Quantitative modelling of swelling in M316 steel

The chemical rate theory is widely used to describe the microstructural evolution in a material during irradiation. We describe recent improvements to the theory that increase its predictive capability. The incubation dose prior to the onset of void swelling is modelled by allowing partition of the gas between the various sinks in the microstructure. New dislocation and void sink strengths have been derived incorporating the field effects. These improvements to the theory have been incorporated into a new FACSIMILE computer code designated VS5. The new code has been successfully employed to model void swelling during HVM, VEC and fast reactor irradiation of 316 steel.     

Effects of stress on swelling in 316 stainless steel

Stress was found to increase the magnitude of irradiation-induced swelling in 316 stainless steel. Measurement of the densities of pressurized tube specimens, irradiated at temperatures of ~ 430–475°C to peak fluences of $\text{~ 9 × 10}{}^{22}\text{n/cm}{}^2$ ($\text{E > 0.1 MeV}$) in EBR-II, has indicated increased swelling in both the annealed and 20% cold worked conditions of this alloy. Swelling in the annealed specimens was observed to increase linearly with hoop stress up to ~ 20 ksi (130 MPa), whereupon further increases in stress resulted in reduced swelling. Swelling in the cold worked material was linear with stress up to levels of ~ 28 ksi (193 MPa).     

Microstructural and microchemical comparisons of AISI 316 irradiated in HFIR and EBR-II

Two alternative interpretations of a unique but limited set of swelling data have been advanced in an attempt to predict the influence of helium on the swelling of 20% cold-worked AISI 316. In this paper it is shown that swelling data for annealed AISI 316 provide substantial insight concerning the role of helium on swelling. Additional insight has been obtained by a series of microstructural and microchemical examinations conducted on specimens of both annealed and cold-worked steel after irradiation in EBR-II and HFIR. These reactors differ greatly in neutron spectra and in AISI 316 generate quite different helium/dpa ratios and solid transmutant levels.At least in the range 500–750°C, the results of these studies show that helium's influence on swelling is manifested in the cavity density but not in the dislocation density or the major features of the microchemical evolution of the alloy matrix. The results also suggest that the influence of helium at high displacement levels is not strong on either the total swelling or the steady-state swelling rate.     

Laser cladding of Colmonoy 6 powder on AISI316L austenitic stainless steel

Stainless steels are widely used in nuclear power plant due to their good corrosion resistance, but their wear resistance is relatively low. Therefore, it is very important to improve this property by surface treatment. This paper investigates cladding Colmonoy 6 powder on AISI316L austenitic stainless steel by CO₂ laser. It is found that preheating is necessary for preventing cracking in the laser cladding procedure and 450 °C is the proper preheating temperature. The effects of laser power, traveling speed, defocusing distance, powder feed rate on the bead height, bead width, penetration depth and dilution are investigated. The friction and wear test results show that the friction coefficient of specimens with laser cladding is lower than that of specimens without laser cladding, and the wear resistance of specimens has been increased 53 times after laser cladding, which reveals that laser cladding layer plays roles on wear resistance. The microstructures of laser cladding layer are composed of Ni-rich austenitic, boride and carbide.     

Swelling rate versus swelling correlation in 20% cold-worked 316 stainless steels

A quantitative correlation of the swelling rate versus swelling is presented. Swelling data of 20% cold-worked 316 stainless steels were analyzed using the power law swelling equation. The prolonged transient region with keeping the suppressed swelling rate was clearly demonstrated for the improved 316 stainless steels like PNC316 and 316Ti. Rate theory analyses lead to the role of precipitates as point defect sinks for retardation of the void growth.     

The effect of pulsed irradiation on the swelling of 316 stainless steel in fusion reactors

A time-dependent rate theory formulation has been used to study the effects of pulsed irradiation on point defect and void behavior at elevated temperatures. It is found that point defects in pulsed tokamaks, θ-pinchs and inertial confinement fusion reactors (ICFR) display non-steady-state behavior. The pulsed nature of the irradiation has been shown to produce considerable deviations from steady-state void growth behavior at high temperatures (0.3 T_m to 0.5 T_m). In particular, the amount of swelling in the first-wall can be reduced for ICFR pulsing conditions and pulse widths ranging from a nanosecond to a microsecond. The amount of reduction increases with increased pellet yield at a fixed operating temperature, geometry and ICFR plant power output.     

Compatibility of AISI 316 L stainless steel with the Li17Pbg,eutectic

The compatibility of AISI 316 L stainless steel with the Li₁₇Pb₈₃, eutectic has been studied in the temperature range 623–873 K for times up to 6000 h. In the corrosion layers formed there is a strong Ni depletion and Pb and Li penetration in the matrix.Tests at 623 K in Li₁₇Pb₈₃ on notched tensile specimens under a constant uniaxial tensile load, below the engineering yield stress, have evidenced that. many cracks filled with Pb and possibly Li are formed after relatively short times.     

Investigation on the formation of serrated grain boundaries with grain boundary characteristics in an AISI 316 stainless steel

The formation of serrated grain boundaries (GBs) depending on the GB characteristics has been investigated by using an electron backscattered diffraction (EBSD) technique and a transmission electron microscopy (TEM) in an AISI 316 stainless steel. It was observed that at the early stage of aging treatment, the GB morphology was changed from flat to wavy at random GBs without any indication of M₂₃C₆ carbide formation, and no GB serration at special GBs (lower than Σ29) was found. The comparison study on the misorientation angle between two neighboring grains indicated that the occurrence of GB serration at random GBs is attributed to the reduction of the total GB energy. Random GBs with high energy tend to be serrated, resulting in the formation of two segments with lower energies. On the other hands, the special GBs may be less likely to form serrated GBs due to their lower GB energy.     

The boronizing effect on the radiation shielding and magnetization properties of AISI 316L austenitic stainless steel

The boronizing effect on the radiation shielding properties and magnetization of AISI 316L austenitic stainless steel has been investigated. For this purpose the linear attenuation coefficients of steel have been measured at the photon energies of 662, 1170 and 1332 keV and the results were compared with the calculation at the photon energy of 1-10⁸ keV. It was clearly seen from this work that both the magnetization and radiation shielding properties of the steel have been improved by boronizing process.     

The effect of vacancy loops on the swelling expected for 316 steel under dual-beam irradiation

The theoretical interpretation of simultaneous heavy-ion irradiation and continuous helium injection experiments is extended to include the role of vacancy loops in the evolution of the microstructure. Whilst we find that their inclusion does not alter our previous conclusions concerning the role of the gas in explaining a high-temperature swelling peak, they do influence the details of the swelling response. This detailed influence is such that the results expected from dual-ion simulation experiments should be both more representative of the neutron irradiations and easier to observe than we had previously believed.     

Effect of pre-strain on creep of three AISI 316 austenitic stainless steels in relation to reheat cracking of weld-affected zones

Microstructural modifications induced by welding of 316 stainless steels and their effect on creep properties and relaxation crack propagation were examined. Cumulative strain due to multi-pass welding hardens the materials by increasing the dislocation density. Creep tests were conducted on three plates from different grades of 316 steel at 600 °C, with various carbon and nitrogen contents. These plates were tested both in the annealed condition and after warm rolling, which introduced pre-strain. It was found that the creep strain rate and ductility after warm rolling was reduced compared with the annealed condition. Moreover, all steels exhibited intergranular crack propagation during relaxation tests on Compact Tension specimens in the pre-strained state, but not in the annealed state. These results confirmed that the reheat cracking risk increases with both residual stress triaxiality and pre-strain. On the contrary, high solute content and strain-induced carbide precipitation, which are thought to increase reheat cracking risk of stabilised austenitic stainless steels did not appear as key parameters in reheat cracking of 316 stainless steels.     

Effect of Condition of Recrystallization Heat Treatment on High-Temperature Mechanical Properties of an Irradiated AISI 316 Austenitic Steel

A study was made of the effects brought upon the radiation-induced high-temperature embrittlement of AISI 316 austenitic steel by different conditions to the specimens to produce recrystallization.

Cold worked specimens were recrystallized at temperatures 950°–1,100°C held for periods ranging 2~60 min. The specimens were then irradiated to 1.7×10²¹nvt(< MeV) at 55°C after which they were subjected to tensile testing at 650°C.

In the specimens recrystallized at 950°C, carbide precipitation was observed to have occurred, and these specimens were found less liable to show radiation-induced embrittlement. On the other hand, specimens recrystallized at 1,025° and 1,100°C became completely solution treated, and exhibited severe radiation-induced embrittlement. It is surmisted that the carbides precipitated on the grain-boundaries tend to inhibit propagation of grain-boundary cracks, and hence contribute to lessing radiation-induced embrittlement.     

Spectroscopic analysis of proton-induced fluorescence from yttriumorthosilicate

The results of a 3-MeV-proton irradiation test on two yttrium orthosilicate doped with cerium (YOS:Ce) crystal samples are reported. The principle goal of this test was to determine the proton dose required to reduce the resulting YOS:Ce fluorescence light to half of its original value (half brightness dose) at ambient temperature and 150°C. Results from this test will also provide basic information concerning potential changes in spectral composition and fluorescence peak widths for YOS:Ce at ambient temperature and 150°C     

Effect of flowing sodium on corrosion and tensile properties of AISI type 316LN stainless steel at 823 K

AISI type 316LN stainless steel was exposed to flowing sodium in mass transfer loop (MTL) at 823 K for 16 000 h and then examined for changes in the tensile properties due to the mass transfer and corrosion effects. Comparisons in microstructural and mechanical properties were made between annealed, thermally aged and sodium exposed materials. Microstructural examination of thermally aged and sodium exposed materials revealed precipitation of carbides at the grain boundaries. The sodium exposed samples contained a degraded layer at the surface up to a depth of around 10 μm and a surface carburized layer of about 30 μm. There was about 15% increase in yield strength and a decrease of about 20% in ductility for the sodium exposed material vis-a-vis thermally aged material and this was attributed to carburization effects and microstructural changes.     

High temperature creep and cyclic deformation behaviour of AISI 316 L(N) austenitic steel and its modelling with unified constitutive equations

Creep tests at constant stress and low cycle fatigue (LCF) tests were performed with a view to investigating and modelling the deformation behaviour of AISI 316 L(N) austenitic stainless steel at 700 °C. All experiments were done on samples taken from two different sheets of the same batch of material.The creep stresses were selected from the high stress range. The results obtained from creep tests on samples from different sheets are compared with each other. The differences between them and the results of a creep test carried out at constant load are indicated.The LCF experiments were strain controlled. The effects of strain rate and strain amplitude on the cyclic hardening behaviour were investigated.The parameters of a set of constitutive equations are determined from these data. The quality of the parameter fit is discussed.     

Long term corrosion on T91 and AISI1 316L steel in flowing lead alloy and corrosion protection barrier development: Experiments and models

Considering the status of knowledge on corrosion and corrosion protection and especially the need for long term compatibility data of structural materials in HLM a set of experiments to generate reliable long term data was defined and performed. The long term corrosion behaviour of the two structural materials foreseen in ADS, 316L and T91, was investigated in the design relevant temperature field, i.e. from 300 to 550 °C. The operational window of the two steels in this temperature range was identified and all oxidation data were used to develop and validate the models of oxide scale growth in PbBi. A mechanistic model capable to predict the oxidation rate applying some experimentally fitted parameters has been developed. This model assumes parabolic oxidation and might be used for design and safety relevant investigations in future. Studies on corrosion barrier development allowed to define the required Al content for the formation of thin alumina scales in LBE. These results as well as future steps and required improvements are discussed. Variation of experimental conditions clearly showed that specific care has to be taken with respect to local flow conditions and oxygen concentrations.     

Intergranular damage in AISI 316L(N) austenitic stainless steel at 600 °C: Pre-strain and multiaxial effects

This study is devoted to the effect of a multiaxial stress state and of pre-straining on the creep properties of an austenitic stainless steel. Creep tests on both smooth and notched specimens have been carried out on type 316L(N) steel at 600 °C. In comparison to the annealed state, pre-straining caused a substantial increase in creep lifetime but also a dramatic drop in intergranular damage resistance. The effect of a pre-strain on creep ductility was so strong that compact tension specimens in pre-strained state tested under relaxation conditions cracked, whereas specimens in annealed state were not prone to cracking. A model taking into account both pre-strain and multiaxial effects was developed and identified on the basis of local intergranular micro-cracks measurements on notched specimens. It satisfactorily predicts the results of relaxation crack propagation tests. This model may also provide a useful estimation of the relaxation cracking risk of 316L(N) as a function of pre-strain level and stress triaxiality ratio.