발간논문

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Radioactive sulfur(S^(35)) in the form of powdered FeS^(35) was introduced into the sulfur-free silicon-iron. The ingot was hot rolled at 950˚∼1000℃ to certain thickness such that subsequent cold rolling with 80% reduction in thickness resulted in 0.3∼0.4㎜ thick samples. 0.025w/o S^(35)-melted silicon-iron, sulfur-free 3.26w/o Si silicon-iron, cold rolled commercial silicon-iron and manganese-free 3.3w/o Si silicon-iron sheets samples were put together into the fused clear quartz capsules with dry pure hydrogen to a pressure of 25㎝ Hg. The sealed capsules were heat treated at various constant temperatures and then were rapidly ejected from the furnace and quenched into ice water by crushing the capsules. Autoradiography by using the AR-10 stripping film which was established by the author, was applied for specimens. Microstructures, autoradiographs and electron-microstructures were studied. It was found qualitatively that: (1) cold rolled silicon-iron showed relatively uniform distribution of sulfur in the alloy. (2) hotrolled silicon-iron showed the segregation of sulfur in the grain boundaries and uniform distribution of sulfur in the matrix. (3) the amount of grain boundary diffusion depends on the prior amount of sulfur and manganese in the silicom-iron. (4) The pinning mechanism seems to be the equilibrium grain boundary adsorption of sulfur.

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Porous chromium plating is used in the automobile parts industry for plating engine cylinders or cylinder liners, and piston rings. Porous chromium plating with oil retaining characteristics makes the automobile parts more corrosion-and wear-resistant. The mast conventional process for porous chromium plating is electrochemical etching after chromiumplating. The present study was undertaken to investigate effects of bath composition, plating temperature ancnd ent density on the type of porous plating achieved, surface condition, current efficiency, hardness and crack size. The change of porosity ratio was also examined with regard to etching and honing. Major results obtained can be summarized as follows: 1. The current efficiency decreased with a rise of bath temperature and sulfate ratio but decreased with a rise of current density. 2. The crack size increased with a rise of bath temperature and sulfate ratio but slightly decreased with a rise of current density. 3. The optimum conditions for obtaining pit-type, intermediate-type and channel-type porousplating were the current density of 50 A/d㎡ at 50℃, the current density of 50∼60 A/d㎡ at 55℃ and the current density of 60 A/d㎡ at 60℃, respectively. 4. A fluosilicate self-regulating solution for porous chromium plating that is stable and is of high current efficiency was developed by controlling the solubility of sodium fluosilicate. When this plating solution was used, pit-type and intermediate-type porousplating were obtained at 50℃ and 60℃, respectively. 5. The etching process after chromium plating had to he adjusted, depending on plating thickness, honing thickness and type of porous plating.

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This report made on the fundamental problems of the scoring of lubricated gear by using sliding wear tester experimentally and analytically. The research shows that the mechanism of scoring different from that of destructive damage by stress and fatigue. As the sliding frictions increased by high contact pressure, the oil films destroyed partially and becomes the state of boundary lubrication. At this state the scoring damage will be occurred by flash temperature high up instantaneously in the very small part of the contact surface of gear materials at very lower temperature than the original melting point of gear materials. It depends mostly on the viscosity and atmosphere of the various lubricants. And the results shows that the scoring will he occurred the value of the modulus of dimensionless parameter λ is over than (1×10^(-3)). here, β=ηn/p(dimensionless parameter of lubrication) μ=β.λ ∴λ=μ/β η: Absolute viscosity of lubricants p: Contact pressure n: Number of revolution μ: Coefficient of friction And studied compratively on the value of the flash temperature measured by using thermocouple with the Bloks formula on the ascending temperature of the contact surface of tooth.

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Manufacturing of piston ring by powder metallurgy technique was studied with water-atomized iron powder. Effects of chemical composition, pressing, sintering and coinning were investigated. The results indicated that the requirement of mechanical property of a piston ring can be achieved by conventional powder metallurgy with 0.75% carbon iron powder with 1% molibdenum when it is mixed with 3% copper powder pressed under 80,000 psi, sintered and repressed.

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The relationships between the degree of pre-work and the annealing condition for the deep drawing of 70/30-and 90/10-brass were studied. In the grain size control, it was found that the 90/10 brass showed relatively large deviation according to the different degree of pre-work, while the 70/30-brass was nearly uneffected. To get the optimum grain size for the deep drawing of Alpha-brass, 0.035㎜-0.05㎜ in average grain diameter, the 70/30-brass was sufficient to anneal 30 min. at 600℃ without considering the degree of pre-work 33% to 55%. But, for the 90/10-brass, it was resulted that the sample pre-worked about 60% needed 60 min. annealing at 600℃, and pre-worked under 50% was required the different annealing condition which was higher in temp. and longer in time than that of the 60℃ worked sample. And especially in 70/30-brass, the annealing condition mentioned above could be applied to the work-anneal cycle.

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The equation for thermionic emission has been derived from Eyring`s absolute reaction rate theory, which can be used to evaluate the reflection coefficient. The reflection coefficient γ was found to be γ=0.273×10^(-5)◎ where, M is the atomic weight of the metal, ρ the density of the metal, n the number of free electrons assigned to an atom, and T the absolute temperature of the metal. The values of the relflection coefficient for pure metals at various temperatures were computed and found to be very small.

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