Fracture Toughness and the Master Curve for Modified 9Cr-1Mo Steel

Modified 9Cr-1Mo steel is a primary candidate material for the reactor pressure vessel of a Very High Temperature Gas-Cooled Reactor (VHTR) in the Korean Nuclear Hydrogen Development and Demonstration (NHDD) program. In this study, the T0 reference temperature, J-R fracture resistance and Charpy impact properties were evaluated for commercial Grade 91 steel as part of the preliminary testing for a selection of the RPV material for the VHTR. The fracture toughness of the modified 9Cr-1Mo steel was compared with that of SA508-Gr.3. The objective of this study was to obtain the pre-irradiation fracture toughness properties of the modified 9Cr-1Mo steel as reference data for an investigation of radiation effects. Charpy impact properties of the modified 9Cr-lMo steel were similar to those of SA508-Gr.3. T0 reference temperatures were measured as -67.7 and -72.4℃ from the tests with standard PCVN (pre-cracked Charpy V-notch) and half-sized PCVN specimens respectively, which were similar to the results for SA508-Gr.3. The K(jc) values of the modified 9Cr-1Mo steel with the test temperatures are successfully expressed by the Master Curve. The J-R fracture resistance of the modified 9Cr-1Mo steel at room temperature was nearly identical to that of SA508-Gr.3; in contrast, it was slightly higher at an elevated temperature.