Type IV cracking of P92 steel welded joint used in China power plants

ABSTRACT

P92 (9Cr-1.8W–0.5Mo-NbV) martensite steel is widely used in high-temperature pipes of ultra-supercritical boilers in China. During high-temperature operation, microstructural evolution of the heat affected zone (HAZ) across welded joint leads to type IV cracking failure. In this article, microstructural evolution and type IV cracking of P92 steel welded joint in an actual 605℃ supercritical boiler were analysed. The results show the cracking appeared in the fine-grained heat affected zone (FGHAZ). Laves phase and M₂₃C₆ phase clustered around the cavity. Their precipitation and coarsening promote the nucleation and growth of cavities. The Z phase was also observed in the heated affected zone. Compared with other zones, FGHAZ has lower dislocation density and more degeneration of tempered martensite lath, the coarsening of Laves phase and M₂₃C₆ phase is more severer in FGHAZ. These factors led to the deterioration of the creep properties and type IV cracking.

KEYWORDS:

• Type IV cracking
• P92 steel welded joint
• creep
• heat-affected zone

Acknowledgments

The authors would like to thank the support from “The National Key Research and Development Program of China （Grant No. 2021YFC3001801)”.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Key Research and Development Program of China [2021YFC3001801].