Effect of titanium and vanadium nano-carbide size on hydrogen embrittlement of ferritic steels
T. Boot (TU Delft - Team Vera Popovich)
Pascal Kömmelt (Tata Steel Europe Limited)
Hans J.C. Brouwer (TU Delft - Team Marcel Hermans)
Amarante J. Bottger (TU Delft - Team Amarante Bottger)
V. Vera (TU Delft - Team Vera Popovich)
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Abstract
The effect of TiC and VC nano-precipitate size on the hydrogen embrittlement of ferritic steels was studied in this work. Steels containing two size distributions (10 nm or less and 10 - 100 nm) of TiC and VC carbides are subjected to tensile tests in-situ in an electrochemical hydrogen charging environment. Hydrogen is found to be trapped in interstitial matrix sites on the precipitate/matrix interface with activation energies of 14 - 20 kJ/mol and inside misfit dislocation cores with energies of 27 - 37 kJ/mol. All steels are embrittled by 15 to 20%, except the TiC steel with semi-coherent carbides up to 100 nm, which is embrittled by 37%. This is caused by accelerated intergranular fracture as a result of hydrogen trapped in dislocation pile-ups around grain boundary precipitates. The steel with coherent VC nano-carbides retained the highest strength and ductility during in-situ testing. This is therefore the optimal carbide configuration for use in hydrogen environments.
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