Crevice Corrosion Resistance Research Articles

Effect of Fluoride Ions on Crevice Corrosion and Passive Behavior of Alloy 22 in Hot Chloride Solutions

Alloy 22 (UNS N06022) is a Ni-Cr-Mo-W alloy highly resistant to localized corrosion. Alloy 22 may be susceptible to crevice corrosion in pure chloride (Cl−) solutions under aggressive environmental conditions. The effect of the fluoride (F−) over the crevice corrosion induced by chloride ions is still not well established. The objective of the present work was to explore the crevice corrosion resistance of this alloy to different mixtures of fluorides and chlorides. Cyclic potentiodynamic polarization (CPP) tests were conducted in deaerated aqueous solutions of pure halide ions and in different mixtures of chloride and fluoride at 90°C and pH 6. The range of chloride concentration [Cl−] was 0.001 M ≤ [Cl−] ≤ 10 M and the range of fluoride to chloride molar concentration ratio [F−]/[Cl−] was 0.1 ≤ [F−]/[Cl−] ≤ 10. Results show that Alloy 22 was susceptible to crevice corrosion in all the pure chloride solutions but was not in the pure fluoride solutions. Fluoride ions showed an inhibitor behavior only in mixtures with a molar ratio [F−]/[Cl−] > 2. For mixtures with a molar ratio [F−]/[Cl−] of 7 and 10, the inhibition of crevice corrosion was complete.

Effects of flux cored arc welding parameters on pitting corrosion resistance of duplex stainless steel clad metals

Most engineering applications require both high strength and corrosion resistant materials for long reliability and performance. This can be achieved by cladding the surface of steel with a metallurgically compatible corrosion resistant alloy. In recent years, duplex stainless steel has been extensively used for weld cladding. It has excellent pitting and crevice corrosion resistance, high yield strength, good toughness and weldability. During cladding, pitting resistance may be compromised by the formation of intermetallic precipitates, or by excessive precipitation of secondary austenite in the surface regions. Redistribution of alloying elements as a result of such transformations may lead to local reductions in pitting resistance. This may result from the dilution of the filler metal with the base metal and the heat input during cladding. Hence, control of dilution and heat input is very important to maintain the required pitting corrosion resistance. The present paper highlights an experimental study and analysis of various welding parameters influencing PREN and pitting potential in duplex stainless steel cladding deposited by flux cored arc welding (FCAW). Pitting resistance equivalent number (PREN) was found to decrease with increased welding current and welding speed and to increase with increased welding angle and tip to workpiece distance. Pitting potential increased with increased welding current, and tip to workpiece distance and heat input during cladding, and decreased with increased welding speed and welding angle.

Corrosion resistance of Cr-Ni-Mo steel intended for urological stents

This work presents the influence of the surface treatment and plastic strain of Cr-Ni-Mo stainless steel, intended for implants applied in urogenital surgery, on the steel's corrosion resistance. Tests were carried out in simulated urine at a temperature of 37 1C and pH = 66,4. In particular, pitting and crevice corrosion resistance tests were carried out. Furthermore, through the applied technique of stent implantation, the deformability of the passive layer was evaluated. The deformability tests of the passive layer were carried out with the use of a bend test followed by a corrosion test.

ICONE15-10414 CORROSION RESISTANCE OF TITANIUM ALLOY ON THE OVERPACK FOR HIGH-LEVEL RADIOACTIVE WASTE DISPOSAL

Crevice corrosion of titanium and its alloys were investigated in 10% sodium chloride at 100 ℃ simulating the environment of the overpack near the seaside. The pH and Chloride ion concentration inside the crevice were monitored by using W/WO3 and Ag/AgCl microelectrode, respectively. The pH and Cl^- concentration within the crevice were calculated from the standard potential-pH and potential-log [Cl^-] calibration curves. The effect of Mo on the crevice corrosion of titanium was mainly studied. The passivation behavior of the titanium and Ti-15%Mo alloy were also studied using electrochemical impedance studies. A marginal decrease in pH and increase in Cl^- ion concentration were observed for pure titanium at 100 ℃, where there was large increase of the crevice current. On other hand, there was no apparent change in pH and Cl^- ion activity inside the crevice for Ti-15%Mo alloy, where there was no increase of the crevice current. Based on the results, it has been documented that the Ti-15%Mo alloy was not susceptible to crevice corrosion in 10 % NaCl solutions at 100 ℃. The corrosion reaction resistance (R_t) was found to increase with addition of Mo as an alloying element and also increase with applied anodic potential. Hence, Mo is able to be an effective alloying element, which enhanced the crevice corrosion resistance of titanium.

Cytotoxicity study of plasma-sprayed hydroxyapatite coating on high nitrogen austenitic stainless steels

Stainless steel has been frequently used for temporary implants but its use as permanent implants is restricted due to its low pitting corrosion resistance. Nitrogen additions to these steels improve both mechanical properties and corrosion resistance, particularly the pitting and crevice corrosion resistance. Many reports concerning allergic reactions caused by nickel led to the development of nickel free stainless steel; it has excellent mechanical properties and very high corrosion resistance. On the other hand, stainless steels are biologically tolerated and no chemical bonds are formed between the steel and the bone tissue. Hydroxyapatite coatings deposited on stainless steels improve osseointegration, due their capacity to form chemical bonds (bioactive fixation) with the bone tissue. In this work hydroxyapatite coatings were plasma-sprayed on three austenitic stainless steels: ASTM-F138, ASTM-F1586 and the nickel-free Böhler-P558. The coatings were analyzed by SEM and XDR. The cytotoxicity of the coatings/steels was studied using the neutral red uptake method by quantitative evaluation of cell viability. The three uncoated stainless steels and the hydroxyapatite coated Böhler-P558 did not have any toxic effect on the cell culture. The hydroxyapatite coated ASTM-F138 and ASTM-F1586 stainless steels presented cytotoxicity indexes (IC50%) lower than 50% and high nickel contents in the extracts.

Corrosion characteristics of newly developed structural DMR-1700 steel and comparison with different steels for industrial applications

Corrosion characteristics of different steels in industrial environment were studied systematically to understand the protective nature of oxide scales that form on their surfaces with a view to explore the possibility of using a newly developed ultrahigh strength steel, DMR-1700, for fabrication of components to use in industrial applications. Further, the studies related to pitting and crevice corrosion resistance of a variety of steels under industrial environmental conditions have been carried out for comparison purposes. The surface morphologies of corroded steels were observed by scanning electron microscope (SEM) in order to understand the nature of corrosion. The corrosion mechanism of steel components that fail under industrial environmental conditions has been discussed. Based on the results obtained with different techniques, the newly developed DMR-1700 ultrahigh strength low alloy steel in association with successfully developed high-performance protective coating has been recommended for manufacture of components to use in industrial systems. This steel helps in improving the efficiency of the systems significantly by eliminating failures during service.

An electrochemical study of the crevice corrosion resistance of NiTi in Hanks’ solution

The crevice corrosion resistance of NiTi in Hanks’ solution at 37 °C was assessed by employing electrochemical methods. NiTiCu, commercially pure Ti (cp Ti), Ti6Al4V, and 316L stainless steel were included in the study for comparison. The susceptibility to crevice corrosion was investigated by using a potentiostatically controlled stimulation–repassivation scheme in the presence of a crevice former. Susceptibility to crevice corrosion is characterized by the critical potential for crevice corrosion ( E cc), which is defined as the highest potential at which crevice-corroded surfaces repassivate after stimulation. The crevice corrosion rates in the propagation stage, which was characterized by crevice solution with low pH value and high chloride concentration, were assessed by determining the galvanic current between a small sample in contact with simulated crevice solution and a large sample of the same material in contact with bulk solution. Based on the results of the stimulation–repassivation tests, the susceptibility of various samples to crevice corrosion in Hanks’ solution at 37 °C and pH 7.4 may be ranked in ascending order as: cp Ti ≈ Ti6Al4V ≪ 316L < NiTiCu < NiTi. The beneficial effect of Cu could be attributed to the redeposition of Cu inside the crevice, as evidenced by EDS analysis. Once crevice corrosion had started, the crevice corrosion current densities for different samples did not differ much, all being of the order of a few mA/cm 2 in a model crevice solution of high acidity (pH 1) and high chloride concentration (146 g/L of NaCl).

Characterization of newly developed structural DMR-1700 steel and comparison with different steels for chemical applications

A systematic corrosion study on super duplex stainless steel, 316L, 304, EN 24 and DMR-1700 steels has been carried out to understand the protective nature of oxide scales that form on their surfaces under acidic environmental conditions. Further, the studies related to pitting and crevice corrosion resistance of above steels have been undertaken in acidic environment for comparison purpose. The surface morphologies of corroded steels have been observed under scanning electron microscope (SEM) in order to understand the nature of corrosion. The corrosion mechanism due to which the components of steels fail under acidic environmental conditions has been discussed. Based on the studies with different techniques, DMR-1700 steel has been recommended for manufacture of components used in chemical applications in association with appropriate protective coating, which in turn helps in improving the efficiency of the systems significantly.

The Effect of Mill Scale and Magnetite on Crevice Corrosion Resistance of Carbon Steel in Concentrated Lithium Bromide Solutions

In order to evaluate the effect of mill scale and magnetite on crevice corrosion resistance of carbon steel which is used as a regenerator vessel material in the absorption refrigeration cycle, immersion test and electrochemical measurements of carbon steel in concentrated lithium bromide solution were carried out. As a result, when there was mill scale on surface of carbon steel and there existed magnetite as impurity in concentrated lithium bromide solution, probability of crevice corrosion became higher. It was supposed that reason was as follows : the existence of mill scale on carbon steel mainly restrained anodic reaction of iron and the existence of magnetite promoted cathodic reaction on the surface of carbon steel. Therefore, spontaneous potential of carbon steel became nobler than its repassivation potential of crevice corrosion. It was found that adding reducing agent to the solution was very effective for crevice corrosion protection.

Corrosion resistance properties of glow-discharge nitrided AISI 316L austenitic stainless steel in NaCl solutions

Glow-discharge nitriding treatments can modify the hardness and the corrosion resistance properties of austenitic stainless steels. The modified layer characteristics mainly depend on the treatment temperature. In the present paper the results relative to glow-discharge nitriding treatments carried out on AISI 316L austenitic stainless steel samples at temperatures ranging from 673 to 773 K are reported. Treated and untreated samples were characterized by means of microstructural and morphological analysis, surface microhardness measurements and corrosion tests in NaCl solutions. The electrochemical characterization was carried out by means of linear polarizations, free corrosion potential–time curves and prolonged crevice corrosion tests. Nitriding treatments performed at higher temperatures (>723 K) can largely increase the surface hardness of AISI 316L stainless steel samples, but decrease the corrosion resistance properties due to the CrN precipitation. Nevertheless nitriding treatments performed at lower temperatures (⩽723 K) avoid a large CrN precipitation and allow to produce modified layers essentially composed by a nitrogen super-saturated austenitic metastable phase (S-phase) that shows high hardness and very high pitting and crevice corrosion resistance; at the same polarization potentials the anodic current density values are reduced up to three orders of magnitude in comparison with untreated samples and no crevice corrosion event can be detected after 60 days of immersion in 10% NaCl solution at 328 K.

Improvement of Corrosion Resistance of High-Velocity Oxyfuel-Sprayed Stainless Steel Coatings by Addition of Molybdenum

To improve the marine corrosion resistance of stainless steel coatings fabricated by high-velocity oxyfuel (HVOF) spraying with a gas shroud attachment, the molybdenum (Mo) content of stainless steel was increased to form coatings with a chemical composition of Fe balance-18mass%Cr-22mass%Ni-2∼8mass%Mo. These coatings were highly dense, with <0.1 vol.% in porosity, and less oxidized, with 0.5 mass% in oxygen content at most. The corrosion mechanism and resistance of the coatings were investigated by electrochemical measurement, chemical analysis, and statistical processing. The general corrosion resistance of the coatings in 0.5 mol/dm3 sulfuric acid was improved with increases in Mo content, and the corrosion rate could be decreased to 8.8 × 10−2 mg/cm2 per hour (∼1 mm/year) at 8 mass% Mo. The pitting corrosion resistance of the coatings in artificial seawater was improved with increases in Mo content and was superior to that of the 316L stainless steel coating. The crevice corrosion resistance of the coatings in artificial seawater was improved and the number of rust spots at 4 mass% Mo was decreased to 38% of that for the 316L coating. Accordingly, Mo is highly effective in improving the corrosion resistance of the stainless steel coatings by HVOF spraying.

Corrosion characteristics of DMR-1700 steel and comparison with different steels in marine environment

In the present paper, a systematic corrosion study has been carried out on DMR-1700 steel to understand the protective nature of oxide scale that forms on its surface under marine environmental conditions. Further, the studies related to oxide scales as well as pitting and crevice corrosion resistance of both stainless steels and widely used low alloy steel EN24 in marine environment have been studied for comparison purpose. The surface morphologies of corroded steels have been observed under scanning electron microscope (SEM) in order to understand the nature of corrosion. A high performance protective coating that has been developed for protection of low alloy steels DMR-1700 and EN24 against corrosion is presented after stressing the importance of surface engineering in enhancing the life of steels. Based on the studies with different techniques, DMR-1700 steel has been recommended for manufacture of components used in aerospace systems in association with appropriate protective coating for improving their efficiency.

Aspects of selective and pitting corrosion in cast duplex stainless steels

Duplex stainless steels are excellent materials for industrial applications and their use has increased in the oil, chemical, petroleum (offshore), and electric power industries. Pitting resistance equivalent (PRE) is the first parameter used to characterise the pitting and crevice corrosion resistance. Nevertheless, there are other aspects to be considered, such as the precise values of the PRE in the α and γ phases and the selective corrosion processes that may occur at grain boundaries. This paper indicates that α/γ and α/σ interfaces are preferential sites for the nucleation and growth of pits and for consequent selective corrosion, with increasing tendency in the ferritic phase. In addition, the selective dissolution potential is more reactive (and therefore, is of greater significance) than the pitting potential.

Corrosion behavior between dental implant abutment and cast gold alloy

Two types of HL hexed abutments of a Steri-Oss system, gold/plastic coping and gold coping, were compared in terms of corrosion behavior. The anodic polarization behavior and the galvanic corrosion between abutments and Type III gold alloys, before and after casting, were analyzed. In addition, the crevice corrosion of the casting samples was analyzed with cyclic potentiodynamic polarization tests using the |Er-Ecorr| value and scanning electron microscopy. Before casting, gold/plastic coping and gold coping were shown to have similar corrosion patterns in the anodic polarization test. Type III casting gold alloy was shown to have a lower higher than that of gold coping, but the passive region for the gold/plastic coping was smaller than that of gold coping. The contact current density between the cast gold alloys and gold/plastic before casting was higher than that between gold coping and cast gold alloy. The contact current density of the samples after casting was shown to be similar to that before casting. The crevice corrosion resistance of cast samples using gold coping was lower than that of cast samples using gold/plastic coping, and severe corrosion was observed by SEM at the abutment-casting gold alloy interface.

Effect of nickel alloying on crevice corrosion resistance of stainless steels

The crevice corrosion behaviour of stainless steels containing 25 mass% Cr, 3 mass% Mo and various amounts of Ni was investigated in natural seawater. The results showed that ferritic steels containing nickel were more resistant to corrosion than both ferritic steels without nickel and austenitic steels. The superiority of the Ni bearing ferritic steel over the other steels was in close agreement with the depassivation pH of those steels in acidic chloride solutions. The results showed that the addition of Ni to ferritic steel was effective in decreasing the depassivation pH and the dissolution rate in acidic chloride solutions at crevices.

耐食・耐摩耗性を備えた肉盛材料の開発

For fluid machinery used in seawater, the overlaying technique is an effective means for the resistance to corrosion, erosion and abrasive wear in terms of cost, performance and repair. Therefore, we had attempted to combine the manufacturing technique of anti-wear resistant Co based KV powder and Crevelloy alloy with excellent crevice corrosion resistance. As the results, the overlayer containing 15%massVC, 35%massCr, and 15%massMo shows high hardness and excellent anti-corrosion property. High hardness of overlayer is mainly caused by matrix phase with lamellar structure consisting Ni-Cr-Mo-Fe alloy phase and carbide phase. Corrosion property was evaluated by cyclic potentiodynamic anodic polarization curve measurement in 3.0%NaCl aq. at 25°C, pitting potential measurement in 3.5%NaCl aq. at 80°C and 6-months immersion test in seawater. Erosion property was evaluated by slurry jet test and vibratory cavitation erosion test. From the evaluation results, developed material VCRMO is recommended as overlaied alloy for seawater applications.

115 窒素添加による高窒素鋼の局部腐食特性向上とその発現機構(各種特性・用途(2))

The effects of nitrogen on localized corrosion resistance of HNS developed at NIMS were investigated in terms of crevice corrosion in artificial seawater at 35C. Synergistic effect between N and Mo was also discussed. High nitrogen steels containing molybdenum showed crevice corrosion resistance superior to that of molybdenum-free steel. Possible mechanism of improvement of localized corrosion by N alloying was also discussed. It was found that not only the buffer effect of pH by ammoniac ions but also inhibitor effect by nitrate ions played important role for improving localized corrosion property of HNS.

Localized Corrosion Behavior of High Nitrogen-bearing Austenitic Stainless Steels in Seawater Environment

Crevice corrosion behavior of high nitrogen-bearing stainless steels with up to 1.1 mass% nitrogen were investigated in artificial seawater. Specimens were highly purified and contained ultra-high nitrogen of about 1 mass% obtained by using nitrogen gas pressurized electroslag remelting (P-ESR) system. 23% Cr-4%Ni-0 to 2%Mo-0.7 to 1.1 %N stainless steels were used as test specimens. Crevice corrosion resistant properties of the stainless steels were evaluated by means of electrochemical corrosion test method using multiple crevice assemblies. Crevice corrosion was confirmed by visual observation to be generated after test and by in-situ current response under test. It was seen that there was a positive correlation between nitrogen content and crevice corrosion potential. High nitrogen-bearing austenitic stainless steels produced by P-ESR had good crevice corrosion resistance. It was also found that ultra-high nitrogen stainless steels containing molybdenum had superior crevice corrosion resistance. Surface of high nitrogen stainless steel was analyzed using X-ray photoelectron spectroscopy (XPS). After polarization at the passive potential region (at +300 mV vs. SCE), an alloying nitrogen or nitride peak of N1s spectra appeared at higher take-off angle measurement, indicating that nitrogen concentrated at the inner layer of the interface between passive film and bulk metal. Enriched nitrogen at the interface may be possible to improve crevice corrosion resistance.

CARLSON ALLOY 904L

Abstract Carlson Alloy 904L is a 21Cr-24Ni-4.5Mo-1.5Cu low-carbon austenitic alloy that resists corrosion in a wide range of both oxidizing and reducing environments. It has good pitting and crevice-corrosion resistance and eliminates stress-corrosion cracking in most common chloride environments. The alloy resists intergranular corrosion in postwelded or stress-relieved conditions because of its very low carbon content. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: SS-844. Producer or source: G.O. Carlson Inc.

ステンレス鋼のすき間腐食過程における表面pH分布測定

In the generation and growth process of crevice corrosion, it is considered that pH of the solution inside the crevice decreases because of hydrolysis reaction by metallic ion. In this study, in-situ measurement for surface pH distribution of the stainless steel in crevice corrosion process was carried out by a scanning chemical microscopy (SCHEM) using photo current characteristics of semiconductor.17%Cr-14%Ni-2%Mo austenitic stainless steels were used as test specimens. Test specimens were immersed in artificial seawater with addition of hydrogen peroxide. As a result of the tests, although surface showed uniform pH distribution in early stage, the decrease of pH at one area near the crevice was observed in latter stage. The area extended as the time passed. This area almost agreed with the position at which crevice corrosion occurred. From these results, it was proven that SCHEM was promising to investigate crevice corrosion behavior of the stainless steel. The effect of nitrogen in stainless steel on the crevice corrosion resistance was also investigated.