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논문 : 고 Mn계 TWIP 강의 미세조직과 기계적 성질
정종구 ( J. K. Jung ),이오연 ( O. Y. Lee ),박영구 ( Y. K. Park ),김동은 ( D. E. Kim ),진광근 ( K. G. Jin ),김성규 ( S. K. Kim ),송기홍 ( K. H. Song ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.10
The austenitic Fe-Mn alloys have received considerable attention as a possible candidate for the automotive structural materials due to their high strength and high formability with high elongation. This research investigates the effect of alloying elements on the phase transformation, deformation behavior and mechanical properties in high Mn steels for the development of a high strength high ductility steel. The mechanical stability of austenitic phases is very important for high ductility and it depends largely on the composition of carbon, manganese and aluminum. The dominant deformation mode shifts from TRIP to TWIP mode as the amount of C, Mn and Al is increased. Especially, even a small amount of Al addition facilitates significantly TWIP deformation due to the increase of stacking fault energy in Fe-Mn alloys, this leads to increase the ductility and also decrease the crack sensitivity.
Ti-Ni-B 형상기억합금의 마르텐사이트변태 및 인장변형거동에 미치는 열처리의 영향
이오연,박영구,안행근 ( O . Y . Lee,Y . K . Park,H . K . Ahn ) 한국열처리공학회 1995 熱處理工學會誌 Vol.8 No.1
The purpose of this study is to investigate the effect of heat treatments on the martensitc transformation and tensile deformation behavior in Ti-Ni-B alloys with various boron concentration. Three types of heat treatment are given to the specimens; i) solution treatment ii) aging iii) thereto-mechanical treatment. In solution treated specimens, R-phase transition which is related to abnormal increase of electrical resistance prior to martensitic transformation has been formed at a boron content of 0.2at% and the M, temperature has been decreased with the increasing of boron content. However, It has not been affected by aging, while that of thereto-mechanically treated specimens has been remarkably increased in the vicinity of recrystallization temperature. The thereto-mechanically treated specimen has showed a good thermal fatigue characteristics, shape memory effect and superelasticity in comparison with the solution treated specimen.
Ti-Ni-Cu 형상기억합금의 상변태 및 초탄성에 미치는 가공열처리의 영향
이오연,박영구,쳔병선 ( O . Y . Lee,Y . K . Park,B . S . Chun ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.4
Transformation behavior and superelastic behavior of Ti-Ni-Cu alloys with various Cu content has been investigated by means of electrical resistivity measurement, X-ray diffraction, tensile test and transmission electron microscopy. Two types of heat treatment are given to the specimens : i) Solutions treatment. ii) thermo-mechanical treatment. The transformation sequence in solution treated Ti-Ni-Cu Alloys substituted by Cu for Ni up to 5at.% occurs to B2◎B19` and it proceeds in two stages by addition of 10at.%Cu, i. e, B2◎B19◎B19`. Also, it has been found that Ti-30Ni-20Cu alloy transformed in one stage : B2◎B19. The thermo-mechanically treated Ti-47Ni-3Cu alloy transformed in two stages : B2◎rhomboheral phase◎B19`, while transformation sequence in Ti-45Ni-5Cu and Ti-40Ni-l0Cu alloy transformed as same as solution treated specimens. The critical stress for inducing slip deformation in solution treated and thermo-mechanically treated Ti-40Ni-l0Cu alloy is about 90㎫ and 320㎫ respectively.
Cu-Zn-Al 형상기억 합금의 열사이클에 따른 집합조직의 변화에 관한 연구
홍대원,박영구 ( D . W . Hong,Y . K . Park ) 한국열처리공학회 1992 熱處理工學會誌 Vol.5 No.3
The shape memory effect results from the martensite transformation of each individual grain. Thus it is necessary to study the texture and its variation. In this study the change of texture during thermal cycling and it`s effect on shape memory ability are investigated. The major component of the rolling texture in the parent phase is identified (001)[110], and minor components are (112)[110], (111)[112]. {hkl}<100> fiber texture is developed at 45° from rolling direction. In the case of martensite phase, it is estimated that the major component is (011)[100] and the minor components are (105)[501], (010)[101] and (100)[001]. According to thermal cycling, severity of texture, especially (001)[110] component in parent phase and (011)[100] component in martensite phase are increased. The shape memory ability is increased with increase of thermal cycles and also increased as the direction of specimen approach to 45° from rolling direction. After first thermal cycling the temperature of transformation can be define clearly and Ms and As are raised by thermal cycling.
4~8%Mn 열연 TRIP강의 잔류오스테나이트 생성과 기계적 성질
김동은,박영구,이오연,진광근,김성주,Kim D. E.,Park Y. K.,Lee O. Y.,Jin K. G.,Kim S. J. 한국재료학회 2005 한국재료학회지 Vol.15 No.2
The aim of this research is to develop the TRIP aided high strength low carbon steels using reverse transformation process. The $4\~8\%$ Mn steel sheets were reversely transformed by slow heating to intercritical temperature region and furnace cooling to room temperature. The stability of retained austenite depends on the enrichment of carbon and manganese by diffusion during the reverse transformation. The amount of retained austenite formed after reversely transformed at $625^{\circ}C$ for 6 hrs was about $50\;vol.\%$ in the $8\%Mn$ steel. The change in volume fraction of retained austenite with a holding temperature was consistent with the changes in elongation and the strength-ductility combination. The maximum strength-ductility combination of 40,000 $MPa{\cdot}\%$ was obtained when the $8\%Mn$ steel reversely transformed at $625^{\circ}C$ for 12 hrs. However, it's property was significantly decreased at higher holding temperature of $675^{\circ}C$ resulting from the decrease of ductility.
우기도,박영구,김석원,진영철,류재화,나종필 ( K . D . Woo,Y . K . Park,K . W . Kim,Y . C . Jin,J . H . Ryu,J . P . Ra ) 한국열처리공학회 1998 熱處理工學會誌 Vol.11 No.2
N/A The graphitization is affected by the addition of small amount of the elements, such as Si, Al, Ni, B, Cr and Mn etc. Boron is well known as the most effective element for the graphitization of cementite in high carbon steels. But a study on quantitative analysis of B effect on the graphitization is few reported. Therefore the effect of boron addition in Fe-0.65%C-1.0%Si-0.5%Mn steels on the graphitization is investigated quantitatively using hardness tester, optical microscope and scanning electron microscope, neutron induced microscopic radiography. The graphitization in high carbon steels is promoted with 0.003∼0.005%B addition. But the graphitization in steels which has no boron takes long holding time at 680∼720℃. The hardness of quenched steel containing 0.003%B is higher than that of 0.005%B added steel due to complete dissolution of fine graphites into the austenite. The 0.003%B added high carbon steel graphitized at 680℃ for 25hr is useful steel for the agricultural implements and automobile parts which needed a good formability and high hardness.
Ti-Nb-P 첨가 극저탄소 고강도 강판의 기계적 성질과 연성-취 천이거동
박종재,이오연,박영구,한상호,진광근,Park J. J.,Lee O. Y.,Park Y. K.,Han S. H.,Chin K. G. 한국재료학회 2004 한국재료학회지 Vol.14 No.12
The purpose of this research is to investigate the mechanical property and ductile-brittle transition temperature of Ti-Nb-P added extra low carbon interstitial free steel having a tensile strength of 440 MPa. The mechanical property and transition temperature of hot rolled steel sheets were more influenced by the coiling temperature rather than by the small amount of alloying element. Further, at the same composition, the property of the specimen coiled at low temperature was superior to that obtained at higher coiling temperature. The fracture surface of 0.005C-0.2Si-1.43Mn steel coiled at $630^{\circ}C$ showed a ductile fracture mode at $-100^{\circ}C$, but coiling at $670^{\circ}C$ showed a transgranular brittle fracture mode at $-90^{\circ}C$. The galvannealed 0.006C-0.07Si-1.33Mn steel sheet annealed at $810^{\circ}C$ has tensile strength and elongation of 442.8 MPa and $36.6\%$, respectively. The transition temperature of galvannealed 0.006C-0.07Si-1.33Mn steel sheet was increased with a drawing ratio, and the transition temperature of the galvannealed 0.006C-0.07Si-1.33Mn steel was $-60^{\circ}C$ at a drawing ratio of 1.8
박영구,우기도,이창희,류재화,나종필 한국열처리공학회 1999 熱處理工學會誌 Vol.12 No.2
The graphitization is affected by the addition of small amount of the elements(such as Si, Al, Ni, B, Cr and Mn etc.) and the pre-treatment(such as cold rolling). Boron is well known element to accelerate the graphitization of cementite in high carbon steels. Also, cold rolling is known to accelerate the graphitization. But the graphitization nucleation mechanism by cold rolling is few reported. Therefore the effect of cold rolling in Fe-0.5%C-1.0%Si-0.47%Mn-0.005%B steel on the graphitization is investigated quantitatively using hardness test, optical microscope and scanning electron microscope, neutron induced microscopic radiography. The nucleation of graphite in cold-rolled Fe-0.5%C-1.0%Si-0.47%Mn-0.005%B steel is formed at void which is formed at pearlite/pearlite boundary by cold rolling. But the effect of cold rolling on graphitization in boron addition steel is more effective than that of no boron addition steel due to segregation of BN at void in boron addition steel.