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Microstructures of the two heats of Modified 9Cr-1Mo steel that exhibit comparable creep strength
but largely different creep ductility were analyzed to identify the factors that can reduce their
creep ductility. The critical difference between the microstructures of the two heats was the size
and distribution of prior austenite grains (PAGs). For the heat with higher creep ductility, the size
of the PAGs was ordinary, approximately 20 μm. In contrast, the microstructure of the heat with
low creep ductility was characterized as a mixture of regions with ordinary-sized PAGs and
extraordinary coarsened PAGs of several hundred micrometers. The creep deformation of the heat
with low creep ductility was found to localize in the regions with ordinary-sized PAGs, which led
to the development of creep cavities and cracks, eventually reducing the creep ductility.

Rights:

• Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International
  

Keyword: ferritic heat-resistant steel, creep ductility, microstructure, EBSD, prior-austenite grain

Date published: 2025-07-15

Publisher: Iron and Steel Institute of Japan

Journal:

• ISIJ International (ISSN: 09151559) vol. 65 issue. 8 ISIJINT-2025-049

Funding:

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.2355/isijinternational.isijint-2025-049

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Updated at: 2025-12-06 12:30:10 +0900

Published on MDR: 2025-12-06 08:33:57 +0900