Duplex Stainless Steel Research Articles

Experimental Study on Tribological Properties of Coated Surface and Textured Surface under Seawater Lubrication Conditions

In order to improve the tribological properties of the flow distribution pair of the seawater axial piston pump, SAF2507 super duplex stainless steel and carbon-fiber-reinforced polyetheretherketone (CF/PEEK) were selected as the matching materials. The surface coating treatment and surface texture treatment were carried out on the flow distribution pair, and the friction and wear test were carried out by MMD-5A. In order to fully understand the friction and wear properties of the surface coating flow distribution pair and the surface texture flow distribution pair, and analyze the friction and wear mechanism, the data of the friction coefficient, wear loss, and wear surface morphology were obtained in the experiment. The results show that the coating surface has little difference in the test, the texture surface significantly reduces the friction coefficient, and the wear scar density is significantly reduced. Adding texture to the surface of the lower sample is better than adding it to the surface of the upper sample. The research results are helpful in improving the tribological performance of the flow distribution pair of the seawater axial piston pump.

Cavitation Erosion of the Austenitic Manganese Layers Deposited by Pulsed Current Electric Arc Welding on Duplex Stainless Steel Substrates

Fe-Mn-Cr-Ni alloys like Citomangan, delivered in the form of powders, tubular wires, and coated electrodes, are intended for welding deposition operations to create wear-resistant layers. Their main characteristic is their high capacity for surface mechanical work-hardening under high shock loads, along with high toughness and wear resistance. In order to increase the resistance to cavitation erosion, hardfacing of Duplex stainless steel X2CrNiMoN22-5-3 with Citomangan alloy was performed using a new welding technique, namely one that uses a universal TIG source adapted for manual welding with a coated electrode in pulsed current. Cavitation tests were conducted in accordance with the requirements of ASTM G32—2016 standard. Comparing the characteristic cavitation erosion parameters of the manganese austenitic layer, deposited by this new welding technique, with those of the reference steel, highlights an 8–11 times increase in its resistance to cavitation erosion. Metallographic investigations by optical microscopy and scanning electron microscopy (SEM), as well as hardness measurements, were carried out to understand the cavitation phenomena.

PVD coating strategies: Developing a combination of AlCrN and AlTiSiN for enhanced surface performance during threading of super duplex stainless steel

Super duplex stainless steel (SDSS) is one of the difficult-to-machine materials due to its high tendency to work-harden and low thermal conductivity. According to recent findings, PVD hard coatings based on Al, Cr, and Ti are recommended for SDSS machining. In this work, three different PVD coating systems were applied for the threading process of SDSS. Monolayer Al50Cr50N, Al60Cr40N, and multilayer Al60Cr40N/Al50Ti45Si5N were deposited on cemented carbide inserts. This paper highlighted the effect of alloying and coating architecture design on the cutting tools' mechanical properties, tribological characteristics, and wear performance. A novel balanced combination of AlCrN/AlTiSiN multilayer coating with a Si content of 5 at. % was proposed, and it exhibited improved adhesion, beneficial mechanical properties, and superior cutting tool life. Furthermore, tribological characteristics under extreme environments were analyzed through a heavy-load, high-temperature tribometer, as well as XPS and AES measurements. The surface integrity of workpiece material machined by various coatings was also examined through microstructure, microhardness, and residual stress measurements. The depth profiles of residual stress reveal that the machining process significantly impacts the outcome, influenced by the tribological properties of the coatings. Specifically, the AlCrN/AlTiSiN coating exhibits a minimal effect on the surface. These investigations enhance the comprehension of the mechanisms that cause material mechanical surface transformation in threading operations, contributing to a deeper understanding of machining processes.

CORROSION EVALUATION OF LPBF-MANUFACTURED DUPLEX STAINLESS STEEL

In this study, the effect of as built and heat-treated additively manufactured 2507 super duplex stainless steel (SDSS) on electrochemical corrosion performance was examined. The corrosion was studied by Tafel polarization and electrochemical impedance spectroscopy (EIS) methods in a 3.5% NaCl solution. For this purpose, the as-built and heat-treated printed samples (solution annealed and stress-relieved) were examined by LOM/SEM and X-ray diffraction to evaluate the phase changes of steel at different processing stages. The correlation between corrosion resistance, structure, and heat treatment was assessed. As a result of the very fast cooling rate of the LPBF process, SDSS reveals ferrite as the major phase in the printed samples. To enhance the corrosion resistance of LPBF-produced duplex stainless steel, it's crucial to balance its two-phase structure and minimize residual stresses. The ferrite grains are elongated in the build direction, with some austenite precipitation along the grain boundaries or as Widmanstatten laths. The stress-relieved and as-printed SDSS exhibits reduced corrosion characteristics by around 20% compared to the solution-annealed SDSS, according to anodic polarization curves. Based on EIS results, the solution-annealed SDSS revealed an almost double increase in corrosion resistance (based on charge transfer resistance values) compared to the as-printed and stress-relieved conditions.

On the divergent effects of stress on the self-organizing nanostructure due to spinodal decomposition in duplex stainless steel

Duplex stainless steels suffer from serious embrittlement due to the self-organization of the nanostructure caused by phase separation (PS) in ferrite. As duplex stainless steel (DSS) components are often subjected to stress during service, the effect of elastic tensile stress (ETS) on phase separation (PS) in alloy 2507 has been investigated in this study. The alloy was aged at 400 and 450 °C for different times under an applied ETS. The nanostructure evolution and mechanical properties were analyzed using small-angle neutron scattering and analytical transmission electron microscopy as well as Vickers-hardness and nanoindentation measurements. The results show that the applied ETS can suppress spinodal decomposition (SD) in ferrite in DSS 2507, which may be due to that ETS increases the critical compositional fluctuation wavelength for SD and thus increases the diffusion distance and barrier to the occurrence of SD. The suppressive effect is more obvious at longer aging time for the same level of applied stresses. It is also indicated that the suppressive effect of ETS seems to change non-monotonically with stress levels and the medium stress level is likely to have the largest suppressive effect. The suppressive effect of ETS on PS may significantly delay the embrittlement and extend the service longevity of DSS components within the miscibility gap. These results further the understanding of the effect of ETS on PS and elastic stress should be considered in the configurations of computational simulations of PS and evaluation of the service longevity of DSS components.

In situ chemical analysis of duplex stainless steel weld by laser induced breakdown spectroscopy

The high corrosion resistance and good mechanical properties of duplex stainless steel (DSS) are due to its special chemical composition, which is a balanced phase ratio of ferrite (α) and austenite (γ). Many industrial applications require the integration of DSS components. For this, Gas tungsten arc welding (GTAW) is an excellent choice, as it allows an automated operation with high reproducibility. However, when the weld pool solidifies, critical ratios of α- and γ- phases can occur, which lead to solidification cracking, increased susceptibility to corrosion, and a decrease in ductility and critical strength. Previous studies have shown that these defects can be caused by the accumulation of manganese and chromium in the heat affected zone (HAZ), requiring ongoing monitoring of this accumulation. A suitable method for such monitoring is laser-induced breakdown spectroscopy (LIBS), which can be used in two operating modes: calibration using standard reference samples and calibration-free. Unlike conventional quantitative LIBS measurements, which require reference samples to generate a calibration curve, calibration-free LIBS (CF-LIBS) allows chemical compositions to be determined solely from the emission spectrum of the plasma. Numerous publications show that CF-LIBS is a fast and efficient analytical method for the quantitative analysis of metal samples. In this work, CF-LIBS is applied to spectra obtained during GTAW DSS welding and the result is compared with those obtained by PLS analysis. A good correlation was found between both types of analysis, demonstrating the suitability of the CF-LIBS method for this application. The CF-LIBS method has a significant advantage over conventional LIBS due to the rapid in situ measurement of concentrations of major alloying elements without calibration procedure. This, combined with fast feedback and appropriate adjustment of welding parameters, helps prevent welding defects.

Effect of Secondary Phase on Electroless Ni Plating Behaviour of Super Duplex Stainless Steel SAF2507 for Advanced Li-Ion Battery Case.

The development of Li-ion battery cases requires superior electrical conductivity, strength, and corrosion resistance for both cathode and anode to enhance safety and performance. Among the various battery case materials, super duplex stainless steel (SDSS), which is composed of austenite and ferrite as two-phase stainless steel, exhibits outstanding strength and corrosion resistance. However, stainless steel, which is an iron-based material, tends to have lower electrical conductivity. Nevertheless, nickel-plating SDSS can achieve excellent electrical conductivity, making it suitable for Li-ion battery cases. Therefore, this study analysed the plating behaviour of SDSS plates after nickel plating to leverage their exceptional strength and corrosion resistance. Electroless Ni plating was performed to analyse the plating behaviour, and the plating behaviour was studied with reference to different plating durations. Heat treatment was conducted at 1000 °C for one hour, followed by cooling at 50 °C/s. Post-heat treatment, the analysis of phases was executed using FE-SEM, EDS, and EPMA. Electroless Ni plating was performed at 60-300 s. The plating duration after the heat treatment was up to 300 s, and the behaviour of the materials was observed using FE-SEM. The phase analysis concerning different plating durations was conducted using XRD. Post-heat treatment, the precipitated secondary phases in SAF2507 were identified as Sigma, Chi, and CrN, approximating a 13% distribution. During the electroless Ni plating, the secondary phase exhibited a plating rate equivalent to that of ferrite, entirely plating at around 180 s. Further increments in plating time displayed growth of the plating layer from the austenite direction towards the ferrite, accompanied by a reduced influence from the substrate. Despite the differences in composition, both the secondary phase and austenite demonstrated comparable plating rates, showing that electroless Ni plating on SDSS was primarily influenced by the substrate, a finding which was primarily confirmed through phase analysis.

Microstructural and Corrosion Behavior of Thin Sheet of Stainless Steel-Grade Super Duplex 2507 by Gas Tungsten Arc Welding

<div>Super duplex stainless steel (SDSS) is a type of stainless steel made of chromium (Cr), nickel (Ni), and iron (Fe). In the present work, a 1.6 mm wide thin sheet of SDSS is joined using gas tungsten arc welding (GTAW). The ideal parameter for a bead-on-plate trial is found, and 0.216 kJ/mm of heat input is used for welding. As an outcome of the welding heating cycle and subsequent cooling, a microstructural study revealed coarse microstructure in the heat-affected zone and weld zone. The corrosion rate for welded joints is 9.3% higher than the base metal rate. Following the corrosion test, scanning electron microscope (SEM) analysis revealed that the welded joint’s oxide development generated a larger corrosive attack on the weld surface than the base metal surface. The percentages of chromium (12.5%) and molybdenum (24%) in the welded joints are less than those in the base metal of SDSS, as per energy dispersive X-ray (EDX) analysis. Corrosion modeling is done using the COMSOL Multiphysics software. Electrochemical corrosion modeling is used to determine the electrolyte potential (i.e., 0.09 V) and current density (i.e., 0.2 A/m<sup>2</sup> to 1.8 A/m<sup>2</sup>). An entire mesh model contains 6240 elements. The largest and smallest element sizes are 4 mm and 0.1 mm, respectively. The maximum element rate of growth is 1.2.</div>

Correction: Gargalis et al. A Comparative Investigation of Duplex and Super Duplex Stainless Steels Processed through Laser Powder Bed Fusion. Metals 2023, 13, 1897

In the original publication [...]

Low temperature nitriding behavior in annealed 2205 duplex stainless steel

ABSTRACT Low-temperature gaseous nitriding response of annealed 2205 stainless steel was investigated through a series of nitriding treatments at different temperatures in the range 380–430°C for 25 h. Reflected light microscopy, X-ray diffraction and hardness indentation were utilized to investigate the dependence of the formation of nitrides and cracks on pre annealing temperatures and subsequent nitriding parameters. For most annealing and nitriding conditions applied, the surface adjacent region of the steels was transformed into expanded austenite, or a mixture of expanded austenite and expanded ferrite, supplemented by the presence of iron-based nitrides. Nitriding at a relatively low temperature at a gentle nitriding potential was found to be acceptable as it resulted in a sound nitrided case, where neither chromium nitrides nor cracks developed. Annealing at a relatively low temperature can improve the threshold of nitriding temperature up to 400°C without cracking, while annealing at a high temperature promotes the formation of nitrides.

Physical simulation of low temperature phase separation during multipass welding of super duplex stainless steel

This study aimed to investigate the degree of low-temperature phase separations and 475 °C -embrittlement in physically simulated multipass super duplex stainless steel (SDSS) welds. A single bead weld was produced using gas metal arc welding and multiple thermal cycles with different peak temperatures were applied using a Gleeble physical simulator with fixed and moving jaws to simulate the influence of constrained designs, to mimic the welding of thick SDSS components. The samples were studied using atom probe tomography and the results were correlated with toughness and ferrite microhardness. The results showed that the microhardness of the ferrite in the constrained simulated multipass reheated weld increased from 304 HV to 374 HV after 5 min aging at 475 °C. The amplitude of the Cr concentration of the same sample, showing the level of Fe-Cr phase separation, increased from 1.025 to 1.045 after 5 min aging at 475 °C. Despite the clear development of phase separation in the ferrite, the toughness did not drop. It can be concluded that reheated SDSS welds are not susceptible to 475 °C -embrittlement during short fabrication times of up to 5 min for the austenite level of 50%.

Comparative statistical analysis of pitting in Two 2205 duplex stainless steel variants

The inherent variability of pitting poses challenges in accurately evaluating the pitting resistance due to potential disparities in test results. This study compares the pitting resistance of two commercial 2205 duplex stainless steels. Counterintuitively, the variant with higher Pitting Resistance Equivalent Number, exhibits a lower Critical Pitting Temperature. Through the potentiostatic pulse test and potentiostatic polarization, this variant is observed to have a greater number of pitting initiation sites. Further investigation, using SEM inclusion statistics, reveals an increased presence of inclusions rich in calcium oxides as the underlying cause of this unexpected phenomenon.

Experimental investigation of cold-formed stainless steel built-up closed section stub columns

This paper presents an experimental investigation on the performance of cold-formed stainless steel built-up closed section stub columns. The built-up sections were composed by assembling two channel components at the flanges, which were brake-pressed from high-strength austenitic and duplex stainless steel thin sheets. Three types of built-up sectional profiles were formed by connecting two unstiffened channels (i.e., unlipped channels), two edge-stiffened channels (i.e., lipped channels) as well as one unstiffened channel and one edge-stiffened channel, respectively, using self-plugging rivets. Four sectional series were devised to cover nominal overall web height-to-plate thickness ratio values of 50, 60, 67 and 80. In order to obtain the actual material properties considering the cold-work effect, tensile coupon tests were carried out on both flat and corner longitudinal coupon specimens. In addition, a total of 29 fixed-ended stub columns including 19 specimens without holes and 10 specimens with circular web holes were tested under axial compression. The experimental results involving failure modes, ultimate capacities and responses of load versus axial shortening were obtained and fully documented. The effects of sectional profile types, overall web height-to-plate thickness ratio and hole diameter-to-overall web height ratio on the performance of cold-formed stainless steel built-up closed section stub columns were examined. Moreover, the appropriateness of design rules as prescribed in the recently updated American Specification ASCE/SEI 8–22 was evaluated. It was revealed that the codified design provisions generally provided unconservative strength predictions for the high-strength austenitic and duplex stainless steel built-up closed section stub columns both without and with circular web holes. Reliability analyses were performed in this study, and the compressive strength predictions of the built-up closed sections according to the existing design rules were found to be unreliable for the high-strength austenitic stainless steel stub columns without holes as well as the duplex stainless steel stub columns without and with circular web holes.

Microstructures and Corrosion/Localised Corrosion of Stainless Steels, Incoloy and Their Weldments in Nitrite-Containing Chloride Environments.

Prompted by the unexpected observation of the pitting of the weldments of a highly corrosion- and pitting-resistant duplex stainless steel, SAF2507, in chloride solutions with nitride addition, the pitting and corrosion resistance of SAF2507 and its weldments were investigated in chloride solutions with and without different levels of nitrite. The Incoloy 825 and 316L austenitic stainless steels were included for the purpose of developing a comparative appreciation. The microstructures of the weldments were characterised, and 316L showed a profound influence of nitrite addition in inhibiting pitting, while 'meta-stable' pitting transients that were clearly visible in the chloride solution without nitrite were absent when nitrite was added. Both the parent metal and the weldment of SAF2507 had similar pitting potential (Ep) in 0.1 M NaCl without nitrite, which was the highest Ep among the three alloys tested. Additions of nitrite at low concentrations had an inhibitive effect on pitting, whereas higher nitrite contents had a deleterious effect on pitting resistance. On the other hand, Incoloy 825 showed a trend of Ep ennoblement with an increasing nitrite content of 0.1 M NaCl, and the weldment underwent greater ennoblement. Moreover, 316L showed a trend similar to Incoloy 825; however, the Ep ennoblements were significantly more pronounced for both the weldment and the base metal of 316L.

Correction to “Dynamic and localized microelectrochemical approaches to evaluate the corrosion resistance of newly developed lean duplex stainless steel alloys”

Correction to “Dynamic and localized microelectrochemical approaches to evaluate the corrosion resistance of newly developed lean duplex stainless steel alloys”

Synergistic addition of Cu and Ce enhanced sulfate reducing bacteria-assisted corrosion cracking resistance of 2205 duplex stainless steel

The corrosion behaviors of 2205, 2205-Cu, and 2205-Cu-Ce duplex stainless steels (DSSs) were studied under static load in the presence of sulfate-reducing bacteria (SRB). The results demonstrated that the addition of Cu and Ce effectively enhanced the resistance of 2205 DSS to SRB-assisted cracking, and 2205-Cu-Ce DSS exhibited the best corrosion resistance and mechanical properties. The Synergistic addition of Cu and Ce not only inhibited the formation of SRB biofilm but also enhanced the hydrogen-induced cracking resistance of DSSs due to the hydrogen trapping by Cu-rich precipitates.

Properties of Duplex Stainless Steels

Properties of Duplex Stainless Steels

Corrosion of Duplex Stainless Steel Manufactured by Laser Powder Bed Fusion: A Critical Review

Corrosion of Duplex Stainless Steel Manufactured by Laser Powder Bed Fusion: A Critical Review

Stress corrosion cracking behavior and mechanism of 2205 duplex stainless steel under applied polarization potentials

In this work, a non-steady electrochemical model for assessing stress corrosion cracking (SCC) of 2205 duplex stainless steel (DSS) under applied polarization potentials was proposed, and the SCC mechanism was revealed. With the negative shift of potentials, hydrogen enhances SCC susceptibility by deteriorating passive film, inhibiting repassivation and causing serious damage. In particular, at −850 mV (vs. SCE), the synergetic effect of anodic dissolution (AD) and hydrogen embrittlement (HE) causes severe pitting and SCC. The negative shift of applied potentials changes the preferential pit/SCC initiation site due to high hydrogen concentration in austenite.

Study on pitting behavior of HDR duplex stainless steel at different film-forming potentials

Study on pitting behavior of HDR duplex stainless steel at different film-forming potentials