Pitting Resistance Research Articles

Evaluation of the Corrosion Resistance of 904L Composite Plate in a High-Temperature and High-Pressure Gas Field Environment

In order to study the corrosion resistance of 904L composite plate pressure vessels under a high-temperature and high-pressure gas field environment, the pitting corrosion and stress corrosion cracking resistance of a 904L composite plate body and weld material were compared with those of a 2205 composite plate and 825 composite plate, which are used in high-temperature and high-pressure gas field environments. The results showed that the pitting resistance of the 904L composite plate was lower than that of the 825 composite plate and higher than that of a 2205 solid-solution pure material plate and a 2205 composite plate. The corrosion resistance of the 625 welding material is higher than that of the E385 welding material. In the simulation of the corrosion environment of a high-temperature and high-pressure gas field, the corrosion rates of the 904L composite plate body, welding seam, and surfacing welding were all less than 0.025 mm/a, indicating slight corrosion, and the sensitivity coefficient of chloride stress corrosion cracking was less than 25%, indicating low sensitivity. The 904L composite plate met the requirements of corrosion resistance for pressure vessel materials in a high-temperature and high-pressure gas field environment.

Effect of rare earth Ce treatment on the microstructure and properties of 430 ferritic stainless steel bearing Sn and Cu

The effects of rare earth Ce on purifying molten steel, modifying inclusions and micro-alloying in 430 ferritic stainless-steel bearings with Sn and Cu has been studied in this paper. The results demonstrate that Ce can purify molten steel, modify inclusions, enhance the mechanical properties and improve the pitting and corrosion resistance of the experimental steel. Ce effectively purifies the molten steel, reducing the total oxygen (T. O) content to as low as 0.00086 wt.% and sulphur (S) content to 0.0020 wt.%. The transformation of inclusions in the steel follows the sequence of MnS·Al2O3 → CeAlO3 → Ce2O2S → Ce2O3 with increasing Ce content. The number of inclusions initially decreases and then increases, with the experimental steel containing 0.012 wt.% Ce showing the best cleaning effect. Additionally, Ce treatment only slightly improves the mechanical properties of the experimental steel, but significantly enhances its pitting corrosion resistance and intergranular corrosion resistance by changing the enrichment state of carbides and impurity elements at the grain boundaries. In detail, Ce can partially inhibit the precipitation of M23C6 type carbides at grain boundaries, thereby improving the intergranular corrosion resistance of the experimental steel.

Minor tungsten addition enhances corrosive resistance in CoCrFeNi high-entropy alloy at elevated seawater temperature

Most research on the corrosive CoCrFeNi high-entropy alloy (HEA) has mainly modulated element species and atomic concentration recently. However, the corrosive resistance of the passive film in the elevated temperatures environment inevitably need to be extensively explored for application. In this work, the microstructure and corrosion behavior in the elevated temperatures of face-centered cubic (FCC) CoCrFeNiWx (x = 0 and 0.2) HEAs are investigated. The mechanism of passivation layers on the corrosion behavior of HEAs is further discussed for comparison to the alloy of addition tungsten. Through potentiodynamic polarization curves in 3.5 wt% NaCl solution from 25 °C to 70 °C, the addition of tungsten can raise the critical pitting temperature, while maintaining a lower passivation current density and a larger passivation range at the same time. The high resolution X-ray photoelectron spectrometer (HRXPS), electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) are all conducted to analyze the passivation composition and chemical reaction of the present alloys detailly. The CoCrFeNiW0.2 HEA exhibits the uniform Cr2O3 layer on the FCC matrix; the proportion of dispersive WO3 layer on the μ phase precipitates form a double-layer passive film under elevated temperature in 3.5 wt% NaCl. It shows that the synergistic effect of the double-layer passive film significantly enhances the pitting and corrosive resistance in this HEA.

Clarifying the Relationship Between Chemical States of P in Fe–P Alloys and Pitting Corrosion Resistance

Fe–0.002 P, Fe–0.05 P, Fe–0.2 P, and Fe–2 P alloys (numbers indicate the mass%) were fabricated, and their pitting potentials, depassivation pH values, and active dissolution rates were measured. The order of pitting potentials was (high) Fe–0.002 P ≥ Fe–0.05 P ≥ Fe–0.2 P ≫ Fe–2 P (low), and that of depassivation pH values was (low) Fe–0.002 P ≤ Fe–0.05 P ≤ Fe–0.2 P ≪ Fe–2 P (high). Both parameters changed significantly between the Fe–0.2 P and Fe–2 P alloys. No evidence of grain boundary segregation of P was observed in the Fe–0.05 P alloy. In the Fe–0.2 P alloy, grain boundary segregation of P was observed, but no pitting occurred at the grain boundaries. In the Fe–2 P alloy, Fe3P precipitated at the grain boundaries and in grains, but pitting corrosion occurred in the alloy matrix and not in Fe3P. This indicated that P in the solid solution was the main cause of the decrease in pitting corrosion resistance. The P concentration in the surface oxide film on Fe–2 P was higher than that on Fe–0.2 P, and the P in the films was determined to be FePO4. The decrease in the pitting resistance with an increasing P concentration was due to FePO4.

Effect of graphene on microstructure, strain hardening and corrosion behaviour of dual phase Mg-Li matrix processed through liquid metallurgy route

The significance of this study lies in the potential enhancement of magnesium (Mg)-based materials through the addition of graphene, aiming to improve their mechanical properties and corrosion resistance. This research investigates the development of graphene-Mg composites, employing a liquid metallurgy route to fabricate a dual-phase structured Mg-8Li composite. Mg-Li dual-phase composites are of interest due to their lightweight nature and promising mechanical properties, making them suitable for applications in aerospace, automotive, and structural engineering. Graphene was incorporated into the Mg matrix at varying percentages (0.2, 0.4 and 0.6 wt.%), and the resulting materials were subjected to microstructural, mechanical, and corrosion analyses. Microstructural characterization results reveals that the increase in graphene content results in decrement in grain size of α-Mg and β-Li up to ∼33 and ∼11.5% respectively. Likewise, additions of graphene improvise tensile and yield strength of base matrix up to ∼47 and ∼44% respectively. Strain hardening exponent (n) values of base material decrease from 0.21 to 0.17 with respect to graphene addition which confirms the effect of graphene that acts as effective barrier to slip that decreases the deformation. Corrosion analysis revealed a decrease in corrosion rate and increased pitting resistance with the addition of graphene, indicating improved corrosion resistance. Electrochemical impedance spectroscopy results depict that the composite with 0.4 wt.% graphene exhibits larger semi conducting loop with higher charge transfer resistance ( Rct) value of 128 Ω cm2.

Effect of Cr on the microstructure and corrosion behavior of nickel-based alloys in hydrochloric acid

Nickel-base alloy is a type of metal material with excellent properties and is widely used in many fields. However, in the harsh environment of the acid solution, corrosion causes the reduction of the service life of the alloys, thereby limiting the alloys' use and development. In this paper, the effect of Chromium (Cr) content on the microstructure and corrosion behavior of nickel-based alloys in hydrochloric acid (HCl) was studied by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), electron backscatter diffraction (EBSD) and electrochemical workstation. Meanwhile, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition and properties of the surface passive films. For the Cr20 and Cr30 alloys with a single face-centered cubic (FCC) structure, the Cr2O3 content in the passive films increased with the Cr content, effectively improving the corrosion resistance. As the Cr content continued to increase, the second phases having a body-centered cubic (BCC) lattice were precipitated both in the Cr40 and Cr50 samples, inducing microgalvanic corrosion, thus deteriorating the corrosion resistance. XPS results showed that, in the Cr30 alloy, the relative content of Cr2O3 and the bound water were the highest, indicating that its passive film had the best corrosion resistance. For the passive film, the pitting resistance was related to Cr content, appropriate Cr content improved the corrosion resistance.

Corrosion Behavior of Cobalt–Chromium‐Based Laser Claddings Reinforced with Boron Nitride, Graphene Oxide, and Graphite.

In this article, the corrosion resistance of a cobalt–chromium‐based laser cladding reinforced with different microparticles: boron nitride, graphene oxide, and graphite, added for increased tribological performance, is explored. Samples are fabricated by premixing cobalt–chromium powder with microparticle additions and cladding onto 316L stainless steel base metal. The corrosion behavior is measured in industrially relevant applications: 1 m acetic acid and 3.5 wt% NaCl, using open‐circuit potential, electrochemical impedance spectroscopy, linear polarization resistance, and cyclic polarization. Laser ablation–inductively coupled plasma–mass spectrometry is used to analyze the distribution of the chemical elements throughout the coatings. The reference cladding's corrosion resistance is outstanding in both electrolytes, with a corrosion rate (CR) of ≤0.19 μm year−1 and no pitting tendencies. With the addition of microparticles, the claddings maintain their remarkable pitting resistance, but show an increase in CR up to 0.98 μm year−1 due to the nonuniform distribution of the microparticles into the matrix.

Pitting behavior of austenitic stainless-steel welded joints with dense inclusions and methods to enhance pitting resistance

PurposeThis study aims to assess the pitting resistance of austenitic stainless steel welded joints fusion zone (FZ) with high density of inclusions before and after surface treatment, including potentiostatic pulse technique (PPT) and pickling.Design/methodology/approachThe potentiodynamic polarization tests and critical pitting temperature tests were carried out for estimating pitting resistance. The PPT and pickling were performed as surface treatment. Scanning electron microscope (SEM) and energy dispersive spectrometer were used for characterize the microstructure and elemental distribution. Electron back-scattered diffraction (EBSD) was used to assess the portion of phases and morphology of grains.FindingsThe weld metal exhibits a higher degree of alloying compared to the base metal, and it contains d-phase and sulfur-containing inclusions. Sulfur-containing inclusions serve as initiation sites for pitting, and they diminish the pitting resistance of weld metal. Both PPT and pickling can remove sulfur-containing inclusions, but PPT causes localized dissolution of the weld metal matrix around the inclusions, while pickling does not. Because of the high density of inclusions, certain pits initiated by PPT are significantly deeper, which makes the formation of stable pitting easier. Because of the high density of inclusions, certain pits initiated by the PPT are deeper. This characteristic facilitates the progression of these initial defects into fully developed, stable pits.Originality/valueAnalysis of pitting initiation in shielded metal arc welding FZ with PPT and ex situ SEM tracking observation. Explanation of why the PPT surface treatment is not able to enhance the pitting resistance of stainless steel with a high inclusion density.

Synergistic improvement of pitting and wear resistance of laser powder bed fusion 420 stainless steel reinforced by size-controlled spherical cast tungsten carbides

The spherical cast WC/W2C is selected to produce a martensitic stainless steel-based composite using the laser powder bed fusion technique. W and C reacted with Fe and Cr, creating a strong bond between the particles and the matrix, reducing the wear rate by over 98 %. W and C diffuse to the matrix, increasing the hardness over 100 HV0.5. The interface between cast WC/W2C and matrix is sensitive to pitting corrosion through galvanic effects. However, the formation of austenite and WO3 from spherical cast WC/W2C decomposition improves the critical pitting potential and passive film stability.

A hybrid machine learning strategy for pitting probability prediction of stainless steels

Pitting corrosion represents a substantial threat to passive metals, potentially leading to stress-corrosion cracking and the abrupt failure of materials. The complex relationship between the internal alloy compositions and external environmental factors complicates the precise prediction of pitting probability. In this study, a hybrid machine learning strategy is developed to predict the probability and boundary of pitting corrosion in stainless steel, considering the collaborative effects of different factor pairs rather than a single factor. The strategy integrates both black-box (adaptive boosting) and white-box (symbolic classification) algorithms, where the former is constructed to determine the pitting probability with an F1 score of 0.85, and the latter is designed to achieve recognition of critical factor pairs. This work aims to offer a systematic diagram and new insights in understanding and optimizing the pitting resistance of stainless steel.

Development of a novel Ti35Nb25Zr15Mo15V10 high-entropy alloy for metallic biomaterials

Ti–6Al–4V alloy has been widely used as implant materials for biomedical applications. However, the inadequate corrosion resistance and the released metal ions could result in inflammation, cytotoxicity, and shorten the lifespan of implants. To extend the service life of biomaterials, the Ti35Nb25Zr15Mo15V10 high-entropy alloy was designed based on empirical and thermodynamic calculations to achieve a high-performance biomaterial with a potential to replace Ti–6Al–4V alloy. Investigations on the fabricated alloy revealed formation of body-centered cubic solid solution with no intermetallic compound. Nanoindentation experiments indicated a Young's modulus of 118 for the designed alloy which is lower than the elastic modulus of the Ti–6Al–4V alloy. Corrosion behavior of the Ti35Nb25Zr15Mo15V10 and Ti–6Al–4V alloys were investigated and the results represented a low passive current density of ∼10−2 A/m2 for the novel alloy which displayed superior corrosion resistance. In addition, the developed alloy provided higher bio-corrosion resistance compared with the Ti–6Al–4V alloy with superior pitting resistance and low concentration of released ions in a PBS solution. The Ti35Nb25Zr15Mo15V10 alloy revealed acceptable in-vitro biocompatibility performance for adhesion, viability, and proliferation of MG63 pre-osteoblasts. The preliminary benefits of the designed alloy over current metallic implants provide an opportunity to explore the development of new orthopedic-implant alloys.

Pitting Initiated by MnO·Cr2O3–MnS and MnS Inclusions in a Si‐/Mn‐Killed Stainless Steel

Two types of inclusions in the stainless steels are detected: MnO·Cr2O3–MnS dual‐phase ones and pure MnS ones. The increase of sulfur content can inhibit the formation of MnO–Cr2O3–MnS inclusions and reduce the harm of MnO·Cr2O3–MnS inclusions on the pitting corrosion of stainless steels. When the sulfur content increases from 26 to 70 ppm, the average pitting potential increases from 0.34 to 0.4 VSCE due to the decrease in the number density of MnO–Cr2O3–MnS inclusions. A Cr‐depletion zone exists in the steel matrix around MnO–Cr2O3–MnS inclusions. The size of pits induced by MnO·Cr2O3–MnS inclusions is larger, which poses a more serious threat to the pitting resistance of stainless steels.

HOMA-IR Index and Pediatric Psoriasis Severity-A Retrospective Observational Study.

Psoriasis is a chronic inflammatory disease with specific cutaneous and nail lesions. Recent data has emphasized its systemic nature, highlighting metabolic conditions found in patients. Insulin resistance was identified in adult psoriasis, sometimes related to psoriasis severity. Data regarding this relationship in children are limited. Consequently, we tested the association between the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) and Psoriasis Area and Severity Index (PASI) using a retrospective dataset of 43 children with various types of psoriasis. First, we attempted to replicate the relationship between the HOMA-IR and PASI. Second, we explored potential associations between these variables and others in the dataset. The results illustrated no association between HOMA-IR and PASI (p-value = 0.512). The exploratory findings hinted at a connection between nail pitting and insulin resistance (p-value = 0.038), yet Bonferroni adjustments suggested the risk of a false-positive finding. Noteworthy associations were found between the HOMA-IR and body mass index (BMI) (p-value = 0.001), the PASI and quality of life impairment (p-value = 0.005), and psoriasis severity and type (p-value = 0.001). The null hypothesis that insulin resistance in children is not positively associated with psoriasis severity cannot be rejected. Pilot estimates of variables and covariates of interest are provided for further confirmatory studies assessing this hypothesis.

Improved Ability to Resist Corrosion of Selective-Laser-Melted Stainless Steel Based on Microstructure and Passivation Film Characteristics

The local corrosion resistance of forging and selective laser melting (SLM) 304 steels was explored by intergranular corrosion analysis, double-loop electrochemical potentiodynamic reactivation, dynamic polarization experimentation, structural analysis, and passivation film characteristics analysis. The ability to resist sensitization of SLM 304 steel is greater than that of forging 304 steel at a temperature of 650 °C for 9 h. Moreover, the pit corrosion resistance of forging and SLM 304 steels is weakened by sensitization, while the pit corrosion resistance of SLM 304 steel is much greater than that of forging steel. Therefore, SLM technology can improve the ability to resist sensitization and pit corrosion of 304 steel. Analysis showed that the ability to resist corrosion of the passivation film of SLM 304 steel is greater than that of forging steel. In addition, corrosion pits are easier to generate at the interface of forging steel and SLM 304 steel. The grain boundary corrosion of SLM 304 steel intensified while the corrosion of the melt pool boundaries weakened after the sensitization treatment, resulting in a decrease in pit corrosion resistance. The coupling effect of these different structures and passivation films decides the pit and sensitization resistance of forging and SLM 304 steels. Clarifying the corrosion mechanism of forging and SLM steels is of great significance for scientific research and the widespread use of SLM technology.

Study on mechanism underlying the acceleration of pitting corrosion of B30 copper–nickel alloy by sulfate-reducing bacteria in seawater

In this paper, the relationship between the pitting corrosion formation of B30 copper–nickel (CuNi) alloy and the metabolism of sulfate-reducing bacteria (SRB) was investigated. Combined with the influence of temperature during the actual operation of the cooling systems, the evolution law of the alloy passivation film was analyzed, and the mechanism of SRB promoting the accelerated development of B30 CuNi alloy pitting corrosion was revealed. The results show that SRB significantly promoted the pitting formation and development of B30 CuNi alloy. The maximum pitting depth was 3.9 μm in the sterile system and 15.3 μm with SRB, which was 3.9 times higher than that of sterile system. The loose porous Cu2S film formed by SRB metabolites and copper matrix was easily penetrated by corrosive anions, which promoted copper dissolution and led to pit nucleation. The sulfide adsorbed on the surface prevented or delayed the passivation of B30 CuNi alloy by blocking the adsorption site of O atom, and the corrosion nuclei continued to grow. The non-uniformity caused by the film peeling accelerated the longitudinal development of pitting corrosion, and the expansion and coalescence of adjacent pits caused the transverse development of pitting corrosion. Temperature had a certain influence on the SRB and the formation of B30 CuNi alloy passivation film. The passivation film was formed rapidly at 50 °C with poor quality and the passivation property of Cu2O film was weakened. With the increase of temperature, the pitting potential of sterile system negative shifted from 0.447 to 0.360 V (vs. SCE), while SRB system from 0.340 to 0.198 V (vs. SCE), and the pitting resistance decreased. The passivation film with defects and the Cu2S reduced the barrier efficiency of the film and accelerated the pitting corrosion of B30 CuNi alloy.

Study on Microstructure and Properties of Cold Metal Transfer and Pulse Hybrid Welded Super Duplex Stainless Steel

The investigation focuses on the microstructure, impact toughness, and pitting corrosion resistance of cold metal transfer and pulse hybrid welded joints of unified numbering system (UNS) S32750 duplex stainless steel. The results show that the filler pass exhibits the highest austenite ratio (47.9%), whereas the heat‐affected zone (HAZ) shows the lowest (32.3%). Notably, secondary austenite (γ2) is present in both the backing pass and HAZ, but conspicuously absent in the filler pass, indicating that reheating from subsequent weld pass is a prerequisite for the precipitation of γ2. Additionally, chromium nitride (Cr2N) also precipitates in the HAZ and backing pass. Comparative analysis with the weld metal (WM) and base metal (BM) indicates that the HAZ displays lower impact toughness, primarily attributing to imbalanced phase ratio, coarse ferrite grains and the brittle Cr2N. Owing to the lower austenite content and Cr2N precipitation in the backing pass, its toughness (122.6 J cm−2) is found to be inferior to that of the filler pass (130.1 J cm−2). Furthermore, the HAZ with a lower critical pitting temperature compared to the WM (79.1 °C) and BM (87 °C), and exhibits the worst pitting corrosion resistance due to the abundant precipitation of secondary phases and excessive ferrite with low pitting resistance equivalent number.

Стойкость против питтинговой коррозии как критерий безопасности эксплуатации металлического оборудования

Pitting corrosion is hazardous for personnel of chemical plants operating with tanks, reactors, and pipelines. Pitting is a pinpointed corrosive damage rapidly penetrating a metal and causing its through-perforation. Chemical and thermal burns and poisoning of personnel are also potential. When designing the equipment, it is required to select materials able to resist pitting corrosion in the operational medium. Quick methods of pitting resistance of material include the comparison of critical potentials determined by potentiodynamic polarization curves. The potential of the studied sample is given a value equal to the corrosion value that is increased at the rate of 0.2–2 mV/s. At the same time, values of current density are registered. The gradual increase of current density is followed by its decrease, and the metal turns to a passive state. With a certain value of pitting formation potential, the current density increases acutely; and pittings are formed on the metal surface. When the potential is decreased, current density within a certain range of values remains relevant to the current density at the pitting formation potential but then decreases to the values relevant to dissolution in a passive state. This occurs at the re-passivation potential. Earlier, values of potentials of pitting formation and corrosion were compared. Later, it was proved that the evaluation of the pitting resistance of metals based on the comparison was not correct as pittings could also be formed at the potentials lower than the pitting formation potential. The correct evaluation of metal pitting resistance can be obtained based on the comparison of re-passivation and corrosion potentials. Until now, however, the pitting formation potential has been used for the evaluation. Based on the experimental potentiodynamic polarization curve of stainless steel Х20Н6Г11 and the results of corrosion tests, it has been established that metal corrodes at potentials above the re-passivation potential but lower than the pitting formation potential. When potentials are lower than the re-passivation potential, pittings are not formed.

Effect of laser shock peening on stress corrosion cracking of TC4/2A14 dissimilar metal friction stir welding joints

Stress corrosion cracking (SCC) of welded joints is a significant issue that affects the widespread application of multimetal welded structures in aerospace, transportation, and other fields. This paper investigates the effect of laser shock peening (LSP) on the SCC of TC4/2A14 friction stir welded (FSW) joints with dissimilar metals. The microstructural evolution, mechanical properties, and corrosion behavior with and without LSP treatment were investigated using optical microscopy, transmission electron microscopy, X-ray analysis, electrochemical testing, and slow strain rate tensile testing (SSRT). The results showed that the LSP significantly refined the grains and induced work-hardening on the near-surface of the material. After LSP, the compressive residual stresses on the surface of the titanium and aluminium sides were −817.6 MPa and −153.6 MPa for the joint, respectively. Corrosion resistance was also improved, with the self-corrosion current density on the Al side of the joints reduced by 77% and the SCC susceptibility index (Issrt) reduced from 0.140 to 0.121. The enhanced SCC resistance of the LSP-treated TC4/2A14 dissimilar metal FSW joints is primarily due to grain refinement, work-hardening effect, and high-level compressive residual stress. These factors not only enhance the material strength and improve the pitting resistance of the joints but also prevent the initiation and propagation of SCC.

Comparative statistical analysis of pitting in Two 2205 duplex stainless steel variants

The inherent variability of pitting poses challenges in accurately evaluating the pitting resistance due to potential disparities in test results. This study compares the pitting resistance of two commercial 2205 duplex stainless steels. Counterintuitively, the variant with higher Pitting Resistance Equivalent Number, exhibits a lower Critical Pitting Temperature. Through the potentiostatic pulse test and potentiostatic polarization, this variant is observed to have a greater number of pitting initiation sites. Further investigation, using SEM inclusion statistics, reveals an increased presence of inclusions rich in calcium oxides as the underlying cause of this unexpected phenomenon.

Microstructures and Corrosion/Localised Corrosion of Stainless Steels, Incoloy and Their Weldments in Nitrite-Containing Chloride Environments.

Prompted by the unexpected observation of the pitting of the weldments of a highly corrosion- and pitting-resistant duplex stainless steel, SAF2507, in chloride solutions with nitride addition, the pitting and corrosion resistance of SAF2507 and its weldments were investigated in chloride solutions with and without different levels of nitrite. The Incoloy 825 and 316L austenitic stainless steels were included for the purpose of developing a comparative appreciation. The microstructures of the weldments were characterised, and 316L showed a profound influence of nitrite addition in inhibiting pitting, while 'meta-stable' pitting transients that were clearly visible in the chloride solution without nitrite were absent when nitrite was added. Both the parent metal and the weldment of SAF2507 had similar pitting potential (Ep) in 0.1 M NaCl without nitrite, which was the highest Ep among the three alloys tested. Additions of nitrite at low concentrations had an inhibitive effect on pitting, whereas higher nitrite contents had a deleterious effect on pitting resistance. On the other hand, Incoloy 825 showed a trend of Ep ennoblement with an increasing nitrite content of 0.1 M NaCl, and the weldment underwent greater ennoblement. Moreover, 316L showed a trend similar to Incoloy 825; however, the Ep ennoblements were significantly more pronounced for both the weldment and the base metal of 316L.