Effects of Irradiation on the Tensile and Fracture Properties of 316L Stainless Steel

Transcription

1 Effects of Irradiation on the Tensile and Fracture Properties of 316L Stainless Steel R. Chaouadi, E. Stergar and S. Gavrilov, Boeretang 200, 2400 Mol, Belgium 1 International Light Water Reactors Material Reliability Conference Chicago, 1 4 August 2016

2 Objectives and Motivation 316L Irradiation hardening saturation at high dpa (roughly above 5 dpa) Most significant effects observed at low fluence levels, typically between 0 and 1 dpa Focus on the 0 1 dpa region Tensile properties evolution Crack resistance behavior Correlation between tensile properties and crack resistance 2

3 Irradiation Hardening of 316L DATA from Robertson et al., ASTM STP 1325 (1999) ITER MPH (Material Properties Handbook) Elen et al., JNM (1992) Maloy et al., OECD/NEA (2002) More significant effects observed in the low dpa range In particular 0 1 dpa RADAMO-12ext Irradiation Program 3

4 PCCv specimens Irradiation Program RADAMO 12ext microstructural bar tensile specimens Irradiation 4 3=12 tensile specimens: L=24 mm, 2.4 mm (A) 3 microstructural bars: 32 mm long, 8.5 mm (A) 6 PCCv (PreCracked Charpy specimens) (E) dosimeters : (A) and (E) 4

5 3 tensile specimens/position Dosimetry and Test Matrix Tensile specimens corresponding to 5 different dpa levels : dpa PCCv specimens corresponding to 5 different dpa levels : dpa Tensile tests at 25 C and 290 C Crack resistance tests at 25 C and 290 C 5

6 Tensile Test Results 6

7 Tensile Test Results From the 3 available specimens One test at 25 C One test at 290 C One spare specimen yield strength Significant effect on the tensile curve 7

8 Tensile Test Results 8

9 Tensile Test Results Strength Significant yield strength increase in the 0 1 dpa range 9

10 Tensile Test Results Strength onset of plastic flow localization Significant Yield strength increase in the 0 1 dpa range (damage rate) 10

11 Tensile Test 25 C De offset De offset yield strength (s y ) Superposition of the irradiated flow curves on the unirradiated one by shifting in the true strain direction (s y irrad (0.2%)= s y unirrad (0.2%+De offset ) Irradiation effect similar to strain hardening 11

12 Crack Resistance Characterization 12

13 Four different techniques are used Crack Resistance Test Results Unloading compliance (UC) Potential drop (PD) ASTM E1820 Normalization data reduction (NDR) Energy normalization used at Test temperatures 25 C 290 C 13

14 Tensile Test Results Strictly speaking, test results are not valid according to E1820 size requirement (inadequate specimen size) Not so critical as we under-estimate actual resistance curve 14

15 Crack Resistance Test Results Based on energy normalization technique 15

16 Crack Resistance Test Results J 0.2 mm J Q No significant effect on initiation toughness (J Q and J 0.2 mm ) and tearing resistance (T M ) T M 16

17 SEM Examination of the Fracture Surfaces TSW4-19 (0.18 dpa) TSW4-18 (0.68 dpa) TSW4-17 (0.79 dpa) DCT (2.5 dpa) No significant effect of irradiation on dimple size suggesting a constant critical void growth rate 17

18 Conclusions The damage rate increases significantly in the low neutron dose range (<1 dpa) Despite the significant changes of the tensile properties (strength and ductility) in the low dpa range, fracture behavior remains almost unaffected Fracture surface examination by SEM show very similar dimple structure Ductility loss is compensated by strength increase allowing an unvariable critical void growth rate 18

19 Closing Remarks Additional tests on specimens irradiated at 300 C to 2.5 dpa (in progress) Microstructural examination Crack resistance tests on specimens irradiated to 5 30 dpa (LEXUR-II) longer term 19