Parametric study of irradiation effects on the ductile damage and flow stress behavior in ferritic-martensitic steels (original) (raw)
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Journal of Nuclear Materials, 2008
Hardening and embrittlement are controlled by interactions between dislocations and irradiation induced defect clusters. In this work we employ the visco plastic self consistent (VPSC) polycrystalline code in order to model the yield stress dependence in ferritic steels on the irradiation dose. We implement the dispersed barrier hardening model in the VPSC code by introducing a hardening law, function of the strain, to describe the threshold resolved shear stress required to activate dislocations. The size and number density of the defect clusters varies with the irradiation dose in the model. We find that VPSC calculations show excellent agreement with the experimental data set. Such modeling efforts can both reproduce experimental data and also guide future experiments of irradiation hardening.
Journal of Nuclear Materials, 2006
Tensile testing has been performed at 25 and at 400°Contwoferritic/martensiticsteels(JFMSandHT−9)afterirradiationinFFTFtoupto400°C on two ferritic/martensitic steels (JFMS and HT-9) after irradiation in FFTF to up to 400°Contwoferritic/martensiticsteels(JFMSandHT−9)afterirradiationinFFTFtoupto70 dpa at 373-433°C. As observed in previous studies, this range of irradiation temperatures has a significant effect on hardening. The percent increase in yield stress decreases with increasing irradiation temperature from 373 to 433°C. The JFMS alloy, which has 0.7 wt% silicon, exhibits approximately a factor of two increase in yield strength between tests at 427 and at 373°C, and shows an increase in hardening with increasing dose. A comparison of the JFMS tensile properties to the properties of other ferritic/martensitic steels suggests that this hardening is due to precipitation of a Si-rich laves phase in this alloy. The HT-9 alloy, which contains more chromium and more carbon but less silicon (0.2 wt%), less molybdenum and less nickel, hardens during irradiation at 373°C, but shows less hardening for irradiations performed at 427°C and no increase in yield stress with increasing dose beyond 10 dpa. Published by Elsevier B.V.
Hardening mechanisms of reduced activation ferritic/martensitic steels irradiated at 300°C
Journal of Nuclear Materials, 2009
It has been reported that reduced-activation ferritic/martensitic steels (RAFMs), such as F82H, ORNL9Cr-2WVTa, and JLF-1 showed a variety of changes in ductile-brittle transition temperature and yield stress after irradiation at 300°C up to 5 dpa, and those differences could not be interpreted solely by the difference of dislocation microstructure induced by irradiation. In this paper, various microstructural analyses on low-temperature irradiated RAFMs were summarized with the emphasis on F82H, and a possible mechanism for the irradiation hardening was suggested. The possible contribution of dislocation channeling structure and back stress were indicated.
Continuum Mechanics and Thermodynamics
The European reduced activation ferritic/martensitic steel Eurofer97 in irradiated states displays significant nonlinear material behavior involving irradiation hardening, loss of strain hardening, and uniform elongation, as well as irradiation-induced embrittlement. Nonlinear behavior of irradiated steel modeled on the continuum scale will help to estimate the maximum operating range of the irradiated components beyond the onset of localized plastic flow. In this work, a thermodynamic framework for modeling irradiation-influenced deformation is established based on irradiation defect density and a thermodynamically consistent finite strain formulation of an existing viscoplastic model using the Dual Variables concept is presented. The model is implemented in ABAQUS allowing the simulation of tensile tests conducted on irradiated and unirradiated materials which shows the model’s ability to capture the post-yield and post-necking behavior observed in experiments up to ductile failure.
Nuclear Materials and Energy, 2020
In this work, we used Dislocation Dynamics (DD) simulations to investigate the role of the hierarchical defects microstructure of ferritic-martensitic steel Eurofer97 in determining its hardening behavior. A Representative Volume Element (RVE) for DD simulation is identified based on the typical martensitic lath size. Material properties for DD simulations in b.c.c Eurofer97 are determined, including the dislocation mobility parameters. The dependence of material parameters on temperature is fitted to experimental yield strength measurements carried out at room temperature and 330 • C, respectively. Voids and precipitates observed in the microstructure, such as M 23 C 6 and Tantalum-rich MX, are considered in our DD simulations as inclusions with realistic size distribution and volume density, while 〈1 1 1〉-and 〈1 0 0〉-type irradiation loops are included directly in the DD simulations. The lath structure, together with its typical precipitates arrangement and the different crystallographic orientation of the martensitic blocks can also be captured in the simulations. DD simulations are used to extract microstructure-specific hardening parameters, which can be used to simulate the properties of Eurofer97 at the engineering scale.
Engineering Failure Analysis, 2010
The Master Curve (MC) methodology, originally proposed by Kim Wallin, is a standardised engineering tool for analysing the fracture toughness of ferritic steels in the ductile to brittle transition (DBT) region by means of the reference temperature T 0 . This temperature is normally estimated from quasi-static fracture toughness tests, nevertheless, it has been recently extended to the determination of dynamic fracture toughness. The aim of the present contribution is to characterise the fracture resistance in the DBT region under high strain rate conditions by applying the MC methodology to the steel of the Santa María de Garoña Spanish nuclear power plant (NPP). In this sense, 15 Charpy instrumented tests were performed on pre-cracked specimens from the surveillance program of the plant. The dynamic reference temperature, T 0,dyn , was obtained and compared with the quasi-static reference temperature, T 0,sta . The reliability of a semi-empirical formula proposed by Wallin to obtain T 0,dyn from T 0,sta has been analysed for this material.