Characterization of Nano-Sized Precipitates in Microalloyed Steels
J. Lu, H. Henein and D. G. Ivey
Microalloyed steels are widely used in oil and gas pipelines. They have good strength,
toughness and weldability, which are attributed in part to the presence of nano-sized Nb/Ti
carbonitride precipitates. In order to understand the strengthening mechanisms and to optimize
the strengthening effects, it is necessary to quantify the size distribution, volume fraction and
chemical speciation of these precipitates. However, characterization techniques suitable for
quantifying fine precipitates are limited. In this paper, chemical dissolution and electrolytic
dissolution techniques have been developed to extract the nano-sized precipitates from a Grade
100 (YS = 690 MPa) microalloyed steel. Matrix dissolution methods have been shown to be an
effective technique to quantitatively determine the amount of the microalloying elements in solid
solution and precipitate form. Scanning/transmission electron microscopy and x-ray diffraction
are combined to analyze the composition of precipitates. Dark field imaging is used to
characterize the size distribution of the precipitates.
Keywords: microalloyed steels, pipelines, chemical dissolution, electrolytic dissolution
Publisher: Materials Science and Technology Conference (MS&T) 2007
Product Format: PDF
Date Published: September 16, 2007
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