Stress corrosion cracking in the context of deep geological nuclear disposal – investigations on P235 and P265 steels

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Abstract
Stress corrosion cracking of P235 and P265 steels is investigated through slow strain rate and constant deformation tests on samples exposed in a cell reproducing the underground conditions of the French deep geological nuclear disposal, at 25 and 90°C. The samples were taken from the base metal, the heat affected zone and the fusion zone of a P265 steel weld joint. Tests were performed at the free corrosion potential and under polarisation in the cathodic or anodic domains. Long-term constant deformation tests were also carried out to evaluate the behaviour of the material under static loading in hydrated clay environment. The results show a significant sensitivity of the tested materials to environmental cracking in the experimental conditions, with an enhancement of the effect of the environment for the weld metal. A mechanism of hydrogen embrittlement is proposed to be responsible for the cracking phenomenon. Susceptibility to environmental assisted cracking observed during these tests indicates the need to optimise welding parameters and steel chemical composition and metallurgy, particularly regarding the presence of inclusions in the base metal and stress relief of the weld metal. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

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