Studies of minor phase evolution in a 12CrMoVNb martensitic steel, creep tested for durations of up to 100000 h at 550°C and 600°C, have revealed the presence of a hitherto unknown complex nitride precipitate having a tetragonal unit cell similar to that of Z phase, previously only reported in certain niobium bearing austenitic steels. This paper describes the electron diffraction and X-ray microanalysis studies leading to the discovery of this phase, and the conclusion that it is a new form of Z phase enriched in vanadium. A modified crystallographic model is proposed for this new complex nitride phase, as are the precipitation sequences leading to its formation.
MST/3575
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References
1.
WICKENSA., STRANGA., and OAICESG.: in Proc. Conf. on ‘Engineering aspects of creep’. Sheffield, UK, September 1980, The Institution of Mechanical Engineers, 11.
2.
ROBERTSB. W. and STRANGA.: in Proc. Conf. on ‘Refurbishment and life extension of steam plant’, London, UK, October 1987, The Institution of Mechanical Engineers, 205.
3.
SMITHE. and NUTTINGJ.: Br. J. Appl. Phys.,1956,7,214.
4.
CHICKWANDAH. K., STRANGA., and McLEANM.: in ‘Materials for advanced power engineering’, (ed. D. Coutsouradis et al.), 291-300; 1994, Dordrecht, Kluwer.
5.
CHICKWANDAH. K.: ‘Microstructural stability of 12CrMoVNb power plant steels’, PhD thesis, Imperial College, London, UK, January 1994.
6.
BAKERR. G. and NurrnstoJ.: in‘Precipitation processes in steels’, 1; 1959, London, The Iron and Steel Institute.
7.
‘International tables for X-ray crystallography’; 1962, Birmingham, The Kynoch Press.
8.
STONEP. G.: in Proc. Conf. on ‘High temperature properties of steels’, Eastbourne, UK, April 1966, The Iron and Steel Institute, 505-511.
9.
ETTMAYERP.: Monatsh. Chem.,1971,102, 858.
10.
HUGHESH.: J. Iron Steel Inst.,1967,205, 775–778.
11.
JACKD. J. and JACKK. H.: J. Iron Steel Inst.,1972,209, 790–792.
12.
HALOJ.: 1995, Personal communication.
13.
GERLACHH.: in Proc. Conf. ‘High temperature properties of steels’, Eastbourne, UK, April 1966, The Iron and Steel Institute, 517-518.
14.
STRANGA. and VODAREKV.: in Proc. Conf. on ‘Creep resistant metallic materials’, Hradec nad Moravici, Czech Republic, September 1996, Vitkovice as., to be published.
