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Aluminium-alloyed austenitic steels Fe-14Cr-2Mn-20Ni-0.5Cu-3Al and Fe-14Cr-5Mn-12Ni-3Cu-2.5Al were tested at 500 °C in static Pb-Bi eutectic for 10,000 h. The concentration of oxygen in the liquid metal was changed in a controlled way over the course of the test from ∼10−6 to ∼10−9 mass% which provided conditions for oxidation and dissolution, respectively. Both steels showed slight oxidation of surface. Steel with higher Ni content revealed also initiation of dissolution corrosion in the view of rare pit-type damages. The structural and compositional features of oxide films, sub-oxide zones and corrosion damages are discussed.

This work addresses the effect of deformation twinning on the dissolution corrosion behaviour of 316 L austenitic stainless steels in contact with static liquid lead-bismuth eutectic (LBE). For this purpose, plastically deformed 316 L steel specimens with distinctly different deformation twin densities were simultaneously exposed to oxygen-poor (

This study addresses the effect of plastic deformation on the dissolution corrosion behavior of a Type 316L austenitic stainless steel. Dissolution corrosion was promoted by low oxygen conditions in liquid lead-bismuth eutectic (LBE). Specimens with controlled degree of plastic deformation (20%, 40%, and 60%) and a non-deformed, solution-annealed specimen were simultaneously exposed for 1,000 h at 500°C to static LBE with low oxygen concentration ([O] < 10−11 mass%). The corroded specimens were analyzed by various material characterization techniques. All exposed specimens exhibited dissolution corrosion. The non-deformed steel showed the least dissolution attack (maximum depth: 36 μm), while the severity of attack increased with the degree of steel deformation (maximum depth in the 60% steel: 96 μm). It was, thus, concluded that increasing the amount of plastic deformation in a Type 316L stainless steel results in higher dissolution corrosion damages for steels exposed to low oxygen LBE conditions. Addit...

Cracking jumps were observed in notched T91 (9Cr-1Mo ferritic-martensitic steel) specimens tested in liquid lead-bismuth eutectic (LBE) at 350 °C under tensile loading. The cracking jumps manifested themselves as being regular steps at tensile curves, while as being fatigue striation-like markings at fracture surfaces. The markings were consisted of liquid metal embrittlement (LME) zones and ductile zones. The liquid LBE was adsorbed at crack tip and likely reduced the interatomic bonding strength, leading to cracking in a brittle way and release of elastic energy in the load line. This unique phenomenon was found to be associated with coupled effects of LME and compliance/stiffness of tensile machines.

Heavy liquid metals such as lead bismuth eutectic (LBE) are chosen as the coolant to innovative Generation IV (Gen IV) reactors where ferritic/martensitic T91 steel is a candidate material for high temperature applications. It is known that LBE has a degrading effect on the mechanical properties of this steel. This degrading effect, which is known as liquid metal embrittlement (LME), has been screened by several tests such as tensile and small punch tests, and was most severe in the temperature range from 300 °C to 425 °C. To meet the design needs, mechanical properties such as fracture toughness should be addressed by corresponding tests. For this reason liquid-metal embrittlement of T91 steel was investigated by fracture toughness tests at 350 °C. Tests were conducted in Ar-5%H 2 and LBE under the same experimental conditions Tests in Ar-5%H 2 were used as reference. The basic procedure in the ASTM E 1820 standard was followed to perform tests and the normalization data reduction (NDR) method was used for the analysis. Comparison of the tests demonstrated that the elastic–plastic fracture toughness (J 1C ) of the material was reduced by a factor in LBE and the fracture mode changed from ductile to quasi-cleavage. It was also shown that the pre-cracking environment played an important role in observing LME of the material since it impacts the contact conditions between LBE and steel at the crack tip. It was demonstrated that when specimens were pre-cracked in air and tested in LBE, wetting of the crack surface by LBE could not be achieved. When specimens were pre-cracked in LBE though, they showed a significant reduction in fracture toughness.

The influence of displacement rate and temperature on the severity of liquid metal embrittlement (LME) was investigated by performing fracture toughness tests on the ferritic-martensitic T91 steel in liquid lead-bismuth eutectic (LBE) at three different displacement rates at 200 °C and 350 °C. Compact tension specimens were used for testing and all specimens were pre-cracked in LBE environment at 350 °C prior to testing. The energy normalization (EN) method was used to construct the J-R curves. J Q of each specimen was calculated and the fracture surfaces were investigated by scanning electron microscope (SEM). The results were compared to the tensile test results of the same material where reduction in total elongation was used to determine the susceptibility to LME. Comparison of tests at 200 °C and 350 °C showed that the LME effect was less prominent at 200 °C which was evidenced by the higher J -values obtained at this temperature and the fracture surfaces which overall had a significant distribution of dimples and larger secondary cracks. The observation of reduced LME effect at lower temperature was found to be in accordance with the tensile data within the strain rates discussed in this paper. Although the tensile test results show reduced LME effect as the strain rate is sufficiently reduced at 350 °C, the fracture toughness tests point to a more severe LME effect with decreasing displacement rate. An LME mechanism of T91 in LBE was discussed based on the observations given in this work. The fracture toughness values in LBE were found to be very low to support the selection of T91 material for the LBE cooled nuclear reactors. Moreover, as the obtained toughness values do not reflect the conservative estimation of the LME effect, incorporation of LME in the design of such reactors is not feasible in the current state.

Long-term corrosion behavior of T91 ferritic/martensitic steel in oxygen-doped flowing Pb–Bi eutectic is investigated by exposure for up to 20,000 h at 400 °C, 2 m/s and 2 × 10−7mass% dissolved oxygen. The corrosion phenomena and kinetics of interaction are characterized qualitatively and quantitatively. The steel shows major oxidation resulted in the formation of a bilayer Fe3O4 / Fe(Fe,Cr)2O4 scale. After 20,000 h, the scale thickness averages 12.6 (±2.7) μm. The metal recession due to oxidation does not exceed 5 (±1) μm. Besides oxidation, the localized dissolution of the steel is observed reaching of ∼100 μm in depth after 20,000 h.

This work focuses on the effect of dissolved oxygen concentration in liquid lead-bismuth eutectic (LBE) on the onset of dissolution corrosion in a solution-annealed 316 L austenitic stainless steel. Specimens made of the same 316 L stainless steel heat were exposed for 1000 h at 450 °C to static liquid LBE with controlled concentrations of dissolved oxygen, i.e., 10−5, 10−6, and 10−7 mass%. The corroded 316 L steel specimens were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A complete absence of dissolution corrosion was observed in the steel specimens exposed to liquid LBE with 10−5 and 10−6 mass% oxygen. In the same specimens, isolated “islands” of FeCr-containing oxides were also detected, indicating the localized onset of oxidation corrosion under these exposure conditions. On the other hand, dissolution corrosion with a maximum depth of 59 μm was detected in the steel specimen exposed to liquid LBE with 10−7 mass% oxygen. This suggests that the threshold oxygen concentration associated with the onset of dissolution corrosion in this 316 L steel heat lies between 10−6 and 10−7 mass% oxygen for the specific exposure conditions (i.e., 1000 h, 450 °C, static liquid LBE).

This work presents first results of the study on the influence of the LBE oxygen concentration on the initiation of dissolution corrosion in 316L austenitic stainless steels. 316L steel specimens were exposed at 450 °C to static liquid LBE with controlled and constant oxygen concentration of 10−5, 10−6 and 10−7 mass% for 1000 hours. Corroded specimens were analysed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Limited oxidation corrosion and no dissolution corrosion was observed in the specimens exposed to LBE containing 10−5 and 10−6 mass% oxygen, while dissolution corrosion with a maximum depth of 59 μm was found in the specimen exposed to LBE containing 10−7 mass% oxygen.

T91 ferritic-martensitic steel is one of the candidate materials to future fast reactors where lead-bismuth eutectic (LBE) is chosen as the coolant. The interaction of the steel with LBE coolant should be investigated by means of mechanical tests and detailed microstructural analysis. Quantitative analysis requires fracture toughness tests in LBE. However tests in LBE are not easily applied with conventional methods due to the conductive nature of LBE. In addition, there are no standards or guidelines for fracture toughness tests in LBE. In this work fracture toughness tests in inert environment and LBE are compared and technical problems encountered during tests in LBE are discussed.

The chemical and electrochemical conditions within a crevice of Type 316 stainless steel in boric acid–lithium hydroxide solutions under PWR-relevant conditions were modelled with a computational electrochemistry code. The influence of various variables: dissolved hydrogen, boric acid, lithium hydroxide concentration, crevice length, and radiation dose rate was studied. It was found with the model that 25 ccH 2 /kg (STP) was sufficient to remain below an electrode potential of -230 mV she , commonly accepted sufficient to prevent stress corrosion cracking under BWR conditions. In a PWR plant various operational B–Li cycles are possible but it was found that the choice of the cycle did not significantly influence the model results. It was also found that a hydrogen level of 50 ccH 2 /kg (STP) would be needed to avoid substantial lowering of the pH inside a crevice.

The local environment in an occluded region of a pressurized water reactor (PWR) depends on its geometry, its access to the bulk and the nature of the electrode kinetics at the metal surfaces. In PWR-relevant, oxygen-free, boric acid–lithium hydroxide solutions the dominant anodic and cathodic electrode reactions are found to be hydrogen oxidation and water reduction, respectively. The hydrogen oxidation reaction kinetics have been quantified using potentiostatic measurements – at 300 °C, under various dissolved hydrogen concentrations, for 1000 ppmB and 2 ppmLi. The reaction kinetics have been verified by modelling of a crevice experiment performed in an autoclave at 300 °C for 1000 ppmB, 2 ppmLi and 25 STP ccH 2 /kg.

Liquid metal embrittlement (LME) induced quasi-brittle fracture characteristics of a 9Cr–1Mo ferritic–martensitic steel (T91) after fatigue cracking in lead–bismuth eutectic (LBE) have been investigated at various length scales. The results show that the LME fracture morphology is primarily characterized by quasi-brittle translath flat regions partially covered by nanodimples, shallow secondary cracks propagating along the martensitic lath boundaries as well as tear ridges covered by micro dimples. These diverse LME fracture features likely indicate a LME mechanism involving multiple physical processes, such as weakening induced interatomic decohesion at the crack tip and plastic shearing induced nano/micro voiding in the plastic zone.

The crack propagation rate of Type 316 stainless steel in boric acid–lithium hydroxide solutions under PWR-relevant conditions was modelled. A film rupture/dissolution/repassivation mechanism is assumed and extended to cold worked materials by including a stress-dependent bare metal dissolution current density. The chemical and electrochemical conditions within the crack are calculated by finite element calculations, an analytical expression is used for the crack-tip strain rate and the crack-tip stress is assumed equal to 2.5 times the yield stress (plane-strain). First the model was calibrated against a literature published data set. Afterwards, the influence of various variables – dissolved hydrogen, boric acid and lithium hydroxide content, stress intensity, crack length, temperature, flow rate – was studied. Finally, other published crack growth rate tests were modelled and the calculated crack growth rates were found to be in reasonable agreement with the reported ones.

The crack propagation rate of Type 304 stainless steel in diluted sulphuric acid solutions was modelled based on finite element calculations of the chemical and electrochemical conditions within the crack and an analytical expression for the crack-tip strain rate. The slip/dissolution/repassivation mechanism was assumed. The influence of various variables – dissolved oxygen, sulphuric acid content, stress intensity, crack length, temperature, flow rate, sensitization and yield strength – was studied and found to be in agreement with experimental observations. The model was calibrated against one data point. The effect of temperature on thermal conductivity, electrode reaction kinetics, equilibrium constants, yield strength and crack geometry was considered and the thermal activation energy for the crack propagation rate could almost fully be accounted for.

In this paper we try to relate Stress Corrosion Cracking (SCC) initiation in stainless steels (SS) to the performance and nature of the anodic oxide film that develops during exposure to 300°C water containing boric acid and lithium hydroxide in an autoclave. In-situ electrochemical impedance spectra (EIS) have been obtained while exposing the samples. EIS reveals the behaviour of the oxide layer and the electrochemical processes that take place at the material-oxide-solution interface. After these exposures the oxide films were analyzed by X-ray photoelectron spectroscopy (XPS) to obtain the composition of the oxide film. The results showed that the oxide layers consisted of a mixed oxihydrate (iron-nickel based), dominating at the subsurface region and in larger depth, mainly consisted of chromium-iron oxides. The behaviour of the oxide film is being modelled using an extension to the point defect (PDM) / mixed conduction (MCM) series of models describing interface chemistry and vacancy and electron transport in the film.

This article describes the calculation of the polarisation behaviour of a metal in an aqueous environment using a computational electrochemistry code based on finite elements. The corrosion system consisted of three parallel reactions (oxygen reduction, hydrogen evolution and metal dissolution), taking place in the centre at the surface of the rotating disc electrode (RDE). The selected problem is simple enough to be solved analytically, which allows verification of the finite element calculation. Simultaneously, the example is rich enough to demonstrate the potential and the advantages of finite element simulation for corrosion science and engineering. The analytical and finite element calculations were in excellent agreement. The influence of the speed of the RDE, of the bulk concentration of dissolved oxygen and of the bulk hydrogen ion concentration on the polarisation behaviour have been determined. The use of finite elements had the following specific advantages. Firstly, no prior assumption on the diffusion layer thickness had to be made. Secondly, transport by diffusion, convection and electro-migration were taken into account. Thirdly, the finite element approach is general and flexible enough to tackle more complex systems. The calculations presented here are a first step towards the finite element simulation of stress corrosion cracking of stainless steel in an aqueous nuclear environment.