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51318-11046-The investigation of Incoloy 800H Relaxation Crack Mechanisms

In the present study, detailed microstructure of the crack-tip region of a failed tube was examined using SEM, TEM and EBSD to clarify the relaxation crack mechanism.  Details of the microstructural findings and a proposed mechanism of stress relief cracking will be discussed.

 

Product Number: 51318-11046-SG
Author: Yunjo Ro / Ihho Park / Gyutae Park / Jaewoong Kim
Publication Date: 2018
Industry: Petroleum Refining
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In the refining industry, Incoloy 800H (UNS N08810) has been employed for components operating in the intermediate temperature regime (500~700℃). However, it is known to suffer from relaxation cracking in the HAZ after short duration in service. In the present study, detailed microstructure of the crack-tip region of a failed tube was examined using SEM, TEM and EBSD to clarify the relaxation crack mechanism. The current findings suggest that dislocation enhanced M23C6 precipitation near grain boundary promoted oxidation near grain boundary, and then a crack propagated along the oxide layer or interface between the oxide layer and base metal. Details of the microstructural findings and a proposed mechanism of stress relieve cracking will be discussed.

Key words: 800H (UNS N08810), Relaxation Crack, Oxide

In the refining industry, Incoloy 800H (UNS N08810) has been employed for components operating in the intermediate temperature regime (500~700℃). However, it is known to suffer from relaxation cracking in the HAZ after short duration in service. In the present study, detailed microstructure of the crack-tip region of a failed tube was examined using SEM, TEM and EBSD to clarify the relaxation crack mechanism. The current findings suggest that dislocation enhanced M23C6 precipitation near grain boundary promoted oxidation near grain boundary, and then a crack propagated along the oxide layer or interface between the oxide layer and base metal. Details of the microstructural findings and a proposed mechanism of stress relieve cracking will be discussed.

Key words: 800H (UNS N08810), Relaxation Crack, Oxide

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