Journal
ACTA MATERIALIA
Volume 54, Issue 2, Pages 435-443Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2005.09.015
Keywords
in situ TEM; fatigue crack growth; grain boundary structure; crack closure; pipeline steels
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Microstructural refinement of structural materials generally improves their tensile properties but deteriorates their fatigue properties. However, pipeline steels with ultra-fine acicular ferrite (UFAF) possess not only high strength and toughness, but also a low fatigue-crack-growth rate (FCGR) and long fatigue-propagation life. In this paper, the micro-fracture mechanisms of an UFAF pipeline steel are investigated by in situ tensile testing in a transmission electron microscope. The results indicate that a grain-boundary-film structure composed of martensite/austenite could significantly influence the crack propagating behavior in the UFAF steel, consequently lowering the FCGR by enhancing roughness-induced crack closure during cyclic loading. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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