Kyu Seop Park*, Fujimitsu Masuyama** and Takao Endo*
* Faculty of Engineering, Yokohama National University, Yokohama 240-8501 ** Nagasaki Research & Development Center, Mitsubishi Heavy Industries, Ltd., Nagasaki 851-0392Creep behavior of a Mod.9Cr-1Mo steel statically aged under various conditions has been analyzed using the Omega method. The aging temperature and time are between 873 and 948 K, and between 100 and 10000 h, respectively. Tertiary creep was expressed by the following equation;
ln ε=ln ε0+Ωε,
where ε0 is the imaginary initial creep rate and Ω is the strain rate acceleration factor. The imaginary initial creep rate was expressed as a function of aging time, ta and aging temperature, Ta as follows;
ε0=Aa·tntaa·exp (−Q0a/RTa)·σna0·exp (−Qa/RT),
where the values of Aa, nta, Q0a, na and Qa are 1.02×103 s−1, 0.19, 52 kJ/mol, 13.0 and 623 kJ/mol in this order.
Behavior of primary creep was approximated by a logarithmic creep equation containing two parameters, which were correlated with the imaginary initial creep rate. Consequently, creep life was estimated from a knowledge of imaginary initial creep rate. It was found that the calculated creep life from the modified Omega method in which primary creep was taken into account, agreed well with the measured one.
aging, modified 9chromium-1 molybdenum steel, creep life, Omega method, creep behavior