Influence of chemical compositions and creep test conditions on UK R5 creep ductility parameter lambda of W-Mo-balanced 9Cr steel

ABSTRACT

The influence of boron nitride (BN) particles, W and Mo concentrations and creep test conditions of stress, temperature and test duration on the creep ductility parameter λ in UK R5 has been investigated for five heats of W-Mo-balanced 9Cr steel with 1.5% Mo equivalent at 600, 650 and 700 ^oC. With increasing time to rupture t_r, the λ at first decreases only a little bit, then increases for up to a time showing a maximum peak and finally significantly decreases. The BN particles are responsible for the decreases in λ at long times by accelerating the formation of creep voids. The evaluation of creep rupture ductility based on the λ should be restricted to the long-time region at low stresses after reaching a maximum peak in λ, where the λ decreases with increasing t_r mainly by a decrease in total elongation.

KEYWORDS:

• 9Cr steel
• W-Mo balance
• boron nitride
• creep ductility parameter
• total elongation
• time to rupture
• minimum creep rate
• creep void

Acknowledgments

The author would like to thank Dr A. Shibli at European Technology Development, United Kingdom and Dr J. A. Siefert at Electric Power Research Institute, USA for providing documents relating to R5.

Disclosure statement

No potential conflict of interest was reported by the author.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.