The high temperature corrosion behavior of 18-8 Austenitic Super304H in coal ash/flue gas environment at 650 ℃ is investigated by means of XRD

SEM

EDS and EBSD and so on. The results show that

after corrosion for 70

150

320 and 700 h

the average thickness of corrosion layer are 2.5

5.2

11.5 and 27.8 mm

respectively. The corrosion layer is mainly composed of loose Fe_2O_3 at outer layer and dense Cr_2O_3 and internal vulcanization products at inner layer. After corrosion for 150 h

the protective Cr_2O_3 layer gradually desquamates and internal vulcanization products accumulate and then expand at the grain boundary. With the diffusion and dissolution of Fe to the outside of oxide film

a "nodular" Fe_2O_3 is formed and finally becomes a multilayered raised corrosion product. With the increase of corrosion time

the size of the "nodular" corrosion products gradually increases to more than 10 mm and the corrosion layer is more likely to rupture and peel off

which decreases the corrosion resistance of the alloy.