SB-06-4(038) Changes in Precipitates of Modified 9Cr-1Mo Steel During Long-term Creep Deformation at 873K and 923K(Changes in Microstructure 1)

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Degradation of a Mod. 9Cr-1Mo steel during long term creep deformation is caused by heterogeneous recovery preferentially occurred at vicinity of prior austenite grain boundary (PAGB). In order to understand a mechanism of preferential recovery, changes in precipitates during long term creep deformation at 873K and 923K have been investigated. Precipitates of M_<23>C_6, Nb (C, N) and V (C, N) have been observed in both the as tempered condition and all the creep ruptured specimens, except for no Nb (C, N) in the specimen creep ruptured after 41,425.2h at 923K-50MPa. Laves phase (Fe_2Mo) has been observed in the specimen creep-ruptured at 873K. Moreover, precipitation of modified Z-phase (Cr(Nb,V)N), has been observed in the specimen creep-ruptured after more than several thousands hours at the both temperatures. Precipitation of modified Z-phase preferentially takes place at the vicinity of PAGB. Tendency of decrease in a number density of MX carbonitrides with increase in a number of modified Z-phase particles was observed. The coarsening rate of modified Z-phase is much larger than those of M_<23>C_6, Nb (C, N) and V (C, N). It has been concluded that precipitation and coarsening of modified Z-phase is one of the reasons that promote a preferential recovery at the vicinity of PAGB.
社団法人日本機械学会の論文
2001-06-03