S31803 Duplex Stainless Steel Research Articles

Influence of Heat Treatment Temperature on Microstructure, Hardness and Sensitization of UNS S32205 Duplex Stainless Steel

Improper thermal cycles on duplex stainless steels can lead to the formation of detrimental phases or alter the proportion of ferrite and austenite phases, thus influencing the material’s mechanical properties and corrosion resistance. Therefore, this study aimed to evaluate the effect of aging (at 850 and 950 °C) and solubilization (at 1000 and 1150 °C) thermal treatments on microstructure, indentation hardness, elasticity modulus, and susceptibility to intergranular corrosion of UNS S32205 duplex stainless steel. The sigma phase (σ) formation in the aged samples, with hardness values between 8 and 10 GPa, was confirmed. Furthermore, the pieces treated from 1000 °C upwards showed that increased temperature favored the formation of more equiaxial grains and the ferrite fraction growth. The thermal treatments barely affected the elasticity modulus of austenite and ferrite grains, increasing the hardness of ferrite. The effect of sulfuric acid concentration in the intergranular corrosion was evaluated. Also, the deconvolution of the corrosion curves permits the determination of the influence of the different phases in the corrosion performance. These tests revealed sensitization only at the σ phase grain boundaries in the samples treated at 850 °C in electrolytes containing H2SO4 2.5 mol/L and HCl 1 mol/L. Although the treatment at 950 °C led to the σ phase formation, its higher corrosion resistance was ascribed to the lower volumetric fraction of this phase, its morphology, and its increased Cr mobility compared to the 850 °C treatment. Therefore, it was shown that the σ characteristics and the sulfuric acid concentrations are determining factors in the UNS S32205 intergranular corrosion resistance.

Environmentally Assisted Cracking of Duplex and Lean Duplex Stainless Steel Reinforcements in Alkaline Medium Contaminated with Chlorides

Herein, the corrosion performance of different stainless steel (SS) reinforcing bar grades in alkaline solution is presented, including UNS S32205 duplex stainless steel (DSS), UNS S32304 and UNS S32001 lean DDS (LDSS). The electrochemical dissolution kinetics were studied by potentiodynamic polarization and the Tafel slope method. The environmentally assisted cracking (EAC) mechanisms of the different SS grades in the presence of Cl− were revealed with the slow strain rate test (SSRT). The higher activation of the anodic branch and the loss of toughness were related to the austenite-to-ferrite phase ratio. UNS S32205 DSS presented the slowest anodic dissolution kinetics, mainly due to the higher austenite content compared to the other LDSS; however, it suffered a more severe EAC than the UNS S32304 LDSS. In the case of UNS S32001 LDSS, even while having the lowest Ni content (i.e., large ferrite α-phase ratio), it experienced the least decrease in elongation as well as low anodic dissolution kinetics for Cl− contents up to 8 wt.%, where the Cl− threshold was reached.

Corrosion Study on Duplex Stainless Steel UNS S31803 Subjected to Solutions Containing Chloride Ions.

In the present work, the influence of a corrosive environment and temperature on the corrosion resistance properties of duplex stainless steel S31803 was evaluated. The corrosive process was carried out using solutions of 1.5% HCl (m/m) and 6% FeCl3 (m/m), at temperatures of 25 and 50 °C. The microstructure of UNS S31803 duplex stainless steel is composed of two phases, ferrite and austenite, oriented in the rolling direction, containing a ferrite percentage of 46.2% in the rolling direction and 56.1% in the normal direction. Samples, when subjected to corrosive media and temperature, tend to decrease their mechanical property values. It was observed, in both corrosive media, that with increasing test temperature, there is an increase in the corrosion rate, both uniform and pitting. The sample in HCl solution obtained a uniform corrosion rate of 0.85% at 25 °C and 0.92% at 50 °C and pitting rates of 0.77% and 1.47% at the same temperatures, respectively. When tested in FeCl3 solution, it obtained uniform corrosion of 0.0006% and 0.93% and pitting of 0.53% and 18.5%, at the same temperatures. A reduction in dissolution potentials is also noted, thus characterizing greater corrosion in the samples with increasing temperature.

Microstructural characteristics of different heat-affected zones in welded joints of UNS S32304 duplex stainless steel using the GMAW process: analysis of the pitting corrosion resistance

Abstract The influence of specific microstructural characteristics on the properties of single-pass welding joints was assessed by optical processed images, transmission electron microscopy, microhardness measurements and corrosion tests conducted in various regions of the heat-affected zone (HAZ) in a lean duplex stainless steel. The welded joints were obtained with heat inputs of 1.5 and 2.5 kJ/mm using a gas metal arc welding (GMAW) process with a shielding gas enriched in Ar. Three selected regions in the HAZ showed different ferrite grain sizes and austenite fractions. The place in the welded joint where the HAZ was narrowest, and therefore experiences the highest cooling rate, is most prone to the formation of cubic CrN metastable nitrides. Conversely, the place where the HAZ was wider promotes the precipitation of stable Cr2N nitrides with more coalesced intragranular austenite (IGA) particles, where presumably random interfaces predominate. The HAZ region where the cooling rate was the highest presented more pitting corrosion resistance.

Transformation of inclusions in S32101 duplex stainless steel during continuous casting

In this study, the formation and characteristics of inclusions in S32101 duplex stainless steel (DSS) during continuous casting were investigated by analyzing inclusions in the tundish and continuous casting slabs. The composition of inclusions changed significantly during the continuous casting. The inclusion type in the tundish was primarily CaO-SiO2-Al2O3-MgO-MnO. There are two types of inclusions in the continuous casting slab: CaO-SiO2-Al2O3-MgO-MnO inclusions with dense Al2O3 and MnO, and Al2O3-MnO inclusions. TiN wraps the outer layers of both types of inclusions. The results obtained from thermodynamic calculations agreed with the experimental results. The weight percentage of Al2O3 and MnO in the inclusions increases significantly with the solidification process. In addition, the Al2O3-MnO inclusions were formed in the slab. TiN precipitates during the solidification of the S32101 DSS. The CaO-SiO2-Al2O3-MgO-MnO and Al2O3-MnO inclusions can be used as the nucleation sites of TiN.

Seawater Corrosion Resistance of Duplex Stainless Steel and the Axial Compressive Stiffness of Its Reinforced Concrete Columns

In order to explore the corrosion resistance of duplex stainless steel under seawater corrosion and the compressive stiffness of its reinforced concrete columns, this study first performed seawater corrosion resistance tests on HRB400 ordinary steel rebar and S32205 duplex stainless steel rebar. The effect of the corrosion product film on the corrosion behavior was investigated through polarization curve tests and electrochemical impedance spectroscopy tests. The results showed that the corrosion rate of S32205 duplex stainless steel in a seawater environment was approximately 1/15 that of the HRB400 ordinary steel rebar. The anodic polarization curve of duplex stainless steel rebars exhibited a greater slope than that of carbon steel rebars. In the simulated seawater environment, the corrosion rate of these two kinds of steel bars showed different trends. The corrosion rate of ordinary steel bar HRB400 first decreased and then increased, while that of duplex stainless steel S2205 increased steadily. Furthermore, 18 short concrete columns reinforced with ordinary and duplex stainless steel rebars were subjected to the axial compression test and stiffness analysis; the stiffness of the short columns was calculated from the test data. The theoretical values agreed with the test values, with a stiffness calculation error of less than 5%.

Nd: YAG laser beam welding of UNS N07718 superalloy and UNS S32304 duplex stainless steel: Phase transformations and mechanical properties of dissimilar joints

This article implies the phase transformations and mechanical behavior of dissimilar laser welded UNS N07718 superalloy/UNS S32304 duplex stainless steel. Laser power, welding speed, and focal point were the variables of the laser beam welding (LBW) approach. Optical microscopy and electron backscattered diffraction (EBSD) analysis were utilized. They demonstrated that the weld metal (WM) mainly had an austenitic microstructure with a face-centered cubic structure in the form of columnar and equiaxed dendrites. Also, the occurrence of directional solidification in WM was verified by EBSD. The heat-affected zone (HAZ) microstructure of Inconel 718 superalloy included austenite grains with normal grain growth, annealing twins, and precipitates. There was a ferritic-austenitic microstructure in the HAZ of 2304 duplex stainless. In this area, the volume fraction of the ferrite phase was excessively higher than that of the austenite phase and the austenite was characterized as Widmanstätten plates and grain boundary austenite. Furthermore, abnormal ferrite grain growth was identified in this. Welding defects e.g., molten spatter, solidification crack, and lack of penetration were observed, as well. Based on the uniaxial tensile test, it was realized that the highest failure load (9.7 ± 0.4 kN) was achieved in the laser power of 1900 W, welding speed of 3 mm/s, and focal point of 0 mm. Therefore, these variables were known as the optimum variables of the LBW process. All laser weldments failed from the WM and fractography via scanning electron microscopy (SEM) showed a mixture of dimple and cleavage features in the fracture surfaces of the laser welds.

Atomic-scale mechanism of effect of co-separation of elements at interface of ferrite and austenite on Cr-depleted zone of duplex stainless steel

Three-dimensional atom-probe tomography and first-principles calculation combined with density functional theory were used to study the effect of the co-segregation of different elements formed during the solidification process of S32205 duplex stainless steel on the Cr-depleted zone at the interface between ferrite and austenite. It was found that the co-segregation of different elements formed during the solidification process of duplex stainless steel can also form Cr-depleted zone at the interface between ferrite and austenite. Moreover, Mo, Si, B, C and P atoms promote co-segregation with Cr atoms, which promotes the formation of Cr-depleted zone at the interface between ferrite and austenite in duplex stainless steel. Mo and Si strongly promote the segregation of Cr at the interface between ferrite and austenite, thereby promoting the formation of Cr-depleted zone. B, C and P elements also promote the segregation of Cr element at the interface between ferrite and austenite and the formation of Cr-depleted zone, but their effect is weaker than that of Mo and Si elements. These conclusions provide a new theoretical basis for improving the intergranular corrosion performance of duplex stainless steel.

Anisotropic response in mechanical and corrosion performances of UNS S31803 duplex stainless steel fabricated by laser powder bed fusion

Mechanical and corrosion behaviors perpendicular to build direction (XOY) and along build direction (XOZ) of UNS S31803 duplex stainless steel (DSS) fabricated by laser powder bed fusion (LPBF) were investigated. With the post-annealing, the steel exhibited a ferrite-austenite microstructure. For XOY plane, austenite displayed a primarily <101> texture while ferrite kept <001> preferred orientation, and mainly held a Nishiyama-Wassermann orientation relationship. However, for XOZ plane, austenite showed a mixed texture. The average size of ferrite grains was larger for XOZ plane than XOY. The austenite in XOY plane was mostly island morphology grains, while in XOZ plane, there were a large number of coarse columnar grains. A higher geometrically necessary dislocation density and proportion of low-angle grain boundaries on XOY plane were observed. The yield strength and ultimate tensile strength values perpendicular to build direction were higher than those along build direction. While the total elongation perpendicular to build direction was lower. Moreover, the XOY plane shows slightly better corrosion resistance than the XOZ.

Annealing parameters effect on microstructure evolution, tensile properties and deformation behaviors of direct-cold-rolled UNS S32101 duplex stainless steel with heterogeneous layered structure

Microstructure evolution, strain-induced martensite transformation (SIMT) kinetics, tensile properties, deformation behaviors of UNS S32101 duplex stainless steel (DSS) with heterogeneous layered structure (HLS) were investigated. HLS composed of multiscale grains (spanning coarse, fine, and ultrafine grains) was prepared by direct cold rolling in combination with short-time annealing, being dominated by coarse-grained ferrite (CGed α) and fine-grained austenite (FGed γ). A quantitative SIMT kinetics model was established to predict the α′-martensite fraction at various strain/annealing parameters, indicating that increased average grain size (AGS) for γ not only contributed to the SIM formation but also promoted the monotonic increase of SIMT rate until annealing for 10 min. Relatively high stacking fault energy (SFE, 35.89∼39.34 mJ/m2) favored mechanical twinning as the dominant deformation mode of γ accompanied by SIMT and dislocation glide. And α deformation was mainly coordinated by wavy slip. Both SFE and Olson-Cohen parameters were strongly correlated with the γ AGS, which could reasonably interpret the dependence of SIMT on the AGS. The A and B values increased progressively with grain coarsening along with the rapid decline in SFE, facilitating the martensite formation. Further increasing the AGS beyond the peak region severely suppressed SIMT probably due to the low probability of martensite embryo generation at deformation twins (DTs) intersections, coinciding with the sharp decrease A value.

Effects of Cu Content on Inclusions and Pitting Corrosion in S32205 Duplex Stainless Steel

Cu is an austenite‐forming element in duplex stainless steel, and the precipitation of Cu‐rich phase can improve the strength of the alloy. However, the role of Cu element in the corrosion resistance of stainless steel is widely controversial. Herein, the effects of different Cu content on the formation of inclusions and the pitting resistance of duplex stainless steel are studied by using potentiodynamic anodic polarization test, immersion corrosion, scanning electron microscope, and electron probe microanalysis. The results show that the pitting potential decreases significantly with the increase of Cu content, which greatly reduces its ability to resist Cl− corrosion. The reason is that Cu increases the driving force for the formation of Al‐containing oxides, which increases the number and size of Al‐containing inclusions formed in the process of melting and solidification. At the same time, Cu promotes the formation of Cr‐depleted zone, which promotes the formation of microcracks and pitting corrosion between steel matrix and inclusions in duplex stainless steel.

Secondary-phase Transformation of Duplex Stainless Steels during Industrial Manufacturing

A new type of lean S32205 duplex stainless steel was studied on its secondary phase formation during industrial manufacturing. Different from the common S32205 duplex stainless steels, such lean S32205 duplex stainless steels contain more carbon and nitrogen elements, which promotes the formation of Cr2N and Cr23C6 secondary precipitations. The secondary-phase transformation is preferred at boundaries, either in the ferrite phase or at interphase interfaces after rolling, and even a few secondary precipitates can be found at the as-cast ferrite grain interiors as well. The influence of the secondary phase transformations on pitting resistance and hot ductility was investigated.

Stress Corrosion Cracking Mechanisms of UNS S32205 Duplex Stainless Steel in Carbonated Solution Induced by Chlorides

Herein, the chloride-induced stress corrosion cracking (SCC) mechanisms of UNS S32205 duplex stainless steel (DSS) reinforcing bars in alkaline and carbonated solutions are studied. Electrochemical monitoring and mechanical properties were tested using linear polarization resistance and electrochemical impedance spectroscopy, coupled with the slow strain rate tensile test (SSRT) to evaluate the SCC behavior and unravel the pit-to-crack mechanisms. Pit initiation and crack morphology were identified by fractographic analysis, which revealed the transgranular (TG) SCC mechanism. HCO3− acidification enhanced the anodic dissolution kinetics, thus promoting a premature pit-to-crack transition, seen by the decrease in the maximum phase angle in the Bode plot at low frequencies (≈ 1 Hz) for the carbonated solution. The crack propagation rate for the carbonated solution increased by over 100% compared to the alkaline solution, coinciding with the lower phase angle from the Bode plots, as well as with the lower charge transfer resistance. Pit initiation was found at the TiN nonmetallic inclusion inside the ferrite phase cleavage facet, which developed TG-SCC.

A Novel Method for Detecting the Onset and Location of Mechanical Failure by Correlating Engineering Stress With Changes in Magnetic Properties of UNS S32205 Duplex Stainless Steel Using Quantum Well Hall Effect Sensors

A Novel Method for Detecting the Onset and Location of Mechanical Failure by Correlating Engineering Stress With Changes in Magnetic Properties of UNS S32205 Duplex Stainless Steel Using Quantum Well Hall Effect Sensors

Effect of wire EDM process parameters on material removal rate of duplex stainless steel (S31803)

Machining of high-strength alloy is needed for special requirements requiring less wear, such as sliding objectives in applications like cams, gears etc. High-strength alloy material profile machining is challenging in conventional machining; Wire-EDM is one of the machining processes to fulfil the requirement with a good surface finish. The present work is an experimental study on material removal rate in Wire-EDM machining on S31803 Duplex Stainless Steel (DSS) material at different thicknesses. Thickness is considered as 5 mm, 10 mm, 15 mm and 20 mm where the nozzle distance altered as 19, 29, 39 and 49 with pulse off time 1,2,3,4 s. L16 orthogonal array from Taguchi method of experiments considered for the present study. Material of 10 mm thickness with 4 s pulse off time at 29 nozzle distance gives better material removal rate when compared with other samples.

The Microstructure and Pitting Corrosion Behavior of K-TIG Welded Joints of the UNS S32101 Duplex Stainless Steel

In this paper, the microstructure and pitting corrosion resistance of S32101 duplex stainless steel keyhole tungsten inert gas welded joints with different heat inputs were studied. The electrochemical experiments were conducted in a 1 mol/L NaCl solution at room temperature. The pitting rupture potential of the heat affected zone and the weld metal zone under different heat inputs were tested. The research showed that with the increase of heat inputs, more ferrite was converted to austenite and the number and size of intragranular austenite grains in the weld metal zone increased. The austenite content of the heat affected zone and the weld metal zone increase with the increase of heat inputs, and the CrN and Cr2N in the heat affected zone and the weld metal zone were mainly precipitated in the ferrite, in the austenite and ferrite/austenite interfaces. The pitting rupture potential value of the heat affected zone and the weld metal zone were increased with the increase of heat inputs, and the pitting corrosion resistance of the heat affected zone and weld metal zone were also increased with the increase of heat inputs. The relationship between the position CrN and Cr2N, the austenite content and the pitting corrosion resistance were elucidated, and the initiation mechanism of the pitting was investigated. Additionally, in this work, the heat affected zone and weld metal zone made at 2.46 kJ/mm heat inputs had the best pitting corrosion resistance. The research results provided useful information for improving the pitting corrosion resistance of S32101 duplex stainless steel keyhole tungsten inert gas welded joints.

Obtainment of a new metal matrix composite from the recycling of UNS S31803 duplex stainless steel by powder metallurgy

The purpose of circular economy is to maximize resources efficiency. With the increase in consumption of raw materials, energy and waste generation, recycling is necessary for environmental and industrial reasons. Thus, the powder metallurgy, together with mechanical milling, stands as a new method for scraps recycling. This study aimed to produce UNS S31803 duplex stainless steel powders, with vanadium carbide (VC) addition as reinforcement, through mechanical milling. Different uniaxial compaction pressures (700, 800 and 900 MPa) were used, as well as sintering temperatures (1200, 1240 and 1280 °C) and times (1, 1.5 and 2 hours), in order to determine the best conditions. Particle size analysis, scanning electron microscopy and x-ray diffraction were used to characterize the powders. It was observed that the use of VC increased the comminution during the milling process, being obtained an average particle size of 42 μm. The highest density obtained was of 82% and hardness of 72%, in comparison with the steel from the manufacturing process. According to the analysis, it was verified that this method is viable, becoming an alternative route to reuse UNS S31803 duplex stainless steel scraps.

Effect of Solution Heat Treatment by Induction on UNS S31803 Duplex Stainless Steel Joints Welded with the Autogenous TIG Process

In the oil and gas industry, the manufacture of equipment using materials that resist aggressive media is one of the greatest challenges. UNS S31803 duplex stainless steel is widely used for this purpose owing to its good combination of mechanical and corrosion resistance. The objective of this work was to evaluate the effect of induction solution heat treatment using autogenous TIG welding on UNS S31803 DSS sheets. Sheet samples were subjected to two different treatment parameters for a duration of 10 s and at temperatures of 1050 and 1150 °C. The results obtained with the treatments were compared with those of the as-welded condition, which was the reference condition. Quantitative and qualitative analyses of the samples were carried out, in addition to microstructural characterization using confocal microscopy and a corrosion resistance study as per ASTM G48 standard. We observed that the best results were obtained with a treatment of 10 s at 1150 °C, which was able to eliminate chromium nitrides and re-establish the proper balance of the ferrite and austenite phases. In addition, the treatment was able to reduce hardness and provide welds free of cracks and discontinuities, also presenting a low corrosion rate.

Correlation of microstructure and dynamic softening mechanism of UNS S32101 duplex stainless steel during elevated temperature tensile testing

The dynamic substructural development and softening mechanism of UNS S32101 duplex stainless steel were comprehensively investigated by employing hot-tensile tests at various strain rates of 0.1–10 s−1 at a fixed temperature of 1200 °C. Different flow behaviors were attributed to the microstructural evolution and restoration process under various hot-deformation conditions. The alternative restoration mechanisms of ferrite in the current alloy were closely associated with the evolution of the misorientation angle in the (sub)grains, depending on the applied strain rates. Therein, three distinct softening mechanisms were found in ferrite, i) subgrain coalescence (SC) at 0.1 s−1, ii) continuous dynamic recrystallization (CDRX) at 1 s−1 and iii) subgrain rotation-assisted discontinuous dynamic recrystallization (SR-assisted DDRX) at 10 s−1. During SR-assisted DDRX process, new DRX nuclei were preferentially formed at the high-angle grain boundaries/phase boundaries (HAGBs/PBs) through the growth of highly misoriented subgrains. In contrast to ferrite, the available dynamic softening behavior of austenite, unlike the classical DDRX mechanism characterized by strain-induced boundary migration (SIBM), is affected by a limited number of pre-existing HAGBs. At lower strain rates of 0.1 and 1 s−1, the nucleation process of DRX in austenite is analogous to the CDRX behavior, whereas the growth characteristics conform to DDRX, thus, it can be called dynamic recovery-assisted DDRX (DRV-assisted DDRX). At a high strain rate of 10 s−1, DRX nucleation mainly took place through the strain-induced twin boundaries (TBs) transformation into HAGBs, and then rapidly grew via SIBM, referred to as TB-assisted DDRX.

In Situ Observation and Phase-Field Simulation Framework of Duplex Stainless-Steel Slab during Solidification

The melting and solidification process of S32101 duplex stainless steel (DSS) was investigated using high-temperature confocal microscopy (HTCM). The method of concentric HTCM was employed to study microstructure evolution during the solidification process of S32101 DSS. This method could artificially create a meniscus-shaped solid–liquid interface, which dramatically improved the quality of in situ observations. During the heating stage, γ-austenite transformed to δ-ferrite, and this transformation manifested itself in the form of grain boundaries (GBs) moving. The effects of cooling rate on the solidification pattern and microstructure were revealed in the present research. An enhanced cooling rate led to a finer microstructure, and the solidification pattern changed from cellular to dendritic growth. As the temperature decreased, the commencement and growth of precipitates were observed. In this paper, the experimental data, including parameters such as temperature, cooling rate, and growth mode, were used as the benchmark for the simulation. A simulation framework using Micress linked to a 1D heat transfer model enabling consistent analysis of solidification dynamics in DSS across the whole cast slab was established. Simulating the dendrite growth and elemental segregation of DSS at specific cooling rates shows that this framework can be a powerful tool for solving practical production problems.