Prakt. Met. Sonderband 38 (2006) 279 
amount of MX precipitates increased significantly during exposure and even more during 
ribution of the creep testing of the TAF material. These fine MX-type particles increase further the 
e EFTEM creep resistance of the material. The effect of the precipitation of the Laves phase on the 
specimen creep properties is probably small due to the low number and relatively large size of the 
e adopted precipitates in comparison to the M23Cs and V(C,N) precipitates. The disappearance of MX 
where the in the cases of FB8 and FB6 is due to the nucleation of the Z-phase in these steels. This 
ed by the Z-phase coarsens quickly and consumes the fine MX particles in this process. In the case 
rocessing of the CB6 steel, the slight decrease in MX size can also be attributed to the beginning 
degree of nucleation of the Z-phase (fraction 2 %). 
Fig. 5. 
a. ZL 33 a 105 154 Sl 1% 017 = 8 od oo | I 
Fig. 6: Growth of M23Ce (left) and MX (right) particles in 9-12% Cr steels at 650 °C. 
4. Conclusions 
It is on one side the small initial size and slow coarsening of the M23Cg precipitates and on 
the other side the dynamic precipitation of small V(C,N) particles along with the absence of 
y ihe total Z-phase which strengthen the more creep resistant TAF steel during creep. The origin of 
the M23Ce the slow coarsening of the M23Ce precipitates can be mainly attributed to the high boron 
bout 99 % content of this material. The reason for the dynamic precipitation of the V(C,N) particles 
of these could be the relatively short tempering time of 2 hours at 700 °C and the high austenitizing 
ce for the temperature of the TAF material (1150 °C) which promote probably the dynamic 
les. which precipitation during the creep process. 
ion of the 
ecipitation 
steel Acknowledgement 
3 nm. and The authors wish to thank their partners of the COST projects for the creep test 
steel ' This specimens. Thanks are also expressed to the German COST536 ACCEPT partners for the 
h is. very financial support and to the BMWA for the partial funding of this work under the project 
fter creep number 0327705B. . Many thanks also to D. Kuppler, H. Strunk, and G. Strohschein for 
developed technical support. 
nonstrates 
t material. . 
e boron is Literature 
itionally to 
precipitate [1] Kern, T.-U., Mayer, K.H., Berger, C., Zies, G., Schwienheer, M.: “Stand der 
initial size Entwicklungsarbeiten in COST 522 fir Hochtemperatur-Dampfturbinen®, 27. 
and other Vortragsveranstaltung der FVHT in Dusseldorf, 2004 
f less then [2] Fujita, T.: “Studies on 9-12%Chromium Heat Resistant Steels” (collated papers 
snally. the containing research work of T. Fujita from 1964 to 1998), University of Tokyo, 1998