Toshio OGATA Materials Information Station National Institute for Materials Science

1. Hydrogen Environment Embrittlement on Austenitic Stainless Steels from Room Temperature to Low Temperatures Toshio OGATA Materials Information Station National Institute for Materials Science

2. Background: Hydrogen system for clean energy Application Production Hydrogen station/Storage Transportation Transport Liquid or High pressure gas Production/ Liquefier, compress Storage+Compress Production Filling Vehicle/Home • Promotion of Fuel-cell vehicle (Oct. 2002) • Cruising range: 300 km to 500 km • Pressure of tank: 35 MPa to 70 MPa • hydrogen environment embrittlement of the materials which are not hydrogen-charged but used under high pressure hydrogen environment

3. No data on high pressure & low temperatures 70 MPa & 20-100 K Request of data on low temperature & high-pressure hydrogen environment Produce high pressure hydrogen gas by quickly evaporating liquid hydrogen without compressor Hydrogen station/Storage Storage+Compress Production Filling Difficult for the traditional method to evaluate hydrogen environment embrittlement at low temperature using a high pressure chamber. Breakthrough in testing was required

4. Current equirements in Japan for the materials for use in H2 • Less influence of high-pressure (70MPa or more) in hydrogen environment and at low temperatures • Relative reduction of area in H2 > 0.7 to 0.8 • Reduction of are in H2 > 0.6 to 0.7 • Japanese steel makers developed the materials but still expensive • Looking for the possibility of cheaper materials

5. Testing machine for high-pressure hydrogen environment Tester Tester Regulations Not easy high pressure gas High pressure Gas Fear Expensive Test piece Facillities & maintenance 70 MPa cylinder Sealing is difficult Chamber Machine at AIST This kind of method requires facilities of high pressure hydrogen for testing and regulations: cost very expensive, not easy to carry out

6. Simple method for evaluating Hydrogen environment embrittlement • Produce any environments in a small hole inside specimen • Inner diameter of the hole is less than 2 mm (1 mm is enough) • Hydrogen environment is one of the application of this method • Applied to tensile tests , fatigue tests and other uni-axial tests • Has been applied for a patent in Japan (2006-077403) Pressure gauge Tester specimen

7. Load-displacement curves Load (kN) Load (kN) Displacement (mm) Stroke (mm) Displacement (mm) Load (kN) Displacement (mm)

8. Fracture surfaces of 304 RT H2:13 MPa 2 mm 100mm 77 K H2:13 MPa 190 K H2:13 MPa 316L 190K H2:13MPa 100mm 100mm

9. Hydrogen environment embrittlement for SUS 304, 304L, and 316L Previous report from AIST for various austenitic stainless steels at 80-300 K under 1.1 MPa H2 using high pressure chamber In these steels, effects of hydrogen embrittlement from RT to 200 K was explained by increase of a’-phase behavior The results by this method were the same to the usual methods using a high pressure chamber, which proves the effectiveness of this simple method. The effect of stress induced hydrogen and vacancy diffusion

10. Amount of strain-induced martensite during tensile tests at low temperatures in hydrogen and helium environment 80 60 40 Amount of strain-induced martensite(%) 20 SUS316L He 0

11. Gas change tests 70MPa He ガス置換 70MPa H2 H2->He @11MP 70MPa He Gas change to He 70MPa H2 H2->He @11MP Stress Displacement

12. Gas change tests Stress Displacement

13. S-N curves for SUS304 H2 H2 He 190K He RT RT190K □　　◇　70MPaHe ■　　◆　70MPaH2 R=0.01

14. S-N curves for SUS304L 190K 190K RT RT

15. S-N curves for SUS3１６L 190K RT RT190K △□△□He ▲　　▲10MPaH2 ■■　70MPaH2 R=0.01

16. Fatigue properties for SUS304L and yield strength Stress-strain curves of SUS304L S-N curves of SUS304L 400 190K 190K 300 ←σ0.2@190K ←σ0.2@RT Stress (MPa) 200 RT sa=200MPa sa 100 sa=150MPa RT 0 10 Amount of martensite during tensile tests 8 RT190K □　　◇　He ■　　◆　10MPaH2 ■　　◆　70MPaH2 6 Amount of strain-induced martensite(%) 190K 4 RT 2 0 Strain(%)

17. Summary No effect of hydrogen on the amount of martensite was observed during tensile tests. In the meta-stable stainless steels, there is no HEE until the certain amount of deformation in tensile tests. No HEE until at a certain stress level or amount of bcc phase. Fatigue life of SUS 304 and 304L in hydrogen environment decreased at 200 MPa or 250 MPa, at RT and 190K. No influence at a stress level of 150 MPa (yield strength). In SUS316L, influence of hydrogen is small even at a stress level of 250 MPa. No effect of HEE on austenitic stainless steels unless the amount of the ferrite phase is small. Probably, less than 10 %.

18. Thank you for your attention

19. Plastic strain vs. Ferrite content

20. Ferrite contents less than 10% strain