PSI - Issue 13

Galina Maier et al. / Procedia Structural Integrity 13 (2018) 1053–1058 Galina G. Maier et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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4. Conclusions The influence of electrochemical H-charging on tensile behaviour and fracture mechanisms of V-alloying and V free high-nitrogen austenitic steels, Fe-23Cr – 17Mn – 0.1C – 0.6N (0V-HNS) and Fe-19Cr – 22Mn – 1.5V – 0.3C – 0.9N (1.5V-HNS), was investigated. Independently on chemical composition, concentration of interstitial atoms in austenite solid solution of the steels was the same due to V-alloying promotes particle strengthening of the 1.5V-HNS. V alloying steel possesses higher values of a yield stress, tensile strength and strain-hardening coefficient in comparison with V-free steel, due to particle-strengthening and smaller grain size in 1.5V-HNS in comparison with 0V-HNS. After hydrogen-charging, increase of a yield stress and tensile strength of both steels was observed. Hydrogen charging drastically reduces a total elongation in 0V-HNS and provides insufficient embrittlement in 1.5V-HNS. For both steels, the formation of brittle surface layers occurs under hydrogen-charging, the mean thicknesses of these layers depend on chemical composition of steels and reaches 84  m for 0V-HNS, and 30  m for 1.5V-HNS. Hydrogen-charging changes the fracture mode of surface layer from predominantly transgranular in 0V-HNS to predominantly intergranular fracture in 1.5V-HNS. The estimation of hydrogen diffusion shows that hydrogen diffusivity is 7-times faster for V-free coarse-grained austenitic steel than that for fine-grained particle strengthened V-alloying steel. This is associated with higher fraction of hydrogen trap sites (grain boundaries and “parti cle/austenitic matrix ” interfaces) in 1.5V-HNS in comparison with 0V-steel. Astafurova, E.G., Moskvina, V.A., Maier, G.G., et al., 2017. Effect of hydrogenation on mechanical properties and tensile fracture mechanism of a high-nitrogen austenitic steel. Journal of Materials Science 52(8), 4224-4233. 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