Investigation on creep behaviours of centrifugal casting 27Cr44Ni5W3Al+MA alloy used as ethylene pyrolysis furnace tube at 1050°C

For centrifugal casting 27Cr44Ni5W3Al+MA alloy used in ethylene pyrolysis furnace, its creep behaviours at 1050°C are investigated. The results show that the alloy undergoes three stages during the creep tests under different stress levels ranging from 18 MPa to 30 MPa. The apparent stress index n of the alloy is 6.11, and the creep deformation mechanism is mainly dislocation climbing. During the creep test, the fishbone-like M7C3 inside eutectic precipitates in casted alloy gradually transform to massive M23C6 at the edge of the precipitate. Creep induced voids germinate and connect at the interface of austenite/M23C6 and austenite/Ni3Al, the cavities expand along the M23C6 and Ni3Al, forming micro-cracks and the alloy eventually cracks.