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Electrochemical investigations (polarization curves, polarization resistance measurements), together with weight loss measurements and quantitative chemical analysis of the solutions after immersion of samples were used to evaluate the corrosion behaviour of type 304L and 316L sintered austenitic stainless steels in sulphate and chloride containing solutions. The samples were sintered in nitrogen based atmosphere, at 1120 and 1190°C, and in vacuum at 1200°C and submitted to X-ray diffraction analysis and SEM observation together with EDS microanalysis before and after the corrosion tests. A correlation is tempted between the corrosion behaviour and the mechanical properties of samples as Rockwell hardness, shrinkage, unnotched impact strength, ultimate tensile strength. 相似文献
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1 INTRODUCTIONAluminumanditsalloysarewidelyusedinthetelecommunications,electronicsandaviationindus triesbecauseoftheirgoodelectricalconductivityandprocessability .Buttheyareverysusceptibletopittingcorrosioninaqueousenvironments ,andthe pittingcorrosion p… 相似文献
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Nucleation of crevice corrosion of five stainless steels in NaCl solution has been studied using potentiokinetic and galvanostatic methods. It is inferred that a well reproducible critical potential for crevice corrosion nucleation exists. This potential depends on the type of steel and is more negative than the critical potential for pit nucleation. The difference between the potential for crevice corrosion and that for pitting is higher for more resistant steels than for less resistant ones. A mechanism explaining the crevice corrosion in chloride solutions is proposed. 相似文献
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Jaromú Touek 《工业材料与腐蚀》1977,28(9):619-622
In the temperature range from 6 to 40°C the temperature dependence of pitting corrosion may be expressed by the Arthenius-equation. The lowering of the breakdown potential in this range shows a linear dependence on the reziprokal value of the absolute temperatur. From the temperature dependence of the breakdown potential and of current density it is possible to calculate the activation energy of dissolution within the pits (4,5 –4.8 kcal). In the temperature range from 40 to 70°C the temperature dependence of the breakdown potential is relatively small. This fact apparently indicates a change in pitting kinetics above 40°C. It is concluded from other results obtained that in this temperature range the formation of oxide layers in the pits is accelarating so that passivation is accelerated and the breakdown potential increases. 相似文献
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Thermal analysis has been used to determine the melting behaviour of alkali metal sulphate deposits typical of those found on superheater tubes in coal-fired power station boilers. Additions of 5–30 m/o Fe2(SO4)2 to Na2SO4K2SO4 mixtures under a simulated flue gas (N2 + 15 v/o CO2 + 1 v/o O2 + 0.3 v/o SO2) are shown to reduce the melting point from 820°C to below 550°C. Alkali-iron trisulphates are formed which re-solidify on heating above 720°C by decomposition of Fe2(SO4)3 at low thermodynamic activity. It is suggested that the effect of heat flux and SO3 potential gradient on the melting behaviour of a superheater deposit could account for the observed ‘bell-shaped’ temperature dependence of corrosion rate in the range 550–750°C. Results are presented of laboratory corrosion tests on three commercial austenitic stainless steels using a melt of composition 74 m/o Na2SO4 + 20 m/o K2SO4 + 6 m/o Fe2 (SO4)3. A model is proposed for corrosion by an acid fluxing mechanism involving refractory metal alloy elements in the steels. The model offers a quantitative basis for prediction of fireside corrosion resistance in coal-fired boilers, and a comparison of relative corrosion rates of a range of steels in laboratory tests, probe trials and service performance confirms the validity of the present model. 相似文献
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1 INTRODUCTIONBecauseofitshighmechanicalperformanceandlowdensity ,LY12alloy(USAA2 0 2 4 )iswidelyusedintheaircraftindustryfornumerousapplicationssuchasfuselage ,doorskin ,dorsalfinandtrailingedgepanels .Nevertheless ,thisalloycaneasilybeaffectedbylocalizedcorrosion ,suchaspittingandexfoliation ,especiallyinchloridecontainingenvironment .Thislocalizedattackcanresultinprematurebreakdownofstructuralparts[1] .Inordertominimizethelocalizedattackonthealuminumalloy ,thecorrosionmecha nismshou… 相似文献
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Pitting corrosion behaviour of PM austenitic stainless steels sintered in nitrogen-hydrogen atmosphere 总被引:1,自引:0,他引:1
PM 304L and 316L stainless steel have been compacted at 400, 600 and 800 MPa and sintered in vacuum and in nitrogen-hydrogen atmosphere. Postsintered heat treatments (annealing solution and ageing at 375, 675 and 875 °C) have been applied. Pitting corrosion resistance has been studied using anodic polarization measurements and the ferric chloride test. Anodic polarization curves reveal that densities and atmospheres are relevant on anodic behaviour. Pitting resistance is higher for PM 316L and for higher densities and vacuum as sintered atmosphere. Ageing heat treatments at medium and high temperatures are detrimental to passivity although susceptibility to pitting corrosion barely changes. But heat treatments at 375 °C even show certain improvement in pitting corrosion resistance. The results were correlated to the presence of precipitates and mainly to the lamellar constituent which appears in some samples sintered in nitrogen-hydrogen atmosphere. The role of nitrogen on the samples sintered under nitrogen-hydrogen atmosphere and its relation to the microstructural features was described. 相似文献
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J.B. Bajat I. Milošev R.M. Jan?i?-Heinemann V.B. Miškovi?-Stankovi? 《Corrosion Science》2010,52(3):1060-1069
The corrosion protection of vinyltriethoxysilane (VTES) films on aluminium during exposure to 3% NaCl was investigated using electrochemical impedance spectroscopy (EIS), potential-time measurements and optical microscopy coupled with image analysis. Composition and thickness of films were analyzed using Auger electron spectroscopy (AES) combined with depth profiling. It was shown that films deposited from 5% solution were significantly thicker and exhibited lower porosity and better corrosion stability, as compared to films deposited from 2 vol.% solution. VTES films deposited from 5 vol.% solutions and cured for 30 min exhibited better protection properties than other investigated films. 相似文献
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The influence of Cu and Sn on the pitting corrosion resistance of AISI 304 and 316 stainless steels in chloride-containing media has been investigated. The corrosion behaviour was evaluated by cyclic polarization, potentiostatic CPT measurements and electrochemical impedance spectroscopy in 3.5 wt% NaCl. The corrosion resistance was also studied in FeCl3 under Standard ASTM G-48. According to the results, Cu addition favours pit nucleation but inhibits its growth, whereas Sn exerts the opposite effect, favouring pit growth and inhibiting its nucleation. Studies by SEM, X-ray mapping and EDS analysis showed Cu-, Cl- and O-rich corrosion products that reduce the extent of corrosion damage. 相似文献
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《腐蚀工程科学与技术》2013,48(2):132-135
AbstractThe effect of a maraging heat treatment on the mechanical properties and corrosion behaviour of a special grade of heat treatable stainless steel has been studied. Although the mechanical properties such as strength and hardness of this steel are enhanced after the maraging heat treatment, its corrosion resistance is reduced as a result of the formation of intermetallic precipitates at the grain boundaries. In addition, oxide scales are formed on the surface of the specimens after the heat treatment owing to high temperature oxidation and these scales play an important role in the corrosion behaviour of the aged specimens. Corrosion studies have been conducted on underaged, peak aged, and overaged specimens with and without oxide scales and on specimens in the solution annealed condition. Impedance and potentiostatic anodic polarisation techniques in 3·5%NaCl of pH 1, 4, 7, and 10 at room temperature have been used. The corrosion performance order of this maraging steel with oxide scales in acidic, neutral and alkaline solutions is solution annealed> overaged> underaged> peak aged. The removal of oxide scales from the surface of the aged specimens by electropolishing considerably enhances the corrosion resistance without altering the performance order. The surface treated specimens behave in a similar manner to the solution annealed specimens in chloride solutions of pH 7 and 10. This tremendous increase in the corrosion resistance value is a result of the formation of a passive. film on the surface of the specimens during the surface treatment. In immersion tests the surface treated specimens show no signs of corrosion after immersion in 3·5%NaCl at room temperature for a prolonged period of time. 相似文献
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The effect of test temperature on SCC behavior of austenitic stainless steels in boiling saturated magnesium chloride solution 总被引:1,自引:0,他引:1
The stress corrosion cracking (SCC) of the austenitic stainless steels of types 304, 310 and 316 was investigated as a function of test temperature in boiling saturated magnesium chloride solution (MgCl2) using a constant load method. Both of types 304 and 316 exhibited similar corrosion elongation curves, while the corrosion elongation curve of type 310 was different from those of types 304 and 316, in terms of the three parameters such as time to failure (tf), steady-state elongation rate (lss) and transition time to time to failure ratio (tss/tf) obtained from the corrosion elongation curves for these stainless steels. The relationship between the time to failure and a reciprocal of test temperature fell in two straight lines on a semi-logarithmic scale as well as the relationship between the steady-state elongation rate and a reciprocal of test temperature. These regions were considered to correspond to a SCC-dominated region and a hydrogen embrittlement (HE)-dominated region from the value of (tss/tf) and the fracture appearance. The relationship between the steady state elongation rates versus time to failure on a logarithmic scale became a straight line, whereas the slopes of the line for the stainless steels were different with the different fracture mechanism such as SCC and HE. It was found that the linearity of the relationship can be used to predict the time to failure for the stainless steels in the corrosive environment. In addition, type 310 did not suffer from HE, which means that type 310 showed only SCC. This would be explained by whether or not a formation of α′-martensite takes place. 相似文献
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Corrosion studies of austenitic and duplex stainless steels in aqueous lithium bromide solution at different temperatures 总被引:1,自引:0,他引:1
A. Igual Muoz J. García Antn S. Lpez Nuvalos J.L. Guin V. Prez Herranz 《Corrosion Science》2004,46(12):2955-2974
The corrosion behavior of three stainless steels EN 14311, EN 14429 (austenitic stainless steels) and EN 14462 (duplex stainless steel) was studied in a commercial LiBr solution (850 g/l LiBr solution containing chromate as inhibitor) at different temperatures (25, 50, 75 and 85 °C) by electrochemical methods.Open circuit potentials shifted towards more active values as temperature increased, while corrosion potentials presented the opposite tendency. The most resistant alloys to general corrosion were EN 14429 and EN 14462 because they had the lowest corrosion current for all temperatures. In all the cases corrosion current increases with temperature.Pitting corrosion resistance is improved by the EN 14462, which presented the highest pitting potential, and the lowest passivation current for the whole range of temperatures studied. The duplex alloy also presents the worst repassivation behavior (in terms of the narrowest difference between corrosion potential and pitting potential); it does not repassivate from 50 °C. 相似文献
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The corrosion resistance of three indigenous nitric acid grade (NAG) type 304L stainless steel (SS), designated as 304L1, 304L2 and 304L3 and two commercial NAG SS designated as Uranus-16 similar to 304L composition and Uranus-65 similar to type 310L SS were carried out in nitric acid media. Electrochemical measurements and surface film analysis were performed to evaluate the corrosion resistance and passive film property in 6 N and 11.5 N HNO3 media. The results in 6 N HNO3 show that the indigenous NAG 304L SS and Uranus-65 alloy exhibited similar and higher corrosion resistance with lower passive current density compared to Uranus-16 alloy. In higher concentration of 11.5 N HNO3, transpassive potential of all the NAG SS shows a similar range, except for Uranus-16 alloy. Optical micrographs of all the NAG SS revealed changes in microstructure after polarization in 6 N and 11.5 N HNO3 with corrosion attacks at the grain boundaries. Frequency response of the AC impedance of all the NAG SS showed a single semicircle arc. Higher polarization resistance (RP) and lower capacitance value (CPE-T) revealing higher film stability for indigenous NAG type 304L SS and Uranus-65 alloy. Uranus-16 alloy exhibited the lowest RP value in both the nitric acid concentration. Auger electron spectroscopy (AES) study in 6 N and 11.5 N HNO3 revealed that the passive films were mainly composed of Cr2O3 and Fe2O3 for all the alloys. The corrosion resistance of different NAG SS to HNO3 corrosion and its relation to compositional variations of the NAG alloys are discussed in this paper. 相似文献
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Corrosion behaviour of intermetallic aluminide coatings on nitrogen-containing austenitic stainless steels 总被引:1,自引:0,他引:1
The present work reports the effect of aluminide layers on the aqueous corrosion behaviour of four different 316L stainless steels containing various nitrogen contents (0.015%, 0.1%, 0.2% and 0.56% N). Diffusion annealed aluminide layers are generated over the surface by heat treatment of the aluminium precoated alloys at 750 °C for 25 h in nitrogen atmosphere. X-ray diffraction patterns of the surface modified samples showed the presence of AlN, Al13Fe4 and FeAl2 phases. Diffusion of aluminum into the alloy, and the formation of AlN by the reaction of aluminium with matrix nitrogen, was identified using secondary ion mass spectrometry (SIMS). The nitrogen peak in the diffused layer was found to increase with increasing nitrogen content of the base alloy. SEM observation of cross-sectionally mounted alloys showed the presence of spherical AlN phase in addition to iron aluminide intermetallic phases. The role of such a composite surface layer containing intermetallic aluminides and nitride on the corrosion resistance of austenitic stainless steels in 0.5 M NaCl and 0.5 M sulphuric acid is discussed in greater detail based on open circuit potential (OCP)–time measurements, potentiodynamic polarisation studies and electrochemical impedance spectroscopy (EIS) investigations. The aluminide layered alloy with 0.1% N content showed better corrosion performance. The presence of nitrogen was found to have a positive effect in enhancing the hardness of the composite layer. Role of matrix nitrogen on the microstructure and microchemical distribution at the surface, and its role on corrosion resistance in acidic and chloride media are discussed in detail. 相似文献