Evaluation of the ductile–brittle transition temperature in the NESC-I material using small punch testing

• Small punch fracture testing was applied to an RPV steel from the NESC-I project.
• Four different procedures for DBTT evaluation from SP test data were assessed.
• Fracture mode transition temperature TFM was identified as a valid parameter.
• Results were compared to original NESC-I data and α correlation factors evaluated.

Small punch (SP) fracture testing with subsequent SEM fractographic analysis was applied to an A 508 Class 3 reactor pressure vessel (RPV) steel, used originally in the NESC-I spinning cylinder experiment, in order to determine the SP ductile–brittle transition temperature of both the base material and the sub-clad heat affected zone. In addition to the evaluation of the SP transition temperature, TSP, corresponding to the mean value of upper and lower shelf SP fracture energies, three alternative procedures were assessed. The SP transition temperatures were then compared to original NESC-I data obtained using conventional testing methods, which yielded values of the empirical correlation factor α consistent with those reported in literature for RPV steels of similar composition. The evaluation of the fracture mode transition temperature TFM from the SP test was identified as a viable procedure, in particular for the case when lower shelf energy data cannot be obtained due to technical limitations associated with very low testing temperatures.