The paper studies the features of martensitic transformation during plastic deformation (uniaxial tension and compression) of austenitic steels 12X18N10T and AISI304 irradiated with thermal neutrons to a fluence of 3.7·1020 n/cm2 . The nickel equivalent and stacking fault energy values for 12X18N10T and AISI304 steels are calculated. It is established that AISI304 steel is more prone to martensitic transformation. The mechanical characteristics of the studied steels under uniaxial tension are determined. It is shown that with similar strength characteristics, the plasticity of irradiated AISI304 steel is twice as high as that of 12X18N10T steel. This fact is due to the more intense martensitic transformation during the plastic deformation of AISI304 steel.

In this work, the influence of alloying elements (nitrogen, manganese, copper, and tungsten) and neutron irradiation in the VVR-K reactor up to a maximum fluence of 2·1020 n/cm2 on the resistance to pitting corrosion of austenitic steel AISI 316 LN, subjected to provoking heating at temperatures in the range of 500-800 °C. It has been established that alloying with nitrogen and manganese significantly improves the corrosion properties of AISI 316 LN steel, and the addition of copper and tungsten reduces the resistance to pitting corrosion. It has been shown that provoking heating at temperatures from 500 to 800 °C with an interval of 100 °C worsens the corrosion resistance of steels in a non-irradiated state due to the formation of chromium nitrides and carbides, and the addition of copper reduces the degree of sensitization. According to the results obtained, it was established that neutron irradiation to a maximum fluence of 2·1020 n/cm2 of the studied steels after cold rolling and not subjected to provoking heating led to a decrease in the corrosion rate. Provoking heating at temperatures of 700–800 °C of neutron-irradiated samples of steels 211 L-213 L led to an increase in the corrosion rate, especially in steels alloyed with copper. Neutron irradiation greatly enhances the sensitization effect.

The article is devoted to the study of the resistance of structural materials of the BN-350 reactor to pitting corrosion in an aqueous medium containing chlorine ions in the presence of organic corrosion inhibitors. The results of accelerated testing of samples of austenitic steels 12Cr18Ni10Ti, 08Cr16Ni11Mo3Ti and Cr13Mo2NbVB (EP-450) ferrite-martensitic steel for pitting corrosion in a 10% aqueous solution of iron three-chloride hexahydrate without an inhibitor and in the presence of various concentrations of corrosion inhibitor are presented. The effect of heat treatment on the pitting resistance of structural steels is studied and the role of carbide precipitates of MC and M 23 C 6 types in pitting defects formation is discussed.

Elemental composition and morphology of a previously unidentified radiation-induced ferrite phase were investigated in a 300-series steel irradiated by neutrons in-service up to 57.6 dpa. Specimens of 18Cr-10Ni-Ti stainless steel (AISI 321 analog) were cut from a hexagonal wrapper of a fuel assembly irradiated in the BN-350 sodium-cooled fast reactor. An Fe-rich bcc-phase was observed primarily on grain boundaries. In this phase, the concentration of Cr is ∼8–12% (compared to ∼19% in the matrix), the concentration of Ni is ∼1.5–3% (∼9% in the bulk material), and the concentration of Mn is ∼0.23% (1.3% in the matrix). This Fe-rich phase is distinctly different from the retained-ferrite phase, commonly found in commercial austenitic steels. The extensive appearance of this Fe-rich ferrite on grain boundaries suggests that enhanced surface–intergranular corrosion may occur in water-cooled power reactors, arising from the low Ni, Mn, and Cr concentrations in this phase.

The effect of neutron irradiation on the mechanical properties of commercially pure iron upon plastic deformation at elevated temperatures has been studied. The interaction of impurity atoms with radiation-induced defects has been found to suppress dynamic strain aging. A significant decrease in plasticity due to blue brittleness has not been observed in the samples irradiated by neutrons. High-energy particles have also been revealed to increase the plasticity of irradiated Armco iron and the number of microstructural deformation mechanisms during plastic flow at elevated temperatures.

The reduction of ductility of austenitic stainless steels as a result of long-term operation in the nuclear reactor core is an important problem of modern radiation materials science. Understanding the mechanisms of the effect of neutron irradiation on the mechanical properties of austenitic steels is impossible without research of localization processes occurring during the deformation. In this paper, it was found that the value of the true local deformation corresponding to the onset of neck formation in face-centered cubic structured metals decreases with an increase in the radiation dose, while the true stress remains almost constant. Additional hardening of AISI 304 steel due to the intensive formation of the martensitic α’-phase increases not only the stress at which a neck is formed in this alloy, but also the true local deformation. As a result, the uniform elongation increases and remains high after neutron irradiation to 0.05 dpa. The forehanded formation of the martensitic α’-phase in sufficient quantity before the necking onset can be considered as an additional deformation mechanism that will increase the ability of the material to deform uniformly.

Low-temperature radiation hardening and embrittlement is a major life-limiting radiation effect in austenitic stainless steels (AuSS). A strain-induced phase transformation to martensite is observed during plastic deformation of low-Ni AuSS, often increasing strain hardening and reducing ductility. However, in this paper we show an unexpectedly high ductility of 18-37% during room-temperature mechanical testing of a 0.12C-18Cr-10Ni-0.8Ti AuSS (AISI 321 analogue) cut from the hexagonal wrapper of a fuel assembly irradiated in the BN-350 sodium-cooled fast reactor located in Aktau, Kazakhstan. Using digital image correlation, we reveal two completely different deformation mechanisms in samples with the same chemical composition, irradiated to very similar doses. The roles of the martensitic. gamma -> alpha' transformation and neutron irradiation parameters explain the differences between plastic deformation mechanisms in the specimens.

New results of the experiments on the study of nature and patterns of the effect of anomalously high ductility of austenitic meta-stable irradiated steels are discussed, the possible causes of its formation and the relationship with the deformation “wave” are analyzed, and the recommendations for “wave” modeling are provided in the paper.

Mechanical tests of 12Cr18Ni10Ti (AISI 321 analogue: 10 Ni, 0.12 C, 0.5 Ti, 18 Cr, <2 Mn, and Fe for balance) commercial stainless steel accompanied by “Digital marker extensometry”, and magnetometry, have been carried out after neutron irradiation to a maximum fluence of 1 × 10 23 n/m 2 ( E > 1 MeV). The plastic instability stress and strain of the necking onset have been estimated. The results of three independent methods are in good agreement. The true local strain at the beginning of the necking process in the 12Cr18Ni10Ti steel has been established to decrease with increasing fluence, whereas the true plastic instability stress remains almost the same.

The influence has been studied of thermo-mechanical treatment, sensitization conditions, and neutron irradiation on the pitting corrosion resistance of austenitic 316LN stainless steel variants in 10% FeCl3·6H2O at 22 °C. Variants of this steel were modified with additions of nitrogen, manganese, copper, and tungsten, as well as testing cast, cold-rolled, grain boundary engineered (GBE), and as-received variants. It was found that the 316LN steel variant with additions of 0.2% N and 2% Mn had the best pitting corrosion resistance of all studied conditions. When irradiated in a light water reactor (LWR) to a maximum fluence of 3 × 1017 n/cm2 (E > 1.1 meV, Tirr < 50 °C), neutron irradiation surprisingly increased the resistance of GBE steels to pitting corrosion. An anisotropy of corrosion resistance of GBE and cold rolled steels was observed.