Aging Phenomena during In-Service Creep Exposure of Heat-Resistant Steels

An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M7C3 to the more stable M23C6 carbi...

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Bibliographic Details
Published inMetals (Basel ) Vol. 9; no. 7; p. 800
Main Authors Haidemenopoulos, G. N., Polychronopoulou, K., Zervaki, A. D., Kamoutsi, H., Alkhoori, S. I., Jaffar, S., Cho, P., Mavros, H.
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 01.07.2019
Subjects
aging
Aging (metallurgy)
Alloys
Carbides
cast reformer tubes
creep
Ductility
Elongation
Exposure
G-phase
Heat resistant steels
High temperature
Intermetallic compounds
Morphology
Nickel
Niobium
Room temperature
Rounding
Scanning electron microscopy
Silicides
steam reforming
Steel
Transformations
Tubes
Ultimate tensile strength
Japan
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Summary:An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M7C3 to the more stable M23C6 carbide takes place at high exposure temperature (910 °C and above). The primary MC carbides transform to the Ni-Nb silicide or G-phase during creep exposure. The presence of Ti in the steel prevented the transformation of MC carbides to the G-phase. Morphological changes like needle to globular transitions, rounding of carbide edges, and carbide coarsening take place during creep exposure. The room-temperature tensile elongation and ultimate tensile strength are significantly reduced during creep exposure. The above aging phenomena are precursors to creep damage.
ISSN:2075-4701
2075-4701
DOI:10.3390/met9070800