Irradiation and Annealing Behavior of 15Kh2MFA Reactor Pressure Vessel Steel

Abstract

This work deals with the mechanical properties of reactor pressure vessel (RPV) steels used in the pressurized water reactors (PWR) of former Soviet type WWER-440. The materials under investigation were a forging (base metal 15Kh2MFA) and the corresponding weld. Charpy V-notch specimens and tensile test specimens were irradiated in the PWR WWER-2 Rheinsberg at about 270°C up to the two neutron fluence levels of 4 × 1018 and 5 × 1019 n/cm2 (E > 1 MeV). Post irradiation annealing heat treatments were performed, among others a 475°C/152 h treatment of technical interest. A set of experimental data is given regarding the influence of sampling depth (through thickness position within the forging), neutron irradiation, and annealing on the properties derived from instrumented Charpy impact testing, tensile and hardness tests. The ferrite content varies through the thickness of the forging. The variation of the mechanical properties can be explained qualitatively with the varying ferrite content. The surface layer of the forging is more sensitive to neutron irradiation than material from the 1/4-T position. To evaluate the effect of annealing heat treatment, the kinetics of the recovery process for the hardness has been investigated. The recovery coefficients for different mechanical properties and parameters have been compared. The annealing behavior is too complex to predict the effect of a large-scale annealing of an RPV on the basis of single hardness measurements.