Empirical Correlation of Specimen Size Effects in Charpy Impact Properties of 11Cr-0.5Mo-2W, V, Nb Ferritic-Martensitic Stainless Steel

An effect of specimen size on the Charpy impact property was evaluated in the ferritic-martensitic 11Cr-0.5Mo-2W, Nb, V stainless steel (PNC-FMS). The upper shelf energy (USE) is expressed by the power law equation as USE[J]=m(Bb) n where m is the material constant (m=0.277 in PNC-FMS), B[mm] is the specimen thickness and b[mm] is the ligament size. The normalizing exponent n was empirically derived using the USE of the full size specimen as n=1.38×10–3USEfull+1.20. The n value varies in the range of 1.2 to 1.7, which is affected by the fracture volume below the notch. The PNC-FMS wrapper takes n=1.42. The ductile-to-brittle transition temperature (DBTT) of PNC-FMS is correlated as DBTT=115(log10 BKt)—158 using an elastic stress concentration factor Kt that represents the effects of notch size, e.g. notch depth, notch root radius and notch angle.