Cause of Fracture on Flue Gas Turbine Blade

The rotor blade of flue gas turbine in a petrochemical enterprise fractured during operation. The causes of blade fracture failure were analyzed by means of macroscopic observation, scanning electron microscope analysis, metallographic examination, energy spectrum analysis and Brinell hardness test. The results show that due to the improper selection of temperature during forging and heat treatment, the mixed crystal phenomenon appeared and the strength and toughness of the alloy decreased. In the subsequent operation process, the phenomenon of overtemperature operation resulted in the decrease of carbides at grain boundaries and the appearance of chain carbides, which weakened the strengthening effect of grain boundaries and reduced the ability of resistance to crack initiation and propagation. The continuous impact of high temperature flue gas particles caused micro cracks to germinate at the grain boundary weakening area at the edge of the inlet side of the blade. Under the action of alternating stress, the micro cracks propagated along the grain boundaries and formed macro cracks. When the macro cracks develop to a certain size, the fracture along the grain boundaries instantaneously, which resulted in the fracture failure of the blade.