A comparison of the pitting corrosion resistances of the 304 and new 200 series of stainless steels by potential dependent critical pitting corrosion temperatures

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.

Temperature effect on the corrosion and passivation characterization of Ni_(82.3)Cr_7Fe_3Si_(4.5)B_(3.2) alloy in acidic media

The effects of temperature on corrosion and the electrochemical behavior of Ni82.3Cr7Fe3Si4.5B3.2 glassy alloy in HC1,H2SO4,and H3PO4 acids were studied using AC and DC techniques.Impedance data reveal that the susceptibility to localized corrosion increases with increasing temperature.Potentiodynamic polarization curves reveal that the bulk glassy alloy is spontaneously passivated at all the investigated temperature in H2SO4 and H3PO4 solutions.A localized corrosion effect in HCl solution is clearly observed.The apparent activation energies in the regions of Tafel,active,and passive,as well as the enthalpies and entropies of the dissolution process were determined and discussed.The high apparent activation energy（Ea） value for H3PO4 solution in Tafel region is explained by the low aggressivity of PO4^3- ions.

High Temperature Corrosion of Water Wall Materials T23 and T24 in Simulated Furnace Atmospheres

Candidate materials for water wall of supercritical and ultra-supercritical utility boilers,T23 and T24,were chosen as the experimental samples and exposed to oxidizing atmosphere,reducing atmosphere and oxidizing/reducing alternating atmosphere separately.The corrosion temperature was 450-550?C.The effects of oxygen con-tent and temperature on the corrosion in reducing atmosphere and alternating atmosphere were investigated.The scanning electron microscope(SEM) and energy dispersive spectrometer(EDS) were used to examine the corroded samples.The results show that the corrosion kinetics of T23 and T24 can be described by the double logarithmic equation and parabolic equation respectively.To describe the corrosion of materials accurately it is not sufficient to analyze the macro-mass gain and the macro-thickness of the corroded layer only,but the EDS should be applied to examine the migration depth of corrosive elements O and S.It is revealed that the corrosion becomes more severe when H2S is present in the corrosive gas.S is more active than O,and Cr can reduce the migration of oxygen but not S.The combination corrosion of S and O and pure [S] has a stronger corrodibility than pure H2S.T24 suffers the most severe corrosion at oxygen content of 0.8%.Corrosion is aggravated when the corrosion temperature is above 450 ℃ in the alternating atmosphere.T23 has better corrosion resistance than T24 and W contributes a lot to the corrosion resistance of T23.

Influence of Ambient-Temperature Corrosion on the Oxidation Behavior of Al-Si Coatings

The high temperature oxidation behavior of Al Si coatings on the Ni base superalloy DZ125, with and without the ambient temperature corrosion test, was investigated. The results show that the isothermal oxidation behavior of the corroded coating changes, which has the higher mass gain than that of the original coating during the initial oxidation stage. Moreover, the cyclic oxidation resistance of the corroded coating decreases severely. The oxide scale was primarily composed of Al 2O 3, contaminated ...

CO_(2) High Temperature Corrosion and Its Prevention of Chromia Forming Fe-base Alloys

High temperature corrosion of chromia forming Fe-base alloys by CO_(2) produces not only oxidation but also carburisation.The corrosion kinetics in CO_(2)-rich gas is found to be increased compared with that in air or oxygen.As a result,higher alloy chromium levels are required to achieve protective chromia formation in CO_(2).Corrosion reaction mechanisms in CO_(2) are examined and the internal carburisation of alloys in low carbon activity CO_(2) gases are analysed based on the variation of pO_(2) at the interface of oxide and metal.Carbon penetration through chromia oxide scale has been revealed by atom probe tomography.The strategies to resist CO_(2) corrosion are reviewed by alloying of Si and/or Mn,forming additional diffusion barrier layers,and by adding sulphur to modify oxide grain boundaries to reduce carbon diffusion along the grain boundaries.

INFLUENCES OF SMALL AMOUNTS OF Y AND Ce ON HIGH TEMPERATURE CORROSION PROPERTIES OF M38 ALLOY

High temperature corrosion properties of M38 alloy with and without 0.04 wt-%Y and 0.05 wt-%Ce additions were studied in equilibrated S0_(2)+0_(2)gas mixtures at 850℃and 900℃.It was found that adding Y or Ce decreased the corrosion rate of M38 and changed considerably the surface morphologies and composition of corrosion products on M38.The effectiveness of Y and Ce were also discussed.

2D Materials as Protective Coating against Low and Middle Temperature (100°C - 300°C) Corrosion-Erosion in Waste to Energy Plant: Case of Graphene

The combustion of MSW contains several species which if liberated into the flue gas will participate in erosion-corrosion reactions with the alloy surface and with the oxide layers. Actually with the evolution of material science and the discovery of 2D materials, we can handle that situation as well as possible. The graphene as 2D material presents a lot of advantage due to it physical properties such: melting point, boiling point and thermal conductivity, which can help to manage the problem of low and middle temperature (100°C - 300°C) erosion-corrosion into the boiler wall of waste to energy. The aim of the study was focused on analyzing the resistance at low and middle temperature (100°C - 300°C) in the enclosed environment and the corrosion-erosion resistance abilities of the graphene sheet as the 2D protective coating material. This paper analyzed the possibility of using the graphene in the aggressive environment which is waste to energy boiler. The results obtained from this study after simulation using ANSYS software which is one of the best software for simulations showed that Graphene protects the furnace walls against corrosion-erosion for temperatures lower than 400°C and that in the presence of certain impurities such as: sodium (Na), sulfur (S), chloride (Cl) and Phos- phorous (P), Sodium Chloride (NaCl), Hydrogen Chloride (HCl), Dioxide of Carbone (CO2) and Dioxide of Sulfur (SO2).

Accelerated Corrosion of Pure Fe Induced by Gaseous ZnCl_2 at High Tempreratures

ZnCl2 is one of the dominant aggressive species in waste incinerators or other advanced combustion power generation systems. In this study, the influence of minor amount of gaseous ZnCl2 on the corrosion behavior of pure iron was examined at 600-800℃ in a pure oxygen environment. The corrosion rate usually increased markedly with increasing temperatures at a fixed ZnCl2 content or with increased ZnCl2 contents at a constant temperature. The corrosion products were composed of a thin outer layer of ZnFe2O4 spinel and an inner zone with a much thicker layer of Fe2O3, which exhibited a serious separation from the matrix. Moreover, a molten FeCl2 layer was observed at the scale substrate interface. The accelerated corrosion of pure iron was attributed to the existence of FeCl2 with low melting point on the metal surface, which destroyed the cohesion and adhesion of the oxide scale. The results are discussed in relation to the thermodynamic factors and the presence of volatile compounds in the reaction system.

Influence of microstructure on the corrosion resistance of Fe–44Ni thin films

An Fe–44Ni nanocrystalline（NC） alloy thin film was prepared through electrodeposition. The relation between the microstructure and corrosion behavior of the NC film was investigated using electrochemical methods and chemical analysis approaches. The results show that the NC film is composed of a face-centered cubic phase（γ-（Fe,Ni）） and a body-centered cubic phase（α-（Fe,Ni）） when it is annealed at temperatures less than 400℃. The corrosion resistance increases with the increase in grain size, and the corresponding corrosion process is controlled by oxygen reduction. The NC films annealed at 500℃ and 600℃ do not exhibit the same pattern, although their grain sizes are considerably large. This result is attributed to the existence of an anodic phase, Fe0.947Ni0.054, in these films. Under this condition, the related corrosion process is synthetically controlled by anodic dissolution and depolarization.

Analysis of cracks origin behaviors during sulfide stress corrosion (SSC) in HSLA steel at different temperatures by electrochemical noise

The sulfide stress corrosion(SSC)behaviors of the high strength low alloy steel at the different temperatures were investigated by the microstructural observation and electrochemical noise(EN)analysis.With the corrosion temperature increasing from 20 to 40℃,SSC ruptured time is prolonged.The increase in corrosion temperature results in the decrease of the saturation solubility of H_(2)S in the solution and thus increases pH value of solution.The increase in corrosion temperature decreases the size of the holes and cracks in the corrosion product film on the surface of the sample,which is due to the formation of the dense FeS corrosion product film.The current kurtosis results indicate that the time for the first occurrence of crack initiation is postponed by the increase in the corrosion temperature.The standard deviation of current noise signals,current kurtosis,power spectral density and energy distribution plot results shows a great consistency,which suggests that EN analysis method can reflect SSC behaviors in real time.

Uniform corrosion behavior of FeCrAl alloys in borated and lithiated high temperature water

The uniform corrosion behavior of model FeCrAl alloys as well as commercial Zircaloy-4 as reference material were investigated in 360℃borated and lithiated water.The results reveal that FeCrAl alloys exhibited better corrosion resistance than Zircaloy-4.It is found that the oxide films formed on the FeCrAl alloys are composed of outer Fe_(3)O_(4)layer,inner layer consisting of compact spinel layer and porous spinel layer,and transition layer containing Al-Cr-rich oxides and matrix enriched with Fe°.The spinel oxides in the inner layer are FeFe_(2-x-y-z)Cr_(x)Al_(y)MozO_(4).The corrosion mechanism of FeCrAl alloys in high temperature water is discussed.

Effect of temperature on corrosion behavior of alloy 690 in high temperature hydrogenated water

The influence of temperature on the corrosion behavior of Alloy 690 is evaluated using potentiodynamic polarization curves, electrochemical impedance spectra （EIS）, scanning electron microscopy （SEM）, X- ray photoelectron spectroscopy （XPS） and transmission electron microscopy （TEM）. The corrosion rate of Alloy 690 reaches a local maximum at 250℃. The kinetic control step of the growth of oxide film changes from the diffusion process of aqueous-phase ions to the growth of Cr-rich barrier layer in the temperature range of 200-300 ℃. A modified double-layer model is proposed to describe the effect of temperature on the structure and composition of the oxide film.

Role of welding residual strain and ductility dip cracking on corrosion fatigue behavior of Alloy 52/52M dissimilar metal weld in borated and lithiated high-temperature water

Corrosion fatigue behavior of Alloy 52/52 M dissimilar metal weld(DMW)was investigated in borated and lithiated high-temperature water.The fatigue life of Alloy 52/52 M DMW in high-temperature water decreased in comparison with that in air.The fatigue cracks initiated at Alloy 52 M butt weld or at the interface of Alloy 52 buttering and Alloy 52 M butt weld.The welding residual strain and ductility dip cracking in Alloy 52 M butt weld promoted the initiation and propagation of fatigue cracks.The environmentally assisted fatigue damage in high-temperature water is discussed by taking account of microstructure defects.

Influence of Conductivity on Corrosion Behavior of 304 Stainless Steel in High Temperature Aqueous Environment

The influence of conductivity on corrosion behavior of 304 stainless steel （SS） in high temperature water was investigated by using in-situ potentiodynamic polarization curves, electrochemical impedance spectra （EIS） at 300 ℃, and ex-situ scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and X-ray pho- toelectron spectroscopy （XPS）. The structures of oxide films formed on 304 SS change with different conductivities at 300 ℃. With the increase in conductivity, the passive current density increases while the resistances of oxide films decrease. But the resistances do not decrease lineally with the increase in conductivity. A modified double-layer model for oxide structure was proposed to explain the influence mechanism of conductivity on the oxide films on 304 SS in high temperature water. Improving the 10B enrichment level can reduce the conductivity of primary water and increase the corrosion resistance of 304 SS.

Proton irradiation assisted localized corrosion and stress corrosion cracking in 304 nuclear grade stainless steel in simulated primary PWR water

Localized deformation and corrosion in irradiated 304 nuclear grade stainless steel in simulated primary water were investigated.The investigation was conducted by comparing the deformation structure,the oxide scale formed at the deformation structure,and their correlation with cracking.The results revealed that increasing the irradiation dose promoted localized corrosion at the slip step and grain boundary,which was primarily attributed to the strain concentration induced by enhanced localized deformation and depletion of Cr at grain boundary.Further,a synergic effect of the enhanced localized deformation and localized corrosion at the slip step and grain boundary caused a higher cracking susceptibility of the irradiated steel.

Effects of cutting parameter on microstructure and corrosion behavior of 304 stainless steel in simulated primary water

The influence of surface conditions on the corrosion behavior of engineering structures has been paid more attention.However,there is still a lack of systematic research on the effect of cutting parameters on material’s microstructure and performance in service.In this paper,the effect of cutting parameters on microstructure and corrosion behaviors of 304 stainless steel in simulated primary water is well investigated.The results show that different cutting parameters can cause the superficial layer a gradient microstructure with nanocrystalized layer on top and deformation band structures underneath.With the similar surface roughness,the deformation microstructure can be very different due to the different cutting parameters.The effect degree on the depth of deformation zone is feed rate>cutting depth>cutting speed.The larger feed rate,lower cutting depth,lower cutting rate may induce a deeper deformation zone.With the increasing depth away from the machined surface,the localized corrosion rate is decreased,and at the same depth the localized corrosion rate along the deformation bands is higher than that along the grain boundaries(GBs).The nanocrystalized surface has a smallest general corrosion rate due to the quick formation of Cr rich oxide film.However,once the corrosion penetrates through this nanocrystalized layer,subsequent preferential corrosion at deformation bands and GBs will dominate and may lead to the significant increase of corrosion rate of the component in high temperature pressurized water.

Corrosion behavior of Ti60 alloy under continuous NaCl solution spraying at 600℃

The corrosion behavior of Ti60 alloy was investigated under continuous NaCl solution spraying at 600℃.Results indicate that the corrosion rate of the Ti60 alloy is lower than that obtained with the solid NaCl deposit film in HO+O.The outer corrosion products are compact layers mainly containing NaTiOand nanocrystalline TiO.The inner layer is mainly composed of TiO,Ti O and SnO.TiO has a lamellar structure,and TiO has a strip-shaped structure.A mixed corrosion mechanism including classic oxidation and active oxidation occurred under NaCl solution spraying environment:the first stage was controlled by the classic oxidation mechanism with the promotion by the active oxidation following parabolic curves,and the second stage was controlled by the active oxidation mechanism following a linear rise in the mass gain curve.The mixed corrosion mechanism between classic oxidation and active oxidation produced a relatively dense Ti oxides scale,which decreased the corrosion rate.

Effects of surface grinding for scratched alloy 690TT tube in PWR nuclear power plant:Microstructure and stress corrosion cracking

Alloy 690TT tube samples with different scratch depths were repaired by grinding treatments using abra-sive papers of two different particle sizes.The microstructure and stress corrosion cracking(SCC)behavior were studied in detail.During grinding,the plastic accumulation zone vulnerable to SCC was removed.Meanwhile,some residual slip steps remained in the scratched area.Corrosion tests lasting 1000,2000,3000,and 4000 h show that the sensitivity and risk of SCC in the scratched area are decreased by grind-ing.Treatment using abrasive particles of a smaller size is more effective.Nevertheless,deep scratches remained hazardous even after the grinding.

Evaluation of Ni-Fe base alloys as inert anode for low-temperature aluminium electrolysis

Isothermal oxidation behaviors of Ni–Fe(wt.%)and of the same alloy with additions of 10 and 15%Cr alloys in the air at 800℃and 900℃and their anodic behaviors in aluminum electrolysis system at 800℃were evaluated.The composition morphologies of oxide scales were characterized by XRD,SEM,and EDS.Results show that the scales formed on Ni–Fe alloy at both temperatures consisted of an inner(Ni,Fe)Olayer and an outer FeOlayer.For Ni–Fe–10Cr alloy,an external(Ni,Fe)O/FeOlayers and an internal oxidation zone were formed at 800°C,while a continuous CrOlayer forms at the internal oxidation zone/substrate interface at 900°C.A multilayer structure oxide of CrO/(Ni,Fe,Cr)O/(Ni,Fe)O/FeOwas formed on Ni–Fe–15Cr alloy at 800°C,while at 900℃the FeObecomes discontinuous disperses in the(Ni,Fe)Olayer close to the surface.Increases in oxidation temperature or Cr content for Ni–Fe–Cr alloys promote the growth of the inner CrOlayer and simultaneously reduce FeOcontent.After 4 h of electrolysis at an anode current density of 0.25 A cm,the oxidation resistance of Ni–Fe–15Cr anode is superior to the Ni–Fe anode.

Crack Initiation Mechanism of Z3CN20.09M Duplex Stainless Steel during Corrosion Fatigue in Water and Air at 290 °C

The crack initiation mechanism of a Z3CN20.09M duplex stainless steel （DSS） during corrosion fatigue （CF） in water and air at 290 ℃ was investigated by using a CF cracking machine and a scanning electron microscopy （SEM）. The cracks were initiated successively at the persistent stip bands （PSBs）, phase boundaries （PBs） and pitting corrosion points （PCPs） of the specimens when they were tested in water at 290 ℃, while in airat 290 ℃ the cracks were only initiated at the PSBs and PBs. And the cracks were found mainly to initiate at the PSBs and PBs when the specimens were tested in water and air at 290 ℃, respectively. The results also reveal that the cracks were likely to be initiated at the first 20% of fatigue life of the specimens tested in water at 290 ℃. However, the cracks were not found until 50% of fatigue life when tested in air at 290 ℃. Moreover, the crack numbers of the specimens tested in water at 290 ℃ were much more than those tested in air at 290 ℃.