The mean intercept length of the carbides and the martensite shows a general increasing tendency, Acknowl& 
Fig. 11 and 12. Before measuring this parameter on the martensite, the intergranular MC carbides wo 
were deleted manually. The variations observed on the Fig. 12 can be explained by the difficulty to 
recognize these intergranular MC carbides. 
Two of the five images acquired at 45 millimetres depth contain more MC carbides and so their Refere”“% 
carbide interdistance is smaller. The decreasing of the carbide interdistance at 45 millimetres depth} Man 
can be explained by an insufficient number of images to represent the variations of the carbide NE 
interdistance from one image to another. As the number of intergranular MC carbides is very ()) GE 
variable from an image to another, more than five images must be acquired until the mean of the (3) P. La 
carbide interdistance converge. (199% 
z * + 
6 see oo ** 
9 * * > 12 . 2° * 
A. i 4 
’ 5 
U 0 = 
J 10 20 30 40 50 60 0 10 20 30 40 50 60 
Depth (mm) Depth (mm) 
Fig. 9 : Area fraction (%) of carbides Fig. 10 : Carbide interdistance ( m). 
according to the depth. according to the depth. 
16 2 „70 oo 
x eo. ? = 60 A 
5 Er ot as N 
i * 50 
© 10 + i 
© © 8 40 
$e 2 
6 30 -— 
0 10 20 30 40 50 60 0 10 20 30 40 50 60 
Depth (mm) Depth (mm) 
Fig. 11 : Carbide size : mean intercept Fig. 12 : Grain size : mean intercept 
length according to the depth. length according to the depth. 
Conclusion and future developments 
As the spectral segmentation is ,until now, more powerful than the textural segmentation, the 
sample preparation and the acquisition process are primordial to take pictures with the maximum 
contrast between the phases. A judicious etching combined with the use of narrow interference 
filters are in this case a good way to achieve this challenge. 
The final goal of the project is to establish relations between microstructural properties and 
mechanical behaviour. Specimens (10 or 12 mm of diameter) cut off at different place inside the 
shell will be submitted to several mechanical tests. Their microstructure will be analysed from 
polished sections coming from the fracture zones. Possible correlations between mechanical results 
and image analysis parameters must be investigated. 
147