발간논문

Home > KJMM 논문 > 발간논문

The rate of decomposition of zircon sand with molten NaOH was investigated. A change in the reaction mechanism from chemical reaction control to mass transfer control was observed in the temperature range 515℃-635℃. For temperatures above 605℃, the decomposition rate is limited by the rate at which the liquid NaOH defuses to the solid zircon surface. For temperatures below 585℃, the rate is, however, controlled by the slow chemical reaction at the solid surface. The rate of the chemical reaction is well explained in view of the initial nucleation at the solid surface followed by the growth of these nuclei.

keyword :

Chromium films deposited on steel and glass substrates by electron beam evaporation were studied by scanning electron microscopy, x-ray diffraction, and micro-hardness testing. With increasing temperature from room temperature to 850℃, the porous and micro-domed structure of deposits changed into the faceted and the macro-ledge structures at above 300℃, and the smooth and grooved structure above about 750℃. And the [110] grain orientation at room temperature changed into [112]. The volume fraction of [112] was maximum and that of [110] was minimum at about 300℃. With increasing temperature from 300℃, [200] volume fraction was increased up to about 720℃ and grains were almost random oriented above 720℃. The relations between hardness and grain size of films were explained by Hall-Petch equation.

keyword :

In recent years welding technique has been developed noticeably and is used widely in the field of ship building, machine production, pressure vessels, bridge construction and nuclear pressure vessels. Welded structures usually contain residual stresses due to differential contraction between weld metal and base metal. It is recognized that these stresses can lower resistance to brittle fracture by supplying additional energy to a rapidly spreading crack. Stress relief annealing treatment is used after welding process in order to release the residual stress and improve the mechanical properties of the weldments. In this paper, authors conducted the annealing treatment for the weldments in several degrees and inspected their mechanical properties and residual stresses. The results obtained in these tests are as follows: 1) The modulus of elasticity become more closer to the mean value as the annealing temperature is increased. 2) Tensile stress of the weldment is decreased 34% compared to the base metal, and as the annealing temperature is increased the tensile stress shows a little lower values. 3) The impact value seems to be decreased as the modulus of elasticity is increased in the welded zone. 4) Deviations on hardness are greater in the heat affected zone than other parts of the weldment and stabilized as the annealing temperature is increased. 5) The residual stresses are released noticeably in the vicinity of the annealing temperature around 600℃.

keyword :

The effects of the addition of Nickel, Magnesium and Copper to Al-Si alloy on tensile strength, hardness, abrasion resistance and the coefficient of thermal expansion were studied. The results obtained in this study were as follows: 1) The tensile strength in Al-Si alloy showed a maximum when the amount of either Magnesium or Nickel content was 1%, on the other hand, tensile strength increased with an increase in cooper content. The tensile strength of the alloy containing 11% silicon content showed a maximum compared to that of other alloys with different amounts of silicon contents. 2) The hardness showed the highest value when Magnesium was added, and the next highest values were obtained in the order of Copper and Nickel added, respectively. As the amount of silicon content increased, the hardness showed to increase. 3) The abrasion resistance increased with an increase in the addition of elements and the order of effects of additional elements on the abrasion resistance was similar with the case in the hardness. As the amount of silicon content increased, the abrasion resistance showed to increase. 4) The addition of nickel yielded the lowest value of the coefficient of thermal expansion. However, magnesium seemed to show little effect on the coefficient of thermal expansion.

keyword :

Cast iron powder is prepared by pulverization of gay cast iron swarf (grade GC20) with conventional hammer mill. After degraphitization is carried out by extracting the free graphite flakes from the powder, the characteristics of green compacts and sintered products are studied. The results obtained are as follows; 1) The compactability of degraphitized cast iron powder is superior. When compacted between 8-l0ton/㎠ pressure, the green density of compact gets up to about 90% of its parent iron density. 2) The sintered density and green density of compacts are increased with increasing compacting pressure. 3) The strength of sintered product is increased with raising the compacting pressure and with increased sintering temperature and time. The tensile strength of the product compacted with 8ton/㎠ pressure and sintered at 1150℃, 90min in N₂＋3H₂atmosphere, goes up to 42.3㎏/㎟, twice of the tensile strength of its parent iron.

keyword :

This investigation is to develop the nickel-free high manganese austenitic heat resisting steel. The effect of alloying elements on the forgeability, microstructure, creep rupture life, oxidation resistance, PbO corrosion resistance and sulfidation resistance was investigated. It was found that the 12M41 alloy whose composition was 12% Mn, 17% Cr, 4.5% W, 0.9% Mo, 0.3% Nb, 0.3% C, 0.6% N, 0.01 % B exhibited good hot workability, creep rupture life and corrosion resistance.

keyword :

Effects of sub-grain size, dislocation density and inclusions on fracture toughness of structural steel weld metals were investigated by the Electron Microscopy. Impact properties of weld metals welded by MMA with three different welding consumables were evaluated by the Charpy and COD test. Results can be summarized as follows: 1) Impact toughness in the weld metal was extraordinarily varied by welding consumables. 2) For the purpose of getting superior impact properties, the balance between dislocation density and subgrain size should be accomplished, and formation of upper bainite should also be controlled. (Received June 22, 1981)

keyword :

The majority of early ironmaking sites in Korea were situated in the valleys of large rivers near rich iron ore deposits. This study examines, for the first time, the metallurgical characteristics of early iron age artifacts excavated from one of the two major river basins in the Republic of Korea. Chemical analysis and metallographic examination have been carried out on both these artifacts and their related ironmaking residues. From these studies, the technological development of this area at that time has been assessed. It has been shown that, 1) Ironmaking originated in this area in the second or third century B.C. 2) White cast irons were produced from molten metal by high temperature reduction. 3) Steels were produced from sponge iron(Low temperature reduction) by puddling (i.e. repeat forging operations) to eliminate slag. 4) Internal carburization of the low carbon steel produced from sponge iron may have been obtained by multiple piling and forging operations.

keyword :

keyword :