Influence of structural-phase state of ferritic-martensitic steels on the helium porosity development

• Published in: IOP conference series. Materials Science and Engineering 2016-04, Vol.130 (1), p.12004-12009
• Main Authors: Chernov, I I, Staltsov, M S, Kalin, B A, Bogachev, I A, Guseva, L Yu, Dzhumaev, P S, Emelyanova, O V, Drozhzhina, M V, Manukovsky, K V, Nikolaeva, I D
• Format: Article
• Language: English
• Subjects: Annealing; Bubbles; Density; Dispersion hardening steels; Ferritic stainless steels; Fluence; Helium; Ion irradiation; Irradiation; Martensitic stainless steels; Nanoparticles; Normalizing (heat treatment); Plastic deformation; Porosity; Steel; Structural steels; Swelling; Transmission electron microscopy; Water quenching; Yttrium oxide
• ISSN: 1757-8981; 1757-899X
• DOI: 10.1088/1757-899X/130/1/012004

Transmission electron microscopy (TEM) has been used to study the effect of the initial structural-phase state (SPhS) of ferritic-martensitic steels EK-181, EP-450 and EP-450- ODS (with 0.5 wt.% nanoparticles of Y2O3) on the of helium porosity formation and gas swelling. Different SPhS of steel EK-181 was produced by water quenching, annealing, normalizing plus tempered, intensive plastic deformation by torsion (HPDT). Irradiation was carried out by He+-40 keV ions at 923 K up to fluence of 5-1020 He+ m2. It is shown that the water quenching causes the formation of uniformly distributed small bubbles (d̄ ∼ 2 nm) of the highest density (ρ∼ 1025 m-3). After normalization followed by tempering as well as after annealing bubbles distribution is highly non-uniform both by volume and in size. Very large faceted bubbles (pre-equilibrium gas-filled voids) are formed in ferrite grains resulting in high level of gas swelling of the irradiated layer with S = 4,9 ± 1,2 and 3.8 ± 0.9% respectively. Nano- and microcrystalline structure created by HPDT completely degenerate at irradiation temperature and ion irradiation formed bubbles of the same parameters as in the annealed steel. Bubbles formed in EP-450-ODS steel are smaller in size and density, which led to a decrease of helium swelling by 4 times (S = 0.8 ± 0.2%) as compared to the swelling of the matrix steel EP-450 (S = 3.1 ± 0.7%).