The influence of cold work hardening inner surface of austenitic stainless steel tubes used in ultra-supercritical boilers upon the tubes' steam oxidataion behavior has been discussed after comparative analysis of microstructure and form-appearance features of steam oxidation scale formed on the machined area and non-machined area on the inner surface of tube spcimens taken from superheater tubes which had already been in operation for 4 years.The results show that the cold work hardening inner surface is very effective to improve the steam oxidation resisting behavior of TO347HFG and Super 304 fined grain austenitic stainless steel under relatively lower temperature

but the effect of cold work hardening inner surface upon Super 304 steel disappeared entirely in high-temperature steam of about 600 ℃

excepting the scale thickness is slightly thiner

there is little difference of microstructure and form-appearance features between tube specimens with cold work hardening inner surface and that without cold work hardening inner surface.In addition

the steam oxidation resisting behavior of SAVE 24 steel

whose Cr content is more than 22%

is very excellent

there isn't any difference of steam oxidation behavior on the machined area and the non-machnied area of the tested tube specimens.