Ultrahigh strength and low yield ratio of niobium-microalloyed 900MPa pipeline steel with nano/ultrafine bainitic lath

An ultra-low carbon niobium-microalloyed steel with yield strength of a arrow right 4900MPa has been processed on a pilot-plant scale. The microstructure of the steel is primarily characterized by lower bainite and acicular ferrite, with small fraction of lath-martensite and martensite-austenite (MA...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2010-06, Vol.527 (16-17), p.3886-3892
Main Authors: Guo, Aimin, Misra, R.D.K., Xu, Jinqiao, Guo, Bin, Jansto, S.G.
Format: Article
Language:English
Subjects:
Bainite
Cooling
Microstructure
Nanostructure
Niobium
Precipitation
Structural steels
Titanium
Yield strength
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Summary:An ultra-low carbon niobium-microalloyed steel with yield strength of a arrow right 4900MPa has been processed on a pilot-plant scale. The microstructure of the steel is primarily characterized by lower bainite and acicular ferrite, with small fraction of lath-martensite and martensite-austenite (MA) constituents. Bainite is present as fine domains. A combination of niobium and titanium precipitates was observed at the grain boundaries and in the interior of the grains and includes irregular (a arrow right 440-150nm of (Nb, Ti)(C, N)) and fine cuboidal/spherical particles of NbC (a arrow right 430-50nm). It was observed that accelerated cooling inhibited the precipitation of Nb and Ti carbides. The Charpy impact toughness at a degree 20A degree C was 200J and tensile elongation was 15% with the yield ratio of less than 0.84. The good matching of high strength and low yield ratio was realized by two-stage thermo-mechanical rolling combined with fast cooling.
ISSN:0921-5093
DOI:10.1016/j.msea.2010.02.067