Weibull master curves and fracture toughness testing - Part IV - Dynamic fracture toughness of ferritic-martensitic steels in the DBTT-range

Ferritic-martensitic steels are considered to be promising candidates for structural materials in fusion technology. However, they are sensitive to irradiation embrittlement, being characterized by a shift of the ductile-to-brittle transition temperature (DBTT) to higher values. It has already been shown in an earlier publication, that dynamic Weibull master curves are useful in estimating the capacity of materials to undergo stable (micro)cracking prior to brittle failure, if Charpy impact tests are performed in the DBTT-range. Thus, experimental dynamic Weibull master curves of three ferritic-martensitic steels, having been obtained by performing series of instrumented Charpy impact tests at a defined temperature in the DBTT-range, have been evaluated for subsize and, in the case of the reference ferritic-martensitic steel of the European Fusion Technology Program MANET II, for normal-size specimens. It has been observed, that the capacities of stable (micro)cracking of MANET II are nearly optimal and clearly superior to those of the other two considered steels. On the other side, the capacity of stable (micro)cracking prior to failure has been found to be highly specimen-size-dependent, nevertheless it is thought to be an important factor in predicting DBTT-shifts due to irradiation embrittlement. (C) 1999 Kluwer Academic Publishers.