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이호진(H. J. Lee),정신웅(S. W. Jeong),남원종(W. J. Nam) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.10
The Increase of drawing speed has been required in order to improve the productivity in wire industries. However, the occurrence of delamination limits the increasing drawing speed of steel wires. In this study, two specimens with the same drawing schedule but the different drawing speed examined to analyze the mechanism of delamination. The increase of drawing speed accelerated the delamination of steel wires. Strain ageing behavior was investigated using DSC (Differential Scanning Calorimetry) and the distribution of residual stress was also investigated by using XRD.
극저온 압연 및 온간 압연 기술을 이용한 고강도 및 고연성 5052 알루미늄 제조
정신웅(S. W. Jeong),강의구(U. G. Kang),남원종(W. J. Nam) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
The effects of deformation temperatures and post-deformation annealing on mechanical properties, in conjunction with microstructural evolution in the 5052 AI alloy, were investigated. The combination of cryogenic rolling with warm rolling effectively increased tensile strength and yield strength without the decrease of ductility through the formation of ultra fine grains with dynamic recovery in the 5052 Al alloy. And static annealing, as a post heat treatment, enhanced the ductility. Therefore, ultra-fine grained 5052 Al alloy with high strength and a moderate level of ductility could be made by the combination of cryogenic rolling with warm rolling and the additional static annealing process.
고강도 강선의 신선 가공량과 열처리 조건에 따른 시효 거동 및 딜라미네이션 발생에 미치는 영향 분석
정신웅(S. W. Jeong),박정훈(J. H. Park),남원종(W. J. Nam) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
The effects of drawing strains and post-deformation annealing conditions on the aging behavior and the occurrence of delamination in cold drawn hyper-eutectoid steel wires were studied. At low annea-ling temperatures the increased tensile strength for a short annealing time would be attributed to age hardening, which came from the decomposition of the unstable cementite in deformed pearlite. The decrease of tensile strength at the high annealing temperature was due to age softening, which would be attributed to the decreased carbon content in lamellar ferrite through the spheroidization or the re-precipitation of cementite, and recovery or recrystallization of ferrite. The extent for the occu-rrence of delamination during annealing expanded to the high temperature region with the increased amount of deformation in steel wires. At high annealing temperatures, the decreased carbon content dissolved in lamellar ferrite due to age softening would result in the decrease of tensile strength and suppress the occurrence of delamination. The total magnitude of carbon content dissolved in lamellar ferrite either by the partial dissolution of lamellar cementite during wire drawing or by the partial decomposition of lamellar cementite during post-deformation annealing would control the occurrence of delamination in cold drawn steel wires.
탄소 함량에 따른 펄라이트의 변태거동 및 기계적 특성 분석
정신웅(S. W. Jeong),강의구(U. G. Kang),남원종(W. J. Nam) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
During the isothermal transformation, the volume fraction of pro-eutectoid ferrite does not follow the lever rule expressed in the equilibrium phase diagram. Thus, the carbon content in the pearlite varies with the heat treatment conditions. Since carbon content in pearlite is varied with chemical compositions and heat treated conditions, the variation of microstructural features such as volume fraction and the thickness of the cementite should be considered even at the same interlamellar spacing. Thus, the variations of microstructural features with carbon content and transformation temperatures were investigated, correlating with the variations of mechanical properties. In eutectoid steels, interlamellar spacing increases with the increase of transformation temperatures. But, interlamellar spacing does not seem to correlate with the increase of austenitizing temperature. The effect of increasing transformation temperatures resulted in the decrease of strength and the increase of ductility.