Issue 51

M. Cauwels et alii, Frattura ed Integrità Strutturale, 51 (2020) 449-458; DOI: 10.3221/IGF-ESIS.51.33 456 C ONCLUSION he influence of austenite phase fraction on the hydrogen sensitivity of duplex stainless steel was investigated in this work. Heat treatments were performed to create DSS with an austenite fraction of 50% and 44%. Tensile tests in uncharged and hydrogen-charged condition were performed on these materials, based on which the following conclusions can be made: - Both heat treated samples suffered a considerable loss in ductility after hydrogen charging. For the sample with a 50% γ fraction, the elongation at fracture was reduced by 36.5%. For the specimens with 44% γ this was 43.3%. - Loss of ductility, as quantified by the embrittlement index, was larger for the sample with a higher ferrite content. The sample had a higher hydrogen content and a higher hydrogen diffusion coefficient, contributing to its increased sensitivity. - Fracture surfaces of specimens tested under the presence of hydrogen showed brittle fracture features on the edges. The depth of the zone with brittle features was related to the diffusion speed of hydrogen. The hydrogen distribution after one day of hydrogen pre-charging, simulated using the thin-plate solutions of Fick’s second law, showed that hydrogen was not present throughout the thickness of the sample. The sample with 44% γ, which had a higher overall diffusion coefficient for hydrogen, had a larger embrittled zone since hydrogen could diffuse over a greater distance in the given pre-charging time. - Secondary cracking as hydrogen-assisted cracking was observed on the side surfaces of specimens tested with hydrogen and appeared to be primarily transgranular. Tensile specimens tested in air did not show this secondary cracking. A CKNOWLEDGEMENTS he authors acknowledge support from FWO (SB PhD fellow via grant 1S16618N) for L. Claeys, while T. Depover holds a senior postdoctoral fellowship of the Research Foundation - Flanders (FWO) via grant 12ZO420N. The authors also wish to thank the Special Research Fund (BOF), UGent (grant BOF15/BAS/062 and BOF01P03516) and the Research Foundation - Flanders (FWO) via grant 3G056519. R EFERENCES [1] Azevedo, C.R. de F., Pereira, H.B., Wolynec, S., Padilha, A.F. (2019). An overview of the recurrent failures of duplex stainless steels, Eng. Fail. Anal., 97, pp. 161–188, DOI: 10.1016/j.engfailanal.2018.12.009. [2] Johnsen, R. (2017).Hydrogen induced stress cracking of stainless steel in seawater - what do we know and what is still unknown? The Annual Congress of the European Federation of Corrosion, 20th International Corrosion Congress and Process Safety Congress 2017, Prague, Czech Republic. [3] Popov, B.N., Lee, J.W., Djukic, M.B. (2018).Hydrogen permeation and hydrogen-induced cracking. Handbook of Environmental Degradation Of Materials Third Edition, Elsevier Inc., pp. 133–62. [4] Francis, R., Byrne, G., Warburton, G.R. (1997). Effects of cathodic protection on duplex stainless steels in seawater, Corrosion, 53(3), pp. 234–240, DOI: 10.5006/1.3280465. [5] Campbell, H.S., Francis, R. (1995). Simulated service test for hydrogen embrittlement of cathodically protected subsea bolting materials, Br. Corros. J., 30(2), pp. 154–160, DOI: 10.1179/000705995798114087. [6] Depover, T., Laureys, A., Pérez Escobar, D., Van den Eeckhout, E., Wallaert, E., Verbeken, K. (2018). Understanding the Interaction between a Steel Microstructure and Hydrogen, Materials (Basel)., 11(5), pp. 698, DOI: 10.3390/ma11050698. [7] Robertson, I.M., Sofronis, P., Nagao, A., Martin, M.L., Wang, S., Gross, D.W., Nygren, K.E. (2015). Hydrogen Embrittlement Understood, Metall. Mater. Trans. A, 46(6), pp. 2323–2341, DOI: 10.1007/s11661-015-2836-1. [8] Djukic, M.B., Bakic, G.M., Sijacki Zeravcic, V., Sedmak, A., Rajicic, B. (2019). The synergistic action and interplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity and decohesion, Eng. Fract. Mech., 216, pp. 106528, DOI: 10.1016/j.engfracmech.2019.106528. [9] Zapffe, C.A., Sims, C.E. (1941). Hydrogen embrittlement, internal stress and defects in steels, Trans. Am. Inst. Min. Metall. Eng., 145, pp. 1–37. [10] Troiano, A.R. (2016). The role of hydrogen and other interstitials in the mechanical behavior of metals (1959 Edward T T