Microstructural changes caused by yttrium addition to NbTi-modified centrifugally cast HP-type stainless steels

Centrifugally cast heat-resistant HP stainless steels are particularly suitable for applications where service conditions comprise high temperatures and aggressive environments; thus, they are extensively used in reformer furnaces, in which hydrogen production takes place. The demand for better perf...

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Bibliographic Details
Published in:Materials characterization 2007-02, Vol.58 (2), p.132-142
Main Authors: Nunes, F.C., de Almeida, L.H., Dille, J., Delplancke, J.-L., Le May, I.
Format: Article
Language:English
Subjects:
CASTING
CASTINGS
Centrifugal casting
CHROMIUM CARBIDES
CREEP
FRAGMENTATION
FURNACES
HEAT
HYDROGEN PRODUCTION
MATERIALS SCIENCE
MICROSTRUCTURE
NUCLEATION
Precipitation
STAINLESS STEELS
TITANIUM
YTTRIUM
YTTRIUM ADDITIONS
YTTRIUM CARBIDES
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Summary:Centrifugally cast heat-resistant HP stainless steels are particularly suitable for applications where service conditions comprise high temperatures and aggressive environments; thus, they are extensively used in reformer furnaces, in which hydrogen production takes place. The demand for better performance has motivated developments in these steels. The addition of Nb and Ti as microstructural modifiers has proved successful in providing a more stable microstructure. In this work yttrium was added to centrifugally cast NbTi-modified HP steels. It was observed that its presence increased the level of fragmentation of the chromium carbides, a positive aspect for creep resistance. The main cause of the fragmentation is the formation of yttrium carbides, which serve as heterogeneous nucleation sites for the other carbides. One of the tubes, with a lower titanium content, showed the best creep performance among those tubes studied owing to the presence of a smaller volume fraction of the deleterious G phase.
ISSN:1044-5803
1873-4189
DOI:10.1016/j.matchar.2006.04.007