Precipitation in 9Cr–1Mo steel after creep deformation

The carbides present after creep testing a 9Cr–1Mo steel at 566 °C over a range of stress levels giving rupture times of up to 7300 h have been characterized and identified using a transmission electron microscopy, energy-dispersive X-ray spectroscopy and electron diffraction. The initial carbide precipitates present were M7C3, (NbV)C and VC and it was determined that M6C carbide precipitates were present in all specimens after elevated temperature exposure for greater than approximately 1700 h. No precipitation of M23C6 was detected. The evolutionary sequence from the initially present carbides during high temperature exposure involved the formation of the stable M6C carbide directly, without the intermediate formation of M23C6, as is reported to occur in other Cr–Mo steels.