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.