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2¼Cr-1Mo강 압력용기 용접이음부의 재열균열에 관한 역학적 연구
권영섭,노찬승,방한서 朝鮮大學校 機械技術硏究所 1999 機械技術硏究 Vol.2 No.2
구조물에 사용되는 각종 압력용기들의 재질은 고온 및 고압에 견딜 수 있도록 요구되고 있다. 따라서, 내열, 내압 및 내부식성이 뛰어난 2¼Cr-1Mo강의 수요가 향후 증대될 전망이다 용접잔류응력은 일반적으로 응접구조물에 각종 악영향을 미치는 것으로 알려져 있다. 이 때문에 용접잔류응력. 확산성 수소제거 및 용접 열영향부의 연화등을 목적으로 용접후열처리(PWHT)를 수행하나, PWHT를 행하면 사용 강재의 종류에 따라 재열균열이 발생하고 있다. 본 연구에서는 2¼Cr-1Mo강에 대하여 실험과 수치해석 기법을 통하여 용접이음부의 재열균열 감수성평가 및 상당크리프 변형율의 재열균열 발생에 판정에 대한 역학적 지표로서의 적용성을 검토하였다. 2¼Cr-1Mo steels are widely used to fabricate pressure vessels. Residual stresses, in general, are known to be harmful to the soundness of the welded structures. PWHT is release residual stresses, which may cause cracks. But, in those PWHT process, 2¼Cr-1Mo steels are apt to occur reheat crack frequently. In this reason, it is strongly needed to analysis and examine the mechanical behavior of welded joints through welding to PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks are frequently occur are selected for examine the crack-occurrence mechanism.
용접 공정에 따른 2.25Cr-1Mo강 용접이음부의 특성 변화에 관한 연구
방한서(HAN-SUR BANG),오종인(CHONG-IN OH),방희선(HEE-SUN BANG),김형(HYUNG KIM) 한국해양공학회 2005 韓國海洋工學會誌 Vol.19 No.1
In spite of the merits of laser welding being able to obtain the high welding quality such as smaller width of melting and heat affected zone, smaller welding deformation and fine grains of weldment compared to arc welding, laser welding is mainly used in joining of thin steel parts of electronics industry. Laser welding is getting widely used in joining thick plate and special kinds of steel due to its high power. While the arc welding is still applied for 2.25Cr-1Mo steel which is the essential material of atomic power generation equipment, the laser welding is not yet applied despite its high quality. So it has a trial to a special case demanding high welding quality such as atomic power plant. Accordingly, in this research, the mechanical properties of weldments by arc and laser welding were investigated using FEM to confirm the applicability of laser welding to 2.25Cr-1Mo steel. The Charphy test was carried out to understand the effect on the fracture toughness of weldments. The results of examination and test of the mechanical properties showed the validity of this research.
유한요소법에 의한 PREFLEX BEAM의 용접열분포 특성에 관한 연구
방한서(HAN-SUR BANG),주성민(SUNG-MIN JOO),김하식(HA-SIG KIM) 한국해양공학회 2004 韓國海洋工學會誌 Vol.18 No.2
Preflex beam is a method of construction designed to hold the pre-compressive stresses over the concrete pier by the preflexion load. During the fabrication of the girder, welding causes residual stresses. The welding residual stresses must be relieved in order to generate the accurate compressive pre-stresses. In this study, to determine the thermal distribution characteristics on the girder by welding, both three-dimensional finite element analysis and two-dimensional finite element analysis, in a quasi-steady state, is carried out. After comparing each result between the three-dimensional analysis and the two-dimensional analysis, finite element analysis is carried out against the actual girder, and the welding thermal distribution characteristic over the preflex beam is analyzed. It is possible to provide the input data for the analysis of the welding residual stresses.
조선용 극후판 EH36-TMCP강 FCAW 용접부의 역학적 특성에 관한 연구
방한서 ( Han Sur Bang ),고민성 ( Min Sung Go ),김성주 ( Sung Joo Kim ) 조선대학교 공학기술연구원 2009 공학기술논문지 Vol.2 No.3
This work attempts to establish the stability and reliability of welded joint by FCAW for high strength EH32-TMCP ultra thick plate. Experimental results are reported for 37 pass X-groove butt joint of EH32 steel. Abbnevation on Expantion FE analysis has been carried out to simulate the FCA W process on the same specimen model as in experiment. By numerical simulation, thermal and mechanical behavior (residual stress, plastic strain, magnitude of stress and their distribution and production mechanism) has been investigated by heat conduction and thermo elasto-plastic analysis.
고장력강 용접부의 열ㆍ역학적 거동에 관한 수치해석적 연구
방한서(Han-Sur Bang),임래수(Rae-Su Lim),김종명(Jong-Myung Kim) 한국해양공학회 1998 韓國海洋工學會誌 Vol.12 No.4
High tensile steel has been welding in building construction and ship structure to reduce cost as well as weight. Accordingly, welding strength and weldability of high tensile steel is a matter of concern and interest.<br/> In the case of high tensile, brittle fracture and buckling strength are affected by welding residual stresses. For the sound design of structure using high tensile steel, distribution of welding residual stress need to be identified, which should be considered as initial imperfection of welded structure.<br/> Therefore, in this paper, in order to know the thermal and mechanical characteristics of high tensile steel during the welding and the post welding heat treatment, we would be compared with mild steel through numerical analysis of computer program based on the finite element method. The materials, which used study on welding strength, are SWS490, 60㎏f/㎟ class high tensile steel(HT60) and 80㎏f/㎟ class high tensile steel (HT80).
2¼Cr-1Mo강 압력용기 Nozzle 용접이음부의 재열균열에 관한 수치해석적 연구
방한서(HAN-SUR BANG),김종명(JONG-MYUNG KIM) 한국해양공학회 2000 韓國海洋工學會誌 Vol.14 No.1
Recently, various pressure vessels like an atomic reactor and plant facilities become more larger and are needed to bear in both very) high temperature and pressure condition. And, in making such a high pressure vessels, the amount of annual usage of 2¼Cr-1Mo steels which are predominant to resist high temperature, high pressure and corrosive circumstances are increasing. But, despite of this advantages of 2¼Cr-1Mo steel, when PWHT(post welding heat treatment)is carried out lots of reheating cracks are occur. In this reason, it is strongly needed to study and examine the mechanical behavior of welded joints through welding to PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks are frequently occur are selected for analysis the crack-occurrence mechanism.
유한요소법에 의한 평판의 용접 변형에 관한 기초적 연구
방한서(Han-Sur Bang),고민성(Min-Seong Go),방희선(Hee-Seon Bang) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.4
When structures are constructed by welding, heat conduction brings welding deformation. This is accompanied by complicated mechanical phenomenon such as material nonlinear and geometric nonlinear behavior.<br/> Hitherto, the research of welding deformation has been accomplished by an analytical method and experimental data in Korea.<br/> In this paper, the computer program by F.E.M.(finite element method) which could analyze the deformation of thin plate considering phenomena(both material and geometric nonlinear behavior) has been developed and verified. The production mechanism and charactristics in the welding deformation of plate are studied by the results.
방한서(Han-Sur Bang),한길영(Gil-Young Han) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.1
Welding of structure produces welding residual stresses which influence buckling strength, brittle fracture strength and cold crack on the weld parts. Therefore, it is very important to accurately analyze the residual stress before welding in order to guarantee the safety of weldment.<br/> If the weld length is long enough compared to the thickness and the breadth of plate, thermal and mechanical behaviors in the middle portion of the plate are assumed to be uniform along the thickness direction(z-axis). Thus, the following conditions(so-called plane deformation) can be assumed for the plate except near its end ; 1) distributions of stress and strain are independent on the z-axis ; 2) plane normal to z-axis before deformation remains plane during and after deformation.<br/> In this paper, plane-deformation thermal elasto-plastic problem is formulated by being based on the finite element method. Moreover special regards are paid to the fact that material properties in elastic and plastic region are temperature-dependence. And the method to solve the plane-deformation thermal elasto-plastic problem is shown by using the incremental technique. From the results of analysis, the characterisics of distribution of welding residual stress and plastic strain with the production mechanism are clarified.