Pitting Corrosion Behavior Research Articles

Influence of Molybdenum on Microstructure and Pitting Corrosion Behavior of Solution-Treated Duplex Stainless Steel in a Lithium Chloride Solution

Influence of Molybdenum on Microstructure and Pitting Corrosion Behavior of Solution-Treated Duplex Stainless Steel in a Lithium Chloride Solution

Optimizing the Plasma Arc Welding Process Parameters to Attain the Minimum Corrosion Rate in the AISI 409M grade Ferritic Stainless Steel Autogenous Joints

Abstract The combination with good mechanical properties and manufacturing characteristics, makes stainless steel an indispensable tool for the designer. Stainless steels become susceptible to localized intergranular corrosion when chromium carbides form at the grain boundaries during high temperature exposure. This depletion of chromium at the grain boundaries is termed ‘sensitization’, because the alloys become more sensitive to localized attack in corrosive environments. Stainless steels like AISI 409M grade, which are having low chromium content (approximately 11%), are susceptible to localized corrosion. The susceptibility of these alloys are strongly affected by welding processes and filler metals, which change the microstructure of the alloy in order to have optimum mechanical properties. Hence, the present investigation has been carried out to understand the effect of Plasma Arc Welding (PAW) process on pitting corrosion behavior of AISI 409M grade stainless steel joints. Also, the PAW process parameter such as welding speed, voltage, heat input were optimized with help of Response Surface Methodology (RSM) to attain the maximum tensile strength and minimum corrosion rate in the welded joints.

Effect of Deformation-Induced Defects on the Microstructure and Pitting Corrosion Behavior of Al-Ag Alloy

In this study, a wide range of combined ageing treatments and cold work deformations in the Al 4.2 wt% Ag alloy matrix were proposed, aiming to investigate the effect of defects such as precipitates (Ag2Al plates) and dislocations on the mechanical and electrochemical behavior of Al–4.2 wt% Ag alloys. Further reductions of thickness from 10 to 60%, decreases the mean size of Ag2Al plates, along with a denser distribution. The inductive loop at lower frequencies in Nyquist plot attributed to localized corrosion that clearly testified the fluctuations of the anodic branch in the Tafel diagram and the FE-SEM images for the presence of pitting corrosion. Additionally, the pit propagation grade expands repetitively with cold work reduction and fragmentation of pre-precipitates. This was related to an extreme amount of dislocations induced by deformation and fragmented pre-precipitates, which created more preferable locations for the nucleation of pits. Furthermore, Energy Dispersive X-ray Spectroscopy of pits, revealed that the presence of Al-Ag containing particles acted as cathodic sites and caused the anodic matrix dissolution.

Effect of Sulfate and Chloride Ions on Pitting Corrosion Behavior of 2Cr12MoV Steel at pH 6 and 90 °C

Effect of Sulfate and Chloride Ions on Pitting Corrosion Behavior of 2Cr12MoV Steel at pH 6 and 90 °C

Combination of Electrochemical Noise and Acoustic Emission for Analysis of the Pitting Corrosion Behavior of an Austenitic Stainless Cast Steel

The pitting corrosion behavior of a high alloy cast steel is analyzed in a sodium chloride solution by combination of the electrochemical noise technique and the acoustic emission (AE) method. Four corrosion states are identified on the steel surface after the 70 h noise measurement test. The simultaneously monitored AE exhibits two types of acoustic signals. The first type of AE events is attributed to the local passive oxide breakdown and the pit initiation process and the second type of AE events is related to the subsequent associated hydrogen gas bubble evolution.

Effect of Short-Time Aging on the Pitting Corrosion Behavior of a Novel Lean Duplex Stainless Steel 2002

The effect of short-time aging in the temperature range between 400 and 1000 °C on the pitting corrosion behavior and mechanical property of a novel lean duplex stainless steel (LDSS) 2002 was investigated through the potentiostatic critical pitting temperature (CPT) tests and the Charpy impact tests. Both the pitting corrosion resistance and the toughness of aged specimens degraded due to the precipitation of detrimental secondary phases and the most significant reduction of CPT and impact energy emerged at 650 °C concurrently. The CPT of LDSS 2002 specimen aged at 650 °C decreased by 28 °C, and the impact energy dropped from 69 to 29 J/cm2 compared with the solution-annealed sample. Transmission electron microscopy characterization showed that the main precipitates in LDSS 2002 were Cr2N and M23C6 along the ferrite–austenite grain boundaries.

Effects of Cerium on the Inclusions and Pitting Corrosion Behavior of 434 Ferritic Stainless Steel

AbstractThe effects of Ce addition on the inclusions and the pitting corrosion behavior of ferritic stainless steel were investigated. The results showed that Ce2O3·SiO2 and Ce2O2S inclusions were mainly found in 434 ferritic stainless steel containing 0.011% or 0.023 wt% Ce, which is the most appropriate addition of Ce that could contribute to produce the dispersive and fine rare earth inclusions. According to the thermodynamic analysis, Ce inclusions could be produced by rare earth elements combining with oxygen, sulfur, or preexisting SiO2. While the kinetic analysis and mechanism for formation of inclusions suggested that the area ratio of the pure SiO2 inclusion decreased with Ce increasing, and the difference of [Ce] concentration between the original inclusion interface and the SiO2 solid unreacted nuclear interface is the main reason to cause the different process of inclusion modification. Meanwhile, when the content of Ce was 0.011% or 0.023%, the resistance to pitting corrosion increased with the interface areas between the inclusions and the steel matrix decreasing. However, the excessive Ce addition resulted in the increase of size and quantity of inclusions, which would reduce the resistance to pitting corrosion.

A support vector machine‐based ensemble algorithm for pitting corrosion modeling of EN 1.4404 stainless steel in sodium chloride solutions

The resistance to localized corrosion of stainless steel in sodium chloride solutions is evaluated at different conditions. The effects of chloride ion concentration, acidity, and temperature on pitting corrosion resistance are analyzed. In order to develop a model capable of predicting pitting corrosion behavior of EN 1.4404 by an automatic way, a support vector machine‐based ensemble algorithm is proposed. An additional step related to feature selection is included in the model in order to improve the prediction capability. According to the excellent prediction results, the support vector machines (SVM) model is used to perform a sensitivity analysis for the purpose of analyzing the influence of the environmental variables on the breakdown potential and the pitting corrosion status modeling of this grade of stainless steel. Based on this analysis, it can be concluded that the breakdown potential is the main variable to be considered in pitting corrosion modeling whereas temperature is the most important one for breakdown potential modeling.

Passivation and Pitting Corrosion Behavior of a Novel Alloy Steel (00Cr10MoV) in Simulated Concrete Pore Solution

AbstractIn order to prolong the service life of reinforced concrete structures in a severe marine environment, a novel alloy steel (00Cr10MoV) was developed. The passivation behavior of 00Cr10MoV s...

Influence of austenitizing and tempering on the corrosion behavior and sensitization of martensitic stainless steel X50CrMoV15

Electrochemical tests, hardness measurements, and microstructure analysis are performed to study the influence of austenitizing, quenching, and tempering parameters on the corrosion resistance of the martensitic stainless steel grade X50CrMoV15 (1.4116). Different heat treatment states were studied using an adapted EPR‐Test to evaluate the chromium distribution and depletion caused by the formation and dissolution of chromium rich carbides. The EPR results were correlated with pitting corrosion behavior, demonstrating the strong effect of heat treatment parameters on the susceptibility of martensitic stainless steels to corrosion phenomena.

Weld joint design and thermal aging influence on the metallurgical, sensitization and pitting corrosion behavior of AISI 304L stainless steel welds

Experimental investigations were carried out to study the influence of weld joint design and post weld thermal aging treatments on the metallurgical, intergranular and pitting corrosion behavior of AISI 304L stainless steel welded joints. 10 mm thick linear weld joints were fabricated using gas metal arc welding process using single-V and double-V joint design with an average heat input of 503.42 J/mm and 562.78 J/mm respectively. Thermal aging of these welds was carried out at 750 °C for 0.5 h and 4 h, and the cooling media used was furnace, air and water quench (used separately for each specimen), so as to induce variable degree of carbide precipitation in different zones of these welds. Microstructural studies revealed that the extent of carbide precipitation was more in case of welds made using double-V joint design as compared to single-V joint welds. Degree of sensitization (DOS) and pitting performance of these welds evaluated using double loop electrochemical potentiokinetic reactivation (DLEPR) technique and potentiodynamic anodic polarization technique respectively, further showed that single-V joint performed better in terms of corrosion properties owing to lesser precipitation as compared to the double-V joint. This study shows that in comparison to double-V joint, single-V joint design can prove to be an important part of fabrication procedures where service conditions demand better corrosion properties of these welds.

A Study of the Pitting and Uniform Corrosion Characteristics of X65 Carbon Steel in Different H2S-CO2-Containing Environments

There have been increasing concerns related to the challenges posed by hydrogen sulfide (H2S) corrosion to the integrity of oilfield pipeline steels. In environments containing variable quantities of both carbon dioxide (CO2) and H2S gas, the corrosion behavior of carbon steel can be particularly complex. There is still no universal understanding of the changes in the mechanisms, sequence of electrochemical reactions and impact on the integrity of carbon steel materials as a result of changes in H2S-CO2 gas ratio. The film formation process, film characteristics, and morphology in CO2- and H2S-containing systems are also known to be different depending upon the environmental and physical conditions and this influences the rates of both general and pitting corrosion. Questions still remain as to how the combined presence of CO2 and H2S gases at different partial pressure ratios influence the corrosion mechanisms, as well as initiation and propagation of surface pits. This paper presents an investigation into the overall (i.e., general and pitting) corrosion behavior of carbon steel in CO2-H2S-containing environments. The work explores the impact of changes in ratios of CO2 and H2S partial pressures at both 30°C and 80°C in a 3.5 wt% NaCl solution. All experiments are performed at atmospheric pressure, while H2S gas content is varied at 0 ppm (0 mol%), 100 ppm (0.01 mol%), 1,000 ppm (0.1 mol%), 10,000 ppm (1 mol%), and 100,000 ppm (10 mol%) in H2S-CO2 corrosion environments. Corrosion film properties and morphology are studied through a combination of scanning electron microscopy and x-ray diffraction. The results show that the morphology and composition of iron sulfide formed changes with H2S gas concentration because of the continuous interaction of the corrosion interface with the corrosion media even in the presence of initially formed FeS (mainly mackinawite). This often leads to the formation of a different morphology of mackinawite as well as different polymorphs of FeS. This also has the impact of either increasing or decreasing the uniform corrosion rate at low and higher concentration of H2S gas depending on the temperature. Pitting corrosion is also evaluated after 168 h to determine the impact of increasing H2S content on the extent and morphology of pitting corrosion attack. The results from the pitting corrosion investigation show that increased and severe pitting corrosion attack occurs at higher H2S concentration and temperature. The morphology of pitting corrosion attack is also linked to the changes in the H2S content with an indication of a critical concentration range at which the nature of attack changes from narrow and small diameter pits to severe localized attack. The critical concentration threshold for such transition is shown in this study to reduce with increasing temperature.

The effect of welding atmosphere on the pitting corrosion of AISI 304L resistance spot welds

Austenitic stainless steel has excellent properties with respect to general corrosion resistance, while it is sensitive to localized corrosive attacks, such as pitting and crevice corrosion in humid and chloride-containing atmospheres. This pitting corrosion susceptibility increases when it is exposed to conditions like resistance spot welding (RSW) process. The current research deals with the effect of RSW shielding gas atmosphere on the pitting corrosion behavior of AISI 304L austenitic stainless steel weld joints. Optical and SEM investigations show several types of pit sizes and morphologies depending on heat input and shielding gas. Cyclic potentiodynamic polarization (CPP) of welded nuggets shows that argon gas is more effective in the improvement of pitting corrosion resistance at low heat input, while nitrogen demonstrates better corrosion resistance at high heat input.

Pitting corrosion behaviour of 2101 duplex stainless steel in chloride solutions

ABSTRACTThe corrosion behaviour of 2101 duplex stainless steel (DSS) in NaCl solution was studied and compared with that of 2205 DSS. The effects of chloride concentration and solution temperature on pitting corrosion behaviour were focused. The relative sensitivity to pitting corrosion of the constituent phases in both 2101 and 2205 DSSs was also explored. Pitting corrosion susceptibility was evaluated by conducting cyclic polarisation curve measurement. The corrosion morphology was examined by a scanning electron microscope equipped with energy dispersive spectrometer. The experimental results showed that the pitting corrosion resistance of 2101 DSS was inferior to that of 2205 DSS by exhibiting a lower threshold chloride concentration and a lower critical pitting temperature. For both 2101 and 2205 DSSs, the ferrite phase was more susceptible than austenite phase to pitting corrosion.This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).

Dependence of Crystallographic Orientation on Pitting Corrosion Behavior of Ni-Fe-Cr Alloy 028

The influence of crystallographic orientation on the pitting corrosion behavior of Ni-Fe-Cr alloy 028 was studied using a combination of X-ray diffraction (XRD), electron backscatter diffraction (EBSD), potentiodynamic polarization technique, and atomic force microscopy (AFM). The results show that there is anisotropy of pitting corrosion that strongly depends on crystallographic orientation of the surface plane. The distribution of pit density in a standard stereographic triangle indicates that the crystallographic planes close to {100} are more prone to pitting corrosion compared to planes {110} and {111}. The surface energy calculation of (001) and (111) shows that the plane with a high atomic packing density has a low surface energy with concomitant strong resistance to pitting corrosion. A correlation function between crystallographic orientation and pitting corrosion susceptibility suggests a method that not only predicts the pitting resistance of known textured materials, but also could help to improve corrosion resistance by controlling material texture.

Studies on microstructure, mechanical and pitting corrosion behaviour of similar and dissimilar stainless steel gas tungsten arc welds

In the present study, an attempt has been made to weld dissimilar alloys of 5mm thick plates i.e., austenitic stainless steel (316L) and duplex stainless steel (2205) and compared with that of similar welds. Welds are made with conventional gas tungsten arc welding (GTAW) process with two different filler wires namely i.e., 309L and 2209. Welds were characterized using optical microscopy to observe the microstructural changes and correlate with mechanical properties using hardness, tensile and impact testing. Potentio-dynamic polarization studies were carried out to observe the pitting corrosion behaviour in different regions of the welds. Results of the present study established that change in filler wire composition resulted in microstructural variation in all the welds with different morphology of ferrite and austenite. Welds made with 2209 filler showed plate like widmanstatten austenite (WA) nucleated at grain boundaries. Compared to similar stainless steel welds inferior mechanical properties was observed in dissimilar stainless steel welds. Pitting corrosion resistance is observed to be low for dissimilar stainless steel welds when compared to similar stainless steel welds. Overall study showed that similar duplex stainless steel welds having favorable microstructure and resulted in better mechanical properties and corrosion resistance. Relatively dissimilar stainless steel welds made with 309L filler obtained optimum combination of mechanical properties and pitting corrosion resistance when compared to 2209 filler and is recommended for industrial practice.

Effect of Welding Process on Microstructure, Mechanical and Pitting Corrosion Behaviour of 2205 Duplex Stainless Steel Welds

An attempt has been made to weld 2205 Duplex stainless steel of 6mm thick plate using conventional gas tungsten arc welding (GTAW) and activated gas tungsten arc welding (A- GTAW) process using silica powder as activated flux. Present work is aimed at studying the effect of welding process on depth of penetration, width of weld zone of 2205 duplex stainless steel. It also aims to observe the microstructural changes and its effect on mechanical properties and pitting corrosion resistance of 2205 duplex stainless steel welds. Metallography is done to observe the microstructural changes of the welds using image analyzer attached to the optical microscopy. Hardness studies, tensile and ductility bend tests were evaluated for mechanical properties. Potentio-dynamic polarization studies were carried out using a basic GillAC electro-chemical system in 3.5% NaCl solution to observe the pitting corrosion behaviour. Results of the present investigation established that increased depth of penetration and reduction of weld width in a single pass by activated GTAW with the application of SiO2 flux was observed when compared with conventional GTAW process. It may be attributed to the arc constriction effect. Microstructure of the weld zones for both the welds is observed to be having combination of austenite and delta ferrite. Grain boundary austenite (GBA) with Widmanstatten-type austenite (WA) of plate-like feature was nucleated from the grain boundaries in the weld zone of A-GTAW process. Mechanical properties are relatively low in activated GTAW process and are attributed to changes in microstructural morphology of austenite. Improved pitting corrosion resistance was observed for the welds made with A-GTAW process.

Comparative Studies on Microstructure, Mechanical and Pitting Corrosion of Post Weld Heat Treated IN718 Superalloy GTA and EB Welds

In the present study, an attempt has been made to weld Inconel 718 nickel-base superalloy (IN718 alloy) using gas tungsten arc welding (GTAW) and electron beam welding (EBW) processes. Both the weldments were subjected to post-weld heat treatment condition as follows -980°C / 20 min followed by direct aging condition (DA) as 720°C/8 h/FC followed by 620°C/8 h/AC. The GTA and EB welds of IN718 alloy were compared in two conditions as-received and 980STA conditions. Welds were characterized to observe mechanical properties, pitting corrosion resistance by correlating with observed microstructures. The rate of higher cooling ranges, the fusion zone of EBW exhibited discrete and relative finer lave phases whereas the higher niobium existed laves with coarser structure were observed in GTAW. The significant dissolution of laves were observed at 980STA of EBW. Due to these effects, the EBW of IN718 alloy showed the higher mechanical properties than GTAW. The electrochemical potentiostatic etch test was carried out in 3.5wt% sodium chloride (NaCl) solution to study the pitting corrosion behaviour of the welds. Results of the present investigation established that mechanical properties and pitting corrosion behaviour are significantly better in post weld heat treated condition. The comparative studies showed that the better combination of mechanical properties and pitting corrosion resistance were obtained in 980STA condition of EBW than GTAW.

Influence of Welding Process and Post Weld Heat Treatment on Microstructure and Pitting Corrosion Behavior of Dissimilar Aluminium Alloy Welds

Welding of dissimilar Aluminum alloy welds is becoming important in aerospace, shipbuilding and defence applications. In the present work, an attempt has been made to weld dissimilar aluminium alloys using conventional gas tungsten arc welding (GTAW) and friction stir welding (FSW) processes. An attempt was also made to study the effect of post weld heat treatment (T4 condition) on microstructure and pitting corrosion behaviour of these welds. Results of the present investigation established the differences in microstructures of the base metals in T4 condition and in annealed conditions. It is evident that the thickness of the PMZ is relatively more on AA2014 side than that of AA6061 side. In FS welds, lamellar like shear bands are well noticed on the top of the stir zone. The concentration profile of dissimilar friction stir weld in T4 condition revealed that no diffusion has taken place at the interface. Poor Hardness is observed in all regions of FS welds compared to that of GTA welds. Pitting corrosion resistance of the dissimilar FS welds in all regions was improved by post weld heat treatment.

Comparative Studies on microstructure, mechanical and corrosion behaviour of DMR 249A Steel and its welds

DMR249A Medium strength (low carbon) Low-alloy steels are used as structural components in naval applications due to its low cost and high availability. An attempt has been made to weld the DMR 249A steel plates of 8mm thickness using shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW). Welds were characterized for metallography to carry out the microstructural changes, mechanical properties were evaluated using vickers hardness tester and universal testing machine. Potentio-dynamic polarization tests were carried out to determine the pitting corrosion behaviour. Constant load type Stress corrosion cracking (SCC) testing was done to observe the cracking tendency of the joints in a 3.5%NaCl solution. Results of the present study established that SMA welds resulted in formation of relatively higher amount of martensite in ferrite matrix when compared to gas tungsten arc welding (GTAW). It is attributed to faster cooling rates achieved due to high thermal efficiency. Improved mechanical properties were observed for the SMA welds and are due to higher amount of martensite. Pitting corrosion and stress corrosion cracking resistance of SMA welds were poor when compared to GTA welds.