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Application of STEM-EDX Mapping for Characterizing Microstructural Instabilities En 9-12% Chromium Steels With Martensitic-Austenitic Microstructure

Published online by Cambridge University Press:  02 July 2020

U. E. Klotz
Affiliation:
Swiss Federal Laboratories for Materials Testing and Research (EMPA), Überlandstrasse 129, CH-8600Dübendorf, Switzerland
C. Solenthaler
Affiliation:
Institute of Metallurgy, Swiss Federal Institute of Technology (ETH), ETH-Zentrum, CH-8092Zurich, Switzerland
P. J. Uggowitzer
Affiliation:
Institute of Metallurgy, Swiss Federal Institute of Technology (ETH), ETH-Zentrum, CH-8092Zurich, Switzerland
M. O. Speidel
Affiliation:
Institute of Metallurgy, Swiss Federal Institute of Technology (ETH), ETH-Zentrum, CH-8092Zurich, Switzerland
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Extract

Materials for high-temperature application, e.g. in gas-turbine compressor discs or steam turbine rotors, are often susceptible to microstructural instabilities during long-term service. Such instabilities reduce the service life due to a deterioration of the mechanical properties. Therefore, it is most important to identify such instabilities, which often take place in sub-micrometer scale. A class of materials widely used in power generating industries are the martensitic 9-12% Cr steels. In the present work STEM-EDX mappings were used to reveal the distribution of alloying elements in 9-12% Cr steels with a martensitic-austenitic microstructure developed recently.

The chemical composition of the material investigated was Fe-10.1Cr-6.2Co-5.2Mn-2.1Ni-1.2Mo-0.47V-0.1 IN (weight-percent). The material was subjected to a two step heat-treatment of normalizing at 1175°C for 1.5h with subsequent quenching and controlled tempering at 600°C for 20h. Due to the high amount of manganese and nickel a duplex microstructure of 30-40vol.% of austenite in a matrix of tempered martensite is formed during tempering.

Type
Phase Transformations
Copyright
Copyright © Microscopy Society of America

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References

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