The effect of stress state on the fracture behavior of SA508 Gr.3 steel in the transition temperature region has been investigated using notched round tensile specimens of various notch root radii. The test results showed that the fracture stress and fracture strain are strongly dependent on the stress triaxiality ; the fracture stress increases with the stress triaxiality, while the fracture strain decreases with the stress triaxiality. The fracture stress is nearly independent of the test temperature. However, the fracture strain reveals typical ductile-to-brittle transition with lower and upper shelf. The transition behaviors of the fracture strain, such as the ductile-to-brittle transition temperature(DBTT) and upper shelf value, are strongly affected by the stress state. Also, a model for evaluating the fracture toughness($K_c$) from the tensile test results is proposed and applied. The fracture toughness values calculated with the model are statistically analysed according to the ASTM E1921 method and the results are compared with the results from three-point bend(TPB) specimens.
