Search Results (99)

The escalating demands of industrial applications, particularly those involving severe wear, temperature, and corrosive environments, present significant challenges for the long-term strength of critical components, often fabricated from high-value materials such as super duplex stainless steel alloys. Super duplex can withstand the corrosive environment (in particular, crevice corrosion and pitting damage) and maintain mechanical integrity sufficient for high-pressure pumping applications such as seawater injection and crude oil. Conventional repair methodologies frequently result in component rejection due to process-induced distortions or detrimental phase transformations, contributing to substantial material waste and hindering the adoption of circular economy principles. This research addresses this issue by developing and validating a novel repair process utilizing laser metal deposition (LMD) additive manufacturing. The research focuses on establishing optimized process parameters to ensure the salvaging and restoration of damaged super duplex components while preserving their requisite mechanical integrity and corrosion resistance, in accordance with industry standards. Comprehensive characterization, including microstructural analysis, chemical composition verification, hardness profiling, and mechanical fatigue testing, confirms the efficacy of the LMD repair process. This work demonstrates the potential for extending the service life of critical components, thereby promoting resource efficiency and contributing to a more sustainable and resilient industrial paradigm. Full article

One of the most critical aspects of turning, and machining in general, is the surface roughness of the finished product, which directly influences the performance, functionality, and longevity of machined components. The accurate prediction of surface roughness is vital for enhancing component quality and machining efficiency. This study presents a machine learning-driven framework for modeling mean roughness depth (Rz) during the dry machining of super duplex stainless steel (SDSS 2507). SDSS 2507 is known for its exceptional mechanical strength and corrosion resistance, but it poses significant challenges in machinability. To address this, this study employs flank-face textured cutting tools to enhance machining performance. Experiments were designed using the L₂₇ orthogonal array with three continuous factors, cutting speed, feed rate, and depth of cut, and one categorical factor, tool texture type (dimple, groove, and wave), along with surface roughness as an output parameter. Gaussian Data Augmentation (GDA) was employed to enrich data variability and strengthen model generalization, resulting in the improved predictive performance of the machine learning models. MATLAB R2021a was employed for preprocessing, the normalization of datasets, and model development. Two models, Least-Squares Support Vector Machine (LSSVM) and Multi-Gene Genetic Programming (MGGP), were trained and evaluated on various statistical metrics. The results showed that both LSSVM and MGGP models learned well from the training data and accurately predicted Rz on the testing data, demonstrating their reliability and strong performance. Of the two models, LSSVM demonstrated superior performance, achieving a training accuracy of 98.14%, a coefficient of determination (R²) of 0.9959, and a root mean squared error (RMSE) of 0.1528. It also maintained strong generalization on the testing data, with 94.36% accuracy and 0.9391 R² and 0.6730 RMSE values. The high predictive accuracy of the LSSVM model highlights its potential for identifying optimal machining parameters and integrating into intelligent process control systems to enhance surface quality and efficiency in the complex machining of materials like SDSS. Full article

This study analyzes the effects of varying H₂S and CO₂ concentrations and temperature on the pH of geothermal fluids flowing through superduplex S32750 stainless-steel pipelines, classified as corrosion-resistant alloys (CRAs). Corrosive decay is evaluated by comparing OLI Studio software simulations with experimental data from the literature. The results indicate that an increase in the partial pressure of either gas lowers pH levels, with temperature exerting a more pronounced exponential effect on corrosion than gas partial pressure. When both gases are present, the dominant gas dictates the corrosion behavior. In cases where CO₂ and H₂S are in equal proportions, FeS₂ forms as the primary corrosive product due to the higher potential corrosivity of H₂S. The H₂S/CO₂ ratio influences the formation of passive films containing chromium oxides or hydroxides (Cr₂O₃, Cr(OH)₃), iron oxides (Fe₂O₃, Fe₃O₄), or iron sulfides (FeS). Full article

Super duplex SAF2507 stainless steel is widely used in petrochemical piping systems during the transport of substances. The pipelines are subjected to cyclic loads due to road vibration and internal pressure, which causes the ratcheting behavior. In this research project, we conducted a battery of uniaxial ratcheting experiments of super duplex SAF2507 stainless steel under displacement cycling, and the effects of stress amplitude, mean stress, and pre-strain on the ratcheting strain were evaluated. The findings showed that ratcheting strain grew as mean stress and stress amplitude rose under identical stress conditions. Additionally, as pre-strain levels increased, the ratcheting strain was observed to diminish. In addition, a three-dimensional ratcheting boundary graph was created with stress amplitude, mean stress, and ratcheting strain rate. This represented a graphical surface area for the study of ratcheting strain rates for various combinations of mean stress and stress amplitude. A rate-independent model was developed by combining the Armstrong–Frederick (A-F) hardening rule with Ohno–Wang (O-W II) model, called the AF-OW II model. This constitutive model was implemented in the ABAQUS 2021 finite element software to numerically analyze the ratcheting evolution of SAF2507 stainless steel. The results indicated that the calculated results of the AF-OW II model closely aligned with the experimental data. Full article

In situ X-ray diffraction has been used to investigate the stability of expanded austenite during annealing in vacuum for the austenitic stainless steel 316Ti, the super-austenitic stainless steel 904L, and the duplex steel 318LN. Expanded austenite has been formed using plasma immersion ion nitriding before. Time-of-flight secondary ion mass spectrometry before and after annealing yielded complementary information regarding nitrogen depth profiles and CrN precipitation using cluster analysis. The decay of expanded austenite during annealing was found to be thermally activated with an activation energy of 1.8 ± 0.3 eV, starting within five minutes at 550 °C and taking more than two hours below 450 °C. The decay occurs simultaneously throughout the whole nitrogen-containing zone—and not at the surface as during nitriding. Nitrogen diffusion occurring in parallel slightly complicates the data analysis. Further transmission electron microscopy investigations are necessary to understand the microstructure after annealing in vacuum. The limit for operating hard and wear-resistant expanded austenite layers at elevated temperatures of up to 350 °C is given, however, by nitrogen diffusion and not the decay into CrN. Full article

Li-ion batteries are at risk of explosions caused by fires, primarily because of the high energy density of Li ions, which raises the temperature. Battery cases are typically made of plastic, aluminum, or SAF30400. Although plastic and aluminum aid weight reduction, their strength and melting points are low. SAF30400 offers excellent strength and corrosion resistance but suffers from work hardening and low high-temperature strength at 700 °C. Additionally, Ni used for plating has a low current density of 25% international copper alloy standard (ICAS). SAF2507 is suitable for use as a Li-ion battery case material because of its excellent strength and corrosion resistance. However, the heterogeneous microstructure of SAF2507 after casting and processing decreases the corrosion resistance, so it requires solution heat treatment. To address these issues, in this study, SAF2507 (780 MPa, 30%) is solution heat-treated at 1100 °C after casting and coated with Ag (ICAS 108.4%) using physical vapor deposition (PVD). Ag is applied at five different thicknesses: 0.5, 1.0, 1.5, 2.0, and 2.5 μm. The surface conditions and electrochemical properties are then examined for each coating thickness. The results indicate that the PVD-coated surface forms a uniform Ag layer, with electrical conductivity increasing from 1.9% ICAS to 72.3% ICAS depending on the Ag coating thickness. This enhancement in conductivity can improve Li-ion battery safety on charge and use. This result is expected to aid the development of advanced Li-ion battery systems in the future. Full article

Super-duplex stainless steels (SDSSs) were introduced in the oil and gas industry due to their high resistance to pitting corrosion, promoted by the high content of alloying elements. The welding process can cause an unbalanced ferrite/austenite microstructure and, consequently, the possibility of deleterious phases, increasing the risk of failure. The aim of this work is to investigate the behavior of the heat-affected zone (HAZ) of SDSS UNS S32750 steel produced with different thermal inputs simulated in a Gleeble^® welding simulator and correlate these findings with its corrosion properties. The pitting resistance was investigated by electrochemical techniques in sodium chloride solution, and the critical pitting temperature (CPT) was calculated for each evaluated microstructure. The material as received presents 46.19 vol% ferrite and a high corrosion resistance, with a CPT of 71.54 °C. HAZ-simulated cycles resulted in similar ferrite percentages, between 54.09 vol% and 57.25 vol%. A relationship was found between heat input, ferrite content, and CPT: increasing the heat input results in greater ferrite content and lowers the CPT, which may favor the pitting corrosion process. Therefore, it is concluded that the ferrite content directly influences the pitting behavior of the material. Full article

The aim of the present study is to investigate the solubility of nitrogen in super or hyper duplex stainless steel, which is characterized by a very high Cr content, as well as the activity interaction parameters between N and other alloy elements. The chemical equilibrium method was employed in the present experiment. High Cr, Ni, and Mo content Fe−Cr−N−O and Fe−Cr−Ni−Mo−N−O melt are equilibrated at 1873 K under atmospheres of pure nitrogen and Ar/N₂ gas mixture. The melts were placed in Al₂O₃ crucibles and coated with graphite crucibles. The experimental results showed that the solubility of N significantly increased with increasing Cr content, reaching over 1 wt pct at a Cr content of about 40 wt pct. In addition, the solubility of Cr increased slightly with a decrease in Ni content and an increase in Mo content. The activity interaction parameters were fitted using WIPF (Wagner’s Interaction Parameter Formalism), as shown as follows: $e_N^{Cr}=-0.07083$, $r_N^{Cr}=+0.0005888$, $r_N^N=-0.00926$, $e_N^{Ni}=+0.30885$, $r_N^{Ni}=-0.03963$, $e_N^{Mo}=-0.05882$, $r_N^{Mo}=+0.00616$; the comprehensive set of thermodynamic basic parameters obtained in this study can be effectively used to assess the N solubility in USSD with a Cr content exceeding 30 wt pct. Full article

Regulating the phase ratio between austenite and ferrite in welded joints is crucial for welding super duplex stainless steel. Nitrogen plays a significant role in maintaining an optimal phase ratio. In this study, the focusing gas channel of gas-focused plasma arc welding was utilized to introduce nitrogen into the arc plasma, which was then transferred to the weld pool. Experiments with and without nitrogen addition were designed and conducted to examine the effects of nitrogen on the microstructure and properties of SDSS 2507 weld joints. The results show that nitrogen addition increased the austenite content in the weld metal from 22.2% to 40.2%. Nitrogen also altered the microstructure of the austenite, changing it from thin grain boundary austenite and small intragranular austenite to a large volume of coarse, side-plate Widmanstätten austenite. The ferrite in the weld metal exhibited a preferred orientation during growth, while the austenite showed a disordered orientation. Additionally, the maximum texture intensity of the ferrite decreased with nitrogen addition. Nitrogen addition led to an increase in the microhardness of the austenite in the weld metal, attributed to the solid solution strengthening effect of nitrogen and increased dislocation tangling, while it decreased the microhardness of the ferrite. This study enhances the welding theory of 2507 super duplex stainless steel and guides the practical application of gas-focused plasma arc welding for 2507 super duplex stainless steel. Full article

Super duplex stainless steel UNS S32750 is widely used in marine industries, pulp and paper industries, and the offshore oil and gas industry. Welding manufacturing is one of the main manufacturing processes to make material into products in the above fields. It is of great importance to obtain high-quality welded UNS S32750 joints. The austenite content and ferrite content in UNS S32750 play an important role in determining UNS S32750 properties such as mechanical properties and corrosion resistance. However, the phase proportion between the ferrite phase and austenite phase in the welded joint will be changed during welding. Lots of research has been done on how to weld UNS S32750 and how to obtain welded joints with good quality. In this work, the recent studies on welding UNS S32750 are categorized based on the welding process. The welding process for UNS S32750 will be classified as gas tungsten arc welding, submerged arc welding, plasma arc welding, laser beam welding, electron beam welding, friction stir welding, and laser-MIG hybrid welding, and each will be reviewed in turn. The microstructure and properties of the joints welded using different welding processes will also be discussed. The critical challenge of balancing the two phases of austenite and ferrite in UNS S32750 welded joints will be discussed. This review about the welding process for UNS S32750 will provide people in the welding field with some advice on welding UNS S32750 super duplex stainless steel. Full article

In this study, the high-temperature deformation behaviour of the UNS S32750 Super Duplex Stainless Steel (SDSS) alloy was investigated by means of deformability and microstructure evolution in the (1050–1200) °C temperature (T) range. The deformability of the UNS S32750 SDSS alloy was investigated by the up-setting method using a gravity-drop hammer, with the following deformation energy/impact energy ($E^{\ast }$): 545.2 J, 1021.5 J, 1480.6 J, and 1905.3 J. Data referring to deformation resistance (${\sigma }_c^{\prime }$) and mechanical work ($A^{\ast }$) as a function of deformation temperature (T) and deformation energy/impact energy ($E^{\ast }$) were obtained and analysed. It was shown that increasing the deformation temperature leads to an increase in the obtained deformation degree (degree of reduction in height). By analysing the rate of increase in the deformation degree as a function of the applied impact energy, it was shown that the rate of increase in the deformation degree rises with the increase in the applied impact energy. Also, it was observed that the evolution of the deformation resistance (${\mathsf{\sigma }}_{\mathrm{c}}^{\prime }$) as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies and that the evolution of the mechanical work (${\mathrm{A}}^{\ast }$) as a function of temperature (T) shows a decreasing tendency while increasing the deformation temperature for all impact energies. The microstructure evolution of the UNS S32750 SDSS alloy was investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy-Electron Backscatter Diffraction (SEM-EBSD) techniques. It was observed that, in all cases, the microstructure shows intensely deformed grains, strongly elongated in the rolling direction in both ferrite (δ) and austenite (γ) intensely deformed grains. The intensity of grain deformation is increasing with the increase in the applied deformation degree. Also, it was observed that increasing the deformation temperature leads to a strong increase in the weight fraction of the dynamically recrystallised (DRX) ferrite (δ) grains. Full article

The influence of laser beam welding parameters (power, welding rate, focusing, head oscillation, shielding gas) on the microstructure, mechanical properties and corrosion resistance of the super-duplex stainless steel SAF 2507 was studied in this paper. The presented results clearly report the effects of welding parameter changes on the character of the steel’s microstructure. The presence of secondary phase M₂N in weld metals has an important influence on their mechanical properties. Optimal mechanical properties, an acceptable ferrite/austenite ratio, and the minimum content of M₂N nitride required in the weld metal were acquired in the case the following application: 1100 W power, welding speed of 10 mm/s, focusing of 4 mm, and pure nitrogen shielding gas (20 L/min). Full article

The super duplex stainless steel (SDSS) powder SAF2507 was deposited using directed energy deposition. In the as-built state, the microstructure consists of a nearly balanced ferrite–austenite ratio, with an austenite content of 47 vol.%, in contrast to the SDSS processed by the powder bed method, which produces a very low austenite content. This work investigated the differences in the microstructure, mechanical and corrosion properties of the “high-austenite” as-built state and the solution-annealed (SA) state (at 1100 °C for 60 min, followed by quenching in water). In the SA state, an increase in austenite content to 55 vol.% was observed. In addition, the partitioning of alloying elements into austenite and ferrite also occurred, the austenite grains coarsened and a ferrite grain size reduction was found. Microstructural changes were evident in the development of the mechanical properties. The increase in austenite content was accompanied by an increase in the elongation, and conversely, both the yield strength and ultimate tensile strength decreased. No secondary phases, such as carbides or sigma phase, were observed in either state. Both the as-built and solution-annealed samples exhibited a passivation zone in model seawater at 70 °C, but at the same time, the corrosion current density (i_corr) of the as-built state was five times higher. Full article

In this work, the influence of powder reuse up to three times on directed energy deposition (DED) with laser processing has been studied. The work was carried out on two different gas atomized powders: a cobalt-based alloy type Stellite^® 21, and a super duplex stainless steel type UNS S32750. One of the main findings is the influence of oxygen content of the reused powder particles on the final quality and densification of the deposited material and the powder catch efficiency of the laser deposition process. There is a direct relationship between a higher surface oxidation of the particles and the presence of oxygen content in the particles and in the as-built materials, as well as oxides, balance of phases (in the case of the super duplex alloy), pores and defects at the micro level in the laser-deposited material, as well as a decrease in the amount of material that actually melts, reducing powder catch efficiency (more than 12% in the worst case scenario) and the initial bead geometry (height and width) that was obtained for the same process parameters when the virgin powder was used (without oxidation and with original morphology of the powder particles). This causes some melting faults, oxides and formation of undesired oxide compounds in the microstructure, and un-balance of phases particularly in the super duplex stainless steel material, reducing the amount of ferrite from 50.1% to 37.4%, affecting in turn material soundness and its mechanical properties, particularly the hardness. However, the Stellite^® 21 alloy type can be reused up to three times, while the super duplex can be reused only once without any major influence of the particles’ surface oxidation on the deposited material quality and hardness. Full article

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. Full article