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현양기,이재도,Hyeon, Yang-Gi,Lee, Jae-Do 한국기계연구원 2001 硏究論文集 Vol.31 No.-
Evolution of microstructure due to service exposure to high temperature has a strong effect performance of heat resistant steels. In case of modified 9Cr-1Mo steels, precipitation of $Fe_2Mo$-type laves phases and coarcening of $M_23C_6$-type carbides is the primary cause of degradation of mechanical properties such as creep resistance, tensile strength and toughness. Creep tests have been carried out on pre-aging mod. 9Cr-1Mo steels to examine the effect of pre-aging and stress on the creep strength. Based on the results, a nondestructive procedure, where electrochemical technique that quantitatively detect laves phases and $M_23C_6$-type carbides in a material is used, has been proposed to evaluate a residual creep life of mod. 9Cr-1Mo steels.
현양기,강민철,김순호,김인배,Hyeon, Yang-Gi,Gang, Min-Cheol,Kim, Sun-Ho,Kim, In-Bae 한국재료학회 1996 한국재료학회지 Vol.6 No.9
Zr이 0.03wt%함유된 Mg-8.14Li-3.93AI 합금의 시효거동을 미소경도와 미세조직의 변화, 열분석 등으로 조사하였다. Zr의 첨가로 인하여 3원계 Mg-8.23Li-4.02A에 비하여 조직이 미세화되었으며 모든 시효조건에서 경도값이 높게 나타났다. 열분석결과 발열피크는 준안정 석출상인 MgLi2AI($\theta$)의 석출과 $\theta$상에서 안정상인 AILi으로의 변화와 관련된 것이고, 흡열피크는 $\theta$와 AILi상의 재용해에 대응되는 것으로 판단되었다. 피크 경도값(103Hv)은 $\theta$의 석출이 완료되는 393K에서 0.5시간 시효시 나타났으며 피크 경도조건에서의 미세조건은 $\beta$기지에 $\theta$와 AILi상이 공존하고 있음을 투과식 전자현미경으로 확인하였다.
원순호,현양기,이종오,조경식,이재도 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.1
산업현장에서 수소는 설비를 손상시킬 수 있는 주원인 중의 하나이며, 종종 설비를 파괴시키는 사고를 발생시킨다. 수소손상에 의한 결정립계의 공동 또는 미세균열은 강재의 파괴인성과 강도를 떨어뜨리는 원인이 되고, 따라서 과거 제한적인 방법으로 수소손상을 평가하기 위한 시도가 수행되었다. 본 연구에서는 초음파를 적용하여 수소손상을 검출하고 평가하기 위한 연구를 수행하였다. 미세조직시험에 의해 확인된 시험편을 이용하여 초음파의 속도와 감쇠계수를 구한 결과, 수소손상에 의해서 초음파 속도는 감소하고 감쇠는 현저하게 증가하는 것으로 나타났다. 이러한 결과를 바탕으로 수소손상을 검출하기 위한 신뢰성 있는 평가법을 제시하였다. The presence of hydrogen in industrial plants is a source of damage. Hydrogen attack is one such form of degradation and often causing large tube ruptures that necessitate an immediate shutdown. Hydrogen attack may reduce the fracture toughness as well as the strength of steels. This reduction is caused partially by the presence of cavities and microcracks at the grain boundaries. In the past several techniques have been used with limited results. This paper describes the application of an ultrasonic velocity and attenuation in hydrogen damage. Ultrasonic tests showed a decrease in wave velocity and an increase in attenuation. Such results demonstrate the potential for ultrasonic nondestructive testing to quantify damage. Based on this study, reliable recommendation is suggested to detect hydrogen attack.
원순호,현양기,이종오,이재도,조경식,Won, Sun-Ho,Hyeon, Yang-Gi,Lee, Jong-O,Lee, Jae-Do,Jo, Gyeong-Sik 한국기계연구원 2001 硏究論文集 Vol.31 No.-
Hydrogen damage affects carbon steel tubes in many fossil-fuel-fired boilers, often causing large tube ruptures that necessitate an immediate shutdown. Therefore, equipment handling high-temperature, high-pressure hydrogen must undergo careful periodic inspection because of its susceptibility to hydrogen attack. This paper describes the application of an ultrasonic technique for detecting the presence of hydrogen damage in utility boiler tubes. The accuracy of the technique has been shown in laboratory tests. However, it is difficult to evaluate hydrogen attack quantitatively by this technique, because ultrasonic wave is influenced by the test conditions and the material itself.
SCM440(H) 및 SNCM439 강의 열처리 특성에 미치는 질량효과
남기석 ( K. S. Nam ),현양기 ( Y. K. Hyun ),조창용 ( C. Y. Jo ),조유종 ( Y. H. Cho ) 한국열처리공학회 2011 熱處理工學會誌 Vol.24 No.1
Recently, renewable energy sources such as wind turbine, solar cell are interested in preventing global warming which is caused by the consumption of fossil fuel. SCM440H and SNCM439 have been used in the major components of the wind turbine gear because of excellent mechanical properties. In the present study, the heat treated mechanical properties of SCM440H and SNCM439 with 150mm diameter were compared with those with 25 mm diameter which is generally accepted material for structural application. Heat treated SCM440H showed better mechanical properties such as tensile strength, hardness and impact absorbed energy compared with those in SNCM439. Hardenss value between as-quenched and as-quenched followed by tempering showed big difference in SNCM439, however the difference in SCM440H was relatively small. Heat treated mechanical properties of the alloys with 25mm diameter were more uniform value than those with 150mm diameter. (Received November 3, 2010; Accepted November 29, 2010)
열처리공학회지,제27권 제1호(2014) -고온 가스질화 된 STS 430 스트인리스강의 냉간 가공성에 미치는 항온변태 열처리 시간 변화의 영향
김정민 ( J. M. Kim ),현양기 ( Y. K. Hyun ),송상우 ( S. W. Song ),김기동 ( G. D. Kim ),손영호 ( Y. H. Son ),성장현 ( J. H. Sung ) 한국열처리공학회 2014 熱處理工學會誌 Vol.27 No.1
This study is to investigate the phase changes and cold workability after isothermal transformation at l800C by using the high temperature gas nitrided (HTGN) STS 430 ferritic stainless steel specimens. The phase diagram of STS 430 steel obtained by calculation showed that the phase appeared at 11 OO°C showed as α + г →г+ Cr₂N →г+ Cr₂N + CrN with increasing nitrogen concentration. Also. the transformation of г→ Cr₂N during heat treatment isothermally at 780°C, nitrogen pearlite with lamellar type was fully formed at the nitrogen permated surface layer for 10 hrs. However. this transformation was not completed for 1 hr, resulting nitrogen pearlite plus martensite. The cold rolled specimen of isothermally transformed at l80°C for 10 hrs after high temperature gas nitriding decreased the layer thickness of nitrogen pearlite inducing the deformation of hard Cr₂N phase. the dissolution rate of Cr₂N phase increased rapidly with increasing cold rolling ratio. Specimens with the microstructure of nitrogen pearlite (isothermally transformed at l80°C for 10 hrs) were possible to cold rolling without crack formation. However, the mixed structures of nitrogen pearlite + martensite (isothermally transformed at 780°C for 1 hr) were impossible to cold deformation without cracking.