244 Prakt. Met. Sonderband 46 (2014) 
such as hot cracks or lack of fusion were observed in the welded joint. After creep loading particles 
numerous separations of grain boundaries without cavity formation could be seen. The heat trea 
microcracks occur, often as wedge cracks at the grain triple points, which suggests the 
grain boundary sliding as the creep mechanism, typically at high loads. All cracks are 
concentrated along the grain boundaries. The crack paths are, depending on fracture 
location, interdendritic in the weld metal and intercrystalline in the base material. The heat 
affected zone (HAZ) area was free of cracks. 
Fig. 3: ° 
W1, ¢) st 
From the: 
= stabilizati 
} N } . formation 
Fig. 2: virgin a) BM, b) WM; after creep test c) fracture in WM (state A3/W3), d) fracture in At the gre 
BM (state A4/W4) (Fig.4 c). 
3.2.2 TEM INVESTIGATIONS Saree 
; ; ; Es states rat 
The influence of short-term creep loading at 700 °C on the microstructure of welded joints The diffe 
of Alloy 617 in as-welded condition, after PWHT at 980 °C and after creep loading was boundarie 
investigated by TEM in the area of the base material and the weld metal, see Tab. 2. precipitati 
TEM images of all examined states are shown in Fig. 3. In the as-welded condition only strength ¢ 
few M23Cs carbides are found both in the BM and in the WM within the grain and isolated grain bol 
at the grain boundaries (Fig. 3 a and b). The dislocation density in the weld metal is towards t 
10 times higher than in the base material. Y phase was not identified in any state. 980 °C of 
After creep at 700 °C, the density of M23Cs carbides within the grain increases. At the grain stable ant 
boundaries the number of particles increase in BM but decrease in WM. vy ‘phase occurs can abso 
within the grain in both states. Fig. 3 ¢ and d show the results for states after PWHT at grain bou 
980 °C. Compared with the non-heat treated initial state more M23Cs carbides are found in the non-h 
both areas (BM and WM) within the grain and at the grain boundaries. means th: 
After short-term creep loading there is still a difference between two conditions. In heat If areas o 
treated state, the size of My3Cs carbides within the grain increases, the y ‘phase is, that in bo 
however, smaller (Fig. 4 a and b). This could be observed for both the base metal and the low amou 
weld metal. The changes during the creep loading are not significant especially concerning GB-gliding 
M23Cs carbides in the PWHT-state. The density of Mx3Ce particles in heat treated state and maki 
does not increase, however, is increasing in the non-heat treated condition, since only few formation