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Sp-Creep 시험에 의한 고온 크리프 특성 평가 기술 개발(ll) - 보일러 헤더 -
백승세,이동환,하정수,유효선,Baek, Seung-Se,Lee, Dong-Hwan,Ha, Jeong-Su,Yu, Hyo-Seon 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.1
For the development of a new creep test technique, the availability of SP-Creep test is discussed for 1Cr-0.5Mo boiler header material. And some results are also compared with those of 2.25Cr- 1Mo steel which widely uses as boiler superheater tube. The results can be summarized as follows. The load exponents(n) obtained by SP-Creep test for 1Cr-0.5Mo steel are decreased with increasing creep temperature and the values are 15.67, 13.89, and 17.13 at 550$^{circ}C$ ,575$^{circ}C$ and 600$^{circ}C$, respectively. The temperature dependence of the load exponent is given by n = 107.19 - 0.1108T. This reason that load exponents show the extensive range of 10∼16 is attributed to the fine carbide such as M$_{23}$C$_{6}$ in lath tempered martensitic structures. At the same creep condition, the secondary creep rate of 1Cr-0.5Mo steel is lower than the 2.25Cr-1Mo steel1 due to the strengthening microstructure composed by normalizing and tempering treatments. Through a SEM observation, it can be summarized that the primary, secondary, and tertiary creep regions of SP-Creep specimen are corresponding to plastic bending, plastic membrane stretching, and plastic instability regions among the deformation behavior of four steps in SP test, respectively.y.
SP-Creep 시험에 의한 고온 크리프 특성 평가 기술 개발(I) - 보일러 과열기 튜브 -
백승세,나성훈,나의균,유효선,Baek, Seung-Se,Na, Seong-Hun,Na, Ui-Gyun,Yu, Hyo-Seon 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.12
In this study, a small punch creep(SP-Creep) test using miniaturized specimen(10${\times}$10${\times}$0.5mm) is described to develop the new creep test method for high temperature structural materials. The SP-Creep test is applied to 2.25Cr-lMo(STBA24) steel which is widely used as boiler tube material. The test temperatures applied for the creep deformation of miniaturized specimens are between 550∼600$^{\circ}C$. The SP-Creep curves depend definitely on applied load and creep temperature, and show the three stages of creep behavior like in conventional uniaxial tensile creep curves. The load exponent of miniaturized specimen decreases with increasing test temperature, and its behavior is similar to stress exponent behavior of uniaxial creep test. The creep activation energy obtained from the relationship between SP-Creep rate and test temperature decreases as the applied load increases. A predicting equation or SP-Creep rate for 2.25Cr-lMo steel is suggested. and a good agreement between experimental and calculated data has been found.
백승세,나성훈,이해무,유효선,Baek, Seung-Se,Na, Seong-Hun,Lee, Hae-Mu,Yu, Hyo-Seon 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.12
Recently the non-destructive test technique which uses the grain boundary etching characteristics owing to the variation of material structures has been proposed. However, during in-serviced GEM test there are a lot of variables such as the changes of temperature and concentration of etching solution, the roughness condition of surface polished etc.. The purpose of this paper is to investigate the influences of these test variables on GEM test results in order to establish a reliable and sensitive of GEM evaluation technique. The experiments are conducted in various solution temperatures, 10$\^{C}$, 15$\^{C}$, 20$\^{C}$, and 25$\^{C}$ and in 70% and 100% concentrations of that, and in various surface roughnesses polished by #800, #2000, and 0.3㎛ alumina powder. Through the test with variables, it is verified that the decrease of temperature and concentration of etching solution and the coarsened surface roughness by not using polishing cloth and powder induce some badly and/or greatly influences on GEM test results like grain boundary etching width(W$\_$GB) and intersecting point ratio(N$\_$i/N$\_$0/). Therefore, to get reliable and good GEM test results, it must be prepared the surface of specimen polished by polishing cloth and 0.3㎛ alumina powder and the saturated picric acid solution having 25$\^{C}$ and be maintained the constant temperature(25$\^{C}$) during GEM test.
초초임계압 보일러 헤더용 P92 강 용접부의 크리프 특성 평가
백승세(Seung-Se Baek),김회현(Hoi-Hyun Kim),박정훈(Jung-Hun Park),권일현(Il-Hyun Kwon),유효선(Hyo-Sun Yu) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
P92 steel weldment scheduled to use for next generation ultra super critical (USC) boiler header is assessed on creep characteristics. The test method to assess local structure of weldment is small-punch creep (SP-Creep) test, which is a kind of micro test proved the availability on evaluation of mechanical property for local structure. The results are compared with that of tensile creep test for same material and SP-Creep test for X20CrMoV121 (X20) steel weldment. The creep properties of P92 steel weldment are clearly superior than that of X20 steel weldment. Overall, the creep resistance of coarse grain HAZ is inferior to the other structures while fine grain HAZ is most superior in the P92 steel weldment. The power law relationships can be obtained for each weldment structure of USC boiler header.
역해석과 소형펀치 시험에 의한 발전설비 용접부의 소성유동특성 평가
백승세(Seung-Se Baek),권일현(Il-Hyun Kwon),김회현(Hoi-Hyun Kim),이동환(Dong-Hwan Lee),양성모(Sung-Mo Yang),유효선(Hyo-Sun Yu) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
SP test has been confirmed the availability, however the application of SP test is hampered because the relation of stress-strain and load-displacement is not determined definitely. This study suggested an evaluation technique of plastic flow characteristic for X20CrMoV121 steel weldment through inverse analysis using SP test and finite element analysis(FEA). From the result, good agreement was found in load-displacement curves obtained from SP test and FEA. Also, The behavior of load-displacement curve from FEA show a rule that load is increase with increasing K(strength coefficient) and displacement is increase with increasing n(work hardening index). From the inverse analysis, true stress-strain curve could be obtained for each local structure of weldment. And the CGHAZ and WM, which showed lower load- displacement behavior, have smaller work hardening index, while FGHAZ have the largest index.