Evaluation of Crack Arrest Toughness (K-IA) of P91 Steel in Various Cold Worked and Thermally Aged Conditions

摘要

K (IA) is increasingly being regarded as a characteristic fracture toughness below which cleavage fracture does not occur. Its evaluation from small-sized Charpy specimens would be advantageous for applications in power plant industries. In this study, K (IA) has been evaluated for P91 steel in various cold worked and thermally aged conditions. Evaluation of K (IA) requires determination of crack arrest load(P (arrest)) and crack arrest length(a (arrest)). The main challenge is in the determination of a (arrest) due to the non-availability of standard methodologies and the absence of unequivocal microstructural signatures on the fracture surface in this steel to identify crack arrest. a (arrest) has been determined using the analytical Key-Curve methodology which has proven successful for this steel in unaged condition. The applicability of the Key-Curve method is validated by the good agreement of the determined final crack length with that measured optically on unbroken specimens of N&T and subsequently 15% cold-worked P91 steel which had been previously aged at 650 A degrees C for 5000 h. Mean K (IA) varies from 47.46 MPaaem (NT steel aged at 600 A degrees C for 5000 h) to 69.85 MPaaem(NT + 15% cw steel aged at 650 A degrees C for 10000 h) for the various cold worked and aged datasets. K (IA) is found to be an average property unlike initiation toughness (K (Jd)) which shows statistical scatter. Mean K (IA) is found to be in reasonable agreement with the lower bound values of cleavage initiation toughness (K (Jd)) for the datasets in this study.