Correlations Between Charpy V-Notch Impact Energy and Fracture Toughness of Nuclear Reactor Pressure Vessel (RPV) Steels

Both Charpy V-notch (CVN) impact energy and fracture toughness are parameters reflecting toughness of the material. Charpy tests are however easy to perform compared to standard fracture toughness tests, especially when the material is irradiated and quantity is limited. Correlations between the two parameters are therefore of great significance, especially for reactor pressure vessel (RPV) structural integrity assessment. In this paper, correlations between CVN impact energy and fracture toughness of three commonly used RPV steels, namely Chinese A508-3 steel, USA A533B steel, Euro 20MnMoNi55 steel, are investigated with two methods. One method applies a direct conversion using empirical formulas and the other adopts the Master Curve method. It is found that when the empirical formula is used, the difference between the predicted fracture toughness (from the CVN impact energy) and actual test data is relatively small in upper shelf, lower shelf and the bottom of transition region, while relatively large in other parts of the transition region. When the Master Curve method is adopted, whether the reference temperature T₀ is estimated through temperature at 28J or 41J CVN impact energy, the predicted fracture toughness values of the three steels are consistent with actual test data. The reference temperature T₀ is also estimated through the IGC-parameter correlation and through a combination of empirical formula and multi-temperature method. Both procedures show excellent agreement with test results. The mean value of T₀ estimated from T_28J, T_41J, IGC-parameters and the combination method is denoted by T_Q-ave and is then used as the final reference temperature T₀ for the Master Curve determination. Accuracy of T_Q-ave (and therefore the Master Curve method) is demonstrated by comparison with actual test data of the three RPV steels. It is concluded that Master Curve method provides a reliable procedure for predicting fracture toughness in the transition region utilizing limited CVN impact energy data from open literature.