The ingredient

phases

morphology and exfoliation mechanism of oxide formed at steam-side of Φ90 mm x 10 mm tube of steel T91 (/% : 0. 10C

0. 35Si

0. 43Mn

7. 85Cr

0. 81 Mo

0. 24V) for supercritical power unit in vapour at 571. 5 ℃ vapour served for 28800h have been analyzed and studied by optical microscope

scanning electron microscope with energy dispersive spectroscope and X-ray diffractometer. Results show that the thickness of oxide film of steel T91 is about 307. 3 μm with multi-layer structure

its diffusion layer is mixture of Cr

2

O

3

and grains of base metal

the inner oxidized layer is FeCr

2

O

4

the middle oxidize

d layer is mixture of FeCr

2

O

4

and Fe

3

O

4

and the outer oxidized layer is Fe

3

O

4

and Fe

2

O

3

. There are a lot of pores at FeCr

2

O

4

-Fe

3

O

4

interface

by the action of thermal-stress the outer oxidized layer is easily to crack and exfoliate.