• Journal of Korea Foundry Society
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• v.34 no.1
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• pp.1-5
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• 2014

The austempering transformation behavior in Fe-0.7wt.%C-2.3wt.%Si-0.3wt.%Mn steel is investigated. Each specimen was austenitized for 60 min at $900^{\circ}C$, and austempered at $380^{\circ}C$ for different time periods varying from 2 min to 256 min. After the austempering heat treatment, the Stage I and II evolutions are performed using optical metallography, X-ray diffraction and image analyses. Variations in the X-ray diffraction patterns and lattice parameters of the ferrite and austenite demonstrate that the residual austenite decomposes into ferrite and carbide during the Stage II evolution; moreover the amount of ferrite increases during the Stage I evolution. While the amount of austenite increases during Stage I, it dicreases during Stage II. Overall, the variations in the volume fractions of the microstructure and carbide formation in stages I and II meet high temperature austempering reaction of the ausferrite microstructure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.2 s.72
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• pp.115-124
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• 2006

The 1st and 2nd tension forces of the PSSC(Prestressed Steel and Concrete) grider constructed with commercial rolling beams and concrete are optimally designed. The design variables are the 1st and 2nd tension forces due to multi-step prestressing and live load. The objective function is set to the maximum live load. Design conditions are allowable stresses at the top and bottom of slab, beam and infilled concrete due at the several construction stages. A Matlab based optimization program is developed. The results show that the tendon position as well as concrete compression strength have significant influence on the beam strength.

• Journal of Welding and Joining
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• v.6 no.1
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• pp.35-45
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• 1988

오-스테나이트계 스테인레스강에 대한 용접은 용접재료의 개발과 더불어 각종 산업계에 널리 이용되고 있으며 최근 Type 303 오-스테나이트계 스테인레스강 등은 free machining재로써 널리 응용되고 있다. 그러나 이 303계는 피삭성, 절삭성, 칩형성개선을 위한 특수원소(Se, S 등)의 첨가 때문에 용접성에 문제점을 제기하고 있다. 본 연구에서는 Type 303을 중심으로 AISI 304-316NG 및 347NG계의 오-스테나이트계 스테인레스강의 고온연성거동과 고온균열감수성(용접성)에 관한 연구에 대한 검토중 고온연성거동에 관하여 조사하였다. 고온연성평가는 Gleeble Simulator에 의하여 재료와 방향성에 따라 검토하였으며, 그 결과 모든 재료는 압연방향을 종방으로 시험하였을 때는 거의 유사한 고온연성을 나타내었으나 횡방향으로 시험하였을 때는 종방향에 비하여 연성저하를 나타내었다. 이와 같은 고온연성은 후속연구에서 검토될 고온균열 감수성과 밀접한 관련성에 의하여 용접성을 평가할 수 있다.

• Transactions of The Korea Fluid Power Systems Society
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• v.7 no.1
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• pp.1-5
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• 2010

This paper presents the experimental results of the radial piston type oil pump with new mechanism for a metal diaphragm hydrogen compressor. Generally, metal diaphragm type hydrogen compressor systems are operated by oil hydraulic power. In this system an oil compensating pump has been demanded to compensate for a leakage oil head chamber. The metal diaphragm type hydrogen compressor consists of an oil compensating pump, commonly used hydraulic piston pump and driven by main crank shaft. The radial piston type oil compensating pump with new rolling contacted piston mechanism is developed and experimented. The developed piston element of the radial piston pump consists of piston, steel ball, return spring, two check valves, eccentric cam and ball racer. In this study, designed 4 type pistons as and orifice hole. Operating characteristics and pressure ripple characteristics are tested under no load to 60bar loaded with every 20bar increasing step and pressure ripple and flow rate are experimentally investigated.

• Nuclear Engineering and Technology
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• v.45 no.6
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• pp.821-826
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• 2013

In the present study, the effects of various heat treatments on the microstructure and mechanical properties of dual phase ODS steels were investigated to enhance the high strength at elevated temperature. Dual phase ODS steels have been designed by the control of ferrite and austenite formers, i.e., Cr, W and Ni, C in Fe-based alloys. The ODS steels were fabricated by mechanical alloying and a hot isostatic pressing process. Heat treatments, including hot rolling-tempering and normalizing-tempering with air- and furnace-cooling, were carefully carried out. It was revealed that the grain size and oxide distributions of the ODS steels can be changed by heat treatment, which significantly affected the strengths at elevated temperature. Therefore, the high temperature strength of dual phase ODS steel can be enhanced by a proper heat treatment process with a good combination of ferrite grains, nano-oxide particles, and grain boundary sliding.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.4
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• pp.208-218
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• 2006

The effects of the grain size on the magnetic properties in extra-low carbon steel after strain annealing were investigated. Two kinds of sample were prepared. One is the annealed sheet, which was annealed at $670^{\circ}C$ and $850^{\circ}C$ for various time periods after cold rolling. The other is the strain annealed sheet, which was temper rolled by 0.4% and subsequently strain annealed at the temperature ranging between $670^{\circ}C$ and $850^{\circ}C$ for various time periods. The grains after strain annealing became more coarse than those after primary annealing. The grains were coarsened due to the strain induced grain boundary migration (SIGM). It was found that the permeability tended to be increased and coercivity tended to be decreased with the increase of grain size. The optimum magnetic properties was achieved after strain annealing at $850^{\circ}C$ for 30 minites. Under this condition, the coercivity was measured to be 0.6 and the permeability was measured up to be 13000.

• Tribology and Lubricants
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• v.30 no.5
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• pp.291-294
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• 2014

Multiple additives can help improve the performance of generally used lubricants. These additives include MoS2, cadmium, chloride, indium, sulfide, and phosphide, which are harmful to both humans and the environment. Thus, researchers in this industry have been trying to reduce the use of these additives by finding alternatives. Nanodiamonds are one of these candidates. Nanodiamond particles are very hard, chemically stable, and highly heat-conductive. This research involved uniformly dispersing nanodiamond particles in marine engine oils via a matrix synthesis method at various concentrations (0, 0.1, 0.3, 0.5, and 1.0 wt). Friction and wear tests involved constant loads on ball-on-disk specimens, where the ball was AISI 51200 steel, the disk was AISI 1020 steel, and the sliding speed was 0.217 m/s. The lowest wear occurred at a suitable concentration of nanodiamonds (0.3 wt). However, excessive amounts of nanodiamonds caused them to act as abrasive debris because of their hardness, which increased the wear amount. The friction coefficient decreased as the nanodiamond concentration increased because their octagonal, almost spherical shape caused them to act as rolling contact elements between two surfaces.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.5
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• pp.574-583
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• 2008

The results of HAPs emission data using TRI (Toxic Release Inventory), SODAM (Source Data Management system) were investigated and the emissions of 7 heavy metals from their sources and emission processes were also analyzed. Questionnaire for source data analysis as well as the stack sampling were carried out for 17 factories among 6 selected industrial types. The annual amount of emissions was estimated based on the measured concentration and flow rates. All sources were operated with high efficiency control devices and the concentration levels of all heavy metals were shown to be below 0.1 to of regulation standard. The highest emission source of heavy metals was steel manufacturing industry with the annual emission of 342.9 kg/yr and followed by hazardous waste incinerator, paint manufacturing, nonferrous metal manufacturing, rolling & press goods manufacturing and storage battery manufacturing. In the case of Hg, the emissions were quite significant from electric acros of steel manufacturing industry, although the concentration level was below the emission standard, showing the necessity of specific care for its management.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1650-1660
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• 2000

Continuous casting process has been adopted increasingly in recent years to save both energy and labor. It has experienced a rapid development in the production of semi-finished steel products, rep lacing the conventional route of ingot casting and rolling. In order to achieve this merit, however, more studies about the mechanism between roll and slab are needed. In this paper, a dynamic bulging in steel cast slabs was simulated by considering the solidification and heat transfer. This study is to prevent internal cracks of a slab in a bending and unbending zone. The value of moving strand shell bulging between two supporting rollers under the ferrostatic pressure and slab-self weight has been calculated in terms of creep and elasto-plasticity. The strain and strain rate distributions in solidified shell undergoing a series of bulging are calculated with working boundary conditions.

• Applied Microscopy
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• v.7 no.1
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• pp.45-49
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• 1977

For obtaining high manganese steel plates, the study has been made on the optimum conditions in melting, forging, rolling and water toughning treatment practices. The optimum water toughning temperature and time was found to be $1030^{\circ}C$ and 30 min. respectively for the plates of 1 mm thickness. The argon atmosphere is very effective for the prevention of decarburization which can be easily occured in open air. There is a close relation between the degree of c 이 d working and the hardess. The greater the cold reduction ratio is, the smaller the grain size is and it results in the increase of hardness. The improvement of tensile and bending properties can be made by the addition of small amount of nickel, chromium and vanadium.