PSI - Issue 52

Jiri Dvorak et al. / Procedia Structural Integrity 52 (2024) 259–266 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

263

5

Fig. 4. Variation of minimum creep rate with applied stress at 600°C for P92 steel

Fig. 5. Variation of time to fracture with applied stress at 600°C for P92 steel

3.4. Creep damage development and fracture SEM examination of fracture surfaces of creep tested specimens are shown in Fig. 6. Independently of loading condition, both fractures are dominated by plastic strain of the matrix characterised by dimples resulting from coalescence of microvoids at all stresses conditions studied in this investigation. The dimple pattern in Fig.6 is typical of ductile transgranular fracture.

Fig. 6. SEM micrographs of fracture surface of P92 steel after creep testing at 600°C and a) 180 MPa and b)250 MPa.

3.4. Acoustic emission (AE) testing For the purpose of service life prediction of energy equipment, it is important to determine the time period where occurs a significant process of physical microstructural changes in the material. This state is generally represented in creep by the end of the stationary stage and the beginning of the tertiary stage. In this work, the AE signal was recorded during the creep tests at regular intervals three times a day for 15 minutes. In contrast to the classic evaluation of AE, where the overshoot of the signal over a set value is primarily searched for, in this work the events were found and