Author(s)

T. Ogata & M. Yamamoto

Abstract

Micro-crack propagation behavior of Mod.9Cr-lMo steel under high-temperature fatigue in vacuum and air conditions were periodically observed. Micro-cracks propagated in the direction normal to the stress axis in vacuum while they propagated in the maximum shear direction in air conditon. It was found that propagation rate in air was faster than that in vacuum until the crack grew 1mm length due to oxidation effect which was insignificant for the crack larger than 1mm. Acceleration of the crack propagation rate in the compressive hold test was supposed to be caused by accumulation of tensile strain in the center of the specimen due to off-balance of strain distribution between the tension and compression sides. 1. Introduction Mod.9Cr-lMo steels is being used for high-temperature compone

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