• 한국기계가공학회지
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• 제21권1호
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• pp.81-89
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• 2022

It is necessary to increase the surface hardness and improve the wear resistance and peeling resistance through the surface treatment and performance evaluation of the mold steel. As a result of vacuum heat treatment analysis, residual austenite measurement and surface treatment wear test, retained austenite should be removed by sub-zero treatment, and retained austenite was completely removed by treatment at -196℃. The TiMon film coated on the sub-zero treated STD11 specimen showed the lowest coefficient of friction.

• 한국재료학회지
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• 제31권1호
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• pp.29-37
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• 2021

Martensitic stainless steel is commonly used in the medical implant instrument. The alloy has drawbacks in terms of strength and wear properties when applied to instruments with sharp parts. 440C STS alloy, with improved durability, is an alternative to replace 420 J2 STS. In the present study, the carbide precipitation, and mechanical and corrosion properties of STS 440C alloy are studied as a function of different heat treatments. The STS 440C alloy is first austenitized at different temperatures; this is immediately followed by oil quenching and sub-zero treatment. After sub-zero treatment, the alloy is tempered at low temperatures. The microstructures of the heat treated STS 440C alloy consist of martensite and retained austenite and carbides. Using EDX and SADP with a TEM, the precipitated carbides are identified as a Cr23C6 carbide with a size of 1 to 2 ㎛. The hardness of STS 440C alloy is improved by austenitization at 1,100 ℃ with sub-zero treatment and tempering at 200 ℃. The values of Ecorr and Icorr for STS 440C increase with austenitization temperature. Results can be explained by the dissolution of Cr-carbide and the increase in the retained austenite. Sub-zero treatment followed by tempering shows a little difference in the properties of potentiodynamic polarizations.

• 한국산학기술학회논문지
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• 제5권3호
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• pp.204-209
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• 2004

금형부품으로 사용되는 STD11과 STS3의 열처리에 따른 물리적 특성을 비교하여 금형부품으로 사용시 약점으로 지적되어온 물성을 개선시키고자 하였다. STS3와 STD11의 잔류 austenite의 측정과 촉진시효변형시험, Charpy 충격시험결을 실시한 결과 목표경도를 얻기 위한 심냉처리의 효과, 작업안정성과 칫수안정성면에서 STD11이 STS3보다 우수한 것으로 나타났다. STS3에서는 심냉처리에 의한 잔류 austenite의 감소량은 크게 나타나지 않았으며 또한, 변형을 최소화시켜야 하는 금형에서는 심냉처리가 필수적이라는 것을 확인하였다.

• 한국해양공학회지
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• 제28권4호
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• pp.306-313
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• 2014

Super duplex stainless steels (sDSS) are excellent for use under severely corrosive conditions such as offshore and marine applications like pipelines and flanges. sDSS has better mechanical properties and corrosion resistance than the standard duplex stainless steel (DSS) but it is easier for a sigma phase to appear, which depresses the mechanical property and corrosion resistance, compared to DSS, because sDSS has a higher alloy element than DSS. In addition, sDSS has a feeble ductile-brittle transition temperature (DBTT) because it has a 50% ferrite microstructure. In the actual operating environment, sDSS would be thermally affected by welding and a sub-zero temperature environment. This study analyzed how precipitated sDSS behaves at a sub-zero temperature through annealing heat treatment and a sub-zero tensile test. Six types of specimens with annealing times of up to 60 min were tested in a sub-zero chamber. According to the experimental results, an increase in the annealing time reduced the elongation of sDSS, and a decrease in the tensile test temperature raises the flow stress and tensile stress. In particular, the elongation of specimens annealed for 15 min and 30 min was clearly lowered with a decrease in the tensile test temperature because of the increasing sigma phase fraction ratio.

• 대한토목학회논문집
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• 제14권3호
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• pp.645-654
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• 1994

광촉매 산화반응의 기본 운영조건-재순환을 속도 275 mL/min, 산소 공급량 2LPM, $UV+TiO_2+H_2O_2$(500 mg/l)을 새로운 광촉매 산화반응에 의한 유기물질 분해 수처리 공정으로 적용하였다. 탁도와 부유물질의 농도가 증가함에 따라 탁도 10 NTU-부유물질 농도 29 mg/l까지는 페놀분해가 감소하지 않고 약간 증가하는 추세를 보였고, 탁도 50 NTU-부유물질 농도 170 mg/l까지는 어느정도 페놀분해가 감소하고 있으나 탁도와 부유물질이 없는 경우와 비슷한 정도로 페놀 분해가 이루어졌다. 페놀 분해율은 유입페놀 농도가 증가할수록 감소하였다. 본 연구에서 이용한 $UV+TiO_2+H_2O_2$ 광촉매 산화반응은 정수처리공정의 고도산화법, 생물학적 폐-하수 처리의 후처리 공정으로 이용 가능할 것으로 판단된다.

• 문화기술의 융합
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• 제5권4호
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• pp.395-399
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• 2019

본 연구는 감나무 '갑주백목'의 발아 초기에 영하의 온도 처리에 따른 신초 생육 및 착과 특성을 알아보기 위해 수행되었다. 1년생 가지 당 발생된 신초 수, 착과된 신초 수, 그리고 정단부의 신초의 생장 및 착과는 영하온도 처리에 따라 뚜렷이 감소하였다. 그리고 1년생 가지 정단부에서 발생한 신초의 착과 수는 영하온도 처리에 의해 47.2% 감소하였다. 1년생 가지의 착과 신초 수는 그 가지의 눈 고사율 50% 이상 가지에서 유의하게 감소하였다. 특히, 정단부 3개의 눈에서 발생한 착과 수는 영하온도 처리와 이에 따른 눈 고사율 차이의 영향을 뚜렷하게 받았다. 영하온도처리를 받은 1년생 가지의 눈 고사율(X)과 정단부 3개의 눈에서 발생된 과실수(Y) 간 Y=-0.145X+12.950($r^2=0.4672^*$)의 유의한 관계를 나타내었다. 따라서 감나무 발아초기에 영하 온도($-2^{\circ}C$, 3시간)의 영향을 받으면 신초 생장량이 감소되고, 눈 고사율 10% 증가함에 따라 1년생 가지(정단부 3개의 눈) 당 착과 수는 1.4개 감소되는 것으로 생각된다.

• Environmental Engineering Research
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• 제24권4호
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• pp.572-581
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• 2019

The emission of hydrogen sulfide (H₂S) from the Kahrizak landfill was studied. Firstly, the field measurements were conducted in the summer and winter seasons; and the samples were analyzed using Jacob method. We predicted the H₂S concentrations in the downwind using AERMOD and ISCST3. According to the AERMOD, the maximum concentration of H₂S in the summer and winter were 117 ㎍/㎥ and 205 ㎍/㎥ respectively. The downwind concentrations reached zero at the distance of 35 km from the leachate treatment plant. The Geometric mean bias, Geometric variance, Fractional bias, Fraction of predictions within a factor of two of the observations and Normalized mean square error for the AERMOD were 0.58, 1.35, -0.12, 1.91 and 0.042, respectively in the summer and 1.39, 1.35, -0.05, 1.46 and 0.027 in the winter; and for the ISCST3, were 0.85, 1.03, 0.02, 1.45 and 0.04 in the summer and 1.18, 1.03, 0.15, 1.16 and 0.04 in the winter. The results of the AERMOD were compared with the ISCST3 and indicated that the AERMOD performance was more suitable than the ISCST3.

• 열처리공학회지
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• 제37권3호
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• pp.128-137
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• 2024

In this study, the carburizing heat treatment process used in aircraft gear manufacturing was compared with the general carburizing heat treatment process using AISI 9310 steel. The process of carburizing followed by slow cooling, and then quenching after austenitizing(Process A) showed less compressive residual stress and less retained austenite in the surface layer compared to the process of quenching directly after carburizing(Process B). In prpcess B, there was a large amount of retained austenite when quenched immediately after carburization, and when treated with subzero, martensite rapidly increased and the compressive residual stress increased significantly, but at the same time, there is a risk of cracking due to severe expansion in volume. Therefore, in the case of aviation parts, it is believed that a step-by-step heat treatment cycle was adopted to ensure stability against heat treatment cracks. As a result of the final tempering after sub-zero treatment, the A process specimen showed a deeper effective case depth and HV700 depth and a higher hardness value above HV700 than the B process specimen.

• 자원리싸이클링
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• 제31권5호
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• pp.3-19
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• 2022

전기막(Electro-membrane) 기술은 전기투석(ED) 및 바이폴라 전기투석(BMED)과 같이 선택적 투과성을 갖는 이온교환막을 사용하여 전기에너지에 의하여 수용액 내의 물질을 분리·정제하는 공정이다. 전기막(Electro-membrane) 기술은 공정 중에 부산물이 발생하지 않고 회수된 염기나 산을 공정 중에 재사용할 수 있어 환경 친화적인 기술로 주목받고 있다. 본고에서는 전기분리막 기술인 ED와 BMED 기술의 원리 및 셀(Cell) 구성에 따른 여러 가지 특성 및 문제점 등에 대해 조사하고, 특히 금속회수 공정 중 다량 발생되고 있는 황산나트륨(Na2SO4) 폐액 처리와 관련된 연구사례들을 조사·분석하였다.

• 천문학회지
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• 제55권2호
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• pp.37-57
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• 2022

Using I-band images of 35 nearby (z < 0.1) type 1 active galactic nuclei (AGNs) obtained with Hubble Space Telescope, selected from the 70-month Swift-BAT X-ray source catalog, we investigate the photometric properties of the host galaxies. With a careful treatment of the point-spread function (PSF) model and imaging decomposition, we robustly measure the I-band brightness and the effective radius of bulges in our sample. Along with black hole (BH) mass estimates from single-epoch spectroscopic data, we present the relation between BH mass and I-band bulge luminosity (M_BH-M_I,bul relation) of our sample AGNs. We find that our sample lies offset from the M_BH-M_I,bul relation of inactive galaxies by 0.4 dex, i.e., at a given bulge luminosity, the BH mass of our sample is systematically smaller than that of inactive galaxies. We also demonstrate that the zero point offset in the M_BH-M_I,bul relation with respect to inactive galaxies is correlated with the Eddington ratio. Based on the Kormendy relation, we find that the mean surface brightness of ellipticals and classical bulges in our sample is comparable to that of normal galaxies, revealing that bulge brightness is not enhanced in our sample. As a result, we conclude that the deviation in the M_BH-M_I,bul relation from inactive galaxies is possibly because the scaling factor in the virial BH mass estimator depends on the Eddington ratio.