Microstructure and mechanical properties of the TP347HFG high-temperature reheater steel tubes were studied comparatively in supplied state and that serviced for about 50 000 h and 110 000 h at 600 ℃,respectively.The results show that for the TP347HFG steel tube serviced for 50 000 h,normal austenite grain growth takes place,and the accompanying precipitation of the tiny M23 C6 particles leads to the increase of dispersion strengthening effect,resulting in the yield strength higher than that of the steel tube in supplied state.However,the microstructure of the TP347HFG steel tube serviced for 110 000 h is severely degenerated with some abnormally growing austenite grains.Moreover,the coarse M23C6 particles have an increased separation effect on grain boundaries,resulting in a significant decrease of mechanical properties at room temperature and high temperature.Moreover,with the service time increasing,the impact properties and plastic deformation characteristics at fracture of the TP347HFG steel tube are continuously degraded,and the effect of microstructure aging on mechanical properties of the TP347HFG steel tubes in service for different terms turns to be more pronounced.
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