Duplex Stainless Steel Research Articles

Optimization of gas metal arc welding parameters for dissimilar steel welds: A case study on duplex stainless steel 2205 and stainless steel 316L

The significance of welded connections in steel structures necessitates precise structural designs and processing adaptations to ensure robust mechanical strength and durability. Gas metal arc welding (GMAW) employing controlled curves presents advantages over conventional methods, offering enhanced weld bead properties, improved aesthetics, and reduced thermal inputs. This research investigates the impact of GMAW parameters using controlled curves on the microstructure and geometry of welds between dissimilar structural steels—duplex stainless steel 2205 and stainless steel 316L grade 50—commonly employed in construction. The aim is to optimize the GMAW welding process with controlled curves and surface tension transfer between these dissimilar steels. Through a 23-factorial experimental design encompassing feed speed (Va), arc focus (FC), and peak-to-base amplitude (APB), the study examines welding energy, geometry, deposition efficiency, microstructure, microhardness, tensile strength, and corrosion properties. Optimal welding energy fosters refined microstructures and uniform hardness, aiding in predicting weld throat area. Higher energy levels expand the heat-affected zone and coarse grains, while lower energies escalate variability. Predictive models facilitate fine-tuning welding energy and throat area for desirable properties and penetration while minimizing disruptions. This process optimization can be achieved by employing derived equations that limit welding energy and curve parameters, striking a desired balance between cost, structural integrity, and reliability.

Experimental review and accuracy of etchants used for phase analysis of SAF2507 Super Duplex Stainless Steel

The mechanical and corrosion properties of duplex stainless steels (DSS) depend on the distribution of ferrite and austenite as well as the presence of secondary phases. It is therefore necessary to accurately determine both the distribution of the phases and their morphology. The aim of this research is to define a standard method for the determination of the volume fraction of the phases present in a SAF2507 SDSS by analysing images acquired by light microscope. To do this, the material is heat-treated at 850 °C for 5 min, 15 min, 30 min, 1h, 5h to stimulate the formation of the σ-phase. The metallographic etchant capable of maximising phase contrast is then identified. Micrographic analyses are performed using different reagents at different holding times and temperatures, in order to find the best combination. A standard procedure is then defined for the image analysis. The data obtained were are processed to calculate the phase distribution. The results are compared with the quantitative analysis performed using X-ray diffraction as reference.The research evidence that Kalling's reagent is best etchant for fully solubilised materials, as it accurately estimates ferrite and austenite content. On the other hand, Marble's reagent should be preferred for the detection of σ-phase. For comprehensive analysis of all phases, Murakami's reagent is recommended.The approach defined in this paper not only improves the understanding of the microstructure of DSS, but also provides an important tool for industrial quality control and material characterisation.

Revealing the evolution of microstructure and mechanical properties with deposition energy and shielding gas to achieve phase-balanced directed energy deposition of 2205 duplex stainless steel

Directed energy deposition-arc (DED-arc) manufactured duplex stainless steel (DSS) has shown great potential for use in marine propellers. However, challenges remain in achieving phase-balanced DSS deposits through the DED-arc process. To overcome this, we conducted a study that involved regulating the deposition energy and shielding gas with the use of ER2205 wire. The results show that the austenite content in DSS deposits increases with the increase of deposition energy, and the content in the Ar+2%N2-protected deposits is significantly higher than that of Ar+2%CO2-protected deposits. Ultimately, DSS deposits with balanced phase content (austenite content of ∼48.4 %) are obtained at a line energy of 600 J/mm for DED-arc under Ar+2%N2 protection. Unlike the N loss in Ar+2%CO2-protected samples, more nitrogen elements are introduced into the DSS samples by Ar+2%N2 shielding gas. Ar+2%N2-protected samples contain more austenite and exhibit a more homogeneous microstructure, which results in the solid solution strengthening and a significant reduction in the anisotropy of the tensile properties. Furthermore, a more systematic evolution of the microstructure and tensile properties of DSS deposits under the influence of deposition energy and shielding gas is revealed. This study preliminarily obtains the relationship between the DED-arc parameters, microstructure, and tensile properties of DED-arc-fabricated DSS, which will provide an important reference for tailoring microstructure and properties in additive-manufactured DSS.

Passivation characteristics and corrosion behavior of S32202 duplex stainless steel in different temperatures polluted phosphoric acid

The passivation characteristics of S32202 duplex stainless steel in different temperatures polluted phosphoric acid were studied by electrochemical technology and X-ray photoelectron spectroscopy, and its corrosion behavior was studied through immersion corrosion and electrochemical corrosion. The results indicate that as the temperature increases, the open-circuit potential of the sample in polluted phosphoric acid moves forward, and the surface exhibits a rapid passivation process. The main phases of the passivation film are Fe2O3, Fe3O4, Cr2O3, Cr(OH)3, and corresponding phosphates and polyphosphates. The passivation film of the sample in polluted phosphoric acid exhibits n-p-n composite semiconductor properties. As the temperature increases, the electron density and number of defects in the passivation film increase, and the vulnerability of the passivation film increases. The increase in temperature promotes the formation of a porous thick film. The corrosion types of the sample in polluted phosphoric acid are total corrosion, phase boundary corrosion, and intergranular corrosion, accompanied by pitting corrosion in local areas. The corrosion current density and passivation current density of the sample gradually increase with increasing temperature, while the counter-passivation potential and passivation index decrease, the density and protective properties of the passivation film decrease. The doping of phosphate can alleviate the dissolution process of metals, but the increase in temperature increases the solution ionic activity and accelerates the rate of charge transfer at the interface. At the same time, FePO4, CrPO4 and other phosphates are poorly protected, and their large presence is not conducive to the stability of the passivation film structure, resulting in a decrease in the corrosion resistance of the material.

Prediction of surface roughness in duplex stainless steel top milling using machine learning techniques

Prediction of surface roughness in duplex stainless steel top milling using machine learning techniques

A study on the performance of super duplex stainless steel cladding over mild steel using a CMT welding

Low carbon steels can be cladded with super-duplex stainless steels to enhance the surface’s mechanical and wear properties. The current study examines the impact of process parameters on weld bead geometry and dilution % during cold metal transfer (CMT) cladding of super duplex stainless steel 2507 over low carbon steel. Response Surface Methodology (RSM) with a Central Composite Design matrix was used to optimize the process parameters (welding current, welding speed, and nozzle to workpiece distance (NTD)). The adequacy of the model was checked using an ANOVA analysis. The optimal bead width, height, penetration, and dilution values were 8.05 mm, 4.52 mm, 1.56 mm and 14.64%, respectively. The ideal input parameters were 200 A of welding current, 4.64 mm/s of welding speed, and 14 mm of NTD. The welding speed is the most dominant parameter, followed by the welding current and NTD. The cladding samples were prepared from the optimal parameters. The CMT-clad layer’s microstructure, microhardness, and wear properties were also evaluated. The results indicate a dense crack-free and non-porous clad surface was obtained under optimal conditions.

Surface roughness reduction in electron beam powder bed fusion additive manufacturing of super duplex stainless steel 2507: investigating optimisation techniques and face orientation-dependent irregularities

AbstractThe use of additive manufacturing in metals by powder bed fusion via electron beam (PBF-EB) is increasing for fabricating high-quality parts meeting industrial standards. However, high surface roughness poses a consistent challenge in PBF-EB. This study investigates two novel approaches to optimise surface roughness for a given machine and powder combination. Using machine control software’s recently introduced research mode functionality, we develop customised beam control code to effectively explore a vast parameter space. Additionally, we explored the impact of beam travel direction and spot morphology on surface roughness. Line-melt-based contours were explored by specimen manufacturing with layer-wise parameter change, whilst spot-melting-based samples were built using a full factorial design of experiments with four factors at three levels. Initial sample characterisation was done using a stylus-based contact profilometer, followed by detailed evaluation using focus variation microscopy. Results reveal that increasing beam power and spot energy exacerbate surface roughness. We also find that a well-defined energy distribution at the spot's edge contributes to smoother surfaces. Whilst the influence of beam travel direction on surface roughness remains uncertain, our findings underscore the importance of parameter selection in achieving optimal results. By adjusting contouring parameters, we achieve a vertical roughness of Ra17.7 ± 0.9 (Sa 21.6), significantly lower than in the current literature. These findings advance our understanding of surface roughness optimisation in PBF-EB and offer practical insights for improving part quality in industrial applications. By harnessing tailored beam control strategies, manufacturers can enhance the capabilities of additive manufacturing technologies in producing metal components.

Hot compression recrystallization and processing characteristics of 18 %Cr lean duplex stainless steel with Mn addition

The deformation differences of hot compression tests for 18 % Cr lean duplex stainless steels, alloyed with 3.1 and 5.8 wt% Mn concentrations were comparatively investigated. The deformed microstructure revealed that more Mn promoted the formation of austenitic dislocation cells, inhibited the occurrence of dynamic recrystallization (DRX), and resulted in a decrease in the number of refined austenite grains at lower temperatures and strain rates. Meanwhile, more Mn addition promoted ferrite DRX, and delayed austenite DRX initiation deformed at higher strain rates and lower deformation temperatures. The nearly complete refinement of austenite grains formed due to DRX deformation at 950℃/0.01 s−1 with 3.1 % Mn addition, while fine grains caused by ferrite DRX mainly occurred at 850℃/1 s−1 with 5.8 wt% Mn addition. The relationships between the Zener–Hollomon parameter (Z) and critical strain (stress) were established using the power law relation. The stability processing domains with high power efficiency greater than 0.34 narrowed with increasing Mn content, are located in the temperature range of 1000–1150℃ and strain rate range of 0.01–0.03 s−1, and austenite DRX plays a significant role in compression deformation improvement. At a low deformation temperature of 850 ℃, the work hardening rate in the initial strain increased with increasing Mn addition, and a lower strain rate and deformation temperature contributed to the dynamic deformation softening caused by austenite DRX, but ferrite DRX slightly contributed to the improvement of compression deformation. The DRX kinetics models show that the trend of the volume fraction of DRX as a function of processing variables is in good agreement with experimental data.

Microstructural Evolution, Mechanical and Electrochemical Performance of Duplex Stainless Steel Fabricated by Wire Arc Additive Manufacturing with ER2209 Filler Wire

Microstructural Evolution, Mechanical and Electrochemical Performance of Duplex Stainless Steel Fabricated by Wire Arc Additive Manufacturing with ER2209 Filler Wire

Better mechanical properties of SAF2507 duplex stainless steel formed by cold rolling and normalizing

The SAF2507 duplex stainless steel with the heterogeneous structure is produced through cold rolling (ε = 90%) and subsequent 1-min normalizing at 1273 K. Compared with the corresponding initial samples, the grain sizes of ferrite and austenite phases in the 90%-1273 sample are refined by 90%, which led to an increase in the number of grain or phase boundaries between the two phases. The yield strength (YS) of the 90%-1273 sample increased to 715 MPa from 541 MPa, while the uniform elongation of 24.8% is slightly smaller than that of the coarse-grained sample. The higher YS is mainly contributed by the strengthening of grain refinement and dislocation strengthening by incorporating geometrically necessary dislocations (GNDs). During tensile deformation, the accumulation of GNDs in the heterostructured sample continuously generates hetero-deformation-induced (HDI) stress. The HDI stress plays a positive role in the 90%-1273 sample showing an ultimate tensile strength of 939 MPa. Additionally, the amount of twin boundaries in the 90%-1273 sample rose from 4.5% to 35% during tensile deformation, which indicated that the twinning induced plasticity effect was helpful in retaining the ductility of the 90%-1273 sample. This work provides strategies for optimizing the mechanical properties of duplex stainless steels and contributes to understanding the essence of a superior combination of strength and ductility of heterostructured materials.

A proposal for a simple characterization of stainless steel connections through an equivalent yield strength

Notwithstanding some recent contributions, there still appears to be a gap in the literature regarding the express evaluation of the moment–rotation performance of some connections fabricated from austenitic, duplex, or ferritic stainless steel, such as flush end-plate connections (FEP). In the present work, moving from a previous proposal, the authors investigate a simple approach for the practical characterization of these connections. The results from industry standard software, which is dedicated to the analysis of connections based on the component method and widely used in engineering practice, are compared with the results from a more refined numerical model. It is found that, by using conventional carbon steel procedures with an ad hoc ideal material model, the results can be made in line with some experimentally validated numerical simulations for stainless steel. The findings are discussed in detail and may turn useful from both a design and an assessment standpoint.

Nanoindentation Study on the Local Evaluation of Hydrogen-Induced Hardening Performance of Ferrite and Austenite in 2205 Duplex Stainless Steel: Experiment and Finite Element Modeling

Nanoindentation Study on the Local Evaluation of Hydrogen-Induced Hardening Performance of Ferrite and Austenite in 2205 Duplex Stainless Steel: Experiment and Finite Element Modeling

Dislocation structures and residual stresses in duplex stainless steel fabricated by laser powder bed fusion with 430 and 316L powders

The duplex stainless steel is fabricated using laser powder bed fusion (LPBF), with raw materials prepared by mechanically mixing 430 and 316 L powders in a 1:1 mass ratio. The as-built alloys exhibit good overall mechanical properties, and theoretical strength calculations are performed based on the flow strength model. Uniquely, the distribution of dislocations, residual stresses, and strain accommodation mechanisms are investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the microstructure of the as-built alloys is predominantly ferritic phase, with an austenitic phase content of approximately 4 %. The ultimate tensile strength is 938 ± 4 MPa and the elongation is 19 ± 0.58 %. The as-built alloys possess high dislocation densities, with the dislocation density in the ferritic phases being higher than in the austenitic phases. In particular, austenitic phases present barely any local misorientation and minimal rotations within grains, stacking faults are introduced to accommodate the solidification strains. However, ferritic phases exhibit a high dislocations density, with dislocations present on the (101), (011‾) and (211) planes, accommodating solidification strains and cooling stresses through elastoplastic deformation, and building up geometrically necessary dislocations.

Study of Effects of Post-Weld Heat Treatment Time on Corrosion Behavior and Manufacturing Processes of Super Duplex Stainless SAF 2507 for Advanced Li-Ion Battery Cases.

Lithium-ion batteries are superior energy storage devices that are widely utilized in various fields, from electric cars to small portable electric devices. However, their susceptibility to thermal runaway necessitates improvements in battery case materials to improve their safety. This study used electrochemical analyses, including open-circuit potential (OCP), potentiodynamic polarization, and critical pitting temperature (CPT) analyses, to investigate the corrosion resistance of super duplex stainless steel (SAF 2507) applied to battery cases in relation to post-weld heat treatment (PWHT) time. The microstructure during the manufacture, laser welding, and PWHT was analyzed using field-emission scanning electron microscopy, X-ray diffraction, and electron backscatter diffraction, and the chemical composition was analyzed using dispersive X-ray spectroscopy and electron probe micro-analysis. The PWHT increased the volume fraction of austenite from 5% to 50% over 3 min at 1200 °C; this increased the OCP from -0.21 V to +0.03 V, and increased the CPT from 56 °C to 73 °C. The PWHT effectively improved the corrosion resistance, laying the groundwork for utilizing SAF 2507 in battery case materials. But the alloy segregation and heterogeneous grain morphology after PWHT needs improvement.

Achieving enhanced strength-ductility and wear resistance in directed energy deposited super duplex stainless steel via inoculating NbN particles

In wire-based directed energy deposition (DED), super duplex stainless steel (SDSS) typically encounters issues including coarse grains, a contradictory relationship between strength and ductility, and inferior wear resistance properties. Herein, we report the introduction of micron-sized NbN particles into DEDed SDSS to achieve an optimized combination of fine microstructure, high strength, impressively larger ductility and better wear resistance. During the DED process, NbN inoculant dissolves and re-precipitates, forming fine NbN and σ particles around 100 nm in size. These NbN particles act as nucleation sites for equiaxed grains, refining both ferrite and austenite. In addition, Nb and N elements left from NbN dissolution enhance the solution strengthening effect. These factors collectively boost hardness and strength in DEDed SDSS. Furthermore, the high Nb level in DEDed SDSS facilitates a dense Cr2O3 layer formation on the specimen surface during wear tests, enhancing wear resistance. Increased Nb and N also lower stacking fault energy (SFE) of SDSS austenite, promoting the occurrence of deformation twinning, and the improvement of work hardening and ductility during plastic deformation. This work shows the great potential of wire-arc DED technology to fabricate SDSS with unique microstructures, excellent wear resistance, and an exceptional combination of strength and ductility for practical applications.

Drilling performance analysis on super duplex stainless steel (AISI 2507) using scalable pulse power plasma TiSiN- and AlTiN-coated tools and optimizing machining parameters through Taguchi–Fuzzy approach

Drilling performance analysis on super duplex stainless steel (AISI 2507) using scalable pulse power plasma TiSiN- and AlTiN-coated tools and optimizing machining parameters through Taguchi–Fuzzy approach

Laser powder bed fusion of 2507 duplex stainless steel: Microstructure, mechanical properties, and corrosion performance

Duplex stainless steels offer a unique combination of advantages derived from both ferritic and austenitic structures, providing excellent mechanical properties and corrosion resistance. Nevertheless, conventional metallurgical techniques such as casting and rolling encounter challenges when it comes to the rapid fabrication of intricate components. In this study, we explore the microstructure, mechanical properties, and corrosion performance of 2507 duplex stainless steel manufactured through laser powder bed fusion (L-PBF). Through meticulous refinement of L-PBF parameters, we successfully achieved a dense sample featuring a hardness exceeding 400 HV, a relative density surpassing 98 %, and a surface roughness below 15 μm. This was obtained using a scanning speed of 700 mm/s and a laser power of 210 W. Due to the high cooling rate of L-PBF process, L-PBFed 2507 exhibits a ferritic microstructure distinct from that of rolled 2507 duplex stainless steel. Additionally, a considerable presence of internal dislocations can be observed in the L-PBFed 2507 material. The 2507 stainless steel exhibited an outstanding yield strength of 1198 MPa and an ultimate tensile strength of 1269 MPa, surpassing the performance of rolled 2507 duplex stainless steel. The corrosion current density was nearly negligible (approximately 10−6 A cm−2), with a passivation window expanding 1.2 V relative to the corrosion potential and a passivation platform below 10−4 A cm−2. These corrosion characteristics were comparable to those observed in rolled 2507 duplex stainless steel. This research demonstrates the suitability of L-PBFed 2507 stainless steel in environments requiring high strength and corrosion resistance, thereby opening up avenues for high-performance components in advanced engineering applications.

Hot Corrosion Behavior of Electrical Discharge-Coated Duplex Stainless Steel Under Sulfur Environment

Hot Corrosion Behavior of Electrical Discharge-Coated Duplex Stainless Steel Under Sulfur Environment

Influence of Welding Processes on the Microstructure and Mechanical Properties of Duplex Stainless Steel Parts Fabricated by Wire Arc Additive Manufacturing

Influence of Welding Processes on the Microstructure and Mechanical Properties of Duplex Stainless Steel Parts Fabricated by Wire Arc Additive Manufacturing

Evolution of phase ratio and its effect on residual stress for 2205 duplex stainless steel multipass welded joints by thermo-metallurgical-mechanical model

The control of phase ratio and residual stress is a crucial subject for the structural integrity of duplex stainless steel welded components. Therefore, this paper aims to clarify the evolution of phase ratio and its effect on residual stress for duplex stainless steel multipass welded joints by a thermo-metallurgical-mechanical coupled welding model, alongside the crucial experiments which contribute to the development and validation of the coupled model. The developed model takes both the precipitation and dissolution behavior of austenite under repeated thermal cycles into consideration, thereby demonstrating a remarkable ability to predict the distribution of phase ratio and residual stress. The influencing mechanism of solid-state phase transformation on residual stress is discussed extensively. The results reveal that, for the duplex stainless steel welded joints by gas tungsten arc welding, excessive austenite is often formed within the welding zone particularly for the middle passes, while it is the occurrence of ferritization at the heat affected zone. The effect of phase transformation on residual stress is mainly presented by the change of mechanical properties and phase volume. The overtransformation from ferrite to austenite tends to induce a higher tensile residual stress, vice versa, compressive stress. In addition, it is challenging to achieve phase balance through heat input alone. However, a smaller heat input is recommended to minimize residual stress while ensuring welding penetration. This paper serves as a theoretical foundation for controlling the phase ratio and mitigating residual stress during the welding of duplex stainless steel, thereby contributing to the enhancement of weld quality and structural reliability.