Microstructure and Properties of Ni-Fe-base Superalloy for 700 ℃ Advanced Ultra Supercritical Unit Final Superheater

The microstructure and properties of a new Ni-Fe-base HT700T superalloy for 700℃ A-USC unit final superheater were studied. The results show that HT700T alloy was a precipitation-hardening alloy, and the microstructure stability of HT700T alloy at 750℃ was stable. The yield strength at 750℃ was 598 MPa, and remained about 400 MPa after thermal exposure for 3 000 h. The creep rupture strength of the alloy at 750℃/10⁵ h was 103 MPa. The impact energy at room temperature of the alloy after thermal exposure at 750℃ for 10⁴ h was 50 J·cm^-2, which was slightly lower than that before thermal exposure. The resistance to steam oxidation at 750℃ reached the complete oxidation resistance level, and the metal corrosion thickness in simulated flue gas and coal ash at 750℃/2×10⁵ h was 0.2 mm. The comprehensive performance of HT700T alloy could basically meet the service performance requirements of 700℃ A-USC unit final superheater; the industrial manufactured alloy boiler tube had been running normally on the test platform for over 15 000 h.