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.

The effect of annealing and neutron irradiation parameters on changes in the microstructure and corrosion properties of the 12Cr18Ni10Ti austenitic steel has been studied. The values of steady-state potentials, as well as the potentials of passivation, activation, and stable pitting, of the steel in various structural states have been provided. The dependences of the anode current density on voltage have been established. It has been shown that the electrochemical behavior and corrosion resistance of the steel in a chloride-containing medium depend on the intensity of redox processes on the metal surface as well as on the state of the structure at the micro- and nanolevel.

This study observed the effect of neutron irradiation and ageing on the microstructure, hardness, and corrosion resistance of SAV-1 (Al–Mg–Si) alloy. The investigated material was irradiated with neutrons to fluences of 1021–1026 n/m2 in the WWR-K research reactor and kept in dry storage. Long-term irradiation led to an increase in hardness of the alloy and a deterioration of pitting corrosion resistance. Post-irradiation ageing for 1 h at 100–300 °C resulted in a decrease in microhardness of the irradiated SAV-1. The effect of post-irradiation ageing on pitting corrosion was made clear through the formation of Guinier-Preston zones and secondary precipitates in the Al matrix. Ageing at 250 °C corresponded to the development of stable microstructure and the highest corrosion resistance for the irradiated samples. Mg2Si, Si, and needle-shaped β″ precipitates were formed in SAV-1 alloy that was irradiated with low fluences. β″ and clusters of rod-shaped B-type precipitates were observed in highly irradiated samples. The precipitates were similar to those seen in non-irradiated pseudo-binary Al–Mg2Si alloys with Si excess.

Obtaining mechanical properties of neutron irradiated structural materials is made difficult by the high radioactivity of typical specimen sizes. Developing new mechanical tests which obtain the same properties with far smaller specimen sizes would significantly enhance the speed and safety of performing such tests. In this study, we demonstrate the correspondence in mechanical properties between standard, uniaxial tensile testing and a new “Shear Punch” method, involving the shear-based removal of a small (1 mm) disc of material. Two types of steel, 12Cr18Ni9 and 08Cr16Ni11М3, were irradiated with fast neutrons in the BN-350 reactor up to 23 dpa and shear punch tested between 20…300 °C. Excellent correspondence was found between the 0.2% shear and uniaxial tensile yield stresses, validating this technique as a way to obtain the same mechanical properties with greatly reduced sample size.

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 effect of irradiation with neutrons and electrons, as well as temperature effects on stress relaxation processes in austenitic nickel-chromium steels has been investigated. The effect of an increase in the content of the ferromagnetic phase in irradiated samples deformed at cryogenic temperatures and annealed in the temperature range of 400 °C was found.

The effect of neutron irradiation on the Md martensitic point in austenitic chromium-nickel steels X18H9T and 12X18N10T – structural materials of nuclear reactors is considered. It was established that up to a fluence of 2·1020 n/cm2 (E>0.1 MeV), the maximum possible temperature for the manifestation of the phase y→α transition for steel 12X18H10T varies in the range of 100–75 °C.Based on the analysis of the experimental data obtained, it is proposed to consider another characteristic point Mp – a stretching temperature at which the values of the intensities of the direct martensitic y→α transformation are compared for deformable non-irradiated and irradiated steel.

Experimental results on the relaxation of internal stresses in structural stainless steels Х18Н9Т, 12Х18Н10Т and AISI 316 after neutron irradiation, effects of stationary or pulsed electrons of various powers are presented. It has been established that in steels irradiated with low neutron fluxes (1016 ÷ 1018 n/cm2), the deformation by extension as a result of relaxation phenomena is the martensitic γ → α transition begins at lower values of critical stresses than after austenization. At the same time, there is an anomalous effect of reducing the yield strength and reducing the amount of mechanical workexpended on the destruction of the steel sample. The features of the relaxation of internal stresses and the formation of the α-phase in stainless steels under irradiation with electrons of various energies are revealed. It is shown that the radiation relaxation of internal stresses caused by the action of neutrons, pulsed or stationary electrons, changing the conditions for the formation of the α-phase, determines the level of mechanical and corrosion properties of irradiated stainless steel.

Experimental data on the influence of neutron irradiation on the plasticity characteristics of chromium–nickel austenite steels have been analyzed. Special attention is devoted to detection of anomalously high plasticity levels attained at some parameters of irradiation and deformation, which is explained by the formation and propagation of a “phase transformation wave” in the metastable steel. Necessary and sufficient conditions for the realization of this wave are formulated.

In this work, an experiment was conducted for obtaining ultrafine-grained state of long bars of steel AISI-321, in which the workpiece while the minimum technically possible the temperature of 800OС were rolled by a radialdisplacement rolling with a diameter of 30 mm and diameter 13 mm on the mill SVP-08. Microstructure analysis showed the presence of equiaxial ultrafine-grained structure in the peripheral areas of the workpiece and the presence of elongated fibrous texture in the axial zone. The strength of the workpiece has increased more than 2 times, while the plasticity has decreased not so much. The study of microhardness distribution showed a smooth decrease of 10.2 % from the periphery to the center of the produced sample, with an overall growth of microhardness of 2 times relative to the original.

Some methods for determining the moment of localization of plastic deformation during static stretching of samples of constructional austenitic steels are considered. Based on the analysis of the obtained experimental results, a new magnetometric method has been proposed and described, its application for the determination of parameters describing the conditions of nucleation of the neck is illustrated by examples of unirradiated and neutron irradiated 12Х18Н10Т reactor steel.

AbstractExperimental data on the influence of neutron irradiation on the plasticity characteristics of chromium–nickel austenite steels have been analyzed. Special attention is devoted to detection of anomalously high plasticity levels attained at some parameters of irradiation and deformation, which is explained by the formation and propagation of a “phase transformation wave” in the metastable steel. Necessary and sufficient conditions for the realization of this wave are formulated.

The results of experiments on the study of deformation and thermal changes in the electromagnetic properties of austenitic steel Х18Н9 subjected to neutron irradiation in a WWR-K nuclear reactor are presented and discussed. Particular attention is paid to the direct and inverse phase martensitic transformation. The effect of an additional increase in the amount of the ferromagnetic a-phase during annealing (~450°С) of irradiated, deformed at negative temperatures (-20 and -60 °C) of reactor steel is observed.

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.

The effect of thermocycling treatment on the susceptibility to local corrosion and mechanical characteristics of corrosion-resistant steel 12Kh18N10T in different states (after austenitizing, cold rolling, and neutron irradiation) is considered. The possibility of partial recovery of the corrosion and mechanical characteristics of irradiated reactor steel due to low-cycle thermocycling in a temperature range exceeding the irradiation temperature is demonstrated.

Changes in the structure and physicomechanical properties of steel G-91 were studied after low-dose neutron irradiation. The irradiation was carried out in the "wet" channel of the WWR-K research nuclear reactor of INP, Almaty, Kazakhstan, to the fast neutron fluencies 8.6 x 10(19) n/cm(2) at a temperature of < 90 degrees C. It was established that irradiation up to the fluence 8.6 x 10(19) n/cm(2) changes insignificantly a metallography structure of steel G-91. Microstructural changes manifested themselves in a growth of dislocation density and appearance of radiation defects (black dots). The most significant consequence of low-dose irradiation during a long period (up to a year and a half) is severe corrosion, which leads to embrittlement of steel G-91.

Much of today's research in nuclear materials relies heavily on archived, historical specimens, as neutron irradiation facilities become ever more scarce. These materials are subject to many processes of stress- and irradiation-induced microstructural evolution, including those during and after irradiation. The latter of these, referring to specimens “naturally aged” in ambient laboratory conditions, receives far less attention. The long and slow set of rare defect migration and interaction events during natural aging can significantly change material properties over decadal timescales. This paper presents the results of natural aging carried out over 15 years on austenitic stainless steels from a BN-350 fast breeder reactor, each with its own irradiation, stress state, and natural aging history. Natural aging is shown to significantly reduce hardness in these steels by 10–25% and partially alleviate stress-induced hardening over this timescale, showing that materials evolve back towards equilibrium even at such a low temperature. The results in this study have significant implications to any nuclear materials research program which uses historical specimens from previous irradiations, challenging the commonly held assumption that materials “on the shelf” do not evolve.

It is known that microstructure of metallic polycrystalline materials irradiated with neutrons is often characterized by a high degree of heterogeneity in distribution of radiation-induced defects. Depleted zones are located along grain boundaries and their width is not only determined by irradiation temperature and damage dose, but also by migration of point defects and dislocations integrity, that makes it more difficult to interpret experimental results of this phenomenon. At present, denuded zones are still objects for investigation as they influence both operation characteristics of reactor materials and their safe long-term storage. In this work, denuded zones in hexagonal ducts of spent fuel assemblies constructed from 0.08C-16Cr-11Ni-3Mo and 0.12C-18Cr-10Ni-Ti stainless steels from BN-350 fast nuclear reactor were investigated by TEM. There were determined some irradiation parameters affecting the development of denuded zones and their width; void size distributions in near-grain boundary regions are presented. There was shown redistribution of alloying elements at grain boundaries using Energy-dispersive X-ray spectroscopy (EDS).