TY - JOUR
T1 - Changes in Monkman-Grant relation among four creep regions of modified 9Cr-1Mo steel
AU - Maruyama, Kouichi
AU - Sekido, Nobuaki
AU - Yoshimi, Kyosuke
N1 - Funding Information:
The authors could accomplish the present analyses with the aid of the high quality data reported in NIMS Creep Data Sheet No. 43A and JAEA-Data/Code 2008-030. The authors thank National Institute for Materials Science (NIMS) and Japan Atomic Energy Agency for their publication of the creep data sheets. The authors deeply acknowledge Dr. F. Abe, NIMS, for his critical reading of the present manuscript and for his valuable comments. The present study was financially supported by Japan Science and Technology Agency (ALCA program grant No. JPMJAL1101).
Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2019/3/11
Y1 - 2019/3/11
N2 - The relation of creep rupture life to minimum creep rate, namely Monkman-Grant (MG) relation is examined by using a creep database of modified 9Cr-1Mo steel. The database covers wide ranges of creep rupture life up to 1.2 × 10 5 h and of minimum creep rate down to 7.6 × 10 −8 h −1 . The MG plot exhibits a low overall value of MG exponent (p = 0.85) together with wide scatter of data points at long rupture life. Causes of the low p value and the wide scatter are discussed in the present study paying attention to change in creep curve shape with creep rupture life. There are four regions H, M, L 1 and L 2 showing different creep behavior in the steel. Regional MG relations are examined also in each region. Values of p are less than unity and change among the four regions. The p value is especially low (0.62) in long-term region L 2 . The regional p values less than unity result in the low overall p value of 0.85. The especially low regional value of p in the long-term region causes the wide scatter of data points in the overall MG plot. A modified Monkman-Grant equation (Eq. (29)) is proposed taking account of creep deceleration rate A (=−1/(dln ε˙/dε), where ε˙ and ε are the creep strain rate and the creep strain) in primary creep and creep acceleration rate B (=1/(dln ε˙/dε)) in tertiary creep. The rates characterize shape of a creep curve. The modified equation can explain the difference of p values among the four regions.
AB - The relation of creep rupture life to minimum creep rate, namely Monkman-Grant (MG) relation is examined by using a creep database of modified 9Cr-1Mo steel. The database covers wide ranges of creep rupture life up to 1.2 × 10 5 h and of minimum creep rate down to 7.6 × 10 −8 h −1 . The MG plot exhibits a low overall value of MG exponent (p = 0.85) together with wide scatter of data points at long rupture life. Causes of the low p value and the wide scatter are discussed in the present study paying attention to change in creep curve shape with creep rupture life. There are four regions H, M, L 1 and L 2 showing different creep behavior in the steel. Regional MG relations are examined also in each region. Values of p are less than unity and change among the four regions. The p value is especially low (0.62) in long-term region L 2 . The regional p values less than unity result in the low overall p value of 0.85. The especially low regional value of p in the long-term region causes the wide scatter of data points in the overall MG plot. A modified Monkman-Grant equation (Eq. (29)) is proposed taking account of creep deceleration rate A (=−1/(dln ε˙/dε), where ε˙ and ε are the creep strain rate and the creep strain) in primary creep and creep acceleration rate B (=1/(dln ε˙/dε)) in tertiary creep. The rates characterize shape of a creep curve. The modified equation can explain the difference of p values among the four regions.
KW - Creep curve
KW - Creep rupture life
KW - Grade 91 steel
KW - Minimum creep rate
KW - Multi-region creep modelling
KW - Omega creep curve equation
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U2 - 10.1016/j.msea.2019.02.003
DO - 10.1016/j.msea.2019.02.003
M3 - Article
AN - SCOPUS:85061379589
VL - 749
SP - 223
EP - 234
JO - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
JF - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
SN - 0921-5093
ER -