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Metals 2016, 6(4), 90;

Characterization of Precipitates in a Microalloyed Steel Using Quantitative X-ray Diffraction

Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 2V4, Canada
Enbridge Pipelines, 10201, Jasper Ave, Edmonton, AB T5J 3N7, Canada
Suncor Energy, Suncor Energy Centre, 111, 5 Ave SW, Calgary, AB T2P 3E3, Canada
Author to whom correspondence should be addressed.
Academic Editor: Isabel Gutierrez
Received: 29 February 2016 / Revised: 29 March 2016 / Accepted: 8 April 2016 / Published: 19 April 2016
(This article belongs to the Special Issue Microalloyed Steel)
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Quantitative X-ray diffraction (QXRD) (also known as the Rietveld method) was used to analyze the precipitates present in Grade 100 microalloyed steel. The precipitates were extracted from the steel using electrolytic dissolution and the residue from the dissolution was analyzed using XRD. The XRD pattern exhibited three (3) distinct diffraction peaks, and significant broadening of a fourth peak corresponding to the <10 nm size precipitates. QXRD analysis was applied to the XRD pattern to obtain precipitate size, composition, and weight fraction data for each of the four diffraction peaks observed. The predicted mean precipitate diameter and average atomic composition of the nano-size (<10 nm) precipitates was 4.7 nm and (Nb0.50Ti0.32Mo0.18)(C0.59N0.41), respectively. The predicted precipitate size correlates well with the average size of precipitates measured in previous work by the authors using both transmission electron microscopy (TEM) and small angle neutron scattering (SANS). The average atomic composition correlates well with the composition measured in this work using energy dispersive X-ray (EDX) analysis of individual nano-sized precipitates. The calculated weight fraction of the nano-size precipitates in the extracted residue was 42.2 wt. %. The calculated atomic compositions of the other three diffraction peaks were TiN, (Ti0.87Nb0.13)N, and (Nb0.82Ti0.18)(C0.87N0.13) with weight fraction values of 12.9 wt. %, 31.7 wt. %, and 13.1 wt. %, respectively. The sizes of both the (Ti0.87Nb0.13)N and the (Nb0.82Ti0.18)(C0.87N0.13) groups of precipitates were directly measured and were observed to range from 150 nm to 570 nm and from 90 nm to 475 nm, respectively. QXRD was unable to determine a reasonable mean precipitate size for either of these two groups of precipitates. The wide compositional range (i.e., varying levels of Nb and Ti) of these precipitates (as measured by EDX) resulted in XRD peak broadening that was erroneously interpreted as a size broadening effect. View Full-Text
Keywords: microalloyed steel; quantitative X-ray diffraction; precipitates; size; composition microalloyed steel; quantitative X-ray diffraction; precipitates; size; composition

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Wiskel, J.B.; Lu, J.; Omotoso, O.; Ivey, D.G.; Henein, H. Characterization of Precipitates in a Microalloyed Steel Using Quantitative X-ray Diffraction. Metals 2016, 6, 90.

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