Alloy 617 확산용접재의 고온 인장강도

사인진,황종배,김응선,Sah, Injin,Hwang, Jong-Bae,Kim, Eung-Seon 한국압력기기공학회 2018 한국압력기기공학회 논문집 Vol.14 No.1

A compact heat exchanger is one of critical components in a very high temperature gas-cooled reactor (VHTR). Alloy 617 (Ni-Cr-Co-Mo) is considered as one of leading candidates for this application due to its excellent thermal stability and strengths in anticipated operating conditions. On the basis of current ASME code requirements, sixty sheets of this alloy are prepared for diffusion welding, which is the key technology to have a reliable compact heat exchanger. Optical microscopic analysis show that there are no cracks, incomplete bond, and porosity at/near the interface of diffusion weldment, but Cr-rich carbides and Al-rich oxides are identified through high resolution electron microscopic analysis. In high-temperature tensile testing, superior yield strengths of the diffusion weldment compared to the code requirement are obtained up to 1223 K ($950^{\circ}C$). However, both tensile strength and ductility drop rapidly at higher temperature due to the insufficient grain boundary migration across the interface of diffusion weldment. Best fit curves for minimum yield strength and average tensile strength are drawn from the experimental tensile results of this study.

확산접합된 페라이트/마르텐사이트강의 미세조직 및 기계적 특성에 미치는 열처리 효과

사인진,김성환,홍성훈,장창희,Sah, Injin,Kim, Sunghwan,Hong, Sunghoon,Jang, Changheui 한국압력기기공학회 2015 한국압력기기공학회 논문집 Vol.11 No.1

As a measure of improving the mechanical properties of a diffusion bonded joint of a ferritic/martensitic steel (FMS), the post-bonding heat treatment (PBHT) is applied. In the temperature range of normalizing condition ($950-1,050^{\circ}C$), diffusion bonding is employed with compressive stress (6 MPa). Due to the martensite structure distributed in the matrix, Vicker's hardness values of the as-bonded are much higher than those of the as-received. Through the PBHT for 1 h at $720^{\circ}C$, hardness values are recovered to as low as those of the as-received condition. Also, tensile properties of PBHT are similar to those of the as-received at up to the test temperature of $550^{\circ}C$, when the diffusion bonding is carried out over $1,000^{\circ}C$. Based on the creep-rupture testing performed at $650^{\circ}C$ in air environment, the joint efficiency of the PBHTed specimens is about 80% in, which is higher than that of the as-bonded specimens.

θ투영법을 이용한 초내열합금 크리프 거동 평가

사인진(Injin Sah),김상지(Sang Ji Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

고온로 구조재료로 Ni-Cr-Co-Mo 초내열합금이 고려되고 있다.^(1,2) 크리프 변형 및 파단은 고온 운전 조건에서 구조재료 수명을 결정하는 주요 요인이다.^(3-7) 본 연구에서는 θ투영법을 이용하여 초내열합금의 크리프 거동을 평가하였다. 고온 응력-파단 실험 데이터에 비선형최소자승법을 적용하여 θ투영법 매개변수들을 도출하였다. 손상허용인자(λ) 값을 2.0 로 지정하여 3 차크리프 거동을 평가하였다. 비선형최소자승법으로 계산된 매개변수들은 응력 함수에서 선형성을 가졌다. 계산된 최소크리프율은 실험 데이터 범위 내에 포함되는 것으로 나타났다. 설계 관점에서 낮은 응력 수준에서 크리프 곡선들을 제안하였다. Ni-Cr-Co-Mo superalloy is expected to be used as a structural material in high-temperature reactors (HTRs).^(1,2) Creep deformation and rupture is a dominant factor in determining lifetime of structural material at high temperature operating condition.^(3-7) In this study, theta (θ) projection method was employed to characterize creep behavior of a superalloy. Parameters in the theta projection method were derived by applying nonlinear least square fitting (NLSF) method to experimental data of stress-rupture test at high temperatures. Damage tolerance factor (λ) of 2.0 was assigned to evaluate tertiary creep stage. Calculated parameters from NLSF had a good linearity as a function stress. It was revealed that calculated minimum creep rate falls within a range of experimental data. Creep curves at low stress levels were proposed for design aspect.

표면개질이 확산용접부 기계물성에 미치는 영향

사인진(Injin Sah),황종배(Jong-Bae Hwang),박재환(Jaehwan Park),김응선(Eung-Seon Kim) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4

고온로 중간열교환기로 판형열교환기가 고려되고 있다.^(1,2) 판형열교환기는 확산용접 방법을 이용하여 얇은 시트를 접합하여 제작된다. 통상기술로 제작된 확산용접부의 접합계면은 접합계면을 따라 형성된 이차상으로 인해 외부하중에 취약하다.^(3-5) 본 연구에서는 확산용접부 접합계면 미세조직과 기계적 물성 향상을 위한 표면개질 방법을 제안하였다. 전자현미경 분석을 통해 접합계면에 크롬에 의한 탄화물과 알루미늄에 의한 산화물이 거의 형성되지 않는 것을 확인하였다. 이는 접합계면을 가로지르는 결정립계 이동을 촉진시켰고, 접합계면 영역의 미세조직이 접합계면에서 떨어진 영역의 미세조직과 유사하게 만들었다. 상온과 고온 인장실험에서 확산용접부는 모재 수준의 인장강도와 연신율을 보였다. 파단은 접합계면과 떨어진 인장시편 표점영역 안에서 발생하였다. 800 ℃에서 수행된 예비 응력-파단실험에서 확산용접부의 파단강도는 모재의 파단강도 범위 내에 포함되었다. Plate-type heat exchangers are expected to be applied in an intermediate heat exchanger (IHX) in high-temperature reactors (HTRs).^(1,2) Plate-type heat exchangers are manufactured by joining thin sheets through diffusion welding method. Following the conventional method in manufacturing the diffusion weldment, the interface is vulnerable to external loading condition due to secondary precipitates formed along the interface.^(3-5) A surface modification method is proposed in this study to improve the microstructural feature and mechanical properties of the interface. It was revealed in microscopic analysis that the interface is almost free from Cr-rich carbides and Al-rich oxides. This facilitates the grain boundary migration across the interface, and in turn the microstructure of the interface region becomes similar to that of regions remote from the interface. Fracture occurred at a location away from the interface in the gauge section of tension specimens. In room- and high-temperature tensile test, tensile strength and elongation of the diffusion weldment are similar to those of the as-received alloy. In preliminary stress-rupture test at 800 ℃, rupture strengths of the diffusion weldment fall within the range of the as-received alloy.

Alloy 617 확산용접재의 저주기피로 특성

사인진(Injin Sah),박재환(Jaehwan Park),김응선(Eung-Seon Kim) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.3

외부겔화공정을 이용한 이산화우라늄 구형 입자 제조

김연구,사인진,김응선,Kim, Yeon-Ku,Sah, Injin,Kim, Eung Seon 한국재료학회 2020 한국재료학회지 Vol.30 No.10

UO₂ kernels, a key component of fuel elements for high temperature gas cooled reactors, have usually been prepared by sol-gel methods. Sol-gel processes have a number of advantages, such as simple processes and facilities, and higher sphericity and density. In this study, to produce 900 ㎛-sized UO₂ particles using an external gelation process, contact length extension of the NH₃ gas of the broth droplets pass and the improvement of the gelation device capable of spraying 14 M-NH₄OH solution are used to form 3,000 ㎛-sized liquid droplets. To produce high-sphericity and high-density UO₂ particles, HMTA, which promotes the gelation reaction in the uranium broth solution, is added to diffuse ammonium ions from the outside of the gelation solution during the aging process and generate ammonium ions from the inside of the ADU gel particles. Sufficient gelation inside of ADU gel particles is achieved, and the density of the UO₂ spheres that undergo the subsequent treatment is 10.78 g/㎤; the sphericity is analyzed and found to be 0.948, indicating good experimental results.

축방향 열전도와 유로 변형을 고려한 인쇄기판형 열교환기 열적 성능

박병하,사인진,김응선,Park, Byung Ha,Sah, Injin,Kim, Eung-seon 한국압력기기공학회 2018 한국압력기기공학회 논문집 Vol.14 No.1

Printed circuit heat exchangers (PCHEs) are widely used with an increasing demand for industrial applications. PCHEs are capable of operating at high temperatures and pressure. We consider a PCHE as a candidate intermediate heat exchanger type for a high temperature gas-cooled reactor (HTGR). For conventional application using stainless steels, design and manufacturing of PCHEs are well established. For applications to HTGR, knowledge of longitudinal conduction and deformation of channel is required to estimate design margin. This paper analyzes the effects of longitudinal conduction and deformation of channel on thermal performance using a code internally developed for design and analysis of PCHEs. The code has a capability of two dimensional simulations. Longitudinal conduction is estimated using the code. In HTGR operating condition, about ten percent of design margin is required to compensate thermal performance. The cross-sectional images of PCHE channels are obtained using an optical microscope. The images are processed with computer image process technique. We quantify the deformation of channel with dimensional parameters. It is found that the deformation has negative effect on structural integrity. The deformation enhances thermal performance when the shape of channel is straight in laminar flow regime. It reduces thermal performance in cases of a zigzag channel and turbulent flow regime.

고온 S-CO₂ 사이클 열교환기용 스테인리스강 및 Fe-Cr-Ni 합금 확산 접합부의 고온 인장 특성평가

홍성훈(Sunghoon Hong),사인진(Injin Sah),장창희(Changheui Jang) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.4-1

고온 S-CO₂ 사이클 열교환기용 스테인리스강 및 Fe-Cr-Ni 합금 확산 접합부의 고온 인장 특성평가

홍성훈(Sunghoon Hong),사인진(Injin Sah),장창희(Changheui Jang) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.12

소듐냉각고속로(Sodium-cooled Fast Reactor, SFR)의 안전성 향상을 위해 고온 증기 Rankine 싸이클 대신 초임계 이산화탄소(Supercritical CO₂, S-CO₂) Brayton 싸이클을 전력변환 시스템에 사용하는 방안이 제시되고 있다. 이 경우, 중간 열교환기로는 확산 접합(Diffusion Bonding)에 의해 제작되는 미소채널형 열교환기인 PCHE(Printed Circuit Heat Exchanger) 가 고려되고 있다. 따라서 본 연구에서는 PCHE 형 열교환기 후보재료인 다양한 오스테나이트계 합금의 확산접합 특성을 평가하였다. 후보재료별로 다양한 조건에서 확산접합부를 제작하고 상온에서 650℃ 까지의 인장 특성을 평가하였다. 평가 결과 SS 316H 와 SS 347H 는 550℃ 까지 모재와 유사한 특성을 보였지만 Fe-Ni-Cr 합금인 Incoloy 800HT 는 모든 온도에서 인장특성이 감소하였다. 연신율 저하의 원인을 이해하기 위해 접합부 부근의 미세조직을 분석하였다. To improve the inherent safety of the sodium-cooled fast reactor (SFR), the supercritical CO₂ (S-CO₂) Brayton cycle is being considered as an alternative power conversion system to steam the Rankine cycle. In the S-CO₂ system, a PCHE (printed circuit heat exchanger) is being considered. In this type of heat exchangers, diffusion bonding is used for joining the thin plates. In this study, the diffusion bonding characteristics of various austenitic alloys were evaluated. The tensile properties were measured at temperatures starting from the room temperature up to 650℃. For the 316H and 347H types of stainless steel, the tensile ductility was well maintained up to 550℃. However, the Incoloy 800HT showed lower strength and ductility at all temperatures. The microstructure near the bond line was examined to understand the reason for the loss of ductility at high temperatures.

고온가스로용 니켈기초합금의 확산접합 기술 개발

장창희(Changheui Jang),사인진(Injin Sah),김동훈(Donghoon Kim) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.2