Irradiated Austenitic Stainless Steels Research Articles

Effect of injected hydrogen on defect cluster formation in electron irradiated austenitic stainless steel

To investigate the effect of hydrogen on the formation of dislocation loops and voids, electron-irradiation was carried out in a high voltage electron microscope after hydrogen preinjection. Small defect clusters produced by the preinjection at room temperature rapidly disappeared during low fluence electron irradiation (< 0.1 dpa) at 670–770 K, and after further irradiation another type loops developed. It is inferred that the small defect clusters produced by the preinjection are complexes of hydrogen and vacancies. By the electron irradiation to high dose, hydrogen preinjection increased also led to a large increase in the void density. From these results, it can be concluded that a high concentration of hydrogen should interact with vacancies and enhance the void nucleation process in the temperature region below 770 K.

Effects of tensile test temperature on the fracture modes of neutron and helium irradiated austenitic stainless steel

Microtensile specimens of neutron-irradiated Type 304 and 316 stainless steel as well as unirradiated and helium-irradiated Type 316 stainless steel were fractured in an HVEM while recording the crack propagation characteristics on videotape. Investigations of the mode of crack opening and the type of fracture were made as a function of tensile test temperature up to 600°C. The following observations and conclusions were made from these experiments. In high dose neutron-irradiated Type 304 specimens the crack propagation mode was essentially pure Mode I especially at elevated temperatures but at room temperature transgranular failure dominated, and at 600°C intergranular failure dominated. In low-dose neutron-irradiated Type 316 specimens Mode I and II cracking occurred with nearly pure Mode II cases occurring only at the elevated test temperature of 600°C. Most of the nearly pure Mode II cracking was long grain boundaries and was observed in unirradiated specimens at all temperatures, in low-dose neutron-irradiated specimens at 600°C, and in helium-irradiated specimens annealed before tensile testing at room temperature. Therefore the embrittled irradiated specimens which failed intergranularly at elevated tensile test temperature did not fail by grain boundary sliding (Mode II) but failed by Mode I cracking. Irradiation tended to cause rigid crack flank displacements in the direction of the macroscopic tensile axis.

Evolution of cavity size distributions in dual-ion irradiated austenitic stainless steel and Fe-Cr-Ni ternary alloys

The first four moments of experimentally measured cavity size distributions in dual-ion irradiated 304SS, Fe-12Ni-15Cr and Fe-30Ni-15Cr alloys have been calculated for a range of fluences, helium injection rates, and irradiation temperatures. The moments are shown to correctly describe the effects of alloy composition, fluence, helium and temperature on the evolution of the cavity size distributions. Experimentally determined moments are compared with those calculated from cavity nucleation and growth theories. The moments reflect the competition between nucleation and growth processes and provide insight into the details of the transient low swelling regime.

Magnetic properties of irradiated austenitic stainless steel

This report presents results of measurements on the magnetic properties of neutron irradiated austenitic steel. It is shown that exposure to high fluences of energetic neutrons produces significant changes in the magnetic permeability and introduces the phenomenon of time dependent magnetic hysteresis into the behavior of these steels for measurements below room temperature.

Observations on high-temperature deformation and fracture of an irradiated austenitic stainless steel with additions of titanium and boron

A chromium-nickel-molybdenum stainless steel with titanium and boron additions, solution-treated or solution-treated, cold-worked and recovery-annealed, was studied before and after irradiation in a thermal materials-testing reactor. Irradiations were performed at 700°C to almost complete boron-10 burn-up. The post-irradiation creep properties were compared with the creep properties of the steel as delivered and after a parallel annealing at 700°C. Broadly speaking, the creep strength of the solution-treated steels was not altered as a result of irradiation but was decreased by annealing at 700°C. The opposite was true for the cold-worked recovery-annealed material. These effects are due to different modes of TiC precipitation during or before testing and to the degree of recovery after cold work. Irradiation reduced the ductility to a varying degree, depending on the material condition. The smallest change was observed on 1100°C-annealed steel after cold work and recovery-anneal at 850°C. That condition also had the smallest grain size. The effect of irradiation on the ductility may be explained in terms of the diffusion of boron to the grain boundaries during irradiation at 700°C, and the influence of the resulting helium-rich zones at grain boundaries.

A study of void formation in fast neutron-irradiated metals

Experimental observations on the temperature dependence of void formation in Type 304 stainless steel are presented. The average void size is seen to increase while the void number density decreases with increasing irradiation temperature. The total void volume reaches a maximum at an intermediate temperature (∼500°C). A thermodynamically based model for void formation has been developed in an effort to understand these and other experimental observations. The model is a quasi-steady-state approach that attempts to describe the void and dislocation loop nucleation and growth rates as a function of temperature, neutron flux, and type and density of point-defect sinks. The model was written in the form of a computer routine which iterates over small time steps and fitted to experimental observations of void formation in irradiated austenitic stainless steel by adjustment of material constants within reasonable limits. Good agreement was obtained for a wide range of experimental results. Development of the model has emphasized that some kind of preferential attraction between one type of sink and one type of point defect is necessary in order for void growth to occur. The preferential attraction suggested is that between the stress field of a dislocation and the misfit strain of an interstitial. The model also pointed out the necessity of separating the neutron flux and time of irradiation when reporting information on void formation. It is expected that quite different dependences of void size and number density on the total neutron dose would be obtained depending on whether the experimental information was obtained under constant flux or under constant time conditions. It was also concluded that the magnitude and temperature dependence of dislocation loop formation would have a marked effect on void formation.

Growth Mechanism of Voids in Fast Reactor Irradiated Austenitic Stainless Steel

Growth Mechanism of Voids in Fast Reactor Irradiated Austenitic Stainless Steel

Growth Mechanism of Voids in Fast Reactor Irradiated Austenitic Stainless Steel

Growth Mechanism of Voids in Fast Reactor Irradiated Austenitic Stainless Steel

Swelling of austenitic stainless steels under fast neutron irradiation at elevated temperatures

A discussion of studies on volume increase phenomena observed in highly irradiated austenitic stainless steels is given. Volume increases are related to the production of polyhedral cavities. The likely source of swelling is a combination of the effects of two reactions: the helium-producing (n, α) reaction, and the vacancy-producing displacement reaction. It is believed that helium atoms so generated stabilize the cavity nuclei.