By TEM

SEM and EDS etc analysis

the carbides contained in samples of T23 steel after aging in service and creep rupture under high temperature was analyzed

and an approach to the evolution regularity of carbides and its influence upon the performance degradation were made.Results show that:(1) during heat treatment and the subsequence high temperature service of the T23 steel

five kinds of carbide

i.e.M3C

M2C

M7C3

M23C6

and M6C appear;(2) the second-phase in T23 steel under normal condition is mainly composed of M3C

which spheroidized in the tempered process

and then disappeared in re-dissoluation

metastable phase compounds such as(Cr

Fe)7C3 and Mo2C are precipitated

and finally most carbides are transformed into carbide M23C6;(3) Ostwald ripening of M23C6 occurs during service aging or creep rupture under high temperature;particle of M 23 C with small size inside the lattice disappeares gradually

that with large size at grain boundary coagulates and grows

coarsening and forming chain-shaped distribution;as the temperature growing and the operation time prolonging

carbide M 23 C transforms gradually into W-riched M6C phase.Above is the major cause for performance degradation of the T23steel.