•The microbiologically influenced corrosion (MIC) of 2205 duplex stainless steel (DSS) caused by sulfate-reducing bacteria (SRB) was studied via high-resolution characterization.•SRB caused severe ...localized corrosion of 2205 DSS.•The breakage of passive film caused by the vulcanization of Fe3O4 and dissolve of Cr2O3 accelerated corrosion process.•Extracellular electron transfer (EET), breakage of the passive film and inhibition of passive film repair contributed to SRB-induced corrosion in this study.
Sulfate-reducing bacteria (SRB)-induced corrosion of 2205 duplex stainless steel (DSS) was investigated via novel high-resolution characterization. After 28 days of immersion, the corrosion rate of coupons in the SRB-inoculated medium was 10 times higher than that of coupons in the sterile medium. Corrosion products were absent from the top-part of the biofilm where acidic −COOH was present, which indicated corrosion was not caused by metabolites. SRB clung to the matrix and mutually dissolved, which may favor electron transmission. Extracellular electron transfer (EET), breakage of the passive film and inhibition of passive film repair contributed to SRB-induced corrosion in this study.
The challenges in Wire Arc Directed Energy Deposition (Wire-DED) of super duplex stainless steels (SDSS) are the growth of large columnar grains and undesirably high austenite content. This results ...in a detrimental effect on the material properties. Here we report the additively manufactured SDSS with the addition of TiN inoculant via Wire-DED. And the effectiveness of incorporating TiN inoculant into additively manufactured SDSS was explored. The addition of trace amounts of TiN reduced the content of the austenite phase from 74.0% to 61.5%. Additionally, the introduction of TiN facilitated deoxidation and slag formation, leading to decreased inclusion content and a shift in inclusion type, which acted as nucleation sites for ferrite, promoting grain refinement. This results in weakened anisotropy of tensile properties and enhanced corrosion resistance. The anisotropy of the ultimate tensile strength and yield strength reduced from 9% to 3% and from 5% to 2%, respectively. This study demonstrates the potential of TiN inoculation in fabricating Wire-DEDed SDSS with tailored microstructures and improved performance, making them suitable for a wide range of practical applications.
•The potential for columnar grain refinement of SDSS through TiN inoculant in the WAAM process was fully investigated.•The addition of TiN plays a crucial role in modifying the type of inclusions and reducing the density of inclusions.•The addition of TiN promotes the balanced ferrite/austenite ratio in SDSS during WAAM process.•The anisotropy of the mechanical properties was weakened due to the role of TiN inoculant in weakening columnar grains.•TiN addition enhanced the pitting potential and corrosion resistance of SDSS.
Corrosion of 2205 duplex stainless steel with different α fractions affected by Pseudomonas aeruginosa was investigated. It was found that P. aeruginosa accelerated pitting corrosion, and an α ...fraction of 53.8% gave the best corrosion resistance, which was related to the highest resistance, and fewest defects of passive films, and least biofilms. Pits appeared at phase boundaries or α phase in biotic media, due to the preferential attachment of bacteria at phase boundaries and their expansion towards α phase. P. aeruginosa kept high volta differences between α and γ phases to promote the anodic dissolution of α phase.
The raw/processed data required to reproduce these findings cannot be shared at this time as the data are related to an ongoing study.
•Pitting corrosion was accelerated significantly by P. aeruginosa.•An α fraction of 53.8% gave the best corrosion resistance.•Pits appeared at phase boundaries or α phase in biotic media.•P. aeruginosa adhered to phase boundaries preferentially and grew towards α phase.•P. aeruginosa kept high volta potential differences between α and γ phases.
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.
Transformation induced plasticity (TRIP) assisted lean duplex stainless steels (LDSS) possess a multi-phase microstructure during deformation due to strain-induced martensite transformation (SIMT). ...The effect of SIMT on the strain partitioning into constituent phases, which in turn affects the SIMT kinetics is highlighted. The individual stress-strain relationships of each phase are obtained via a microstructure-based model and the gradual fragmentation of austenite grain resulted from SIMT is especially considered. A modified model of partitioned strain in the austenite considering the contribution of martensite is proposed, whereby the actual SIMT kinetics in the parent austenite phase can be quantitatively determined. Besides, the contributed strain of each constituent phase during the progress of deformation can be evaluated directly. Furthermore, EBSD and in-situ tensile tests were carried out to characterize the influences of SIMT and resulting high strain localization on the damage evolution. The cracking nucleation initiates at the α/α′ interface as well as the inside of ferrite near the interface. Subsequently, they grow along the α/α’ interface with further straining and, finally, merge into one interfacial crack. The combined crack forks off at the interface with small curvature, then the secondary cracks penetrate into austenite/martensite layer and ferrite layer, respectively, resulting in the final failure. The overall fracture of LDSS shows the ductile feature, although the ferrite and the martensite in the local region of fracture surface show the trace of quasi-cleavage fracture, the remained austenite exhibits dimple-typed fracture.
This review article presents an overview of the dissimilar welded joint's microstructure and mechanical behavior. Dissimilar metal weldings are generally employed in high-pressure ...tubing/tubing-coupler assembly generally functional in subsea oil-gas production instruments and a wide range of geothermal plants and piping systems for subsea manifolds. Thus, dissimilar metal welding has an essential role in enhancing the subsea oil-gas drilling system's structural integrity. Dual-phase super duplex stainless steel 2507 (super DSS 2507) comprises a balanced phase of austenite and ferrite, establishing great attention of manufacturers and researchers due to its mechanical strength and corrosion resistance properties in several hostile surroundings like marine, offshore, petrochemical, and nuclear power plant. The other most frequently used material in the marine application is nitronic steel (N50), primarily used in subsea oil and gas developments in tube and couplers for its corrosion resistance, high strength, and resistance to galling. Nickel-based superalloy Inconel 625 has significant application in the aviation, petrochemical, and marine industry due to its high tensile, yield, and creep strength with excellent corrosion properties in an unfavorable environment. The dissimilar joining of these materials is repeatedly required in marine and offshore industries. This review focuses on the significant difficulties related to the dissimilar welding of super DSS 2507 with nitronic steel (N50) and Inconel 625. Unlike chemical composition, metallurgical properties, mechanical and physical properties of these steel and nickel alloys lead to the problem like stress corrosion cracking, hydrogen embrittlement, ductility dip cracking and migration of carbon. The other metallurgical problems are deleterious secondary phase formation, carbon diffusion-related problem, δ-ferrite phase present in the fusion zone, and residual stresses are required to be removed or decrease their intensity for the qualification of the weld. The effect of intermetallic phases such as sigma phase, FCC carbides like (M23C6, M6C, and M7C3), laves phase, R and χ-phase, Z-phase on the mechanical property of dissimilar welded joints of each material are reviewed in detail. After the extensive literature review, proper selection of filler metal has also been covered in this article because it plays an essential role in decreasing some of the dissimilar welded joint problems. Heterogeneity across the weldment, unmixed zone formation including peninsula, island, beaches, and filler deficient region, grain boundaries related problems during the dissimilar welded joint of these materials is also discussed thoroughly in this article. The effect of residual stresses in the dissimilar welded joint's distinct condition has also been discussed in detail.
•A detailed investigation of the dissimilar metal welded joint of duplex stainless steel with nitronic steel (N50) and Inconel 625.•Characterization of the interface region of the weld metal and base metal.•A discussion on the solidification mechanism of the weld metal and various phases present in it.•Role of the dissimilar Ni-based filler on microstructure and mechanical behavior of the welded joint.
•TIG Welding causes significant changes in morphology and chemical composition of the phases in the heat affected zone (HAZ).•Thermo-mechanical simulation was used to study the effects of the thermal ...parameter on the microstructure evolution in the HAZ.•Electrochemical polarization showed the different passivation behaviour of the phases in the HAZ.•Surface potential surveys revealed the reduction in internal galvanic activity in the duplex HAZ.
A Gleeble-simulated microstructure of the heat-affected zone (HAZ) of tungsten inert gas (TIG) welded grade 2205 duplex stainless steel (DSS) has been produced. Local changes in microstructure chemistry were correlated to galvanic activity using scanning Kelvin probe force microscopy (SKPFM) and electro-chemical polarization. The simulated HAZ had a marked reduction of SKPFM measured Volta potentials. This was reflected in a clear reduction of the electrochemical potential difference of the activation peak between the ferrite and austenite phase. The implications of these observations are discussed for reducing the likelihood of environmentally assisted cracking.
•Corrosion behaviour of welded lean duplex stainless steel in 1M NaCl was evaluated.•Potentiodynamic and electrochemical impedance spectroscopy tests were applied.•Variable welding parameters forces ...changes in properties of passive oxide film.•Corrosion resistance of welds can be improved to the level of the parent metal.•High austenite content in welds is beneficial for corrosion resistance.
The corrosion characterisation of lean duplex stainless steel (1.4662) UNS S82441 welded joints using the potentiodynamic test and electrochemical impedance spectroscopy in 1M NaCl solution are discussed. The influence of autogenous TIG welding parameters (amount of heat input and composition of shielding gases like Ar and Ar–N2 and an Ar–He mixture), as well as A-TIG welding was studied. The influence of welding parameters on phase balance, microstructural changes and the protective properties of passive oxide films formed at the open circuit potential or during the anodic polarisation were studied.
From the results of the potentiodynamic test and electrochemical impedance spectroscopy of TIG and A-TiG, welded joints show a lower corrosion resistance compared to non-welded parent metal, but introducing heat input properly during welding and applying shielding gases rich in nitrogen or helium can increase austenitic phase content, which is beneficial for corrosion resistance, and improves surface oxide layer resistance in 1M NaCl solution.
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The fusion zone microstructure and mechanical properties of UNS S32750 joints obtained from gas tungsten arc (GTA), gas metal arc (GMA) and flux cored arc (FCA) welding processes were ...investigated. The formation of grain boundary, Widmanstätten and intragranular austenite were observed in the fusion zone of the weldments. Electron back scattered diffraction (EBSD) analysis confirmed the presence of chi (ψ) and sigma (σ) phases in the reheated fusion zones of all the weldments. Tensile failures occurred at the fusion zone for all the weldments and the joint efficiency was found to be greater for GTA welds than the others. The number of welding passes and heat input had a significant impact on the ferrite: austenite ratio. FCA weldments experienced inferior notch toughness at both room temperature and sub-zero temperature owing to the prominent amount of secondary austenite and precipitation of intermetallic phases compared to the other weldments.
The influence of varying the annealing temperature from 1000 °C to 1200 °C on the strain-hardening behavior of a lean duplex stainless steel with a metastable austenite phase was investigated by ...tensile deformation. The results indicated that the tensile properties of the test steel were sensitive to the annealing temperature. The test steel showed enhanced ultimate tensile strength (UTS) and elongation due to the transformation-induced plasticity (TRIP) or/and the twinning-induced plasticity (TWIP) effects. The optimum combination of UTS and ductility with approximately 60 GPa% was obtained at an annealing temperature of 1050 °C. The shape of the strain-hardening curve for the selected annealing temperature range could be divided into two cases: (i) a typical three-stage strain-hardening from 1000 to 1050 °C and (ii) a multiple-stage strain-hardening from 1100 to 1200 °C. Microstructural observations revealed that the typical three-stage hardening was mainly related to a strain-induced martensitic transformation with a sequence of γ→ε→α’, i.e., the TRIP effect. In addition to the strain-induced martensites, mechanical twins were observed in the deformed austenite of the specimens annealed at temperatures above 1100 °C. This result indicated that TRIP and TWIP occurred concurrently in the austenite at higher annealing temperatures. The synergy and mutual competition from the coexistence of TRIP and TWIP caused the multiple-stage strain-hardening.
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