Intergranular Attack Research Articles

SANDVIK 8R70

Abstract Sandvik 8R70 is a molybdenum-containing austenitic stainless steel that is stabilized with an addition of titanium to prevent intergranular attack. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-683. Producer or source: Sandvik.

Microstructural studies on the effect of Si and Cr on the intergranular corrosion in AlMgSi alloys

Microstructural studies on the effect of Si and Cr on the intergranular corrosion of two AlMgSi alloys have been carried out as a function of aging treatment. It was observed that the degree of intergranular attack increases with increasing aging time with a maximum at peak aged condition and then declines. Presence of Si in the alloy has a tendency to segregate at the grain boundary which makes the alloy susceptible to intergranular corrosion. Addition of a small amount of Cr in the alloy improves the resistance to intergranular corrosion.

5517851 Method and apparatus for predicting onset of intergranular attack and stress corrosion cracking in tubing subjected to hostile environment

5517851 Method and apparatus for predicting onset of intergranular attack and stress corrosion cracking in tubing subjected to hostile environment

Pitting corrosion behaviour of UNS N08904 stainless steel in chloride-sulphide solutions

AbstractThe pitting corrosion behaviour of UNS N08904 (type 904L) stainless steel (SS) in 3 × 10-3 M Na2S, in 0·6M NaCl, and in 0·6M NaCl with different concentrations of Na2S at elevated temperature was studied using potentiodynamic anodic polarisation and scanning electron microscopy (8EM). Type 904L S8 did not pit in pure 3 × 10-3M Na2S at 60°C, while pitting corrosion of type 904L SS in chloride-sulphide mixtures occurred at more active potentials than those obtained in pure 0·6M NaCl. The pitting potential (Epit) of type 904L SS in 0·6M NaCl with 3 × 10-3M Na2S decreased with increasing temperature in the range 50–70°C. The value of Epit did not change in acidic chloride-sulphide solutions (pH 3–6), but it became more noble in alkaline chloride-sulphide solutions (pH 8–12). Observations by SEM showed that the large pits formed on type 904L SS in 0·6M NaCl with 3 × 10-3 M Na2S contained some micropits and that there was intergranular attack.

Critical care nursing in the home: An expanding opportunity for nurses, patients, and families

The paper is aimed at the evaluation of intergranular corrosion of friction stir welded AA2024-T3 joints as a function of manufacturing parameters and loading conditions. Tests for intergranular corrosion assessment, long terms exposure tests, corrosion monitoring through electrochemical impedance spectroscopy and microstructural characterization of the corrosion morphologies were performed to evaluate the effect of loading on intergranular corrosion initiation and propagation. Electrochemical impedance spectroscopy spectra were collected during long term exposure tests to determine the onset of the attack and the propagation rate. A slight modification of the impedence modulus was observed during the exposure as a function of the process parameters. On the contrary, relevant effect of loading condition on intergranular corrosion initiation and propagation mechanisms was noticed. Although no stress corrosion cracking phenomena were evidenced, stress enhanced intergranular attack was observed on loaded specimens at the nugget, where coalescence of sub-micrometric and continuous copper-rich precipitates at the grain boundary occurred. These phenomena are mainly attributable to the thermo-mechanical action of the welding process. Intergranular attacks were not observed in the heat-affected zone and in the base metal, where grain recrystallization does not occur.

Decontamination of the reactor coolant pump in Maanshan nuclear power plant

To reduce the radiation dose that accumulated on the reactor coolant pump, decontamination work was carried out at the Maanshan Nuclear Power Plant. A four-step alkaline permanganate (AP)-CanDecon process was applied to remove the activity on the turning vane diffuser and pump impeller. The first step consisted of 8 h of AP treatment and 7 h of decontamination. It was followed by 2.5 h of AP treatment and 5 h of decontamination. An average decontamination factor of 2.9 was obtained. To understand the corrosion of the decontaminating reagents on the materials, coupons were installed in the decontamination tank. These were as-received and sensitized 304SS, alloy 600, casting stainless steel (CF-8), stellite-6, and carbon steels (A508 and A533). The exposure rates (mR h −1) of the carbon steels were approximately five times higher in magnitude than those of the other materials. The decontamination levels (dpm per 100 cm 2) of the A508 and A533 carbon steels were 5432 and 3701 respectively, while most of the rest of the materials were below the low limit of detection. Apparently, the corrosion product on the materials was a major factor in sustaining the exposure rate and the contamination level. The corrosion rate of the materials was also examined and compared with published data. An examination of the surface morphology of the materials after decontamination showed intergranular attack on the 304 stainless steel.

Effect of surface depletion of lithium on corrosion behaviour of aluminium alloy 8090 in a marine atmosphere

Aluminium-lithium alloy 8090 is of great interest due to its low density and good mechanical properties. The high reactivity of lithium, however, makes it more prone to corrosion than other aluminium alloys, limiting its use in certain fields. In general, there is an intergranular attack with exfoliation in the most severely attacked sections of this alloy in marine and industrial environments. This attack also depends on the metallurgical history of the material, i.e. the part of the ingot from which the specimens are extracted. After one and two years' exposure to a moderately aggressive marine atmosphere, it was found that the materials taken from the centre of the ingot have a more widespread attack than specimens taken from the edges. This might be explained by the differing composition of the specimens according to their origin; more precisely, by the uneven distribution of the lithium, which tends to spread though the matrix of the ingot and form a lithium-impoverished layer several microns deep as a consequence of the series of thermal treatments applied.

Mechanistic Aspects of Intergranular Stress Corrosion Cracking of Ferritic Steels

Abstract Evidence of intergranular attack (IGA) in the absence of stress, together with dissolution kinetics, indicates that intergranular stress corrosion cracking (IGSCC) of ferritic steels in va...

Comparación entre los diagramas TTS obtenidos mediante los ensayos normalizados Huey y Strauss modificado para el acero inoxidable AISI 304

This work presents a comparison of Temperature-Time-Sensitization TTS diagrams obtained by Huey and modified Strauss standard, for detecting susceptibility to intergranular attack. The difference between these tests is the use of a strong or a slightly smooth oxidizing electrolyte. The diagrams obtained are different and if a sample tested by modified Strauss is sensitized, then it will be sensitized in the Huey test, but the contrary is not always true. This difference is because a sensitized sample has to have a continuous band lacking in chromium along the grain boundary in order to be sensitized in the modified Strauss test. This condition is not necessary in the Huey test.

Effects of Neutron Irradiation on Transpassive Corrosion Behavior of Austenitic Stainless Steels

Abstract Irradiated and unirradiated austenitic stainless steels (SS) were exposed to a transpassive potential (1,050 mVSCE) in a sulfuric acid (H2SO4) solution, and the corrosion responses were studied. Applicability of the transpassive technique to evaluation of radiation-induced segregation (RIS) of impurities was considered. The charge density during the potentiostatic transpassive test and the corrosion morphology after the test were functions of both the material chemistry and irradiation. The charge density of the unirradiated materials was correlated successfully with the bulk impurity level, as defined in terms of the parameter (wt% silicon + wt% phosphorus × 10). The charge density increased steeply above an impurity level parameter of 0.5, which corresponded to the region where intergranular attack (IGA) became visible. The change in charge density after neutron irradiation also was a function of the impurity level. Irradiation resulted in a considerable increase in charge density and grain-bou...

Effect of the addition of Cr and Nb on the microstructure and electrochemical corrosion of heat-treatable Al-Zn-Mg alloys

The effect of the addition of Cr and Nb on the microstructure and the electrochemical corrosion of the weldable, high-strength and stress corrosion cracking (SCC) resistant Al-5%Zn−1.67%Mg−0.23%Cu alloy (H) has been studied. Combined additions of the alloying elements, J (with Nb), L (with Cr) and O (with Cr and Nb) and different heat treatments, ST (cold-rolled), A (annealed), F (quenched), B (quenched and aged) and C (quenched in two steps and aged), to obtain different microstructures and hardness have been performed. To correlate the electrochemical corrosion with the microstructure of the specimens, corrosion potential (Ecor) measurements in different chloride solutions were performed and optical microscopy, SEM, TEM and EDX were applied. In chloride solutions containing dissolved O2 or H2O2, the present alloys were polarized up to the pitting attack. It was shown that theEcor measurements were very sensitive to the alloy composition and heat treatment, increasing in the order H < J < L < O < Al (for a given heat treatment) and F < A ≈ ST < B < C (for a given alloy). The MgZn2 precipitates of the annealed (A) and cold-rolled (ST) specimens were dissolved in chloride solutions containing oxidizing agents and pitting attack was shown to develop in the cavities where the precipitates were present. In the specimens B and C, the compositions of the precipitate free zones was found to be equal to that of the matrix solid solution and preferential intergranular attack was not evident, this being in agreement with their SCC resistance. The addition of Cr and Nb increased the pitting corrosion resistance. The effects of Cr and Nb were additive, that of Cr being predominant, either, in theEcor shift or in the increase in the pitting corrosion resistance.

Observations of containment corrosion in the vapor over lithium hydride in the temperature range 600–800°C

Types 304L and 309 stainless steel and Alloy X were exposed to the vapor above lithium hydride (LiH) in the temperature range 600–800°C. Results indicate that for the experimental conditions encountered, each alloy is susceptible to intergranular attack and development of porosity in the temperature range near 650–675°C. The mode of attack in all cases was found to be selective leaching of chromium (along with molybdenum in alloy X) initiating and concentrating at grain boundaries. Similar attack was not detected at higher LiH temperatures. Small amounts of nitrogen contamination in the vapor phase were speculated to be responsible for containment susceptibility to corrosion in vapor over LiH.

Assessment of the Corrosion Behavior of SS 304L in Nitric Acid Environments—An Alternative Approach

Abstract Stainless steel (SS) 304L is widely used as a construction material in industries requiring corrosion resistance in nitric acid environments. Representative samples from 20 heats of SS 304L products were subjected to a testing procedure consisting of testing as per the rapid screening test (Practice A) and the Huey test (Practice C) of ASTM A 262, Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels. The presensitization heat treatment of 677°C for 1 h and the modified heat treatment of 677°C for 20 min were used for characterizing the microstructures in Practice A, whereas only the former presensitization heat treatment was used for Practice C. The percent duality after the two heat treatments has been correlated with the corrosion rate obtained in Practice C. A chemical composition based parameter, Cr effective = [% Cr − 0.18 (%Ni) − 100 (%C)], was calculated for all the heats and correlated with the percent duality after the two heat treatments as well as the corrosion rate in Practice C. It is observed that the SS 304L heats with Cr effective &amp;gt;14.0 and &amp;lt;50% grain boundary coverage after the modified heat treatment (Practice A) show low corrosion rates in Practice C. This eliminates the need for carrying out the lengthy Practice C of ASTM. Examples of heats of SS 304L are given to show that the modified presensitization heat treatment has better efficiency in screening materials and also exhibited better correlation with the results obtained in the Practice C. Guide rules for selection of SS 304L heats for nitric acid service are also suggested. Erratum to this paper appears in 23(2).

Corrosion of NdFeB permanent magnets in humid environments at temperatures up to 150°C

The corrosion of NdFeB permanent magnets has been investigated in oxidizing environments containing controlled additions of water vapor in the temperature range 79–155°C under conditions where no condensation of electrolyte occurs. The corrosion occurs by intergranular attack leading to formation of pits. No significant corrosion was observed in dry environments at temperatures up to 155°C, indicating that H 2O vapor is necessary to produce corrosion. Much higher corrosion rates were measured in Ar-20% O 2-water vapor gas mixtures at 145°C than in air-water vapor mixtures at the same temperature, indicating that nitrogen inhibits the attack. The rate of attack in the Ar-20% O 2-water vapor environment increased with time of exposure.

Use of on-line ion chromatography in controlling water quality in nuclear power plants

Electric utilities that operate nuclear power plants must adhere to a tighter range of water coolant specifications that are commonly required in steam systems powered by other means such as coal, oil or natural gas. The reason for this situation is the higher negative impact of a failure in the coolant and steam piping relative to non-nuclear heat sources. This negative impact arises from the unique need of a nuclear reactor core to require cooling after shutdown of the chain reaction —due to the heat from undecayed radioactive fission products in the uranium fuel rods. Also, the cost of down time for repairs of corrosion damage in such stations is greater than for fossil fired plants because these nuclear plants are base loaded (running at ca. 100% power for several hundreds of days) and the replacement power required during their shutdown time must be provided by sources more costly by factors up to ca. 2. Since corrosion damage in nuclear plants usually occurs under crevice conditions in components such as steam generators where boiling occurs, even very small (parts per billion, ppb) initial feedwater concentrations of corrosive impurity salts such as sodium, chloride and sulfate may concentrate to corrosive brines —leading to breaches of the pressure boundaries from localized cracking or intergranular attack. This attack penetrates even the more corrosion-resistant alloys such as Inconel 600, Incoloy 800 and the stainless steels. Ion chromatography is the only technology able to readily measure ppb concentrations of such corrosive ions on a near real time basis, and to differentiate among different oxidation states of ions such as nitrate, nitrite, sulfate, thiosulfate, etc. These oxidation states respond to the general oxidizing tendency of the coolant —another variable that controls localized corrosion. A number of examples of the use of on-line ion chromatography in troubleshooting corrosion problems in light-water reactors will be given.

Intergranular corrosion-fatigue failure of cobalt-alloy femoral stems. A failure analysis of two implants.

Two modular hip implants with a cobalt-alloy head and a cobalt-alloy stem were retrieved after a fracture had occurred in the neck region of the femoral component, eighty-five and seventy months after implantation. Both implants failed less than one millimeter distal to the taper junction between the head and the stem (outside of the taper). The fracture surfaces of the implant were investigated with the use of scanning electron microscopy, to determine the nature of the failure process. The fractures occurred at the grain boundaries of the microstructure and appeared to be the result of three factors: porosity at the grain boundaries; intergranular corrosive attack, initiated both at the head-neck taper and at the free surface; and cyclic fatigue-loading of the stem. The corrosive attack of the free surface was initiated, in part, by the egression of surface grains and by the ingression of fluid into the intergranular regions. Sectioned surfaces showed extensive intergranular corrosive attack in the prosthetic neck localized in the region of the head-neck taper junction and penetrating deeply into the microstructure.

In vivo corrosion of modular hip prosthesis components in mixed and similar metal combinations. The effect of crevice, stress, motion, and alloy coupling

One hundred forty-eight retrieved modular hip prostheses of both mixed (Ti-6Al-4V/Co-Cr) and similar (Co-Cr/Co-Cr) metal combinations were examined and positive evidence of corrosive attack was found in the conical taper region between head and stem. Significant corrosion was observed in both mixed and similar metal combinations with 16% of necks and 35% of heads (for mixed-metal cases), and 14% of necks and 23% of heads (for similar-metal cases) showing moderate to severe corrosive attack. There was a significant correlation between the percentage of prostheses with moderate to severe corrosion and the duration of implantation for both mixed and similar metal cases, indicating that this corrosion process is progressive in time. Moderate to severe corrosion was seen as early as 2.5 and 11 months (mixed and similar metals, respectively). Scanning electron microscopy and x-ray analysis identified several forms of corrosive attack in the cobalt-based component of the taper. These included, for both mixed and same metal combinations: preferential dissolution of cobalt, fretting, and pitting; mixed metals only: the formation of a Ti-Cr-Mo interfacial phase and interdendritic corrosion; and for similar metals: intergranular attack adjacent to grain boundaries enriched in molybdenum and silicon. It is hypothesized that the restricted crevice environment, coupled with high cyclic stresses which cause repeated fracture of the passive oxide films in the taper, result in an unstable electrochemical environment within the crevice for both the cobalt alloy and Ti-alloy passive films. The passivity of these alloys is subsequently lost and active attack of the taper results. Also, the repeated fracturing of the passive films will result in large amounts of corrosion products being formed. This corrosion and particulate accumulation could result in loss of mechanical integrity of the implants in vivo, create particles for third body wear, and release particles into the surrounding tissues.

The IGSCC, sensitization, and microstructure study of Alloys 600 and 690

Both Alloys 600 and 690 were studied to understand the effect of heat treatment on the sensitization and SCC behavior of these alloys. The microstructural evolution and chromium depletion near the grain boundaries were carefully studied using analytical electron microscopy. The majority of the precipitates formed in Alloy 600 was found to be M 7C 3 with a hexagonal structure ( a 0 = 1.398 nm, c 0 = 0.45 nm ); whereas the carbides found in Alloy 690 were identified as M 23C 6 with an fcc structure ( a 0 = 1.06 nm ). Modified Huey test performed in boiling 40% HNO 3 was used to study the effect of heat treatment and degree of sensitization. Constant load tests and constant extension rate tests were performed in the solution containing sodium thiosulfate to study the SCC resistance of these alloys. The results of the constant load tests for Alloy 600 indicated that the susceptibility to SCC is sensitive to the chromium depletion depth at grain boundary, and the minimum value to prevent SCC failure is approximately 8 wt%. No SCC was observed for Alloy 690 tested using constand load and CERT in the same environments. All tests showed that Alloy 690 has a far better resistance to intergranular attack and SCC than Alloy 600, which is believed due to its high chromium content. It is therefore anticipated that Alloy 690 now a better substitute to Alloy 600 as a steam generator tubing material for pressurized water reactor will also offer a superior corrosion resistance when “sensitized” and in particular if exposed to sulfur containing media such as thiosulfate solutions.

Effect of Long-Term 1093 K Exposure to Air or Vacuum on the Structure of Several Wrought Superalloys

Long-term 1093 K heat treatments of three commercial superalloy sheet materials were undertaken in air and vacuum. With either exposure, significant precipitation of second phases occurred in the Co-base Haynes® Alloy 188 (HA 188) and the Ni-base Haynes® Alloy 230 (HA 230); however, much less precipitation was found in the exposed Ni-base alloy Inconel® 617 (IN 617). Although some grain growth occurred in HA 188, no changes in the grain size of either HA 230 or IN 617 were observed after 22,500 h at temperature. Oxidation during air heat treatments led to weight gain due to the formation of chromia + spinel scales and surface-connected grain boundary pits/oxides in all three superalloys. Both the weight gain and depth of intergranular attack were dependent on the square root of time, which is indicative of diffusion-controlled phenomena. Because many alloy samples had neighbors in close proximity, dmost vacuum heat treated specimens did not suffer significant loss of volatile elements. However, some exposed samples were subjected to unrestricted vacuum heat treatments, allowing estimates of volatilization to be made. Based on the data for HA 188, the weight loss during 1093 K vacuum exposure was diffusion controlled once the inhibiting effects of surface films on the as-received alloys were broken down.

Microstructural Control in an Aluminum Core Alloy for Brazing Sheet Applications

The use of aluminum alloys for automotive heat exchangers has increased considerably in the last 15 to 20 years, and in parallel, new alloys have been developed to meet the increased demand for higher strengths and improved corrosion resistance. An Al-Mn alloy, X800, has been developed by Alcan to significantly increase the corrosion resistance of radiator tubes when subjected to typical service environments. Conventional alloy tubes, 3xxx or 6xxx, fail by intergranular attack, whereas X800 utilizes the diffusion of Si during brazing to form a sacrificial layer between core and cladding and thus prevent penetration through the core. The Si penetrates up to a depth of 70 µm into the core alloy and combines with both the Mn in solid solution and the coarse constituent particles to form theα-AlMnSi phase. In contrast to the core, the interface layer exhibits a high dispersoid density, a modified coarse particle chemistry, and a lower Mn level in solid solution after brazing. Three layers remain after brazing; anα-Al residual cladding, the interface layer with a band of dense precipitates (BDP), and the X800 core. Free corrosion potential measurements confirmed the lowering of the potential within the BDP by about 30 mV compared to —710 mV for the brazed X800 core.