Metallographic Investigation of Fractured Bearing Shell
When the metallographic analysis of the causes of fractureing in the
generator guide bearing shell ring used in the bearing of the shaft in
hydroelectric power plants, it was observed that the material was a low
carbon steel when the analysis results were taken into consideration.
The internal structure of this type of steel changes depending on the
carbon content and heat treatment. Also, the use and environmental
conditions are among the factors affecting the structure.
As a result of the metallographic studies carried out on the sample, we
received from the area near the fracture of the fracture formation, in
the optical images given in Figure 3, it is seen that the main structure
(Matrix) is composed of ferrite (yellow regions), and the black regions
which are scattered in the structure are perlite.
As a result of the metallographic studies applied on the sample taken
from the area near the crack formation, it is considered that the
progress is slow due to the thin and regular ferritic structure of the
material. It is possible that the progress of the crack along the grain
boundaries may be caused by dislocation within the structure. It is
clear that the main structure (Matrix) is composed of ferrite (yellow
areas), and the black areas that are scattered within the structure are
perlite, and there are ferrite and cementite structures within the
perlite structure.
When we examine the SEM images in the different magnifications given in
Figure 4, it was observed that the black regions are the main structure
of the ferrite, the white areas seen as lines and layers are perlite and
the structure seen as the lines is composed of the cementite forming the
perlite.