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석탄화력발전소 보일러 배관용 9Cr-2W계 강의 피로 및 크리프 파단 특성
이연수(Lee Yeon-Soo),유석현(Ryu Seog-Hyun),공병욱(Kong Byeong-Ook),이경운(Lee Kyong-Woon),김정태(Kim Jeong-Tae),백정웅(Baek Jeong-Woong),남수우(Nam Soo-Woo) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
Low cycle fatigue and creep rupture properties have been investigated in welded joint of P92 steels for USC thermal power plant. According to the result of continuous Jow cycle fatigue test, fatigue life of base metal was longer than that of weld metal and HAZ with the temperature range. The fatigue life of creep-fatigue interaction test with 10min. hold time was shorter values by accelerated recovery phenomenon in comparison with continuous low cycle fatigue life. The creep rupture strength of cross weld was lower than that of base metal. Fracture position of cross weld after creep was located between FCHAZ and ICHAZ and change of fracture appearance was occurred from ductile to brittle mode at test temperature of 650℃.
Inconel 740H 니켈기 초내열합금과 TP316H 스테인리스강의 이종금속 SMA 용접부의 미세조직과 크리프 파단 특성
신경용(Kyeong-Yong Shin),이지원(Ji-Won Lee),한정민(Jung-Min Han),이경운(Kyong-Woon Lee),공병욱(Byeong-Ook Kong),홍현욱(Hyun-Uk Hong) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.5
The microstructures and the creep rupture properties of dissimilar welds between the Ni-based superalloy Inconel 740H and the non-stabilized austenitic stainless steel TP316H have been characterized. The welds were produced by shielded metal arc (SMA) welding process with the AWS A5.11 Class ENiCrFe-3 filler metal, commonly known as Inconel 182 superalloy. Postweld heat treatment at 760 ℃ for 4 hours was conducted to form γ΄ strengthener in Inconel 740H. The austenitic weld metal produced by Inconel 182 had a dendritic microstructure, and grew epitaxially from the both sides of Inconel 740H and TP316H base metals. Since both Inconel 740H and TP316H did not undergo any solid-state transformation during welding process, there were no heat-affected-zone (HAZ) sub-regions and the coarsoned grains near the weld interface were limited to a narrow region. The hardness of Inconel 182 weld metal was ~220 Hv. The gradual hardness decrease was detected at HAZ of TP316H, and the TP316H base metal displayed the lowest hardness value (~180 Hv) whilst the Inconel 740H showed the highest hardness value (~400 Hv). Fracture after creep occurred at the center of weld metal, regardless of creep condition. It was found that during creep the cracks initiated and propagated along interdendritic regions and grain boundaries at which Laves particles enriched in Nb, Si and Cr were present. The appropriate design of weld metal was discussed to suppress the creep-induced cracking of the present dissimilar weld.
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.