• Title/Summary/Keyword: High nitrogen steel

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A Study on the Effect of Ti Ion Bombardment on the Interface in a Duplex Coating (Duplex coating에서 계면구조에 미치는 Ti 이온충격의 효과에 대한 연구)

  • Baek, Un-Seung;Gwon, Sik-Cheol;Lee, Jae-Yeong;Na, Jong-Ju;Lee, Sang-Ro;Lee, Gu-Hyeon;Lee, Geon-Hwan
    • 연구논문집
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    • s.28
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    • pp.219-227
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    • 1998
  • In order to investigate the interfacial structure between TiN and iron nitride, an AISI 4140 steel was nitrided to form a layer of thickness 15$\mum$ by DC ion nitriding, then the surface was bombarded with Ti ions and subsequently coated a TiN film of 5$\mum$ by arc ion plating method. The interfacial microstructure between TiN and iron nitride was characterized by optical microscope, SEM and XRD. So called black layer was observed in the duplex treatment. It was resulted from the decomposition of iron nitride during the bombardment. Its thickness was increased with increasing bombardment time at high bias voltage. But the thickness was greatly decreased when the iron nitride was bombarded with a nitrogen gas or at a reduced bias voltage. The adhesion strength of the top TiN coating was decreased with increasing thickness of the black layer. Furthermore, the reduced adhesion strength in this system was discussed in view of the interfacial structural relationship between TiN and iron nitride.

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Test of Insulation of Double Pancake Windings for a 1MVA HTS Transformer (1MVA 고온초전도 변압기용 더블 팬케이크 권선의 절연시험)

  • Kim, Sung-Hoon;Kim, Woo-Seok;Choi, Kyeong-Dal;Joo, Hyeong-Gil;Hong, Gye-Won;Han, Jin-Ho;Hahn, Song-Yop;Song, Hee-Suck;Park, Jung-Ho
    • Proceedings of the KIEE Conference
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    • 2003.07b
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    • pp.1015-1017
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    • 2003
  • In a research and development team of high temperature superconducting (HTS) transformer for power distribution, prior to manufacture a single phase 1MVA 22.9 kV/6.6 kV HTS transformer, a 1MVA transformer for insulation test with windings made of copper tapes with the same size as BSCCO-2223 HTS tape was manufactured. The test transformer was composed of both the copper windings of double pancake type and the shell type core of laminated silicon steel plates. The characteristics tests of the test transformer were performed, such as no load test, load test and short test at 77k using liquid nitrogen. Insulation tests, lightning impulse test, power-frequency voltage test and external insulation test, were accomplished also.

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Low Temperature Plasma Nitriding Process of AISI 304L Austenitic Stainless Steels for Improving Surface Hardness and Corrosion Resistance (내식성 및 표면경도 향상을 위한 AISI 304L 스테인리스강의 저온 플라즈마질화 프로세스)

  • Lee, In-Sup
    • Korean Journal of Metals and Materials
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    • v.47 no.10
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    • pp.629-634
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    • 2009
  • The effects of processing parameters on the surface properties of the hardened layers processed by the low temperature plasma nitrocarburizing and the low temperature two-step plama treatment (carburizing+nitriding) were investigated. The nitrogen-enriched expanded austenite structure (${\gamma}_N$) or S phase was formed on all of the treated surface. The surface hardness reached up to 1200 $HV_{0.025}$, which is about 5 times higher than that of untreated sample (250 $HV_{0.1}$). The thickness of hardened layer of the low temperature plasma nitrocarburized layer treated at $400^{\circ}C$ for 40 hour was only $15{\mu}m$, while the layer thicknesss in the two-step plama treatment for the 30 hour treatment increased up to about $30{\mu}m$. The surface thickness and hardness increased with increasing treatment temperature and time. In addition, the corrosion resistance was enhanced than untreated samples due to a high concentration of N on the surface. However, higher treatment temperature and longer treatment time resulted in the formation of $Cr_2N$ precipitates, which causes the degradation of corrosion resistance.

Influence of Gas Composition and Treatment Time on the Surface Properties of AISI 316L Austenitic Stainless Steels During Low-Temperature Plasma Nitrocarburizing Treatment (AISI 316L강의 저온 플라즈마침질탄화처리 시 가스조성과 처리시간이 표면특성에 미치는 영향)

  • Lee, In-Sup
    • Korean Journal of Metals and Materials
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    • v.47 no.11
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    • pp.716-721
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    • 2009
  • The major drive for the application of low-temperature plasma treatment in nitrocarburizing of austenitic stainless steels lies in improved surface hardness without degraded corrosion resistance. The low-temperature plasma nitrocarburizing was performed in a gas mixture of $N_{2}$, $H_{2}$, and carbon-containing gas such as $CH_{4}$ at $450^{\circ}C$. The influence of the processing time (5~30 h) and $N_{2}$ gas composition (15~35%) on the surface properties of the nitrocarburized layer was investigated. The resultant nitrocarburized layer was a dual-layer structure, which was comprised of a N-enriched layer (${\gamma}_N$) with a high nitrogen content on top of a C-enriched layer (${\gamma}_C$) with a high carbon content, leading to a significant increase in surface hardness. The surface hardness reached up to about $1050HV_{0.01}$, which is about 4 times higher than that of the untreated sample ($250HV_{0.01}$). The thickness of the hardened layer increased with increasing treatment time and $N_{2}$ gas level in the atmosphere and reached up to about $25{\mu}m$. In addition, the corrosion resistance of the treated samples without containing $Cr_{2}N$ precipitates was enhanced than that of the untreated samples due to a high concentration of N on the surface. However, longer treatment time (25% $N_{2}$, 30 h) and higher $N_{2}$ gas composition (35% $N_{2}$, 20 h) resulted in the formation of $Cr_{2}N$ precipitates in the N-enriched layer, which caused the degradation of corrosion resistance.

Investigation on Resistance to Hydrogen Embrittlement of High Nitrogen Austenitic Steels for Hydrogen Pipe by the Disc Pressure Test and the Tensile Test on Hydrogen Pre-charged Specimens (디스크 시험 및 수소처리 인장시험에 의한 수소배관용 고질소 스테인리스강의 내수소취성 평가 연구)

  • Dong-won, Shin;Min-kyung, Lee;Jeong Hwan, Kim;Ho-seong, Seo;Jae-hun, Lee
    • Journal of the Korean Institute of Gas
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    • v.26 no.6
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    • pp.16-23
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    • 2022
  • In this study, characteristics of effect on hydrogen gas was investigated to hydrogen embrittlement by disk and tensile tests. The developed and commercial alloy was fabricated to a plate material made from an alloy ingot. The prepared materials were processed in the form of a disk to measure rupture pressure by hydrogen and helium gas at a rate of 0.1 to 1,000 bar/min. In the hydrogen pre-charged tensile test, a specimen was hydrogenated using an anode charging method, and the yield strength, ultimate tensile strength, elongation, and reduction in area rate were carried by a strain rate test. Also, the microstructure was observed to the fracture surface of the tensile test specimen. As a result, the developed materials satisfied endurable hydrogen embrittlement, and the fractured surface showed a brittleness fracture surface with a depth of several ㎛, but dimple due to ductile fracture could be observed.

Effects of Vessel on the Quality Changes during Fermentation of Kochujang (고추장의 숙성 중 발효 용기가 품질변화에 미치는 영향)

  • Chung Sun-Kyung;Kim Young-Sook;Lee Dong Sun
    • Food Science and Preservation
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    • v.12 no.3
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    • pp.292-298
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    • 2005
  • Kochujang(Korean red pepper paste) of 600 g was fermented in the different types of vessels (glass, polypropylene(PP), polyethylene terephthalate(PET), stainless steel and Korean porcelain called onggi) with 627 mL of volume during 4 months. The quality changes were monitored for physical, chemical and microbiological attributes. Onggi which had high porosity in the micro-structure provided kochujang with higher microbial counts of aerobic bacteria, lactic acid bacteria and yeasts than those of the other containers. Compared to kochujang fermented in the other containers, kochujang in Onggi showed higher protease activity, amino type nitrogen, and free amino acid content. The kochujang in Onggi also attained higher acidity, lower pH and higher reducing sugar concentration than those in the other containers. All changes were completed 2 or 3 months. Onggi showed water loss and salt increase of the kochujang comparable to those in the other vessels, which was from gradual clogging of the micropores during storage. All physical, chemical and microbiological changes made the kochujang in Onggi attain the sensory quality significantly better than those fermented in the other vessels.

Effect of Water Chemistry Factors on Flow Accelerated Corrosion : pH, DO, Hydrazine (유동가속부식에 영향을 미치는 수화학 인자 : pH, 용존산소, 하이드라진)

  • Lee, Eun Hee;Kim, Kyung Mo;Kim, Hong Pyo
    • Corrosion Science and Technology
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    • v.12 no.6
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    • pp.280-287
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    • 2013
  • Flow accelerated corrosion(FAC) of the carbon steel piping in pressurized water reactors(PWRs) has been major issue in nuclear industry. Severe accident at Surry Unit 2 in 1986 initiated the worldwide interest in this area. Major parameters influencing FAC are material composition, microstructure, water chemistry, and hydrodynamics. Qualitative behaviors of FAC have been well understood but quantitative data about FAC have not been published for proprietary reason. In order to minimize the FAC in PWRs, the optimal method is to control water chemistry factors. Chemistry factors influencing FAC such as pH, corrosion potential, and hydrazine contents were reviewed in this paper. FAC rate decreased with pH up to 10 because magnetite solubility decreased with pH. Corrosion potential is generally controlled dissolved oxygen (DO) and hydrazine in secondary water. DO increased corrosion potential. FAC rate decreased with DO by stabilizing magnetite at low DO concentration or by formation of hematite at high DO concentration. Even though hydrazine is generally used to remove DO, hydrazine itself thermally decomposed to ammonia, nitrogen, and hydrogen raising pH. Hydrazine could react with iron and increased FAC rate. Effect of hydrazine on FAC is rather complex and should be careful in FAC analysis. FAC could be managed by adequate combination of pH, corrosion potential, and hydrazine.

Plasma nitriding on chromium electrodeposit

  • Wang Liang;K.S. Nam;Kim, D.;Kim, M.;S.C. Kwon
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2001.11a
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    • pp.29-30
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    • 2001
  • This paper presents some results of plasma nitriding on hard chromium deposit. The substrates were C45 steel and $30~50{\;}\mu\textrm{m}$ of chromium deposit by electroplating was formed. Plasma nitriding was carried out in a plasma nitriding system with $95NH_3{\;}+{\;}SCH_4$ atmosphere at the pressure about 600 Pa and different temperature from $450^{\circ}C{\;}to{\;}720^{\circ}C$ for various time. Optical microscopy and X-ray diffraction were used to evaluate the characteristics of surface nitride layer formed by nitrogen diffusion from plasma atmosphere inward iCr coating and interface carbide layer formed by carbon diffusion from substrate outward Cr coating. The microhardness was measured using microhareness tester at the load of 100 gf. Corrosion resistance was evaluated using the potentiodynamic measurement in 3.5% NaG solution. A saturated calomel electrode (SiCE) was used as the reference electrode. Fig.1 shows the typical microstructures of top surface and cross-section for nitrided and unnitrided samples. Aaer plasma nitriding a sandwich structure was formed consisting of surface nitride layer, center chromium layer and interface carbide layer. The thickness of nitride and carbide layers was increased with the increase of processing temperature and time. Hardness reached about 1000Hv after nitriding while 900Hv for unnitrided hard chromium deposit. X-ray diffraction indicated that surface nitrided layer was a mixture of $Cr_2N$ and CrN at low temperature and erN at high temperature (Fig.2). Anodic polarization curves showed that plasma nitriding can greatly improve the corrosion resistance of chromium e1ectrodeposit. After plasma nitriding, the corrosion potential moved to noble direction and passive current density was lower by 1 to 4 orders of magnitude compared with chromium deposit(Fig.3).

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A Pilot Study for Microfiltration of Alcohol Stillage Condensate and Permeate Recycle to Fermentation Broth (알코홀 증류폐액의 Pilot Scale 정밀여과와 여과액의 발효 재활용에 대한 연구)

  • 김영범;이기세;남궁견;김종현
    • KSBB Journal
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    • v.16 no.4
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    • pp.403-408
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    • 2001
  • Distillation condensate generated from downstream processing of microbial alcohol fermentation imposes a serious burden to biological wastewater treatment or anaerobic digestion due to its high contents of SS (suspended solids) and TN (total nitrogen), A pilot scale microfiltration of the stillage condensate with a stainless steel SCEPTER membrane of 0.1 ${\mu}$m pore size was carried out to remove SS which was mostly composed of microbial cell residue. A stable permeate flux was achieved when the decanter effluent containing 0.7% of SS was filtered under the conditions of X10 VCR (volume concentration ratio), 2.5 bar of TMP (transmembrane pressure), and 60$^{\circ}C$. When stillage condensate with 2.6% SS was treated directly with microfiltration, VCR below X3 was recommended for a long duration of filtration. The permeate and retentate obtained from microfiltration were recycled to make-up medium of fermentation. Adding permeate or retentate up to 30% of fermentation volume showed no distinguished undesirable influence during the course of alcohol fermentation. Although only slight improvements in the final amount of CO$_2$ evolution and alcohol content were observed, fermentation rate increased so that the required time to reach 450 L/ton of CO$_2$ evolution was shortened to 72% of that with normal media.

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Assembly and Test of the In-cryostat Helium Line for KSTAR (KSTAR 저온용기 내부의 헬륨라인 설치 및 검사)

  • Bang, E.N.;Park, H.T.;Lee, Y.J.;Park, Y.M.;Choi, C.H.;Bak, J.S.
    • Journal of the Korean Vacuum Society
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    • v.16 no.2
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    • pp.153-159
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    • 2007
  • In-cryostat helium lines are under installation to transfer a cryogenic helium into cold components in KSTAR device. In KSTAR, three kinds of helium should be supplied into the cold components, which are supercritical helium Into superconduction(SC) magnet system, liquid helium into current lead system, and gas helium into thermal shields. Cryogenic helium lines consist of transfer lines outside the cryostat, in-cryostat helium lines, and electrical breaks. In-cryostat helium lines should be guaranteed of leak tightness for tong time operation at high internal helium pressure of 20 bar. We wrapped the helium line with multi-layer insulator(MLI) to reduce radiation heat and insulated the surface of the high potential part with prepreg tape. The electrical break was fabricated by brazing ceramic tube with stainless steel tube. To ensure the operation reliability at operation temperature, all the electrical break have been examined by the thermal cycle test at liquid nitrogen and by the hydraulic test at 30 bar. And additional surface insulation was prepared with prepreg tape to give structural safety. At present most of the in-cryostat helium lines have been installed and the final inspection test is progressing.