PSI - Issue 14

Takuya Yoshimoto et al. / Procedia Structural Integrity 14 (2019) 18–25 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 5. Relationship between hydrogen content and mean graphite diameter.

3.2 Hydrogen-induced ductility loss

Figure 6 shows the stress-strain curves obtained by a series of tensile tests for four kinds of FCD400 with different graphite diameter. As demonstrated, the strength properties were slightly decreased by hydrogen. On the other hand, the ductility in all material was markedly reduced by hydrogen. Hydrogen-induced ductility loss, that is relative reduction of area (RRA), is often employed as a measure of susceptibility to hydrogen embrittlement (Michler et al. (2010); San Marchi et al. (2010)). The RRA is the ratio of reduction of area of H-charged specimen to that of uncharged specimen. The RRAs of these four specimens are listed in Table 2 together with the mean graphite diameter. The hydrogen contents of the tensile-fractured specimens are also shown in Table 2. The RRAs are plotted as a function of mean graphite diameter in Fig. 7. In Material S U , M and L , the reduction of area was remarkably decreased by hydrogen, and RRAs were almost equal in these materials regardless of graphite size. In Material S L , on the other hand, although the ductility was somewhat affected by hydrogen, the RRA in Material S L was much larger than that of other materials.

Fig. 6. Stress-strain curves of four kinds of FCD400 with different graphite diameter: (a) Material S U and S L ; (b) Material M; (c) Material L.