2.4. Metallographic inspection
By reviewing the original documentation from the time of delivering and installing of the shaft, it was discovered that
heat treatment of the shaft was done by applying the regime shown of Fig. 10:
Such a heat treatment regime indicates that complete austenization was done, with complete breaking of the microstructure
that had remained from the casting process.
However, the microstructure of the material is the cast ferrite-pearlite one, with oxide type non-metallic inclusions and
with minimal participation of dendrite structure, Fig. 11a. Dendrite structure presence points to the possibility of incomplete
or irregularly executed shaft flange heat treatment, which explains the observed scatter of results in all the mechanical tests.
It was also determined that there were large non-metallic oxide inclusions in the structure, which occurred in sequences.
The fine microcracks were found in microstructure, Fig. 11b.