Search

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. [ABSTRACT FROM AUTHOR]

Potentiodynamic polarization and potentiostatic passive measurements were performed to study the effects of alternating voltage (AV) interference on duplex stainless steel (DSS) 2205 corrosion. The results reveal that AV signals cause positive shift in open circuit potential (OCP) and strong oscillations on polarization curves of DSS 2205. For potentiostatic passive condition, the passive current increases with increasing the amplitude of AV signals with a frequency of 50 Hz. The vibrations on polarization and passivation are weakened after increase in frequency (>50 Hz). AV signals with frequency smaller than 50 Hz also induce evident oscillation on OCP, polarization, and passivation on samples. The high‐amplitude AV interferences with 50 and 100 Hz induce big pits on DSS 2205 samples, the pitting corrosion however is inhibited with further increasing the frequency. The AV interferences with different amplitudes induce obvious oscillation on polarization curves of DSS 2205 samples. The oscillation effect on passive property of DSS 2205 is weakened after further increasing AV frequency. [ABSTRACT FROM AUTHOR]

The precipitation and evolution of secondary phases in aged UNS S82441 Duplex Stainless Steel was investigated with morphological observation. The coexistence of nitrides, carbides and sigma and chi phase was found during the initial aging stages. In the initial aging stages, the granular σ and χ phases grow and coalesce according to Ostwald ripening. The intermetallic particles near the austenite/ferrite interfaces tend to grow compared to those in the inner grain. The relationships between aging time and microstructure evolution of this alloy were discussed in detail. After aging, the chromium-depleted zones near the austenite/ferrite interfaces transform to the secondary austenite, while the chromium-depleted zones near the ferrite/ferrite interfaces are replenished with chromium from the matrix. [ABSTRACT FROM AUTHOR]

The surface electrochemical corrosion activity of the economic lean duplex stainless steel LDX2101 was investigated in situ in chloride solution with a combination of long working distance microscope (LWDM) and electrochemical techniques. In addition, the site and chemical composition of the electrochemical active points on the specimen surface were also determined with integrated scanning electron microscope/energy dispersive X-ray spectroscope (SEM/EDS) system. The results demonstrated that: (i) The reaction of α → Cr2N + γ2 precedes that of α → σ + γ2 when LDX2101 was aged at 700°C. (ii) The initiation sites of electrochemical active points could be determined by LWDM in combination with potentiostatic pulse technique (PPT). (iii) The sites of electrochemical active points were found to change from inclusions (MnS/Al2O3) to secondary austenite phase (γ2), with the increase of aging time at 700°C. [ABSTRACT FROM AUTHOR]

Abstract: The influence of microstructure evolution and alloying element redistribution of UNS S32304 duplex stainless steel induced by annealing treatment on the crevice corrosion behaviour was studied. As the annealing temperature was increased from 1030 to 1150°C, the crevice corrosion resistance was decreased and the active peaks were not only increased in magnitude but also shifted towards the more noble direction. Austenite and ferrite have greatly different polarization behaviour within the crevice. This study provides guidance to the material design and usage in industry field in consideration of different polarization behaviour induced by the evolution of microstructure and alloying elements. [Copyright &y& Elsevier]

Abstract: Duplex stainless steel simultaneously comprises various phases, inclusions, precipitates and grain boundaries. It is full of academic and valuable significance for materials designing and processing optimization to ascertain the corrosion resistance of corresponding phases and various microstructures. However, up to date, efficient evaluation technique is still scare mainly due to difficulty in controlling of micropits. In this work, for the first time, optimized potentiostatic pulse technique (PPT) was established and applied to study the rule of initiation of pits of solution annealed and aged DSS in 1.0mol/L NaCl solution. The results showed that the size of pits can be well-controlled by adjusting the condition of potential pulse. Combined with SEM/EDS system observation, it was found that for solution-annealed specimens, sulphide and oxide mixed inclusions were the preferential pit initiation sites, while for aged specimens, majority pits occurred at inclusions in area impoverished in Cr/Mo, which is vicinal to σ phase. The phenomena that growing pits is retarded by precipitation rich in Cr/Mo, i.e. σ phase, was testified and explained. [Copyright &y& Elsevier]

Abstract: The microstructure and localized corrosion behavior of a 2101 lean duplex stainless steel aged at 700°C were investigated. The results showed that changes in the microstructure of the duplex stainless steel, due to the formation of precipitates, affected its pitting corrosion resistance. The values of the pitting potential and the critical pitting temperature dropped drastically before aging time up to 30min. The potentiostatic pitting corrosion measurement indicated more sensitive to the small amount of precipitates compared to the potentiodynamic test. Pitting nucleated mainly in the ferrite phase for the solution-annealed specimen, while the initiation of pitting corrosion for the aged specimen took place at Cr-depletion area around the precipitates, i.e. in the newly formed secondary austenite phase. [Copyright &y& Elsevier]

Abstract: Lean duplex stainless steel 2101 (LDX2101) shows wide application potential due to its better corrosion performance and lower cost than traditional 304 austenite steel. This paper investigates the effects of thermal aging treatments at 700°C for various aging times up to 100h on the selective corrosion resistance of LDX2101 by two non-destructive electrochemical measurements: double-loop electrochemical potentiokinetic reactivation (DL-EPR) and electrochemical impedance spectroscopy (EIS). The evolution of microstructure was examined by optical microscopy, SEM microscopy and X-ray diffraction techniques (XRD). The results showed that the two applied electrochemical measurements agreed very well. Both methods were able to reveal the relationship between microstructure and selective corrosion resistance, which was related to the formation of chromium- and molybdenum-depleted zones around the precipitates, especially the σ phase, during aging. Nevertheless, more information could be obtained using EIS methods, including the interfacial charge transfer reaction and the corrosion product adsorption process. The results suggest that the susceptibility of the aged alloy to selective corrosion is presumably codetermined by the formation of chromium- and molybdenum-depleted areas, as well as by the replenishment of them, in these areas from the bulk during aging. [Copyright &y& Elsevier]

Abstract: Both the critical pitting temperature (CPT) and critical repassivation temperature (T r) for two kinds of duplex stainless steels (DSS, namely UNS S31803 and UNS S32750) were investigated in 1mol/L NaCl solution using the cyclic thermammetry method. Potentiodynamic anodic polarization technique was employed to validate the cyclic thermammetry technique. In addition, the site of pitting nucleated preferentially on the DSS had been confirmed by scanning electron microscopy (SEM). The results demonstrated that there exhibits a hysteresis loop in cyclic thermammetry curve, revealing that the propagating pits could repassivate during the cooling half-cycle. The CPT and T r for UNS S31803 were 59.6°C and 36.5°C, whilst the CPT and T r for UNS S32750 were 87.5°C and 70.5°C, respectively. Pitting was always observed preferentially in the austenite phase. The results can be partially explained based on the changes in chemical composition of ferrite and austenite phases. Moreover, a semi-quantitative model is proposed to explain the existence of T r. [Copyright &y& Elsevier]

The influence of surface roughness on the pitting corrosion behaviour of 2205 duplex stainless steel (DSS) in a chloride-containing environment was investigated using electrochemical noise (EN) techniques and morphology observation. A rougher surface condition increased the frequency of pit initiation because of the increase in more occluded pit sites. Rough surface finish also accelerated pit growth by increasing the actual dissolution rate in the pit. Metastable pits on rougher surfaces had longer lifetimes and grew to larger sizes, as their inner chemical environment was more easily maintained. However back-scatter images showed that pitting initiates on DSS 2205 regardless of the roughness condition. [ABSTRACT FROM AUTHOR]

Abstract: Different welding thermal cycles from single-pass to triple-pass were performed on two kinds of 2304 duplex stainless steel through Gleebe thermal–mechanical simulator. The corresponding microstructure was observed, while the pitting corrosion resistance was investigated in 1.0M NaCl by potentiostatic critical pitting temperature (CPT). The results showed that single-pass welding deteriorated microstructure and pitting corrosion resistance significantly. As the welding pass increased, the ferrite content decreased and CPT increased. However, CPT was still lower than that of the base metal. Nitride precipitated at the boundary between ferrite and austenite phase for low-alloyed 2304 after the single-pass welding thermal cycle. [Copyright &y& Elsevier]

Abstract: The effect of annealing temperature in the range from 1000 to 1200°C on the pitting corrosion behavior of duplex stainless steel UNS S32304 was investigated by the potentiodynamic polarization and potentiostatic critical pitting temperature techniques. The microstructural evolution and pit morphologies were studied using a scanning electron microscopy with energy dispersive X-ray spectroscopy. The results demonstrated that the nucleation of metastable pits transformed from austenite phase to ferrite phase with the increasing annealing temperature. As the annealing temperature increased, the pitting corrosion resistance firstly increased and then decreased. The highest pitting corrosion resistance was obtained at 1080°C with the highest critical pitting temperature value and pitting nucleation resistance. The results could be well explained by the microstructural evolution of ferrite and austenite phases induced by annealing treatment. [Copyright &y& Elsevier]

Abstract: Pitting corrosion resistance of 2304 duplex stainless steels after autogenous plasma-arc welding and subsequent short-time post-weld heat treatment at different temperatures, determined by critical pitting temperature in 1.0M NaCl solution, has been investigated. The results showed that the as-welded joint displayed impaired pitting corrosion resistance and that pitting preferentially occurred at ferrite grain in heat-affected zone near the fusion line. Short-time annealing treatment at 1020–1120°C has a beneficial effect on the pitting corrosion resistance of welded joint. The most favorable annealing temperature for the analyzed welded joints was found to be 1080°C, at which the joint restored the pitting corrosion resistance lost during welding entirely. [Copyright &y& Elsevier]

Abstract: The microstructure and properties of UNS S31803 duplex stainless steel had been investigated following isothermally aging in a temperature range of 450–1000°C for 10min, which simulates a fairly long time relative to a weld thermal cycle. The results showed that specimens aged between 600 and 950°C are subjected to precipitation of secondary phases, such as Cr2N, σ and χ. And the most significant reduction in pitting corrosion resistance and impact energy occurs at 850°C. Moreover, at aging temperatures below 600°C, austenite is the preferred site for pitting initiation, which changes to precipitates modified ferrite phase at higher temperatures above 600°C. [Copyright &y& Elsevier]

Abstract: The effect of annealing temperatures in the range 1000–1200°C on the microstructure and corrosion behavior of 2101 lean duplex stainless steel was investigated. The results demonstrated that the volume fraction of austenite phase decreased with increasing annealing temperature. However, lower values for the pitting potential (E pit) and the critical pitting temperature (CPT) were obtained after annealing at higher temperatures. Pitting was initiated preferentially in the ferrite/austenite boundaries or inside the ferrite domains, indicating that the ferrite phase had inferior pitting corrosion resistance as compared to the austenite phase in as-received steel. Moreover, the PRE values of the ferrite phase fell with the annealing temperature, while the values for the austenite phase rose. No equal PRE values in the ferrite and austenite phase were found for this steel in the range of annealing temperatures. This was determined by evaluating the PRE values of both phases from EDS results and the Thermo-Calc database. [Copyright &y& Elsevier]

Abstract: Effect of aging at 850°C on pitting corrosion of UNS S31803 duplex stainless steel was examined in chloride solution by potentiostatic critical pitting temperature (CPT) measurements. The quantitative metallography coupled with X-ray diffraction technique was employed to follow the microstructure evolution. Moreover, the initiation and propagation of pitting corrosion had been imaged in relation to microstructure variations using scanning electron microscopy (SEM). The results demonstrated that the corrosion behavior is strongly dependent on the microstructure, namely the presence of sigma phase. A deterioration of pitting corrosion resistance is found after aging 4min, resulting in a drop in CPT. In particular, the metastable current transients during CPT test can clearly reflect the initiation of pitting process. Pitting nucleates preferentially in the austenite phase for the solution-annealed specimen, while the initiation of pitting corrosion takes place around sigma phase, in the newly formed secondary austenite for the aged specimen. [Copyright &y& Elsevier]

Highlights • An improved electrochemical method named thermal pulse technique was designed. • The CPT and repassivation temperature (T r) were measured in one thermal pulse. • The T r presented an inverted V-shape trend with the rise of cooling rate. • A model was proposed for the variation of T r in different thermal pulses. • The repassivation behavior was discussed according to the data of T r and E rp. Abstract An improved electrochemical method named thermal pulse technique was designed to measure the current flowing from a potentiostatically maintained UNS S31803 electrode in 1 M NaCl solution, while various thermal pulses were applied on the solutions. Both the critical pitting temperature (CPT) and the repassivation temperature (T r) were measured in one thermal pulse. The T r data presented an inverted V-shape trend as the cooling rate decreased. Both the CPT and T r values declined after multiple thermal pulses. The cyclic potentiodynamic polarization curves present a sharp transition of pitting and repassivation potential at the temperature ranged between the CPT and T r. [ABSTRACT FROM AUTHOR]

Highlights • Pitting corrosion of DSS 2205 interfered by AV was studied using FeCl 3 pitting test. • AV interference triggers pits below the CPT of DSS 2205 sample. • Increase in temperature favors pits formation at higher AV amplitudes. • Increase in frequency fails to suppress pits formation at higher temperatures. • AV with frequency lower than 50 Hz induces etching behaviors on DSS 2205. Abstract The corrosion of duplex stainless steel (DSS) 2205 induced by alternating voltage (AV) is a new degradation case and distinct behaviors of duplex phase under AV interference are still unknown. The standard FeCl 3 pitting test was employed to investigate the pitting corrosion of DSS 2205 with AC interference. The results reveal the AV signal reduces the critical pitting temperature of DSS 2205. The etching behavior occurs under AV signal with high amplitudes in 30 °C solution. However, big pits propagate under AV interference with lower amplitudes in 40, 50 °C solutions. The etching and pitting are suppressed with increasing frequency in 30 and 40 °C solutions. The increase in frequency fails to drastically suppress the pitting corrosion in 50 °C solution. The solution with higher temperature (>50 °C) easily triggers pits on DSS 2205 samples regarding the lower amplitude AV signals and higher frequency. The cross sectional morphologies also reveal that the AV-induced pits exhibit a strong lateral-growth tendency based on the dish shape. [ABSTRACT FROM AUTHOR]

In this article, we reveal that the optimal annealing temperature for DSS 2205 differs between acidic and neutral NaCl environments, rendering the limitation of utilizing pitting resistance equivalent number (PREN) to optimize annealing temperature. Elevating the annealing temperature leads to a better corrosion resistance of ferrite phase in the activation zone through Ni redistribution. In acidic NaCl systems, the optimal annealing temperature for DSS 2205 is co-governed by the Ni content and PREN. This conclusion offers a guidance for heat treatment process of DSS to be used in acidic environments. • Optimizing annealing temperature for stainless steel should consider the certain service environment. • Active dissolution of ferrite is restrained with increasing annealing temperature due to Ni redistribution. • Optimal annealing temperature for 2205 in acidic systems is co-determined by Ni content and PREN. [ABSTRACT FROM AUTHOR]

This research scrutinizes the intricate effects of hydrogen charging on crystal defects and passive film properties in high-defect-density 443 ultrapure ferritic stainless steel. It discerns that with non-saturated hydrogen at hydrogen traps, escalated hydrogen charging current density results in increased hydrogen capture. These trapped atoms fill the defects, thus mitigating the stress level and fostering the growth of chromium oxides within the passive film. Consequently, the alloy's resistance to intergranular corrosion is enhanced. • By cold rolling and short annealing of the 443 UPFSS, hydrogen traps were mainly distributed around the grain boundaries. • Hydrogen atom which was not saturated at the hydrogen trap improved IGC resistance of the specimens. • The decrease in stress was beneficial to the growth of chromium oxide in the passive film. • Saturation of trapped hydrogen atom resulted in an increased susceptibility to IGC of stainless steel. [ABSTRACT FROM AUTHOR]

The effect of cooling rate on microstructure evolution and pitting corrosion resistance of the Gleeble-simulated heat-affected zone of a newly developed duplex stainless steel 2002 was investigated. The results showed that the content of austenite phase and the grain size of the austenite increased as the cooling rate decreased from 100 to 10 °C/s in the temperature range of 1350–800 °C. Meanwhile, the critical pitting temperature (CPT) value increased from 31.2 to 43.6 °C and the pitting potential (E pit ) increased from 0.322 to 0.477 V, indicating that the pitting corrosion resistance increased with the cooling rate decreasing. With the cooling rate of 100 °C/s, the localized pitting attack of the specimens occurred along the ferrite/austenite boundaries but preferentially inside the ferrite domains, which might be attributed to the fact that the precipitation of Cr 2 N led to the Cr-depleted region in the ferrite matrix. When the specimens were subjected to cooling rates of 50, 30 and 20 °C/s, the stable pits were all selectively located at the interior of the ferrite phase, suggesting that the ferrite phase was a weaker phase as compared to austenite phase. At 10 °C/s, the pits of specimens preferentially took place across ferrite/austenite phase boundaries, meaning that the pitting resistance of two phases almost achieved equivalent. Moreover, with the decrease of cooling rate, the pitting resistance equivalent number (PREN) of ferrite phase increased, while that of the austenite phase decreased. In addition, it was found that ferrite showed a lower Volta potential than austenite phase and the Volta potential differences between two phases grew smaller with the cooling rate decreasing. The relationship between PREN and Volta potential of specimens with respect to pitting corrosion resistance of steels was discussed. [ABSTRACT FROM AUTHOR]

Abstract: The effect of laser-beam welding and subsequent short-time post-weld heat treatment at different temperatures and holding time on microstructure evolution and pitting corrosion behavior of UNS S31803 duplex stainless steel was investigated. The results showed the as-welded joint displayed impaired pitting corrosion resistance and that pitting preferentially occurred at ferrite grain in the fusion zone. Short-time heat treatment enhanced the pitting corrosion resistance of welded joint. Optimal post-weld heat treatment of 3min heat treatment at 1080°C was identified at which the joint restored the pitting corrosion resistance lost during welding process. [Copyright &y& Elsevier]

Abstract: Amorphous nanostructured MnO2 film was anodically deposited onto economical duplex stainless steel substrate. The obtained MnO2 film was characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy for microstructural, morphological, and compositional studies. The capacitive behavior was systematically investigated by cyclic voltammetry, charge–discharge cycling and electrochemical impedance spectroscopy (EIS) in 1M Na2SO4 electrolyte at different operating temperatures ranging from 20 to 60°C. The specific capacitance (SC) was improved with an increase of operating temperature, and the highest SC of 398F/g was achieved at a scan rate of 10mV/s and operating temperature of 60°C. The mechanism of SC improvement at elevated operating temperature was investigated using EIS. With an increase of operating temperature, the conductivity of electrolyte was improved, and the charge-transfer resistance (R ct) was decreased. The temperature dependence of 1/R ct follows an Arrhenius equation. The MnO2 film was electrochemically activated at 60°C due to the formation of NayMnO2 after discharging. [Copyright &y& Elsevier]

Abstract: Pitting corrosion resistance of 2304 duplex stainless steel heat-affected zone with different cooling rates has been studied by potentiostatic critical pitting temperature (CPT) in 1.0M NaCl. The results showed that, as cooling rate decreased from 100 to 10°C/s in the temperature range of 1350–800°C, the austenite fraction increased from 27.8% to 35.7%, and the CPT value increased from 14 to 19°C. The morphologies after the CPT tests showed pitting occurred preferentially in the ferrite phase for all specimens. Moreover, relationship between pitting corrosion resistance and microstructure evolution was further discussed. [Copyright &y& Elsevier]

Passivity breakdown on HDSS 2707 has been studied and the electrochemical data are interpreted in terms of the Point Defect Model. Pitting parameters of HDSS 2707 are determined, including the polarizability at bl/s interface, the defect annihilation rate, and the defect diffusion coefficient. The breakdown potential is demonstrated to be linearly related to log [Br-], pH, and the square root of potential scan rate (v 1/2), and follows a near-normal distribution. The critical vacancy concentration calculated from the PDM is consistent with that estimated crystallographically from the chromic barrier layer, and the dominant point defect is further confirmed by Mott-Schottky measurements. • The pitting parameters of HDSS 2707 associated with the PDM are obtained in NaBr solution. • The distribution of E b for HDSS 2707 is consistent with the PDM calculation. • Higher temperature and higher [Br-] lead to a lower standard deviation for a better fit. • The PDM is suitable for the prediction of pitting potential and its near-normal distribution law of HDSS 2707. [ABSTRACT FROM AUTHOR]

Solution-treated 2205 duplex stainless steel (DSS) was cold-worked to different degrees and then charged with hydrogen. The pitting susceptibility and passivation of cold-worked 2205 DSS samples in neutral chloride solutions were investigated by chemical immersion, potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy measurements. The dislocation densities in austenite and ferrite inside 2205 DSS samples both increased as the degree of cold work increased from 0% to 80%. After hydrogen charging, the hydrogen content in 2205 DSS samples increased from 13.52 ppm to 41.49 ppm as the degree of cold work increased from 0% to 80%, accompanied by an increased tendency to form hydrogen blisters. Deformation alone had little effect on the corrosion performance of 2205 DSS samples, but the deterioration effect of hydrogen charging on pitting resistance has been promoted by cold work, which could be ascribed to the increased hydrogen content as the degree of cold work increased. The change in pitting potential before and after hydrogen charging was linearly dependent on the hydrogen content in 2205 DSS samples. Pits preferably nucleated within austenite or at the austenite/ferrite boundaries for the hydrogen-charged 2205 samples regardless of the degree of cold work. [ABSTRACT FROM AUTHOR]