Analysis of Radiation Embrittlement Results from a French Forging Examined in the Second Phase of an IAEA-Coordinated Research Program

Abstract

Test blocks of a manganese-nickel-molybdenum (Mn-Ni-Mo) low-alloy steel, machined from a nozzle cut-out of a 230-mm-thick forging shell, were provided by France in 1978 to be investigated in the second phase of an IAEA-coordinated research program on the behavior of advanced pressure vessel steels under neutron irradiation. The results obtained by different laboratories exhibit a great deal of scatter in Charpy-V transition temperatures, both in the initial condition and after neutron irradiation. Therefore, the shifts in Charpy-V transition curves induced by neutron irradiation at similar fluences of about 3 × 1023 n ∙ m-2 (E ⩾ 1 MeV) cover a wide temperature range from 0 up to 110°C. A more detailed investigation of these results was undertaken, and additional Charpy tests were conducted to clarify the considerable uncertainty about the sensitivity of this forging to radiation embrittlement. The differences in results were found to be due to the various orientations and locations of the Charpy-V specimens extracted by the different laboratories, in some cases to insufficient test data in the transition region of the Charpy curve, and to the detrimental effect on Charpy-V properties of segregated zones (ghost lines) found in specific locations of large forgings.

Absorbed impact energy and mode of fracture: A statistical description of the micro-structural dispersion

“…The fit parameters are listed in Table 1. The overall quality of the fit is satisfactory whereas the extracted value of the transition temperature shift after irradiation, dT 0 % 103 K, is close to the value reported by the authors, dT DBT = 111 K [8]. By rescaling the energy and temperature (Eq.…”

“…Fig. 1a displays data of Charpy V-notched specimens (referred hereafter to as CVN) for steel 16MND5 (close to grade ASME SA508C13) before and after irradiation [8], together with the best fits of Eq. (4) to the data.…”

“…2, the master curve is drawn together with the above experimental data for steel 16MND5 [8] and data for niobium [9], vanadium [10] and tungsten [11]. The fit parameters are listed in Table 1.…”

“…Both Figs. 1b and 2, indicate that in these reference and irradiated materials the mechanisms of plastic energy absorption [8]), Nb (full squares, [9]), V (full circles, [10]) and W (full triangles, [11]). Values of the fitting parameters are given in Table 1.…”

“…In the following paragraphs, the model is introduced and its principal implications are derived. The validation of the model is then made through a comparison with experimental data for steels [8,[13][14][15][16][17] and refractory metals [9][10][11] discussed and reasons in favor of further developing quantitative fractography are given.…”