Loughborough University
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Microstructural evolution of boron nitride particles in advanced 9Cr power plant steels

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journal contribution
posted on 2016-07-26, 13:46 authored by Letian Li, Ryan Maclachlan, Mark JepsonMark Jepson, Rachel ThomsonRachel Thomson
B and N can be used to increase the creep strength of advanced 9Cr power plant steels by means of microstructural stabilization and precipitation strengthening; however, the formation of boron nitride (BN) particles removes B and N from solution and reduces the strengthening effect of B and N simultaneously. In the current study, the BN precipitation/dissolution conditions in 9Cr-3W-3Co-V-Nb steels have been investigated to understand how to prevent the formation of BN. A series of austenitizing heat treatments have been designed using thermodynamic predictions as a guide in an attempt to dissolve the BN present after the production of 9Cr-3W-3Co-V-Nb type steels and to prevent also the precipitation of BN during the subsequent heat treatments. Advanced electron microscopy has been carried out to investigate the evolution of the BN particles in relation to the austenitization temperature. Energy Dispersive X-ray spectroscopy (EDS) has been used to identify the B-containing phases, and a method has been developed using secondary electron images to quantify the amount of BN present within the microstructure. It has been found that BN solubility is sensitive to the B and N levels in the steel composition, as indicated by thermodynamic calculations. However, it is proposed that austenitizing heat treatments at temperatures ranging from 1448 K to 1473 K (from 1175 °C to 1200 °C) with durations from 1 to 7 hours can effectively prevent the precipitation of BN as well as dissolving most of the BN particles formed during initial steel manufacture.


The authors would like to acknowledge the support of the Technology Strategy Board (Project Number TP11/CAT/6/I/BP074G) and the following companies: Alstom Power Ltd., E.ON, Doosan Babcock, Goodwins Steel Castings and the National Physical Laboratory for their valuable contributions to the project.



  • Aeronautical, Automotive, Chemical and Materials Engineering


  • Materials

Published in

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science






3411 - 3418 (8)


LI, L. ... et al., 2013. Microstructural evolution of boron nitride particles in advanced 9Cr power plant steels. Metallurgical and Materials Transactions A, 44 (7), pp.3411–3418


© Springer


  • AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date



The final publication is available at Springer via: http://dx.doi.org/10.1007/s11661-013-1642-x.






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