UNS S31803 Duplex Stainless Steel Research Articles

Mechanical Properties and Corrosion Resistance of Cold Metal Transfer Small-Bore Thin-Walled Tube Butt Welded Joints of UNS S32205 Duplex Stainless Steel

Mechanical Properties and Corrosion Resistance of Cold Metal Transfer Small-Bore Thin-Walled Tube Butt Welded Joints of UNS S32205 Duplex Stainless Steel

A Quantified Study of the Resistance of Duplex Stainless Steels to HISC: Part 1–Significance of the Three-Dimensional Phase Distributions and Morphological Properties on Hydrogen Transport

This paper is associated with a larger program of research, studying the resistance to hydrogen-induced stress cracking (HISC) of a wrought and a hot isostatically pressed UNS S31803 duplex stainless steel (DSS), with respect to both the independent and interactive effects of the three key components of HISC: microstructure, stress/strain, and hydrogen. In the first part presented here, several material properties such as the three-dimensional microstructure, distribution, and morphology/geometry of the two phases, i.e., ferrite and austenite, and their significance on hydrogen transport have been determined quantitatively, using x-ray computed tomography microstructural data analysis and modeling. This provided a foundation for the study to compare resistance to HISC initiation and propagation of the two DSSs with differing microstructures, using hydrogen permeation measurements, environmental fracture toughness testing of single-edge notched bend test specimens, in Part 2 paper of this study (Blanchard, et al., Corrosion 78, 3 [2022]: p. 258–265).

A Quantified Study of the Resistance of Duplex Stainless Steels to HISC: Part 2–Significance of the Hydrogen Permeation Properties and Severity of Stress Raisers on Hydrogen Transport and Cracking

The quantified microstructural analysis performed on a wrought and a hot isostatically pressed UNS S31803 duplex stainless steel (DSS) in the Part 1 publication of this study established the significance of the three-dimensional (3D) distribution and morphology/geometry of the ferrite and austenite phases on hydrogen transport through two DSS product forms (see Blanchard, et al., Corrosion 78, 3 [2022]: p. 249–257). This paper is a follow-up to Part 1 and focuses on the role of the other two key, interrelated components of hydrogen-induced stress cracking (HISC): stress/strain and hydrogen. For this purpose, experimental hydrogen permeation measurements, and environmental fracture toughness testing (i.e., J R-curve testing) using conventional and nonstandard single-edge notched bend test specimens were used. These particularly enabled interpretation of the hydrogen permeation and transport test data, and evaluation of suitability of environmental fracture toughness test methods for the assessment of resistance to HISC in DSSs. The latter is discussed, both from laboratory and component integrity perspectives, in the context of the findings from the 3D microstructural characterization of the two phases, the role of stress raisers and their severity, and hydrogen transport through the bulk and from the surface.

Influence of Welding Energy on Intergranular and Pitting Corrosion Susceptibility of UNS S32205 Duplex Stainless-steel Joints

This study analysed the integrity of welded joints of a UNS S32205 duplex stainless steel, using different welding energies: 0.5 kJ.mm-1, 1.0 kJ.mm-1, and 3.5 kJ.mm-1. Microstructural characterisation, tensile testing, intergranular attack susceptibility testing (ASTM A262 practice A) and pitting/crevice corrosion resistance tests (critical pitting temperature test, ASTM G48 practice C) were performed in these welded joints. The results showed that the tensile properties of the welded joints did not vary significantly with the welding energy. The microstructure's ferrite content in the molten zone (MZ) was proportional to the welding energy: the ferrite concentration in the 0.5 kJ.mm-1 weldings was approximately 75%. When the welding energy increased to 3.5 kJ.mm-1, the amount of ferrite dropped to 54%. The 3.5 kJ.mm-1 welded joint featured a comparatively higher proportion of coarser austenite grains. The HAZ of the 3.5 kJ.mm-1 welded joint was comparatively more susceptible to the intergranular attack along the α/γ interfaces, while in the base metal and the other two welded joints, the intergranular attack along the α/γ interfaces was not prominent. Additionally, the pitting corrosion took place preferentially in the ferrite phase of the HAZ for all welding conditions.

Electrically enhanced plasticity of duplex stainless steel UNS S32750

Electroplastic Effect (EPE) is the influence of electrical current on the microstructure and the plastic flow of materials. In this work, duplex stainless steel UNS S32750 has undergone uniaxial tensile tests with the aid of pulsed electrical current. Different current densities and thermal tests were conducted to separate the EPE from the heating effect. The tested material shows an increase in fracture strain and uniform elongation, while ultimate tensile strength and yield strength were barely affected.

Temperature and time effect of thermal aging treatment on microstructure and corrosion resistance of UNS S31803 duplex stainless steel

Duplex stainless steels correspond to a class of steel in which the microstructure is composed basically by the phases ferrite and austenite. Given the metastable character of ferrite, associated phase transformations can occur during thermal treatments, which can lead to a reduction in corrosion resistance. Therefore, the aim of this work was to evaluate the influence of the solution-treated at 1100°C for 30min and aging at 500 and 600°C for 1, 3 and 12h, on the microstructure and corrosion resistance of DSS UNS S31803. The steels were characterized by SEM, EDS, XRD, hardness, microhardness and thermal analysis. The steels aged at 500°C for 1h presented the phase alpha line dispersed in the ferrite, and the steels aged at 600°C for 12h presented the phases alpha line, sigma and chi. In the assays of double cycle potentiodynamic reactivation in solution of 0.5M H2SO4 and 0.01M KSNC, it was observed that no sensitization occurred. Furthermore, in the tests of cyclic potentiodynamic polarization, in 3.5% NaCl solution, it was verified that the precipitation of the alpha line phase did not alter corrosion resistance; nevertheless, the sigma phase reduced corrosion resistance.

Comparisons of Different Oxide Fluxes in Activated Gas Tungsten Arc Welding of Duplex Stainless Steels for Improved Depth of Penetration and Pitting Corrosion Resistance

ABSTRACT The present work analyses the effect of five types of oxide fluxes – SiO2, TiO2, CrO3, MnO2 and MoO3 – on the depth of penetration and pitting corrosion behaviour of UNS S32205 duplex stainless steel produced with the activated tungsten inert gas welding (A-TIG) process. Five bead-on-plate (BoP) weld samples prepared autogenously with constant weld parameters. Depth of penetration (DP), depth-to-width (D/W) ratio and weld bead width (BW) were measured and compared with reference to the weld thermal cycle. The test results of ferrite measurement and micro-hardness were compared with normal – without flux added TIG-welded sample. Macro analysis of all samples indicates that SiO2 and TiO2 flux offer enhanced penetration depth and D/W ratio, in contrast, to use of other fluxes. Possibly, under the effect of either reversed Marangoni or arc constriction or both, however, all TIG BoP weld samples exhibited poor pitting corrosion resistance. Enhanced heat input due to flux and thus resultant unbalanced ferrite austenite proportion affected pitting corrosion resistance. ASTM A 923 microstructures did not show any presence of nitride formation. Results of energy-dispersive X-ray spectroscopy and scanning electron microscopy analysis of corrosion pits showed no abnormality with the chemistry of standard 2205 DSS.

Electrochemical corrosion behavior and microstructural characteristics of electron beam welded UNS S32205 duplex stainless steel

AbstractDifferent electrochemical techniques were used to study the corrosion behavior of UNS S32205 duplex stainless steel (DSS) welded autogenously using a single‐pass by electron beam welding process, supplemented by microstructural characterization. Furthermore, a comparative study was also performed between multipass gas tungsten arc (GTA)‐welded and EB‐welded DSS for their microstructure and corrosion behavior. The differences in weld thermal cycle and chemical composition influenced the fusion zone microstructure of both the welds and eventually their corrosion properties. The general corrosion resistance of the EB weld was lower than the base metal and higher than the GTA weld despite its weld zone being characterized by a relatively unbalanced phase ratio (α/γ) in comparison to the GTA weld. However, the EB weld showed relatively higher susceptibility to pitting corrosion than the base metal and GTA weld due to its poor repassivation characteristics and poor resistance to pit growth.

Microstructure, crystallographic texture and strain hardening behavior in hot tensile tests of UNS S32304 Lean Duplex stainless steel

Duplex stainless steels can be used for applications in the nuclear industry endorsing its choice as an external shield for Type B packages. The microstructure, crystallographic texture, and the strain hardening behavior of UNS S32304 duplex stainless steel was investigated in hot tensile tests by Electron Backscattering Diffraction technique. Interrupted hot tensile tests with strain rates ε˙ = 10−2 s−1 and ε˙ = 10−1 s−1 were carried out at 700 °C using a Thermomechanical Physical simulator. The α parameter of gamma distribution was associated for the first time with strain in ferrite and austenite phases through the Grain Orientation Spread parameter (GOS). The ferrite phase did not show the dynamic equilibrium between the stored energy and recovery rates. The average GOS in the ferrite phase was larger for ε˙ = 10−1 s−1 due to a smaller time available for dislocation annihilation and rearrangement in dynamic recovery. The grain rotation sequence <100> → <100> - <101> → <101> was found in ferrite phase. In the austenite phase, the dynamic recrystallization was not observed and the <111> and <100> fiber textures parallel to the tensile direction were strengthened. The austenite → ferrite phase transformation occurred during the hot tensile tests and showed the Kurdjumov-Sachs orientation relationship. The modified Crussard-Jaoul analysis showed six-strain hardening stages which were associated with the average GOS and austenite → ferrite phase transformation.

Phase transformations of the duplex stainless steel UNS S31803 under non-isothermal conditions

Precipitation of the intermetallic phases embrittles duplex stainless steels. Currently, most studies in this subject simulated aging phenomena by first holding the material at different isothermal conditions and then, quenching down under high cooling rates to investigate the subsequent microstructures and mechanical properties. In this work, specimens of the duplex stainless steel UNS S31803 were submitted to cooling cycles at controlled rates under non-isothermal conditions. The volume fraction of sigma and chi formed was less than 1%. The value was lower than that assumed by the Sieurin and Sandstrom model. We relate this to the initial DSS morphology, with austenite islands in a ferritic matrix. Here, the number of nucleation sites for the deleterious phases is smaller than the lamellar microstructure of ferrite and austenite usually found in duplex stainless steels.

Comparative Study Between Sensitization Degree of the 0.4% Mo Austenitic Stainless Steel and UNS S31803 Duplex Stainless Steel

This study aims at assessing the degree of susceptibility to intergranular corrosion of the UNS S31803 duplex stainless steel and the 0.4% Mo austenitic stainless steel through the double-loop electrochemical potentiodynamic reactivation (DL-EPR) test. Both steels were subjected to isothermal treatments at 650ºC and 900ºC in order to compare the effect of temperature on the respective degrees of sensitization. It was observed that the 0.4% Mo austenitic stainless steel presented a higher degree of sensitization and, consequently, a greater susceptibility to the intergranular corrosion process when compared to the UNS S31803 duplex stainless steel in the two temperatures studied. It was also observed that, for both steels, the heat treatment at 900ºC resulted in a higher degree of sensitization when compared to the heat treatment at 650ºC.

Surface modification method of duplex type stainless steels by the pack boriding process

This work presents the investigation of a boriding process on two grades of stainless steel namely UNS32750 super duplex stainless steel and UNSS31803 duplex stainless steel in order to improve material properties and possibly to reduce catastrophic failure of industrial components. Usage of duplex stainless steels has become customary in the fields of oil and refinery, marine and pipeline applications due to increased corrosion resistance; however, these materials exhibit low wear characteristics. To overcome this problem, in this work the pack boriding process was employed. Evaluation of effects of the boriding process on the microstructure and mechanical properties was performed using scanning electron and optical microscopy, Vickers hardness tests and wear tests. It was shown that the 4 h process resulted in the greatest boriding layer thickness yielding the maximum surface hardness of 1407 HV in the super duplex stainless steel UNS32750 while this value was 1201 HV in the duplex stainless steel UNSS31803. Wear resistance of borided materials were up to 6-fold greater than those of non - treated materials. Also, the borided duplex materials were shown to be more suitable for industrial applications for valve and shaft components as compared to the boronized super duplex stainless steel.

On the effect of plastic pre-straining on the corrosion behaviour of a duplex stainless steel and how the emergence of slip steps affects the hydrogen evolution reaction kinetics

The effect of increasing pre-straining on the corrosion behaviour of UNS S32304 duplex stainless steel has been studied using potentiodynamic tests in a highly acidic chloride-rich solution. The emergence of slip steps in the austenitic phase has been particularly addressed showing that the hence modified topographies had a significant impact on the kinetics of the Hydrogen Evolution Reaction (HER) that, in turn, tuned a non-monotonic behaviour of the corrosion rate. An attempt is made to link the variation of the Electron Work Function (EWF) of the surface with the electrochemical results by quantifying slip steps using Atomic Force Microscopy.

Effect of Ultrasonic Shot Peening on the Microstructure of Austenitic Stainless Steel 316 and Super Duplex Stainless Steel UNS S32750.

Shot peening for nanocrystallization of the surface region is a good way of improving corrosion-, fatigue-, and wear-resistance, etc. of metallic parts (Lu, K., 2014. Making strong nanomaterials ductile with gradients. Science, 345(6203), pp.1455-1456). The technique has been widely used for various materials as a method of surface modification. SUS316 has excellent corrosion and oxidation resistance with good formability However, its application is limited by the low mechanical strength and hardness. S32750 (duplex stainless steel) is one of most used tubing materials for oil/gas delivery systems in a corrosive environment under high pressure (Nilsson, J.O., 1992. Super duplex stainless steels. Materials Science and Technology, 8(8), pp.685-700). Thus, improving corrosion resistance is a key for the wider application and better maintenance of S32750. In our study, the alloy S32750 was heat-treated at 1070°C to obtain a precipitation-free microstructure (γ and δ dual-phase structure). It was then ultrasonic shot peened and microstructures were analyzed for: (1) surface nanocrystallization, (2) effect of the treatment processing parameters, and (3) the determination of microstructural evolution and the effect of the shot peening process.

Premature Failure of Grade-316Ti Stainless Steel Tubing in a Boiler Feed-Water Heat Exchanger in a Steel Complex

Premature failure of seamless tubes made of 316Ti stainless steel in a boiler feed-water (BFW) heat exchanger occurred at a local steel complex, which led to about 65–70% service-life reduction. The heat exchanger is a fixed-tube-sheet type with hydrogen gas flowing inside the tubes and water circulating through the shell side. The cooled hydrogen gas is purged to box annealing furnaces to create a reducing atmosphere. Failure analysis was conducted on the tubes to determine the contributing factors to premature failure of the heat exchanger. Four issues including corrosion fatigue, pitting corrosion attack, under-deposit corrosion, and fouling contributed to the failure of the tubes in the heat exchanger. The pitting corrosion attack was caused by chloride in circulating water. Chloride was also detected in accumulated deposits on the tubes causing the under-deposit corrosion issue. Contamination of boiler feed-water with Ca, Si, Mg, and Cl occurred during the water treatment process, a congruent phosphate–pH treatment in an in-house water treatment unit. The quality of the supplied water to the heat exchanger does not meet the recommended specifications. As a major recommendation, the tubes of the heat exchanger must be manufactured of super duplex stainless steel UNS S32750, based on specifications of the ASTM A789 standard.

Influence of present phases in corrosion and mechanical behavior of UNS S31803 duplex stainless steel welded by conventional short circuit MIG/MAG process

Duplex stainless steel (AID) is an alloy that, by allying both good mechanical properties and excellent corrosion resistance properties, comes increasing industrial interest every day. These attractions make it widely used in the most diverse industrial sectors such as pulp and paper industry, nuclear power, processing, oil and gas, among others. Its wide application in several industrial sectors constantly demands that this material is subjected to some welding process. Its high corrosion and mechanical resistance are attributed to balanced microstructure in approximately 50% ferrite and 50% austenite. In the present work, UNS S31803 AID plates were welded in a 45° bevel by conventional short-circuit MIG/MAG process, using three different weld energies, in the range of 0.5–0.8kJ/mm. The results showed that the effect of the welding energy on the ferrite volumetric fraction was very marked in the heat affected zone (HAZ) and in the weld metal this effect was not so pronounced. The mechanical properties of hardness and corrosion resistance (intergranular corrosion) were evaluated as a function of the welding energy employed. In general, both hardness and intergranular corrosion resistance were not influenced when the various welding conditions were compared. The toughness were evaluated by the crack tip opening displacement technique, compared to the base metal, and the condition 03 (19V) had the best result.

Effect of Cooling Rate on the Precipitation Behavior of a Fe–Cr–Ni Alloy

Ferrite (δ) in two-phase austenite–ferrite Fe–Cr–Ni alloys decomposes into Mo- and Cr-rich phases like sigma (σ) and chi (χ), when aged in the temperature range of 873–1273 K (600–1000 °C). The precipitation of these phases for a particular Fe-Cr-Ni alloy has an adverse effect on its mechanical properties and corrosion resistance. In the present work, precipitation behavior of UNS S32205 duplex stainless steel (a Fe–Cr–Ni alloy) during controlled cooling and heating (isothermal aging) has been studied in the temperature range of 973–1073 K (700–800 °C). Scanning electron microscope (SEM), X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and energy-dispersive spectrometer (EDS) attached to SEM were used to characterize the microstructures. The effect of precipitation of σ and χ phases on the micro-hardness was also studied. The precipitation sequence for 1023 K (750 °C), when cooled from 12,000 to 5 °C/min, was δ → carbides → χ → σ, while for 1073 K (800 °C), it was found to be δ → χ → σ. The Mo-enriched metastable χ phase nucleates at the initial stage of aging which then transforms to stable σ precipitates. The amount of σ and χ phases increased with temperature and aging time, but temperature was found to have a dominant role than the cooling rate due to higher diffusion of solute atoms at high temperatures. EBSD studies did not show any orientation relationship between parent δ ferrite and σ phase.

Low-field magnetic analysis for sigma phase embrittlement monitoring in thermally aged 22Cr duplex stainless steel

The aim of this study is to evaluate a new nondestructive method designated as Low-Field Magnetic Analysis (LFMA) based on the measurement of magnetic flux density for monitoring sigma (σ) phase precipitation in duplex stainless steel (DSS). In addition, the effect of isothermal aging treatment at 800 °C on the metallurgical degradation of UNS S31803 DSS was investigated. It was found a change in the volume fraction of α-Fe/γ-Fe phases due to α-Fe (ferromagnetic phase) eutectoid decomposition to precipitate sigma and secondary austenite (paramagnetic phases). A significant and gradual reduction of saturation magnetization was observed with the increase of thermal treatment time, indicating a decrease in the quantity of α-Fe phase. Two magnetic methods were used to verify the evolution of the σ phase: M−H measurements at 300 K using a commercial magnetometer and LFMA testing. Both methods were sensitive to small percentages of σ phase in the microstructure. Furthermore, our developed technique presents accurate results for low magnetic fields with high sensitivity and reliability.

Application of electromechanical impedance technique in the monitoring of sigma phase embrittlement in duplex stainless steel

Duplex stainless steels (DSS) have a structure composed of austenite and ferrite in approximately equal volume fractions which provides an excellent integration between mechanical properties and corrosion resistance. However, the formation of intermetallic phases, such as sigma (σ) phase could become a major problem, once a small percentage of this phase originates a drastic deterioration of toughness and ductility, phenomenon known as σ phase embrittlement. In the present work, the effect of the isothermal aging treatment at 800 °C (temperature in which σ phase can be formed) on the degradation of mechanical properties of UNS S31803 DSS was investigated. The results showed that σ phase precipitation occurred regularly and by eutectoid decomposition. The effect of sigma phase on the mechanical properties was analyzed by the microhardness and impact tests at room temperature. The assessment of DSS also includes an σ phase embrittlement monitoring alternative method based on the electromechanical impedance (EMI), using piezoelectric sensors. The basic idea of the σ phase embrittlement monitoring method is that the increase in the hardness and the decrease in the impact toughness will leads to the variation in the EMI signatures by modifying structural stiffness. The proposed methodology is evaluated using the impedance module (|Z|), resistance (R), reactance (X) and by the statistical indexes: Relative Variation of Natural Frequencies (RVNF) and Root Mean Square Deviation (RMSD). This method is considered a nondestructive test, presents accurate results with high sensitivity and reliability providing capacity of determining sigma phase embrittlement and has promising application potential in this and other materials.

Influence of Electropulsing Treatments on Mechanical Properties of UNS S32750 Duplex Stainless Steel.

Prestrained at 5% and 15% duplex stainless steel UNS S32750 specimens have been subjected to electropulsing treatments with current density of 100 A/mm2 and 200 A/mm2 and 100 and 500 pulses for each current density value. Corrosion tests, X-ray diffraction, microhardness and residual stresses were collected before and after the electropulsing treatments. Tensile tests were performed after the electropulsing treatments in order to compare the mechanical response to reference tensile tests performed before pulsing treatments. Increase in fracture strain was observed after pulsing treatment in comparison to the reference tensile tests. A decrease in microhardness was also observed after electropulsing treatments for both degrees of prestrain. Electropulsing treatment almost eliminates the work-hardened state in the 5% prestrained specimens while partially recovered the 15% prestrained material increasing both uniform and fracture strain. Bulk temperature of the samples remained the same for all treatments duration. The effect are to be addressed to a combined effect of increase in atomic flux due to the electrical current and local joule heating in correspondence of crystal defects. Electropulsing treatment applied to metallic alloys is a promising technique to reduce the work hardening state without the need of annealing treatments in a dedicated furnace.