Duplex Stainless Steel Alloy Research Articles

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.

Synthesis and Corrosion Performance Evaluation of Nanostructured Duplex Stainless Steel Alloys Prepared by MA and SPS

Synthesis and Corrosion Performance Evaluation of Nanostructured Duplex Stainless Steel Alloys Prepared by MA and SPS

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”

Development of a duplex stainless steel for dry storage canister with improved chloride-induced stress corrosion cracking resistance

The chloride-induced stress corrosion cracking (CISCC) is one of the major integrity concerns in dry storage canisters made of austenitic stainless steels (ASSs). In this study, an advanced duplex stainless steel (DSS) with a composition of Fe–19Cr–4Ni-2.5Mo-4.5Mn (ADCS) was developed and its performance was compared with that of commercial ASS and DSS alloys. The chemical composition of ADCS was determined to obtain greater pitting and CISCC resistance as well as a proper combination of strength and ductility. Then, the thermomechanical processing (TMP) condition was applied, which resulted in higher strength than ASSs (304L SS and 316L SS) and better ductility than DSSs (2101 LDSS and 2205 DSS). The potentiodynamic polarization and electrochemical impedance spectra (EIS) results represented the better pitting corrosion resistance of ADCS compared to 304L SS and 316L SS by forming a better passive layer. The CISCC tests using four-point loaded specimens showed that cracks were initiated at 24 h for 304L SS and 144 h for 316L SS, while crack was not found until 1008 h for ADCS. Overall, the developed alloy, ADCS, showed better combination of CISCC resistance and mechanical properties as dry storage canister materials than commercial alloys.

Measurement of G-phase volume fraction and number density in duplex stainless steels using transmission electron microscopy

Duplex stainless steels (DSS) have a high toughness and strength due the presence of both austenitic and ferritic phases. These alloys have had limited use in power production applications due to thermal embrittlement caused by spinodal decomposition and development of G-phase precipitates in the ferrite. Lean grade DSS alloys (e.g., 2101, 2003) may offer improved thermal stability due to the reduction of Cr- and Ni-equivalent elements when compared to standard grade compositions (e.g., 2205, 2209). The abundance of the G-phase was measured in five duplex stainless steels, three wrought alloys (2101, 2003, 2205) and their matching filler metals (2101-w, 2209-w), after aging at 427 °C for 1000 h and 10,000 h. The G-phase volume fraction, number density, size, and precipitate spacing were found using quantitative analysis of transmission electron microscopy dark field images and the composition of G-phase precipitates on other clusters were characterized with atom probe tomography (APT). In the welded alloys, the G-phase was found to develop rapidly, relative to the wrought material. A positive correlation was found between the nickel equivalent composition of the alloy and the G-phase volume fraction. The alloys 2205, 2209, and 2101-w, which are higher in Cr and Ni, all showed significant G-phase precipitation, further strengthening the hypothesis that lean grade DSS alloys are more thermally stable against precipitation in the ferrite. Electron diffraction showed a secondary phase present in the 2101 wrought alloy at 10,000 h, but it was not crystallographically consistent with the G-phase; APT showed the presence of nanoclusters rich in both nickel and copper for this alloy. No secondary phases or clusters were found in 2003 after 10,000 h of aging, so it may be a candidate alloy for applications that require long-life times at high operating temperatures.

Developing a 2D finite element cutting model based on individual phases in orthogonal cutting of two-phase duplex stainless steel

This paper presents a novel method to model the metal cutting of 2205 duplex stainless steel alloy. A 2D finite element model was developed to predict the plastic behaviour of two phases of duplex stainless steel, austenite, and ferrite during orthogonal cutting. A mesh based on physical microstructure was created using mapping software OOF2. The finite model was setup on ABAQUS software based on the Lagrangian method. The cutting model allows for tracking of stress and strain on individual phases during chip formation. Simulated and experimental data showed good agreement in comparison of shear angle and cutting strain. Model was created to gain understanding of long-established issues in machining duplex stainless alloys. Future model development required to gain further insight on associated triggering mechanisms.

Microstructure and corrosion behavior of welded joint between 2507 super duplex stainless steel and E690 low alloy steel

Microstructure and corrosion behavior of welded joints between super duplex stainless steel 2507 and low alloy steel E690 were characterized herein. The joints are composed of base metal and heat affected zone (HAZ) of the two steels, weld metal, and dilution zone at the interface between weld metal and HAZ of E690 steel. Concentration gradients of Fe, Ni, Cr, and Mo exist between fusion boundary and Type-II boundary, and martensite band with a high hardness is formed. The changes of microstructure, element diffusion in different regions, and local acidification in E690 HAZ lead to heterogeneous corrosion attacks on the welded joints in artificial seawater. After long-term exposure, a corrosion groove is generated at the HAZ of E690 adjacent to the interface, where high stress corrosion cracking vulnerability is expected.

Age-hardening behaviors of the weld metals of 22% Cr and 25% Cr duplex stainless steels at 400 °C

Duplex stainless steel (DSS) alloys are attractive materials for pressure components in nuclear power plants as they offer a good combination of high strength, corrosion resistance, and weldability. However, DSS suffers from embrittlement and hardening upon exposure to temperatures of 250–500 °C. Most previous studies addressed only solution-treated materials, and limited research has been conducted on weld metals. In this study, the relationship between the nanostructural evolution and hardening of 22% Cr and 25% Cr DSS weld metals (fabricated with grade-2209 and 2594 welding materials, respectively) during aging at 400 °C was investigated. The results revealed that the degree of hardening of ferrite after aging at 400 °C for 1000 h was greater in the 22% Cr DSS weld metal than in the 25% Cr DSS weld metal. The ferrite phases of both samples underwent two different phase decomposition processes during aging, (1) phase separation (α → Fe-rich α + Cr-rich α’) and (2) solute clustering to form G-phase precursors, both of which were identified within the body-centered cubic structure of ferrite in the weld metals. Phase separation was less pronounced, whereas formation of G-phase precursors was more pronounced in the 22% Cr DSS weld metal than in the 25% Cr DSS. These results indicate that the extent of formation of G-phase precursors has a significant influence on predicting the degree of hardening of ferrite. The enhanced formation of G-phase precursors in the 22% Cr DSS weld metal was elucidated using thermodynamic simulations; the formation of the G-phase precursor was predominantly facilitated by the higher Mn fraction in the 22% Cr DSS weld metal. The findings of the present study are expected to aid the selection and/or further improvement of the compositional design of DSS welding materials, thereby increasing the long-term safety of DSS welded components in nuclear applications.

Surface modification of hybrid composite multilayers spin cold spraying for biomedical duplex stainless steel

The performance of biomaterials in biological systems is of critical significance for advancing biomedical implants. Duplex Stainless Steel alloys are the major biomaterials due to their significant characteristics. Many functional coatings are deposited on DSS alloy surfaces utilizing numerous surface coating techniques to improve their bioactivity and protect them from corrosion degradations. Coatings of titanium dioxide (TiO2), Hydroxyapatite (HA), and zinc oxide (ZnO) have received considerable attention in the field of surface bioactive modification of DSS alloy implants. The coating techniques play a key role in increasing the required biological characteristics of DSS alloys, such as biocompatibility, mechanical properties, and corrosion resistance. In this regard, HA-ZnO, HA-TiO2, and TiO2–ZnO from each coating group are divided into single, double, and triple layers. These coatings were prepared by cold spray and deposited on the surface of the DSS alloy, followed by a heat treatment at 250 °C. The surface morphology of coated surfaces was analyzed utilizing field emission scanning electron microscopy (FESEM), atomic force microscopic (AFM), microhardness test, corrosion test in Ringer solution, and antibacterial test. The coatings showed nano-scale surface morphology with advanced crystallization and homogeneous structures; in the corrosion characteristics utilizing potentiodynamic polarization, triple layers of HA-ZnO coatings displayed advanced nanostructures with higher hardness values (514.75HV). The antibacterial test showed the triple layers of HA-TiO2 and two layers of TiO2–ZnO sensitivity to positive bacteria.

The Effects of 475 °C Embrittlement on the Mechanical Behavior of Thermally Aged 2507 and 2101 Duplex Stainless Steel Alloys

The Effects of 475 °C Embrittlement on the Mechanical Behavior of Thermally Aged 2507 and 2101 Duplex Stainless Steel Alloys

A constitutive model for the uniaxial tensile plastic behavior of metals based on the instantaneous strain-hardening exponent

The present work develops a new constitutive equation model for strain-hardening behavior of metallic materials (named herein as the Gonoring model) based on the definition of the instantaneous strain-hardening exponent. This new proposal was applied to experimental uniaxial tensile data of a lean duplex stainless steel alloy UNS s32304 (LDSS 2304) in the as-received (AR) condition and on identical heat-treated specimens at four different temperatures. This choice was justified because this is a steel that presents two phases (ferrite and austenite), which makes it a more universal example from the point of view of applying a new constitutive equation model. These heat treatments induced sigmoidal strain-hardening behavior at uniaxial tensile in this alloy. The Gonoring proposal was able to predict the strain-hardening behavior of both the sigmoidal and parabolic-shaped strain-hardening curve of a lean duplex stainless steel alloy 2304.

Characterization of wear resistance and corrosion during magnetorheological fluid assisted finishing (MFAF) of Ti-6Al-4V and duplex stainless steel for enhanced biocompatibility

The sustainability of biomaterials relies on their interaction with the proteins, fluid, and cells present inside the human body. The biomaterials’ enhanced surface roughness parameters and mechanical properties (i.e. wear resistance) are responsible for reducing degradation (i.e. corrosion rate) to enhance life span during musculoskeletal interaction. The present study compares the biocompatibility between two biomaterials (i.e. Ti-6Al-4V and DSS) polished through the Magnetorheological Fluid Assisted Finishing ( MFAF) process. MFAF process can produce nano-level average surface roughness ( Ra) and is used to improve the quality of the biomaterial's surface. However, apart from Ra, two other surface roughness parameters, namely skewness ( Rsk) and kurtosis ( Rku) analyze the characteristics of the irregularities formed on the polished surface. During the MFAF process, Trochoidal, a high-speed surface finishing toolpath, is used to map the workspace on the Duplex Stainless Steel ( DSS) and Ti alloy (Ti-6Al-4V) biomaterials to enhance their biocompatibility with a reduced finishing time. However, during the pin-on-disc wear tests, an Ultra High Molecular Weight Polyethylene ( UHMWPE) is used as the disc to imitate the interface of the bone with the implants for analyzing wear resistance. During experimentation, it is observed that the wear resistance of DSS and Ti-6Al-4V is improved to 3.19 × 10−6 and 0.123 × 10−5 mm3/min from its initial value of 7.65 × 10−6 and 2.68 × 10−5 mm3/min, respectively. Furthermore, the dependency of initial surface roughness parameters over the wear resistance of the biomaterials is also analyzed. A three-electrode-based electrochemical test with 0.5 M NaCl concentration is utilized to replicate the human body fluid while analyzing the corrosion resistance of the biomaterials. It is observed that the MFAF process enhances the corrosion resistance of the DSS and Ti-6Al-4V to 0.0037 and 0.0114 mm/year, from its initial values of 0.0079 and 0.0130 mm/year, respectively.

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

AbstractA combination of scanning microelectrochemical techniques along with the conventional electrochemical approaches is explored to attain insight information on the localized corrosion on the newly developed lean duplex stainless steel (LDSS) alloys. The obtained results from dynamic electrochemical impedance spectroscopic (DEIS) tests explained the beneficial role of different alloying elements on the passive and transpassive regions of the investigated LDSS alloys in a 3.5% NaCl solution. The scanning vibrating electrode technique (SVET) was effective in examining the anodic and cathodic regions on the corroding LDSS, whereas the scanning electrochemical microscopy (SECM) technique was employed to explore the localized corrosion sites on LDSS in NaCl solution. The acquired SVET results revealed a reduction in the susceptibility of the newly developed alloys to localized corrosion concerning their composition, accounting for the enhanced corrosion resistance. The obtained result from conventional and scanning microelectrochemical techniques obviously revealed the LDSS alloy with the composition of Fe–16Cr–2Ni–2Mn–1Mo exhibited higher localized corrosion resistance in NaCl solution.

Effect of thermal aging on corrosion behavior of duplex stainless steels

Despite their exceptional mechanical and corrosion properties, duplex stainless steels (DSS) have not found widespread use in high-temperature applications due to concerns over thermal aging and embrittlement at elevated operational temperatures (> 300 °C). The present study investigated the effect of thermal aging time on the electrochemical properties of lean and standard grade DSS that are exposed to a range of pressurized water reactors containing LiOH and H3BO3. The results indicated that the electrolyte chemistry plays a significant role in the corrosion behavior of the DSS alloys. Corrosion resistance decreased with thermal aging time for all DSS alloys; however, standard grade DSS (2205 and 2209-w) alloys showed better corrosion resistance than lean grades (2003, 2101, 2101-w). The presence of dissolved oxygen in the electrolytes resulted in a significant increase in corrosion rate for the DSS alloys, but it did not affect the general trend of corrosion rates with aging time. All DSS alloys became vulnerable to pitting corrosion due to chloride addition, but the pitting resistance decreased with increasing thermal aging time. Increased boron B content resulted in degradation of corrosion resistance of the DSS alloys, while minor changes in pH did not show a significant change in corrosion resistance. Mechanical and metallurgical characterization coupled with electrochemical characterization of the DSS alloys gave a comprehensive insight into the effects of thermal aging on the electrochemical response of the DSS.Graphical abstract

Corrosion behaviour of lean duplex stainless steel in advanced oxidation process (AOP) based wastewater treatment plants

The corrosion of lean duplex stainless steel alloys is examined when applied as a construction material in advanced oxidation processes. Both electrochemical and immersion experiments have been carried out when subjecting wastewater to ozone or Fenton oxidation. The electrochemical experiments suggest that the presence of dissolved ozone at the levels tested does not result in an increased pitting susceptibility for none of the alloys included in the research. However, the application of Fenton reagents induces pitting corrosion to the studied lean duplex alloys. The immersion experiments highlight that crevice corrosion occurs during wastewater treatment with both ozone and Fenton reagents.

Immersion pickling of oxide layer on hot-rolled 2205 duplex stainless steel in sulfuric acid with different additives

The oxide layer formed after hot-rolling of duplex stainless steel (DSS) alloy 2205 was studied by electron probe microanalysis (EPMA) with wavelength dispersive spectrometry (WDS). Immersion pickling of the oxide layer on hot-rolled 2205 DSS in sulfuric acid at 80 °C with different additives was investigated via open-circuit potential and SEM imaging. The effects of different pickling solutions on descaling capacity were discussed. Results showed that the outer layer of the oxide layer was mainly iron oxide, whereas the maximum concentration of oxidized Cr occurred inside the layer; oxidized Cr extended far beyond the oxide/metal interface. The removal capacity of the oxide layer was weak with a sulfuric acid solution of 300 g/L. Many surface oxides appeared after the 20 min immersion test. After adding 1 mol/L NaCl, the pickling effect was significantly improved, and the open-circuit potential reduced from 0.3V to –0.32V. However, after a 20-min substrate immersion test, the surface was rough. Continuous addition of 50 g/L hexamethylenetetramine could remove the oxide in 20 min, resulting in a surface with a metallic luster. The initial potential of the reaction was –0.325 V. The potential then rose rapidly to –0.312 V within 280 s. The rapid increase in potential could be attributed to the inhibitory effect of hexamethylenetetramine. The optimum pickling process was as follows: 300 g/L H2SO4 + 1 mol/L NaCl+ 50 g/L hexamethylenetetramine solution at 80 °C in 20 min.

The Effect of Ph and Chloride Concentration on the Corrosion Behavior of Duplex Stainless Steel and Titanium Alloys Ti 6al 2nb 1ta 1mo at Elevated Temperature for Pump Impeller Applications

The Effect of Ph and Chloride Concentration on the Corrosion Behavior of Duplex Stainless Steel and Titanium Alloys Ti 6al 2nb 1ta 1mo at Elevated Temperature for Pump Impeller Applications

Evaluation of impact characteristics of reduced alloy duplex stainless steel sheet

SUS821L1 has been effectively used on bridges and land rocks. However, it has been anticipated that these structures may experience impact loading from earthquakes and tsunamis. It is required to evaluate the mechanical properties of SUS821L1 by impact testing because impact loading yields different mechanical properties than static loading. In this study, a falling drop impact tester with the split-Hopkinson bar method is used to evaluate the impact parameters of SUS821L1. The impact tensile and the static tensile test have demonstrated that the maximum stress is 100MPa greater than the static tensile test and the maximum strain is 3% greater than the impact tensile test.

Wear Behavior and Machining Performance of TiAlSiN-Coated Tools Obtained by dc MS and HiPIMS: A Comparative Study.

Duplex stainless steels are being used on applications that require high corrosion resistance and excellent mechanical properties, such as the naval and oil-gas exploration industry. The components employed in these industries are usually obtained by machining; however, these alloys have low machinability when compared to conventional stainless steels, usually requiring the employment of tool coatings. In the present work, a comparative study of TiAlSiN coating performance obtained by these two techniques in the milling of duplex stainless-steel alloy LDX 2101 was carried out. These coatings were obtained by the conventional direct current magnetron sputtering (dc MS) and the novel high power impulse magnetron sputtering (HiPIMS). The coatings were analyzed and characterized, determining mechanical properties for both coatings, registering slightly higher mechanical properties for the HiPIMS-obtained coating. Machining tests were performed with varying cutting length and feed-rate, while maintaining constant values for axial and radial depth of cut and cutting speed. The surface roughness of the material after machining was assessed, as well as the wear sustained by each of the tool types, identifying the wear mechanisms and behavior of these tools, as well as registering the flank wear values presented for each of the tested tools. The HiPIMS-obtained coating exhibited a very similar behavior when compared to the other, producing similar surface roughness quality. However, the HiPIMS coating exhibited less wear for higher cutting lengths, proving to be a better choice in this case, especially regarding tool life.

Prediction of Mechanical Properties as a Function of Welding Variables in Robotic Gas Metal Arc Welding of Duplex Stainless Steels SAF 2205 Welds Through Artificial Neural Networks

Abstract Dual-phase duplex stainless steel (DSS) has shown outstanding strength. Joining DSS alloy is challenging due to the formation of embrittling precipitates and metallurgical changes during the welding process. Generally, the quality of a weld joint is strongly influenced by the welding conditions. Mathematical models were developed to achieve high-quality welds and predict the ideal bead geometry to achieve optimal mechanical properties. Artificial neural networks are computational models used to address complex nonlinear relationships between input and output variables. It is one of the powerful modeling techniques, based on a statistical approach, presently practiced in engineering for complex relationships that are difficult to explain with physical models. For this study robotic GMAW welding process manufactured the duplex stainless steel welds at different welding conditions. Two tensile specimens were manufactured from each welded plate, resulting in 14 tensile specimens. This research focuses on predicting the yield strength, tensile stress, elongation, and fracture location of duplex stainless steel SAF 2205 welds using back-propagation neural networks. The predicted values of tensile strength were later on compared with experimental values obtained through the tensile test. The results indicate <2% of error between observed and predicted values of mechanical properties when using the neural network model. In addition, it was observed that the tensile strength values of the welds were higher than the base metal and that this increased when increasing the arc current. The welds’ yield strength and elongation values are lower than the base metal by 6%, ~ 9.75%, respectively. The yield strength and elongation decrease might be due to microstructural changes when arc energy increases during the welding.