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UNS N06690 제1열 시제전열관의 U-굽힘성형에서 형상변화와 표면잔류응력
김우곤,장진성,국일현,주진원,김성청,Kim, Woo-Gon,Jang, Jin-Sung,Kuk, Il-Hiun,Joo, Jin-Won,Kim, Sung-Chung 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.1
Surface residual stresses as well as wall thickness and ovality changes after U-bending process on UNS N06690 row-1 heat exchanger tubes, were estimated. Surface residual stresses were measured by Hole Drilling Method(HDM), calculating the stresses from relieved strains of 3 rosette strain gages. After bending of the tubes, dimensional tolerances for wall thickness and ovality were satisfied with ASTM requirements. Residual stresses at the extrados were introduced with compressive stress(-) by bending operations, and its maximum value reached-319 MPa in axial direction at ${\phi}=0^{\circ}$ in position. Tensile residual stresses(+) of ${\sigma}_zz=45$ MPa,${\sigma}_zz=25$ MPa were introduced in the intrados surface at position of ${\phi}=0^{\circ}$ Maximum tensile residual stress of 170 MPa was detected on the flank side at position of ,${\phi}=95^{\circ}$i.e., at apex region. It appeared that higher stress gradients were generated at the irregular transition regions. In the trend of residual stress changes with U-bend position, the extrados is related with the changes of ovality and the intrados is related with the changes of wall thickness.
논문 : 상변태 ; Alloy 690에서의 결정립계 형상 조절
이진규 ( Jin Kyu Lee ),장진성 ( Jin Sung Jang ),김도향 ( Do Hyang Kim ),이창규 ( Chang Kyu Rhe ),국일현 ( Il Hiun Kuk ) 대한금속재료학회 ( 구 대한금속학회 ) 1998 대한금속·재료학회지 Vol.36 No.7
The influence of heat treatments on the grain boundary morphology of alloy 690 (Ni-30Cr-9Fe) was studied. Serrated grain boundaries were produced by isothermal heat treatment at 800℃ after solution heat treatment at 1150℃ or by control cooling in the temperature range of 800℃ and 400℃ with a rate of 5℃/min or below. The amplitude and wavelength of serrated grain boundaries increased with longer isothermal heat treatment time or slower cooling rates, but showed maximum value at some extent, respectively. Precipitates on the serrated grain boundaries were revealed as Cr23C6 having semi-coherent cube-to cube relationship -{100}matrix//{100}ppt <100>matrix//<100>ppt -with one adjacent grain.
Alloy 600 합금의 내부식성 향상을 위한 레이저 표면 합금화
김정수,서정훈,강석중,신진국,국일현 한국레이저가공학회 1999 한국레이저가공학회지 Vol.2 No.1
The surface of Alloy 600 was alloyed using a continuous wave CO₂ laser beam in order to improve its corrosion resistance. Laser surface alloying (LSA) was done by melting the surface electroplated with Cr of the alloy. The Cr concentration of the alloyed surface was 28∼30 at.%, which is similar to that of Alloy 690. Alloying elements in the alloyed layer was observed to be distributed very homogeneously all over the alloyed region. According to the electrochemical and modified Huey tests, the corrosion resistance, in particular the grain boundary corrosion resistance, of the LSA specimens was significantly improved, compared with that of the as-received(AR) specimen. This improved corrosion resistance of the alloyed specimen might be attributed to the high Cr content, which could make possible formation of more stable and dense passive film onto its surface.
Alloy 600의 Primary Water Stress Corrosion Cracking 반응기구에 대한 고찰
정한섭,국일현 한국부식학회 1996 Corrosion Science and Technology Vol.25 No.1
Characteristics of Primary Water Stress Corrosion Cracking of Alloy 600 nuclear steam generator tubing material were reviewed on the basis of literature data. Thermodynamic characteristics and effect of hydrogen overpressure, behavior in water and steam phase, and the effects of important variables, such as microstructure, temperature and stress and strain, were focused. The classical theory of Slip Dissolution and Film Rupture model, and Hydrogen Embrittlement model were found to be inadequate for the thorough explanation of PWSCC. Models proposed recently to overcome the difficulties encountered by the classical models, included Void-Linkage model, Internal Oxidation model, Corrosion Deformation Interaction model, Creep model, and Selective Dissolution-Vacancy-Creep model. Theoretical background and coincidence with experimental evidences of each model were discussed. Existance of grain boundary cavities near advancing crack tip is in controversy among different researches. Dependence of chemistry and structure of Alloy 600 surface film on the corrosion potential, which has to be revealed by further research efforts, may be helpful for understanding the mechanism of PWSCC.