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김정태(Jeong-Tae Kim),지병하(Byung-Ha Chi),강성태(Sung-Tae Kang),석진익(Jin-Ik Suk),김민수(Min-Soo Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
Recently, steam temperature in thermal power plant has been increasing in order to improve the efficiency. Superior high temperature mechanical properties such as creep rupture strength and cyclic fatigue strength are required for materials applied for turbine high and / or intermediate pressure rotor, blades and casing of the advanced steam(ultrasupercritical ; USC) power plant above 593℃. A high strength 9~12% chromium ferritic heat-resistant steels, which contain W and/or Nb, were developed for these applications. This paper reports progress on assessing the required properties such as impact toughness, tensile, shift of fracture appearance transition temperature with long aging treatment, creep, LCF and demonstrates the continued confidence in these materials for potential use for turbine components in the 593℃ steam turbine.
B 첨가 620℃급 터빈 케이싱용 고Cr 페라이트계 주강의 용접성에 미치는 탄소함량의 영향
서원찬(WON-CHAN SEO),방국수(KOOK-SOO BANG),지병하(BYUNG-HA CHI) 한국해양공학회 2008 韓國海洋工學會誌 Vol.22 No.6
Effectsof carbon content on the weldability of B-containing 620℃ grade high Cr ferritic cast steele were investigated. Cast steel with lower carbon content of 0.07% showed lower HAZ hardness because of the formation of lower carbon martensite in HAZ. It also showed less solidification cracking susceptibility in weld metal because of the formation of delta ferrite. However, hot ductility showed no difference between cast steels with lower and higher carbon contents. Cast steel with lower carbon content showed greater HAZ softening after PWHT in the region heated between AC1 and AC3 because of its higher base metal hardness.
원전 터빈로터 중심공 결함 검출을 위한 비파괴 센서 개발 연구
김훈희(Hun-Hee Kim),송성진(Sung-Jing Song),김학준(Hak-Joon Kim),성운학(Un-Hak Seong),지병하(Byung-Ha Chi),박준수(Joon-Soo Park),김동규(Dong-kyu Kim),박대진(Dae-Jin Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Safety and reliability of nuclear power plants is one of important issues. Especially, turbine rotor is important components in nuclear power plants. To insure integrity of turbine rotors, integrated nondestructive evaluation techniques are applied. However, optimization of NDE sensors used in integrates NDE system is required to improve probability of detection. Thus, in this paper, determination of design parameter for eddy current, magnetic flux leakage, and phased array ultrasonic sensors based on simulation technique was performed. In this presented, simulation results with variation of design parameters are presented. And, determine optimized design parameter for PAUT, ECT, MFL sensors will be discuss.
김훈희(Hun-Hee Kim),송성진(Sung-Jing Song),김학준(Hak-Joon Kim),성운학(Un-Hak Seong),지병하(Byung-Ha Chi),박준수(Joon-Soo Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Flaw sizing is very important issue in phased array ultrasonic nondestructive evaluation of materials, components and structures. Especially, cracks are very often encountered in structural components necessitating reliable procedure for determining their size. Therefore, robust and reliable flaw sizing methods are strongly needed. To address such a need, For development of model based flaw sizing method for phased array ultrasonic testing, We need that fabrication of EDM Notches with various size and Simulation of PAUT beam field on cracks using Rayleigh Sommerfeld Integral, Calculation of ultrasonic energy with variation of crack size, Verification of proposed method by the comparison of experimental results. In this paper, principal of flaw sizing methods using PAUT will describe briefly and performance of the methods will be presented
열처리 상태가 10Cr-1Mo-VNbN 주강의 기계적 성질 및 용접성에 미치는 영향
손대영,방국수,이경운,지병하 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.11
Mechanical properties and weldability such as HAZ hardness, cold cracking susceptibility and hot ductility of two differently heat treated 10Cr-1Mo-VNbN cast steels were measured and compared. Because of high hardenability of the cast steel, as-annealed cast steel showed martensitic microstructure and thus had higher hardness than annealed-normalized-tempered cast steel which had tempered martensite. Because the welding electrode used resulted in a high hardness weld metal, both cast steels showed same weld metal cold cracking susceptibility even though the as-annealed cast steel had higher HAZ hardness than the annealed-normalizedtempered cast steel. Both cast steels had excellent hot ductility in high temperature range, indicating no risk of grain boundary liquation cracking in the HAZ. However, the as-annealed cast steel showed an inferior ductility in the intermediate temperature range of 1000~1150℃ because of larger unrecrystallized grain size.
2.25 Cr-1 Mo 강의 템퍼 취화에 미치는 장시간 등온시효의 효과
김동진,김정태,김병훈,공병욱,지병하 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.3
The present research was performed to evaluate the long-term isothermal temper embrittlement resistance and carbide behaviors. The material used in this study is SA336F22, the forged heavy wall 2.25Cr-1Mo steel. Temper embrittlement susceptibility after isothermal aging for 36,000h at 430-515℃ was assessed with the shift of the 50% fracture appearance transition temperature (FATT_(50)), 40ft-lb transition temperature (vTr_(40)) and grain boundary segregation of phosphorus by AES. XRD and TEM-EDS examined the behaviors of carbide. The shift of FATT and vTr_(40) of 2.25Cr-1Mo steel were significantly increased up to 10.000h aging then slowly saturated at 515℃. At lower temperature, however. saturation occurred slowly. The type and composition of carbides were changed to the Mo-rich stable ones(Mo-rich Mo₂C and M_6C), which reduces the Mo content in matrix. And P-segregation was detected on the prior austenite grain boundary after isothermal aging. These results suggested that the temper embrittlement be related with P-segregation caused by Mo-consuming at the matrix.