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소형시험편의 Master Curve 방법을 이용한 원자로 압력용기강의 파괴인성 천이특성평가
양원존,허무영,김주학,이봉상,홍준화,Yang, Won-Jon,Heo, Mu-Yeong,Kim, Ju-Hak,Lee, Bong-Sang,Hong, Jun-Hwa 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.2
Fracture toughness of five different reactor pressure vessel steels was characterized in the transition temperature region by the ASTM E1921-97 standard method using Charpy-sized small specimens. T he predominant fracture mode of the tested steels was transgranular cleavage in the test conditions. A statistical analysis based on the Weibull distribution was applied to the interpretation of the scattered fracture toughness data. The size-dependence of the measured fracture toughness values was also well predicted by means of the Weibull probabilistic analysis. The measured fracture toughness transition curves followed the temperature-dependence of the ASTM master curve within the expected scatter bands. Therefore, the fracture toughness characteristics in the transition region could be described by a single parameter, so-called the reference temperature (T。), for a given steel. The determined reference temperatures of the tested materials could not be correlated with the conventional index temperatures from Charpy impact tests.
양원존(Won-Jon Yang),오충석(Chung-Seog Oh) Korean Society for Precision Engineering 2022 한국정밀공학회지 Vol.39 No.5
The main shaft of a mechanical press inevitably includes significant stress concentrations that can trigger severe mechanical damage and finally lead to failure under repetitive use. In this study, an efficient procedure to quantitatively evaluate the fatigue life of the shaft system including the main shaft and its support bearings, based on the macroscopic failure analysis of the main shaft broken during actual use, was investigated. For this purpose, the bearing support was modeled as an elastic foundation, and the elastic foundation stiffness value was varied to determine the optimal value that best simulates the failure behavior, especially with respect to the failure location and failure sequence, of an actual shaft. While the finite element mesh size was kept the same, only the effect of elastic foundation stiffness was investigated. The optimum value for the main shaft investigated in this study was approximately 60 N/mm³, and the fatigue life of the shaft was evaluated based on the conventional maximum principal stress theory. Based on this, two modified designs to enhance the fatigue life of the existing shaft are proposed.
오주숙 ( Ju Suk Oh ),양원존 ( Won Jon Yang ),이종훈 ( Jong Hoon Lee ),박용호 ( Yong Ho Park ) 한국열처리공학회 2011 熱處理工學會誌 Vol.24 No.3
Residual stress relief by pulse magnetic treatment is attractive because the process is carried out at room temperature and magnetic fields that are easy to produce and control can be used. This study shows that strong pulse magnetic treatment can lead to stress relaxation of structural steels instead of a conventional heat treatment process. And it makes a comparative study about pulse magnetic treatment and tempering by using Larson-Miller equation. When the specimen was subjected to a pulse magnetic treatment process the residual stress in the specimen was reduced by about 13.8%. It could be compared with tempering at 200℃ for 2hours by using thermal effect of Larson-Miller equation. As a result, it is considered that the pulsed magnetic treatment have an effect of the stress relation by tempering at 200℃ for 2 hours.
논문 : Nb 첨가 오스테나이트계 내열 스테인리스강의 열기계적 피로 수명 및 변형 거동
오용준 ( Yong Jun Oh ),박중철 ( Joong Cheul Park ),양원존 ( Won Jon Yang ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.7
Thermomechanical fatigue (TMF) behavior of heat resistant austenitic stainless steel was evaluated in the temperature range from 100℃ to peak temperatures of 600 to 800℃; The fatigue lives under TMF conditions were plotted against the plastic strain range and the dissipated energy per cycle. In the expression of the inelastic strain range versus fatigue life, the TMF data obtained at different temperature ranges were located close to a single line with a small deviation; however, when the dissipated energy per cycle, calculated from the area of the stress-strain hysteresis loops at the half of the fatigue life, was plotted against the fatigue life, the data showed greater scattering than the TMF life against the inelastic strain range. A noticeable stress relaxation in the stress-strain hysteresis curve took place at the peak temperatures higher than 700℃, but all specimens in this study exhibited cyclic hardening behavior with TMF cycles. Re-crystallization occurred during the TMF cycle concurrent with the formation of fine subgrains in the re-crystallized region, which is considered to cause the cyclic hardening of the steel.
정밀금형용 SKD61 강의 복합표면처리에 의한 표면신뢰성 향상
박민혁(Min-Hyeok Park),김동오(Dong-O Kim),엄정원(Joung-Won Eom),김진영(Jin-Yeong Kim),김유진(Yu-Jin Kim),김은우(Eun-Woo Kim),양원존(Won-Jon Yang),심동하(Dongha Shim),변재원(Jai-Won Byeon) 한국신뢰성학회 2022 신뢰성응용연구 Vol.22 No.2
Purpose: The lifespan of a die-casting steel mold depends on its surface hardness and wear resistance. Gas nitriding treatments for forming surface hardening layers have been widely applied to fabricate reliable die-casting molds. In the present study, we propose a complex surface treatment consisting of a micro-shot peening process and a sulfo-nitriding treatment to improve the surface hardness of SKD61 mold steel. Methods: The cross-sectional microstructure of the complex surface-treated SKD61 mold steel was observed using an optical microscope and a scanning electron microscope. The phase of the surface hardening layer was analyzed using an X-ray diffractometer. The micro-hardness and residual stress of the complex surface-treated SKD61 mold steel were evaluated as well. Results: The surface hardening layer consisted of the top-most compound layer and a diffusion layer. The micro-shot peening pretreatment increased the thickness of the compound layer. The general nitriding (GN) treatment led to the formation of the FexN compound layer, while the sulfo-nitriding (SN) treatment led to the formation of the FexN and FeS composite compound layer, which was thicker than the compound layer of the GN specimen. The hardness of GN and SN hardening layers improved by 125% and 135%, respectively, relative to that of the as-received SKD61 mold steel with a hardness of 450 HV. Conclusion: The SN treatment formed a reliable hardening layer with superior hardness than the GN treatment. Furthermore, the thicker sulfo-nitride compound layer produced by the SN treatment can further improve the lifespan of SKD61 steel molds.