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Derivation of Q* Parameter for Evaluating Creep Crack Growth Rate of Modified 9Cr-1Mo Steel
I.M.W. Ekaputra,Woo-Gon Kim(김우곤),Jae-Young Park(박재영),Seon-Jin Kim(김선진),Min-Hwan Kim(김민환),Yong-Wan Kim(김용완) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
The concept of the Q* parameter was first proposed by Yokobori et al. The Q* parameter is defined as the exponent of the exponential function in the thermal activation process equation. In this study, the creep crack growth (CCG) behavior of the modified 9Cr-1Mo steel is evaluated using the Q* parameter. The CCG tests were carried out under various loads at 550oC and 600oC. The K and C* parameters have been used to characterize the CCGR of modified 9Cr-1Mo steel. The results show that the K parameter exhibits the largest scatter data, and there is no systematic trend in each series of tests, while C* showed a narrower scattering of data of CCGR than the K parameter. However, C* decreased during the early stage of crack growth and subsequently increased, i.e., a dual value due to the nose appearance, and it did not distinguish among the series of data under various loads at 550oC and 600oC clearly in a one linear line. The Q* parameter was able to evaluate the CCG by a simple monotical linear function without a dual value owing to nose existing in the early stage, and it exhibited an increase or decrease regardless of the testing conditions. The Q* was regarded as an independent parameter that is not depending on stress and temperature, whereas the C* was regarded as a dependent parameter depending on the creep stress and temperature.
Analysis of Creep Behavior of Alloy 617 for VHTR Application
Woo-Gon Kim(김우곤),Jae-Young Park(박재영),I.M.W. Ekaputra,Min-Hwan Kim(김민환),Seon-Jin Kim(김선진),Yong Wan Kim(김용완) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
Creep rupture data were obtained from a series of creep tests with different applied stresses at 850℃, 900℃ and 950℃ of Alloy 617, which is considered as a prime candidate material for the VHTR application. On the basis of the creep experimental data, the analysis of creep rupture behavior was performed using various creep relations and laws such as Norton’s power law, Monkman-Grant Relationships (MGR), Modified Monkman-Grant Relationships (MMGR), creep damage tolerance factor λ, and Zener-Hollomon Parameter (Z), and then the creep constants used in these equations were determined. The MMGR appeared to be more narrowed in data scattering than the MGR, and it followed well a straight line of m ? 1.0 as m=0.97. In the plot of the Z parameter vs. stress, it obeyed a straight line of the slope of n’=5.87 regardless of the three different temperatures. It would be thus inferred that the same creep mechanism was operative within the present stress and temperature ranges, and creep damage tolerance factor of Alloy 617 was found to be 2.40.
Grade 91 강의 모재와 용접재에 대한 천이영역의 크리프 균열 성장 속도 비교
박재영(Jae-Young Park),김우곤(Woo-Gon Kim),I.M.W.Ekaputra,김선진(Seon-Jin Kim),김민환(Min-Hwan Kim) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
This paper presents a comparison of creep crack growth rate (CCGR) in transient regime for Grade 91 base metal (BM) and weld metal (WM). The CCG data for BM and WM were obtained by the CCG tests performed on 1/2 compact tension specimens under various applied loads at 600℃. The CCG rates were obtained using the empirical equation between da/dt and C<SUB>*</SUB> parameter. The B and q values were determined, and the results of normalized time and transient CCGR behaviors were compared for BM and WM.
초고온가스로 압력용기용 Gr. 91 강의 장시간 크리프 수명 예측 방법 개선
박재영,김우곤,김선진,김민환,Park, Jae-Young,Kim, Woo-Gon,EKAPUTRA, I.M.W.,Kim, Seon-Jin,Kim, Min-Hwan 한국압력기기공학회 2014 한국압력기기공학회 논문집 Vol.10 No.1
Gr. 91 steel is used for the major structural components of Generation-IV reactor systems, such as a very high temperature reactor(VHTR) and sodium-cooled fast reactor(SFR). Since these structures are designed for up to 60 years at elevated temperatures, the prediction of long-term creep life is important for a design application of Gr. 91 steel. In this study, a number of creep rupture data were collected through world-wide literature surveys, and using these data, the long-term creep life was predicted in terms of three methods: the single-C method in Larson-Miller(L-M) parameter, multi-C constant method in the L-M parameter, and a modified method("sinh" equation) in the L-M parameter. The results of the creep-life prediction were compared using the standard deviation of error value, respectively. Modified method proposed by the "sinh" equation revealed better agreement in creep life prediction than the single-C L-M method.