Pitting Corrosion Tests Research Articles

Corrosion Resistance of Stainless Steels Intended to Come into Direct or Prolonged Contact with the Skin.

The biocompatibility of materials in contact with a living tissue becomes a puzzle in the overall picture of assessing the toxic effects of chemicals that come into contact with us. Allergic reactions to substances are a significant and growing health problem affecting large parts of the population in Europe. Wristwatches are objects worn in prolonged contact with the skin, being subject to localized corrosion, especially pitting and crevice types, in sulfide-chloride medium, and high wear in the bracelets joints. Watches of medium quality are usually made of stainless steels. The X2 CrNiMo 17-12-2 316L grade as well as X1 CrNiMo 20-25-5 Cu 1 or 904L are commonly used, having good resistance to generalized corrosion. The passive layer is nevertheless insufficient to ensure complete immunity in all cases of localized corrosion encountered during wear. For this reason, a high-corrosion-resistant steel: X1 CrNiMo 18-15-4 N 0.15 or 317LMN, from three different suppliers was evaluated. Metallographic characterization was carried out. The corrosion behavior evaluation was performed for the generalized corrosion, pitting and crevice corrosion and galvanic corrosion. Galvanic couples steel 317LMN-gold 18K alloy 3N and gold 18K 5M were used. The results of the generalized and pitting corrosion test indicated three basic groups. All of the 317LMNs were similar. The 316L variants tested noticeably worse. The 904Ls were difficult to discern, but certainly easier than the 316Ls and, possibly, at least comparable to the 317LMNs.

Analysis of the surface geometry of the orthodontic archwire and their influence on the bacterial adhesion

Purpose: The aim of this work is to characterize the surface geometry of the orthodontic archiwire and their influence of the pitting corrosion resistance and bacterial adhesion. Design/methodology/approach: In the paper, the results of the SEM/EDS analysis and microscopic observation of the samples surface and analysis of geometrical structure with the use Atomic Force Microscope (AFM) and Confocal Microscopy were presented as well as the pitting corrosion test and surface roughness and microhardness measurements were performed. Additionally the microbiological study after bacterial breeding with the use Scanning Electron Microscope was carried out. Findings: In the basis of the investigation, it can be concluded that the surface geometry of archwire has a significant impact on their pitting corrosion resistance in artificial saliva solution and on the bacterial adhesion. The obtained results show satisfactory properties and surface geometry of the tested orthodontic wires for use in the human oral environment. Research limitations/implications: In the future, it is planned to extend the research with physicochemical properties and the influence of oral hygiene products on the corrosive behaviour of the material. Limitations in the conducted tests refer to archwire design – a small diameter making measurements difficult. Practical implications: The oral environment is an extremely aggressive corrosive environment. The orthodontic elements should have very good corrosion resistance and biocompatibility. The focus should be on continuously improving orthodontic wires in terms of material quality and topography of its surface topography. Originality/value: The research is conducted in the field of biomedical engineering, which is part of material engineering and is used for the field of dentistry and microbiology.

Development of new approaches to the study of pitting corrosion resistance of stainless steels obtained by selective laser melting

This paper presents the results of comparative corrosion resistance studies of stainless steels manufactured by selective laser melting (SLM) in the initial state with subsequent heat treatment and machining. Pitting corrosion tests are carried out, according to ASTM G48 method A in 10% FeCl3·6H2O solution at elevated temperature and exposure time for 5h. The studies were performed on the AISI 321 and AISI 316L stainless steels manufactured by SLM. It was obtained that laser scanning speed decrease led to density rise by other SLM parameters being equal. Porosity affected to the stainless steel corrosion behaviour significant. Metal density decrease resulted to corrosion rate rise. Microstructure examination showed that pitting corrosion development depended on surface steel condition.

Effect of Cooling Time on Microstructure and Properties of 2507 Super Duplex Stainless Steel Welding Heat-Affect Zone

The welding thermal simulation of 2507 Super Duplex Stainless Steel (SDSS) was investigated using Gleeble-3800 thermo-mechanical simulator. The morphology evolution of austenite and ferrite under different t8/5 and t12/8 were observed and compared. The impact tests and pitting corrosion tests under different t8/5 and t12/8 were conducted. The results showed that the austenite content increased and the austenitic morphology changed from allotriomorphic structure to strip or coarse-blocky structures with the increase of t8/5 and t12/8. The effect of t12/8 on the microstructure of welding Heat Affect Zone (HAZ) was more distinct than that of t8/5. The impact toughness of HAZ with the increase of t12/8 was improved due to higher austenite content, while that with the increase of t8/5 was slightly decreased due to the formation of intermediate phase, such as σ phase. The corrosion tests showed that the pitting resistance of HAZ was improved with the increase of t8/5 and t12/8, while the effect of t12/8 was especially evident.

Influence of welding parameters on pit initiation and pit growth in welded joints of X5CrNi18-10 stainless steel

The influence of welding parameters on the resistance to pitting corrosion in welded joints of X5CrNi18-10 stainless steel was studied. Welding was performed by a TIG procedure in a shielding gas containing different amounts of nitrogen. The welding speed, the deposition rate of the filler wire, and the shielding gas flow rate were constant, which allowed the nitrogen content in the weld metal to be directly dependent on the nitrogen content in the shielding gas. It was shown that welding current and arc energy had a significantly lower influence on the resistance to pit formation and pit growth, than the nitrogen content in the shielding gas. Pitting corrosion testing was conducted using the potentiodynamic polarization method. The resistance to pit formation increases with the increase in nitrogen content in the weld metal, while the resistance to pit growth decreases. The microstructure of the weld metal becomes more homogeneous in the presence of nitrogen and the distribution of chromium more uniform, which leads to the increased resistance to pit formation. Also, due to the formation of ammonia ions, the pH value of the solution within the pit is higher than in the bulk solution, which also increases the resistance to pit formation.

Functionalized Electrospun Fibers for the Design of Novel Hydrophobic and Anticorrosive Surfaces

In this work, a novel coating was deposited on aluminum alloy samples by using a combination of electrospinning and chemical vapor deposition (CVD-silanization) techniques in order to create a functionalized film with an enhancement of both corrosion resistance and hydrophobicity. The electrospinning technique makes the fabrication of highly crosslinked electrospun fibers possible by the combination of both poly(acrylic acid) and β-cyclodextrin, respectively, which can be easily functionalized in a further step by using the CVD-silanization process due to the evaporation of a hydrophobic molecule such as 1H,1H,2H,2H-Perflurodecyltriethoxysilane. In addition, the resultant electrospun fibers with a high degree of insolubility have been successfully fabricated and metal oxide nanoparticles (TiO2NPs) have been incorporated into the electrospun polymeric solution in order to improve the corrosion protection. The surface morphology has been determined by using light optical microscopy, atomic force microscopy, scanning electron microscopy, and water contact angle (WCA) measurements. The corrosion resistance has been evaluated by using both potentiodynamic polarization and pitting corrosion tests. Finally, the results related to WCA measurements after CVD-silanization corroborate that the surfaces have been successfully functionalized with a hydrophobic behavior in comparison with the electrospinning process, showing a considerable difference in the roughness.

Corrosion performance of friction surfaced nickel aluminium bronze (NAB) alloy under erosion corrosion and salt fog environment

ABSTRACTIn the present research work, the extruded nickel aluminium bronze (NAB) alloy is friction surfaced over cast NAB alloy as a repairing technique for the deteriorated marine components. The friction surfaced specimens were tested for their corrosion properties. The corrosion tests such as salt fog test, erosion–corrosion test and pitting corrosion test were conducted to investigate the corrosion behaviour of the friction surfaced NAB alloy. It is found that the accumulation of corrosion occurred due to the presence of a continuous network of the ΚIII-phase. The lower corrosion rate is achieved in friction surfaced NAB alloy compared to the base NAB alloy which is contributed by the corrosion resistant contents such as Al and Cu and also by the fine grain microstructure obtained during the friction surfacing process.This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).

Determining the Minimum Corrosion Conditions for the Stir Zone of Friction Stir Welded AA6061 Aluminium Alloy Joints

Joining of aluminium is commonly done in automobile industries because of its light weight and high specific strength. In recent days, friction stir welding (FSW) is widely preferred to join aluminium than fusion-welding processes. In this joint, grains are very fine in stir zone (SZ) compared to the other zones. Due to this extreme change in the microstructure at the SZ, the mechanical properties (tensile strength, hardness, etc) of the FSW joints are superior but the corrosion resistance of SZ is very poor. The concentration of chloride ion, exposure time and pH value are reported to be the more influencing corrosion test parameters. The present work aims to determine combination of these pitting corrosion test parameters to attain a minimum corrosion rate at the SZ of friction stir welded aluminium alloy, AA6061-T6, by response surface methodology (RSM). From the results obtained, chloride ion concentration is reportedly had higher effect on corrosion rate than the other two parameters considered.

Quantitative Correlation of 7B04 Aluminum Alloys Pitting Corrosion Morphology Characteristics with Stress Concentration Factor

The accelerated pitting corrosion test of 7B04 aluminum alloy specimen was carried out according to the spectrum which simulated airport environment, and the corresponding pitting corrosion damage was obtained and was defined through three parameters A and B and C which respectively denoted the corrosion pit surface length and width and corrosion pit depth. The ratio between three parameters could determine the morphology characteristics of corrosion pits. On this basis the stress concentration factor of typical corrosion pit morphology under certain load conditions was quantitatively analyzed. The research shows that the corrosion pits gradually incline to be ellipse in surface and moderate in depth, and most value of B/A and C/A lies in 1 between 4 and few maximum exceeds 4; The stress concentration factor Kf of corrosion pits is obviously affected by the its morphology, the value of Kf increases with corrosion pits depth increasement under certain corrosion pits surface geometry. Also, the value of Kf decreases with surface width increasement under certain corrosion pits depth. The research conclusion can set theory basis for corrosion fatigue life analysis of aircraft aluminum alloy structure.

Preparation of Trivalent Chromium and Rare Earth Composite Conversion Coating on Aluminum Alloy Surface

In this paper, the surface conversion film on 6063 aluminum alloy was prepared by chemical plating process with chromium sulfate, lanthanum sulfate and sodium phosphate as film forming agent. The corrosion resistance and surface morphology of the conversion film were analyzed by pitting corrosion test of copper sulfate and SEM. The results show that when Cr2(SO4)3 is 10 g/L, La2(SO4)3 is 2 g/L, Na3PO4 is 8 g/L, pH value is 3, temperature is 40 °C, reaction time is 10 min, the corrosion resistance of the surface conversion film is the best. The conversion coating is light green, composed of Cr, La, P, Al, O and other elements.

Use of electron microprobe analysis to explain metallurgical phenomena and their effect on properties when welding stainless steel

A modified electron probe microanalysis (EPMA) instrument containing six wavelength dispersive spectrometers has been used for mapping cross-sections of stainless steel base material and welds. It made it possible to measure the composition in specific small areas and to illustrate element partitioning; ranging from centerline segregation to concealed sub-microstructure. Examples from industrial research are given to demonstrate the versatile application field for this established technology. EPMA was used to study the chemical composition of gas tungsten arc welds in the lean duplex grade UNS S32101 performed with and without nitrogen additions to the argon-based shielding gas. The level of nitrogen in the shielding gas not only determined the weld metal nitrogen content, but also affected evaporation of other elements from the weld metal. Mapping could also be used to reveal detailed information about the dendritic substructure in welds and the fusion line that could not be seen with conventional microscopy as the weld metal microstructure is controlled by nitrogen. With the measured local composition, it was possible to calculate the pitting resistance equivalent number, PRE = Cr + 3.3 × Mo + 16 × N (wt%) and thereby visualize the local variation in the microstructure. Nitrogen is strongly concentrated in the austenite and has the largest impact on the PRE. Pitting corrosion testing confirmed that the ferrite phase was most susceptible to pitting attack and that a higher average PRE does not significantly increase the critical pitting temperature. The EPMA instrument was also applied to study all-weld metal of E347T0 type flux-cored wire with and without bismuth additions. Bismuth can have a negative effect on weld metal ductility after post-weld heat treatment and/or applications at high temperature. It has been suggested that this is due to grain boundary bismuth segregation, and it has been debated whether it occurs as bismuth or bismuth oxide Bi2O3. Hot tensile testing confirmed that the bismuth content affects the weld metal ductility at 700 °C and EPMA proved that bismuth segregates as round particles after post-weld heat treatment and not as bismuth oxide.

Effect of Shot-Peening on Hardness and Pitting Corrosion Rate on Load-Bearing Implant Material AISI 304

AISI 304 is a type of stainless steel used for load bearing implants due to relatively low cost. However, its mechanical properties and corrosion resistance must be improved to the level of AISI 316L, cobalt-based alloys, titanium and titanium alloy properties. Its fatigue characteristic is also one of the most important criteria have to be evaluated to achieve the overall service performance requirements, when this material subjected to dynamic load. High surface hardness may delay fatigue crack initiation and decrease corrosion rate because these two processes initiated at surface layer. The purpose of this research is to investigate the change in mechanical and corrosion characteristics of AISI 304 due to shot peening processes.Surface treatment with shot peening process were done by regulating the variation time for 0, 5, 10, 20, 30 and 40 minutes at the firing pressure of 7 bar; using 0,6 mm steel ball with hardness of 40-50 HRC. Firing distance between the nozzle with the specimen surface is 100 mm. Surface hardness was tested using indentation load of 10 grams for 10 seconds. Pitting corrosion test of treated AISI304 and non treated AISI316L was conducted in intravenous Otsu-RL brands as corrosion media. Pitting corrosion was performed using cyclic polarization methodThe hardness of surface layer increase with increasing shot-peening time. According to increase of length of shot-peening time from 0, 5, 10, 20, 30 and 40 minutes the hardness of these specimen increase to 241, 404, 418, 437, 481 and 496 VHN, respectively. The pitting corrosion rate tend to significantly decrease with increasing of shot peening time. According to increase of length of shot peening time from 0, 5, 10, 20, 30 and 40 minutes the pitting corrosion rate of these specimen also decrease to 0.853, 0.619, 0.086, 0.017, 0.116 and 0.036 mpy, respectively. Pitting corrosion rate of AISI316L is 0.042 mpy. Best pitting corrosion rate of treated AISI304 is 2.5 times smaller than that of non treated AISI316L. Therefore, shot-peening could be used to increase hardness number and reduce pitting corrosion rate, significanly.

Accelerated pitting corrosion test of 304 stainless steel using ASTM G48; Experimental investigation and concomitant challenges

Marine and offshore structures constructed with stainless steel are regarded as having high corrosion resistance due to their superior self-passivating properties. However, they are equally susceptible to environmental degradation, especially due to pitting corrosion in highly corrosive marine environments. Pitting immersion tests performed on 304 austenitic stainless steel specimens using ASTM G48 presented significant challenges. Some of the issues encountered during these tests included unspecified experimental factors that control the pitting process such as pH, specimen size limitations, materials’ properties, and the variation on the quality of the test solution. To overcome these challenges, the effect of surface finishes and aeration of the test solution on the corrosion behavior of 304 stainless steel specimens in 6% ferric chloride were examined and compared. The result shows that an aerated solution has much lower concentrations of pits compared to quiescent solutions. Controlled aeration eliminates unwanted crevice corrosion background noise. Subsequently, to suit larger specimens, the ASTM G48 was modified. This study presents the modified ASTM G48 procedure. A series of pitting corrosion tests on stainless steel specimen with different thickness were conducted and data were statistically evaluated. The generalized extreme value distribution, such as Weibull, provides adequate statistical descriptions of the pit depth and pit diameter distributions. The modified ASTM G48 offered advantages in the extraction and interpretation of the data for pit characteristics in the accelerated pitting corrosion test simulating actual marine environment.

Electrochemical and pitting corrosion resistance of AISI 4145 steel subjected to massive laser shock peening treatment with different coverage layers

The effects of massive laser shock peening (LSP) treatment with different coverage layers on residual stress, pitting morphologies in a standard corrosive solution and electrochemical corrosion resistance of AISI 4145 steel were investigated by pitting corrosion test, potentiodynamic polarisation test, and SEM observations. Results showed massive LSP treatment can effectively cause an obvious improvement of pitting corrosion resistance of AISI 4145 steel, and increased coverage layer can also gradually improve its corrosion resistance. Massive LSP treatment with multiple layers was shown to influence pitting corrosion behaviour in a standard corrosive solution.

Investigations on Erosion and Corrosion Behavior of High-Velocity Oxy-Fuel Sprayed WC-Cr3C2-Ni Coatings on AISI 1018 Steel

Abstract WC-Cr3C2-Ni thermal spray coatings was applied on the surface of low carbon steel (AISI 1018) using high-velocity oxy-fuel (HVOF) process. The base metal, coating powder and coated materials were analyzed using scanning electron microscope. Water-jet erosion test (WJET) was used to test the mass loss of the samples with different process parameters such as impingement angle, water jet velocity, erodent discharge, and stand-off distance. As results lower mass loss was observed for the selected process parameters. Pitting corrosion test reveals that better corrosion resistance can be achieved for the low carbon steels by WC-Cr3C2-Ni powder coating.

Corrosion Behavior of API 5L X52 Carbon Steel Coated by Oxygen Plasma Discharge

Surface treatments of materials have attracted intensive studies in recent years, and considered as an important way for providing protection properties. In this paper, oxygen plasma treatment was used on API 5L X52 carbon steel. The produced deposit was characterized by different methods; optical and electronic microscopy, microhardness measurements and X rays diffraction. The resulting layer has been evaluated by electrochemical methods and pitting corrosion tests. The results showed that Fe2O3, which resulted from coating treatment by oxygen plasma, improved the superficial microhardness of steel. In chemical terms, pitting corrosion tests in corrosive solution showed a clear decrease of the weight loss and pitting percentage in coated coupons. Moreover, electrochemical corrosion tests (linear polarization and electrochemical impedance spectroscopy tests) showed that the produced deposit after coating gived a good protection against corrosion. This study demonstrates that oxygen implantation provides protective properties to API 5L X52 carbon steel.

Influence of Cold Work on Pitting Corrosion and Cavitation Erosion of High Interstitial FeCrMnCN Austenites

High interstitial steels (HIS) are based on the joint addition of carbon and nitrogen, which resulted in an austenitic FeCrMn steel grade. In contrast to high nitrogen steels (HNS), they can be produced by conventional metallurgy and offer a unique combination of mechanical properties and corrosion resistance. This makes them promising candidates for the use in environments featuring corrosive or wear attack or even both. Corrosion resistance can be improved by the addition of molybdenum, particularly in the case of media containing chloride ions. In this study, different FeCrMnCN alloys were investigated by means of pitting corrosion testing in sodium chloride solution, as well as cavitation erosion resistance. These properties were examined depending on prestraining, since the latter is used to strengthen this kind of alloys.

Pitting corrosion testing of stainless steel AISI 304 in chloride solutions

Pitting corrosion testing of stainless steel AISI 304 in chloride solutions

Effect of the Purging Gas on Properties of Ti Stabilized AISI 321 Stainless Steel TIG Welds

AbstractGas purging is necessary to provide a high quality of stainless steel pipe welding in order to prevent oxidation of the weld zone inside the pipe. AISI 321 stabilized austenitic stainless steel pipes commonly preferred in refinery applications have been welded by the TIG welding process both with and without the use of purging gas. As purging gases, Ar, N2, Ar +N2 and N2 + 10% H2 were used, respectively. The aim of this investigation is to detect the effect of purging gas on the weld joint properties such as microstructure, corrosion, strength and impact toughness. Macro sections and microstructures of the welds were investigated. Chemical composition analysis to obtain the nitrogen, oxygen and hydrogen content of the weld root was done by Leco analysis. Ferrite content of the beads including root and cap passes were measured by a ferritscope. Vickers hardness (HV10) values were obtained. Intergranular and pitting corrosion tests were applied to determine the corrosion resistance of all welds. Type of the purging gas affected pitting corrosion properties as well as the ferrite content and nitrogen, oxygen and hydrogen contents at the roots of the welds. Any hot cracking problems are not predicted as the weld still solidifies with ferrite in the primary phase as confirmed by microstructural and ferrite content analysis. Mechanical testing showed no significant change according to the purge gas. AISI 321 steel and 347 consumable compositions would permit use of nitrogen rich gases for root shielding without a risk of hot cracking.

Localized Corrosion Risk Assessment Using Markov Analysis

The objective of this work was to develop the foundation for an interactive corrosion risk management tool for assessing the probability of failure of equipment/infrastructure as a function of threats (such as pitting corrosion and coating degradation) and mitigation schemes (such as inhibitors and coatings). The application of this work was to assist with corrosion management and maintenance planning of equipment/infrastructure given dynamic changes in environmental conditions. Markov models are developed to estimate pitting damage accumulation density distributions as a function of input parameters for pit nucleation and growth rates. The input parameters are selected based upon characterization with experimental or field observations over a sufficiently long period of time. Model predictions are benchmarked against laboratory pitting corrosion tests and long-term atmospheric exposure data for aluminum alloys, obtained from the literature. The models are also used to examine hypothetical scenarios for t...