8. Conclusions

microstructure, while numerous finer ones should be considered as of tempering

In the HAZ portion representing above A3 temperature, that is, of mainly austenitic as-welded microstructure, high density of partly spheroidized carbides appear and the largest precipitates seldom appear (Figure 43), while in the HAZ portion near to the fusion surface, the carbides in high-density colonies are partly elongated and aligned in the directions of former martensite laths (Figure 44);

ACT executed on the weld HAZ and interrupted before fracturing of sample allows taking proper specimens for TEM observations, which in turn show clearly how the separation of phases, ferrite and austenite, in the intercritical region pro-

The simulative accelerated creep test was developed for martensitic-ferritic creep resisting steels and welds, based on detailed substructure observations of crept steels. Dislocation configurations governing the real creep were reproduced in a low-cycle compression-tension multicycle procedure carried out at the testing temperatures similar to those of real creep. This procedure applied on Gleeble physical simulator caused in less than 12 h transformation of the initial tempered martensite substructure into fully recrystallized ferrite with spheroidal or coagulated carbides and adequate decrease of hardness similar to that after multiyear

duces during creep the microstructure vulnerable to premature failure.

type (Figure 42).

Figure 44.

Figure 43.

7. Discussion

90

here, some larger precipitates do appear again.

Carbides in FB2 HAZ at location near to fusion line, ACT at 625°C.

Carbides in FB2 HAZ at location above A3 temperature, ACT at 625°C.

Creep Characteristics of Engineering Materials


4.Hardness measured at room temperature after ACT indicates the extent of microstructure transformation; however, when the material will fail cannot be predicted.

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