Microstructure investigation on Type Ⅳ cracking in P92 steel

The microstructures and hardness distribution of P92 welded joint was analyzed, and the creep damages of the joints were observed under various times of creep tests at 650℃ and 70 MPa.It was found that no obvious creep damage was observed in the all zones of P92 welded joints for the 3 000 h creep specimen, many creep voids occurred in fine grain heat-affected zone and intercritical heat-affected zone regions and no creep voids were found in the coarse fine heat-affected zone and the weld metal in 4 032 h creep specimen, the voids grew up and tend to coalesce in 7 000 h specimen, and micro fissures began to form in 7 026 h specimen.Therefore, this creep fracture could be clearly identified as Type IV cracking.