The effect of tensile elastic stress on passivation behavior and surface chemistry of 2205 duplex stainless steel is investigated. Elastic stress increases the potential drop at the film/solution ...interface, donor density and defects diffusion coefficient, resulting in the increase of passive current density. High elastic stress (≥60%σs) leads to the generation of soluble CrO3, the increase of oxidized Cr and Fe(Ⅱ) content and the decrease of film thickness, resulting in the quasi-steady-state current density no longer independent of potential. Passive film become denser from spontaneous passivation to primary passivation and Fe(III) compounds dominate the passive film under secondary passivation.
•Passivation of 2205 DSS under elastic stress is studied.•Elastic stress results in the increase of Iss by decreasing d and increasing φf/s, ND, and D0.•High elastic stress (≥60% σs) leads to further increase of Iss, which is no longer independent of potential.•Elastic stress facilitates the increase of oxidized Cr and Fe(Ⅱ) content.•Potential makes passive film become denser until transpassivation occurs.
•Surface oxide layers formed on 2304 duplex stainless steel are investigated.•The native surface and the passivated surface are compared.•An innovative coupling of XPS and ToF-SIMS is used.•The oxide ...layers formed on austenite and ferrite phases are locally characterized.•The effect of passivation on the surface oxide layer is discussed.
This work reports an innovative methodology based on the coupling of XPS and ToF-SIMS in order to study the surface oxide layer formed on austenite and ferrite phases of duplex stainless steels. The native oxide film obtained after mechanical polishing and the passive film obtained after electrochemical passivation in 0.05 M H2SO4 were investigated. Chromium and molybdenum contents were found to be higher in the oxide layer formed on ferrite phase. Nickel and nitrogen enrichments were found to be more pronounced under the oxide layer formed on austenite phase. The effect of passivation on the surface oxide layer is discussed.
•WAAM process is a promising technology for fabricating super duplex stainless steel components.•WAAM processed SDSS 2594 exhibited excellent pitting resistance and corrosion rate ranged between 1.54 ...and 1.61 mpy.•The PREN was > 40 for all samples and conforms the NACE standards recommended for oil and gas industries.•DLEPR test revealed no sensitization, which is due to the absence of detrimental phases and comparable microstructure.
This work investigates the understanding between microstructure and corrosion behaviour of SDSS 2594 wall component fabricated using gas metal arc welding (GMAW) based wire arc additive manufacturing (WAAM) process, with the help of optical micrographs and electrochemical corrosion tests. Potentiodynamic polarization tests and Electrochemical impedance spectroscopy (EIS) analysis in 3.5% NaCl solution revealed excellent pitting resistance while the corrosion rate ranged between 1.51 and 1.61 mils per year (mpy) with pitting resistance equivalent number (PREN) > 40. The intergranular corrosion (IGC) test results confirmed the absence of sensitization and highlights that the formation of passive film is compact for corrosive environments.
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•Grain size dependent lacy pit covers were observed.•Pitting corrosion occurred via selective dissolution.•Pit morphology was grain size dependent.•Pit stability products <0.3 Am−1 ...(as received) and <0.6 Am−1 (heat treated) were obtained.
The nucleation and growth of pitting corrosion in grade 2202 lean duplex stainless steel has been observed via X-ray Computed Tomography. The charge measured using an electro-chemical in-situ cell was correlated with pit growth characteristics and associated pit shape morphologies. Lacy metal covers were observed with holes formed by selective dissolution of the ferrite. All pits grew into semi-ellipsoid shapes, with large fractions of un-dissolved austenite grains remaining inside pits in heat-treated microstructures. For the as-received microstructure the stability product showed typical values below 0.3 Am−1, with larger stability values observed for the heat-treated sample.
Super duplex stainless steels (SDSS), widely used in industries such as offshore oil and gas, offer a unique combination of high strength and corrosion resistance. However, surface hardening ...treatments are crucial to enhance their performance and extend service life. This work investigates the effect of plasma nitriding on the tribological behaviour of SDSS SAF 2507. Samples are treated without prior polishing (as received, AR) at ultra-low temperatures (250 and 300 °C) aiming to avoid detrimental CrN precipitation. Comprehensive microstructural characterization, corrosion studies, and tribological tests (scratch and ball-on-disc) are conducted on samples that do not present CrN (PN). Results indicate that the hardness of PN samples nearly doubles that of AR samples due to the presence of expanded austenite. Corrosion tests show improvements in passivity for PN samples. In scratch tests, while the AR material undergoes progressive plastic deformation, in PN material the nitrided layer breaks down only after reaching a critical load. In ball-on-disc test, wear rates are remarkably lower for PN condition compared to AR condition. Wear mechanism is tribo-oxidative and abrasive for the AR condition. Wear of PN samples is characterized by asperity break-off and ratcheting. The nitrided layer in PN samples exhibits an enhanced load-bearing capacity that improves wear resistance in both tests.
•SDSS without previous polishing (AR) was plasma nitrided at 250 °C and 300 °C.•Plasma nitrided AR at 250 °C (PN) does not present Cr nitrides.•PN has an expanded austenite layer of 2 μm thickness.•PN has enhanced passivity and hardness than that of untreated material.•The good load-bearing capacity of PN increased its wear resistance.
In this paper, submerged friction stir welding (SFSW), capable of significantly weakening the welding thermal cycle compared to conventional FSW, was employed on SAF2507 super duplex stainless steel ...(SDSS). An ultrafine grained (UFG) dual-phase microstructure, characterized by more uniformly distributed and balanced alpha (α) and gamma (γ) phases with average grain sizes of 0.96 and 0.77 µm, respectively, was achieved in the stir zone (SZ). Such unique microstructure leads to a synergistic enhancement of tensile strength and ductility in the longitudinal SZ at room temperature, which increases from 840 MPa to 18% under AFSW condition to 915 MPa - 22%. As well, this UFG dual-phase microstructure plays a crucial role in determining the resultant higher corrosion resistance. Combining with the reduced width of entire joint, a transverse SFSW joint with a remarkable increased total elongation was successfully achieved. In addition, the relatively lower residual stress across the whole joint actually contributed to the increment of ductility in the SFSW joint, as compared to the traditional FSW joint. The aforementioned results demonstrate an effective strategy in achieving a completely balanced UFG microstructure across the whole SZ during SFSW and a concurrent improvement of strength, elongation and corrosion resistance.
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•Submerged FSW is first employed to avoid the undesirable phase transformation in SDSS.•The thermal cycle of stir zone during submerged FSW of SDSS is revealed for the first time.•A superior FSW joint with excellent combination of high strength and ductility is achieved.•The residual stress and anti corrosion behavior of the submerged FSW joint is discussed in detail.
Microscale changes in the microstructure of and stress distribution in a polycrystalline duplex stainless steel comprising ferrite and austenite caused by plastic tensile deformation are ...characterized to understand the microscopic processes of the crystal plasticity of dual-phase steel. Because the ferrite of the body-centered-cubic structure and the austenite of the face-centered-cubic structure exhibit different mechanical properties, texture changes in the ferrite and austenite caused by uniaxial tensile deformation are investigated based on the electron backscatter diffraction pattern. Residual stresses formed by tensile deformation are characterized using a two-dimensional method based on X-ray diffraction. The results show that the steel exhibits a banded microstructure of ferritic coarse grains and austenitic fine grains, and that the texture is changed by tensile deformation. The grains in the steel are rotated by tensile deformation depending on their orientation with respect to the tensile axis. Residual stress measurements demonstrate that compressive stresses remain in the elastically hard ferrite after tensile deformation, whereas tensile stresses remain in the austenitic phase. The formation of the residual stresses are discussed based on the characteristic microscale plasticity of ferrite and austenite.
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•The existence of a textured heterogeneous microstructure at the millimetric scale of a WAAM material is observed via optical observations and Electron BackScatter Diffraction.•The ...existence of deformation field heterogeneities under uniaxial tension in the plastic domain of a WAAM material is observed via Digital Image Correlation.•The existence of stress field heterogeneities under uniaxial tension in the elastic domain of a WAAM material is observed via Thermoelastic Stress Analysis.•The observed mechanical field heterogeneities are compared and linked to the microstructural heterogeneities.
Wire and Arc Additive Manufacturing (WAAM) is particularly well suited to the fabrication of large-scale structural components. Its use for the deposition of Duplex Stainless Steel (DSS) structures is especially sought upon by the naval industry. Although additively manufactured materials usually come with heterogeneous microstructure, residual stresses, internal and surface defects that must not jeopardize the structural integrity of components. In this context, the present study aims to analyse the as-deposited microstructure of a WAAM DSS and its influence on the mechanical behaviour via mechanical field measurement using both Digital Image Correlation (DIC) and Thermoelastic Stress Analysis (TSA).
The pitting corrosion behaviour of 27%Cr–7%Ni (2707) hyper‐duplex stainless steel (HDSS) at ambient temperature has been assessed using a novel bipolar electrochemistry test set‐up. Application of ...this technique generates a linear potential gradient at the surface of the HDSS 2707 test piece, which allows assessment of the pitting corrosion behaviour at ambient temperature. Pit nucleation and associated growth kinetics can be obtained and characterised. To assess pitting corrosion in high‐alloyed HDSS, the normal bipolar test method had to be modified by superimposing an auxiliary potential. This new test set‐up was demonstrated by characterising the nucleation of pits and associated pit growth kinetics. The latter occurred either at austenite/ferrite interphase or inside ferrite phase, with pit growth within the ferrite phase in the HCl environment.
The method of modified bipolar electrochemistry, which involves the addition of an auxiliary potential, has been effectively employed for assessing the pitting corrosion of the hyper‐duplex stainless steel 2707 at ambient temperature. The pits are initiated at the junction of austenite and ferrite or inside of ferrite, then, propagate by consuming the ferrite.
Microbiologically influenced corrosion (MIC) of 2205 duplex stainless steel (DSS) in the presence of Pseudomonas aeruginosa was investigated through electrochemical and surface analyses. The ...electrochemical results showed that P. aeruginosa significantly reduced the corrosion resistance of 2205 DSS. Confocal laser scanning microscopy (CLSM) images showed that the depths of the largest pits on 2205 DSS with and without P. aeruginosa were 14.0 and 4.9μm, respectively, indicating that the pitting corrosion was accelerated by P. aeruginosa. X-ray photoelectron spectroscopy (XPS) results revealed that CrO3 and CrN formed on the 2205 DSS surface in the presence of P. aeruginosa.
•LPR and EIS showed that P. aeruginosa reduced the corrosion resistance of 2205 DSS.•The largest pit depth on 2205 DSS was 4.9μm after 14days incubation in sterile medium.•The largest pit depth on 2205 DSS was 14μm after 14days incubation with P. aeruginosa.•The accelerated pitting was due to the formation of CrO3 and CrN by P. aeruginosa.
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