PSI - Issue 2_B

A. Laureys et al. / Procedia Structural Integrity 2 (2016) 541–548 A. Laureys/ Structural Integrity Procedia 00 (2016) 000–000

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4. Conclusions

A ULC steel with varying amounts of recrystallization, i.e. fully recrystallized, partially recrystallized, and cold deformed material, was subjected to extreme electrochemical hydrogen charging to provoke hydrogen induced damage in the material. The formation kinetics differed remarkably for cold deformed and recrystallized material. The deformation induced defects in the material clearly play a very important role in the initiation and propagation process of blisters. Also, the morphology of blisters depends on the state of the material, i.e. an increased fraction of deformed microstructure is accompanied by a flattening of blisters. Increasing charging times resulted in an increase of the amount of blisters, which was also the global trend for increasing current densities. Additionally, the mean blister size increased with time, while it decreased with increasing current densities. Higher current densities seem to shift the more favorable process from blister growth to blister initiation. These trends were equal for all the materials. Cross sections of the three materials showed that the hydrogen induced cracks are strongly branched, with each blister consisting of a large entity of thin, branching cracks. The hydrogen induced cracks propagated dominantly transgranularly. Additionally, high misorientations were observed within and along the hydrogen induced cracks. This observation can be considered as a confirmation of the internal pressure theory. Acknowledgements The authors wish to thank the Special Research Fund (BOF), UGent (BOF10/ZAP/121) and the Agency for Innovation by Science and Technology in Flanders (IWT) for support (Project nr SB141399). References Choo, W.Y., Young Lee, J., 1983. Effect of cold deformation on the hydrogen trapping phenomena in pure iron. Metallurgical Transactions A 14, 1299-1305. Condon, J.B., Schober, T., 1993. Hydrogen bubbles in metals. Journal of nuclear Materials 207, 1-24. Garofalo, F., Chou, Y.T., Ambegaokar, V., 1960. Effect of hydrogen on stability of micro cracks in iron and steel. Acta Metallurgica 8, 504-512. Griesche, A., Dabah, E., Kannengiesser, T., Kardjilov, N., Hilger, A., Manke, I., 2014. Three-dimensional imaging of hydrogen blister in iron with neutron tomography. Acta Materialia 78, 14-22. Lee, J.-L., Lee, J.-Y., 1987. The effect of lattice defects induced by cathodic hydrogen charging on the apparent diffusivity of hydrogen in pure iron. Journal of Materials Science 22, 3939-3948. Panagopoulos, C.N., El-Amoush, A.S., Agathocleous, P.E., 1998. Hydrogen-induced cracking and blistering in alpha-brass. Corrosion Science 40, 1837-1844. Pérez Escobar, D., Miñambres, C., Duprez, L., Verbeken, K., Verhaege, M.,2011. Internal and surface damage of multiphase steels and pure iron after electrochemical hydrogen charging. Corrosion Science 53, 3166–3176. Pérez Escobar, D., Depover, T., Duprez, L., Verbeken, K., Verhaege, M., 2012. Combined thermal desorption spectroscopy, differential scanning calorimetry, scanning electron microscopy and X-ray diffraction study of hydrogen trapping in cold deformed TRIP steel. Acta Materialia 60, 2593-2605. Pressouyre, G.M., 1982. In: C.G. Interrante, G.M. Pressouyre (Eds.), Current solutions to hydrogen problems in steels . ASM, Metals Park, OH, pp. 18. Ren, X., Chu, W., Li, J., Su, Y., Qiao, L., 2008. The effects of inclusions and second phase particles on hydrogen induced blistering in iron. Materials Chemistry and Physics 107, 231-235. Ren, X.C., Zhou, Q.J., Shan, G.B., Chu, W.Y., Li, J.X., Su, Y.J., Qiao, L.J., 2008. A nucleation mechanism of hydrogen blister in metals. Metallurgical and Matererials Transactions 39A, 87-97. Tetelman, A.S., Robertson, W.D., 1962. The mechanism of hydrogen embrittlement observed in iron-silicon single crystals. TRANS TMS-AIME 224, 775-783. Wilde, B.E., Kim, C.D., Phelps, E.H., 1980. Some observations on the role of inclusions in the hydrogen induced blister cracking of linepipe steels in sulfide environments. Corrosion 36, 625-632. Young, G.A., Scully, J.R., 1998. The diffusion and trapping of hydrogen in high purity aluminium. Acta Materialia 46, 6337-6349.