2.4 Fractography
According to GB /T13298-2015 Test method for microstructure of
metal , after mechanical polishing, picric acid + hydrochloric acid are
used for erosion, and then metallographic analysis is carried out for
the cracked blade section. The microstructure was analyzed by
metallographic microscope and scanning electron microscope(SEM). The
results(Fig. 6, Fig. 7 )show that the microstructure is low carbon
martensite + dispersed intermetallic strengthening phase, the matrix
structure is normal, and there are many fine branch cracks along the
grain near the main crack.