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V, Nb 첨가 고강도 대형 H 형강의 부위별 미세조직과 경도 분포
하양수 ( Yang Soo Ha ),정재길 ( Jae Gil Jung ),이영국 ( Young Kook Leet ) 한국열처리공학회 2013 熱處理工學會誌 Vol.26 No.2
Abstract The microstructures and hardness distributions of a large-sized high strength H-sectional steel with both V and Nb were systematically examined. The outer surface of the flange part was composed of martensite and bainite due to faster cooling, and had a high hardness value of approximately 310 Hv. However, the amounts of ferrite and pearlite increased and the hardness decreased with increasing the distance from the outer surface at the flange part, except the inner surface. High hardness value of about 290 Hv was measured at the upper surface of the web part having martensite and bainite. The hardness drastically decreased with increasing the web thickness, and then greatly rose again at the lower surface due to bainite formation caused by fast air cooling. The hardness of the flange part was higher than that of the web part due to the larger amount of low-temperature transformed phases, except for the lower surface of the web part. Nb-rich precipitates of 30 to 50 nm and V-rich precipitates less than 20 nm were observed at both flange and web parts However, the particle size was smaller at the flange part than the web part, resulting in the higher strength of the flange part.
Al-Si-Cu계 AC2B 합금의 최적 용체화 처리 조건
정재길 ( Jae Gil Jung ),박준수 ( June Soo Park ),하양수 ( Yang Soo Ha ),이영국 ( Young Kook Lee ),전중환 ( Joong Hwan Jun ),강희삼 ( Hee Sam Kang ),임종대 ( Jong Dae Lim ) 대한금속재료학회 ( 구 대한금속학회 ) 2009 대한금속·재료학회지 Vol.47 No.4
The precipitates, hardness, and tensile properties of Al-6.2Si-2.9Cu AC2B alloy were investigated with respect to solution treatment time at 500℃. Al(Cu)-Al2Cu eutectic, Si, θ-(Al2Cu), and Q-(Al5Cu2Mg8Si6) phases were observed in the as-cast specimen. With increasing the solution treatment time at 500℃, the Al(Cu)-Al2Cu eutectic and θ-(Al2Cu) phases were gradually reduced and finally almost disappeared in 5 h. The mechanical properties, such as hardness, tensile strength, and elongation, were improved with solution treatment time until about 5 h due to the dissolution of the Al2Cu particles. With further holding time, the mechanical properties did not change much. The solution treated specimens for over 5 h at 500℃ exhibit almost the same tensile properties even after aging at 250℃ for 3.5 h. Accordingly, the optimal solution treatment condition of the Al-Si-Cu AC2B alloy is considered to be 5 h at 500℃.
V-Nb Microalloyed 강의 오스테나이트역에서 복합 탄질화물의 재용해 및 석출 거동
이영국 ( Young Kook Lee ),정재길 ( Jae Gil Jung ),하양수 ( Yang Soo Ha ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.12
Dissolution and precipitation behaviors of complex carbonitrides in austenite of a V-Nb microalloyed steel were quantitatively examined through electrical resistivity measurement and transmission electron microscopy. The electrical resistivity increased with solution treatment temperature up to 1240℃ and then was saturated at 225 nΩm for a holding time of 10 min. The electrical resistivity method was also used to quantitatively measure the isothermal precipitation kinetics of the complex carbonitrides in austenite. Nbrich precipitates were observed in austenite at the early stages of precipitation, but Nb was replaced by V up to the equilibrium amount within the precipitates with further holding time. The time-temperatureprecipitation diagram showed a C-type curve; nose temperature and its incubation time were 900℃ and 100 s, respectively.