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압력용기용 강의 석출거동과 인장특성에 미치는 오스테나이트화온도 및 냉각속도의 영향
신재웅 ( Jae Woong Shin ),이상민 ( Sang Min Lee ),김용진 ( Yong Jin Kim ),이상우 ( Sang Woo Lee ) 한국열처리공학회 2016 熱處理工學會誌 Vol.29 No.1
The effects of austenitizing temperature and cooling rate on precipitation behavior and tensile properties were investigated in an Mn-Mo-Nb-V pressure vessel steel. During austenitizing, it was shown that the austenite coarsening was somewhat suppressed by undissolved NbC. After cooling from austenitizing, the microstructure of all the steels mainly consisted of upper bainite. However, the steel comprised a little lower bainite and martensite in the case of aqua oil quenching from 1000oC, which would be due to increased hardenability by partly dissolved Nb and comparatively large austenite grains. The average size of NbC in austenite at higher temperature was analyzed to be smaller than that at lower temperature because of the more dissolution. It wasfound that the NbC did not grow much during fast cooling from austenitizing. Meanwhile, the NbC grew much during slow cooling, probably due to wide temperature range of cooling and sufficiently long time for NbC to grow.It was conjectured the V precipitates newly formed and/or grew during cooling from austenitizing and during tempering. On the other hand, the formation of NbC was almost completed before tempering and little more precipitated during tempering. Among the tempered steels, the steel which was fast cooled from 1000oC showed the highest tensile strength, which seemed to come from the microstructure of fine upper bainite and some low temperature phases as well as the comparatively fine NbC precipitates. (Received January 4, 2015; Revised January 7, 2015; Accepted January 12, 2015)
신재웅(Shin, Jae-Woong),오상훈(Oh, Sang-Hoon),양원직(Yang, Won-Jik) 대한건축학회 2021 대한건축학회논문집 Vol.37 No.6
Nonlinear time history analyses are frequently carried out for performance-based seismic design. In order to carry out these analyses, the selection of appropriate seismic waves is very important. Since no seismic wave data of the design spectral acceleration level existed in Korea, the seismic wave data of the PEER Center is generally used. However, many of seismic waves selected from the PEER Center seismic wave selection system tend to have predominant short period. Therefore, this study proposes a seismic wave selection method with various predominant periods from the PEER Center seismic wave selection system. This paper introduces the current building seismic criteria for design seismic wave selection and the PEER Center seismic wave selection system, and is investigated the maximum response acceleration distribution using the PEER Center seismic wave selection system and the proposed seismic wave selection method. As a result, the maximum response acceleration of the PEER Center seismic wave selection system was distributed in a specific range of predominant period, and no significant difference of the spectral accelerations was found in before and after the site response analyses. On the other hand, the proposed method was properly distributed in various predominant period domains, and the predominant periods maintained almost the same values after the site response analyses.