Localized Corrosion Resistance Research Articles

Embrittlement and Corrosion Decay of a Cast Duplex Stainless Steel

Duplex stainless steels (DSS) are Fe-Cr-Ni-Mo alloys, with low carbon content, which have a favorable combination of mechanical properties and corrosion resistance. These characteristics are mainly attributed to a dual phase and refined microstructure, typical of these alloys, consisting of similar amounts of ferrite and austenite. For this reason, DSS are widely used in various segments of industry, especially in offshore applications. However, DSS components may have a decrease of their properties when they are exposed high temperatures, often due to incorrect manufacturing processes. Intermetallic phases may precipitate causing embrittlement and corrosion resistance decrease. This work presents the effects of short time aging at 475 °C on the mechanical properties and localized corrosion resistance of a cast DSS. The results show that mechanical properties, such as toughness and hardness, are more susceptible to aging, having already been affected during the first 4 hours of heat treatment, while the corrosion was affected in 12 h of aging.

The impact of cold work and hard phases on cavitation and corrosion resistance of high interstitial austenitic FeCrMnMoCN stainless steels

High interstitial austenitic stainless steels have been shown to exhibit superior mechanical properties, which include a unique combination of high strength and high toughness, due to the positive effects of the combination of carbon and nitrogen in solid solution. By the addition of molybdenum, a significant improvement of their localized corrosion resistance has been achieved. Further strengthening is necessary in the case of application in environments featuring both high mechanical loads and corrosive attack, e.g. in bearings in sea water. It can be induced by cold work hardening as well as the addition of hard phases, which in turn can affect the wear and corrosion resistance. In this study, the impact of cold work and the precipitation of niobium carbonitrides on the resistance to cavitation erosion, localized, and general corrosion has been investigated. Two newly developed high interstitial FeCrMnMoCN steels were analyzed by vibratory cavitation testing in distilled water and potentiodynamic polarization measurements in sodium chloride solution and sulfuric acid after cold work strengthening. The latter was induced by cold rolling to different degrees. Microstructural characterization was performed by hardness testing, optical, and scanning electron microscopy. The results show improved strength but decreased cavitation erosion resistance caused by the hard phases. In contrast, neither the localized nor the general corrosion resistance seem severely affected. The cold rolling leads to intense work hardening and enhanced cavitation erosion resistance, while the corrosion behavior is not significantly influenced. In the case of cavitation erosion, the improved resistance of the cold work hardened steel matrix seems to dominate the negative effect of the hard phases. The combination of high wear and high corrosion resistance, even in severely cold work strengthened condition, makes the FeCrMnMoCN austenitic stainless steels promising candidates for application in harsh environments.

Localized Corrosion Characteristics of Nickel Alloys: A Review

There are a great variety of commercial nickel alloys mainly because nickel is able to dissolve a large amount of alloying elements while maintaining a single ductile austenitic phase. Nickel alloys are generally designed for and used in highly aggressive environments, for example, those where stainless steels may experience pitting corrosion or environmentally assisted cracking. While nickel alloys are generally resistant to pitting corrosion in chloride-containing environments, they may be prone to crevice corrosion attack. Addition of chromium, molybdenum and tungsten increases the localized corrosion resistance of nickel alloys. This review on the resistance to localized corrosion of nickel alloys includes specific environments such as those present in oil and gas upstream operations, in the chemical process industry and in seawater service.

Corrosion of Al xCoCrFeNi high-entropy alloys: Al-content and potential scan-rate dependent pitting behavior

The present work investigates the influence of Al-content and potential-scan-rate on stable/metastable pitting of Al xCoCrFeNi high-entropy alloys in a 3.5wt.% NaCl solution. The increased Al content causes the volume fraction of the Cr-depleted phase to increase, resulting in thicker/dispersive passive films that degrade the localized corrosion resistance. The varied stable/metastable pitting behavior under different potential scan rates indicates that pit generation is influenced by the properties of passive films and the interactions between chloride ions and the active sites. Furthermore, a mean-field theory is employed to predict the scan-rate dependent, power-law distribution of current fluctuations.

Performance of Corrosion-Resistant Alloys in Concentrated Acids

Nickel alloys containing optimum amounts of chromium (Cr), molybdenum (Mo) and tungsten (W) are widely used in the chemical processing industries due to their tolerance to both oxidizing and reducing conditions. Unlike stainless steel (SS), Ni–Cr–Mo (W) alloys exhibit remarkably high uniform corrosion resistance in major concentrated acids, like hydrochloric acid (HCl) and sulfuric acid (H2SO4). A higher uniform corrosion resistance of Ni–Cr–Mo (W) alloys, compared to other alloys, in concentrated acids can be attributed to the formation of protective oxide film of Mo and W in reducing acids, and Cr oxide film in oxidizing solutions. The localized corrosion resistance of Ni–Cr–Mo (W) alloys, containing high amount Cr as well as Mo (or Mo + W), is also significantly higher than that of other commercially available alloys. The present study investigates the role of alloying elements, in nickel alloys, to uniform corrosion resistance in concentrated acids (HCl, HCl + oxidizing impurities and H2SO4) and localized corrosion performance in chloride-rich environments using ASTM G-48 test methodology. The corrosion tests were conducted on various alloys, and the results were analyzed using weight loss technique and electrochemical techniques, in conjunction with surface characterization tools.

Effects of nitrogen in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel welding joint

The effects of nitrogen addition in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel (DSS) welds were studied. N2-supplemented shielding gas facilitated the primary austenite formation, suppressed the Cr2N precipitation in weld root, and increased the microhardnesses of weld metal. Furthermore, N2-supplemented shielding gas increased pitting resistance equivalent number (PREN) of austenite, but which decreased slightly PREN of ferrite. The modified double loop electrochemical potentiokinetic reactivation in 2M H2SO4+1M HCl was an effective method to study the localized corrosion of the different zones in the DSS welds. The adding 2% N2 to pure Ar shielding gas improved the localized corrosion resistance in the DSS welds, which was due to compensation for nitrogen loss and promoting nitrogen further solution in the austenite phases, suppression of the Cr2N precipitation in the weld root, and increase of primary austenite content with higher PREN than the ferrite and secondary austenite. Secondary austenite are prone to selective corrosion because of lower PREN compared with ferrite and primary austenite. Cr2N precipitation in the pure Ar shielding weld root and heat affected zone caused the pitting corrosion within the ferrite and the intergranular corrosion at the ferrite boundary. In addition, sigma and M23C6 precipitation resulted in the intergranular corrosion at the ferrite boundary.

Electrochemical anodizing treatment to enhance localized corrosion resistance of pure titanium.

Titanium has outstanding corrosion resistance due to the thin protective oxide layer that is formed on its surface. Nevertheless, in harsh and severe environments, pure titanium may suffer localized corrosion. In those conditions, costly titanium alloys containing palladium, nickel and molybdenum are used. This purpose investigated how it is possible to control corrosion, at lower cost, by electrochemical surface treatment on pure titanium, increasing the thickness of the natural oxide layer. Anodic oxidation was performed on titanium by immersion in H2SO4 solution and applying voltages ranging from 10 to 80 V. Different anodic current densities were considered. Potentiodynamic tests in chloride- and fluoride-containing solutions were carried out on anodized titanium to determine the pitting potential. All tested anodizing treatments increased corrosion resistance of pure titanium, but never reached the performance of titanium alloys. The best corrosion behavior was obtained on titanium anodized at voltages lower than 40 V at 20 mA/cm2. Titanium samples anodized at low cell voltage were seen to give high corrosion resistance in chloride- and fluoride-containing solutions. Electrolyte bath and anodic current density have little effect on the corrosion behavior.

High temperature embrittled duplex stainless steels: influence of the chemical composition on the fatigue crack propagation

Abstract: Austenitic-ferritic (duplex) stainless steels are successfully used in chemical, nuclear, oil and gas industries, due to their good mechanical properties and excellent generalized and localized corrosion resistance in many environments and operating conditions (for example, chloride induced stress corrosion). The aim of this work is the analysis of the influence of the chemical composition and of the high temperature embrittlement processes in three different duplex stainless steels. Scanning electron microscope (SEM) fracture surface analysis was performed to investigate the fatigue crack propagation micromechanisms.

Hydrophobicity and Improved Localized Corrosion Resistance of Grain Boundary Etched Stainless Steel in Chloride-Containing Environment

Localized corrosion of stainless steels by chloride ions in seawater leads to metal degradation while fouling of marine organisms increases the occurrence of localized corrosion. We describe a simple method to increase hydrophobicity of austenitic stainless steel using grain boundary etching that can also inhibit adhesion of bio-organisms present in seawater as well as increase the localized corrosion resistance of stainless steel in chloride-containing aqueous environments. This paper describes the corrosion behavior of stainless steel as a result of grain boundary etching to achieve hydrophobicity. Potentiostatic polarization on stainless steel 316L in a nitric acid solution at an anodic potential of 1.3 V vs. saturated calomel electrode (SCE) results in a grain boundary etched structure and a Cr- and Mo-rich passive film as confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. This modified stainless steel 316L surface exhibits enhanced corrosion resistance to a 0.6 M sodium chloride solution. Specifically, potentiodynamic polarization studies indicate that the breakdown potential increases and the sample-to-sample variability decreases. The modified surfaces show a narrow range of breakdown potentials (0.96 to 1.05 V vs. SCE) compared to as-received stainless steel 316L (0.32 to 0.86 V vs. SCE).

Initiation of Localized Corrosion of Ferritic Stainless Steels by Using the Liquid-Phase Ion Gun Technique

The initiation of localized corrosion of types 430 and 443J1 ferritic stainless steels was evaluated in 0.15 mol dm−3 Na2SO4 solution. A liquid-phase ion gun (LPIG), a silver microelectrode covered with a silver chloride layer, was cathodically polarized to generate Cl− in the vicinity of the stainless steel polarized at 0.4 VSSE. Contact of the stainless steel surface with the Cl−-concentrated environment by the LPIG operation induced a rapid increase in anodic current flow through the stainless steel electrode after the induction period td and consumption of the cathodic electric charge Qd by the LPIG microelectrode. Numerical modeling using the LPIG microelectrode current for td gave a critical Cl− concentration [Cl−]d needed for the initiation of localized corrosion. These parameters obtained by LPIG tests showed that type 443J1 stainless steel was superior to type 430 stainless steel in localized corrosion resistance. AES depth profiling of the stainless steel surfaces after the LPIG operation revealed enrichment of Cl in the outermost oxide film as well as decreased film thickness. The mechanism of degradation of the stainless steel surface due to contact with the Cl−-concentrated solution is discussed. The adsorption of Cl− on the oxide surface is thought to be a trigger of the oxide degradation.

Synergy between molybdenum and nitrogen on the pitting corrosion and passive film resistance of austenitic stainless steels as a pH-dependent effect

This paper brings up some insights upon the pH dependence of the synergistic effect of Mo and N on the localized corrosion resistance of austenitic stainless steels. The objective of this work is to study the synergetic effect of Mo and N additions on corrosion and passive film properties of austenitic grades. A comparison between Mo containing (3 wt% Mo); Mo and N containing (3 wt% Mo and 0.1% N) and free Mo or free Mo and N grades of highly controlled laboratory heats was done considering their localized corrosion resistance and oxide film formation in different aggressive conditions, from neutral to alkaline pH. The passive layer was characterized by EIS and XPS analyses. The combined effect of Mo and N on the pitting potential was confirmed to be synergistic, and not just the addition of their individual effects. Moreover, this effect was found to be pH-dependent, being very positive in acid to neutral conditions whereas it was almost inexistent in high pH.

Effect of N, Mo, and Si on Local Corrosion Resistance of Unstabilized Cr–Ni and Cr–Mn–Ni Austenitic Steels

Features of the effect of both individual and combined alloying with nitrogen, molybdenum and silicon of unstabilized cold-worked and heat-treated austenitic Cr–Ni and Cr–Mn–Ni steels on pitting and intercrystalline corrosion (ICC) resistance in weakly oxidizing media are studied. On the basis of corrosion and electrochemical test results (electrochemical method), an ambiguous effect of alloying cold worked Cr–Mn–Ni steels with nitrogen and molybdenum on pitting corrosion resistance is revealed. It is established that a necessary condition for intergranular corrosion resistance of chromium-nickel steels after prolonged tempering at 550–750°C is the presence of silicon in addition to nitrogen and molybdenum, which participates in improving the passivity of chromium-depleted boundary zones. Silicon added to nitrogen-containing steel alloyed with molybdenum and 0.03 wt.% carbon with a balanced content of Cr, N, Mo and Si facilitates an improvement of passivity for boundary zones impoverished in chromium. Introduction of silicon into nitrogen-containing chromium-nickel steel (0.03% C) alloyed with molybdenum with a balanced content of Cr, Ni, Mo, and Si makes its ICC resistance equal to specially low-alloy stainless steel containing 0.003% C.

Impact of hybrid self-assembled nanophase particle-based sol–gel coatings on the localized corrosion behavior of modified 9Cr–1Mo steel in chloride medium

Corrosion protection coatings were developed based on a hybrid self-assembled nanophase particle process (HSNAP) for the localized corrosion resistance of modified 9Cr–1Mo steel in 0.05 M NaCl solution. The coating sol was prepared using silane-zirconia precursors and a polymeric crosslinking agent. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to study the morphology and composition of the coated specimens, respectively. The thickness of the coatings was determined by a thickness gauge meter and Raman imaging analysis. The corrosion resistance of coated specimens was analyzed using electrochemical impedance spectroscopy, and it was observed that HSNAP-coated specimens showed superior resistance to localized corrosion than the as-received specimens in chloride medium.

Localized Corrosion Resistance of Dissimilar Aluminum Alloys Joined by Friction Stir Welding (FSW)

2XXX and 7XXX high strength aluminum alloys are the most used materials for structural parts of aircrafts due to their high strength/weight ratio. Their joining procedure is an engineering challenge since they present low weldability. Friction Stir Welding (FSW) is a joining technology developed in the early 90 ́s. It is a solid-state welding process, without the use of fillers or gas shield, that eliminates conventional welding defects and has been considered of great interest for application in the aircraft industry. FSW of aluminum alloys results in four regions of different microstructures, specifically: the base material (BM), the heat affected zone (HAZ), the thermo-mechanically affected zone (TMAZ), and the nugget zone (NZ). The complex microstructure of the weld region leads to higher susceptibility to localized corrosion as compared to the BM even when similar alloys are joined. The welding of dissimilar alloys in its turn results in even more complex microstructures as materials with intrinsically different composition, microstructures and electrochemical properties are put in close contact. Despite the great interest in FSW, up to now, only few corrosion studies have been carried out for characterization of the corrosion resistance of dissimilar Al alloys welded by FSW. The aim of this study is to investigate the corrosion behavior of aluminum alloy 2024-T3 (AA2024-T3) welded to aluminum alloy 7475-T761 (AA7475-T761) by FSW. The evaluation was performed in 0.01 mol.L-1 by means of open circuit potential measurements, polarization techniques and surface observation after corrosion tests.

Localized Corrosion Behavior of Stainless Steels Under Loading Stress Environment

Stainless steels are used in various situations because of its high corrosion resistance. For instance, the environments are inside the human body, building materials in seashore, and nuclear power plants. In such an environment, the allowable amount of corrosion is very few. Although stainless steels have high corrosion resistance, it has a number of damage reports caused by its corrosion. Many of stress corrosion cracking (SCC) cases have been mentioned as a factor involved in serious accidents. It is difficult to elucidate the SCC of the generating mechanism, because three elements ( the environment, the material, and the stress ) relate closely to the occurrence of the SCC. There are not so many reports of the influence that stress affects directly to not progress of crack but corrosion. In this study, the purpose is to elucidate the influence of stress loading in localized corrosion of type 304 and 316 stainless steels. As the test materials, type 304 and 316 stainless steel that was a general austenitic stainless steel was used. And the test pieces were covered by epoxy resin after the test pieces were adhered lead cable by Ag paste. Test surface was 10mm × 60mm × 0.05mm. It was grinded in water by emery paper #1000. The test pieces were bent in a U-shape so as to be wide 58.5mm to load stress. In addition, the test pieces of the same shape that was not bending in a U-shape were used as a comparative test piece. All test pieces were cleaned by ultrasonic cleaning in ethanol before its measurement. The Test solution was 0.5M, 0.154M NaCl solutions. Counter electrode was Pt. The reference electrode was Ag / AgCl / KCl sat.. Potential sweep range was -1V to 1.5V, potential sweep speed was 1mV / s. Test temperature was 25℃. In case of type 316 stainless steel in 0.5M NaCl solution, the stress loading caused the pitting potential shift to the ignoble potential and the passive current density was increased. Since the stress loading made surface passive film deformed, and the defects appeared on the surface of passive film, the defects caused that the newly formed surface is exposed. Although cathodic polarization behavior did not indicate the difference of loading stress, it is obviously that the current density increased caused by loading stress in anodic one. And the polarization behavior of type 316 stainless steel in 0.154M NaCl solution was similar to 0.5M one. Both are regarded that the decrease of pitting corrosion potential is caused by loading stress and the promotion of localized corrosion reaction. In the environment in the presence of chloride ions, pitting corrosion potential decreases with increasing chloride ion concentration because of that chloride ion promotes incidence of pitting corrosion. Since there was a significant difference in the pitting potential to the type 304 and 316 stainless steel, the type 316 stainless steel has a higher localized corrosion resistance than the type 304. However, the type 316 stainless steel is than the 304, pitting corrosion potential difference of the test piece which is not loaded with the specimen loaded with stress was large. It is indicates that the type 316 stainless steel is easily influenced by loading stress than the 304 for pitting corrosion sensitivity in this experiment.

Study of Multiphase Automotive Sheet Steel Local Corrosion Resistance by Electrochemical Methods

The nature of corrosion process development is studied by observing surface condition with potentiometric polarization. It is established that an increase in martensite content within steel structure increases the intensity of corrosion process development considerably. The high sensitivity of the corrosion test method developed to steel structural state (structural component content), and also prospects for using it instead of tests in accordance with GOST 9.911−89 are demonstrated.

A Review on the Properties of Iron Aluminide Intermetallics

Iron aluminides have been among the most studied intermetallics since the 1930s, when their excellent oxidation resistance was first noticed. Their low cost of production, low density, high strength-to-weight ratios, good wear resistance, ease of fabrication and resistance to high temperature oxidation and sulfurization make them very attractive as a substitute for routine stainless steel in industrial applications. Furthermore, iron aluminides allow for the conservation of less accessible and expensive elements such as nickel and molybdenum. These advantages have led to the consideration of many applications, such as brake disks for windmills and trucks, filtration systems in refineries and fossil power plants, transfer rolls for hot-rolled steel strips, and ethylene crackers and air deflectors for burning high-sulfur coal. A wide application for iron aluminides in industry strictly depends on the fundamental understanding of the influence of (i) alloy composition; (ii) microstructure; and (iii) number (type) of defects on the thermo-mechanical properties. Additionally, environmental degradation of the alloys, consisting of hydrogen embrittlement, anodic or cathodic dissolution, localized corrosion and oxidation resistance, in different environments should be well known. Recently, some progress in the development of new micro- and nano-mechanical testing methods in addition to the fabrication techniques of micro- and nano-scaled samples has enabled scientists to resolve more clearly the effects of alloying elements, environmental items and crystal structure on the deformation behavior of alloys. In this paper, we will review the extensive work which has been done during the last decades to address each of the points mentioned above.

Effect of Nitrogen on the Corrosion Behavior of Austenitic Stainless Steel in Chloride Solutions

The effect of partial replacement of nickel with nitrogen on the corrosion resistance of newly designed austenitic stainless steel samples without and with heat treated was investigated in 3.5wt% and 5wt% NaCl solution using open-circuit, potentiodynamic, cyclic anodic polarization and electrochemical impedance spectroscopy techniques. The results showed that, passivation in sample 1 where the highest addition of nickel and low addition of nitrogen is different from that for sample 4 where the nitrogen is greatest and the nickel is reduced almost to the third comparing sample 1. The difference in responses of heat treated samples to localized and general corrosion could be attributed to the difference in their phase compositions. The appearance of ferrite phase for samples (2, 4, 5 and 6) after heat treatment resulted in lowering the general and localized corrosion resistance than as forged samples in contrast with samples 1 and 3, where they still pure austenite. The obtained results are confirmed by surface examination.

Repassivation behavior of 316L stainless steel in borate buffer solution: Kinetics analysis of anodic dissolution and film formation

The repassivation behavior of metals or alloys after oxide film damage determines the development of local corrosion and corrosion resistance. In this work, the repassivation kinetics of 316L stainless steel (316L SS) are investigated in borate buffer solution (pH 9.1) by using the abrading electrode technique. The current densities flowing from bare 316L SS surface are measured by potentiostatic method and analyzed to characterize repassivation kinetics. The initial stages of current decay (t<500ms) are discussed according to a film growth model, which describes the initial current transient should be divided into substrate dissolution current and passive film formation current based on Avrami kinetics. Then the two independent components are analyzed individually. The film formation rate and the thickness of film are compared in different applied potential. It is shown that anodic dissolution dominates the repassivation for a short time during the early times, and a higher applied potential will promote the anodic dissolution of metal. The film growth rate increases slightly with increasing in potential. Correspondingly, increase in applied potential from 0VSCE to 0.8VSCE results in thicker monolayer, which covers the whole bare surface at the time of θ=1. The electric field strengths through the thin passive film could reach 3.97×106Vcm−1.

Effect of microstructure and chemical composition on localized corrosion resistance of a AISI 304L stainless steel after nanopulsed-laser surface melting

Changes induced in the surface properties of AISI 304L stainless steel when it is treated with a nanopulsed ytterbium-doped fiber laser were investigated to determine the microscale distribution of its physico-chemical properties. A Gaussian energy distribution was created with a radius of 71μm (1/e2) at the focal point. Local investigations were carried out using transmission electron microscopy to consider the effect of overlapping individual laser impacts. The results obtained reveal that laser surface melting leads to changes in the crystallographic structure of the steel through the formation of a δ-ferritic phase. It also results in the creation of an oxide layer that increases the corrosion resistance of the steel, with the chemical composition, structure and thickness of this layer being dependent on the overlap percentage and the position along the beam radius. Measurement of the localized corrosion resistance in a 30gL−1 NaCl solution using polarization curves found that optimal laser treatment conditions can led to an increase in the breakdown potential of more than 500mV, which corresponds to a significant improvement in corrosion resistance.