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곽재현(Jai-hyun Kwak),진영훈(Young-hoon Jin),김지원(Jiweon Kim),이규영(Kyooyung Lee),신동석(Dongseoug Sin) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
The effect of chemical compositions, microstructure of hot bands and transformation behavior during continuous annealing in TRIP-assisted steels, in conjunction with Al, were investigated by taking into account of transformation behavior and mechanical properties of steels. Transformation behavior of austenite was estimated by dilatation from intercritical annealing to isothermal bainitic transformation. The higher tensile strength of annealed sheets could be obtained by finer microstructure of hot band. Cr, Al and B were useful elements to increase the tensile strength and elongation in 1.2㎬ grade TRIP steel. Since B inhibits the transformation of ferrite from austenite, steel containing Al and B had the maximum volume fraction of untransformed austenite. Al and B addition increased the amount of retained austenite and thinned the shape of austenite lath. The trial of galvanealed and cold rolled steel sheet were done at Kwangyang works POSCO. The tensile strength above 1200㎫ with elongation above 18% could be obtained by 0.27% carbon steel.
박성준(Seong-Jun Park),강전연(Jun-Yun Kang),황병철(Byoungchul Hwang),김성준(Sung-Joon Kim),곽재현(Jai-Hyun Kwak) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
Mechanical properties and microstructure of light-weight steels containing 5wt.% aluminum were investigated. Theses steels were manufactured under continuous annealing conditions. They showed two-phase microstructure composed of ferrite and austenite. Density of the investigated steels were in range of 7.2~7.3/㎤, which was equivalent to 7~8% reduction in density compared with iron. Mechanical properties such as ultimate tensile strength and total elongation showed increase proportional to austenite fraction. Strain-induced martensitic transformation was observed in a composition, which resulted in considerable enhancement of strength and elongation. Mechanical stability of austenite could be controlled by annealing conditions.
논문 : 탄소함량이 다른 경량철강판의 냉간 압연에 의한 파괴기구
한승엽 ( Seung Youb Han ),신상용 ( Sang Yong Shin ),이성학 ( Sung Hak Lee ),김낙준 ( Nack J. Kim ),곽재현 ( Jai Hyun Kwak ),진광근 ( Kwang Geun Chin ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.5
An investigation was conducted into the effects of κ-carbides on the cracking phenomenon, which often occurred in cold-rolled light-weight steel plates. Three kinds of steels were fabricated by varying the C content, and their microstructures and tensile properties were investigated. In the two steels that contained a high carbon content, the band structures of ferrites and κ-carbides that were severely elongated along the rolling direction were well developed, whereas continuous arrays of κ-carbides were formed in the steel that contained a low carbon content. Detailed microstructural analyses of the deformed region beneath the tensile fracture surface showed that the cracks initiated at arrays of κ-carbides or κ-carbides formed interfaces between the band structures, which initiated cleavage fractures in the ferrite bands, while the bands populated with a number of κ-carbides did not play an important role in propagating the cracks. Thus, the minimization of interfacial κ-carbides or κ-carbide arrays by increasing the carbon content was essential for preventing cracking from occurring during cold rolling.
304 스테인리스강에서 석출탄화물이 공식거동에 미치는 영향
곽재현,김관휴 대한금속재료학회(대한금속학회) 1985 대한금속·재료학회지 Vol.23 No.9
In order to investigate the relation between the pitting corrosion and precipitated carbides, the heat treatment of specimens was carried out in two ways: Solution treatment and carbides precipitation treatment. The experiment was focused on the polarization curves of specimens immersed in HCl solution and on the microscopic analysis of the corroded specimens through a potentiodynamic method. It was Found out that the intergranular and pitting corrosion occurred remarkably in 0.1N and 1N HCl solution when carbides were precipitated around the grain boundary of the 304 stainless steel. The intergranular corrosion was noticed in the region of passivation and the pitting was prominent in the region of passivation break-down. The distribution of pits on solution treated 304 stainless steel was random, while that of pits on carbides precipitated specimen was concentrated around the grainboundary in 0.1N and 1n HCl solution. It was ascertained that the pitting resistance of the solution treated 304 stainless steel was better than that of carbidds precipitated specimen.
알루미늄-킬드 저탄소강의 드로잉컵에서 귀생성에 대한 해석
허무영,곽재현 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.10
The formation of the ears on the drawn cups of the annealed low carbon steel was interpreted by the development of the recrystallization textures. The annealing textures depended on the degree of cold rolling reductions. The inhomogeneous textures were developed through the layers of steel sheet. The 4-fold and the 6-fold ears at the drawn cups were related to the {111}//ND fiber orientations, respectively. The assumption that the amount of slip of an active slip system is propotional to the Schmid factor of the slip system was applied to calculate the R value of an orientation. A large strain at 0˚, 90˚, 180˚, 270˚ to the RD on the 4-fold ear was explained by (0˚, 10˚, 0˚) preferred orientation in the texture. A large strain on the 6-fold ear was explained by the development of the orientations near {111}〈110〉.
냉연 강판의 표면 점녹 형성에 미치는 대기환경 및 Cl 이온의 영향
정진환,곽재현,한상호 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.2
Since the pin point rust is the major quality problem of cold rolled steel sheets, the effects of atmospheric conditions and chloride ions on the formation of pin point rust were investigated. To know rust susceptibility, annealed specimens were prepared and placed in the cold rolling plant by everymonth in 1994. Temperature and relative humidity around annealed specimens were continuously measured by using thermohygrograph(model R-704). From the experimental results, the propensity of rust formation was remarkably influenced by absolute humidity which was calculated from the temperature. It was considered that relative humidity was not related to the rust formation When impurities containing water or moisture were deposited on the surface of steel sheets, rust formed preferentially at those sites and then propagated as the form of thin long tubes due to the Cl ions.
미니밀공정에서 저탄소강판의 에지 크랙 방지를 우한 최적 Mn/S 비 및 조압연 전 열처리조건
조경목,정진환,곽재현 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.1
Thin slab-direct hot rolling, called mini-mill process, is expected as a future process for production of low carbon steel sheets. However, there are several problems to be solved in the processing, one of which is edge cracking in low carbon steel sheet. To prevent the edge cracks of low carbon steel sheet, an isothermal preheat treatment was adopted before roughing in the mini-mill process. From the metallurgical viewpoint, the effect of Mn/S ratio on the edge cracks of low carbon steel sheet was investigated as well. It was found that edge cracking of low carbon steels contained 0.4% Mn or higher could prevented with isothermal preheat treatment at 1150℃ for 5 minutes before roughing. Reducing S content below 0.01%, 0.3% of Mn is enough to prevent edge cracks with isothermal preheat treatment at 1150℃ for 3 minutes before roughing. A concept of edge crack index is proposed for more accurate estimation of the total amount of edge cracking as a function of Mn/S ratio in this study.
연속소둔 저탄소강의 미세조직과 r 값에 미치는 Mn 및 열연귄취온도의 영향
조경목,정진환,곽재현,장삼규 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.12
Systematic microstructure control of low carbon steels processed by the continuous annealing could improve formability. In the present study, microstructure evolution including grain size, carbides and MnS(or (Fe, Mn)S) precipitates in hot coiled and annealed low carbon Al killed steel sheets was investigated as the function of Mn content and hot coiling temperature. r ̄-value and mechanical properties were measured to check the formability of the steels. Results showed that increased r ̄-value revealed for the steel containing low Mn and coiled at high temperature due to the coarsened carbides in hot rolled steel sheets. It was found that the improvement of r ̄-value is closely related to the development of high intensity of {222} texture and low intensity of {200} and {110} texture, which were obtained with coarsened carbides during the recrystallization stage. Lowering Mn content might improve the strength of low carbon Al-killed steel as a result of grain refinement by fine Mn-sulfides precipitation. However there exists the lower limit of Mn content of the steels to prevent hot rolled edge cracks and to maintain higher elongation. Optimum Mn content was found about 0.1wt.% for the 0.02wt.%C-0.008wt.%S steels used in this study.