A discussion on evaluation criteria for crevice corrosion of various stainless steels

In this study,crevice corrosion performances of a newly developed LDSS 2002 and three commercial stainless steels(AISI 304,AISI 316L and DSS 2205)were investigated and discussed.Crevice repassivation potential(ER,CREV),which was measured by the potentiodynamic-galvanostatic-potentiodynamic(PDGS-PD)test,was applicable to crevice corrosion evaluation of 304 and 316 L stainless steels.However,much lower(ER,CREV values were obtained for DSS 2205 and LDSS 2002.These abnormal(ER,CREV values for duplex stainless steels may be related to the selective attack of the less corrosion-resistant phase,the lower corrosion potential in the crevice-like solution,and more crevice corrosion sites in the PD-GS-PD test.A critical chloride concentration of crevice corrosion(CCCCREV)measurement was introduced for crevice corrosion evaluation of various stainless steels.The derived CCCCREVwas proved to be a valid criterion for crevice corrosion evaluation of both the austenitic and duplex stainless steels.An order of crevice corrosion resistance of AISI 304≈LDSS 2002相似文献   

Interplay of microbiological corrosion and alloy microstructure in stress corrosion cracking of weldments of advanced stainless steels

This paper presents an overview of the phenomenon of stress corrosion cracking (SCC) of duplex stainless steels and their weldments in marine environments and the potential role of microbial activity in inducing SCC susceptibility. As a precursor to the topic the paper also reviews the performance of the traditional corrosion-resistant alloys and their weldments and the necessity of using duplex stainless steels (DSS), in order to alleviate corrosion problems in marine environments. Given that the performance of weldments of such steels is often unsatisfactory, this review also assesses the research needs in this area. In this context the paper also discusses the recent reports on the role of microorganisms in inducing hydrogen embrittlements and corrosion fatigue.     

Influence of laser surface alloying with chromium and nickel on corrosion resistance of type 304L stainless steel

Abstract

The influence of laser surface alloying (LSA) with Cr and Cr + Ni on the corrosion behaviour of type 304L stainless steel (SS) was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) in chloride (0·5M NaCl) and acidic (1 N H₂SO₄) media. Surface alloying was carried out by laser cladding type 304L SS substrate with premixed powders of AISI type 316L SS and the desired alloying elements. The results indicated that Cr surface alloyed specimen exhibited a duplex (γ + α) microstructure with Cr content of ～24 wt-%, whereas Cr + Ni surface alloyed specimen was associated with austenitic microstructure with Cr and Ni contents of ～22 wt-% each. The potentiodynamic polarisation results in chloride solution indicated that LSA with Cr + Ni considerably enhanced the pitting corrosion resistance compared with LSA with Cr alone. In acidic media, such beneficial effects were not observed. Electrochemical impedance spectroscopy results showed an increase in semicircle arc for both chloride and acidic media for both Cr and Cr + Ni clad samples indicating improvement in the oxide film stability compared with untreated specimen. The polarisation resistance was higher and capacitance values of the laser clad specimen were lower than those in the untreated specimen. The microstructural changes and compositional variations produced by LSA are correlated to the corrosion behaviour.     

The effect of SO3 on vanadate-induced hot corrosion

Unrefined fuel oils may contain considerable amounts ofboth sulphur and vanadium. Despite this, exposure to combustion gases seldom yields deposits which consist ofboth vanadates and sulphates. Calculations for the sodium sulphate/vanadate system show that this is due to thermodynamics ofthe system. Sodium sulphate cannot exist in equilibrium with fused vanadate unless the sulphur trioxide pressure in the ambient atmosphere is high or the vanadium to sodium ratio in the deposits is less than one.

Thermogravitmetric studies which delineate the conditions for simultaneous sulphate- and vanadate-induced corrosion at 650 to 8OO°C have been performed. NiCrAlY coatings with K-sodium vanadyl vanadate deposits and the deposit alone have been exposed to oxygen containing 4% sulphur dioxide at 650 to 8OO°C. The results generally confirm the calculations from available thermodynamic data, but the solubility ofsulphur oxide in fused sodium vanadate is higher than expected from the literature values. The ' corrosion mechanism changes from initial vanadate-induced to essentially sulphate-induced hot corrosion when the sodium trioxide pressure is high enough that sodium sulphate may be formed.     

Stress corrosion cracking of AISI 321 stainless steel in acidic chloride solution

The stress corrosion cracking (SCC) of AISI 321 stainless steel in acidic chloride solution was studied by slow strain rate (SSR) technique and fracture mechanics method. The fractured surface was characterized by cleavage fracture. In order to clarify the SCC mechanism, the effects of inhibitor KI on SCC behaviour were also included in this paper. A study showed that the inhibition effects of KI on SCC were mainly attributed to the anodic reaction of the corrosion process. The results of strain distribution in front of the crack tip of the fatigue pre-cracked plate specimens in air, in the blank solution (acidic chloride solution without inhibitor KI) and in the solution added with KI measured by speckle interferometry (SPI) support the unified mechanism of SCC and corrosion fatigue cracking (CFC).     

Atmospheric corrosion of reference metals in Antarctic sites

This paper presents the results obtained at three Antarctic test sites participating in the “Ibero-American Map of Atmospheric Corrosiveness” (MICAT), a project on atmospheric corrosion carried out during the period 1988–1994 at some 70 sites distributed across 12 countries of the Latin-American region, Spain and Portugal. The three Antarctic sites are located near the coastline.The singular climatic characteristics of Antarctic regions are related with the purity of the air, the absence of rainfall and the formation of ice on the metallic surface during an important part of the exposure time. However, electrochemical activity is possible below ice layers. This situation affects the structure and morphology of corrosion product films and the resulting corrosion rates of metallic surfaces.     

The effects of saline aqueous corrosion on fatigue crack growth rates in 316 grade stainless steels

A study of fatigue crack propagation rates of 316 grade stainless steels in air and in an aqueous saline environment was carried out in an attempt to assess the fatigue properties encountered when such materials are used as surgical implants. The effects of variables such as temperature, pH, oxygenation level, bulk electrode potential, mean stress, frequency and stress waveform on the Paris crack growth law parameters were determined. Corrosion fatigue effects were observed in the aqueous saline environment, and a mechanism to describe this effect is proposed.     

The effect of TiN inclusions and deformation-induced martensite on the corrosion properties of AISI 321 stainless steel

Stainless steel of type 321 is commonly used for the production of exhaust systems because of its temperature resistance and welding properties, which are better than those of AISI 304 or similar steels. AISI 321 is a titanium stabilized austenitic stainless steel, where this element is added to form carbides in order to avoid chromium impoverishment due to chromium carbide formation. Cold shaping can, in the case of austenitic stainless steel, cause the formation of deformation induced martensite, which can improve its mechanical properties, but unfortunately can also spoil its good resistance to corrosion. Titanium nitride inclusions are cathodic with respect to steels, and therefore cause their anodic dissolution. Martensite is, however, more susceptible to the corrosion than austenite in steels. The main aim of this study was to analyze the pitting corrosion and stress corrosion cracking which is initiated on prototype cold-formed outer exhaust sleeves during the testing of different cleaning procedures before chromium plating. Various microscopic methods were used to identify the initiation of corrosion and its propagation.     

Influence of glyoxal on localized corrosion of austenitic stainless steel in spring water

This paper presents the research regarding the influence of glyoxal on electrochemical and corrosion behaviour of austenitic stainless steel in water. For this purpose, model solutions containing glyoxal in water in concentrations ranging from 0.1 to 1 % were prepared. Spring water was used as control electrolyte. From the potentiostatic polarisation data (using the standard three‐electrode system), the corrosion current (i_corr), corrosion potential (E_corr) and polarisation resistance (R_p) were calculated. The research included also the conductivity, total dissolved soils, salinity, resistivity and pH, absolute potential, and relative potential of model solutions. The presence of glyoxal at the highest concentration of 1 % in the water solution has accelerating effect on corrosion.     

Effect of dissolved oxygen on electrochemical corrosion behavior of 2205 duplex stainless steel in hot concentrated seawater

The corrosion behavior of 2205 duplex stainless steel was investigated in hot concentrated seawater with different dissolved oxygen(DO) concentration by electrochemical measurement techniques and surface analysis methods. DO obviously enhances the cathodic reaction process, the formation of passive film and polarization resistance. With increasing the DO concentration from 0.34 to 3.06 mg L^-1, the relative contents of Fe₂O₃ and Cr₂O₃ and the Cr-enrichment gradually enlarge in the passive film. The higher DO concentrations result in lower defect densities and thicker of space charge layers in the passive films,whichmayeffectively inhibit the intrusion of aggressive chloride ions. The increment inDOconcentration clearly increases the pitting potential, but decreases the repassivation potential. It may weaken both the occurrence and repassviation tendencies of stable pitting corrosion.     

Effect of partial replacement of carbon by nitrogen on intergranular corrosion behavior of high nitrogen martensitic stainless steels

The microstructure evolution and intergranular corrosion (IGC) behavior of high nitrogen martensitic stainless steels (MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M₂₃C₆ to M₂N, furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.     

Effect of aluminum on microstructure,mechanical properties and pitting corrosion resistance of ultra-pure 429 ferritic stainless steels

Effect of aluminum on microstructure, mechanical properties and pitting corrosion resistance of ultra-pure 429 ferritic stainless steels has been investigated. Aluminum can significantly increase the ratio of equiaxed crystal grains, but the promotion effect has great relation with aluminum content. Aluminum can stabilize ferrite phase and significantly reduce recrystallization temperature. Increased aluminum content can also lead to the precipitate of AlN and Al₂O₃ at higher temperature. The increased amount of AlN may partly contribute to the reduced nitrogen element to form austenite at high temperature, hence the high temperature phase transformation of α + γ → α occurs. The fine and large number of Al₂O₃ particles can refine grain size and then promote recrystallization. The highest intensity of γ-fiber texture {1 1 1}〈1 1 2〉 is observed in the steel with 0.19 wt.% aluminum, which can improve the formability of steels. With the increase of aluminum content, the tensile strength increases linearly but the elongation and plastic strain ratio first increase then decrease, the working hardening index varies slightly among the steels. Appearance of Al₂O₃ inclusions with small size and decreased content of MnS benefit pitting corrosion resistance. However, the large dimension Al₂O₃ inclusions have significantly negative influence on pitting corrosion resistance.     

Accelerated hot corrosion studies of cold spray Ni–50Cr coating on boiler steels

In the current investigation Ni–50Cr powder was deposited on two boiler steels SA-213-T22 and SA 516 (Grade 70) by cold spray process. The hot corrosion performance of coated as well as bare boiler steels was evaluated in an aggressive environment of Na₂SO₄–60% V₂O₅ under cyclic conditions at an elevated temperature of 900 °C. The kinetics of the corrosion was approximated by the weight change measurements made after each cycle for a total period of 50 cycles. Each cycle consisted of 1 h heating in a tube furnace followed by 20 min cooling in ambient air. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDAX) techniques were used to analyse the corrosion products. Both the uncoated boiler steels suffered intensive spallation in the form of removal of their oxide scales, which may be attributed to the formation of unprotective Fe₂O₃ dominated oxide scales. The Ni–50Cr coated steels showed lesser weight gains and the oxide scales remained intact till the end of the experiment. The phases revealed in the oxide scales of the coated specimens were mainly oxides of chromium and nickel and their spinels which are reported to be protective against the hot corrosion.     

Influence of shot peening on high-temperature corrosion and corrosion-fatigue of nickel based superalloy 720Li

High-temperature corrosion fatigue, a combination of corrosion with a fatigue cycle, is an emerging generic issue affecting power generation and aero gas turbine engines and has the potential to limit component life. Historically, surface treatments, such as shot peening have been used to improve component life and have been optimised for fatigue response. Research into optimisation of shot peening techniques for hot corrosion and high-temperature corrosion fatigue has shown 6–8A 230H 200% coverage to provide overall optimum performance for nickel-based superalloy 720Li based on the limited data within this study. Utilisation of electron backscatter diffraction techniques, in combination with detailed assessment of corrosion products have been undertaken as part of this work. The resultant cold-work visualisation technique provides a novel method of determining the variation in material properties due to the shot peening process and the interaction with hot corrosion. Through this work it has been shown that all three shot peening outputs must be considered to minimise the effect of corrosion fatigue, the cold work, residual stress and surface roughness. Further opportunity for optimisation has also been identified based on this work.     

Pitting corrosion of 2Cr13 stainless steel in deep-sea environment

Pitting corrosion of 2Cr13 stainless steel was investigated by deep-sea exposure test at various depths of 500 m,800 m and 1200 m in the South China Sea for 4 months.With the aid of electrochemical measurements in simulated deep-sea environments and grey relational analysis,the influence of deepsea environments on passive film and the mechanism of pitting corrosion were discussed.The results indicated that with the increase of sea depth,pitting depth of 2Cr13 stainless steel increased,which can be attributed to the change of chemical composition and the degradation of pitting resistance of passive film.Film growth was greatly retarded in the condition of low seawater temperature and low dissolved oxygen content of deep sea,resulting in an unstable and vulnerable film.Pitting depth was most influenced by hydrostatic pressure,which can increase the adsorption and penetration of Cl-ion,and promote the proliferation of point defects in passive film,leading to rapid deconstruction of protective oxides of the film.Pitting sensitivity of 2Cr13 stainless steel increased eventually with the combination of accelerated dissolution and suppressed self-healing of passive film in deep sea.     

The influence of chromium on early high temperature corrosion of ferritic alloys under SO2 atmosphere

Comprehensive insights into the early stages of corrosion mechanisms provide fundamental knowledge to further understand and model long time material behaviour. The present work studies the early stages of combined oxidation and sulphidation of ferritic model alloys for time scales up to 250 h at 650°C to observe the influence of chromium during the corrosion under SO₂. Model alloys were used to focus on the reaction of the intended elements: Fe, Cr, S, and O. Pure iron simultaneously forms magnetite and iron-sulphide in an early stage of corrosion, covered by a pure oxide layer after 100 h. Iron with 13 wt-% Cr shows hematite and mixed Fe–Cr-oxides first, before sulphides nucleate in the inner corrosion zone. With increasing ageing time a magnetite layer is observed below the hematite layer. Quantitative phase fractions of all corrosion products observed were determined from cross section images. Characterisation of the Fe13Cr corrosion scale by FIB revealed a highly porous structure in the inner corrosion zone where Cr-rich (Fe, Cr)-sulphides are present, and caused the scale to spall easily.     

Influence of sigma phase on corrosion behavior of 316L stainless steel in high temperature and high pressure water

In order to elucidate the impact of σ phase on the oxidation film formation and stress corrosion cracking (SCC) resistance of 316L stainless steel, corrosion, SCC and three-point bending tests were conducted and the microstructures of the σ phase in 316L safe-end pipes were characterized via optical microscopy, environmental scanning electron microscopy and scanning Kelvin probe force microscopy. The results indicated that the σ phase was detrimental to the SCC resistance of 316L in high temperature and high pressure environments and the existence of inherently hard and brittle σ phase could change the cracking mode.     

Influence of Cl-, Br-, NO 3 - and SO 4 2- ions on the corrosion behaviour of 6061 Al alloy

The effects of anions like Cl^-, Br^-, NO ₃ ^- and SO ₄ ^2- on the anodic dissolution of the monolithic Al 6061 alloy have been investigated at neutral pH through immersion testing and electrochemical techniques like potentiodynamic polarization and a.c. impedance spectroscopy. Scanning electron microscopy was employed to characterize the corroded surface and to observe the extent of pitting in different media. From the evaluated corrosion parameters it was found that the dissolution of the matrix was extensively reduced in presence of aqueous solutions containing Br^-, NO ₃ ^- and SO ₄ ^2- ions while Cl^- ions aggravated corrosion by penetrating into the barrier oxide film on the surface of the material. Pronounced effect of pitting was observed in presence of Cl^- and the level of pitting in NO ₃ ^- and Br^- were mild. In presence of SO ₄ ^2- ions passivity was extended over a wide potential range and breakdown of passivity occurs when the material was polarized beyond pitting potential. The departure of capacitive behaviour towards resistive behaviour was clearly observed through impedance measurements when investigations were conducted in Cl^- media and in presence of the other electrolytes. Corrosion rates were, however, controlled during prolonged exposure in the electrolytic media, specially in case of chloride media, due to the predominance of film repair kinetics.     

微量Cr的添加对铜在含SO2环境中耐蚀性的影响

采用TEM,SEM和XPS等测试分析方法,研究了微量Cr的添加对铜合金在二氧化硫环境中耐蚀性的影响.结果表明:微量Cr的加入提高了合金的耐蚀性,随着添加量的增多,合金的耐蚀性进一步提高;另一方面,由于合金中低含量的Cr不能在试样表面独立成膜,耐蚀性的提高很大程度上依赖于致密腐蚀产物层对含Cr层的保护作用,所以微量Cr的加入对合金耐蚀性的改善是轻微的.同时,Cr的分布不均对合金的耐蚀性有一定的破坏作用.     

Influence of nitriding on corrosion resistance of martensitic X17CrNi16‐2 stainless steel

Nitriding increases surface hardness and improves wear resistance of stainless steels. However, nitriding can sometimes reduce their corrosion resistance. In this paper, the influence of nitriding on the corrosion resistance of martensitic stainless steel was investigated. Plasma nitriding at 440 °C and 525 °C and salt bath nitrocarburizing were carried out on X17CrNi16‐2 stainless steel. Microhardness profiles of the obtained nitrided layers were examined. Phase composition analysis and quantitative depth profile analysis of the nitrided layers were preformed by X‐ray diffraction (XRD) and glow‐discharge optical emission spectrometry (GD‐OES), respectively. Corrosion behaviour was evaluated by immersion test in 1% HCl, salt spray test in 5% NaCl and electrochemical corrosion tests in 3.5% NaCl aqueous solution. Results show that salt bath nitrocarburizing, as well as plasma nitriding at low temperature, increased microhardness without significantly reducing corrosion resistance. Plasma nitriding at a higher temperature increased the corrosion tendency of the X17CrNi16‐2 steel.