To advance the understanding of the corrosion behavior of stainless steel bellows in marine atmospheric environments and enhance the precision of service life predictions,this study employs finite element simulations ...To advance the understanding of the corrosion behavior of stainless steel bellows in marine atmospheric environments and enhance the precision of service life predictions,this study employs finite element simulations to investigate the pitting corrosion rates and pit morphologies of bellows peaks and troughs under varying electrolyte film thicknesses.The model incorporates localized electrochemical reactions,oxygen concentration,and homogeneous solution reactions.For improved computational accuracy,the fitted polarization curve data were directly applied as nonlinear boundary conditions on the electrode surface via interpolation functions.Simulation results reveal that the peak regions exhibit faster corrosion rates than the trough regions.With increasing electrolyte film thickness(from 10μm to 500μm),corrosion rates at both peaks and troughs decrease progressively,and after 120 hours of simulation,the maximum corrosion rate at the peaks declines from 0.720 mm/a to 0.130 mm/a,and at the troughs from 0.520 mm/a to 0.120 mm/a,with the disparity in corrosion rates diminishing over time.Furthermore,as corrosion progresses,pits propagate deeper into the substrate,exhibiting both vertical penetration and lateral expansion along the passive film interface,ultimately breaching the substrate.This research offers valuable insights into designing corrosion mitigation strategies for stainless steel bellows in marine environments.展开更多
The micro-area characterization experiments like scanning Kelvin probe force microscope(SKPFM)and Kernel average misorientation have the defects of complex sample preparation and occasional errors in test results,whic...The micro-area characterization experiments like scanning Kelvin probe force microscope(SKPFM)and Kernel average misorientation have the defects of complex sample preparation and occasional errors in test results,which makes it impossible to accurately and quickly analyze the pitting behavior induced by inclusions in some cases,prompting attempts to turn to simulation calculation research.The method of calculating band structure and work function can be used to replace current-sensing atomic force microscopy and SKPFM to detect the potential and conductivity of the sample.The band structure results show that Al_(2)O_(3) inclusion is an insulator and non-conductive,and it will not form galvanic corrosion with the matrix.Al_(2)O_(3) inclusion does not dissolve because its work function is higher than that of the matrix.Moreover,the stress concentration of the matrix around the inclusion can be characterized by first-principles calculation coupled with finite element simulation.The results show that the stress concentration degree of the matrix around Al_(2)O_(3) inclusion is serious,and the galvanic corrosion is formed between the high and the low stress concentration areas,which can be used to explain the reason of the pitting induced by Al_(2)O_(3) inclusions.展开更多
Precipitation-strengthened HEAs exhibit outstanding integration of strength and toughness at ambient temperature.Nevertheless,precipitates generally reduce the localized corrosion resistance in aggressive solution env...Precipitation-strengthened HEAs exhibit outstanding integration of strength and toughness at ambient temperature.Nevertheless,precipitates generally reduce the localized corrosion resistance in aggressive solution environments.To solve this problem,a strategy of introducing nano-sized L12 precipitates in CoCrFeNiAlTi HEAs has been proposed in this work.Results demonstrate the pitting corrosion potential can be elevated from 258 mVSCE to 603 mVSCE by increasing the precipitate content to 38 wt.%.Such an improvement in localized corrosion resistance can be attributed to two aspects.Firstly,L12 precipitates tend to be dissolved during the corrosion process,which promotes the heterogeneous nucleation of protective Cr2 O3 due to the rapid deposition of oxides/hydroxides of Al/Ti,and improves the passive film stability due to the Crrich FCC matrix.Secondly,the dissolution kinetic inside the pits can be suppressed on account of the enrichment of Cr element in the FCC matrix,thus inhibiting the pitting growth.In summary,the current work not only reveals the mechanisms of the nano-sized L12 precipitates upon the corrosion behavior,but also provides a strategy for designing corrosion-resistant HEA.展开更多
Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments,severely compromising its structural integrity.The study systematically investigates the pittin...Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments,severely compromising its structural integrity.The study systematically investigates the pitting behaviour of 9Cr18 bearing steel under salt spray conditions,focusing on the progressive evolution of surface morphology and cross-sectional characteristics of pits on finished bearings.Scanning electron microscopy,energy-dispersive spectroscopy and X-ray diffraction were employed to examine the surface morphology,elemental composition and phase structure of corrosion products over varying salt spray exposure durations.The results show that 9Cr18 steel exhibits localized pitting with“volcanic crater”-like pits in the early stage of salt spray corrosion.After 48 h,pitting develops into a“multi-point”pattern,marking the initial transition toward uniform corrosion.Until 240 h,corrosion products completely cover the surface,indicating the complete transformation from localized pitting to uniform corrosion.The high carbon and chromium content in 9Cr18 steel promotes carbide precipitation and uneven distribution in the matrix.Cr-depleted regions near the carbide/matrix interface serve as preferential sites for pitting initiation.The low effective utilization of chromium reduces the overall corrosion resistance of 9Cr18.展开更多
Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment.In the case of stainless steels,non-metallic inclusions have been identified as the most suscepti...Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment.In the case of stainless steels,non-metallic inclusions have been identified as the most susceptible sites for pitting,and have therefore garnered significant attention.This review critically ex-amines the issue of how inclusions induce pitting,with a particular focus on three mechanisms:sponta-neous dissolution of inclusions,active dissolution of Cr-depleted regions,and propagation of microcracks at the inclusion-matrix interface.While researchers have made significant strides in understanding these mechanisms over the past few decades,many gaps and controversies remain.Details such as the ini-tial driving force of inclusion dissolution and factors affecting Cr-depleted regions require further study.Moreover,some old concepts and methods need to be revised to arrive at more credible conclusions.This review aims to delve deeply into these important issues and provide inspiration for future research.展开更多
The transpassivation and pitting corrosion behavior of a high-nitrogen stainless steel(HNS),Fe18Cr15Mn3Mo0.92N,were systematically investigated by electrochemical analysis,morphology observation,and X-ray photoelectro...The transpassivation and pitting corrosion behavior of a high-nitrogen stainless steel(HNS),Fe18Cr15Mn3Mo0.92N,were systematically investigated by electrochemical analysis,morphology observation,and X-ray photoelectron spectroscopy surface analysis.It was surprisingly found that no pitting corrosion occurred in the transpassivation region of HNS.This electrochemical corrosion behavior is untypical for stainless steels,i.e.,the traditional critical pitting potential method was invalid for HNS.Both N and Cr enrichments in the transpassivation film on HNS were found extremely higher than those in the passivation film.The N existed in the form of[CrN]complex,which could stabilize the above both films.Besides,the corrosion product of N was detected as NH_(3) that exhibited an effective corrosion inhibition effect.On this basis,although the transition of Cr from 3-valent to 6-valent was confirmed,the transpassivation film on HNS still maintained it high stability and no pitting was found to occur.Therefore,the real pitting resistance of HNS should be higher than the expected before.And the stable transpassivation film played an important role in its untypical pitting corrosion resistance.展开更多
The influence of the aluminum content on the pitting corrosion of a 304 stainless steel by a Cl−solution was investigated.The number,area,and composition of non-metallic inclusions were modified by the addition of alu...The influence of the aluminum content on the pitting corrosion of a 304 stainless steel by a Cl−solution was investigated.The number,area,and composition of non-metallic inclusions were modified by the addition of aluminum in the steel,which was responsible for the variation of the corrosion degree of the 304 stainless steel.Inclusions detection,corrosion test,electrochemical test,thermodynamic calculation,and first-principles calculation were performed to evaluate the pitting corrosion of the stainless steel.The initiation of the pitting corrosion by three types of inclusions,including(Mn,Si,Cr,S)O,(Mn,Al,Cr)O,and Al_(2)O_(3)were in-situ observed.After corroding for 880 min,the corrosion index of(Mn,Si,Cr,S)O,(Mn,Al,Cr)O,and Al_(2)O_(3)was 0.38%,0.02%,and 0.00%min−1,respectively.With the increase in aluminum content in the steel,the pitting potential of the stainless steel was 0.131,0.304,and 0.338 V,respectively,indicating that a higher aluminum content in the steel was beneficial to improving the pitting corrosion resistance of the 304 stainless steel.展开更多
1.Introduction CO_(2)corrosion of pipelines is one of the major threats in the oil and gas industry[1].Chromium steels(CrSs)and more expen-sive stainless steels(SSs)can mitigate CO_(2)corrosion[2,3].A higher content o...1.Introduction CO_(2)corrosion of pipelines is one of the major threats in the oil and gas industry[1].Chromium steels(CrSs)and more expen-sive stainless steels(SSs)can mitigate CO_(2)corrosion[2,3].A higher content of Cr results in greater uniform corrosion resistance to CO_(2),which is generally attributed to the enrichment of Cr in the corro-sion product film[4,5].The film,which mainly consists of FeCO_(3),Fe(OH)_(3),Cr(OH)_(3),and Cr_(2)O_(3),forms a passive layer on the metal surface,and the enrichment of Cr in this layer helps block corro-sive anions from contacting with the steel surface[6-8].展开更多
Mo has been widely reported as a conducive element for the corrosion resistance of massive alloy sys-tems.However,the mechanism of Mo optimizing the corrosion resistance is complicated,and in-depth studies are still r...Mo has been widely reported as a conducive element for the corrosion resistance of massive alloy sys-tems.However,the mechanism of Mo optimizing the corrosion resistance is complicated,and in-depth studies are still required.The present work comprehensively and quantitatively studied the critical influ-ences of Mo on the passivation and repassivation behavior of CoCrFeNi HEA based on the dissolution-diffusion-deposition model proposed in our previous work.The experimental results indicated that Mo remarkably eliminated the metastable pitting corrosion,significantly improved the breakdown potential and perfectly protected the CoCrFeNiMo_(0.2)HEA from pitting corrosion.The modelling and X-ray photo-electron spectroscopy(XPS)results both show that in the passivation process,MoO_(2)was the last product to deposit,thereby existing in the outer layer of the passive film.Mo addition increased the Cr content by weakening the deposition of Fe_(2)O_(3)and Fe_(3)O_(4)and also improved the Cr_(2)O_(3)/Cr(OH)3 ratio by promot-ing deprotonation of Cr(OH)_(3),thus enhancing the quality of passive film.Besides,when pitting corrosion occurred,MoO_(2),MoO_(3),and FeMoO_(4)were the first products to deposit and accelerated the repassivation process of HEA by timely covering the matrix in the pit cavity,thereby preventing further corrosion of the matrix.展开更多
Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of col...Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.展开更多
The pitting corrosion resistance of duplex stainless steels UNS S31803 annealed at different temperatures ranging from 1050 ℃ to 1200 ℃ for 24 h has been investigated by means of potentiostatic critical pitting temp...The pitting corrosion resistance of duplex stainless steels UNS S31803 annealed at different temperatures ranging from 1050 ℃ to 1200 ℃ for 24 h has been investigated by means of potentiostatic critical pitting temperature （CPT）. The microstructural evolution and pit morphologies of the specimens were studied through optical microscopy and scanning electron microscopy. The potentiostatic CPT measurements show that the CPT was elevated with the annealing temperature increased from 1050 ℃ to 1150℃ and decreased as the temperature further increased to 1200 ℃. The specimens annealed at 1150 ℃ exhibited the highest CPTand the best pitting corrosion resistance. The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases. The results were explained by the variation of pitting resistance equivalent number （PREN） of ferrite and austenite phases as the annealing temperature was varied.展开更多
The pitting corrosion behaviors of 7A60 aluminum alloy in the retrogression and re-aging （RRA） temper were investigated by electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, ...The pitting corrosion behaviors of 7A60 aluminum alloy in the retrogression and re-aging （RRA） temper were investigated by electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, and the microstructure and the second phase content of the alloy were observed and determined by scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS）. The results show that there exist two different corrosion stages for 7A60 alloy in 3.5%NaCl solution, and the corrosion process can be detected by the appearance of EIS spectrum with two capacitive time constants and the wavelet fractal dimension D extracted from EN. SEM and EDS results also demonstrate that severe pitting corrosion in 7A60 alloy is mainly caused by electrochemical active MgZn2 particles, secondly by Al2MgCu and Mg2Si. Al7Cu2Fe particles make little contribution to the pitting corrosion of 7A60 alloy.展开更多
Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemic...Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.展开更多
In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary elec...In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary electron microscope(ASPEX PSEM detector),scanning electron microscope(SEM),transmission electron microscope(TEM),scanning Kelvin probe force microscope(SKP),potentiodynamic and potentiostatic polarizations were employed.The results obtained indicate that BASE steel contains Al_(2)O_(3)/Mn S,Al_(2)O_(3) and Mn S inclusions,while REM steels contain(La,Ce,Cr,Fe)-O and(La,Ce,Cr,Fe)-O-S inclusions.Compared with BASE steel,REM steel is more susceptible to induce the metastable pitting nucleation and repassivation,whereas it restrains the transition from metastable pitting to stable pitting.Adding 0.021%rare earth element to BASE steel can reduce the number and area of inclusions,while that of 0.058%can increase the number and enlarged the size of inclusions,which is also the reason that pitting corrosion resistance of 58 REM steel is slightly lower than that of 21 REM steel.In the process of pitting corrosion induced by Al_(2)O_(3)/Mn S inclusions,Mn S is preferentially anodic dissolved,and also the matrix contacted with Al_(2)O_(3) is subsequently anodic dissolved.For REM steels,anodic dissolution preferentially occurs at the boundary between inclusions and matrix,while(La,Ce,Cr,Fe)-O inclusions chemically dissolve in local acidic environment or are separated from steel matrix.The chemically dissolved substance(La^(3+) and Ce^(3+))of(La,Ce,Cr,Fe)-O inclusions are concentrated in pitting pits,which inhibits its continuous growth.展开更多
Effects of Mo and Mn elements on pitting corrosion resistance of lean duplex stainless steel in C1- media solution have been studied. Gravimetric tests in 6 mass% FeCl3 at 35 ℃ and potentiodynamic analysis in 3.5 mas...Effects of Mo and Mn elements on pitting corrosion resistance of lean duplex stainless steel in C1- media solution have been studied. Gravimetric tests in 6 mass% FeCl3 at 35 ℃ and potentiodynamic analysis in 3.5 mass% NaCI were carried out. The corrosion potential （Ecoor） and the pitting potential （Epit） are shifted to a more noble po tential because of the presence of Mo around the pits. While the presence of Mn could sharply reduce the value of pitting resistance equivalent number （PREn） and the pits can be formed more easily. The pits are found generating at the phase with a lower PREn. The identical tendencies between the Epit and PREn of weaker phase are the same. A corrosion mechanism has been proposed to determinate pitting corrosion behavior based on microstructural observations.展开更多
The effect of solution annealing temperature ranging from 950 to 1 200 ℃ on the microstructure and corrosion performance of duplex stainless steel （DSS） 2204 were investigated. The proportion of the ferrite phase i...The effect of solution annealing temperature ranging from 950 to 1 200 ℃ on the microstructure and corrosion performance of duplex stainless steel （DSS） 2204 were investigated. The proportion of the ferrite phase increased while the austenite phase decreased and the ferrite stabilizing elements diluted in the ferrite phase with the increase of annealing temperature. The critical pitting temperature （CPT） of specimens annealed at 1000℃ was higher than those annealed at 950℃, whereas further increasing the annealing temperature to 1200℃ decreased the CPT. The pitting initiation sites were observed in the austenite phase, at the boundary of ferrite/austenite phase and inside the ferrite phase for specimens annealed at 950, 1000℃ and exceeding 1 100℃, respectively. The evolution trend of the CPT and the pit initiation site were analyzed by the pitting resistance equivalent number.展开更多
The pittings of five carbon steels have been studied by using anodic polarization test and microscope observation. The results show that pitting susceptibilities are related to the types and shapes of inclusions which...The pittings of five carbon steels have been studied by using anodic polarization test and microscope observation. The results show that pitting susceptibilities are related to the types and shapes of inclusions which are the sites of pitting initiation. The pitting initiating at inclusion needs a potential which is defined as pitting potential and the pitting potential is determined by the type and shape of inclusion. The influence of oxygen content in steel on pitting potential is also discussed.展开更多
This study researched the relationship between the applied potential and the critical pitting temperature （CPT） of the 304 and new 200 series of stainless steels. The fluctuation about the potential dependent CPT fo...This study researched the relationship between the applied potential and the critical pitting temperature （CPT） of the 304 and new 200 series of stainless steels. The fluctuation about the potential dependent CPT for the stainless steels was investigated and the CPT range was obtained. The difference between the potential dependent CPTs of the 304 and 200 series of stainless steels with an applied potential of 100 mV （ vs SCE）, were presented, and by this means the pitting corrosion resistances of them were compared.展开更多
The effect of the sulfur content on the microstructure and inclusions of 316 L stainless steel was studied by optical microscopy,scanning electron microscopy,and image analysis,and the effect of sulfur on the pitting ...The effect of the sulfur content on the microstructure and inclusions of 316 L stainless steel was studied by optical microscopy,scanning electron microscopy,and image analysis,and the effect of sulfur on the pitting corrosion resistance of 316 L stainless steel was studied by conducting ferric chloride immersion test and plotting the electrochemical polarization curves.The results show that the added sulfur is mainly in the form of manganese sulfide inclusions in 316 L stainless steel.With increases in the sulfur content,the grade and percentage of the sulfide in the steel gradually increased,and its distribution became increasingly dense.When the sulfur content exceeded0.1%,the number of sulfide inclusions in the sample increased sharply.When the sulfur content reached 0.199%,the sulfides in the steel were primarily in spindle form,and a large number of spindles were found to refine the grain size of 316 L stainless steel.The pitting corrosion weight loss rate of 316 L stainless steel increased with increases in the sulfur content,while the pitting potential gradually decreased.However,the pitting potential of 316 L stainless steel rebounded when the sulfur content reached 0.199%,which may be related to the grain refinement of the test steel and requires further study.展开更多
Passive metals have superior resistance to general corrosion but are susceptible to pitting attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Ove...Passive metals have superior resistance to general corrosion but are susceptible to pitting attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Over the past decades, the mechanism of pitting corrosion has attracted corrosion community striving to study. However, the mechanism at the pitting initiation stage is still controversy, due to the difficulty encountered in obtaining precise experimental information with enough spatial resolution.Tracking the accurate sites where initial dissolution occurs as well as the propagation of the dissolution by means of multi-scale characterization is key to deciphering the link between microstructure and corrosion at the atomic scale and clarifying the pitting initiation mechanism. Here, we review our recent progresses in this issue by summarizing the results in three representative materials of 316F, and Super 304H stainless steel as well as 2024-Al alloy, using in situ ex-environmental TEM technique.展开更多
基金supported by the National Natural Science Foundation of China(No.52074130)Engineering Research Center of Resource Utilization of Carbon-containing Waste with Carbon Neutrality,Ministry of Education,200237 Shanghai,PR China.
文摘To advance the understanding of the corrosion behavior of stainless steel bellows in marine atmospheric environments and enhance the precision of service life predictions,this study employs finite element simulations to investigate the pitting corrosion rates and pit morphologies of bellows peaks and troughs under varying electrolyte film thicknesses.The model incorporates localized electrochemical reactions,oxygen concentration,and homogeneous solution reactions.For improved computational accuracy,the fitted polarization curve data were directly applied as nonlinear boundary conditions on the electrode surface via interpolation functions.Simulation results reveal that the peak regions exhibit faster corrosion rates than the trough regions.With increasing electrolyte film thickness(from 10μm to 500μm),corrosion rates at both peaks and troughs decrease progressively,and after 120 hours of simulation,the maximum corrosion rate at the peaks declines from 0.720 mm/a to 0.130 mm/a,and at the troughs from 0.520 mm/a to 0.120 mm/a,with the disparity in corrosion rates diminishing over time.Furthermore,as corrosion progresses,pits propagate deeper into the substrate,exhibiting both vertical penetration and lateral expansion along the passive film interface,ultimately breaching the substrate.This research offers valuable insights into designing corrosion mitigation strategies for stainless steel bellows in marine environments.
基金supported by the National Natural Science Foundation of China(Nos.52364044 and 52204364)Central Guidance on Local Science and Technology Development Fund Projects of Inner Mongolia Autonomous Region(No.2022ZY0090)Basic Scientific Research Business Expenses of Colleges and Universities in Inner Mongolia Autonomous Region(Nos.2023QNJS011 and 0406082226).
文摘The micro-area characterization experiments like scanning Kelvin probe force microscope(SKPFM)and Kernel average misorientation have the defects of complex sample preparation and occasional errors in test results,which makes it impossible to accurately and quickly analyze the pitting behavior induced by inclusions in some cases,prompting attempts to turn to simulation calculation research.The method of calculating band structure and work function can be used to replace current-sensing atomic force microscopy and SKPFM to detect the potential and conductivity of the sample.The band structure results show that Al_(2)O_(3) inclusion is an insulator and non-conductive,and it will not form galvanic corrosion with the matrix.Al_(2)O_(3) inclusion does not dissolve because its work function is higher than that of the matrix.Moreover,the stress concentration of the matrix around the inclusion can be characterized by first-principles calculation coupled with finite element simulation.The results show that the stress concentration degree of the matrix around Al_(2)O_(3) inclusion is serious,and the galvanic corrosion is formed between the high and the low stress concentration areas,which can be used to explain the reason of the pitting induced by Al_(2)O_(3) inclusions.
基金supported by the National Natural Science Foun-dation of China(Nos.U1908219,52171163)the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-CN-2021-2-2)+1 种基金the Applied Basic Research Program of Liaoning Province(grant no.2022JH2/101300005)the Central Guidance for Local Science and Technology Development Funds of Liaoning Province(grant no.2023JH6/100100016).
文摘Precipitation-strengthened HEAs exhibit outstanding integration of strength and toughness at ambient temperature.Nevertheless,precipitates generally reduce the localized corrosion resistance in aggressive solution environments.To solve this problem,a strategy of introducing nano-sized L12 precipitates in CoCrFeNiAlTi HEAs has been proposed in this work.Results demonstrate the pitting corrosion potential can be elevated from 258 mVSCE to 603 mVSCE by increasing the precipitate content to 38 wt.%.Such an improvement in localized corrosion resistance can be attributed to two aspects.Firstly,L12 precipitates tend to be dissolved during the corrosion process,which promotes the heterogeneous nucleation of protective Cr2 O3 due to the rapid deposition of oxides/hydroxides of Al/Ti,and improves the passive film stability due to the Crrich FCC matrix.Secondly,the dissolution kinetic inside the pits can be suppressed on account of the enrichment of Cr element in the FCC matrix,thus inhibiting the pitting growth.In summary,the current work not only reveals the mechanisms of the nano-sized L12 precipitates upon the corrosion behavior,but also provides a strategy for designing corrosion-resistant HEA.
基金supported by the National Natural Science Foundation of China(No.52404354).
文摘Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments,severely compromising its structural integrity.The study systematically investigates the pitting behaviour of 9Cr18 bearing steel under salt spray conditions,focusing on the progressive evolution of surface morphology and cross-sectional characteristics of pits on finished bearings.Scanning electron microscopy,energy-dispersive spectroscopy and X-ray diffraction were employed to examine the surface morphology,elemental composition and phase structure of corrosion products over varying salt spray exposure durations.The results show that 9Cr18 steel exhibits localized pitting with“volcanic crater”-like pits in the early stage of salt spray corrosion.After 48 h,pitting develops into a“multi-point”pattern,marking the initial transition toward uniform corrosion.Until 240 h,corrosion products completely cover the surface,indicating the complete transformation from localized pitting to uniform corrosion.The high carbon and chromium content in 9Cr18 steel promotes carbide precipitation and uneven distribution in the matrix.Cr-depleted regions near the carbide/matrix interface serve as preferential sites for pitting initiation.The low effective utilization of chromium reduces the overall corrosion resistance of 9Cr18.
基金supported by The National Natural Science Foundation of China(Nos.52271053 and 52271096)'the Shanghai Rising-Star Program(No.23QA1400500)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001).
文摘Pitting is a common type of localized corrosion in passive alloys that can cause rapid failure of material or equipment.In the case of stainless steels,non-metallic inclusions have been identified as the most susceptible sites for pitting,and have therefore garnered significant attention.This review critically ex-amines the issue of how inclusions induce pitting,with a particular focus on three mechanisms:sponta-neous dissolution of inclusions,active dissolution of Cr-depleted regions,and propagation of microcracks at the inclusion-matrix interface.While researchers have made significant strides in understanding these mechanisms over the past few decades,many gaps and controversies remain.Details such as the ini-tial driving force of inclusion dissolution and factors affecting Cr-depleted regions require further study.Moreover,some old concepts and methods need to be revised to arrive at more credible conclusions.This review aims to delve deeply into these important issues and provide inspiration for future research.
基金financially supported by the National Natural Science Foundation of China(Grant No.51801220).
文摘The transpassivation and pitting corrosion behavior of a high-nitrogen stainless steel(HNS),Fe18Cr15Mn3Mo0.92N,were systematically investigated by electrochemical analysis,morphology observation,and X-ray photoelectron spectroscopy surface analysis.It was surprisingly found that no pitting corrosion occurred in the transpassivation region of HNS.This electrochemical corrosion behavior is untypical for stainless steels,i.e.,the traditional critical pitting potential method was invalid for HNS.Both N and Cr enrichments in the transpassivation film on HNS were found extremely higher than those in the passivation film.The N existed in the form of[CrN]complex,which could stabilize the above both films.Besides,the corrosion product of N was detected as NH_(3) that exhibited an effective corrosion inhibition effect.On this basis,although the transition of Cr from 3-valent to 6-valent was confirmed,the transpassivation film on HNS still maintained it high stability and no pitting was found to occur.Therefore,the real pitting resistance of HNS should be higher than the expected before.And the stable transpassivation film played an important role in its untypical pitting corrosion resistance.
基金the National Natural Science Foundation of China(Grant No.U22A20171)the High Steel Center(HSC)at North China University of Technology,Yanshan University,and University of Science and Technology Beijing,China.
文摘The influence of the aluminum content on the pitting corrosion of a 304 stainless steel by a Cl−solution was investigated.The number,area,and composition of non-metallic inclusions were modified by the addition of aluminum in the steel,which was responsible for the variation of the corrosion degree of the 304 stainless steel.Inclusions detection,corrosion test,electrochemical test,thermodynamic calculation,and first-principles calculation were performed to evaluate the pitting corrosion of the stainless steel.The initiation of the pitting corrosion by three types of inclusions,including(Mn,Si,Cr,S)O,(Mn,Al,Cr)O,and Al_(2)O_(3)were in-situ observed.After corroding for 880 min,the corrosion index of(Mn,Si,Cr,S)O,(Mn,Al,Cr)O,and Al_(2)O_(3)was 0.38%,0.02%,and 0.00%min−1,respectively.With the increase in aluminum content in the steel,the pitting potential of the stainless steel was 0.131,0.304,and 0.338 V,respectively,indicating that a higher aluminum content in the steel was beneficial to improving the pitting corrosion resistance of the 304 stainless steel.
文摘1.Introduction CO_(2)corrosion of pipelines is one of the major threats in the oil and gas industry[1].Chromium steels(CrSs)and more expen-sive stainless steels(SSs)can mitigate CO_(2)corrosion[2,3].A higher content of Cr results in greater uniform corrosion resistance to CO_(2),which is generally attributed to the enrichment of Cr in the corro-sion product film[4,5].The film,which mainly consists of FeCO_(3),Fe(OH)_(3),Cr(OH)_(3),and Cr_(2)O_(3),forms a passive layer on the metal surface,and the enrichment of Cr in this layer helps block corro-sive anions from contacting with the steel surface[6-8].
基金funded by the National Natural Science Foun-dation of China(Grant Nos.U1960203,52004060,52325406,and 52174308)Science Fund for Distinguished Young Scholars of Liaon-ing Province(Grant No.2023JH6/100500008)Fundamental Re-search Funds for the Central Universities(Grant Nos.N2125017 and N2225031).Special thanks are due to the instrumental analysis from the Analytical and Testing Centre,Northeastern University.
文摘Mo has been widely reported as a conducive element for the corrosion resistance of massive alloy sys-tems.However,the mechanism of Mo optimizing the corrosion resistance is complicated,and in-depth studies are still required.The present work comprehensively and quantitatively studied the critical influ-ences of Mo on the passivation and repassivation behavior of CoCrFeNi HEA based on the dissolution-diffusion-deposition model proposed in our previous work.The experimental results indicated that Mo remarkably eliminated the metastable pitting corrosion,significantly improved the breakdown potential and perfectly protected the CoCrFeNiMo_(0.2)HEA from pitting corrosion.The modelling and X-ray photo-electron spectroscopy(XPS)results both show that in the passivation process,MoO_(2)was the last product to deposit,thereby existing in the outer layer of the passive film.Mo addition increased the Cr content by weakening the deposition of Fe_(2)O_(3)and Fe_(3)O_(4)and also improved the Cr_(2)O_(3)/Cr(OH)3 ratio by promot-ing deprotonation of Cr(OH)_(3),thus enhancing the quality of passive film.Besides,when pitting corrosion occurred,MoO_(2),MoO_(3),and FeMoO_(4)were the first products to deposit and accelerated the repassivation process of HEA by timely covering the matrix in the pit cavity,thereby preventing further corrosion of the matrix.
基金funded by the‘Research Project of the Sucheng to Sihong Section of the Yanluo Expressway-Measurement Technology and Application of Bridge Quality Project Based on UAV Binocular Imaging(No.00-00-JSFW-20230203-029)’,received by H.Z.Wang.
文摘Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.
基金supported by the National Natural Science Foundation of China(Grant Nos.51131008 and 51371053)the National Key Technology R&D Program(No.2012BAE04B00)
文摘The pitting corrosion resistance of duplex stainless steels UNS S31803 annealed at different temperatures ranging from 1050 ℃ to 1200 ℃ for 24 h has been investigated by means of potentiostatic critical pitting temperature （CPT）. The microstructural evolution and pit morphologies of the specimens were studied through optical microscopy and scanning electron microscopy. The potentiostatic CPT measurements show that the CPT was elevated with the annealing temperature increased from 1050 ℃ to 1150℃ and decreased as the temperature further increased to 1200 ℃. The specimens annealed at 1150 ℃ exhibited the highest CPTand the best pitting corrosion resistance. The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases. The results were explained by the variation of pitting resistance equivalent number （PREN） of ferrite and austenite phases as the annealing temperature was varied.
基金Project(13JCZDJC29500)supported by the Key Project of Tianjin Natural Science Foundation,ChinaProjects(2011CB610505,2014CB046801)supported by the National Basic Research Program of ChinaProject(20120032110029)supported by the Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘The pitting corrosion behaviors of 7A60 aluminum alloy in the retrogression and re-aging （RRA） temper were investigated by electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, and the microstructure and the second phase content of the alloy were observed and determined by scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS）. The results show that there exist two different corrosion stages for 7A60 alloy in 3.5%NaCl solution, and the corrosion process can be detected by the appearance of EIS spectrum with two capacitive time constants and the wavelet fractal dimension D extracted from EN. SEM and EDS results also demonstrate that severe pitting corrosion in 7A60 alloy is mainly caused by electrochemical active MgZn2 particles, secondly by Al2MgCu and Mg2Si. Al7Cu2Fe particles make little contribution to the pitting corrosion of 7A60 alloy.
基金supported by the National Natural Science Foundation of China and Baosteel Group Corporation (No.50534010)
文摘Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.
基金supported by the National Natural Science Foundation of China(No.51801219)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2019193)+1 种基金the Scientific Research Project of China Three Gorges Corporation(No.JD-YJ-05006)the National Key Research and Development Program of China(No.2017YFB0702302)。
文摘In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary electron microscope(ASPEX PSEM detector),scanning electron microscope(SEM),transmission electron microscope(TEM),scanning Kelvin probe force microscope(SKP),potentiodynamic and potentiostatic polarizations were employed.The results obtained indicate that BASE steel contains Al_(2)O_(3)/Mn S,Al_(2)O_(3) and Mn S inclusions,while REM steels contain(La,Ce,Cr,Fe)-O and(La,Ce,Cr,Fe)-O-S inclusions.Compared with BASE steel,REM steel is more susceptible to induce the metastable pitting nucleation and repassivation,whereas it restrains the transition from metastable pitting to stable pitting.Adding 0.021%rare earth element to BASE steel can reduce the number and area of inclusions,while that of 0.058%can increase the number and enlarged the size of inclusions,which is also the reason that pitting corrosion resistance of 58 REM steel is slightly lower than that of 21 REM steel.In the process of pitting corrosion induced by Al_(2)O_(3)/Mn S inclusions,Mn S is preferentially anodic dissolved,and also the matrix contacted with Al_(2)O_(3) is subsequently anodic dissolved.For REM steels,anodic dissolution preferentially occurs at the boundary between inclusions and matrix,while(La,Ce,Cr,Fe)-O inclusions chemically dissolve in local acidic environment or are separated from steel matrix.The chemically dissolved substance(La^(3+) and Ce^(3+))of(La,Ce,Cr,Fe)-O inclusions are concentrated in pitting pits,which inhibits its continuous growth.
文摘Effects of Mo and Mn elements on pitting corrosion resistance of lean duplex stainless steel in C1- media solution have been studied. Gravimetric tests in 6 mass% FeCl3 at 35 ℃ and potentiodynamic analysis in 3.5 mass% NaCI were carried out. The corrosion potential （Ecoor） and the pitting potential （Epit） are shifted to a more noble po tential because of the presence of Mo around the pits. While the presence of Mn could sharply reduce the value of pitting resistance equivalent number （PREn） and the pits can be formed more easily. The pits are found generating at the phase with a lower PREn. The identical tendencies between the Epit and PREn of weaker phase are the same. A corrosion mechanism has been proposed to determinate pitting corrosion behavior based on microstructural observations.
基金Item Sponsored by National Natural Science Foundation of China(51131008,51371053)National Key Technology Research and Development Program of China(2012BAE04B00)Doctoral Fund of the Ministry of Education of China(20120071110013)
文摘The effect of solution annealing temperature ranging from 950 to 1 200 ℃ on the microstructure and corrosion performance of duplex stainless steel （DSS） 2204 were investigated. The proportion of the ferrite phase increased while the austenite phase decreased and the ferrite stabilizing elements diluted in the ferrite phase with the increase of annealing temperature. The critical pitting temperature （CPT） of specimens annealed at 1000℃ was higher than those annealed at 950℃, whereas further increasing the annealing temperature to 1200℃ decreased the CPT. The pitting initiation sites were observed in the austenite phase, at the boundary of ferrite/austenite phase and inside the ferrite phase for specimens annealed at 950, 1000℃ and exceeding 1 100℃, respectively. The evolution trend of the CPT and the pit initiation site were analyzed by the pitting resistance equivalent number.
文摘The pittings of five carbon steels have been studied by using anodic polarization test and microscope observation. The results show that pitting susceptibilities are related to the types and shapes of inclusions which are the sites of pitting initiation. The pitting initiating at inclusion needs a potential which is defined as pitting potential and the pitting potential is determined by the type and shape of inclusion. The influence of oxygen content in steel on pitting potential is also discussed.
文摘This study researched the relationship between the applied potential and the critical pitting temperature （CPT） of the 304 and new 200 series of stainless steels. The fluctuation about the potential dependent CPT for the stainless steels was investigated and the CPT range was obtained. The difference between the potential dependent CPTs of the 304 and 200 series of stainless steels with an applied potential of 100 mV （ vs SCE）, were presented, and by this means the pitting corrosion resistances of them were compared.
文摘The effect of the sulfur content on the microstructure and inclusions of 316 L stainless steel was studied by optical microscopy,scanning electron microscopy,and image analysis,and the effect of sulfur on the pitting corrosion resistance of 316 L stainless steel was studied by conducting ferric chloride immersion test and plotting the electrochemical polarization curves.The results show that the added sulfur is mainly in the form of manganese sulfide inclusions in 316 L stainless steel.With increases in the sulfur content,the grade and percentage of the sulfide in the steel gradually increased,and its distribution became increasingly dense.When the sulfur content exceeded0.1%,the number of sulfide inclusions in the sample increased sharply.When the sulfur content reached 0.199%,the sulfides in the steel were primarily in spindle form,and a large number of spindles were found to refine the grain size of 316 L stainless steel.The pitting corrosion weight loss rate of 316 L stainless steel increased with increases in the sulfur content,while the pitting potential gradually decreased.However,the pitting potential of 316 L stainless steel rebounded when the sulfur content reached 0.199%,which may be related to the grain refinement of the test steel and requires further study.
基金supported financially by the National Natural Science Foundation of China (Nos. 51771212 and 11327901)the Innovation Fund in IMR (No. 2017-ZD05)
文摘Passive metals have superior resistance to general corrosion but are susceptible to pitting attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Over the past decades, the mechanism of pitting corrosion has attracted corrosion community striving to study. However, the mechanism at the pitting initiation stage is still controversy, due to the difficulty encountered in obtaining precise experimental information with enough spatial resolution.Tracking the accurate sites where initial dissolution occurs as well as the propagation of the dissolution by means of multi-scale characterization is key to deciphering the link between microstructure and corrosion at the atomic scale and clarifying the pitting initiation mechanism. Here, we review our recent progresses in this issue by summarizing the results in three representative materials of 316F, and Super 304H stainless steel as well as 2024-Al alloy, using in situ ex-environmental TEM technique.
