S32750 Super Duplex Stainless Steel Research Articles

A Review of Welding Process for UNS S32750 Super Duplex Stainless Steel.

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.

High-Temperature Deformation Behaviour of UNS S32750 Super Duplex Stainless Steel (SDSS) Alloy.

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∗): 545.2 J, 1021.5 J, 1480.6 J, and 1905.3 J. Data referring to deformation resistance (σc') and mechanical work (A∗) as a function of deformation temperature (T) and deformation energy/impact energy (E∗) 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 (σc') 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 (A∗) 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.

High-speed cutting performance characteristics of Ti(C, N)–W cermet tools against S32750 super-duplex stainless steel round bars

In this study, TiC0.5N0.5–60 wt% W and TiC0.5N0.5–70 wt% W cermet cutting tool specimens consisting of Ti(C, N) core, W-rich Ti(C, N) rim, and W-based alloy phases with much higher strengths than conventional heat-resistant tool materials at temperatures above 1673 K were fabricated by spark plasma sintering, electric discharging, and polishing. The cutting performance characteristics of the cermet cutting tool specimens were then examined and compared with those of commercially available NX2525, JX1, and HTi10 cutting tool specimens when cutting S32750 super-duplex stainless steel round bars under dry condition at a cutting speed of 800 m/min. The NX2525, JX1, and HTi10 specimens were TiC–Ni-based cermet containing Mo, Nb, and Co, WC–Al2O3-based composites, and WC–Co cemented carbide, respectively. The TiC0.5N0.5–70 wt% W and TiC0.5N0.5–60 wt% W cermet cutting tool specimens exhibited the first and second longest lifetimes among all the noncoated cutting tool specimens. The lifetime of the TiC0.5N0.5–70 wt% W cermet cutting tool specimen was extended by coating it with TiAlN film by physical vapor deposition. In contrast, the TiC0.5N0.5–60 wt% W and TiC0.5N0.5–70 wt% W cermet specimens exhibited compressive strengths much higher than those of the NX2525, JX1, and HTi10 specimens at 1973 K, whereas all the specimens exhibited similar compressive strengths at room temperature.

Microstructural Characterization of Aged Welded Joints of a UNS S32750 Superduplex Stainless Steel

Microstructural Characterization of Aged Welded Joints of a UNS S32750 Superduplex Stainless Steel

Tribocorrosion assessment of low-temperature plasma nitrided super duplex stainless steel

The tribocorrosion of low-temperature plasma nitrided UNS S32750 super duplex stainless steel was investigated according to procedures for passivating materials. Nitrided and non-treated samples were compared through two reciprocating sliding tests in NaCl solution: the continuous test, without significant passive layer growth, and the intermittent one, with repassivation. Open circuit potential and linear polarization resistance (LPR) characterized the electrochemical response. LPR was successfully introduced to evaluate the polarization resistance evolution during the continuous test. Corrosion and mechanical wear components were quantified. The mechanical wear dominated, and nitrided samples showed lower wear volume loss. After the intermittent test, their values were further reduced. Such improvement was explained by the higher load bearing capacity and repassivation ability of the nitrided surfaces.

Machinability investigation of S32750 super duplex stainless steel using magnetorheological fluid-assisted nano polished cemented carbide tool inserts

Machinability investigation of S32750 super duplex stainless steel using magnetorheological fluid-assisted nano polished cemented carbide tool inserts

Machinability investigation of S32750 super duplex stainless steel using magnetorheological fluid-assisted nano polished cemented carbide tool inserts

Machinability investigation of S32750 super duplex stainless steel using magnetorheological fluid-assisted nano polished cemented carbide tool inserts

Influence of Si and Mo on the Sigma-Phase Precipitation in S32750 Super Duplex Stainless Steel Slab

In this study, we investigated the effect of Si and Mo on the sigma-phase precipitation in S32750 super duplex stainless steel slab. The activity for Mo with increasing Si and Mo was calculated by the Wagner formula, and the equilibrium solidification phase diagrams of S32750 duplex stainless steels with different Si and Mo contents were calculated using the thermo-calc software. The sigma phase precipitated mainly at ferrite/austenite phase boundaries and grew up towards the interior of ferrite phase in S32750 SDSS slab. The area fraction and size of the sigma phases significantly increased with increasing Mo content and Si content. Also, the increment in Mo and Si content affected the Mo concentration in sigma phase. The sample（Mo:3.4%,Si：0.3%） had a lowest sigma-phase area fraction of 2.84% and had lowest Mo content in σ phase.The calculation results showed that the increase of Mo and Si content increased the initial precipitation temperature and maximum precipitation amount of σ phase in S32750 SDSS equilibrium phase diagram. The activity of Mo also increased with increasing Si content and Mo content. That is, Mo and Si elements promoted the precipitation of σ phase.

A Comparative Performance Investigation of Single- and Double-Nozzle Pulse Mode Minimum Quantity Lubrication Systems in Turning Super-Duplex Steel Using a Weighted Pugh Matrix Sustainable Approach

This study investigates the performance comparison of machining of UNS S32750 super-duplex stainless steel under single- and double-nozzle pulse mode minimum quantity lubrication (MQL) conditions. The pulse mode MQL system delivers lubricant pulses at specific intervals. The Taguchi L9 design, with three factors and their three levels, was taken to perform the CNC turning experiments under both single-nozzle and double-nozzle MQL cooling environments. The surface roughness (Ra), tool-flank wear (VB), tool-flank temperature (Tf), power consumption (Pc), and material removal rate (MRR) are evaluated and compared as performance indicators. In comparison to single-nozzle MQL, the responses of Ra, VB, Tf, and Pc were found to be decreased by 11.16%, 21.24%, 7.07%, and 3.16% under double-nozzle conditions, respectively, whereas MRR was found to be 18.37% higher under double-nozzle conditions. The MQL pulse time was found to be an important variable that affects Ra, VB, Tf, and MRR significantly. Under both cooling scenarios, common wears such as abrasion, built-up edges, adhesion, and notch wear are detected. Furthermore, the Pugh matrix-based sustainability evaluation results revealed that the double-nozzle MQL technique was superior to single-nozzle MQL, achieving improved sustainability for machining super-duplex stainless steel.

Micro-electrochemical insights into pit initiation site on aged UNS S32750 super duplex stainless steel

An aging treatment of UNS S32750 super duplex stainless steel at 1173 K for 1.0 ks produced σ and secondary austenite (γ2) phases in the α and γ phase boundary regions. Small amount of Mn-Cr oxide and MnS complex inclusions were present in the steel. No pitting was observed during the potentiodynamic polarization of a small area (200 × 200 µm) without inclusions in 1 M MgCl2 at 348 K. Because the electrode area included α, γ, σ, and γ2 phases, these phases and their boundaries alone could not act as initiation sites for pitting. The electrode area size was gradually reduced from 3 × 3 mm to 1 × 1 mm, and pitting corrosion was observed to occur at the Mn-Cr oxide and MnS complex inclusions in a region that appeared to be the γ2 phase near the σ phase.

Correction of Phase Balance on Nd:YAG Pulsed Laser Welded UNS S32750 Using Cobalt Electroplating Technique

Super-duplex stainless steel (SDSS) shows high mechanical and corrosion resistance because of the balanced structure of austenite and ferrite. However, maintaining this phase ratio after welding is a challenge. The use of austenite stabilizing components is recommended to balance the microstructure. The addition of alloying elements presents a challenge because of the characteristics of Nd:YAG pulsed laser welding. An approach, which has proven to be effective, is to use metal electroplating to prepare the surfaces of the mechanical SDSS components that will be welded, therefore promoting the phase balance in the fusion zone. While the effects of metals such as nickel as an austenite stabilizer are well recognized, cobalt’s effects require more research. The present work investigated the influence of the use of cobalt addition in the joining process by preliminary electroplating on UNS S32750 SDSS Nd: YAG pulsed laser welding, specifically regarding microstructure and microhardness. Three conditions were investigated, changing the thickness of the deposited cobalt layer. The addition of cobalt modified the morphology and increased the volume fraction of austenite. An austenite volume fraction of around 48% was obtained using a 35 μm thick cobalt coating. The microhardness was affected by austenite/ferrite proportions. The microhardness dropped from about 375 HV to 345 HV as the cobalt layer’s thickness rose, being similar to that of the base metal. The effect of cobalt as an austenite stabilizer was observed, and the cobalt electroplating technique was effective to correct the phase balance on UNS S32750 laser welding.

DL-EPR vs. LSV-KOH: from simple detection of deleterious phases to analysis of morphology and high accuracy on determination of sigma phase in UNS S32750 stainless steel

ABSTRACT An optimised electrochemical technique, linear sweep voltammetry (LSV) in KOH solution (LSV-KOH) was confronted with the double loop electrochemical Potentiokinetic reactivation (DL-EPR) to verify which is the best technique to quantify deleterious phases (DP) in a UNS S32750 super duplex stainless steel. DL-EPR presented an error in determination of deleterious phases in the range of 6.9–100%. LSV-KOH show a better accuracy in quantification of deleterious phases volume fractions, the error range for LSV-KOH was 2.4–26.2%. When the morphology of sigma changes from lamellar to divorced, was observed modifications on LSV-KOH voltammograms. In specimens where lamellar morphology is present, the voltammograms show two peaks curve. Meanwhile, in specimens where occurred also divorced precipitation of sigma the voltammograms changes to a 3 peaks curve. This feature is due to the dissolution of sigma phase boundaries which has different compositions according to the form of sigma precipitation.

Study of the Passivation Film on S32750 Super-Duplex Stainless Steel Exposed in a Simulated Marine Atmosphere

The corrosion behavior and passivation mechanism of S32750 super-duplex stainless steel exposed in a simulated marine atmosphere were studied using electrochemical methods, XPS and SEM. Passivation and local corrosion occurred on the metal surface when S32750 SDSS was exposed in the simulated marine atmospheric environment. The passivation film is composed of two chromium-enriched layers. The outer layer is a very thin film at the metal/atmosphere interface of the specimen surface with higher chromium content, whereas the chromium in the inner layer seems a little depleted. The outer and inner layers had similar Fe components, and Fe3+ oxide/hydroxide was the primary oxide in the film. The outer layer contains CrO3, whereas the inner layer has Cr3+ as its primary oxide. Pitting occurred when exposure time exceeded 24 d, and the Cr content of the specimen decreased. Therefore, S32750 SDSS exposed for 24 d exhibited the best corrosion resistance.

INVESTIGATION ON EFFECT OF PULSED CURRENT MICRO PLASMA ARC WELD PARAMETERS ON UNS S32750 SUPER DUPLEX STAINLESS STEEL SHEETS

In this paper, a 0.33mm thick UNS S32750 super duplex stainless steel sheet is butt welded with welding with a micro-plasma arc. Peak current, base current, pulse width, and pulse rate are regarded welding input factors, whereas the tensile strength and hardness of the welded joint are known as output parameters. 31 distinct combinations of tests are carried out by integrating the response surface method (RSM) with central composite design (CCD) and taking into account four factors and five levels of weld process parameters. The main plots are used to visualize the variance in output responses as a function of weld input parameters. MINITAB software is used to establish mathematical models that take into account linear functions. At a 95% confidence level, ANOVA is used to compare two variables. The dominant parameter is identified using contour plots, and the optimum combination of welding parameters is determined using surface plots. Various welding parameters and their effect on stainless duplex steels have been comprehensively explored in this study.

Effect of secondary austenite on fatigue behavior of S32750 super duplex stainless steel

Tension-tension fatigue tests were carried out to investigate the effect of secondary austenite (γ2) on the fatigue behavior of S32750 super duplex stainless steel (SDSS). Stress-life curves were fitted and analyzed in detail. It was demonstrated that γ2 deteriorates the fatigue resistance of SDSS. To further study the role of γ2 in fatigue deformation, fracture surfaces were examined. γ2 increased the probability of ferrite as a crack initiation source, which could be attributed to the combined variation of the ferrite/austenite interface relationship and alloying elemental distribution. γ2 increased the ratio of Kurdjumov-Sachs/Nishiyama-Wassermann crystallographic orientation, making the slip systems crossing the ferrite/austenite boundaries easier to affect the formation of fine-scaled dislocation structure in ferrite. Moreover, segregation of N enhanced the strength of γ2, thus leading to the earlier plastic deformation of partial ferrite in the fatigue deformation process.

Kinetics of the UNS S32750 Super Duplex Stainless Steel Low-Temperature Plasma Nitriding

This work reports an experimental investigation on the thermodynamic and kinetic view-point of the nitrided layer growth behavior, carried out separately at ferrite and austenite phase grains, for the UNS S32750 super duplex stainless steel (SDSS). For this purpose, and motivated by the DSSs distinct behavior showing formation of two- or single-phase nitrided layers, which apparently depend on the steel substrate chemical composition, two series of treatment were studied here, one varying the nitriding temperature on the 300-450 °C range for 4 h time, and other one varying the time on the 2-8 h range at 350 °C. Microstructural characterization of studied layers by means of SEM and EDS analysis, XRD and microhardness measurements showed precipitation-free nitrogen-expanded austenite layer formation on both steel phases for all samples treated up to 400 °C. The nitriding kinetics study showed that the layer thickness on both steel phases is proportional to the square root of the treatment time and follows an Arrhenius law for the studied treatment temperatures. The nitrogen diffusion activation energy, separately determined from the layer growth on each steel phase, was 115±3.2 and 120±5.4 kJmol-1, for austenite and ferrite grains, respectively.

Effect of the nanostructuring by high-pressure torsion process on the secondary phase precipitation in UNS S32750 Superduplex stainless steel

In this work, the precipitation and the morphology of secondary phases after severe plastic deformation (SPD) processing followed by an isothermal treatment was investigated. High-pressure torsion (HPT) was the SPD process carried out on superduplex 2507 (UNS S32750) stainless steel material under P = 6 GPa at room temperature. At this high strain levels (ε up to 170) samples have shown grain size decrease and strained microstructure with high dislocation density and nanostructure features. After a short isothermal treatment at 830 °C, the sigma phase and chromium nitrides were revealed as the main secondary phases identified by scanning and transmission electron microscopy and element analysis by energy dispersive spectroscopy. Scanning precession electron diffraction and automated crystal orientation mapping have been carried out in order to confirm the precipitation of the secondary phases. In fact, the results provide evidence that the precipitation of chromium nitrides seems to be the preferred nucleation site for sigma phase at higher deformation strain, in addition to the intergranular precipitation of sigma. Both the sigma phases nucleated integranularly and besides chromium nitrides are randomly orientated.

Microstructure Evolution during Hot Deformation of UNS S32750 Super-Duplex Stainless Steel Alloy.

The present paper analyzes UNS S32750 Super-Duplex Stainless Steel hot deformation behavior during processing by upsetting. The objective of this paper is to determine the optimum range of deformation temperatures, considering that both austenite and ferrite have different deformation behaviors due to their different morphology, physical, and mechanical properties. Because the capability of plastic deformation accommodation of ferrite is reduced when compared to austenite, side cracks and fissures can form during the hot deformation process. Consequently, it is important to find the optimum conditions of deformation of this type of stainless steel to establish the best processing parameters without deteriorating the material. The experimental program involved the application of hot deformation by the upsetting method on a series of samples between 1000 °C and 1275 °C, with a total degree of deformation of 30%. The resultant samples were examined by SEM-EBSD to establish and analyze the evolution of the phases present in the structure from several points of view: nature, distribution, morphology (size and shape), and their structural homogeneity. The GROD (Grain Reference Orientation Deviation) distribution map was also determined while taking into account the possible precipitation of the secondary austenite phase (γ2-phase) and the analysis of the dynamic recrystallization process according to the applied deformation temperature. The main conclusion was that UNS S32750 SDSS steel can be safely deformed by upsetting between 1050–1275 °C, with an experimented total degree of deformation of 30%.

Evolution of Microstructure and Texture in UNS S32750 Super Duplex Stainless Steel Weldments

Evolution of Microstructure and Texture in UNS S32750 Super Duplex Stainless Steel Weldments

Evaluation of 475 °C embrittlement in UNS S32750 super duplex stainless steel using four-point electric conductivity measurements

One of the consequences of the 475 °C embrittlement of duplex stainless steels is the reduction of the resistance to localized corrosion. Therefore, the detection of this type of embrittlement before the material exhibits significant loss in toughness, and corrosion resistance is important to ensure the structural integrity of critical components under corrosion threats. In this research, conductivity measurements are performed using the alternating current potential drop (ACPD) technique with using a portable four-point probe as a nondestructive evaluation (NDE) method for detecting the embrittlement in a 2507 (UNS S32750) super duplex stainless steel (SDSS) aged at 475 °C from as-received condition to 300 h. The electric conductivity results were compared against two electrochemical tests namely double loop electrochemical potentiokinetic reactivation (DL-EPR) and critical pitting temperature (CPT). Mechanical tests and the microstructure characterized using scanning electron microscopy (SEM) imaging are conducted to track the progress of embrittlement. It is shown that the electric conductivity correlates with the changes in impact energy, microhardness, and CPT corrosion tests result demonstrating the feasibility of the four-point probe as a possible field-deployable method for evaluating the 475 °C embrittlement of 2507 SDSS.