J. Phys. IV France
Volume 112, October 2003
Page(s) 445 - 448

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.

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.

© EDP Sciences 2003