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SCM440 강의 유도 경화에 미치는 유도코일 이동속도 및 주파수 의 영향에 관한 연구
남기우,신기항,최병철,이금화,박종규 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.5
In this study, microstructure, hardening layer hardness, and case depth were evaluated after induction hardening(IH) of base metal specimen(BM) treated with annealing and quenching-tempering specimen(QT) treated with quenching and tempering. The microstructure after IH was significantly influenced by the microstructure before IH and the induction coil heating movement speed, but the effect of the induction frequency was very small. The hardness of the hardened layer at an induction coil heating movement speed of 15 mm/s or less was more influenced by the microstructure before IH than the induction coil travel speed and induction frequency. The induction coil travel speed has the significantly effect on the case depth, the induction frequency has effect and the microstructure before IH has a small effect.
내부 경화형 구상흑연주철 롤 동체와 넥의 미세조직과 경도에 미치는 탄소 영향
이상묵,신기항,최병철,남기우 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.1
This study was investigated the effect of carbon on the micro-structure and hardness of ductile cast iron roll with internal curing capacity. Spheroidal graphite existed at roll body with rapid cooling, but granular graphite existed at roll neck with slow cooling. The volume fraction of graphite increased at roll body with rapid cooling, That of roll neck with slow cooling decreased, but graphite size increased. The volume fraction of cementite decreased, but volume fraction increased. The cementite size was larger at roll neck than roll body. The hardness was decreased at roll body and roll neck due to volume fraction of cementite. The hardness of roll body was higher than roll neck.
유도경화한 SCM440 강의 잔류응력 깊이에 따르는 무해화 균열 크기 평가
박종규,신기항,최병철,박인덕,남기우 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.4
In this study, the harmless crack size( ) according to the residual stress depth was evaluated using the fatigue limit of SCM440 steel by quenching-tempering(QT) and induction hardening(IH), and threshold stress intensity factor of QT steel. Because the residual stress increased rapidly as the crack depth increased, was determined at the depth of all the crack aspect ratio(As) regardless of Type I-III, and also increased according to the residual stress depth. was minimal at As =1.0 and maximal at As =0.1, but was almost similar on each Type. was small the dependence on As.
유/무기하이브리드 코팅액에 의한 Al6061-T6의 내식 특성
박미향,신기항,최병철,안병현,이금화,남기우 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.4
In this study, the corrosion resistance by salt spray was evaluated using A6061-T6 for an electric vehicle battery pack case coated with an organic/inorganic hybrid solution. The lowest curing temperature of 190 ℃ resulted in significant corrosion and pitting. Meanwhile, no corrosion was observed in the coated specimens at 210 ℃ and 230 ℃ except at 210 ℃ - 6 min and 8 min. The surface of the as-received coating specimen observed by FE-SEM exhibited streaks and dents in the rolling direction, but the coating surface was clean. On the 190 ℃ - 6 min coating specimen, which had a lot of corrosion, rolling streaks spread, and dents were caused by corrosion. The 200 ℃ - 12 min coating specimen did not show corrosion, but it showed an etched surface. In the line profile, Si, the main component of the coating solution, was detected the most, and Ti was also detected. In the coating specimens with salt spray, O increased and Si decreased, regardless of corrosion. The peeling rate by adhesion evaluation was 26 - 87% for the 190 ℃ coating specimen, 4 - 83% for the 210 ℃ coating specimen, and 94 - 100% for the 230 ℃ coating specimen. The optimal curing conditions for the coating solution used in this study were 210 ℃ for 10 min.
역변태 온도 및 시간이 다른 STS316L의 기계적 및 탄성파 특성
도재윤,탁영준,신기항,남기우 한국산업융합학회 2022 한국산업융합학회 논문집 Vol.25 No.6
In this study, the mechanical properties of 80% cold-rolled austenitic 316L stainless steel were evaluated using specimens subjected to reverse transformation at 500–750℃ for 20 minutes and reverse transformation at 700℃ for 2–60 minutes. Also, for the elastic wave obtained from the tensile test, the dominant frequency according to the reverse transformation condition was investigated by time-frequency analysis. The SEM image of the 80% cold-rolled material was transformed into martensite and showed line and cross shapes. The TEM image showed that line shapes were shown at the grain, and grain boundary of martensite. The higher the heat treatment temperature and the longer time, the larger the grain. Tensile strength decreased as the heat treatment temperature and time increased, but elongation increased. Hardness was proportional to tensile strength. This is because the grain with different directions showed the same direction due to reverse transformation. The dominant frequency was decreased and then increased as the temperature and time increased. This is because the direction of the grain is different at a low temperature and the same direction is shown at a high temperature.
윤서현,최병철,신기항,남기우 한국산업융합학회 2023 한국산업융합학회 논문집 Vol.26 No.2
The subway is one of the most common and important means of transportation in modern society. In order to use the subway safely, tracks are necessary, but trains are prone to derailment and collisions. In order for the train to run safely on the track, the fishplate that connects the line connection is used. The damaged railway was a fishplate for connecting subway lines used for 11 years, and damage analysis and countermeasures were presented. Beach marks were observed on both fracture surfaces, and striations appeared at the range of crack propagation. The damaged part is Cr carbide, which has a higher hardness than the base metal, and is judged to be embrittled and destroyed by fatigue. The SM50C fishplate was subjected to a cyclic stress of about 59% of the upper limit of tensile-compression fatigue limit, but inclusions were the cause of failure. In order to prevent fatigue failure of the SM50C steel fishplate, the occurrence of inclusions should be minimized and processed to have a homogeneous structure when manufacturing the fishplate. In addition, compressive residual stress is given through surface modification such as peening to control crack generation. It is necessary to minimize the change in shape that can become a stress concentration part along with accurate fastening of the bolt, and to design the stress distribution to be as uniform as possible.
서브제로 온도 및 시간이 다른 STS316L의 탄성파 특성
이금화,구경희,탁영준,권영국,신기항,남기우,Lee, Gum-Hwa,Gu, Kyoung-Hee,Tak, Young-Joon,Kwon, Yung-Kug,Shin, Ki-Hang,Nam, Ki-Woo 한국산업융합학회 2022 한국산업융합학회 논문집 Vol.25 No.5
In this study, STS316L rolled at five rolling degrees were treated with two types of subzero temperatures for 10, 30, and 60 minutes, respectively, and the dominant frequencies of elastic waves was investigated. The dominant frequency was higher as the subzero temperature was lower and the subzero treatment time was longer at each rolling degree. On the other hand, the dominant frequency was higher as the elongation decreased. In the time-frequency analysis for subzero temperature and time of the specimen with a rolling degree of 33%, the dominant frequency was higher at a subzero temperature of -196℃ than -50℃ regardless of subzero treatment time.