate by acidic solutions of thiourea and that by conventional cyanidation techniques. Dissolution rates are dependent both on thiourea and oxidant concentration, and appear to be controlled partially by chemical phenomena and partially by transport of ions (thiourea and oxidant) to the metal surface. A transition from diffusion control to reaction control has been noted at higher agitation levels.

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Solubility of nitrogen in liquid iron, iron-chromium and iron-nickel alloys has been measured by the sampling method under 1 atm N₂pressure. Experiments were carried out at the temperature range of 1829-2205K and at the composition range of 0-30.2% Cr and 0-40.0% Ni. Results obtained are as follows: 1) Nitrogen solubility measured in pure iron was, log (wt % N)_Fe=-341/T-1.157. 2) Interaction parameters in liquid Fe-Cr and Fe-Ni alloys were, 3) Enthalpy change of nitrogen solubility in Fe-Cr and Fe-Ni slloys were,

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Alumina coating on various substrates by chemical vapor deposition process has been investigated with different treating conditions in a vertical reactor. Satisfactory deposition was resulted with H₂/CO₂mole ratio is unit and AlCl₃mole fraction is 0.03. Deposition rate was found to be proportional to the square root of total gas flow rate. Since cromium and nickel act as inactive site for adsorption of reactant gas, deposition rate of iron and carbon steel were superior to that of stainless steels.

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In this study, the influence of deformation on the mechanical properties of amorphous Fe_(40)Ni_(40)P_(13)C_7, ribbon made by single roll melt spinning was investigated. As-quenched ribbon was rolled about ∈_T (thickness reduction ratio)=1∼6% and continuous bending deformed about ∈_M(Max. plastic strain)＝1.0∼2,5%. The fracture of rolled ribbon occurs along the plane of shear band formed by rolling. Tensile strength decreases with thickness reduction. These results are attributed to the work softening in the shear band by rolling. The fracture plane of continuous bending deformed ribbon is not a single plane, but double plane. (The shear band plane formed by bending and the flat plane orientated with 45˚∼50˚to the tensile axis). In this case, the shear band present obstacle to the propagation of the slip during tensile test and tensile strength increases.

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The effect of hydrogen on the tensile properties of low carbon steel was investigated at room temperature for the wide ranges of charging current density and strain rate. As the current density increased, the yield point phenomena gradually disappeared, i.e., the upper yield point disappeared, the yield elongation decreased and the stress continuously increased in yield elongation range. The results were explained in terms of the generation of mobile dislocations based on the observation of Lu¨ders band. The observed yield point phenomena did not changed even after removing the hydrogen dissolved in the specimen by vacuum treatment. A change in the average dimple size was observed for the hydrogen removed specimen. This was caused by the irreversible lattice defects generated during hydrogen charging. The flow stress of the specimen prestrained and hydrogen-charged was higher than the uncharged specimen. This lattice hardening should be explained by a non-Cottrell type of interaction between hydrogen and dislocations.

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