Retardation of Small Creep-Fatigue Crack in Gr. 91 Steel Through the Combined Effects of Stress Relaxation, Microstructural Evolution, and Oxidation

Bahl, S and Dryepondt, S and Allard, LF and Suwas, S and Shyam, A (2018) Retardation of Small Creep-Fatigue Crack in Gr. 91 Steel Through the Combined Effects of Stress Relaxation, Microstructural Evolution, and Oxidation. In: METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 49A (12). pp. 6110-6121.

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Abstract

This investigation reports an unusual effect of hold time (up to 10seconds) on retardation in the growth of creep-fatigue small cracks at 550 degrees C in Grade 91 steel. The observed phenomenon was interpreted by elucidating multiple processes that are active in the plastic zone at the crack tip. To this effect, microstructural and mechanical responses of the crack tip plastic zone were compared with the mechanical and microstructural responses during low cycle fatigue/creep-fatigue. It is proposed that the stress relaxation that occurs during the hold time can reduce the stress intensity in the plastic zone of crack tip thus, contributing to retardation in the small crack growth rate. Aside from stress relaxation, stress intensity in the crack tip can be further reduced by the phenomenon of cyclic softening that occurs because of plasticity-induced microstructural coarsening. Separately, the contribution of oxidation-induced crack tip shielding is also considered to explain the observed effects of hold time on crack growth rates. Taken together, a combination of stress relaxation, enhanced rate of cyclic softening, and higher degree of oxidation with the introduction of a hold time is demonstrated to be responsible for reduction in the crack growth under creep-fatigue conditions.

Item Type:	Journal Article
Publication:	METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
Publisher:	SPRINGER
Additional Information:	Copyright for this article belongs to SPRINGER
Keywords:	Oxidation;
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	11 Dec 2018 12:14
Last Modified:	11 Dec 2018 12:14
URI:	http://eprints.iisc.ac.in/id/eprint/61220

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