DBTT shift of Optifer-IX, Eurofer 97 and MA956 steels after irradiation evaluated with small punch tests

C.F Yao,Y Dai

doi:10.1016/j.jnucmat.2020.152725

Abstract

In order to analyze the irradiation-induced changes of ductile-to-brittle transition temperature (DBTT) of ferritic/martensitic (FM) steels, small punch (SP) tests were conducted on the specimens of Optifer-IX, Eurofer 97 and MA956 steels after irradiation in a target of the Swiss spallation neutron source (SINQ) at doses between 8.5 and 18.8 dpa and temperatures between 165 and 365°C. The SP test results demonstrate that the DBTT of the three steels increases with irradiation dose, which is in agreement with the previous results of SP and Charpy impact tests on FM steels irradiated at SINQ. Both SP and SEM observation results indicate that, among the three steels, Eurofer 97 possesses the highest resistance to irradiation-induced embrittlement. On the other hand, the ferritic ODS steel MA956 exhibits the poorest radiation resistance, manifested by the higher DBTT in both unirradiated and irradiated conditions and higher DBTT shift after irradiation as compared to Optifer-IX and Eurofer 97 steels.

Highlights

High-Chromium ferritic/martensitic (FM) steels show high strength at elevated temperatures [1] and excellent swelling resistance to neutron irradiation [2], which make them attractive for applications in the future fusion reactors and generation nuclear energy systems, e.g. lead cooled fast reactors
The results demonstrate the non-saturate ductile-to-brittle transition temperature (DBTT) shift at doses above 10 dpa, which indicates that helium has a great impact on the embrittlement of FM steels
small punch (SP) testing was performed on FM steels Optifer IX and Eurofer 97 and ferritic ODS steel MA956 irradiated at doses up to 18.8 dpa in the fourth target of SINQ to enrich the existing DBTT database of FM steels under irradiation of neutrons and high-energy protons

Summary

Introduction

High-Chromium ferritic/martensitic (FM) steels show high strength at elevated temperatures [1] and excellent swelling resistance to neutron irradiation [2], which make them attractive for applications in the future fusion reactors and generation nuclear energy systems, e.g. lead cooled fast reactors. It has been established that the DBTT evaluated with SP testing (DBTTSP) can be correlated with that of Charpy impact testing (DBTT): DBT TSP = αDBT T (1). The DBTT shift ( DBTT) of FM steels such as F82H, Optifer, Eurofer and Optimax was evaluated by Charpy impact testing on specimens KLST size, namely 3 × 4 × 27 mm3 [10] after irradiation in the targets of the Swiss spallation neutron source (SINQ) at the Paul Scherrer Institute (PSI). SP testing was performed on FM steels Optifer IX and Eurofer 97 and ferritic ODS steel MA956 irradiated at doses up to 18.8 dpa in the fourth target of SINQ to enrich the existing DBTT database of FM steels under irradiation of neutrons and high-energy protons

Experimental

Load-displacement curves

Evaluation of DBTTSP

Analysis of the fracture mode