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Core-Shell Structure of Intermediate Precipitates in a Nb-Based Z-Phase Strengthened 12% Cr Steel

Published online by Cambridge University Press:  20 March 2017

Masoud Rashidi ,
Hans-Olof Andrén  and
Fang Liu
Masoud Rashidi*
Affiliation:
Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
Hans-Olof Andrén
Affiliation:
Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
Fang Liu
Affiliation:
Department of Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
*
*Corresponding author. [email protected]
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Abstract

In creep resistant Z-phase strengthened 12% Cr steels, MX (M=Nb, Ta, or V, and X=C and/or N) to Z-phase (CrMN, M=Ta, Nb, or V) transformation plays an important role in achieving a fine distribution of Z-phase precipitates for creep strengthening. Atom probe tomography was employed to investigate the phase transformation in a Nb-based Z-phase strengthened trial steel. Using iso-concentration surfaces with different concentration values, and subtracting the matrix contribution enabled us to reveal the core-shell structure of the transient precipitates between MX and Z-phase. It was shown that Z-phase forms by diffusion of Cr into NbN upon ageing, and Z-phase has a composition corresponding to Cr1+xNb1−xN with x=0.08.

Keywords

Atom probe tomographyphase transformation9–12% Cr steelsZ-phaselocal magnificationprecipitates
Type
Materials Science (Metals)
Information
Microscopy and Microanalysis , Volume 23 , Special Issue 2: Atom Probe Tomography & Microscopy 2016 , April 2017 , pp. 360 - 365
Copyright
© Microscopy Society of America 2017 

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