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최현호 ( Choi Hyunho ),김인배 ( Kim In-bae ),김문옥 ( Kim Moon Ok ) 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.24 No.1
In this study, expansion joint gap data (12,825) of 4,821 bridges are empirically analyzed for identifying influencing factors. From this, it is investigated that joint gap has a much differences depends on bridge types such as steel and con’c and temperature as well known as main influencing factors. However, some factors can be ignored. It is concluded that more detail analysis considering influencing factors is needed to modify design and maintenance standards for expansion joint.
이헌봉,최상헌,김인배 ( Hun Bong Lee,Sang Hyun Choi,In Bae Kim ) 한국열처리공학회 1993 熱處理工學會誌 Vol.6 No.3
Effects of oxide film which is grown by heat treatment on the hydrogen embrittlement (HE) of 17-4 PH stainless steel were investigated. Specimems were tensile tested after catholic hydrogen charging and the behaviors of HE were evaluated from the elongation change. It was found that specimems solution treated at 1040℃ for 1/2hour showed best retardation ability to HE for both aging conditions i.e. 480℃×1hr and 620℃×4hrs. X-ray and Auger study revealed that the major composition of oxide films are Cr₂O₃and CuCr₂O₄.
INCONEL 718 초내열 합금의 열처리에 따른 미세조직 변화
최중환,이기룡,조창용,김인배 ( J . H . Choi,K . R . Lee,C . Y . Jo,I . B . Kim ) 한국열처리공학회 1992 熱處理工學會誌 Vol.5 No.2
Microstructural evolution of wrought Inconel 718 superalloy with different heat treatment conditions was studied. Heat treatment was performed via conventional(CHT), modified(MHT), Merrick(MeHT) and modified Merrick(MMeHT) methods. The size of γ` and γ precipitates which are principal strengthening phases in Inconel 718 superalloy increase in order of CHT, MHT, MeHT. For the case of MMeHT, a coexistence of fine γ` precipitate and very coarse particles due to exess growth of γ which is called bimodal distribution, was observed. CHT gave the finest grain size. (Ti, Nb)C carbide and needle-like δ phase were formed together at grain boundaries for CHT, and were formed both inside and at boundaries of grains for MHT, MeHT and MMeHT. Morphology of partially serrated grain boundaries was developed in all heat treatment conditions except CHT.
최중환,김장량,이상래,김인배,Choi, Joong-Whoan,Kim, Jang-Ryang,Lee, Sang-Lae,Kim, In-Bae 한국재료학회 2000 한국재료학회지 Vol.10 No.7
The effects of RRA treatment on the microstructures and mechanical properties of 7050 Al alloy were investigated by differential scanning calolimetry, transmission electron microscopy, microhardness measurement and electrical conductivity. The hardness of 2nd-step aged specimen at $175^{\circ}C$ was decreased to mimimum value and increased to a peak hardness, and then re-decreased with retrogression treatment. It was found that the hardness of 2nd-step aged specimen was further increased by 3rd step aging treatment($120^{\circ}C$x24h). The initial decrease in hardness during 2nd-step aging was due to the partial dissolution of pre-existing GP zone, the major precipitation hardening phase at T6 condition. It was confirmed that the major precipitation hardening phase at 3rd-step aging was GP zone and η' phase. The electrical conductivity increased continually through 2nd-step and 3rd-step aging treatment. It was conclude that the optium 2nd-step aging condition was at $175^{\circ}C$ for 50min by considering the hardness and electrical conductivity. 7050 AI합금을 RRA 처리하였을 때 경도, 전기전도도 및 미세조직의 변화를 조사하였다. 120도씨에서 24시간 동안 1차 시효처리한 후 175도씨에서 2차 퇴화처리하였을 때 경도값의 변화는 초기에 감소하다가 피크 경도를 보인 다음 다시 감소하였으며, 3차 재시효처리재가 2차 시효처리재 보다 큰 경도값을 나타내었다. 2차 퇴화처리시 초기 경도 감소는 T6의 주 강화상인 GP zone의 부분적인 분해에 의한 것이며, 3차 재시효 처리하였을 때 강화상은 GP zone과 파이상이었다. 120도씨에서 24시간 동안 1차 시효처리한 후 175도씨에서 2차 퇴화처리하였을 때 전기전도도 변화는 퇴화 쵤부터 연속적으로 증가혀였으며, 3차 재시효처리에 의해 2차 퇴화처리시 보다 %IACS가 0.5 ~ 2.7 증가하였다. 3단시효에 의해 T6정도의 강도를 유지하면서 38%IACS값 이상의 전기전도도를 얻을 수 있는 최적 퇴화처리 조건은 $175^{\circ}C$ 50분이었다. 이는 퇴화처리 경도곡선의 극소점 또는 극대점과 무관하며 오히려 약간 과시효 조건이다.
고강도 강판 저항 점용접부 강도 및 파단에 미치는 Paint Baking의 영향
최철영 ( Chul Young Choi ),이동윤 ( Dong Yun Lee ),김인배 ( In Bae Kim ),김양도 ( Yang Do Kim ),박영도 ( Yeong Do Park ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.12
Conventional fracture tests of resistance spot welds have been performed without consideration of the paint baking process in the automobile manufacturing line. The aim of this paper is to investigate the effect of the paint baking process on load carrying capacity and fracture mode for resistance spot welded 590 dual phase (DP), 780DP, 980DP, 590 transformation in duced plasticity (TRIP), 780TRIP and 1180 complex phase (CP) steels. With paint baking after resistance spot welding, the l-shape tensile test (LTT) and nano-indentation test were conducted on the as-welded and paint baked samples. Paint baking increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial interfacial fracture (PIF) to button fracture (BF). Improvement in fracture appearance after LTT is observed on weldments of 780 MPa grade TRIP steels, especially in the low welding current range with paint baking conditions. The higher carbon contents (or carbon equivalent) are attributed to the low weldability of the resistance spot welding of high strength steels. Improvement of the fracture mode and load carrying ability has been achieved with ferrite hardening and carbide formation during the paint baking process. The average nano-indentation hardness profile for each weld zone shows hardening of the base metal and softening of the heat affected zone (HAZ) and the weld metal, which proves that microstructural changes occur during low temperature heat treatment.
자동차 차체용 TRIP강판의 저항 점용접부 Partial Interfacial Fracture 특성에 관한 연구
최철영 ( Chul Young Choi ),김인배 ( In Bae Kim ),김양도 ( Yang Do Kim ),박영도 ( Yeong Do Park ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.2
Resistance spot welding of TRIP780 steels was investigated to enhance understanding of weld fracture mode after tensile shear testing (TST) and L-shape tensile testing (LTT). The main failure mode for spot welds of TRIP780 steels was partial interfacial fracture (PIF). Although PIF does not satisfy the minimum button diameter (4√t) for acceptable welds, it shows enough load carrying capacity of resistance spot welds for advanced high strength steels. In the analysis of displacement controlled L-shape tensile test results, cracks initiated at the notch of the faying surface and propagated through the interface of weldments, and finally, cracks change path into the sheet thickness direction. Use of the ductility ratio and CE analysis suggested that the occurrence of PIF is closely related to high hardness and brittle welds, which are caused by fast cooling rates and high chemical compositions of TRIP steels. Analysis of the hold time and weld time in a welding schedule demonstrated that careful control of the cooling rate and the size of a weld nugget and the HAZ zone can reduce the occurrence of PIF, which leads to sound welds with button fractures (BFs).