Application of the master curve to inhomogeneous ferritic/martensitic steel

Three sizes of fracture toughness specimens of F82H steel were tested to verify the master curve concept. Specimens were tested at several temperatures in the transition region with at least four tests at each temperature to allow application of the Weibull statistic/master curve analysis procedure. The largest specimens were 1 T C(T) compact specimens. Broken halves of 1 T C(T) specimens were later used to machine and test smaller, 0.4 T C(T) and 0.18 T DC(T), specimens more suitable for irradiation experiments. The scatter of fracture toughness was rather high relative to scatter predicted by conventional master curve concept, but was similar for larger and smaller specimens. It was assumed that this material exhibited inhomogeneity of fracture toughness. Random inhomogeneity analysis provides a very good description of the scatter of fracture toughness data of F82H steel. At the same time, values of T0 derived using conventional and random inhomogeneity analyses are similar. TEM and SEM analysis helped identify microstructural features that might be responsible for such behavior.