Effect of morphology of copper precipitation particles on hydrogen embrittlement behavior in Cu-added ultra low carbon steel

Abstract

Changes in fracture and hydrogen evolution behaviors in Cu-added ultra low carbon steels due to hydrogen charging were examined by small punch (SP) tests and thermal desorption spectroscopic (TDS) analyses, respectively, to understand effect of morphology of copper precipitation particles on susceptibility to hydrogen embrittlement. The SP tests and TDS analyses were applied to the hydrogen-charged steels, which had been thermally aged at 500°C for duration ranging from 2 × 103 to 5 × 106 s and provided with various kinds of fine particles. Experimental results revealed that the higher strength steel bas a larger reduction in strength due to hydrogen charging. This degradation of the strength due to hydrogen charging was strongly dependent on the morphology of copper precipitation particles although, basically, the degradation had a tendency to be more pronounced with increasing hydrogen content. More hydrogen can be allowed in the steel in which the ε-copper exists. The grown copper particles, such as an ε-copper, are preferable to the copper clusters and/or the twinned 9R structures as trapping site for hydrogen and contribute the suppression of the reduction in strength caused by hydrogen.