Evaluation of Tensile Properties and Ductile-Brittle Transition Temperature in Bainitic Low Alloy Steels using a Small Punch Test

摘要

Small punch (SP) test was performed to evaluate tensile properties and ductile-brittle transition behavior of various reactor pressure vessel (RPV) steels with bainitic microstructure in the temperature range of R.T. to -196 deg C. The testing specimens were taken from 1/4t location of one weld and six forged RPV steels manufactured by the different processes and machined to a dimension of 10X10X0.5 mm. Yield strength and maximum strength from SP test were successfully correlated with yield strength in all temperature ranges and tensile strength in the upper shelf region of SP energy versus temperature curves. Weibull statistical analysis was a useful method to determine the mean value of SP energy in the transition region and the SP transition temperature even for the very limited number of SP specimens. Transition temperature determined at mid-point of upper and lower SP energy (T_sp) was successfully correlated to the index transition temperature from standard Charpy impact test and T_0 value from the precracked V-notched three-point bend fracture(PCVN) test. From the observation of the outer surface of the tested SP specimens, it was found that the SP energies were proportional to the lengths of the largest residual crack that did not lead to a fatal main crack. Small punch local fracture stress obtained by considering Griffith theory exhibited some meaningful agreement with local fracture stress obtained from the PCVN test.