Duplex Stainless Steel Research Articles

Effect of arc energy on the microstructure and electrochemical behavior of duplex stainless steel weld overlay deposited by GMAW process

Effect of arc energy on the microstructure and electrochemical behavior of duplex stainless steel weld overlay deposited by GMAW process

Sigma‐Phase Distribution in 2507 Super Duplex Stainless Steel Continuous Casting Slabs

The sigma‐phase distribution in a 2507 super duplex stainless steel continuous casting slab is analyzed using microstructural analyses and thermodynamic calculations. The sigma phase contains high Cr and Mo contents, and precipitates along the phase boundary between austenite and ferrite and grows toward the interior of the ferrite phase in the continuously cast slab. The sigma‐phase fraction at the center of the width direction is higher than that in the one fourth width. Furthermore, the sigma‐phase fraction at the center of the thickness direction is higher than those at the upper and lower surfaces, which is due to the lower cooling rate at the center. The Brinell hardness (HB) at the center increases to 313 HB with an increasing sigma‐phase fraction. The sigma‐phase fraction at the one fourth thickness near the lower surface is higher than that at the one fourth thickness near the upper surface at the same cooling rate. Additionally, Mo and Ni are severely segregated in this zone. A higher Mo content influences the precipitation and stabilization of the sigma phase. Furthermore, Scheil–Gulliver calculations indicate that compositional segregation results in an increase in the sigma‐phase precipitation temperature range.

Effects of Base Metal Preheating on the Microstructure, Mechanical Properties, and Corrosion Resistance of UNS S32750 SDSS Pulsed Nd:YAG Laser Welding

Super duplex stainless steel has a microstructure consisting of equal proportions of austenite and ferrite. However, welding with Nd:YAG pulsed laser results in an imbalanced microstructure that compromises the steel’s properties. This paper studied the effects of preheating the base metal on pulsed Nd:YAG laser welding. Four conditions were evaluated (no preheating and heating at 100 °C, 200 °C, and 300 °C). The analysis included studying the microstructure, microhardness, and corrosion resistance. Preheating the base metals was found to be an effective method for increasing the volume fractions of austenite. The preheated samples showed an improvement in corrosion resistance compared to the untreated sample. The microhardness varied, with the ferrite amount being higher in the untreated sample.

Maintaining Excellent Mechanical Properties via Additive Manufacturing of Low-N 25Cr-Type Duplex Stainless Steel.

Duplex stainless steel (DSS) exhibits good mechanical properties and corrosion resistance, and has attracted more and more attention within the fields of both science and technology. However, the increasing levels of N and of Cr, Mo, etc., as alloying elements in DSS increase production difficulty. In particular, the N element increases the risk of Cr2N precipitation, which can seriously deteriorate the thermal plasticity of DSS, while increasing its strength. For this reason, a low-N-content 25Cr-type DSS was designed in order to adapt additive manufacturing processes. With regard to the nano-inclusions of oxide precipitation and effective grain refinement, and considering the benefits of selective laser melting fabrication, a low-N 25Cr-type duplex stainless steel with a 0.09 wt.% N content achieved high mechanical properties, with a yield strength of 712 MPa and an elongation of 27.5%, while the V-notch impact toughness was 160 J/cm2. The microstructure evolution and the reasons behind the improvement in mechanical properties will be discussed in detail.

Effect of cutting parameters on pitting corrosion resistance of S32760 duplex stainless steel

AbstractTo improve the performance in service of S32760 duplex stainless steel (DSS) in the marine environment, the influence of cutting parameters of S32760 DSS on the pitting corrosion resistance of the workpiece is studied. Cutting experiments are performed on S32760 DSS by varying the cutting parameters to investigate their effects on the surface morphology. The electrochemical experiments are conducted on the workpiece immersed in the 3.5 wt% sodium chloride solution to investigate how the cutting parameters affect the pitting corrosion resistance of S32760 DSS. The results indicate that the pitting corrosion resistance is influenced by the cutting speed and feed rate, which in turn affects the surface roughness. The cutting depth does not have a significant impact on the surface roughness but significantly affects the pitting resistance. The recommended cutting parameters are as follows: feed rate of 0.1 mm/r, cutting speed of 130 m/min, and cutting depth of 0.4 mm.

Microstructure and corrosion resistance of 23Cr9Ni4Mo2Mn filler duplex stainless steel 2205 fabricated by wire arc additive manufacturing with subsequent severe shot peening and Ni58Cr20Fe5Mo10 plasma spray coating

In the current study, 23Cr9Ni4Mo2Mn (FeAs) filler and duplex stainless steel 2205 materials were used in multi-layer deposition processes for wire arc additive manufacturing (WAAM) process. The WAAM samples were prepared with WAAM coated (WAAM-C) and Post-shot peening coated WAAM (PSPC-WAAM) in order to improve the microstructure and surface properties. The severe shot peening process and Ni58Cr20Fe5Mo10 plasma spray coating was increase the corrosion resistance and outer layer strength, whereas different types of structure were observed in the WAAM-DSS plates: Solid phase martensite (SPM), acicular austenite phase (AAS), FeCr2O4, martensite-austensite phase (MAP) and multi-phase ferrite structure. The severe shot peening procedure and Ni58Cr20Fe5Mo10 plasma spray coating samples were clearly visible in the Electron Backscatter Diffraction (EBSD) analyses, which also showed that the outer and inner surface layers of the samples contained CrFe2O4, NiFe2O4 cubic ferromagnetic oxide, and BiFeO3 phase. Direct mixing of the 23Cr9Ni4Mo2Mn filler with the base materials produced a homogenous structure with a high bonding strength. Bi1<001>, Bi2<111>, and Bi3<110> of the BiFeO3 crystal structure were discovered in the inner surface layer according to the PSPC-WAAM sample of angle 0–1800 texture results, whereas the WAAM-C sample of the outer layer revealed that As1<001>, As2 < 100>, and As3 < 111> of the α-martensite structure were exposed at the outer surface layer. PSPC-WAAM had a 6 % increase in hardness over WAAM-C in both the inner and outer surface regions. Hardness value of PSPC-WAAM was 286 HV on NiCr bulk structure demanded, whereas ferrite secondary phase of WAAM-C have increased the hardness value at 224 HV compared to the base materials. Both the PSPC-WAAM and WAAM-C samples achieved improved corrosion resistance and strong surface bonding. The WAAM, WAAM-C, and PSPC-WAAM samples were the subject of potential dynamic experiments, AFM and wear properties.

Effect of Co on the corrosion resistance and erosion-corrosion behavior of duplex stainless steel surfacing layer

Effect of Co on the corrosion resistance and erosion-corrosion behavior of duplex stainless steel surfacing layer

Comparative Study on the Corrosion Behavior of Materials in Heat Recovery Steam Generators for Combined Cycle Power Plant, Based on Sulfuric Acid Concentrations: Carbon Steels vs. Duplex Stainless Steel (UNS S32205)

This study examined the effects of sulfuric acid concentrations on the corrosion behaviors of three types of commercial steels, conventional carbon steel (SA192), sulfuric acid dew resistant steel (S-TEN), and duplex stainless steel (S32205), considered to be potential materials for the heat recovery steam generator (HRSG) in combined cycle power plants. Based on the results of electrochemical polarization, immersion and wet-dry cycle tests, when exposed to a high sulfuric acid concentration (50%), SA192 and S-TEN exhibited higher corrosion resistance than S32205, which was due to the formation of a stable FeSO4 scale on the carbon steel materials. With prolonged exposure, S-TEN with slightly higher concentrations of Cu and Sb showed lower weight loss than SA192. Conversely, when subjected to low sulfuric acid concentrations (5 and 10%), S32205 exhibited passivation behavior, and showed significantly superior corrosion resistance (i.e., much smaller weight loss) than the other two steel samples. The examination of localized corrosion damages through cross-section observation using a scanning electron microscope revealed also that S32205 suffered less damages from the wet-dry cycling. The long-term superior corrosion resistance of duplex stainless steel in low sulfuric acid concentrations, compared to carbon steel and sulfuric acid due resistant steel, make it a promising candidate material for the HRSG in combined cycle power plants.

Assessing the viability of high-frequency spot melting for super duplex stainless steel 2507 via electron beam powder bed fusion

This study investigates the use of Electron Beam Powder Bed Fusion (PBF-EB) spot melting on SDSS 2507, a material known for its high tensile strength, corrosion resistance, and welding properties. Spot melting, a localized melting technique, utilize a stationary beam to create melt pools before rapidly repositioning to form new ones, offering precise control over material properties in additive manufacturing. We conducted a design of experiments with 32 samples and analysed them using SEM, XRD, EBSD, optical microscopy, nanoindentation and statistical modelling.Elevated PBF-EB processing temperatures significantly influence microstructure and phase composition. XRD analysis identified the presence of the detrimental sigma phase. EBSD analysis revealed a composition primarily consisting of austenite (63 %) and sigma phase (33.5 %), with residual ferrite (3.5 %). Statistical modelling demonstrated that a combination of spot-time, spot distance, focus offset, and layer thickness was the most reliable predictor for density while area energy proved to be the most accurate predictor for hardness, with R2adj values of 0.766 and 0.802, respectively.Our study confirms that PBF-EB is capable of processing SDSS 2507 through spot melting, resulting in high-density samples at high productivity rates. The presence of sigma phase shows a need for post build heat treatment to achieve the desired phase distribution. This research enhances the understanding of the process and also holds promise for industrial applications.

Flow Stress of Duplex Stainless Steel by Inverse Analysis with Dynamic Recovery and Recrystallization Model

Flow Stress of Duplex Stainless Steel by Inverse Analysis with Dynamic Recovery and Recrystallization Model

Study of fatigue fracture characteristics for duplex stainless steel STHE welded joint specimen

A shell and tube heat exchanger (STHE) welded joint is considered for fatigue fracture mechanism. The joint is made up of a protruding tube fabricated to a tubesheet by means of welding. A super duplex stainless steel (DSS) material is used for the tube and tubesheet. Fatigue test was newly conducted using the single tube test specimen. The initial cracking plane was moved from the minimum sectional-area plane that was perpendicular to the loading direction, and the crack growth was almost planar. Stress analysis is carried out using finite element method (FEM) and the stress distributions are carefully studied by comparing the simple perforated plate. In addition, three-dimensional crack propagation (CP) simulation is performed employing extended finite element method (X-FEM). Fracture phenomenon is verified using the experimental and numerical crack front geometries. The fracture mechanics parameter is evaluated and verified with empirical formulae. CP behaviors are carefully discussed based on the fracture mechanics parameter. The CP life is presented for three loading amplitudes. The FAT class of the STHE welded joint is studied based on the available design standards such as BS, IIW and JSSC. Finally, the fatigue fracture characteristics of the STHE welded joint specimen are shown through the experimental and numerical methods.

Electrochemical and mechanical characterization of welded super duplex stainless steel .

Electrochemical and mechanical characterization of welded super duplex stainless steel .

Features of welding duplex stainless steels in wet underwater welding in comparison with welding in air (Review)

Features of welding duplex stainless steels in wet underwater welding in comparison with welding in air (Review)

Hot deformation behavior and microstructure evolution of each single phase in DSS

This paper presents a systematic experimental study to clarify the relationship between the hot deformation conditions and microstructure evolution and flow stress of the individual ferrite and austenite phases of duplex stainless steels (DSS), and to quantitatively compare the deformation behaviors of each phase under the same hot working conditions. Single-phase steels with the ferrite and austenite chemistry of the phases in the DSS were prepared for this investigation. The microstructure evolution and deformation behavior of the individual phases were investigated in one-pass hot uniaxial compression tests up to a strain of 0.8 at a wide range of working temperatures from 1000 to 1250 °C and strain rates from 0.1 to 30.0 s−1. The compressed microstructures of each phase were investigated, and microstructure evolution maps were proposed to demonstrate the relationship between the compressed microstructure and deformation conditions. The flow curves of each phase were also analyzed quantitatively, showing that the ferrite phase had lower hot strength and a lower work hardening exponent n, and higher strain rate sensitivity m and temperature sensitivity A compared to the austenite phase. The strength ratio of each phase from early to late deformation was expressed using the Zener-Hollomon parameter, and equations and constants for the strength ratio of the phases were proposed.

Sigma phase kinetics in DSS filler metals: A comparison of sigma phase formation in the as-welded microstructure of super duplex stainless steel and hyper duplex stainless steel

This study investigates and compares the kinetics of sigma phase formation in established Super Duplex Stainless Steel (SDSS) and recently developed Hyper Duplex Stainless Steel (HDSS) filler metal wires. Experimental sigma phase time-temperature-transformation (TTT) maps were developed, revealing nearly equivalent interface area/volume, resulting in similar sigma phase kinetics for 1% volume despite the higher Cr and Mo content in HDSS. However, the growth rate to 5% and 10% sigma phase volumes was slightly higher in HDSS. The sigma phase kinetics in both SDSS and HDSS were analyzed using the exponential Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach based on experimental TTT data. Linearized plots from the JMAK calculations showed a transition in kinetics mechanism from eutectoid decomposition and interface-controlled growth to a diffusion-controlled growth stage in both materials. The higher volumes and morphologies of the sigma phase were found to be diffusion-dependent, mainly occurring during the second kinetics stage. The influence of HDSS's higher Cr and Mo content on the growth rate was observed for these higher volumes. For applications within the 1% sigma phase limit, both wires exhibited equivalent susceptibility to sigma phase formation, regardless of the higher alloying in HDSS.

Optimizing rotary friction welding parameters to attain maximum strength in duplex stainless steel tube joints

Optimizing rotary friction welding parameters to attain maximum strength in duplex stainless steel tube joints

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.

Effect of explosive welding on the interface characteristics of S32750/Q245R composite plate

ABSTRACT Super duplex stainless steel S32750 has excellent corrosion resistance. It is combined with carbon structural steel Q245R through explosive welding, not only with good mechanical properties but also with a satisfactory economic cost. In this paper, the characteristics of the bonding interface of S32750/Q245R explosive welding composite plate were analyzed. The interface of the composite plate exhibits a consistent wavy bonding interface with vortices. The adiabatic shear band was only observed on the S32750 plate side near the bonding interface, while defects such as pores, cracks, and inclusions were also detected at the bonding interface. The EBSD analysis revealed the presence of a layer of fine-grained grains close to the interface of the S32750 side, and the grains beyond this fine-grained layer were elongated and shaped like fibers. The largest plastic deformation occurs near the interface on the super duplex stainless steel side. The microhardness test results indicate that the highest hardness presents near the interface of the S32750/Q245R composite plate side, with the hardness being slightly higher at the wave waist than the wave peak and trough. The hardness of the composite plate showed a decreasing trend from the bonding interface to the plate edges on both sides.

Influence of Pulsed Arc Parameters on the Tig Welding Process for the Stainless Steel Duplex UNS S31803.

The influence of parameters involved in the pulsed electric arc, used as an energy source in the tungsten inert gas (TIG)-mediated welding of Duplex UNS S31803 stainless steel, to attend the manufacture of flexible pipes for the extraction of oil and gas is presented. A fundamental part in the manufacturing process of flexible pipelines is the welding of these strips so that corresponding TIG welds will be subjected to the same process and work conditions. Therefore, it is necessary to maintain the same properties in the welded regions. Covering the effects of each parameter of the pulsed electric arc such as peak and base current as welds, cyclic ratio, and pulsation frequency is a desirable endeavor. The final objective is the mitigation of problems that have a great impact on production, such as weld breakage during the conformation of the strip in the process and test failures. With this, tensile, bending, and ferrite percentage tests were performed on 12 samples that qualified as satisfactory in the visual aspect. A minimum tensile strength of 734.57 MPa and a maximum of 775.77 MPa were obtained where all values found are above the tensile strength limit of the base material of 620 MPa. With the completion of the study, it is possible to understand not only the response of the process to each parameter but also the tendency when changing them. Moreover, it is possible to explore the possibility of guiding the changes to achieve results about the visual aspect and the mechanical properties of the welded material.

A comparative study into the fracture toughness properties of duplex stainless steels

Beside their high mechanical strength, duplex stainless steels are a suitable choice in highly corrosive environments. These types of steels are used in steel bridges more and more frequently exposed to low temperatures and fatigue loads. However, for low temperature applications, it must be guaranteed that brittle fracture is avoided since duplex stainless steel shows a toughness-temperature relationship similar to that of carbon steel. For this reason, in the frame of the German national FOSTA research project “P 1390”, comprehensive investigations have been started into the material selection of duplex stainless steel to avoid brittle fracture considering the fracture mechanic based background of EN 1993-1-10. For this purpose, Charpy-V impact tests and fracture toughness tests have been systematically carried out for various duplex stainless steels in order to create the basis for the development of toughness requirements for new duplex classes. The validity of the already existing Master Curve concept and the applicability of the transition temperature correlation for duplex stainless steels based on experimental fracture toughness and Charpy-V impact tests have been investigated. The aim of this contribution is to present first results of these investigations.