Fracture Toughness of Ferritic Steels: Lower Bounds and their Implications on Testing and Application

For physical reasons fracture toughness KJc of ferritic steels in the brittle-to-ductile transition regime is affected by a pronounced scatter, which requires statistical methods to be applied for evaluation of test results as well as for application in safety analysis of structures. For this purposes the probabilistic Master-Curve-approach according to ASTM E1921 is often used. However, for engineering purposes like a screening safety analysis of a defect-containing component it is usually preferable to use a deterministic lower bound. However, within the framework of ASTM-standards there is no possibility to determine KIc experimentally. So KIc needs to be determined indirectly from the reference temperature T0. In the present paper it is shown how lower bounds of fracture toughness – either plane strain KIc for large components or thickness-dependent KJc for smaller ones - can be derived from T0, and how the latter can be determine with sufficient accuracy from one or a few KJc values.