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Corrosion intergranulaire des aciers inoxydables austénitiques en milieu acide nitrique oxydant

Abstract : The aim of this thesis is to better understand the susceptibility of non-sensitized austenitic stainless steels to intergranular corrosion in a concentrated boiling nitric acid environment containing oxidizing ions. It focuses more specifically on the effect of metallurgical parameters. For this purpose, the corrosion behavior of 6 stainless steels is studied in oxidizing nitric acid, using linear voltammetry and immersion tests. Among the studied stainless steels, one grade (Uranus S1N) is resistant to intergranular corrosion but exhibits a higher surface corrosion rate. This steel differs from the others by its high silicon content (4 wt.%). The effect of silicon of surface and intergranular corrosion is confirmed thanks to the fabrication and study of experimental alloys with silicon contents varying between 1 and 4 wt.%. Among the stainless steels susceptible to intergranular corrosion, all the grain boundaries are attacked, except the majority of the twin boundaries. In addition, a higher chromium content leads to lower surface and intergranular corrosion rates.The chemical compositions of grain boundaries were studied by atomic probe tomography for two stainless steels: 304L and Uranus S1N, susceptible and resistant to intergranular corrosion, respectively. The results evidence intergranular segregation of impurities and carbon in both alloys. The enrichment factors are slightly higher in Uranus S1N than in 304L. However, silicon enrichment of the grain boundaries was evidenced in none of them. The results show that, if impurities have an effect on the susceptibility to intergranular corrosion, the effect seems inhibited by a high amount of silicon. Based on these results, several propositions are made to account for the susceptibility to intergranular corrosion of austenitic stainless steels in oxidizing nitric acid.
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Submitted on : Tuesday, January 5, 2021 - 12:20:40 PM
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Adrien Emery. Corrosion intergranulaire des aciers inoxydables austénitiques en milieu acide nitrique oxydant. Matériaux. Université Paris sciences et lettres, 2020. Français. ⟨NNT : 2020UPSLM031⟩. ⟨tel-03097345⟩



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