Prediction of Fracture Toughness K_IC Transition Curves of Pressure Vessel Steels From Charpy V-Notch Impact Test Results

A single and generalized prediction method of fracture toughness K_IC transition curves of pressure vessel steels has been greatly desired by engineers in the petro-chemical and nuclear power industries, especially from the viewpoint of life extension of reactor pressure vessels. In this paper, the toughness degradation of Cr-Mo steels during long-term service was examined and the two prediction methods of fracture toughness K_IC transition curves were studied using the data of 54 heats. 1) The toughness degradation of 2 1/4Cr-1Mo steels levels off within around 50,000 h service. 2) The FATT versus J-factor (=(Si+Mn)(P+Sn)×10⁴) and/or X (=(10P+5Sb+4Sn+As)x10⁻²) relationships to estimate the maximum embrittlement of Cr-Mo steels were obtained. 3) A master curve method developed by authors et al.; that is, the method using a K_IC/K_IC−US versus excess temperature master curve of each material was presented for 2 1/4Cr-1Mo, 1 1/4Cr-1/2Mo, 1Cr and 1/2Mo chemical pressure vessel steels and ASTM A508 C1.1, A508 C1.2, A508 C1.3 and A533 Gr.B C1.1 nuclear pressure vessel steels, where K_IC−US is the upper-shelf fracture toughness and excess temperature is test temperature minus FATT. 4) A generalized prediction method to predict the K_IC transition curves of any low-alloy steels was developed. This method consists of K_IC/K_IC−US versus T–T₀ master curve and temperature shift ΔT between fracture toughness and CVN impact transition curves versus yield strength relationship, where T_o is the temperature showing 50 percent K_IC−US of the material. 5) The K_IC transition curves predicted using both methods showed a good agreement with the lower bound of measured K_JC values obtained from J_C tests.