Effects of chemical compositions of austenitic stainless steel parent metals and weld metals on hydrogen environment embrittlement (HEE) properties were investigated by Slow Strain Rate Testing (SSRT) in gaseous hydrogen environment pressurized at 45MPa. Test results were discussed based on the formation of strain-induced martensite (α′) phase and -ferrite phase. Both solution heat treated parent metals and as-welded metals with higher Md 30 showed higher HEE susceptibility at lower testing temperatures due to an increase in volume fraction of α′ phase during straining. -ferrite phase in weld metals, below 20 volume in this study, showed no effect on hydrogen embrittlement.The detrimental effect of α′ phase would be due to their successive formation at the crack tip. On the contrary, -ferrite phase which was finely dispersed in advance in the weld metals did not affect hydrogen induced crack propagation.
Fatigue properties in high pressure gaseous hydrogen environment were investigated for pipe materials used in fuel cell vehicles and hydrogen stations. Cyclic pressurization tests were conducted using a tubular specimen filled with hydrogen pressurized up to 90MPa. Tested materials were types 316L, 304 and A286 stainless steels, low alloy steels such as JIS SCM435 (1.0Cr-0.2Mo), Cr-Mo-V steels. The fatigue life in hydrogen was compared with that in inert gas to evaluate the effect of gaseous hydrogen on fatigue properties. The fatigue life in hydrogen was slightly shorter than that in argon in the case of a stable stainless steel type 316L. In contrast, a metastable stainless steel type 304 showed a remarkable degradation of the fatigue life in the hydrogen environment. Although the fatigue lives in hydrogen of type 316L and 304 stainless steels decreased with the increase in the cycle times, the fatigue lives remained unchanged over 10 2 of the cycle time. The fatigue life of low alloy SCM435 steel in hydrogen extremely decreased. The fatigue life of high-strength austenitic steel A286 in hydrogen is much better than that of low alloy SCM435 steel at the same tensile strength. The Cr-Mo-V steels showed longer fatigue lives than JIS SCM 435 at same strength levels in hydrogen. Fracture surfaces revealed transgranular cracking for the Cr-Mo-V steels, while intergranular cracking was observed for SCM435 with tensile strength more than 1.2GPa. It was assumed that the carbide precipitation affected the fracture morphology.
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