Z phase precipitation in martensitic 12CrMoVNb steels

V. Vodarek; A. Strang

doi:doi:10.1051/jp4:2003921

Numéro		J. Phys. IV France Volume 112, October 2003


Page(s)		445 - 448
DOI		https://doi.org/10.1051/jp4:2003921

J. Phys. IV France 112 (2003) 445
DOI: 10.1051/jp4:2003921

Z phase precipitation in martensitic 12CrMoVNb steels

V. Vodarek¹ and A. Strang²

¹ VITKOVICE - R & D, Pohranicni 31, 70602 Ostrava 6, Czech Republic
² Department of Engineering, University of Leicester, Leicester, U.K.

Abstract
Precipitation of Z phase contributes significantly to degradation of creep properties of 12CrMoVNb steels because its precipitation is accompanied by dissolution offinely dispersed nitrides and carbonitrides of M2X and/or MX type. The orientation relationship between Z phase and the ferritic matrix was determined as: $(001)_{\rm z}// (001)_{\alpha}$ , $[010]_{\rm z} // [010]_{\alpha}$ . Prolonged thcrmal/creep exposure is accompanied by recrystallisation of the matrix and this orientation relationship is destroyed. Nevertheless Z phase particles preserve the form of thin plates. Z phase is a nitride which is rich in vanadium, niobium and chromium and its composition depends on both the temperature of precipitation and the initial chemical composition of steels. The composition of Z phase does not change during long term exposure at the original precipitation temperature. A relationship between the composition of Z phase and its temperature of formation may be able to be used as a temperature exposure indicator of steels. However it is also necessary to know the Z phase composition for a given cast of material.