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고에너지 전자빔 투사를 이용한 TiC, TiB<sub>2</sub> 및 VC/ 탄소강 표면합금화 연구
유정훈,신기삼,윤재홍,이찬규,허성강,이재현,오준철,이성학,어광준,Yoo, Jung-Hoon,Shin, Kee-Sam,Yoon, Jae-Hong,Lee, Chan-Gyu,Hur, Sung-Gang,Lee, Je-Hyun,Oh, Jun-Chul,Lee, Sung-Hak,Euk, Kwang-Jun 한국재료학회 2002 한국재료학회지 Vol.12 No.12
Surface alloying using TiC, $TiB_2$ and VC ceramic particles on carbon steel has been performed using high voltage electron beam. Each type of ceramic particles was mixed with flux of Al and $MgF_2$ in 1 to 4 ratio. The microstructures of the surface alloyed layers consisted of melted region, interface region. heat affected region and the unaffected matrix. The surface layer of the TiC surface alloyed had a cubed primary and a eutectic type of TiC. $TiB_2$ in surface layer of $TiB_2$ surface alloyed were incompletely melted with$ TiB_2$ particles as observed before the alloying. On the surface layer of the VC surface alloyed, very well defined cell structure was observed with VC on the cell boundary. In addition, ~50 nm in diameter VC particles in high density were ubiquitous in the matrix. Those fine VC particles prominently improved the hardness and wear resistance of the surface layer of the VC surface alloyed.
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 $Ni_{57}Zr_{20}Ti_{18}Si_5$.
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.
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.
피닝 처리에 따른 304 스테인레스 강의 마모 특성 평가 및 미세구조 분석
정진성(Jine-Sung Jung),이한상(Han-Sang Lee),신기삼(Kee-Sam Shin),김선진(Sun-Jin Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
In most case of materials damages were happened at the surface. The various methods for increasing the fatigue life were existed like as the diffusion coating process, flame hardening, surface rolling and shot peening. The peening of these techniques was applied to the various industries during long times. We investigated on the wear properties and micro-structure before and after shot peening. The 304 stainless steel was used as the test materials. Firstly, the optimum peening condition was determined by the Almen intensity and rotary bending fatigue test. Secondly, the surface roughness and residual compressive stresses were evaluated with the stylus and X-ray diffraction equipment. And then, the wear tests were performed on abrasion and solid particle erosion. Finally, the micro-structure of tested specimens was analyzed using by X-ray diffraction, scanning electron microscope and transmission electron microscope. The residual compressive stress was existed to about 70㎛ depth, the wear properties also was increased and the twins were found in micro-structure.
고에너지 전자빔 투사방법으로 제조된 VC / 탄소강 표면합금화 재료의 템퍼링에 의한 경도향상
이성학(Sung Hak Lee),어광준(Kwang Jun Euh),김용찬(Yong Chan Kim),신기삼(Kee Sam Shin),김락준(Nack J. Kim) 대한금속재료학회 ( 구 대한금속학회 ) 2002 대한금속·재료학회지 Vol.40 No.9
This study aimed at improving hardness by tempering of VC/carbon steel surface-alloyed material fabricated by high-energy electron-beam irradiation. The mixture of VC powders and flux (50%MgO-50%CaO) was placed on a plain carbon steel substrate, and then electron beam was irradiated on this mixture using an electron beam accelerator. The surface-alloyed layer of 1.8 mm in thickness was homogeneously formed without defects. The microstructural analysis indicated that VC particles were coarsely formed along solidification cell boundaries, and the matrix inside cells was mostly composed of lath-type martensite and fine cuboidal VC particles. A large amount (10.1 vol.%) of these VC particles in the lath-type martensitic matrix improved hardness four times greater than that of the substrate. When the VC/steel surface alloyed material was tempered, a number of fine VC particles were precipitated in, the tempered martensitic matrix, thereby leading to the additional hardness improvement. Therefore, the hardness of the surface-alloyed layer was further enhanced by tempering, while the residual stress in the layer could be removed and the fracture toughness could be increased.
논문 : 초음파 나노표면개질 공정기술에 의한 AISI304 스테인리스강의 표면나노구조화 및 압축잔류응력 형성
조인식 ( In Shik Cho ),동계령 ( Ji Ling Dong ),유대황 ( Dae Hwang Yoo ),서정화 ( Jung Hwa Suh ),아마노프 ( Auezhan Amanov ),신기삼 ( Kee Sam Shin ),이창순 ( Chang Soon Lee ),편영식 ( Young Shik Pyoun ),박인규 ( In Gyu Park ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.9
In this paper, the Ultrasonic Nanocrystalline Surface Modification (UNSM) surface treatment process was used to induce compressive residual stress and nanocrystalline structure by severe plastic deformation on the UNSM-treated surface. The test results for AISI304 stainless steel demonstrated that the grain size was found to be 23 nm, the dislocation density was increased by 0.2085×10(18) m-2, and the volume fraction of martensite is defined as 27.6% from austenite so that the surface hardness of the surface is increased from 200 Hv up to 515 Hv. The initial tensile residual stress is changed from 300 MPa to a compressive residual stress of 500 MPa after UNSM treatment. In addition, UNSM was applied under five various conditions, and the results of those conditions were defined as a function of depth quantitative.