Behavior Of Duplex Stainless Steel Research Articles

Effect of annealing process on microstructure, residual stress, and fatigue behaviour of AISI 2205 duplex stainless steel

ABSTRACT This study investigated the microstructure, residual stress, and fatigue behavior of duplex stainless steels that have been annealed with different annealing processes. A cold-rolled AISI 2205 Duplex Stainless Steel (DSS) sample was annealed in three ways for this purpose. In modes 1 and 2, samples were annealed at 500°C for 6 and 8 hours, respectively. The sample was annealed for 6 hours at 950°C for mode 3.The Optical Microscopy (OM) technique was used to determine the crystallographic texture and microstructural characteristics. An X-ray Diffraction (XRD) analysis was used to determine the residual stresses in austenite and ferrite phases on pre- and post-heat-treated samples. The Scanning Electron Microscope (SEM) technique was utilized to assess fatigue cracks. The results showed that the texture microstructure of the specimens using mode 1 and 2 were remained; the grain had a smaller fragmentation. The elongation grains of the specimen after mode 3 were smaller, relatively spheroidal, and more homogeneous. There was a reduction in residual stress after mode 3 annealing process. The fatigue strength of the specimens that under applied this process was 11.1% higher than that of specimens in the as-received state.

Understanding heterogeneity and anisotropy of Duplex Stainless Steel's elastic/plastic nature through property mapping technique

Accelerated property mapping, an advanced indentation technique was used to describe the nanomechanical behaviour of duplex stainless steel (DSS) surfaces prior to and post heat treatments. Heterogeneity in deformation responses and relative elastic and/or plastic nature of DSS was assessed on longitudinal and transverse directions through load–displacement curves, property maps, histograms of hardness (H), modulus (E) and indentation works. Empirical ratios such as H/E, (H/E)1/2, H3/E2 and plasticity index were employed to understand the anisotropy across the directions.

Dynamic Constitutive Model and Numerical Simulation of S32760 Duplex Stainless Steel Based on Dislocation Theory

Background: To describe the complex mechanical behavior of S32760 duplex stain-less steel under high strain rate and high-temperature loading conditions. Objective: The constitutive model of S32760 duplex stainless steel suitable for high strain rate was constructed from the micro-scale. Methods: Based on the theory of dislocation dynamics, the effects of different strain rates and strains on the plastic deformation of ferrite and austenite were analyzed, and the thermal stress term and non-thermal stress term of ferrite and austenite phases were coupled. Results: The simulation results of the model show that the S32760 dual-phase constitutive model has a high degree of fit with the experimental data at high strain rates. Conclusion: Compared with the classical J-C model, the results show that the constitutive model of this patent has more accurate predictability than the J-C model in describing the mechanical behavior of duplex stainless steel in the high strain range of 5000s-1 to 10000s-1.

Tribological Behavior of Duplex Stainless Steel with Laser Peening Treatments Without Coating

Tribological Behavior of Duplex Stainless Steel with Laser Peening Treatments Without Coating

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

Electroplastic Effect during Tension and Bending in Duplex Stainless Steel.

The deformation behavior of duplex stainless steel under tension and bending, accompanied by a pulsed current and when heated by an external source, is investigated. The stress-strain curves are compared at the same temperatures. The contribution to the decrease in flow stresses is greater when using a multi-pulse current at the same temperature, compared to external heating. This confirms the presence of an electroplastic effect. An increase in the strain rate by an order of magnitude reduces the contribution of the electroplastic effect from single pulses to the reduction in flow stresses by 20%. An increase in the strain rate by an order of magnitude reduces the contribution of the electroplastic effect from single pulses to the reduction in flow stresses by 20%. However, in the case of a multi-pulse current, the strain rate effect is not observed. Introducing a multi-pulse current during bending reduces the bending strength by a factor of two and the springback angle to 6.5.

Experimental investigation and micromechanical modeling of load partitioning behavior of duplex stainless steel 2205 during cyclic hardening

This paper aims to understand the load partitioning behavior between austenite and ferrite of duplex stainless steel 2205 under cyclic loading by experiments, including a series of low cycle fatigue tests and electron back scattered diffraction observation. Meanwhile, a crystal plasticity finite element model was developed to predict the cyclic micromechanical response of two constituent phases. The results show that more slip bands were found within the austenite. The cyclic plasticity of 2205 started within the austenite, and gradually translated into the ferrite with the elevation of applied cyclic amplitude. The plastic deformation within the austenite was inclined to form at the phase boundaries, while it promoted at grain boundaries in the ferrite. The micromechanical elasto-viscoplastic parameters of two constituent phases were calibrated accurately. The proposed crystal plasticity finite element model has a great ability of predicting not only the time- and amplitude- macroscopic cyclic hardening behavior but also the micro-deformation within two constituent phases, even the cyclic hardening of 2205 with different phase ratios can also be reproduced accurately. The prediction error on cyclic stress amplitude of 2205 during cyclic hardening can be controlled within 3.2%.

A microstructure-based three-scale homogenization model for predicting the elasto-viscoplastic behavior of duplex stainless steels

A new microstructure-informed three-scale homogenization scheme for elasto-viscoplastic heterogeneous materials is developed. It is applied to predict the mechanical behavior of cast duplex austenitic-ferritic (AF) steels, which are widely used in primary loop of pressurized water reactors (PWR). At the first scale (microscale), the elasto-viscoplastic behavior of single crystals for both phases is modeled using linear elasticity and a viscoplastic crystal plasticity model. An “affine” type formulation based on the first moments of stresses is applied to the inelastic non-linear part of the deformation. Then, at the second scale (mesoscale), an EBSD-informed two-phase austenite/ferrite laminate structure (LS) model is developed with {110}-type habit planes (HP) in ferrite and a Kurdjumov-Sachs orientation relationship (KS-OR) between both phases. At the third scale (macroscale), the model considers a single ferritic primary grain as an aggregate of spherical two-phase laminate structure domains corresponding to the 24 KS-OR variants. The elasto-viscoplastic self-consistent scheme (EVPSC) is used through the Translated Fields (TF) method to obtain the effective behavior at this scale. The TF-EVPSC scheme is also used for an ensemble of primary ferritic grains to identify materials parameters from experimental tensile curves corresponding to as received and aged specimen. From EBSD measurements, the crystallographic data are thoroughly analyzed to physically feed the three-scale model. The results are discussed in terms of stress/strain responses in ferrite and austenite, which are correlated to the different KS-OR variants and HP orientations. The effect of primary ferritic grain crystallographic orientation and aging is also studied regarding monotonic and cyclic tests to study the possible origins of backstress in this material.

Strengthening Effect of Nb on Microstructure and Cavitation Erosion Behavior of Duplex Stainless Steel Surfacing Layer

Strengthening Effect of Nb on Microstructure and Cavitation Erosion Behavior of Duplex Stainless Steel Surfacing Layer

Biaxial deformation behaviour of duplex stainless steels: Experiments and crystal plasticity based stress predictions

Biaxial tensile tests are performed on two phase duplex stainless steel using a newly developed multiaxial testing rig integrated with a digital image correlation mapping facility. A cruciform-shaped specimen geometry is subjected to equibiaxial tensile (EBT) loading, and the load–strain response is captured. Unlike uniaxial tensile testing, a well-defined gauge area is absent in biaxial specimens; hence, stress cannot be estimated directly. Finite element analysis is used to calculate the stress state. The phenomenological finite element model failed to capture the inherent anisotropy of the material; hence, a crystal plasticity finite element based method is used to estimate the stresses. It is observed that the 0.2% proof stress increased, but the strain to failure remained constant in comparison with uniaxial tensile properties. The work hardening behaviour is isotropic similar to that observed during uniaxial testing. The goss and rotated goss orientations in austenite accommodated most of the strain along RD and TD, respectively. During EBT, the change in austenite and ferrite textures is minimal and similar to their single phase counterparts reported in the literature. The EBT test results indicate that the influence of micromechanical interactions between the phases on the work hardening behaviour and texture evolution is weak.

Partitioning behavior of N and its effect on hot deformation behavior of duplex stainless steels 2101 and 2205

Partitioning behavior of N and its effect on hot deformation behavior of duplex stainless steels 2101 and 2205

Micromechanical Observation and Numerical Simulation for Local Deformation Evolution of Duplex Stainless Steel.

The characteristics of local strain distribution and evolution of duplex stainless steel during the tensile process were studied using the digital image correlation (DIC) technique. In addition, the finite element inversion of nanoindentation experiments of austenitic and ferrite phases in duplex stainless steel was carried out to obtain the stress-strain response of the two phases. Further, based on the representative volume element (RVE) and the material parameters obtained from the finite element inversion method, the local stress and strain behavior of duplex stainless steel at microscale was simulated numerically. The results fit well with the experiments, showing that the austenite phase is softer than ferrite phase, with the larger strain zone concentrated in the austenite phase and the larger stress zone concentrated in the ferrite phase. The grain boundaries are prone to obvious stress and strain concentrations. The local stress and strain distributions are influenced by the shape and interaction of the grains, while the distribution features become more obvious as the load increases. The research results effectively reveal the two-phase interaction and local failure mechanism of duplex stainless steel, and may provide a reference for material preparation and safety design of related structures.

Characterization of the Isothermal and Thermomechanical Fatigue Behavior of a Duplex Steel Considering the Alloy Microstructure

Isothermal and thermomechanical fatigue behavior of duplex stainless steel (DSS) X2CrNiMoN22-5-3 was investigated. The aim of this work was to understand the fatigue behavior by correlation of the isothermal and thermomechanical fatigue behavior with microstructural observations. Fatigue tests at plastic-strain-amplitude of 0.2% were carried out at 20, 300 and 600 °C, while in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) experiments were performed between 300 and 600 °C. During the 20 °C fatigue test, a continuous softening was observed. Transmission electron microscopy examinations reveal pronounced planar slip behavior in austenite. At 300 °C, deformation concentrates in the ferrite, where strong interactions between CrxN and dislocations were observed that explain the pronounced cyclic hardening. DSS studied exhibits softening throughout the whole isothermal fatigue test at 600 °C. In ferrite, during the 600 °C fatigue test, the G phase, γ′ austenite precipitated, and an unordered dislocation arrangement was observed. The stress responses of the TMF tests can be correlated to those of the isothermal fatigue tests. In IP mode, a positive mean stress resulted in premature failure. No γ′ austenite but the formation of subgrains in the ferrite phase was observed after TMF tests. The plastic deformation of the austenite at high temperatures results in an unordered dislocation arrangement.

Effect of Sigma Phase on Corrosion Behavior of Duplex Stainless Steel

Effect of Sigma Phase on Corrosion Behavior of Duplex Stainless Steel

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

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

Effect of laser beam welding on microstructure, tensile strength and fatigue behaviour of duplex stainless steel 2205

This study focuses on the microstructure, tensile and fatigue properties of laser beam welded butt joints in 4 mm thick sheets of duplex stainless steel 2205. The microstructural characteristics of the joints were investigated via optical microscopy and electron backscattered diffraction. A 300 μm wide heat affect zone with increased ferrite content and a nearly fully ferritic 800 μm wide fusion zone were found. No porosity could be found with X-ray radiography. Microhardness measurements revealed increased strength in the fusion and heat affect zones of the weldments. Uniaxial tensile and stress controlled fatigue tests were performed in order to characterize the mechanical properties of specimens containing laser beam welded joints and the base material. The specimens containing weldments were stronger, but less ductile than the base material, due to the weld metal restricting deformation. The as-welded joints exhibited worse fatigue performance than the base material due to the notch at the excess weld metal. The fatigue properties of the specimens containing joints could be elevated to the base material level by a laser surface remelting treatment.

Behaviour of duplex stainless steel bolted connections

This study deals with the behaviour of duplex stainless steel bolted connections. The aim of the study is to respond to the question if the current stainless steel design specifications are able to predict the behaviour of such connections. Firstly, the net cross-section capacity of duplex stainless steel plates subjected to tensile loading are presented. They were conducted to obtain the stress–strain curves and tensile fracture behaviour used to support the finite element (FE) fracture simulations. Secondly, nonlinear FE models are developed for duplex stainless steel bolted connections subjected to tensile loading. The FE models are validated against experimental data in terms of load–displacement curves, failure modes and ultimate loads. Then, a numerical parametric study that consists of 133 duplex stainless steel grade EN 1.4162 bolted connection specimens is carried out. The failure modes of bolted connections are carefully examined, including combined tear out and bearing, bearing and net section, looking at the influence of parameters such as end distance, edge distance and spacing between the bolts in the connections. The results are compared to the design rules prescribed in the current stainless steel design specifications. Generally, it is found that the Australian/New Zealand (AS/NZS), American (SEI/ASCE) Specification and European codes conservatively predict the ultimate strengths of the bolted connections, whereas the strengths predicted by the AS/NZS and SEI/ASCE specifications are overall more accurate and less scattered.

Comparison of corrosion behavior of 2205 and 2507 duplex stainless steel in simulated flue gas condensate of a waste incineration power plant

Abstract The corrosion behavior of duplex stainless steel 2205 DSS and 2507 DSS in simulated flue gas condensate of a waste incineration power plant at 180 °C was compared by micro-area electrochemical testing, surface and weight loss analysis. The results showed that the corrosion resistance of the two stainless steels decreased with the increase of Cl− concentration. After 48 h of corrosion, when the Cl− concentration was not less than 6 g·L−1, active sites where current density increased suddenly appeared on the surface of 2205 DSS, accompanied by the obvious increase of surface roughness and the weight loss. The lowest Cl− concentration that caused the appearance of active sites on the surface of 2507 DSS was 20 g·L−1, with less surface corrosion products and lower degree of general corrosion.

Slurry Erosion Behavior of Cast 25 Cr Austenitic-Ferritic Steel with Niobium Addition for Subsea Pipelines

Austenitic-ferritic steel, as suggested by its name, has an equal fraction of austenite and ferrite phases, also known as duplex stainless steels (DSS), are one of the highly used materials for subsea pipelines applications. The presence of slurries is inevitable in subsea pipelines. This technical work elucidates the slurry erosive wear behavior of duplex stainless steel and the impact of the addition of niobium (Nb) on the phenomena. Vacuum induction melting was used to produce duplex stainless steel, and its Nb added casts. The aim of the work is to compare both castings' for erosive wear behavior using a slurry jet erosion tester. Computational thermodynamic software Thermo-calc was used to investigate the presence of numerous phases in the system. X-ray diffraction (XRD) has confirmed the formation of niobium carbide in the steel, indicated by Thermo-calc. The effect of slurry velocity (30, 40, and 50 m/s) and impingement angle of slurry (30°, 45°, and 90°) on wear characteristics of these castings were analyzed using volume loss measurements, optical profilometry, and scanning electron microscopy (SEM). The erosion rate of both the materials increased with increasing velocity, whereas erosion was more at shallow angles of impact and increased significantly at the slurry jet's normal incidence. Refinement of austenitic grains in the ferritic pool hints at an increase in heterogeneous nucleation in Nb-doped samples; at the same time, the samples have shown increased hardness and superior erosion resistance against the slurry jet impact.