Swelling In Austenitic Steels Research Articles

Use of a Model for the Final Stage of Transient Swelling to Predict the Radiation-Induced Porosity in Kh18N9 Steel during Operation in the BN-600 Reactor Internals

A model is developed to describe the final stage of transient swelling of austenitic steels, at which vacancy pores do not form. The evolution of an ensemble of radiation pores is determined by the following two processes: the growth of vacancy pores due to an unbalanced vacancy influx and the coalescence of growing pores. The evolution of an ensemble of pores during long-term operation is estimated using the model and the results of transmission electron microscopy studies of irradiated Kh18N9 steel samples, which are made of the BN-600 reactor internals having operated for 22 and 33 years. Time dependences of the average size, the concentration, the integral surface of pores and the swelling during operation for up to 50 years are plotted.

Analysis of the influence of type of stress state on radiation swelling and radiation creep of austenitic steels

We present some findings of the analysis of experimental data on the influence of the type of stress state on radiation swelling in austenitic steels. A constitutive equation has been derived which provides a description of the effect of triaxial stress state on swelling in austenitic steels allowing for the contributions of spherical and deviatoric stress components. The authors put forward a physical interpretation of the derived relationship between radiation swelling and stress state. The dependence of radiation creep on swelling has been defined more accurately taking into account the stress state. The values of the coefficients involved in the constitutive equation and radiation creep dependence have been determined.

Effects of dose rate on microsturctural evolution and swelling in austenitic steels under irradiation

Effects of dose rate on microstructural evolution in a simple model austenitic ternary alloy are examined. Annealed specimens are irradiated with fast neutrons at several positions in the core and above core in FFTF/MOTA between 390°C and 435°C in a wide range of doses and dose rates. In Fe–15Cr–16Ni, swelling seems to increase linearly with dose without incubation dose. Cavities are observed even in the specimens irradiated to 0.07 dpa at 1.9×10−9dpa/s. Both cavity nucleation and growth are enhanced by low dose rates. These are mainly caused by accelerated formation of dislocation loops at lower dose rates. Low dose rates enhance swelling by shortening incubation dose for the onset of steady-state swelling. In the specimens irradiated at higher dose rates to higher doses, high density of dislocation increases average cavity diameter, however decreases cavity density.

Effect of nickel content on creep strength of Fe-15Cr-Ni-2.5Mo-0.3Ti austenitic steels for fast breeder reactor fuel cladding tube

The fuel cladding tubes of fast breeder reactors (FBR) are subjected to internal pressure caused by fission product gases at temperatures above 923 K under fast neutron irradiation. Therefore, resistance to swelling and creep strength are the principle requisites for cladding materials. Austenitic steels such as type 316 steel have been selected for cladding material. The resistance to swelling of austenitic steels is known to be suppressed by cold working [1] and increasing nickel content [2]. However, the effect of nickel content on the creep strength of austenitic steels is not well understood. This letter describes the effect of nickel content ranging from 15 to 35 wt % on the creep strength of cold-worked Fe-15Cr-Ni-2.5Mo -0.3Ti austenitic steels strengthened by the precipitation of MC type (TIC) carbides. The chemical compositions of the test materials are given in Table I. Only the nickel content was varied, ranging from 15 to 35 wt %, and the other compositions, including molybdenum, titanium, phosphorus and boron (elements that have been found to be effective in improving the creep strength), were held constant. The test materials were melted in a vacuum-induction furnace and cast into 10 kg ingots. Th%ingots were hot forged and hot rolled to sheets of 6 mm thickness. After solution treating at 1373K and cold rolling to 2.5ram thickness, they were final solution treated at 1373 K or 1423 K. The sheets were cold rolled for 20% before creep-rupture testing. Creep-rupture tests were performed at 973 K using plate specimens 2 mm thick and with gauge section 6 mm wide and 25 mm long. The microstructures of the specimens were examined by transmission electron microscopy (TEM).

The effect of radiation-induced segregation on void swelling in electron-irradiated austenitic Fe-Cr-Ni-Ti-P Alloy

It has been reported that the void swelling in austenitic steels at higher temperatures is enhanced by a nickel depletion in matrix . The objective of the present study is to understand the effect of solute addition on void swelling, in association with microchemical changes, in austenitic steels during electron irradiation.Four types of model alloys (Fe-16Cr-17Ni, Fe-16Cr-17Ni-0.25Ti, Fe- 16Cr-17Ni-0.1P, Fe-16Cr-17Ni-0.25Ti-0.IP) and JPCA-2 were used in this study. Irradiation and in-situ observation were carried out with 1.0 MeV electrons utilizing JEM-1000 of HVEM Lab. Kyushu Univ.Fig. 1 shows the irradiation temperature dependence of nickel concentration in matrix after irradiated at 2 dpa. The ternary alloy and alloys containing phosphorus(or titanium) only show a strong nickel depletion in matrix due to nickel segregation to defect sinks. Our previous results about void swelling in these alloys showed that the temperature, where nickel depletion in matrix became prominent, corresponded to that of maxium void swelling. On the other hand, void swelling and the nickel depletion were not detected in Fe-16Cr-17Ni-0.25Ti-0.IP and JPCA-2.

Phenomenological theories on irradiation effects of steels

Change in microstructure and mechanical properties of irradiated materials could be analysed by use of phenomenological theories. In this study, an analysis is presented to describe the microstructural evolution produced by irradiation, such as void swelling in austenitic steels, and the mechanical property changes, such as hardening and ductility loss of ferritic steels, based on the phenomenological theories.