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남찬희(C. H. Nam),진호태(H. T. Jin),손일헌(I. H. Son),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
In this paper, two-dimensional finite element approach of prediction the plastic deformation of tiny pinhole defects on the initial bloom surface, which were formed during continuous casting process of the base material of bloom. The initial pinhole shapes of which plastic deformations are to be traced are assumed V-shaped and U-shaped. Two different kinds of pass schedule of consecutive rolling stages are assumed to investigate the defect closing or lapping behaviors, i.e., one pass schedule of two forward rolling stages and another pass schedule of reverse rolling stage after forward rolling stage. The dimensions of the processes and the sizes of pinholes are also assumed to reflect the actual three-dimensional rolling processes. It has been shown that most plastic deformation occurs at the entry side and lapped or closed defects slightly open when they pass through the exit side. It is noteworthy that the reverse rolling decreases the lapped defect formed in the previous pass, implying that there exists an optimized pass schedule design to minimize the surface defect.
ECAP-Conform을 활용한 연속 하이브리드 공정 개선
주호선(H. S. Joo),황선광(S. K. Hwang),백현무(H. M. Baek),임용택(Y. T. Im),손일헌(I. H. Son),배철민(C. M. Bae) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.10
A continuous hybrid process is combined with wire-drawing, equal channel angular pressing (ECAP) and rolling process as a continuous severe plastic deformation technique to manufacture high-strength wires. In this study, ECAP Conform process was applied instead of ECAP and rolling processes in the continuous hybrid process to improve applicability of the process. The round groove in the feeding roll of the ECAP-Conform was used to manufacture circular shape wires. For verification of the designed process, finite element analysis was carried out with various shear friction factors of the workpiece with the given feeding roll and dies. This approach could be helpful in reducing the roll jumping and buckling involved with the continuous hybrid process.
남찬희(C. H. Nam),이민철(M. C. Lee),손일헌(I. H. Son),전만수(M. S. Joun) 한국소성가공학회 2014 한국소성가공학회 학술대회 논문집 Vol.2014 No.10
In this paper, plastic deformation of tiny initial defects on initial material surfaces is simulated using finite element method. First, the difficulty of the simulation is discussed from standpoint of mesh generation and remeshing. 2D predictions are compared to 3D predictions to supply a proper model for engineering solutions. The reason of the difference between axi-symmetric defect, that is, a ring-type and a cone-type defect is discussed. Cone-type defect and its variants in upsetting are traced to reveal their similarity and/or hetereogeneity with ring-type defect which can be traced by axi-symmetric approach. Based on the predictions and their discussions, a proper 2D analysis model is proposed for revealing the effect of surface defect on the product quality.
블룸 압연공정 중 외부 기공의 압착에 의한 열연코일 결함 길이의 근사적 예측
남찬희(C. H. Nam),엄재근(J. G. Eom),이민철(M. C. Lee),손일헌(I. H. Son),전만수(M. S. Joun) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
In this paper, three-dimensional finite element approach of predicting the plastic deformation of tiny pinhole defects on the initial bloom surface, which are supposed to be formed during continuous casting process of the base material of bloom. The initial pinhole shapes of which plastic deformations are to be traced are assumed U-shape, based on the observation of pinholes found in the literature. The surface defect closing phenomena are simulated until defects are almost closed and assumption of uniform contraction is utilized to estimate the surface line defect.
고탄소강 온간공형압연의 초기조직에 따른 기계적 성질 고찰
오영석(Y. S. Oh),손일헌(I. H. Son),정경환(K. H. Jung),김동규(D. K. Kim),이덕락(D. L. Lee),임용택(Y. T. Im) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
It is well known that the ultrafine-grained steels, which guarantee both high strength and toughness, were manufactured by warm caliber rolling (WCR) owing to the continuous severe plastic deformation (SPD) technique. In this study, the effect of initial microstructure on the strength and toughness was investigated after WCR of the high carbon steel. The experiments were carried out with two kinds of starting microstructures. For comparison, the reference microstructure of austenite phase was prepared and assumed to be the case of conventional hot rolling. The experiments were conducted at the temperature of 500℃ and the accumulative reduction in area was about 83%. Based on this study, it was found that the product of WCR showed better mechanical properties in terms of strength and toughness compared to the conventional hot rolling. The improvement of strength and toughness was attributed to the grain refinement and delamination of lamellar structure consisting of ferrite and cementite, respectively.
황선광(S. K. Hwang),백현무(H. M. Baek),주호선(H. S. Joo),김신회(S. H. Kim),임용택(Y. T. Im),손일헌(I. H. Son),배철민(C. M. Bae) 한국소성가공학회 2013 한국소성가공학회 학술대회 논문집 Vol.2013 No.10
In this work, a multi-pass continuous hybrid (CH) process is designed and its practicality is investigated for manufacturing high performing low-carbon steel wires in a continuous way. For this purpose, the multi-pass CH process was experimentally set up and applied up to five passes with route A at room temperature and was compared with those for the multi-pass wire drawing(WD) process. According to the present investigation, the grain-refined wires, which have many well defined high angle grain boundaries, with the enhanced ultimate tensile strength and comparable ductility were successfully produced by the five-pass CH process compared to the WD process. In addition, the fatigue limit of the specimen produced by the CH process was enhanced due to the grain-refined microstructure of the specimen compared to the one of the WD process. Based on these observations, it was found that the multi-pass CH process can effectively produce a fine-grained wire with enhanced mechanical properties compared to the WD process.
이정완(J. W. Lee),황선광(S. K. Hwang),백현무(H. M. Baek),임용택(Y. T. Im),손일헌(I. H. Son),배철민(C. M. Bae) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.10
In this study, an asymmetric drawing process is designed as a new process to manufacture high-strength wires. It is the same process with conventional wire-drawing except for geometry of drawing dies. To compare the asymmetric drawing and wire-drawing, three-dimensional finite element analyses were carried out. Effective strain of the asymmetric drawing was higher than the one of the wire-drawing. For verification of the designed process, experiments of the asymmetric drawing and wire-drawing with the same reduction of area per each pass were conducted with low carbon steel. Tension test results showed that UTS value of the drawn wires by the asymmetric drawing was higher than the one of the conventional wire-drawing. This result indicated that the asymmetric drawing process could manufacture high-strength wires compared to the conventional wire-drawing.