Precipitate Phases in an 11% Cr Ferritic/Martensitic Steel with Tempering and Creep Conditions

Precipitates in an 11% Cr ferritic/martensitic steel containing Nd with tempering and creep conditions were investigated using transmission electron microscope with energy-dispersive X-ray spectroscopy. The precipitates in the steel with a tempering condition were identified to be Cr-rich M23C6 carbide, Nb-rich/V-rich/Ta–Nb-rich MX carbides, Nb-rich MX carbonitride, and Fe-rich M5C2 carbide. Nd-rich carbonitride, which is not known to have been reported previously in steels, was also detected in the steel after tempering. Most of the Nb-rich MX precipitates were dissolved, whereas the amount of Ta-rich MX precipitates was increased significantly in the steel after a creep test at 600 °C at an applied stress of 180 MPa for 1,100 h. No Fe2W Laves phase has been detected in the steel after tempering. (Fe, Cr)2W Laves phase with a relatively large size was observed in the steel after the creep test.