발간논문

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The Corrosion of carbon steel by V₂O_5-Na₂SO₄ mixture has been investigated over the temperature range of 600° to 1000℃ at the atmospheric pressure of air and nitrogen. The material is severely corroded at the temperatures above the melting point of the mixture and the corrosion rate is logarithmic. The most corrosive mixture is approximately 70% V₂O_5-30% Na₂SO₄ at the temperatures below 850℃. The corrosion attack is caused by the oxygen absorption power of the molten compounds, but there appears to be a strong indication that the molten salts corrode the metallic material by reacting directly with absorbed oxygen at the very high temperatures and especially when the molar ratio of V₂O_5 to Na₂SO₄ is less than 40`60.

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The objective of this research is to increase productivity and improve quality of products, by studying the standard cupola operation condition with Anthracite and cokes as fuel, pig iron and steel scrap as raw material. The study was carried out using a 2.5 ton/hr capacity hot blast water cooled cupola. Cupola Operations were done on the following functional subjects to study the variation of chemical composition mechanical property and micro-structures. a. The effect of cokes as fuel by mixing pig iron with steel scrap. b. The effect of Anthracite as fuel by mixing pia iron with steel scrap, c. The effect of mixing cakes and Anthracite with steel scrap and pig iron. The optimum was found to be 50% Anthracite, 55% steel scrap and tuyere angle was 10∼15˚.

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The changes of diffusivities of carbon in gamma phases of Fe-Ni-C alloys containing nickel contents of 0.001 to 5.03 weight pct at the temperature range of 870℃ to 1000℃ were studied. The diffusivities of carbon were calculated from the solution of Fick`s second law for a semi-infinite solid. The carbon diffusivity increases with increasing nickel content in gamma range of Fe-Ni-C system, hence the nickel will also affect the diffusion of carbon in bct martensite as well as bcc ferrite of the alloy.

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ASTM A-53B was used as a mild steel, and corrosion inhibiting effect of souium chromate, meta-phosphate, and zinc-salt for coiling water system was studied by measurements of polarization characteristics and weight loss test in circulating water system. Results are summarized as: 1) Using only sodium chromate with low concentration (below 20 ppm CrO₄) pitting corrosion and tuberculation could not be prevented. 2) Mixture of sodium chromate and meta-phosphate with concentration range tested did not exhibit good inhibiting effect. 3) Mixture of meta-phosphate and zine salt at low concentration was shown 90-95% protection and did not be found any tuberculation. 4) Polarization characteristics could be used for suitable and rapid selections of inhibitor and its concentration for the cooling water system.

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