Neutron irradiation effects on mechanical properties of new EUROFER97 grades developed by SCK CEN and OCAS NV

Neutron irradiation effects on mechanical properties of new EUROFER97 grades developed by SCK CEN and OCAS NV S.Valiyev1,3, A. Puype2, A. Zinovev3, D. Terentyev3, W.Wale1, and R. H. Petrov1 1Ghent University, Technologiepark Zwijnaarde 46, 9052 Zwijnaarde 2OCAS NV, Pres. J.F. Kennedylaan 3, 9060 Zelzate, Belgium 3Belgian Nuclear Research Centre, SCK•CEN, Mol, Belgium E-mail: [email protected] Introduction Reduced Activation Ferritic Martensitic (RAFM) steels are considered the baseline structural materials for the ITER Tritium Breeding Module (TBM) and Eurofer97 is playing as the reference RAFM alloy for European developed TBM concepts. The currently designed operational temperature window of Eurofer97 is constrained at low temperatures by irradiation-induced hardening and embrittlement, and at high temperatures by creep phenomena. To address these limitations, new grades of Eurofer97 have been developed at SCK CEN and OCAS NV. These advanced variants aim to extend the operational temperature range (350 - 550 °C) of the alloy. For low-temperature applications (280-300 °C), the focus has been on reducing the ductile-to-brittle transition temperature (DBTT). For high-temperature (up to 650 °C) application, strength improvements have been achieved by promoting the precipitation of stable tantalum (Ta) and vanadium (V) carbonitrides, which strengthen the steel and resist coarsening under prolonged thermal exposure without degrading low temperature properties. Results Materials and Methods Discussion Conclusion Irradiation up to 3 dpa at 300 °C led to pronounced hardening and a reduction in ductility in all material grades. LT grades exhibited a lower DBTT and a smaller DBTT shift, indicating better resistance to embrittlement. In contrast, HT grades particularly grade U showed a significantly higher DBTT shift, reflecting increased susceptibility to irradiation induced embrittlement. Despite these effects, all specimens maintained total elongation above 15% at room temperature and 10% at 300 °C, with ductile fracture behavior confirmed by the presence of dimples on fracture surfaces. www.sckcen.be 123Posternr Element E J X U W Cr 8.83 9 9 8.6 8.85 C0.107 0.107 0.107 0.04 0.047 Mn 0.527 0.39 0.39 0.41 0.41 V0.2 0.22 0.22 0.23 0.29 N0.019 0.022 0.022 0.062 0.029 W1.081 1.1 1.1 0.85 0.96 Ta 0.117 0.11 0.2 0.38 0.1830 Si 0.0352 <0.04 <0.04 0.030 Code Material type Heat ID Final heat treatment Manufacturer/ Provider E (Ref) EUROFER97/2 (plate) 993391 980°C/0.5h + WQ + 760°C/1.5h + AC Saarschmiede JEUROFER-LT P420 880°C/0.5h + WQ + 750°C/2h + AC OCAS NV/ SCKCEN XEUROFER-LT P421 880°C/30 min + quench + 750°C/120 min OCAS NV/ SCKCEN UEUROFER-HT M472 1050°C/30 min + quench + 720°C/90 min OCAS NV/ SCKCEN WEUROFER-HT M475 1050°C/30 min + quench + 740°C/50 min OCAS NV/ SCKCEN Table 2. Heat treatment and processing route of EUROFER97 grades. Table 1. Chemical compositions of EUROFER97 grades in wt %. −100 −50 050 100 0 2 4 6 8 10 Absorbed energy [J] Temperature [°C] P421 (X) P420 (J) M472 (U) M475 (W) E97/2 (E) Irradiation up to 3 dpa at 300°C Drawing of (a) the miniaturized tensile sample and (b) KLST samples included in irradiation campaign LOT SDQ and E. Lower than EUROFER97 Higher than EUROFER97 U W X E J 20 40 60 80 100 120 140 RT 300 °C RT 300 °C ΔYS (%) Materials Lot E Dose: 3.1–3.4 dpa Temp: 275–300 °C Lot SDQ Dose: 2.96–3.22 dpa Temp: 275–300 °C U W X E J 10 20 30 40 50 60 70 80 90 100 RT 300 °C RT 300 °C ΔUTS (%) Materials Lot E Dose: 3.1–3.4 dpa Temp: 275–300 °C Lot SDQ Dose: 2.96–3.22 dpa Temp: 275–300 °C U W X E J −100 −90 −80 −70 −60 −50 RT 300 °C RT 300 °C ΔUE (%) Materials Lot E Dose: 3.1–3.4 dpa Temp: 275–300 °C Lot SDQ Dose: 2.96–3.22 dpa Temp: 275–300 °C U W X E J −60 −50 −40 −30 −20 −10 RT 300 °C RT 300 °C ΔTE (%) Materials Lot E Dose: 3.1–3.4 dpa Temp: 275–300 °C Lot SDQ Dose: 2.96–3.22 dpa Temp: 275–300 °C Relative changes in tensile properties (a) (b) Irradiation at BR2 up to 3 dpa at 300 C U W X E J 400 500 600 700 800 900 1000 1100 1200 YS (MPa) Materials Non-irradiated RT 300°C Irradiated RT 300°C U W X E J 500 600 700 800 900 1000 1100 1200 UTS (MPa) Materials Non-irradiated RT 300°C Irradiated RT 300°C U W X E J 5 10 15 20 25 30 35 40 TE (%) Materials Non-irradiated RT 300°C Irradiated RT 300°C U W X E J 0 2 4 6 8 UE (%) Materials Non-irradiated RT 300°C Irradiated RT 300°C 1. Tensile test results of non-irradiated and irradiated materials 2. Impact test results of irradiated materials. 3. Hardness test results of non-irradiated and irradiated materials E J X W U 0 100 200 300 400 500 Vickers Hardness (HV) Materials Irradiated Unirradiated E J X W U 0 20 40 60 80 100 120 140 ΔVickers Hardness (HV) Materials P420 P421 E97/2 M475 M472 −60 −40 −20 0 20 40 60 80 60 80 100 120 140 160 DBTT after irradiation Shift in DBTT DBTTirr[°C ] ΔDBTT [°C ] Irradiation up to 3dpa at 300 °C Relationship between UTS and Vickers Hardness −100 −80 −60 −40 −20 020 40 60 80 100 0 20 40 60 80 100 Shear Fract. App. Temperature [°C] P421 (X) P420 (J) M475 (W) E97/2 (E) M472 (U) E J X W U 0 10 20 30 40 50 60 70 Increase in Vickers Hardness (%) Materials Irradiation up to 3 dpa at 300 °C Irradiation induced Shift in DBTT RT 300 °C The presence of dimples on the fracture surfaces of irradiated samples tested at both room temperature and 300 °C confirms that fracture occurred in a ductile manner. For conventional tempered martensitic steels values for α changes between 2.6 and 3.5 and for ferritic steel reported value is about 3.05. α =3.25 260 270 280 290 300 310 320 330 340 800 900 1000 1100 1200 E J U W X UTS [MPa] Vickers Hardness [HV5] Linear Fit of "UTSirr" vs "Vickers Hardnessirr" Equation y = a + b*x Plot UTS Weight No Weighting Intercept 0 ± -- Slope 3.2484 ± 0.07 Residual Sum of Sq 10703.14805 Pearson's r 0.9989 R-Square (COD) 0.99781 Adj. R-Square 0.99726 Irradiation up to 3dpa at 300 °C