Chromium Depletion Research Articles

Recrystallisation behaviour of a fully austenitic Nb-stabilised stainless steel.

We have performed an in-depth characterisation of the microstructure evolution of 20Cr-25Ni Nb-stabilised austenitic stainless steel during 1 h isochronal annealing up to 1100°C using scanning electron microscopy. This steel grade is used as cladding material in Advanced Gas-cooled fission reactors, due to its resistance to thermal creep and oxidation. The initial deformed microstructure undergoes recrystallisation via a strain-induced boundary migration mechanism, attaining a fully recrystallised microstructure at 850°C. A number of twins are observed in the vicinity of deformation bands prior to the start of recrystallisation. New Nb(C, N) particles form gradually in the microstructure, and the particle dispersion presents a maximum volume fraction of 2.7% at 930°C. At higher temperatures, the smaller particles become unstable and gradually dissolve in the matrix. Consequently, the Zener pinning pressure exerted on the grain boundaries is progressively released, triggering the growth of the austenite grains up to an average size of ∼47 μm at 1100°C. The observed temperature window for recrystallisation and grain growth can be predicted by a unified model based primarily on the migration of high- and low-angle grain boundaries. LAY DESCRIPTION: Austenitic stainless steel containing high percentage of chromium and nickel is currently used as fuel cladding material in the British Advanced Gas-cooled Reactors (AGR). This material has been chosen because of its high resistance to thermal creep and corrosion, both enhanced by the presence of a fine dispersion of carbonitrides precipitated during the cladding thermomechanical processing. During the time spent in the reactor core, few fuel cladding elements can become susceptible to local chromium depletion at grain boundaries, which is ascribed to the time evolution of the microstructural damage caused by the neutron bombardment in the reactor core. This depletion might increase the susceptibility of this steel to intergranular corrosion attacks during medium-to-long term storage of spent fuel elements in water ponds. The severity of the local chromium depletion depends not only on the irradiation conditions, but also on the grain boundary geometry. We have investigated the recovery, recrystallisation and grain growth of AGR stainless steel during 1 h annealing at selected temperatures relevant for the thermomechanical processing of the steel claddings, focusing on the formation and evolution of grain boundaries and second phases. These two features play a key role in the progression of the neutron damage and the subsequent development of local chromium depletion during reactor service operations. A deep understanding of the mechanisms and conditions behind their formation during the thermomechanical processing of the cladding material and their interaction with each other constitutes the foundation to evaluate, and potentially mitigate, the effect of irradiation on the cladding material.

Irradiation assisted stress corrosion cracking of commercial and advanced alloys for light water reactor core internals

Thirteen alloys including high- and low-strength nickel-base alloys, austenitic stainless steels, and ferritic alloys were irradiated using 2 MeV protons to a damage level of 2.5 dpa at 360 °C and assessed for their susceptibility to irradiation assisted stress corrosion cracking (IASCC) in both BWR normal water chemistry (NWC) and PWR primary water. Cracking susceptibility was highest for high strength nickel-base alloys, followed by the low strength nickel-base alloys and then the low strength iron-base alloys. Cracking in the nickel-based alloys was worst in normal water chemistry, which was reversed for the iron-based alloys. In general, cracking correlated with the degree of microstructure changes, though no single feature could be linked to cracking. IGSCC occurred in both the unirradiated and irradiated conditions in high strength nickel-base alloys with susceptibility being considerably higher following irradiation. In all cases, slip was planar, and the degree of slip localization correlated with the probability of IG crack initiation. Low strength nickel-base alloys showed the same dependence on environment as high strength alloys but were considerably less susceptible to IASCC initiation. Among the low strength iron-base alloys, alloy 800 was most susceptible to IASCC initiation in both BWR NWC and PWR primary water, which also correlated with grain boundary chromium depletion and silicon segregation. Across all alloys, cracking correlated with both the degree of localized deformation and the hardness in the irradiated condition. The agreement is expected as increased hardening also correlates with localized deformation, which is likely a necessary, though insufficient condition for cracking.

Production and use of radioactive [82Br]KBr in high-temperature corrosion studies

The applicability of radioactive species in high-temperature research as tracers was studied with KBr and an Nb-stabilised austenitic stainless steel. KBr-induced high-temperature corrosion was addressed by using radioactive [82Br]KBr and measuring the radioactivity of the sample surface with a high-resolution phosphor imaging device.Neutron activation by cyclotron proved to be a very cost-effective way to produce radioactive [82Br]KBr with a high radionuclidic purity and a negligible level of unwanted side products. KBr reacts rapidly with steel, forming potassium chromate and metal bromides, both of which are reducing the protective properties of the surface oxide through chromium depletion and increasing porosity.

Controlling the carbide formation and chromium depletion in W-Cr alloy during field assisted sintering

Tungsten is a refractory metal, suitable for a broad range of high-temperature applications, due to its high melting point and high-temperature strength. Recently, tungsten alloys became of great interest in thermonuclear fusion research. The alloys maintain low sputtering yield and high melting point, but greatly improve some drawback properties comparing to pure tungsten. These alloys are commonly prepared by mechanical alloying and compacted using Spark Plasma Sintering/Field Assisted Sintering. Powder in a graphite die is consolidated by applying pulsed electric current and pressure. Graphite foil is commonly placed between the die and the powder, to prevent adhesion. However, for number of applications it is necessary to avoid carbon contamination. In the present study we have examined carbon contamination mechanism of W - 10 wt.%Cr - 1 wt.%Hf alloy during Field Assisted Sintering along with the alloy's properties. The experiments have shown that the graphite foil leads to significant dealloying via mechanism of liquid phase sintering. As a result, tailored properties of the material are deteriorated after several minutes of the consolidation process. Therefore, application of carbon diffusion barrier was proposed, examined and compared with the alloy sintered with graphite foil.

Study of Steel Corrosion Cracking Mechanisms for VVER RPV Internals Based on Simulation Tests

Different hypotheses of irradiation assisted stress corrosion cracking for materials of internals in the light water reactor environment were analyzed. Irradiation-induced grain boundary chromium depletion, localized deformation, and material hardening were considered. Heat treatment and cold working of 18Cr–10Ni–Ti steel were made to simulate the influence of neutron irradiation. Autoclave tests in the light water reactor environment at a temperature 290°C and at a strain rate of 3 × 10–7 s–1 were carried out. 18Cr–10Ni–Ti steel specimens in the initial state, after heat treatment, and after heat treatment followed by cold working were used. Fracture surfaces and lateral surfaces of specimens were examined by scanning electron microscopy. The microstructure of the material was also examined using transmission electron microscopy. It was shown that the grain boundary chromium depletion and the material hardening are not the main causes of corrosion cracking of 18Cr–10Ni–Ti steel in the primary coolant deoxygenated environment. The localization of deformation has a profound effect on corrosion cracking in the absence of the grain boundary sliding. The conditions determining the crack propagation by the corrosion cracking mechanism are defined.

Influence of solidification induced composition gradients on carbide precipitation in FeNiCr heat resistant steels

Secondary precipitation of Cr-rich carbides in heat resistant austenitic stainless steels has been investigated both experimentally and using finite element simulations. The microstructural evolutions in two commercial grades were characterized using electron microscopy. A special emphasis was given on the peculiar spatial distribution of M23C6 secondary carbides exhibiting precipitate free zones surrounding primary carbides, and high density precipitate zones extending with longer aging times. Solidification induced chemical composition gradients were clearly exhibited in the as-cast alloys with significant chromium depletion in the vicinity of primary M7C3 carbides. It is then proposed that these gradients play a major role in the secondary precipitation mechanism. Classical nucleation and growth theories have been adapted to account for (i) the flux of solutes with large difference in diffusion coefficients, (ii) the initial composition gradients in the matrix and, (iii) the chemical driving force for nucleation and growth of M23C6 carbides. Within this framework, the whole kinetics has been reproduced. It clearly shows that the spatial distribution of secondary carbides that play a key role in the creep resistance of these alloys is the result of a complex interaction between initial composition gradients in as-cast alloys and solute flux resulting from phase transformation during aging.

Magnetization study of the sensitization in SS304LN

Sensitization is precipitation of chromium carbide in stainless steels during exposure to high temperatures service that leads to premature corrosion failure of components. It is well known that during sensitization process, chromium carbide forms at the grain boundary along with chromium depletion near the grain boundary resulting in the change of the magnetic property of the steel from paramagnetic to ferromagnetic. From this study, it is clear that the magnetic characterisation is sensitive enough to detect the sensitisation. However, the magnetic behavior has contributions from both ferromagnetic and super paramagnetic nature of the phase.

Effect of Solution Annealing Time on the Microstructure and Corrosion Resistance of Duplex Stainless Steel

The formation of intermetallic phases during thermal treatments is a decisive point for the performance of duplex stainless steels, which may prevent the obtaining or provoke degradation of their properties. This paper presents an investigation on the corrosion resistance of duplex SAF 2205 steel as received and after solution annealing treatment. The objective was to evaluate the correlation between the solution annealing time, the resulting microstructural changes and the corrosion resistance of the steel through electrochemical tests of cyclic potentiodynamic polarization and double-cycle potentiokinetic reactivation (DL-EPR). The heat treatments were performed at 1100° C for 30, 120 and 240 min with subsequent air cooling. The results of the DL-EPR showed that although there was no presence of intermetallic phases even with the absence of intermetallic phases, the solution annealing time influenced the degree of chromium depletion of the samples, so that with the increase of time, there was an increase in the degree of chrome depletion.

Characterization of the oxide scale formed on external surface of HP reformer tubes

This work presents the characterization of the external oxide scale of a centrifugally cast HP steel tube, modified with Nb and Ti, after 90,000h of operation in a steam reforming furnace, showing different aging states as a function of the column height and exposure temperature. The objective was to relate the oxide microstructural morphology to its magnetic response for three different microstructural aging states. The morphological and compositional characterization was performed by high resolution scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. The magnetic response of the external surface was analyzed by magnetic force microscopy and scanning magnetic susceptometer. The results showed the formation of a multilayer oxide scale with different compositions along its thickness. In addition, a microstructural modification was identified in the scale-matrix interface, due to the depletion of chromium. It was also observed that the magnetic response is dependable both on the oxide scale thickness and the chromium carbides depleted zone. Magnetic force microscopy was able to identify the origin of the magnetic response resulted from the steel tube surface.

Compatibility Analysis of Chromites in Dual-Phase Composites for Oxygen Transport Membranes

An oxygen transport membrane (OTM) is a promising way of supplying oxygen from air to high temperature processes, such as gasification.[1] Several studies have demonstrated that mixed ionic-electronic conducting (MIEC) perovskites with composition AxSr1-xCoyFe1-yO3-d (A=La, Ba) have high oxygen-ionic and electronic conductivity, which are the basic requirements for an OTM material. However, these perovskites have a limited pO2 operation range, suffering irreversible chemical decomposition at pO2 values below 10-12. [2] YCrO3-based perovskites show high electronic conductivity and thermo-chemical stability both at high temperatures (~1000 ºC) and in reducing environments (pO2 ~10-20 atm). [3,4] Hence, chromites in combination with highly stable ionic-conductors (e.g. ceria or zirconia-based materials) as dual-phase composites are alternative OTM materials. However, their chemical compatibility and stability together with ion-conductors in reducing conditions, as well as their oxygen permeation in different atmospheres, needs to be further investigated. This study analyses the stability of dual-phase composites consisting of 30 vol.% perovskite Y0.8Ca0.2Cr0.8Co0.2O3 (YCCC) and 70 vol.% ionic conductors Ce0.9Gd0.1O1.95 (CGO10) or (Sc2O3)0.1(Y2O3)0.01(ZrO2)0.89 (10Sc1YSZ) as OTM materials. These dual-phase composites were sintered in air between 1200 ºC and 1450 ºC to analyze the effect of temperature on the composites, and stability tests were made by exposing the composites to humidified 5% H2/N2 at 850 ºC. SEM-EDS, XRD and thermal analyses were performed to characterize the composites and identify possible secondary phases that could detriment their performance. Oxygen flux tests were performed using 1 mm thick pellets in air/N2, air/CO2 and air/H2-3%H2O gradients at temperatures up to 950 ºC. In 10Sc1YSZ-containing samples, densification was inhibited in the studied temperature range, which might be related to evaporation of transition metals from the perovskite B site, Ca mobility and possible reactions with Zr. Metal evaporation was slightly intensified after reducing conditions, resulting in relative densities <80%. Chromium depletion from the composite and formation of Cr2O3 crystals was observed in samples sintered at 1450 ºC. On the other hand, CGO10-based composite reached ~ 90% of relative density at 1200 ºC, though CaCrO4 formation, probably related to Ca excess in the perovskite, was identified. Nevertheless, higher stability towards reducing conditions was observed. Initial oxygen permeation tests performed in dense CGO10-YCCC composite pellets show fluxes up to 0.4 Nml·cm-2·min-1 at 950ºC in air/N2 gradient. The CGO10-YCCC dual-phase composite is therefore a promising material, which is now under further optimization and development as a tubular, multilayer OTM. [1] Julbe, A. et. al. Catalysis Today, 104 (2005), 102-113 [2] Niedrig, C. et al. Journal of The Electrochemical Society, 160 (2) F135-F140 (2013). [3] Gupta, S. et al. Materials Science and Engineering, 90 (2015), 1–36. [4] Suvorov, S.A. et al. Refractories and Industrial Ceramics, 45-2 (2004), 94-99.

Phase Transformations in Co-Ni-Cr-W Alloys During High Temperature Exposure to Steam Environment

Three model alloys, Co-10Ni-20Cr-15W, Co-30Ni-20Cr-15W and Ni-20Cr-15W (all in wt.%) were investigated in Ar-50%H2O at 700 and 750 °C for up to 3000 h reaction. The results showed the formation of thin chromia scales on the sample surfaces in all cases. For the Co-base alloys, accompanied by the Cr2O3 formation, a chromium depletion zone was detected underneath the oxide scale along with Co3W with some amount of dissolved Cr and Ni. This kind of Co3W was enriched along the oxide/alloy interface. The formation of this intermetallic phase was considered to follow nucleation and subsequent growth based on morphology and composition analyses. Increasing nickel content reduced the amount of Co3W formation. For the nickel-base alloy Ni-20Cr-15W, no intermetallic phase was detected. The formation of the Co3W intermetallic was discussed based on phase transformation induced by chromium depletion. The effect of nickel on this phenomenon was also discussed according to thermodynamic phase equilibrium analysis.

Age-hardening behaviour, microstructure and corrosion resistance of the copper alloyed stainless steel 1.4542

The copper alloyed stainless steel 1.4542 (X5CrNiCuNb16-4) is used in different areas due to its good mechanical properties and corrosion resistance. Strength and corrosion resistance can be adjusted by the heat treatment, which is of importance for the application of this alloy. The mechanical properties (strength and hardness) are attributed to the dispersive precipitation of the copper rich ϵ–Phase. The additional precipitation of chromium carbides can reduce the corrosion resistance. Different ageing states were produced to investigate the precipitation behaviour with various methods. Furthermore, the influence of cold-rolling on the precipitation behaviour was studied in comparison to a solution annealed state without deformation. The microstructure was studied by SEM and the variations of hardness and magnetic proportion were characterised. The electrochemical potentiodynamic reactivation (EPR) was used to determine the corrosion resistance and detect chromium depletion in all heat-treated states. The results show that a work hardening accelerates the precipitation rate, while ageing at 600 °C reduces the corrosion resistance due to chromium depletion.

Proton irradiation damage in cold worked Nb-stabilized 20Cr-25Ni stainless steel

Micro-scale damage with a topographical contrast has been observed in cold-worked Nb-stabilised 20%Cr-25%Ni stainless steel, following irradiation with 2.2 MeV protons at 400 °C and a dose rate of ∼10−5 dpa/s. After an irradiation dose of 3 and 5 dpa, microstructural changes were found to a depth of 22 μm below the irradiated surface, coincident with the estimated mean range of protons in the material as predicted by the TRIM code. Large variations of intragranular mis-orientations, in combination with a depletion of chromium at grain boundaries, were observed in the proton-irradiated layer. This was accompanied by an increase in nano-hardness, which was linked to a partial transformation of tangled dislocation networks into dislocation loops. Such visible microstructural changes have not been reported before in the absence of post-irradiation annealing treatments.

Effect of short duration solution treatment at temperatures below 1000 °C on σ‐phase precipitation in a super duplex stainless steel alloy

AbstractSuper duplex stainless steel alloys are characterized by a high content of chromium, nickel, molybdenum and nitrogen. In these steels, the main role of chromium, nickel and molybdenum alloying elements is to increase corrosion resistance. Increased mechanical properties are obtained by adding nitrogen, which promotes structural hardening. The microstructure of super duplex stainless steels consists of a mixture of ferrite and austenite phases, while other phases are also formed, such as: sigma, chi, chromium nitride, carbides and secondary austenite. All secondary phases are considered deleterious phases due to their negative effect on corrosion resistance and mechanical properties. The precipitation formation mechanism of the sigma phase assumes depletion of chromium and molybdenum from the matrix, worsening the alloy properties. The aim of the present work is to show the microstructural changes occurring during a short duration (10 minutes) solution treating of an UNS S32760/1.4501/F55 alloy, three temperatures being considered: 800 °C, 900 °C and 1000 °C. Scanning electron microscopy (energy dispersive spectroscopy and electron backscattered diffraction) was used for quantifying the alloying elements distribution, to distinguish between the observed phases, and to better understand the evolution of each phase.

Understanding Corrosion of Ni-Cr Alloys in Molten Chloride Salts

Molten chloride salts possess many attractive properties for use as a coolant and storage medium in advanced nuclear reactors and in concentrating solar power systems. Among the many challenges is the corrosion of salt-facing structural components. In molten halide salts, the passive films that typically form on the surface of corrosion resistant alloys either do not form, or are unstable due to the very low oxygen activities. Therefore, corrosion of materials is dependent largely on interfacial dissolution reactions between the molten salt and the bare metal surface in which alloy constituents with the most stable chlorides tend to be the most likely to dissolve. For most common structural alloys, chromium has the most stable chloride, and thus selective dissolution of chromium from the alloy into the salt is the dominant form of material degradation in molten halides. While this fact is well known and backed-up by experimental data, the mechanism of chromium depletion from alloys is not yet known. To truly understand corrosion in molten salts, the mechanism of chromium depletion from alloys must be understood and quantified. This talk will discuss results of a combined experimental and computational strategy aimed at fundamentally understanding corrosion of alloys in molten chloride salts. Controlled capsule tests are conducted in which model Ni-Cr alloys are exposed to molten KCl-MgCl2 at temperatures in excess of 600°C to measure degradation in molten salt. In an effort to maintain greater control of the molten salt environment, new processes to sufficiently purify salts are discussed. Quantification of salt impurities is matched to corrosion results in an effort to quantify the effect of salt impurity concentrations on corrosion rates. Traditional experimentation is coupled with x-ray spectroscopy and thermodynamic modeling to identify relevant reactions and to develop a thermodynamic description of the alloy-salt system. This work is funded by the Laboratory Directed Research and Development Fund at Oak Ridge National Laboratory.

Oxidation and Hot Corrosion Behaviors of Service-Exposed and Heat-Treated Gas Turbine Vanes Made of IN939 Alloy

Oxidation and hot corrosion tests were conducted on service-exposed and heat-treated IN939 alloys at 830, 930 and 1030 °C for testing times up to 800 h. The degradation behaviors were studied using optical and scanning electron microscopes. The oxidation results showed no tangible weight change in the samples at 830 °C. At 930 °C, after initial weight gain, the oxidation samples showed weight loss; whereas a continuous weight loss was observed at the higher temperature of 1030 °C. In the hot corrosion tests, however, a large weight loss occurred in the samples even at 830 °C, indicating an effect of fuel impurities on the high-temperature behavior of the alloy. SEM observations revealed that the main features of oxidation and hot corrosion of the alloy were internal oxidation of aluminum and depletion of chromium in the regions beneath the surface scales.

Molten salt corrosion behavior of structural materials in LiCl-KCl-UCl3 by thermogravimetric study

The corrosion resistance of structural materials has been recognized as a key issue in the various unit operations such as salt purification, electrorefining, cathode processing and injection casting in the pyrochemical reprocessing of spent metallic nuclear fuels. In the present work, the corrosion behavior of the candidate materials of stainless steel (SS) 410, 2.25Cr-1Mo and 9Cr-1Mo steels was investigated in molten LiCl-KCl-UCl3 salt by thermogravimetric analysis under inert and reactive atmospheres at 500 and 600 °C, for 6 h duration. Insignificant weight gain (less than 1 mg/cm2) in the inert atmosphere and marginal weight gain (maximum 5 mg/cm2) in the reactive atmosphere were observed at both the temperatures. Chromium depletion rates and formation of Cr-rich corrosion products increased with increasing temperature of exposure in both inert and reactive atmospheres as evidenced by SEM and EDS analysis. The corrosion attack by LiCl-KCl-UCl3 molten salt, under reactive atmosphere for 6 h duration was more in the case of SS410 than 9Cr-1Mo steel followed by 2.25Cr-1Mo steel at 500 °C and the corrosion attack at 600 °C followed the order: 9Cr-1Mo steel >2.25Cr-1Mo steel > SS410. Outward diffusion of the minor alloying element, Mo was observed in 9Cr-1Mo and 2.25Cr-1Mo steels at both temperatures under reactive atmosphere. Laser Raman spectral analysis of the molten salt corrosion tested alloys under a reactive atmosphere at 500 and 600 °C for 6 h revealed the formation of unprotected Fe3O4 and α-as well as γ-Fe2O3. The results of the present study facilitate the selection of structural materials for applications in the corrosive molten salt environment at high temperatures.

Diagnostics of the effect of prior cold deformation and aging time on intergranular corrosion resistance in case of austenitic stainless steel

Intergranular corrosion of commercial stainless steel type X6CrNiTi18-10 (1.4541, AISI 321) is frequently observed in several process environments. These localized attacks are normally attributed to the carbide precipitation and concomitant depletion of chromium near grain boundary due to steel exposure to sensitization temperature. Such undesirable microchemistry is expected to be changed further if the material undergoes deformation prior to sensitization. Present paper deals with the influence of a wide range of cold rolling (5, 10, 15 and maximum 40% cold deformation) and the sensitization time (aging at 700°C for 0.12, 0.5, 1, 4, 16 and 32 hours) on intergranular corrosion (IGC). The assessment of the degree of intergranular corrosion was based on the measurement of mass loss and observation of corroded surfaces on optical microscope. The consequences of deformation on IGC have been investigated by using EN ISO 3651-1methods (Huey test). Cold deformation before sensitization reduces the intensity of intergranular corrosion of this steel. The deformed structure created during the cold work process, numerous slip planes and the twins boundaries are just like the grain boundaries and the places where the chromium carbides preferentially precipitates.

Corrosion of steel alloys in molten NaCl + Na2SO4 at 700 °C for thermal energy storage

Stainless steel 316, duplex steel 2205 and carbon steel 1008 were examined for compatibility with the eutectic mixture of NaCl + Na2SO4 at 700°C in air for thermal energy storage. Electrochemical measurements combined with advanced microscopy techniques were employed. Results confirmed oxidation to be the primary attack to all metals. Ferritic alloy 1008 was found the most vulnerable alloy with severe oxidative attack. Alloys 316 and 2205 showed close performance while grain boundary oxidative and sulfur attack threatened these materials. Alloy 2205 showed chromium depletion followed by selective oxidation of ferrite in the presence of a semi-protective film on the surface.

Optimization of the Double Loop Electrochemical Potentiokinetic Reactivation Method for Detecting Sensitization of Nickel Alloy 690

Nickel alloy 690 (UNS N06690) is one of the current choices for nuclear power plant steam generator tubing. The severity of certain stress corrosion cracking submodes in Ni-Cr-Fe alloys, such as Alloy 690, may be a function of the alloy sensitization condition. Sensitization results from chromium carbide precipitation at or near grain boundaries when the alloy is exposed to temperatures from 500°C to 800°C, which causes local chromium depletion in the adjacent matrix. The objective of this work was to study the parameters that control the double loop electrochemical potentiokinetic reactivation (DL-EPR) method and to develop an optimized test routine for Alloy 690. Alloy 690 specimens were tested under different thermal treatments, tailored to obtain a variety of concentrations of chromium in solid solution near the grain boundary (GB) region. The DL-EPR method was applied to Alloy 690 in solutions with different concentrations of sulfuric acid and potassium thiocyanate, at 30°C and 50°C. The optimal condition for detecting sensitization of Alloy 690 was 0.5 M H2SO4 + 0.001 M KSCN, at 30°C. Optical micrographs confirmed an intergranular type of attack under thermally aged (sensitized) conditions. The ratio of the reactivation to the activation peak intensities (Ir/Ia) obtained in the DL-EPR test agreed well with mass loss obtained in boiling nitric acid solution with Cr(VI) additions (modified Huey test). Chromium depletion profiles near the GB of thermally treated specimens under different conditions were measured with the energy dispersive x-ray spectroscopy technique, performed on a transmission electron microscope. A model available in the literature was fitted to those results. The Ir/Ia ratio for Alloy 690, obtained when using the optimal DL-EPR testing conditions, correlated well with the Cr depletion zone width and depth near the GB.