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7050 Al합금의 가공열처리가 미세조직변화와 피로성질에 미치는 영향
김문호,권숙인 ( M . H . Kim,S . I . Kwun ) 한국열처리공학회 1991 熱處理工學會誌 Vol.4 No.4
The effects of thermomechanical treatments on microstructure and fatigue properties of 7050 Al alloy were investigated. The precipitation kinetics changed to a faster rate due to cold deformation employed in this special TAHA thermomechanical treatments including pre-aging, plastic deformation and two step final-aging. The G.P. zones in the under-aged condition were cut by dislocations and dissolved during the plastic deformation. During the low cycle fatigue, the T6` condition showed cyclic hardening behavior whereas the TMT5, TMT27 and T76 conditions showed cyclic softening at above 0.7% total strain amplitudes. The ΔK_(th) value of TMT27 was improved more than two times, compared with that of T76 condition. The T6` with small shearable precipitates resulted in the markedly high ΔK_(th) value. This is thought to be resulted from dislocation reversibility and roughness-induced crack closure due to planarity of slip.
김명한,권숙인,강춘식,나달주 ( M . H . Kim,S . I . Kwun,C . S . Kang,D . J . Na ) 한국주조공학회 1987 한국주조공학회지 Vol.7 No.3
This paper presents experimental data for the computerization of green sand control. The results can be summarized as follows: 1. To obtain the proper compactability at the mixer, the addtion of moisture is far more efficient than the control of mixing time or addtion of clay. 2. The log R(% clay/% moisture) vs. log compactability curve moves upward as the amount of clay increases and moves downward as the amount of seacoal, dead bentonite or coked seacoal increases. 3. The ratio of dead to initial clay amount or coked to initial seacoal amount is changed according to sand to metal ratio, mainly, and according to pouring temperature, partly, at a shake out time of 12hrs.
기계적합금화로 제조된 Ni-20Cr-20Fe-5Nb 합금에서 PCA로서 H<sub>2</sub>O의 역할과 시효석출거동
김일호,권숙인,이원식,채수원,황선근,김명호,Kim Il-Ho,Kwun S.I.,Lee Won-Sik,Chae S.W.,Hwang S.K.,Kim M.H. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.3
The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.
플라즈마 이온질화한 SACM645 강의 미세조직 및 피로균열 발생의 해석
김경태,권숙인 ( K . T . Kim,S . I . Kwum ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.1
The fatigue crack initiation behavior of plasma ion nitrided SACM645 steel was investigated through the rotary bending fatigue test and residual stress measurement by XRD. It was shown by XRD and EPMA that the plasma ion nitrided surface was composed of γ`(Fe₄N)phase and ε(Fe_(2-3)N)phase, and that the nitrogen atoms existed in Fe matrix in diffusion layer. The OM. SEM and Auger spectroscopy showed that the depth of compound layer, mixed compound and diffusion layer, and diffusion layer was 8㎛, 30㎛ and 300㎛, respectively. However, the microhardness test showed that the depth of hardened layer was 500㎛. The tensile strength of the ion nitrided SACM645 was lower than that of the unnitrided SACM645, and the ion nitrided specimen was fractured without plastic deformation. The nitrided SACM645 showed much poorer low cycle fatigue properties than the unnitrided one. In rotary bending fatigue, the fatigue strength of the ion nitrided SACM645 was higher than that of the unnitrided specimen, and the fatigue crack initiation sites changed by applied fatigue stress levels. The XRD result showed that the ion nitrided SACM645 has the compressive residual stress from surface to 600㎛ deep and the tensile residual stress from 600㎛ to deeper site. It is thought that crack initiation takes place at the point where the total stress of residual stress arid applied stress is maximum.
초내열합금 wide-gap 브레이징부의 미세조직 및 기계적 성질 변화에 미치는 첨가금속분말의 영향
김용환,권숙인,변재원,이원식,Kim Y. H.,Kwun S. I.,Byeon J. W.,Lee W. S. 한국재료학회 2005 한국재료학회지 Vol.15 No.6
The effect of IN738 additive powder on microstructure and mechanical properties of the wide-gap region brazed with BNi-3 filler metal powder was investigated. The wide-gap brazing was conducted in a vacuum of $2\times10^{-5}torr\;at\;1200^{\circ}C$ with various powder mixing ratios of additive to filler powders. The microstructures of the wide-gap brazed region were analyzed by SEM and AES. The region brazed with only BNi-3 filler metal powder had a microstructure consisted of proeutectic, binary eutectic and ternary eutectic structure, while that brazed with a mixture of IN738 additive powder and BNi-3 filler metal powder had a microstructure consisted of IN738 additive powder, binary eutectic of $Ni_3B-Ni$ solid solution and (Cr, W)B. The fracture strength of the wide-gap brazed region was about 680 MPa regardless of the additive powder mixing ratios. Cracks were initiated at the (Cr, W)B and binary eutectic of $Ni_3B-Ni$ solid solution, and propagated through them in the wide-gap brazed region, which lowered the fracture strength of the region.
페라이트기 9Cr 내열강의 크리프-피로손상에 따른 미세조직 및 초음파 비파괴평가
김정석,권숙인,박익근,Kim, Chung-Seok,Kwun, S.I.,Park, Ik-Keun 한국재료학회 2007 한국재료학회지 Vol.17 No.8
The microstructural evolution of ferritic 9Cr-1Mo-V-Nb steel, subjected to creep-fatigue at $550^{\circ}C$, was evaluated nondestructively by measuring the ultrasonic velocity. The variation of the ultrasonic velocity with the fatigue life fraction exhibited three regions. In the first region ($N/N_f$<0.2), a significant increase in the velocity was observed, followed by a slight increase between the fatigue life fractions of $0.2N_f$ and $0.8N_f$, and then a decrease in the final region. The change of the ultrasonic velocity during creep-fatigue was interpreted in relation to the microstructural properties. This study proposes an ultrasonic nondestructive evaluation method of quantifying the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.
보자력 측정에 의한 아공석강 및 공석강의 열처리에 따른 미세조직 평가
변재원,김정석,권숙인,Byeon Jai Won,Kim C. S.,Kwun S. I. 한국재료학회 2004 한국재료학회지 Vol.14 No.8
The microstructures of variously heat treated hypoeutectoid($0.45\%$ carbon) and eutectoid($0.85\%$ carbon) steel were characterized by magnetic coercivity measurement. The effect of spheroidization of cementites on the coercivity was investigated for $0.45\%$ carbon steel. In case of $0.85\%$ carbon steel, microstructural parameters such as prior austenite grain size, phase and pearlite interlamellar spacing were measured along with coercivity to investigate the relationships between them. Prior austenite grain size had little effect on the measured coercivity. Coercivity was observed to be high in order of martensite, pearlite and ferrite phases. The linear decrease of coercivity with increasing pearlite interlamellar spacing was found. The effect of each microstructural factor on the coercivity and the potential of coercivity as a nondestructive evaluation parameter for assessing microstructures of steel products are discussed.
Al-Mg합금의 압연변수에 다른 미세구조의 변화와 고온인장특성
김태규,전채홍,권숙인,박종우 ( Tae Kue Kim,C . H . Jeon,S . I . Kwun,Jong Woo Park ) 한국열처리공학회 1997 熱處理工學會誌 Vol.10 No.2
The effect of alloying elements, precipitate size, its distribution, and dislocation substructure resulted from warm rolling or cold rolling in the superplastic Al-Mg alloy system was investigated. One of the major requirements for fine structure superplasticity is that the grain size should be very small. Fine grain structure is controlled by the dislocation substructure and the dynamic recrystallization during hot or warm working. The recovery of Al-Mg base alloys was constrained resulting in relatively high dislocation density when the alloys were warm rolled. In particular, Al-Mg-Zr alloy exhibited the smallest sub-grain size among Al-Mg alloys containing Mn, Cu, Zr as a third element. The Al-Mg-Mn alloy cold rolled 80% after hot rolling showed the maximun strain rate sensitivity exponent, m, of 0.75 under strain rate of 7.1×10^(-4)/s at 500℃. The elongation of the alloys was limited in spite of high m values due to large dispersoids containing appreciable amount of Fe impurities.
순수 지르코늄의 ECAP공정에서 금형의 변형 및 채널각이 재료의 변형거동에 미치는 영향
권기환,채수원,권숙인,김명호,Gwon, Gi-Hwan,Chae, Su-Won,Gwon, Suk-In,Kim, Myeong-Ho 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.11
Among severe plastic deformation processes, ECAP has drawn much attention due to its advantages including ultra-fine grain size material production. In this paper, ECAP process with pure -Zirconium is investigated due to its applicability to nuclear reactors. The finite element method is employed to investigate the deformation behavior of materials during ECAP process. In particular, effects of process parameters such as die deformation and channel angles on the material behaviors have been investigated. Experimental studies have also been performed to verify the numerical results.