Theme 2: Characterisation of machined surfaces. F. Scenini, M.G. Burke, L. Chang, L. Volpe and J. Duff

Transcription

1 NNUMAN Theme 2: Characterisation of machined surfaces NNUMAN Final Advisory Board 12 th September 2017 F. Scenini, M.G. Burke, L. Chang, L. Volpe and J. Duff 2017 The University of Manchester, all rights reserved.

2 Theme 4 philosophy Materials in new nuclear plants required to perform for 60 years + Limitations Impossible to test for long period Strategy Accelerated tests required It is impossible to test all the manufactured samples Identify the extreme cases and search for trends A balance between engineering approach (testing) and scientific approach (understanding) is required 2 2

3 Achievements Developed and validated testing relevant to LWR Low pressure / high T rig Slow strain rate testing Identified optimized machining parameters (reduced SCC susceptibility) Develop an understanding of role of machining on microstructure and materials performance Identified role of C surface contamination on SCC initiation Ongoing work tests in more realistic conditions 3

4 Achievements Developed and validated testing relevant to LWR Low pressure / high T rig Slow strain rate testing Identified optimized machining parameters Understood role of machining on microstructure and materials performance Identified role of C surface contamination Ongoing work tests in more realistic conditions 4

5 Materials Performance Centre Validation low P testing rig Alloy 600 𝑹= 𝒑 𝑶 𝟐 𝑵𝒊/ Currently under study More oxidizing environment Ni/NiO NiO stability transition R = 1/24 R = 1/6 R=1 𝑵𝒊𝑶 /𝒑 𝑶 𝟐 More reducing environment Ni stability R=6 R = 24 Developed and validated testing relevant to LWR Low pressure / high T rig - Quicker/cheaper testing - Obtained mechanistic understanding of SCC (Molander et al., 2011) 5

6 Development SSRT in LWR Materials Performance Centre distance 50 µm Extensive IG and TG cracking 50 µm Limited IGSCC No SCC Threshold for SCC identified at strain ~2% on OPS sample 6

7 Achievements Developed and validated testing relevant to LWR Low pressure / high T rig Slow strain rate testing Identified optimized machining parameters (reduced SCC susceptibility) Develop an understanding of the role of machining on microstructure and materials performance Identified role of C surface contamination on SCC initiation Ongoing work tests in more realistic conditions 7

8 Optimization of machining parameters for annealed 316 SS Cracks confined in the machined layer Crack depth (Micron) Average crack depth Maximum crack depth 1-N-C 2-N-C 3-N-C Sample 2 industrial number standard 1 is best productivity Slip band Interface Nano grains 3 optimized machining Machining mark orientation appeared to affect SCC initiation Residual stress does not have a measurable effect on SCC initiation susceptibility Successfully identified the optimized machining parameters and correlated with SCC behavior of Annealed 316SS Distritubion of regions cracks stopped

9 Achievements Developed and validated testing relevant to LWR Low pressure / high T rig Slow strain rate testing Identified optimized machining parameters (improved SCC resistance) Develop an understanding of role of machining on microstructure and materials performance Identified role of C surface contamination on SCC initiation Ongoing work tests in more realistic conditions 9

10 Materials performance of forged 304 SS Materials Performance Centre Polished surface Machined surface Metallographic cross section of machined surface Crack mainly on the polished surface IG in nature Effect of machining parameters not as obvious as for annealed materials Apparent improved resistance possibly associated to presence of ultrafine-grained layer Similar trend identified for cold worked 316 SS 10

11 NNUMAN Thanks for your attention! 11