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.