274 Prakt. Met. Sonderband 38 (2006) 
One of the most promising ways to stabilize the M23Cs particles is the addition of boron. use 
Examples of these boron containing steels are X10CrWMoVNbNB-9-2 (P92) and Spe 
X14CrMoVNDbB-9-1 (FB2), which have shown auspicious improvements over the 
previously used X10CrMoVNbN-9-1 (P91), X12CrMoVNbN-10-1 and X12CrMoWVNbN- For 
10-1-1 (E911). Recent research results suggest that the creep properties can be further grir 
improved by increasing the boron content and adjusting the nitrogen content accordingly. inv: 
This should lead to an increased amount of fine vanadium carbonitrides and prevent the tw 
formation of boron nitride at the same time [11]. The potential for the improvement by che 
alloying boron is demonstrated by the development of the 10.5 wt% Cr TAF steel by Fujita ED 
and coworkers about 30 years ago [12]. However, the high B content of about 300 to apj 
400 ppm in the TAF steel leads although to some drawbacks such as reduction of the hot ex 
workability of large turbine components. In accordance with the current experiences it are 
reduces for example the hot workability of large turbine components. Nevertheless, the of 1 
quantitative investigations of the microstructure of this steel with modern analysis 
techniques are of great importance for the development of new 9-12 wt. % Cr steels with 2.3 
moderate boron contents. This is especially important, since available data for the 
microstructure of the TAF steel, dated from 1982, give only a qualitative view of the Foi 
observed phases [13]. sal 
pel 
For our own investigations, we used a TAF test melt from Saarschmiede in Völklingen, Spe 
produced in the framework of the COST 501 research project. Long-term creep tests have che 
been performed on this material. Some results of these investigations are shown ten 
exemplarily and are compared to the COST steel FBS. the 
2. Experimental Details 
21 LOM and SEM Investigations 
The light optical microscopy (LOM) analysis was done using a Leitz Aristomet. The 
specimens were prepared by standard metallographic methods such as cutting, grinding 
and polishing. To develop the microstructure the specimen were etched by 3% HNO,. 
Scanning electron microscopy (SEM) investigations were carried out using a JEOL JSM 
6400 operated at 10 kV for the analytical measurements and at 25 kV for acquiring 
images. For the analytical measurements the SEM is equipped with an energy-dispersive 
X-ray spectrometer (EDX) system (TN5500 from NORAN) which allows the detection of 
elements with an atomic number > 5 (Boron). The SEM investigations were done at 
polished or etched samples used also for LOM or at metal foils prepared for the TEM 
studies. 
2.2 TEM Characterisation 
Conventional transmission electron microscopy (TEM) investigations were performed . 
using a JEOL JEM 2000 FX operated at 200 kV to determine the subgrain size and 
dislocation density. For analytical measurements the TEM is equipped with an EDX Tr 
detector (Kevex Sigma 1 from NORAN, capable for detection of elements with an atomic 8, 
number > 11) and with a Gatan energy filter. The latter was used for acquiring elemental pr 
maps. A detailed description of energy filtered TEM (EFTEM) measurements can be found x 
for example in [14, 15]. For the quantitative evaluation of the precipitate state (type, size, } 
shape and distribution) a digital image processing system (SEM-IPS 500, Kontron) was