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Mod.9Cr-1Mo강의 항온변태시 기계적 특성변화에 미치는 Cr탄화물의 영향
허성강,이재현,구지호,신기삼,신종호,Hur, Sung-Kang,Lee, Jae-Hyun,Gu, Ji-Ho,Shin, Kee-Sam,He, Yinsheng,Shin, Jong-Ho 한국재료학회 2012 한국재료학회지 Vol.22 No.1
In this study, mechanical tests and microstructural analyses including TEM analyses with EDX of precipitates in modified 9Cr-1Mo steel were carried out to determine the cause of embrittlement observed after heat-treatment, which limits the usage of the alloy for power plants. Mod. 9Cr-1Mo steel specimens at austenite temperature were quenched to the molten salt baths at $760^{\circ}C$ and $700^{\circ}C$, in which the specimens were kept for 10 min ~ 10 hr with subsequent air-cooling. Impact tests showed that the impact value dropped abruptly when the specimens were kept longer than 30 min at $\sim760^{\circ}C$ reaching to minima in about 1 hr, and then increasing at further retention. The tensile strength of the specimens reached the minimum value without much change afterward, whereas the values of elongation showed the same trend as that of the impact value. The isothermally heat-treated steel at $700^{\circ}C$ also showed a minimum impact value in about 1 hr. These results suggest that the isothermal heattreatment at 760 and $700^{\circ}C$ for about 1 hr induces temporal embrittlement in Mod. 9Cr-1Mo steel. The microstructural examination of all the specimens with extraction replica of the carbides revealed that the specimens with temporal embrittlement had $Cr_2C$, indicating that the cause of the embrittlement was the precipitation of the $Cr_2C$. In addition, TEM/EDX results showed that the Fe/Cr ratio was 0.033 to 0.055 for $Cr_2C$, whereas it was 0.48 to 0.75 for $Cr_{23}C_6$, making the distinction of the $Cr_2C$ and $Cr_{23}C_6$ possible even without direct electron diffraction analyses.
허성강,구지호,신기삼,신종호,Hur, Sung-Kang,Gu, Ji-Ho,Shin, Kee-Sam,He, Yincheng,Shin, Jong-Ho 한국재료학회 2011 한국재료학회지 Vol.21 No.11
It is well known that modified 9Cr-1Mo steel has a low thermal expansion and high thermal conductivity with excellent high temperature properties compared to austenitic stainless steel. For these advantages, the steel is very popular for the boiler tube of thermal power plants. Normalizing is commonly utilized to obtain martensite in this steel, which shows an unusual toughness for martensite. However, some accidents related to this steel have been reported recently, opening the necessity for further study. As a particular behavior of the steel, an abrupt drop of the impact value has been identified upon tempering at 750$^{\circ}C$ for about 1 hour. It is well known that $Fe_3C$ forms during autotempering and turns to $Cr_2C$ at an early stage and then transforms to $Cr_{23}C_6$. In this study, the cause of the abrupt drop of the impact value was investigated with an impact test, microstructural observation, nanodiffraction and phase analyses using instruments such as optical and transmission electron microscopes (TEM) with an extraction carbon replica of the carbides. The analyses revealed that the $M_2C$ that formed when retained for about 1 hour at 750$^{\circ}C$ causes a drastic decrease in the mechanical properties. The sharp drop in mechanical properties, however, disappeared as the $M_2C$ transformed into $M_{23}C_6$ with longer retention.
백남익,허성강,나형용 ( Nam Ik Baik,Sung Kang Hur,Hyung Yong Ra ) 한국주조공학회 1989 한국주조공학회지 Vol.9 No.5
N/A Metal fibers of Al and stainless steel were fabricated by the PDME method and the Taylor process. Tensile strength of metal fiber produced by both the PDME method and the Taylor process was much higher than that of conventionally solidified materials. Utilizing the PDME method, Al fiber with 100㎛ was fabricated under Ar gas atmosphere, and stainless steel fiber with 50㎛ was fabricated under 0.06 Torr vacuum. Continuous fiber of stainless steel was made by the Taylor process and the surface of this fiber was smother than that fabricated by the PDME method.
초초임계압 발전용 소재의 장시간 열처리에 따른 미세조직 변화와 기계적 특성의 상관관계 연구
주성욱,유정훈,신기삼,허성강,이재현,석진익,김정태,김병훈,Joo Sungwook,Yoo Junghoon,Shin Keesam,Hur Sung Kang,Lee Je-Hyun,Suk Jin Ik,Kim Jeong Tae,Kim Byung Hoon 한국재료학회 2005 한국재료학회지 Vol.15 No.1
For the good combination of high-temperature strength, toughness and creep property, $9-12\%$ chromium steels are often used for gas turbine compressors, steam turbine rotors, blade and casing. In this study, the correlation of microstructural evolution and mechanical properties was investigated fur the specimens heat-treated at 600, 650 and $700^{\circ}C$ for 1000, 3000 and 5000 hrs. The microstructure of as-received specimen was tempered martensite with a high dislocation density, small sub-grains and fine secondary phase such as $M_23C_6$. Aging for long-time at high temperature caused the growth of martensite lath and the decrease of dislocation density resulting in the decrease in strength. However, the evolution of secondary phases had influence on hardness, yield strength and impact property. In the group A specimen aged at $600^{\circ}C\;and\;650^{\circ}C$, Laves phase was observed. The Laves phase caused the increase of the hardness and the decrease of the impact property. In addition, the abrupt growth of secondary phases caused decrease of the impact property in both A and B group specimens.
구자민,신기삼,김윤배,배종수,허성강,Koo, Ja-Min,Shin, Kee-Sam,Kim, Yoon-Bae,Bae, Jong-Soo,Hur, Sung-Kang 한국재료학회 2005 한국재료학회지 Vol.15 No.12
PAS(Plasma Activated Sintering) process was tried to apply for the fabrication of BMG(Bulk Metallic Glasses) of $Ni_{57}Zr_{20}Ti_{18}Si_5}\;and\;Ni_{57}Zr_{20}Ti_{18}Si_3Sn_2$ from the as-atomized amorphous powder. Compressive strength for the BMG(bulk Metallic Glasses) of $Ni_{57}Zr_{20}Ti_{18}Si_5$ were lower than those of BMG rods produced by warm extrusion ,or copper mold casting method. Microstructural examination by optical microcope, SEM ana EDS showed that oxidation had occurred during PASintering. In order to prevent the powder from the oxidation during PASintering, Ni coating for $Ni_{57}Zr_{20}Ti_{18}Si_5$ amorphous powder by electroless-plating method was performed. Microstructural examination for Ni coated layers after PASintering indicated that the Ni coating had been so effective to prevent powder from oxidation during PASintering. Sintering behaviors of $Ni_{57}Zr_{20}Ti_{18}Si_3Sn_2$ represent the same as those of $Ni_{57}Zr_{20}Ti_{18}Si_5$.