An investigation into the hydrogen embrittlement susceptibility of experimental 304 stainless steel alloys modified with ruthenium and palladium additions

Doyle, Richard John-Paul (2016). An investigation into the hydrogen embrittlement susceptibility of experimental 304 stainless steel alloys modified with ruthenium and palladium additions. University of Birmingham. Ph.D.

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Abstract

The motivation for this work was provided by the results of an interdisciplinary, multi-university research programme funded by the Ministry of Defence. The significant finding in question was that the stress corrosion cracking (SCC) resistance of AISI type 304 stainless steel (SS) alloys can be significantly improved by the addition of the platinum group metals (PGM), ruthenium and palladium. The increased SCC resistance could be attributed to the enhancement of the cathodic hydrogen reduction reaction. Thus, the primary objective of this work was to confirm that the increase in hydrogen production at the surface would not counteract the improvement in SCC resistance by increasing the susceptibility to hydrogen embrittlement (HE).

Electrochemical hydrogen charging was employed and melt extraction was used to measure the bulk concentration of absorbed hydrogen as a function of alloy chemistry. Both Ru and Pd doped experimental 304 SSs showed a decrease in the concentration of absorbed hydrogen compared to an experimental standard 304 SS (i.e., a controlled, non PGM-doped reference 304). This result is thought to be due to the PGMs enhancing the recombination kinetics of adsorbed hydrogen. Ru proved more effective than Pd at hindering absorption and this is likely associated to the more homogenous distribution of Ru in solid solution.

Slow strain rate tensile (SSRT) testing was performed in air at sub-ambient temperatures on pre-hydrogen charged specimens. PGM addition was found not to increase the susceptibility of 304 to HE. Conversely, an approximately equal enhancement of the HE resistance was observed for the addition of both Ru and Pd. The modest improvements are attributed to the reduced concentration of absorbed hydrogen, with a further possible beneficial trapping effect of Pd concentrated bands, contributing to the HE resistance of Pd doped 304.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):