Microstructure of TP347HFG steel under high temperature stress

The precipitated phase of TP347HFG steel under high temperature stress was studied by transmission electron microscopy and scanning electron microscopy. The results show that the precipitated phases were M₂₃C₆ and NbC carbides with face-centered cubic structure. The former was distributed in the grain and grain boundary, and the latter was dispersed in the grain. With the extension of test time, the number of M₂₃C₆ increased significantly, but the size did not change significantly. There were many primary carbides in TP347HFG steel. Under the action of long-term high temperature stress, carbides were easy to accumulate at grain boundaries and their vicinity, which promoted the formation of cracks.