[ materials ]
Table 4 . Main values from testing at 85 – 87.5 MPa H 2 compared to requirements in SAE J2579
Property |
Rp0.2 ( MPa ) |
Rm ( MPa ) |
A (%) |
Rm / Rp0.2 |
Requirement |
> Spec . min . |
> Spec . min . |
> 12 |
> 1.07 |
Grade |
Spec . min . |
H 2 |
Spec . min . |
H 2 |
H 2 |
H 2 |
EN 1.4404 |
220 |
302 |
515 |
683 |
70.4 |
2.26 |
EN 1.4435 |
220 |
300 |
515 |
653 |
82.1 |
2.17 |
UNS S31675 |
430 |
661 |
690 |
1001 |
46.5 |
1.51 |
UNS S21900 |
827 |
1085 |
979 |
1201 |
29.5 |
1.11 |
elements described in the nickel equivalent formula suppress the formation of deformation martensite .
The results for the non-cold-worked grades are not surprising : good results were obtained for EN 1.4435 , UNS S31603 with high nickel content , as well as for UNS S31675 , and lower resistance was observed for EN 1.4404 , UNS S31603 with lower nickel content . 4 , 6 Avoiding deformation martensite has been proposed as a key factor for austenitic stainless steels to achieve good resistance to embrittlement in hydrogen gas . 8 The two grades with lower nickel content in the study have increased levels of Mn and N , which compensate for the reduced Ni . Even though the nickel content is 9.6 % and 7.2 % for UNS S31675 and UNS S21900 , the nickel equivalents are above 33 . EN 1.4404 has a nickel content of 11.4 % but only 27.4 nickel equivalent value . Therefore , the use of the Ni-equivalent seems more appropriate than only comparing the Ni content for describing the resistance to hydrogen embrittlement in hydrogen gas , as discussed earlier . 5 , 6 , 9
The results show that UNS S21900 and UNS S31675 , which have higher mechanical strength , both have good resistance to embrittlement in hydrogen gas . UNS S31675 is similar to EN 1.4435 . The cold-worked condition of the UNS S21900 tube results in a ductile fracture in the hydrogen testing .
Conclusion
All four tested materials , including coldworked UNS S21900 , passed the acceptance criteria defined in SAE J2579 . The comparison of ductility parameters for hydrogen-charged specimens with those in an inert environment , combined with the study of the fracture surface , demonstrated the importance of sufficiently good austenite stability . The grades with a Ni-equivalent around and above 30 showed negligible influence of hydrogen . In contrast , EN 1.4404 , with a lower Ni-equivalent , experienced brittle failures .
References
¹ SAE International . ( 2018 ). Standard for Fuel Systems in Fuel Cell and Other Hydrogen Vehicles ( SAE Standard No . J2579 ). ² Metallurgical and Materials Transactions A 41 ( 2010 ): p . 3348 . ³ Sandia National Laboratories . ( 2005 ). Technical Reference on Hydrogen Compatibility of Materials : Austenitic Stainless Steels : 21-6-9 ( code 2202 ).
4
International Journal of Hydrogen Energy 41.33 ( 2016 ): p . 15095 .
5
Journal of Alloys and Compounds 696 ( 2017 ): p . 869 .
6
Metallurgical and Materials Transactions A 48 ( 2017 ): p . 5717 .
7
Kivisakk , U ., Bosbach , B ., Cederberg , E ., Borggren , U ., & Zhou , N . ( 2023 ). Stainless Steels for Automotive Applications – Hydrogen Embrittlement Testing for High Pressure Hydrogen Gas Using Different Methods . Paper presented at the 2023 AMPP Annual Conference , paper no . 19214 , Houston , TX .
8
Acta Metallurgica et Materialia 38.11 ( 1990 ): p . 2031 .
9
Metals 11.4 ( 2021 ): p . 637 .
Hydrogen Tech World | Issue 17 | August 2024 47