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김상재(Sang-Jai Kim),임경수(Kyung-Soo Im),김영석(Young-Suk Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.8
The aim of this study was to obtain a better understanding of delayed hydride cracking (DHC) of Zr-2.5Nb pressure tube with hydrogen concentration. After the ratcheting heat treatment, DHC tests were conducted at 200 and 250℃ on Cantilever Beam (CB) specimens with 60, 80ppm H to determine the threshold stress intensity factor, K<SUB>1H</SUB> in radial direction of the Zr-2.5Nb tube. Over a hydrogen concentration range of 80 ppm, K<SUB>1H</SUB> for the Zr-2.5Nb tube 13 ㎫ vm, However, at 60ppm, K<SUB>1H</SUB> increased unexpectedly to a higher value at 250℃. Based on the results, K<SUB>1H</SUB> for Zr-2.5Nb tube is discussed with the fracture surface and a supersaturated concentration of hydrogen..
방향에 따른 Zr-2.5Nb 압력관의 DHC 임계응력확대세기, K<SUB>IH</SUB>
김상재(Sang-Jai Kim),김성수(Sung-Soo Kim),정용무(Yong-Moo Cheong),임경수(Kyung-Soo Im),김영석(Young-Suk Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
The object of this study is to obtain a better understanding of delayed hydride cracking (DHC) of Zr-2.5Nb pressure tube with crack growth directions; the radial and axial direction of the tube. DHC tests were conducted at temperatures ranging from 160~280℃ on curved compact tension (CCT) and cantilever beam (CB) specimens with 60 ppm H to determine the threshold stress intensity factor, K<SUB>IH</SUB> in axial and radial directions of the Zr-2.5Nb tube, respectively. Over a temperature range of 160 ~ 250℃, K<SUB>IH</SUB> of the Zr-2.5Nb tube was constant independent of temperatures in both directions of the tube. K<SUB>IH</SUB> was higher in the radial direction than that in the axial direction: 5.84 ㎫√m in the axial direction and 8.44 ㎫√m in the radial direction. Furthermore, K<SUB>IH</SUB>had a strong dependence of the supersaturated hydrogen concentration in Zr-2.5Nb pressure tube. Thus, K<SUB>IH</SUB> was nicely described as a function of the supersaturated hydrogen concentration over TSSD independent of temperatures. K<SUB>IH</SUB> was discussed with the supersaturated hydrogen concentration and orientations.
GTA 용접처리한 Zircaloy-4판재의 미세조직 및 기계적 성질
조충형(Chung-Hyung Joh),김상재(Sang-Jai Kim),김선식(Seon-Sik Kim),임경수(Kyung-Soo Im),김영석(Young-Suk Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
To predict degradation of the reflector vessel made of annealed zircaloy-4 alloys their microstructures and tensile properties were investigated because irradiation growth strongly depends on metallurgical variables as composition, dislocation density, texture, grain size and residual stress. The plate has fully recrystallized grains, low dislocation density, two kinds of second phase particles as Zr(Fe,Cr)₂ and Zr₃Fe or Zr(Fe, Cr)₂, and a texture where most of basal poles are oriented toward the direction normal to thickness. Further study is necessary to evaluate basal pole intensity, f<SUB>L</SUB> with high confidence because its small change strongly affects the irradiation growth. The plate shows that higher YS, similar strength and larger elongation in the RD, compared to those in the direction normal to the RD. Welded region shows somewhat lager strength and YS at RT and smaller elongation than matrix. The welded region is concluded to have low residual stress as a results of post-weld anneal and similar hardness as that of matrix.
장입한 수소량이 Zr-2.5Nb 압력관의 K<SUB>1H</SUB>에 미치는 영향
김상재(Sang-jai Kim),김영석(Young-suk Kim),임경수(Kyung-soo Im),송택호(Song-taek Ho) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8
The aim of this study was to obtain a better understanding of delayed hydride cracking (DHC) of Zr-2.5Nb pressure tube with hydrogen concentration. DHC tests were conducted at 280℃ on Curved Compact Tension (CCT) and Cantilever Beam (CB) specimens with 60, 80, 100 ppm H to determine the threshold stress intensity factor, K1H in axial and radial directions of the Zr-2.5Nb tube, respectively. Over a hydrogen concentraion range of 80~100 ppm, K1H for the Zr-2.5Nb tube 5.84 ㎫√m in the axial direction and 8.4 ㎫√m in the radial direction, both of which were constant independent of hydrogen concentraion, However, at 60ppm, K1H increased unexpectedly to a higher value. Based on the results, K1H for Zr-2.5Nb tube is discussed with the fracture surface and a supersaturated concentration of hydrogen.
Better Understanding of Delayed Hydride Cracking in Zr-2.5Nb TUbes
김영석(Kim Young Suk),Soon Sam Park,김성수(Sung Soo Kim),정용무(Yang Moo Cheong),안상복,임경수(Kyung Sao Im) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
This study focuses on the elucidation of delayed hydride cracking (DHC) of zirconium alloys, which has not been clearly understood up to date. DHC tests were conducted on the compact tension (CT) specimens of a CANDU Zr-2.5Nb pressure tube with hydrogen concentration varying from 12 to 100 ppm. DHC tests were conducted on the compact tension specimens of Zr-2.5Nb with hydrogen concentration varying from 12 to 100 ppm. Hydrogen was charged electrolytically into the CT specimens followed by a homogenization treatment. The DHCV for Zr-2.5Nb pressure tube had a temperature dependence with an activation energy of 49 KJ/mol in a temperature range from 144 to 250℃ and decreased with decreasing hydrogen concentration. The threshold stress intensity factor, KIH in the axial direction of Zr-2.5Nb tube also had a dependence of hydrogen concentration: a drastic decrease of KIH to a constant with increasing hydrogen concentration. Thus, DHCV and KIH were nicely described as a function of the supersaturated hydrogen concentration over TSSD independent of temperatures. Based on these results, we propose that KIH is a critical stress intensity factor to nucleate hydrides at the crack tip region, reducing a supersaturated hydrogen concentration at the crack tip region to the equilibrium terminal solid solubility for dissolution (TSSD) at any temperatures. Therefore, we conclude that the gradient of the equilibrium hydrogen concentration or TSSD at the crack tip region and the supersaturated one at the matrix region is a governing factor to initiate DHC.
수소량에 따른 Zr-2.5Nb 압력관의 DHC 속도 및 K<SUB>IH</SUB>
김영석(Kim Young Suk),박순삼(Soon Sam Park),김성수(Sung Soo Kim),정용무(Yong Moo Cheong),임경수(Kyung Soo Im) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
To obtain a better understanding of DHC phenomenon, this study focused on the effect of DHC velocity and threshold stress intensity factor, K1H, of Zr-2.5Nb tubes as a function of hydrogen concentrations. DHC tests were conducted on the compact tension specimens of Zr-2.5Nb with hydrogen concentration varying from 12 to 100 ppm. Hydrogen was charged electrolytically into the CT specimens followed by a homogenization treatment. The DHCV for Zr-2.5Nb pressure tube had an activation energy of 49 KJ/㏖ in a temperature range of 144 and 250℃ and decreased with decreasing hydrogen concentration. The threshold stress intensity factor, K1H in the axial direction of Zr-2.5Nb tube also had a dependence of hydrogen concentration: a exponential decrease of K1H to a constant with increasing hydrogen concentration. Thus, DHCV and K1H were nicely described as a function of the supersaturated hydrogen concentration over TSSD independent of temperatures. Based on these results, we propose that K1H is a critical stress intensity factor to drop a supersaturated hydrogen concentration at the crack tip region to the equilibrium solubility for dissolution at any temperatures. Hence, the lower the initial hydrogen concentration at the matrix region, the smaller a concentration gradient between the crack tip and the matrix region, lowering DHCV.
실험환경과 수소량에 따른 CANDU Zr-2.5Nb압력관의 DHCV 특성
조선영(Sun Young Cho),정용무(Yong Moo Cheong),김성수(Sung Soo Kim),임경수(Kyung Soo Im),김영석(Young Suk Kim) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
Even though CANDU Zr-2.5Nb Pressure tube has been used in the water under the high temperature and pressure, the evaluation of DHCV for the pressure tube has been limited in the air. Therefore, it is necessary for DHCV of real condition such as in the water under the high temperature and pressure to be evaluated. The test was carried out under the simulated condition using the water of 182℃ and 250℃ for the pressure tubes which were saturated at 34ppm and 60ppm with the hydrogen. At each temperature, DHCV in the air was faster than that in the water. In addition, the difference of DHCV between in the air and in the water was increased as the temperature grew up. In terms of safety, DHCV in the water under the high temperature and pressure was conservative as compared with that in the air. The reason why DHCV in the air was different from that in the water under the high temperature and press따e seemed to be due to the corrosion resistance of pressure tube, the formation of the corrosive film at the crack tip and the influence of compression under the high temperature and pressure water.
김상재(Sang-Jai Kim),정용무(Yong-Moo Cheong),오동준(Dong-jun Oh),임경수(Kyung-Soo Im),김영석(Young-Suk Kim) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
The aim of this study was to obtain a better understanding of delayed hydride cracking (DHC) of Zr-2.5Nb pressure tube with crack growth direction. Curved compact tension (CCT) and cantilever beam (CB) specimens were used to determine the DHC velocity in the longitudinal and radial directions, respectively. DHC tests were conducted at 250 oC after charging the specimens with hydrogen to 60ppm H. The DHC velocity of the Zr-2.5Nb tube was anisotropic with crack growth direction: DHCV in the axial direction was 4 times faster than that in the radial direction and the incubation time till the growth of the DHC crack was 5 times faster in the axial direction than that in the radial direction This anisotropic DHC behavior of the Zr-2.5Nb tube with crack growth direction is discussed on the nucleation and growth pattern of hydrides on the cracking plane.
CANDU Zr-2.5Nb 압력관에서 수소화물 재석출 거동
윤여범(Yeo-Bum Yun),김영석(Young-Suk Kim),정현철(Hyeon-Cheol Jeong),임경수(Kyung-Soo Im),김성수(Sung-Soo Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8
The objective of this study is to investigate the reorientation of zirconium-hydrides in the water-quenched and furnace-cooled Zr-2.5Nb tubes with different peak temperatures and applied stress. To this end, cantilever beam (CB) specimens containing 60 ppm hydrogen were subjected to a thermal cycle treatment where the peak temperature changed from 310 to 380 ℃ and stresses were applied at the test temperature of 250 ℃approached by cooling from the peak temperature. The water-quenched CB specimens with a fine distribution of smaller hydrides had an enhanced reorientation of hydrides from the circumferential direction to the radial direction compared to the furnace-cooled CB. Further, the number of reoriented hydride increased remarkably with increasing peak temperature from 310℃ to 380℃. The reoriented hydrides increased with increased applied stress during the thermal cycle. The reorientation behavior of the hydrides ahead of the crack tip is discussed in terms of plastic deformation caused by changing when to apply stress to the CB specimens subjected to a thermal cycle.