Abstract: In order to explore the creep fracture mechanism of P12 heat-resistant steel, a series of creep tests were carried out on P12 heat-resistant steel under 630 ℃ and 70 MPa stress conditions. Then the creeped specimens were examined by metallographic microscopy and analyzed by scanning electron microscopy to obtain the microstructure evolution during high temperature creep. And the level of carbide precipitation and pearlite spheroidization of P12 heat-resistant steel under creep was quantitatively analyzed by combining computer image processing technology. The results show that the prolongation of creep time increases the precipitation of carbides in P12 heat-resistant steel. On the one hand, the amount of carbides increases continuously, on the other hand, the size of carbides increases accordingly. The level of pearlite spheroidization also increases with the accumulation of creep time. When the creep time is 360 hours, the level of pearlite spheroidization is up to grade 3. In addition, the amount and size of cement carbon in the pearlite structure decreases sharply with the increase of creep time. The deterioration of the microstructure of P12 heat-resistant steel during creep may be an important factor for its creep fracture. In order to predict the service life of P12 high-temperature steam pipe, a series of high-temperature endurance tests were carried out to determine the relationship between Manson-Haferd parameter PMH(σ) and stressσ of P12 heat-resistant steel. Then Based on the Manson-Haferd parameter method, the service life of P12 high-temperature steam pipe with stress σ of 43.15 MPa and service temperature of 520 ℃ is predicted to be 199.8 thousand hours.

Key words: P12 heat-resistant steel, creep rupture, microstructure, structural evolution, life prediction, Manson-Haferd parameter method