Abstract
Contrary to expectations, long-term performance of creep stress enhanced ferritic steels (CSEF) falls short of predictions based on short-term data. This discrepancy is attributed to the formation and growth of creep voids, leading to reduced ductility. This study investigates cavities in creep-tested P92 steel, revealing an association with large ceramic particles (1-2 μm) in standard samples. Three distinct particle compositions were identified: boron nitride (BN), manganese sulfide, and γ-Al2O3. Statistical analysis showed a strong correlation between BN particles and cavity formation. Using a 3D “slice and view” technique with a focused ion beam/field emission gun scanning electron microscope (FIB-FEGSEM), the study revealed irregular shapes for both cavities and associated particles. Furthermore, analysis of the head-gauge transition area (lower stress exposure) showed small cavities near BN particles, suggesting preferential nucleation on these hard, irregular features. These findings strongly support the hypothesis that BN particles play a key role in cavity nucleation, impacting the long-term performance of P92 steel.
