A statistical analysis of test results on 1000 transportation and storage casks revealed the main parameters that determine the properties of DI (ductile iron, a special form of cost iron). These data were used to established a test program in which the mechanical properties (particularly fracture toughness) of 24 DI alloys were determined as a function of their microstructure. Furthermore, the analysis emphasized the effect of test specimen size and different test data evaluation methods. Results of the test program show the prominent effect of pearlite content and graphite nodule structure in the mechanical and fracture toughness characteristics of DI. As the first-order parameter, the pearlite content is responsible for the transition from linear-elastic to elastic-plastic material behavior. The structure of the graphite nodules has a strong effect on the magnitude of the material property values. On the lower shelf, materials with small, homogeneously distributed graphite nodules show higher K(sub IC)-values (matrix-oriented fracture). On the upper shelf, materials with larger graphite nodules show higher fracture toughness (graphite-oriented fracture). With smaller specimens, conservative values were calculated on the upper shelf. This is important for transportation and storage containers of radioactive materials.
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