Analysis of swelling behaviour of ferritic/martensitic steels

ABSTRACT

Ferritic/martensitic steels show exceptional void-swelling resistance during neutron irradiation compared to conventional austenitic stainless steels, such as Types 316 and 304. Explanations for the difference have been proposed based on the different crystal structures and the different microstructures of the steels. In this paper, swelling behaviour of ferritic/martensitic steels HT9 and modified 9Cr–Mo are analysed to demonstrate how the complicated tempered martensite microstructure determines their excellent swelling resistance. The variation in steady-state swelling rate observed for different heats and different heat treatments is explained in terms of how chemical composition and heat treatment affect the microstructure. Microstructures of these steels are characteristically non-uniform, containing precipitate-rich and precipitate-deficient regions. Swelling resistance increases as number and size of precipitate-deficient regions are reduced by proper heat treatment.

KEYWORDS:

• Ferritic/martensitic steels
• microstructure
• irradiation effects
• void swelling
• heat treatment
• chemical composition

Acknowledgements

Thanks are expressed to the following people who helped in completion of this work: Dr L. K. Mansur for helpful discussions on void swelling theory and for reading and commenting on the manuscript; Dr P. Hosemann for discussions on microstructure and for reading and commenting on the manuscript; Dr K. Ferrell, Dr R. Gold, Dr M. J. Hackett, Dr D. R. Harries, and Dr F. W. Wiffen for reading and commenting on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

Funding was provided by TerraPower LP, Bellevue, Washington, USA.