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18 Ni 마르에이징 강의 기계적 성질에 미치는 Mo 첨가량의 영향
김학모,김인배,박세윤 ( Hak Mo Kim,In Bae Kim,Se Yoon Park ) 한국열처리공학회 1991 熱處理工學會誌 Vol.4 No.3
Effects of Mo content and aging conditions on the amount of retained austenite and mechanical properties of 18 Ni maraging steels were investigated. Maraging steels were fabricated with variation of Mo content, 3, 5, 7, 9% and heat treated by austenitizing at 840℃ for 1 hour and then aged at 480℃ for 0.5∼100 hours. It was found that the amount of retained austenite after aolution treatment was negligible up to 5% Mo. 8 and 11 volume percents of retained austenite were obtained with 7 and 9% Mo respectively. The maximum hardness and yield strength without great loss of impact toughness were attained in the range of 4∼8 hours of aging time at 480℃ with 5% Mo. It was concluded, as a result, that the optimum Mo content for the good combination of strength and toughness is to be 5% Mo.
18Ni 마르에이징 강의 기계적 성질에 미치는 시효처리의 영향
김학모,김인배,박세윤 ( Hak Mo Kim,In Bae Kim,Se Yoon Park ) 한국열처리공학회 1991 熱處理工學會誌 Vol.4 No.1
Effects of aging treatment on the mechanical properties of a 18 Ni maraging steel were investigated by considering the reverted austenite. Specimens were heat treated by austenitizing at 840℃ for 1 hr and then aged for various times at 480℃ and 520℃. The main results obtained are as follows : 1) The amounts of reverted austenite are increased up to about 4% at 480℃ and about 22% at 520℃ with 1 to 48 hrs aging time. 2) Decreasing tendencies of impact energy and fracture toughness with increasing aging time are diminished after aging for 2 hrs at two aging temperatures of 480℃ and 520℃. 3) Peak hardness and yield strength are obtained after aging for 4 hrs at 480℃ and 2 hrs at 520℃ respectively. From the above results, it was concluded that the optimum aging condition with which showed good strength and toughness combination are given to be 480℃ for 4 hrs and 520℃ for 2 hrs.
김대상(Dae Sang Kim),김웅진(Ung-Jin Kim),성근열(Keun-Yeol Sung),김학모(Hak-Mo Kim) 한국산학기술학회 2018 한국산학기술학회논문지 Vol.19 No.9
본 연구에서는 교대에 작용하는 수평력을 저감시키는 총 11 케이스의 설계에 대한 건설비 분석을 실시하였다. 역T형 교대의 뒤채움재 개선과 토목섬유 보강재를 이용하여 교대를 보강한 철도용 보강 교대(Reinforced Abutment for Railways) 적용을 고려한 2종류의 교대 형식에 대하여 검토하였다. 첫 번째 종류의 경제성 분석에서는 역T형 교대의 배면 뒤채움 재료의 내부 마찰각을 35°에서 40°와 50°로 증가시키는 케이스를, 두 번째 종류의 경제성 분석에서는 토목섬유를 적용한 철도용 보강 교대 설계 케이스에 대한 경제성을 비교 분석하였다. 뒤채움 재료의 개선을 통해 내부 마찰각을 40° 혹은 50°로 적용할때 교대에 가해지는 수평토압은 하중 조건에 따라 18∼48% 까지 감소하였으나 교대 건설 비용 저감효과는 2.0∼3.9%로 크지 않았다. 그러나, 철도 교대 구조로서 토목섬유 보강 교대를 적용한 결과 교대에 작용하는 수평력을 이론적으로 0까지 저감시킬 수 있어 교대 벽체 두께, 저판 길이 및 말뚝 기초의 수 및 재질 변경으로 최대 30%까지 건설비 저감 효과가 있는 것으로 검토되었다. This study evaluated the construction costs of 11 design cases to decrease the horizontal forces applied to an abutment. They include two kinds of abutment types, which are used to improve the backfill materials for reversed T-shaped abutment and geosynthehtic reinforced abutment for railways (RAR). In the first economic analysis, the internal friction angles of the backfill materials were increased from Φ=35° to Φ=40° and 50° for a reversed T-shaped abutment. The second analysis examined cases with the design of a geosynthehtic RAR. When the friction angles were 40° or 50° after improvement of the backfill material, the reduction in the construction cost of the abutment was not as large (2.0-3.9%), even though the horizontal forces on the abutment were decreased by 18-48%. However, in the case of applying the RAR, a maximum cost reduction of 30% was achieved by decreasing the horizontal force to zero. The cost reduction results from the decreased wall thickness, base slab size, and the number of pile foundations for the abutment, as well as changing the material.