Creep Deformation Behaviour and its Effect on Creep Life and Rupture Ductility of W-Mo-balanced 9Cr Steels

ABSTRACT

The creep deformation behaviour and its effect on the creep life and rupture ductility are investigated for W-Mo-balanced 9Cr steels at 600 °C to 700 °C. The creep life is described as t_r = 1.5/[$\dot{\epsilon }$_min (dln$\dot{\epsilon }$/d$\epsilon$)], where $\dot{\epsilon }$_min and dln$\dot{\epsilon }$/d$\epsilon$ reflect the creep deformation behaviour in the transient and acceleration creep regions, respectively. The creep life is also correlated with the time to minimum creep rate t_m as t_r = gt_m, where g slightly increases with decreasing stress. The logarithm of creep rate linearly increases with strain in the initial stage of acceleration creep region. This is followed by a decrease in dln$\dot{\epsilon }$d$\epsilon$ with strain at high stresses, resulting in ductile failure at large strains, while it is followed by an increase in dln$\dot{\epsilon }$/d$\epsilon$ with strain at low stresses, resulting in rupture at small strains.

KEYWORDS:

• 9cr steel
• w-Mo balance
• time to rupture
• reduction of area
• transient creep region
• acceleration creep region
• creep rate
• minimum creep rate
• time to minimum creep rate
• strain to minimum creep rate

Acknowledgments

The author would like to thank Mr. K. Yokokawa, Mr. O. Kanemaru, Mr. T. Ohba, Dr. H. Kushima and Mrs. H. Miyazaki at NIMS for their assistance in carrying out long-term creep test.

Disclosure Statement

No potential conflict of interest was reported by the author.