Pitting Resistance Research Articles

Metallurgical and corrosion characterization of electron beam welded duplex stainless steel joints

Electron beam welding (EBW) process was employed autogenously to fabricate 12 mm and 18 mm thick full-penetration butt welds of 2205 duplex stainless steel (DSS). The welds were evaluated for their metallurgical characteristics (microstructure, ferrite content and microhardness) and corrosion (intergranular and pitting) behavior in the as-welded, aged (850 °C/30 min) and aging followed by solution treated (1050 °C/30 min) conditions. The EB welds showed a relatively higher propensity to pitting corrosion than the base metal while they remained immune to the intergranular corrosion based on the degree of sensitization. Thermal aging-induced Cr and Mo-rich intermetallic σ-phase and Cr-based carbides further led to degradation of pitting resistance while their sensitization behavior remained largely unaltered. The solution treatment promoted the formation of austenite and partial dissolution of secondary phases in the welds which favored the pitting resistance restoration tendencies. This study highlights that two factors viz. microstructural phase imbalance and weld zone size would play a significant role in influencing the corrosion properties of DSS EB welds. Thus, better pitting corrosion performance could be expected from the welds fabricated using welding procedures that would result in small sized fusion zones and a lesser degree of phase imbalance.

Staged Local Dissolution of Stainless Steel in Chloride Solutions

The paper defines galvanostatic polarization parameters (current density and test duration) to simulate self-dissolution conditions; the results are confirmed by potentiostatic tests. It is shown that under the conditions of self-dissolution simulation, increasing the solution concentration reduces the nucleation rate, while prolonging the pitting development time. Spectral analysis of chronopotentiograpms reveals low-frequency potential fluctuations that characterize the nucleation and passivation of pits at the onset of pitting corrosion. The paper describes the basic regularities observed in the alteration of surface electrochemistry by impedance spectroscopy; such alteration corresponds to the transition from the passive area to the pitting area. The researchers propose optimal electric equivalent circuits to reflect the surface conditions in early nucleation of pits. The paper also proposes an additional pitting resistance criterion, that is, cumulative electric-charge density.

Corrosion behavior of 2205 stainless steel in simulated flue gas condensate with different chloride concentrations in a waste incineration power plant

AbstractThe effect of Cl− on the initial corrosion behavior of 2205 duplex stainless steel (2205 DSS) in simulated flue gas condensate from a waste incineration power plant was investigated using Mott–Schottky plot, micro‐area electrochemical methods, and microscopic surface morphology observation. The results show that at 150°C, the carrier concentration of the 2205 DSS passive film was maintained at a small value and changed little when the Cl− concentration is less than 25 g/L, indicating that it has good pitting resistance. When the Cl− concentration reaches 30 g/L and above, the carrier concentration of the passive film increases remarkably, and pitting corrosion appears on the 2205 DSS surface. At 180°C, there is no obvious pitting on the surface when the Cl− concentration is not more than 15 g/L. When the Cl− concentration is 20 g/L or above, the carrier concentration of the passive film significantly increases, and pitting corrosion appears on the surface. When the Cl− concentration reaches 30 g/L, the carrier concentration of the passive film increases sharply. The passive film on a 2205 DSS surface is seriously damaged and accompanied by the occurrence of uniform corrosion.

Use of the Potentiostatic Pulse Technique to Study and Influence Pitting Behavior of 317L Stainless Steel

Potentiostatic pulse technique (PPT) measurements with different parameters were performed on 317L stainless steel. It is revealed that the selection of time parameters can control pitting size and the influences of cycle number concentrate in the first few cycles. The most stable pits initiated and grew simultaneously in the first cycle. Additionally, critical pitting temperature (CPT) measurements were performed after PPT measurements. The results verify that CPT values and their distribution range are influenced by test conditions. The CPT values of samples have an obvious increase after PPT tests. Therefore, by choosing appropriate parameters, PPT method can be used to change the surface condition of stainless steel sample and then improve its pitting resistance.

Influence of Deformation and Annealing on Microstructure and Corrosion Behavior of Austenitic Stainless Steel

Microstructure and corrosion behavior of warm deformed 316LN stainless steel was investigated in primary water reactor (PWR) environment by electrochemical corrosion test methods and SEM. An attempt has been made to understand the effect of warm deformation and heat treatment on the microstructure and electrochemical behavior of 316LN stainless steel. The corrosion rate is drastically increases after deformation as compare to un-deformed samples because protective oxide film is destroyed after deformation. The results indicate that the corrosion rate decrease after stress relief and solution annealing of deformed samples because heat treatment improved the repassivation capacity of deformed samples. The Ecorr shifted toward the passive direction after stress relief and solution annealing of deformed samples which indicate that a more protective passive film (Cr2O3) form on the surface of the deformed samples. It can be seen that the stress relief and solution annealing heat treated samples have less pit as compare to un-deformed samples which indicate that deformed samples have more pitting resistance as compare to un-deformed samples. Surface of the samples after corrosion test in PWR solution is investigated by SEM and it is observed that number of pits and depth of pits reduced after solution annealing and stress relief treatment of deformed sample as compare to un-deformed samples

The Pitting Behavior of Newly Modified 17-4 Precipitation Hardened Stainless Steel with Different Nb, N, and Mo Contents

The effect of the addition of Nb, N, and Mo to 17-4 precipitate hardening stainless steel (17-4 PH steel) on its pitting behavior in a simulated geothermal environment was investigated using a cyclic polarization test, and the pitting potentials and the repassivation potentials of the materials were acquired to evaluate their pitting resistance. Nb and N were found to lower the pitting potential of 17-4 PH steel, while Mo increased it. In the case of repassivation potential, the addition of all these elements seemed to have a slightly negative impact. Cr-rich oxide, Nb carbonitride (Nb (C, N)), and reversed austenite were found in the materials. The element distribution of/around the Cr-rich oxide inclusion and the Nb (C, N) precipitate of the material were studied. A Cr-depleted zone was found around the inclusion/precipitate, which rendered the surrounding area to be more susceptible to pitting corrosion. Pit embryos and well-developed pits were observed after the cyclic polarization tests. Pits tended to initiate in the vicinity of the inclusion/precipitate, and the dissolution of the oxide around the pit embryo was seen, which was believed to cause the local deterioration of the electrochemical environment. Lacy cover with narrow strip-shaped holes was found above the well-developed pit, and the forming mechanism of these holes was believed to be the dissolution of martensitic.

Improving the Mechanical Properties of AISI 2205 Duplex Stainless Steel by Cryogenic Treatment Process

The Duplex stainless steel AISI 2205 is well known for its corrosion resistance, applicable to high pitting and stress resistance. Cryogenic treatment is chosen to boost the mechanical properties of AISI 2205 Stainless Steel. The specimens undergo cryogenic treatment, one of them being treated to the saturated limit. For comparison purpose, one specimen is kept as untreated. Wear test will be conducted at a constant speed and variable load by a pin on disc wear testing apparatus. Wear test is completed to assess the capability of utilizing a specific surface building innovation to diminish wear for a particular application and to research the impact of treatment conditions on the wear execution, so upgraded surface treatment conditions can be figured it out. Eventually, all specimens were undergone with Scanning Electron Microscope analysis.

Machinability and tool wear mechanism of Duplex stainless steel – A review

This paper reviews the machining characteristics and tool wear mechanism of Duplex stainless steel. The Duplex alloy is a combination of Cr-Ni-Mo-Fe based alloys, it consist an equal grains proportion of γ-Austenite (FCC) and α-ferrite (BCC). Duplex stainless steel indicates the improved yield strength, corrosion resistance, better toughness, adequate pitting resistance. The Duplex stainless steel are used in many applications as nuclear plants, chemical equipments, vessels, heat exchangers, cellulose and sea water processing. Duplex stainless steel are considered as a poor machinable materials because of high austenite, nitrogen content and increase of alloy composition. The machining of Duplex stainless steel is difficult due to work hardening rate, high strength, low thermal conductivity, fracture toughness and BUE formation. In the ferrite phase the Duplex stainless are solidified completely for standard grades and cooling rates. Formation of tool wear as a result of high impact of heat on the cutting tool, lower cutting speed and less heat dissipation. The paper influences the overview study of machining of Duplex stainless steel by non-conventional and non conventional processes, it indicate the possible ways and future scope for the effective machining of DSS. The present work intends the machining behavior and Tool wear mechanism of Duplex stainless steel and recommended the tougher insert grade for machining Duplex stainless steel.

Characterizations of dissimilar S32205/316L welds using austenitic, super-austenitic and super-duplex filler metals

UNS S32205 duplex stainless steel plates were welded to AISI 316L stainless steel using the pulsed gas tungsten arc welding process with three different filler metals: ER2594, ER312, and ER385. The microstructures of the welds were characterized using optical and scanning electron microscopy, and all of the specimens were evaluated by ferrite measurements. The mechanical properties were studied through hardness, tensile, and impact tests. In addition, the pitting resistance equivalent number was calculated and cyclic polarization tests were performed to evaluate the corrosion resistance of the weld metal. The results showed that chromium nitride was formed in the heat-affected zone of the duplex side, whereas no sigma phase was detected in any of the specimens. The ferrite number increased from the root pass to the final pass. The absorbed energies of the impact test decreased with increasing ferrite number, whereas the tensile strength was enhanced. The fully austenitic microstructure of the specimen welded with ER385 exhibited the highest resistance to pitting corrosion at 25°C, and the super-duplex weld metal presented superior corrosion resistance at 50°C.

Effect of Corrosion Characteristics on Long-Term Aging of Austenitic 304 Steel

The objective of this study is to investigate the effect of long-term aging on electrochemical corrosion characteristics of austenitic AISI 304 steel. AISI 304 steel was subjected to aging treatment for an extended period at 700 °C up to a maximum of 10,000 h. The variation in the microstructure of aged specimens was observed with an optical microscope (OM) and a scanning electron microscope (SEM). The electrochemical polarization test was conducted to obtain the corrosion current density (Icorr) and corrosion potential (Ecorr). The metastable intermetallic M23C6 carbides generated in the vicinity of γ/γ grain boundaries and coarsened with aging time. The δ-ferrite island decomposed into σ-phase and M23C6 carbide with an aging time increase. As the aging time increased, the current density increased, but the corrosion potential of the austenitized specimen exhibited a minimum value of 0.04 μA/cm2. The highest pitting resistance exhibited at the austenitized specimen due to the absence of carbides. Consequently, the corrosion resistance of austenitic AISI 304 steel decreases with long-term aging time. The microstructural analyses well support this result.

Effect of siliconizing with molten salt on the wear resistance and corrosion resistance of AISI 302 stainless steel

An alloyed FeSi intermetallic compound layer was prepared on the surface of 302 stainless steel via a nonelectrolytic molten salt silicon infiltration method at different holding times (2 h and 4 h). The wear resistances of the substrate and siliconized layers were evaluated through microhardness, toughness, friction and wear testing. The corrosion behavior and electrochemical corrosion performance of the substrate and siliconized layers in H2SO4 were evaluated through static immersion and electrochemical testing, and the main factors affecting the corrosion behavior were analyzed. The results showed that the 2-h and 4-h siliconized layers exhibited better wear resistance and pitting resistance than the 302 substrates; these enhancements were mainly due to the alloyed FeSi intermetallic compound formed on the surface of the siliconized layer. However, the 2-h and 4-h siliconized layers exhibited different wear resistance and corrosion resistance. The wear volume of the 2-h siliconized layer was 82.5% less than that of the base material and approximately 40% that of the 4-h siliconized layer. The 4-h silicon-infiltrated layer exhibited excellent pitting resistance and passivation characteristics in 10 wt% H2SO4, and the self-corrosion current density of this layer was orders of magnitude less than that of the 2-h silicon-infiltrated layer

Influence of intermetallic precipitation on metallurgical, mechanical and pitting behavior of AISI 2205 duplex stainless steel welded joints

Post weld thermal aging of DSS (duplex stainless steel) welds resulted into complex precipitation that comprised of intermetallic carbides, oxides and sigma-phase in different zones of the welds. Maximum ferrite dissolution was observed in the weld metal followed by the HAZ (heat affected zone) and the base metal. Sigma phase precipitated preferentially along γ/δ (austenite/ferrite) interfaces besides the formation of secondary austenite (γ2). Precipitated joints showed an increase in microhardness and yield strength, whereas their UTS (ultimate tensile strength) did not alter much. Aging resulted into a significant loss of tensile ductility (percentage elongation) which showed a degradation of 15.27% and 62.46% for the base metal and the weld metal respectively. The base metal’s impact toughness did not show any appreciable loss, but a severe degradation of around 96% occurred in the impact toughness of the aged weld metal. Fatigue crack growth behavior showed that weld metal possessed superior fatigue strength than the base metal, which upon aging reduced drastically to 48.24 % and 28.44 % respectively. Pitting corrosion studies showed that weld metal exhibited superior pitting resistance than the base metal, and both of them suffered a loss of pitting resistance due to precipitation.

UR 367

Abstract UR 367 is a 6% Mo high-performance, super austenitic, stainless steel with a pitting resistance equivalent number (PREN) ≥ 43. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as forming, machining, and joining. Filing Code: SS-1311. Producer or source: Industeel USA, LLC.

Influence of carbon on the corrosion behaviour of interstitial equiatomic CoCrFeMnNi high-entropy alloys in a chlorinated concrete solution

We investigated the corrosion behaviour and passive film characteristics of interstitial equiatomic CoCrFeMnNi high-entropy alloys (HEAs) with various carbon concentrations in 3.5 wt.% NaCl-saturated Ca(OH)2 solution. The results showed that the carbon caused complex effects on corrosion behaviour. The properties of the passive film were modified by carbon; specifically, the doping concentration first continuously decreased to a minimum and then began to increase when the carbon concentration changed from 0 to 0.8 at.%. The HEA with 0.5 at.% carbon showed the best pitting resistance, which was attributed to the enrichment of the Cr and Co elements within the passive film.

Bifunctional TiO2/AlZr Thin Films on Steel Substrate Combining Corrosion Resistance and Photocatalytic Properties

A novel multi-functional bilayer coating combining an anti-corrosion Al–Zr (4 at.% Zr) underlayer and an anti-biofouling TiO2 top layer was deposited on high-speed steel (HSS) substrates. Al–Zr (4 at.% Zr) film, deposited by DC magnetron sputtering, which is a single phased supersaturated solid solution of Zr in Al, is used to provide sacrificial corrosion resistance of steels and TiO2 is added as a top layer to induce photocatalytic activity and hydrophilic behavior which can generate antifouling properties in order to slow down the biofouling process. The top TiO2 films, deposited at 550 °C by AACVD (aerosol-assisted chemical vapor deposition), consisting of anatase TiO2 microflowers physically attached to the TiO2 thin films present a high decomposition rate of Orange G dye (780 × 10−10 mol L−1·min−1). The enhanced photocatalytic performance is associated with the rough network and the presence of TiO2 microflowers capable of supporting the enhanced loading of organic contaminants onto the film surface. Electrochemical tests in saline solution have revealed that bilayer films provide cathodic protection for the steel substrate. The Al–Zr/TiO2 bilayer presents a lower corrosion current density of 4.01 × 10−7 A/cm2 and a corrosion potential of −0.61 V vs Ag/AgCl, offering good protection through the preferential oxidation of the bilayer and an increased pitting resistance. The proposed functionalized coating combining anticorrosion and photocatalytic properties is a promising candidate for an anti-fouling system in sea water.

Machine Learning for Corrosion Resistance Alloys

Determining the ability of corrosion resistance of alloys is of great importance to many applications. While one could call the pitting resistance equivalence number (PREN) a quantitative description of the relative corrosion resistance of stainless steels, it is an empirical value based on the chemical composition of the elements in alloys only, derived by mathematically fitting of experimental alloy data. It provides no scientific insight. In this work we collect a large number of experimental data published in the literature on corrosion of alloys to study the factors that determine the corrosion resistance of materials. A database that includes the alloy composition, electrochemical parameters as well as polarization testing parameters was therefore generated. Machine learning approaches (Lasso and Ridge regression) were used to find the unexpected correlations between aforementioned experimental parameters and the materials' properties. We further use the machine learning to prioritize the features that determine the corrosion resistance and anticipate that this work can be an useful tool for materials design.

The Impact of Crushed Rock Spoil on Pitting Corrosion of Selected Stainless Steels

The paper presents the results of the pitting resistance investigations of selected stainless steels in the chloride environment and the simultaneous impact of erosive factors using the cyclic polarization technique. Additionally, using electrochemical techniques, ie: electrochemical impedance spectroscopy (EIS) and measurement of corrosion potential, the behavior of the passive layer of selected stainless steels in the environment of chlorides and erosion was examined. On the basis of the obtained results, the resistance of stainless steels 1.4301 and 1.4404 was found, both on the effect of chloride ions and erosive factors in the studied systems. Both tested steels are susceptible to pitting corrosion. It was found that a good measure of erosive impact on stainless steel is both impedance spectrum analysis and continuous monitoring of the corrosion potential of steel.

Effect of Plastic Deformation on Pitting Mechanism of SS304

Localized corrosion induced by plastic deformation has been reported for many alloys used in structural and functional applications. To understand the interplay of plastic deformation and pitting corrosion, samples of stainless steel 304 were subjected to different levels of plastic tensile strain and their corrosion behavior was studied. Plastic deformation is believed to alter materials’ surface condition, hence deteriorating the pitting resistance of materials. Results from this study suggest that in situ plastic deformation from 0.1 to 9 pct decreases the pitting potential of SS 304 to a similar level. Upon releasing the stress, slip steps formed at the metal surface due to plastic deformation contribute to the decrease in the pitting resistance of SS 304. Residual strain hinders pit repassivation to a minor extent. Results from electrochemical tests on samples with different levels of plastic strain are discussed in this paper.

Composition-Nanostructure Steered Performance Predictions in Steel Wires.

Neutron scattering in combination with scanning electron and atomic force microscopy were employed to quantitatively resolve elemental composition, nano- through meso- to metallurgical structures and surface characteristics of two commercial stainless steel orthodontic archwires—G&H and Azdent. The obtained bulk composition confirmed that both samples are made of metastable austenitic stainless steel type AISI 304. The neutron technique’s higher detection sensitivity to alloying elements facilitated the quantitative determination of the composition factor (CF), and the pitting resistance equivalent number (PREN) for predicting austenite stability and pitting-corrosion resistance, respectively. Simultaneous neutron diffraction analyses revealed that both samples contained additional martensite phase due to strain-induced martensite transformation. The unexpectedly high martensite content (46.20 vol%) in G&H was caused by combination of lower austenite stability (CF = 17.37, p = .03), excessive cold working and inadequate thermal treatment during material processing. Together, those results assist in revealing alloying recipes and processing history, and relating these with corrosion resistance and mechanical properties. The present methodology has allowed access to unprecedented length-scale (μm to sub-nm) resolution, accessing nano- through meso-scopic properties. It is envisaged that such an approach can be extended to the study and design of other metallic (bio)materials used in medical sciences, dentistry and beyond.

Influence of the individual microstructural features on pitting corrosion in type 304 austenitic stainless steel

The individual role of microstructural features viz. grain boundary character distribution (GBCD), grain size and residual strain on pitting corrosion is assessed in type 304 stainless steel employing potentiodynamic and potentiostatic polarization tests. Greater fraction of Σ3n (n ≤ 3) boundaries and J3-type triple junctions have resulted in better pitting resistance in the optimized GBCD specimen. The presence of higher dislocation density in the deformed specimen has resulted in greater pit generation rate. The fine-grained microstructure has exhibited inferior pitting resistance due to its higher random high angle boundary surface area which serve as preferential sites for nucleation and growth of pits.