A round robin program of Master Curve evaluation using miniature C(T) specimens (comparison of T0 for a weld metal)

The Master Curve approach for the fracture toughness evaluation is expected to be a powerful tool to ensure the reliability of long-term used RPV steels. In order to get sufficient number of data for the Master Curve approach coexistent with the present surveillance program for RPVs, the utilization of miniature specimens, which can be taken from broken halves of surveillance Charpy specimens, is important. CRIEPI has been working on applying the miniature C(T) specimens (Mini-C(T)), whose dimensions are 4 x 10 x 9.6 mm, on the Master Curve fracture toughness evaluation. Miura (2010) had verified the basic applicability of Mini-C(T) specimens for typical Japanese RPV steels. Subsequently, an international round robin activity by Yamamoto (2012, 2013, 2014) assured the robustness of the testing procedure to the difference in testing machines or operators. Similar activity is being carried out for the weld metal materials and the basic applicability of Mini-C(T) was confirmed by Yamamoto (2015). The present paper describes the round robin activity for an un-irradiated weld metal, which is used for the weld filler of PRV plate steels. Four institutes are involved with the round robin tests and 78 fracture toughness data points in total were generated in conformity with ASTM E1921-10e1 (ASTM (2010)). All the participants successfully evaluated the valid reference temperature, To, with their own data set. The discrepancy among the 4 data sets was at the most 14 oC, which is considered as the acceptable scatter range specified in ASTM E1921-10e1. Weibull distribution of the 78 data points suggests that the tested material is in good agreement with the assumption of the Master Curve method, where the Weibull exponent is 4, the minimum fracture toughness is 20 MPa√m. From overall examination results, it was concluded that the miniature C(T) specimen can be used for the Master Curve evaluation of tested PRV weld metal.