Complete and Incomplete Wetting of Ferrite Grain Boundaries by Austenite in the Low-Alloyed Ferritic Steel

Low-carbon low-alloyed ferritic steels are the main material for the production of high-strength pipes for the transportation of oil and gas. The formation of brittle carbide network during the lifetime of a pipeline could be a reason for a catastrophic failure. Among other reasons, it can be contro...

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Bibliographic Details
Published in:Journal of materials engineering and performance 2012-05, Vol.21 (5), p.667-670
Main Authors: Straumal, B. B., Kucheev, Y. O., Efron, L. I., Petelin, A. L., Majumdar, J. Dutta, Manna, I.
Format: Article
Language:English
Subjects:
Brittleness
Cementite
Characterization and Evaluation of Materials
Chemistry and Materials Science
Corrosion and Coatings
Covering
Engineering Design
Ferritic stainless steels
Grain boundaries
Low alloy steels
Materials Science
Morphology
Quality Control
Reliability
Safety and Risk
Steels
Tribology
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Summary:Low-carbon low-alloyed ferritic steels are the main material for the production of high-strength pipes for the transportation of oil and gas. The formation of brittle carbide network during the lifetime of a pipeline could be a reason for a catastrophic failure. Among other reasons, it can be controlled by the morphology of grain boundary (GB) carbides. The microstructure of a low-alloyed ferritic steel containing 0.09 at.% C and small amounts of Si, Mn, Nb, Cu, Al, Ni, and Cr was studied between 300 and 900 °C. The samples were annealed very long time (700 to 4000 h) in order to produce the equilibrium morphology of phases. The (α-Fe)/(α-Fe) GBs can be either completely or incompletely wetted (covered) by the γ-Fe (austenite) above the temperature of eutectoid transition. The portion of (α-Fe)/(α-Fe) GBs completely wetted by γ-Fe is around 90% and does not change much between 750 and 900 °C. The (α-Fe)/(α-Fe) GBs can be either completely or incompletely wetted (covered) by the Fe 3 C (cementite) below the temperature of eutectoid transition. The portion of (α-Fe)/(α-Fe) GBs completely wetted by Fe 3 C changes below 680 °C between 67 and 77%. The formation of the network of brittle cementite layers between ductile ferrite grains can explain the catastrophic failure of gas- and oil-pipelines after a certain lifetime.
ISSN:1059-9495
1544-1024
DOI:10.1007/s11665-012-0130-6