Effects of Alloying Elements on Fracture Properties of Niobium Stabilized Austenitic Steels at Elevated Temperature

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Abstract:

The present work is a further investigation into the effects of the carbon (C), nitrogen (N) and niobium (Nb) contents on then fracture properties of the Type 347 stainless steels at 316oC. 9 heats of systematically designed alloys were examined. Through SEM-EDS, TEM and XRD analyses, two kinds of precipitates, Nb(C,N), CrNbN were identified in the Type 347 steels with a high ratio of wt% N to wt% C, on the other hand only Nb(C,N)s were found in the Type 347 steels with a low ratio of wt% N to wt% C. The tearing moduli were decreased in the range of 52~60% as the carbon content increased from 0.03wt% to 0.05wt%. The tearing moduli were lowered by 52~59% in the alloys with a high nitrogen. It was deduced from the microstructure analysis results that the coarse Nb-rich precipitates control the fracture resistance of the Type 347 as they act as the potential sites for the nucleation of micro-voids.

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Key Engineering Materials (Volumes 345-346)

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461-464

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August 2007

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© 2007 Trans Tech Publications Ltd. All Rights Reserved

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[4] ASTM, Standard Designation E963-95: (ASTM, USA, 2003). wt% N wt% C 0. 03 0. 07 0. 11 0. 02 403 423 445 0. 03 401 425 449 0. 05 403 423 453 Fig. 4. SEM micrograph showing a sectioned specimen after J-R test. Table 2. Ultimate tensile strength of Type 347 stain- steel at 316oC as a function of contents of carbon and nitrogen. Nb(C, N).

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