• Journal of the Korean Society for Heat Treatment
• /
• v.29 no.6
• /
• pp.277-283
• /
• 2016

The influences of cooling pressure of quenching process on the mechanical properties such as hardness, impact endurance and anti-thermal fatigue behaviour of STD61 steel were investigated. The specimens were heat-treated using a vacuum furnace in which they were austenitized at $1,030^{\circ}C$ for 1hour under the pressure of $10^{-3}$ torr and cooled with quenching gas of various pressure, i.e. 1, 2 and 6 bar. According to the observation on the specimens prepared with quenching from austenizing temperature, the mechanical properties of the samples with higher quenching pressure were better than those of prepared at lower quenching pressure. The samples prepared with high quenching pressure showed the more homogeneous microstructure with finer carbides. The size of carbides such as VC and (Fe, Cr)C in quenched specimens decreased with increasing gas quenching pressure. It is considered that the rapid cooling with pressure may restrict the formation and growth of carbide.

• Proceedings of the KWS Conference
• /
• 2010.05a
• /
• pp.72-72
• /
• 2010

최근 오일샌드, 극지유전, 심해저자원 등 극한지 자원개발이 활발해짐에 따라 수요가 증대되고 있는 극한지용 내마식 소재는 내마식성과 함께 저온 인성이 요구된다. 철계 합금에서 관찰되는 변형유기 마르텐사이트 상변태는 입자의 충돌에 의한 충격을 흡수하고 소재의 표면을 가공경화시켜 내마식성 향상 및 저온 인성에 기여할 수 있을 것으로 기대되고 있지만 합금조성의 정교한 제어가 필요하기 때문에 오버레이 용접에 적용하기 위해서는 모재와의 희석률을 제어하는 방안이 필요하다. 용접플럭스 설계기술은 용접시 금속이행모드, 용융지 유동거동 등과 같은 용접현상 제어를 통해 오버레이 용접재료의 용접성과 용접부 희석률을 최적화할 수 있는 기술이다. 본 연구에서는 내마식 고인성 오버레이 용접재료의 개발을 위해 Fe-12Cr-1.2C 합금조성을 갖는 메탈코어드 와이어에 대하여 아크안정제로 사용되는 Ca 함유 용접플럭스 첨가가 용착부 형상 및 희석률 변화에 미치는 영향을 조사하였다.

• Journal of Korean Society on Water Environment
• /
• v.22 no.4
• /
• pp.666-671
• /
• 2006

Effects of a rainfall event (July 28, 2005) on the hydrochemical characteristics of the Jungrang river, the biggest tributary of the Han river, was investigated. Significant spatial variations in the hydrochemical characteristics were observed. At JR2 location, concentrations of T-N and T-P were relatively low indicating occurrence of active oxidation in the stepped drop structure. At JR3 location, concentrations of Na, K, Cl, $NH_4-N$ and EC were elevated suggesting increased discharge from the nearby waste-water treatment plant and tributaries. The rain event diluted major dissolved ion concentrations in the river by 12~52%. The $NO_3-N$ levels were preserved during the rain then increased about twofold after rainfall, suggesting increased discharge of nitrate-contaminated groundwater. Heavy metals including Cd, Co, Cr, Cu and Pb were not detected in all water samples and the leachates from surface sediment samples. Concentrations of Fe, Mn, Al and Zn were below the Korean Drinking Water Guideline. Results of this study suggested that establishment of water-quality monitoring protocols describing temporal and spatial variations in parameters sensitive to rainfall events, relatively steady factors, and contaminant sources is required.

• Journal of Korean Society of Water and Wastewater
• /
• v.13 no.2
• /
• pp.47-54
• /
• 1999

SRB(Sulfate Reducing Bacteria) converts sulfate into sulfide using an organic carbon source as the electron donor. The sulfide formed precipitates the various metals present in the AMD (Acid Mine Drainage). This study is the fundamental research on heavy metal removal from AMD using SRB. Two completely mixed anaerobic reactors were operated for cultivation of SRB at the temperature of $30^{\circ}C$ and anaerobic batch reactors were used to evaluate the effects of carbon source, COD/sulfate($SO_4^=$) ratio and alkalinity on sulfate reduction rate and heavy metal removal efficiency. AMD used in this study was characterized by low pH 3.0 and 1000mg/l of sulfate and dissolved high concentration of heavy metals such as iron, cadmium, copper, zinc and lead. It was found that glucose was an organic carbon source better than acetate as the electron donor of SRB for sulfate reduction in AMD. Amount of sulfate reduction maximized at the COD(glucose)/sulfate ratio of 0.5 in the influent and then removal efficiencies of heavy metals were 97.5% of Cu, 100% of Pb, 100% of Cr, 49% of Mn, 98% of Zn, 100% Cd and 92.4% of Fe. Although sulfate reduction results in an increase in the alkalinity of the reactor, alkalinity of 1000mg/1 (as $CaCo_3$) should be should be added continuously to the anaerobic reactor in order to remove heavy metals from AMD.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.1
• /
• pp.42.3-42.3
• /
• 2017

We present the analysis of chemical abundances and kinematics for six hypervelocity star (HVS) candidates. These objects are G/K-type low-mass stars in the Galactic disk, while other HVSs previously found are B-type high-mass objects in the Galactic halo. The stellar orbits and kinematics of our HVS candidates suggest that they do not originate in the Galactic center or in an accretion event, indicative of yet-unknown mechanisms that produce kinematically-extreme disk stars. In order to study in detail their origin, we obtained medium-resolution (R~6000) spectra of these stars and derived abundances of several chemical elements (Mg, Ca, Si, Ti, Cr, Fe, and Ni). From the comparison of the chemical abundances with the Galactic stellar components (disk, bulge, halo, and dwarf galaxies) and the kinematic properties of our HVSs, we conclude that two of them are likely ejected from the Galactic disk, one originated from the Galactic center as for the young B-type HVSs, and the other one might be ejected from either the Galactic disk or other regions.

• Journal of Ocean Engineering and Technology
• /
• v.22 no.6
• /
• pp.46-51
• /
• 2008

The effect of the addition of Co and N and subzero treatment on tensile strength and damping capacity was investigated in Fe-Cr-Mn alloy. Austenite was transformed into martensite by cold rollins increasing the degree of cold rollins led to an increase in the volume fraction of martensite. The damping capacity linearly increased with increasing volume fraction of ${\varepsilon}$ martensite in cold rolled specimens and subzero treated specimens after cold rolling. The volume fraction of ${\varepsilon}$ martensite, tensile strength and damping capacity was also increased by the addition of Co, while this treatment decreased the elongation. However, the volume fraction of ${\varepsilon}$ martensite, elongation and damping capacity were reduced by the addition of N, although the tensile strength increased. Tensile strength and damping capacity werealso increased by subzero treatment, while elongation decreased.

• Proceedings of the Korean Environmental Sciences Society Conference
• /
• 2005.11a
• /
• pp.29-32
• /
• 2005

주거지역 A와 주거지역 B의 PM10 평균농도 비교에서 산업지역과 인접한 주거지역 A에서 계절에 관계없이 26-32% 높은 농도를 나타내어 산업지역에 인접한 주거지역 A가 먼 주거지역 B 보다 PM10의 영향에 더 크게 노출된 것을 확인 할 수 있었다. PM10에 포함된 Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn 등의 무기성분은 대부분 인위적인 발생원과 관련성이 있는 대기 오염물질로, 인위적인 배출원의 영향정도를 파악하기 위하여 풍성계수 분석결과 높은 풍성계수를 나타내어 인위적인 오염원임을 확인 할 수 있었고, 그 평균농도는 주거지역 A가 주거지역 B 보다 높게 나타나 주거지역 A가 주거지역 B 보다 산업 오염원의 노출에 더 많은 영향을 받는 다는 것을 확인 할 수 있었다. 또한 이들 무기화합물질의 상관성 분석결과 높은 상관성과 통계적인 유의성 (p<0.01)이 있었으며, 공통의 오염원을 추정 할 수 있었다. PM10의 가능한 오염원 기여도 평가에 있어서, 주거지역 A에서는 제철관련 오염원과 토양오염원의 공통 오염원 기여도가 33.4%로 나타나 산업관련 오염원의 기여도를 뚜렷하게 분리하여 평가하기는 곤란하였으나, 주거지역 B에서 토양관련 오염원의 독립적인 농도 기여도가 54%로 높게 나타났기 때문에, 상대적으로 산업지역과 인접한 주거지역 A에서 산업관련 오염원 기여도가 높은 것을 알 수 있었다.

• Journal of the Korean Home Economics Association
• /
• v.43 no.7 s.209
• /
• pp.109-116
• /
• 2005

Using buffer solutions, consisting of pH 4, 5, 6, 7, and 8, silk fiber fabric specimens, pre-mordanted with one of the mordanting agents, Sn, Al, Cu, Cr, and Fe, were dyed using cochineal dyestuff. The color of the dyed silk fabric specimens was predominantly red(R) for the acidic range of pH 4 and 5, and predominantly purple(RP) for the neutral range of pH 6,7, with 8, with the pH boundary differentiating between the shades being between pH 5 and 6. As a general trend, the chroma value decreased as the pH changed from acid to alkali, and the highest chroma value us attained between pH 4 and 5. Regardless of the mordanting conditions, the trend was that $ {\Delta}E$ showed the highest measured value in the acidic range of pH 4 and 5, and it dropped abruptly after the pH 6.

• Journal of Advanced Marine Engineering and Technology
• /
• v.23 no.3
• /
• pp.360-368
• /
• 1999

The paper describes spectroscopic characteristics of plasma induced in the pulsed YAG laser welding of alloys containing a large amount of volatile elements. The authors have conducted the spectroscopic analyses of laser induced Al-Mg alloys plasma in the air and argon atmosphere. In the air environment the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn and singly ionized Mg lines as well as the intense molecular spectra of ALO and MgO formed by chemi-cal reactions of evaporated Al and Mg atoms from the pool surface with oxygen in the air. In argon atmosphere MgO and AlO spectra vanished but AlH spectrum was detected. the hydrogen source was presumable hydrogen dissolved in the base metals water absorbed on the surface oxide layer or $H_2$ and $H_2O$ in the shielding gas. The resonant lines of Al and Mg were strongly self-absorbed in particular self-absorption of the Mg line was predominant. These results show that the laser induced plasma was made of metallic vapor with relatively low temperature and high density.

• Fisheries and Aquatic Sciences
• /
• v.13 no.2
• /
• pp.112-117
• /
• 2010

Altered mRNA expression of two metallothionein isoforms (MT-IA and MT-IB) in response to acute heavy metal exposure was examined in mud loach, Misgurnus mizolepis, fry using a real-time RTPCR assay. Sublethal exposure (1 or 5 ${\mu}M$) to Cd, Cr, Fe, Mn, Ni, and Zn resulted in highly variable transcriptional responses of the two MT isoforms to the heavy metal ions, including upregulation, a steady state, and downregulation. Overall, the most potent inducer of both MT isoforms was Cd (up to 6-fold). Another exposure experiment using a series of doses of Cu revealed that the stimulation patterns of the two MT isoforms differed: MT-IA transcription was soon saturated at higher concentrations (about 2-fold at 1-4 ${\mu}M$ of Cu), whereas the activation of MT-IB was more dependent on the treatment dose (increased up to 5-fold at 3 ${\mu}M$). The isoform-specific allotment of constitutive and inducible functions was not as clear in fry as in adult tissues. Coordinated interaction between the MT-IA and MT-IB isoforms was hypothesized based on the finding that MT-IA represented a primary action under 'less stressful' or 'sublethal' conditions, whereas the activation of MT-IB became important under 'more stressful' or 'lethal' circumstances in this species.