발간논문

Home > KJMM 논문 > 발간논문

The effects of stress on the first stage graphitization have heen studied by using nodular cast irons solidified under three levels of stress of approximately 1.38×10^6, 2.45×10^6, and 4.83×10^6 dyne/㎠ The results obtained ara as follows. (1) The first stage graphitization of the cast iron is accelerated with stress level, and the higher the annealing temperature, the greater the effect of stress on the graphitization. (2) The activation energies for graphite nucleation and graphite growth decrease from 33,000 to 22,000 ㎈/㏖ and from 29,000 to 20,000 ㎈/㏖ respectively as the stress level is increased up to 4.83×10^6 dyne/㎠. (3) As-cast hardness of the cast iron increases with increasing stress level. (4) Free cementite particles distributed in the as-cast structure and the pearlite lamella spacing in the matrix become smaller at the higher stress level.

keyword :

The effects of copper, magnesium, phosphorus and sulfur on the refinement of primary silicon crystals in high silicon-aluminum alloys were examined by metallography. The effects of the refinement and the subsequent heat-treatment of the alloys on the hardness, the tensile strength, the machinability were also studied. The results obtained are as follows: 1. The addition of phosphorous or sulfur after the addition of copper or magnesium was more effective to the refinement of the primary silicon crystals than that of copper or magnesium only. 2. The tensile-strength and the machinability were improved by the refinement of primary silicon crystals and the subsequent heat-treatment but the hardness was not affected.

keyword :

Most study on fading phenomena in making spheroidal graphite cast iron was on fading only after inoculation. Definite conclusion of variable fading phenomena depending upon additive or inoculant or various components and their relationship one another has not been reached. It is important to investigate the factors of fading phenomena mentioned above, so in this study we tried to investigate some of these factors. When the specimen which was inoculated ten minutes after the addition was compared with the specimen held for ten minutes after the addition only and with the specimen held for tea minutes after the addition immediately followed by inoculation, the specimen inoculates ten minutes after the addition was best in microstructure, tensile strength and hardness.

keyword :

Two types of aluminum-steel fiber composite were prepared by a casting method; one was fabricated with aluminum-coated steel fiber, and the other the aluminum-uncoated steel fiber. Then the mechanical properties and plastic behaviors of these composites were investigated by Instron machine. The ultimate tensile strength of aluminum-uncoated steel fiber composite increases linearly with increasing fiber content. However, the values of the composite tensile strength do not agree with the theoretical values indicated by the rule of mixture. The aluminum-uncoated steel fiber composite shows a better combination of tensile strength and elongation than the aluminum-coated steel fiber composite, though the bond between fiber and matrix of the former composite is poorer than that of the latter. This is considered to be attributed to the intermetallic compound formed on the surface of the aluminum-coated steel fiber, which is brittle and acts as a crack nucleation source during plastic deformation.

keyword :

This study aimed at obtaining some basic knowledge on the chlorination characteristics of synthetic scheelite. Favorable conditions were found to be the chlorine flow rate 580cc/min, mole ratio of scheelite to charcoal 1/6, particle size of scheelite and charcoal 200/325 mesh respectively, briquette size 5/7 mesh, and chlorination temperatures higher than 700℃. The chlorination could be described as the first order reaction, and the activation energies under such conditions were estimated to be 14.3 ㎉/mole and 3.8 ㎉/mole respectively in the temperature range of 500-600℃ and 600℃-900℃. This large difference in activation energy may be attributed to the change in reaction pass with varying reaction temperature. Two kinds of tungsten oxychloride such as WO₂Cl₂ and WOCl₄ were obtained as the products and each could be particularly formed with suitable selection of the temperature and the scheelite to charcoal mixing ratio.

keyword :

The rate of absorption of hydrogen in stagnant pure liquid silver have been measured using a steady state gas-liquid metal diffusion cell technique.^(1)) The appropriate solution of Fick`s first law have teen used to examine the data and calculate hydrogen diffusion coefficient (D_H). The rate have been found to be controlled by the diffusion of hydrogen in liquid metal. The diffusion coefficient of hydrogen (D_H) in pure liquid silver in the range of 1010℃ to 1130℃ can be described by the following Arrhenius equation; D_H=5.75×10^(-2) exp (-1511±197)/RT ㎠/sec where the uncertainty in activation energy corresponds to the 90 pct. confidence level.

keyword :

keyword :

keyword :

keyword :

N/A

keyword :