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Precipitates in Nb and Nb–V Microalloyed X80 Pipeline Steel

Published online by Cambridge University Press:  06 August 2013

Zhongyi Li ,
Delu Liu ,
Jianping Zhang  and
Wenhuai Tian
Zhongyi Li*
Affiliation:
Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China Maanshan Iron & Steel Co. Ltd., Maanshan, Anhui 243000, China
Delu Liu
Affiliation:
Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China
Jianping Zhang
Affiliation:
Maanshan Iron & Steel Co. Ltd., Maanshan, Anhui 243000, China
Wenhuai Tian
Affiliation:
Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083, China
*
*Corresponding author. E-mail: lizhongyii@sina.com
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Abstract

Precipitates in two X80 pipeline steels were studied by transmission electron microscopy equipped with an energy filtering system. The steels are microalloyed with niobium and niobium–vanadium (Nb–V), respectively, and produced by continuous hot rolling. Besides the precipitates TiN and (Ti, Nb) (C, N), which were 10–100 nm in size, a large number of precipitates smaller than 10 nm distributed in the two steels have been observed. In the Nb–V microalloyed steel, only a few titanium nitrides covered by vanadium compounds on the surface have been observed. It is inferred that the vanadium exists mainly in the matrix as a solid solution element. The fact has been accepted that there was no contribution to the precipitation strengthening of the X80 steel by adding 0.04–0.06% vanadium under the present production process. By contrast, the toughness of the Nb–V steel is deteriorated. Therefore, a better toughness property of the Nb microalloyed X80 results from the optimum microalloying composition design and the suitable accelerating cooling after hot rolling.

Keywords

X80 pipeline steelprecipitateelectron energy filtering microscopymicroalloyed steelNb carbonitrideTi nitrideTEM
Type
Research Article
Information
Microscopy and Microanalysis , Volume 19 , Supplement S5: IUMAS , August 2013 , pp. 62 - 65
Copyright
Copyright © Microscopy Society of America 2013 

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