Microstructure Of Duplex Stainless Steel Research Articles

Effect of welding processes on ferrite content, microstructure and mechanical properties of super duplex stainless steel 2507 welds

Abstract Super duplex stainless steel (SDSS) plates of 6 mm thickness have been welded using tungsten inert gas, activated tungsten inert gas, electron beam welding and friction stir welding processes. Among these, in the first two, melting and solidification of material occurs slowly whereas, it is faster in electron beam welding process and no melting occurs in friction stir welding. Macro and microstructural studies, hardness surveys, tensile tests and percentage of ferrite content were compared for all the welds. The ferrite–austenite phase balance is 50 % each, with electron beam weld metal at about 65 % ferrite. This showed the hardness of the weld metal and heat affected zones to be higher than base metal. The weldment joint efficiencies are more than 90 %. The fracture location is found to be in the weld metal for tungsten inert gas and activated tungsten inert gas weld, in the nugget for friction stir welds and in the base metal for electron beam welds. The ductility of electron beam weld joints is 32 % while it is around 20 % for the others. The preferred order while choosing the welding process should be activated tungsten inert gas welding, tungsten inert gas welding, electron beam welding, and friction stir welding.

Effect of aging on the microstructure and properties of ASTM A890 3A duplex stainless steel

Exposure of duplex stainless steels to high temperatures could result in microstructure changes generating precipitated phases and significantly affecting material properties. In this paper, the effects of aging at 450–850 °C on the microstructure and properties of ASTM A890 3A duplex stainless steel were studied. The microstructures were different after aging at different temperatures: only γ2 was precipitated after aging at 450 and 550 °C, γ2, M23C6, and σ phases were observed at 650 °C, and an additional phase of χ was found at 750 °C. Aging at 450 °C increased the strength of duplex stainless steel while aging at other temperatures negligibly affected strength. Aging at 450 °C and 650–850 °C significantly decreased the impact toughness. Correspondingly, the fracture was partially or completely transformed from a ductile fracture mode before aging to a brittle fracture mode after aging. Aging deteriorated the corrosion resistance of duplex stainless steel. Aging at 750 °C had the most significant effect: the breakdown potential decreased by 28%, and the membrane resistance decreased by 81.9% relative to those without aging. The above changes in properties were closely related to the embrittlement of duplex stainless steel at 475 °C and the precipitation of the σ-phase and χ-phase.

Effect of heat treatment atmospheres on microstructure evolution and corrosion resistance of 2205 duplex stainless steel weldments

The effects of post heat treatment atmosphere on microstructure and corrosion resistance of duplex stainless steel welded joints were investigated. Post weld heat treatment (PWHT) was carried out with and without protective atmospheres. Nitrogen and argon are used as protective gases individually. Detailed microstructure examination (optical and SEM) demonstrates that nitrides precipitates are highly observed in the welded zones for nitrogen protected samples. An observed drop of ferrite volume fraction in post weld heat treated samples compared with welded samples without heat treatment leading to corrosion resistance enhancement of heat treated welded joints. An exception for using nitrogen as heat treatment atmosphere a decreased corrosion resistance of weldments is investigated due to nitride precipitates. An increase in the weld zone hardness for post weld heat treated samples compared with base alloy. The initial hardness of duplex stainless steel was 286 Hv while average hardness of weld zone was 340, 411, 343, and 391 Hv for as welded, PWHT using air, argon, and nitrogen atmospheres, respectively. Weld zone hardness increased to 33, 44, 20, and 37%. A significant decrease in the ultimate tensile strength and elongation after PWHT. The initial Ultimate tensile strength duplex stainless steel base material was 734.9 MPa while Ultimate tensile strength of the welded joints was 769.3, 628.4, 737.8, and 681.4 MPa for the following conditions: as welded, PWHT using air, argon, and nitrogen atmospheres, respectively.

Effect of Heat Input on the Microstructure and Mechanical Properties of Local Dry Underwater Welded Duplex Stainless Steel

Duplex stainless steel welded metals were underwater local dry prepared on S32101 lean duplex stainless steel trapezoidal groove plates with a self-made drain cover employing Supercore 2205P flux-cored filler wire. Different heat inputs were employed to investigate the effects on mechanical characteristics and the microstructure of welded metals. The results demonstrated that as the heat was applied, austenite concentrations in the weld metals increased. It was found that the austenite concentration and the fraction of Σ3-austenite twin-grain boundaries followed the same trends. With increasing heat input, the recrystallized ferrite and austenite grains initially decreased and subsequently increased, whereas the fraction of interphase boundaries between special ferrite and austenite exhibited the reverse trend. With a heat input of 1.4 kJ/mm, the toughness and plasticity of the weld metals were enhanced by an increase in austenite content, Σ3 recrystallized grains, and austenite twin-grain boundaries. The plasticity and tensile strength values of the welded metal changed more when the heat input was raised from 1.0 to 1.2 kJ/mm than when it was raised from 1.2 to 1.4 kJ/mm. Considering energy conservation, it is recommended to adopt 1.2 kJ/mm for welding heat input.

Effect of Mn on Microstructure and Corrosion Resistance of Duplex Stainless Steel Surfacing Layer

Effect of Mn on Microstructure and Corrosion Resistance of Duplex Stainless Steel Surfacing Layer

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

Effect of In-Situ Ti2N on Microstructure and Properties of SAF2906 Duplex Stainless Steel Fabricated by Laser Melting Deposition

Effect of In-Situ Ti2N on Microstructure and Properties of SAF2906 Duplex Stainless Steel Fabricated by Laser Melting Deposition

Numerical Prediction for the Effects of Welding Interpass Temperature on the Thermal History and Microstructure of Duplex Stainless Steels

Numerical simulation was used to predict the thermal behavior and the resulting microstructure at the heat-affected zone (HAZ) of a 170 mm diameter and 3.5 mm thickness super duplex stainless steel (SDSS) UNS S32750 tube. In order to evaluate the thermal response from the model, a usual welding situation involving interpass temperature (IT) and its influence on the HAZ microstructure was exploited. Thus, two superimposed autogenous welding passes were simulated, the first clockwise with the tube in the room temperature and the second, counterclockwise, with the tube at the temperature of 250oC. Even subjected to successive thermal cycles and high interpass temperature, the proportion and morphology of the phases at the HAZ and Fusion Zone (FZ) did not present significant differences when comparing the two welding passes. Meanwhile, nitrogen losses should be avoided during welding in order to obtain a balanced microstructure in DSS welds, contributing to guarantee satisfactory toughness in addition to resistance to pitting corrosion. The predictions from the simulation were validated by using experimental results obtained from the autogenous TIG (Tungsten Inert Gas) process.

Dissimilar welding of super duplex stainless steel (SDSS) and pipeline steel – A brief overview

There are different grades of stainless steels available in the market for its better corrosion resistance but super duplex stainless steel find their name due to the presence of two phase microstructure. Due to the complex metallurgical behavior the welding of super duplex stainless steel is quite difficult as compared to the normal grades of the stainless steel. Austenite and ferrite are the two main phases present in super duplex SS almost in equal proportions. To provide better strength, corrosion resistance and sulfide stress cracking than the normal stainless steels, these super duplex SS (SDSS) are specially designed to meet the requirements of structural and pressure vessel applications. This paper basically study about the dissimilar welding challenges during welding of various grades of super duplex stainless steels. Different secondary phases has been formed in the microstructure of duplex stainless steels (DSSs) when these steels are exposed to higher temperatures. These secondary phases degrade their performance at excessive higher temperatures. To minimize the degradation of the engineering performance of DSSs at higher temperatures various types of isothermal treatments have been used.

Effects of Heat Treatment on Microstructure and Mechanical Properties of a Transformation-Induced Plasticity-Aided Economical Duplex Stainless Steel

In order to obtain steel with high tensile strength and elongation and good pitting resistance, the economical duplex stainless steel with and without the addition of tungsten (W) was prepared in this paper. The comparison and distribution of the two phases were controlled by optimizing the heat treatment process. The highest product of tensile strength and elongation of Cr19 series duplex stainless steel (DSS) DSS were obtained after solution treatment at 1050 °C for 5 min, up to 58692 Mpa%(876 Mpa * 67%), when the area f.raction of α was about 50.7%. The addition of tungsten reduces tensile strength due to the increased area fraction of α at 1050–1150 °C. Finer grain size leads to higher tensile strength after solution treatment at 1050 °C. The microstructure is characterized by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The steels exhibit an excellent transformation-induced plasticity (TRIP) effect after the solution treated is at 1050 °C, which may primarily be due to the existence of a more unstable austenite phase. The TRIP effect acts through the phase transformation of γ to α′-M during high deformation, and the orientation relationship of {111}γ || {110}α′-M & <110>γ || <001>α′-M belongs to the standard variants of Nishiyama–Wassermann relationship.

Effect of Solution Treatment Temperature on Microstructure, Mechanical Properties, and Corrosion Resistance of 5A Super Duplex Stainless Steel

Effect of Solution Treatment Temperature on Microstructure, Mechanical Properties, and Corrosion Resistance of 5A Super Duplex Stainless Steel

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.

Study on Microstructure and Corrosion Resistance of Duplex Stainless Steel 2205 in Real Seawater Rich containing Mold

Study on Microstructure and Corrosion Resistance of Duplex Stainless Steel 2205 in Real Seawater Rich containing Mold

New comprehension on the microstructure, texture and deformation behaviors of UNS S32101 duplex stainless steel fabricated by direct cold rolling process

The effect of cold deformation on the detailed microstructure evolution, texture development and deformation behaviors/mechanisms of UNS S32101 duplex stainless steel (DSS2101) during the direct cold rolling process was investigated. The results showed that throughout the cold deformation process, the negative texture of {001}<110> component was nonexistent in deformed ferrite, and most texture components were mainly concentrated on α/γ-fibers. Detwinning in austenite was substantial responsible for the reorientation in {111}<112> towards {111}<110> of γ-fiber in ferrite rather than martensite transformation. Austenite texture were composed of {110}<100> Goss and {110}<115> Goss/Brass components at heavy deformation (50% and 70%). The refinement and deformation behavior in ferrite was attributed to microbands (MBs) subdivision and dislocation activities, whilst that of austenite mainly occurred through twinning, strain induced detwinning (SID) and strain induced martensite (SIM).

Detailed Hall–Petch Analysis of Cold Rolled and Annealed Duplex 2205 Stainless Steel

The grain size of duplex 2205 stainless steel is controlled by cold rolling followed by annealing, where grain refinement and grain coarsening are achieved via primary recrystallization and grain growth, respectively. Annealing treatment is conducted at 620 and 1120 °C, followed by water quenching, where the former temperature results in the formation of χ‐phase (chi‐phase) during annealing heat treatment. Based on tensile testing and Hall–Petch analysis, simple equations are proposed for relating the yield stress and ultimate tensile strength to the grain size and relative volume fractions of ferrite and austenite in the dual‐phase microstructures. The outcome of this research is helpful in controlling the microstructure and mechanical properties of duplex stainless steels.

Study on the evolution of microstructure and mechanical properties of lean duplex stainless steel 2101 with 60 GPa% PSE prepared using a short process

Owing to the special dual phase structure and high N content of duplex stainless steel, hot-working performance is poor, which is also a significant factor complicating its production. Therefore, a short process of direct cold rolling following solution treatment of the casting billet is proposed in this study. In addition, the synergistic deformation behavior of multiphase during the deformation of LDX 2101, as well as the action mechanism of the transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) composite deformation mechanisms in austenite is investigated. Further, the strain-hardening and fracture mechanisms of LDX 2101 are investigated using in-situ electron back-scattered diffraction (EBSD). The results indicate that when the strain is small (ε < 0.2), the TWIP effect dominates, and the deformation twins contribute to the strain hardening rate. Conversely, when the strain (ε ≥ 0.2) is increased，the strain distribution in metastable austenite increases and the stability decreases. Meanwhile, the TRIP effect can be induced by the deformation twins. Furthermore, as martensite's nucleation position increases, the TRIP effect begins to dominate. As a result, austenite does not complete the transformation of martensite during the early stages of deformation, but rather during the middle and late stages, delaying the generation of necking and improving the elongation. Therefore, the reason for LDX 2101's high strength and elongation can be attributed to the synergistic effect of TWIP and TRIP. However, the twin formation is selective. Additionally, cracks are most frequently found at the α/α′ interface and at the torsion of the shear bands within the ferrite grain. Consequently, LDX 2101 failed due to the propagation and bonding of open cracks.

Simulation of nucleation and growth of austenite in duplex stainless steels – metallurgical study on weld metal of duplex stainless steel SUS329J1

The microstructure of duplex stainless steels is formed by dendrite growth in the primary ferrite-phase and by subsequent solid-state transformation to the secondary austenite-phase. In this study, formation of austenite by solid-state transformation in duplex stainless steels was evaluated. The nucleation and initial growth of austenite was simulated by the software TC-PRISMA. The formation temperatures of austenite in previous works were corresponding to the calculation obtained by adjusting the interfacial energy. Moreover, the microstructure formation process both in grain boundary and intragranular was simulated using a multi-phase field method (MICRESS software). The growth of austenite was assumed to be under paraequilibrium considering the diffusion control of nitrogen and its morphology was assumed to be an acicular growth. The microstructure morphologies were relatively similar to those obtained by the experiments. The simulation method in this study can analyse complex microstructural morphology as well as predict the composition distributions. This method is considered to be highly effective in designing duplex stainless steels and in evaluating the microstructure morphology in welding process.

Correlation of Microstructure, Texture and Dynamic Softening Mechanism of Uns S32101 Duplex Stainless Steel During Elevated Temperature Tensile

Correlation of Microstructure, Texture and Dynamic Softening Mechanism of Uns S32101 Duplex Stainless Steel During Elevated Temperature Tensile

Effect of nitrogen protection on weld metal microstructure and intergranular behavior of S32101 duplex stainless steel 15 m water depth hyperbaric laser underwater welding

In this study, 16-mm-thick S32101 duplex stainless steel were welded using hyperbaric underwater laser welding system in 0.15 MPa. The misorientation angle distribution of grain boundaries in the weld metal was analyzed using the electron backscatter diffraction technique. The ionic currents near the surface of metallography were measured by the Scanning Vibrating Electrode Technique (SVET) and performed to evaluate the intergranular corrosion (IGC) resistance based on corrosion current density. The volume fractions of ferrite and austenite and the grain boundary misorientation angle affect the IGC sensitivity of the welded joints. The relationship between the grain boundary misorientation angle of the austenite and corrosion resistance was analyzed. When the weld metal was shielded with nitrogen, and the volume fraction of austenite and the frequency of Σ3 coincidence site lattice boundary in the weld was increased. The misorientation angle distribution in the austenite and the frequency of Σ3 coincidence site lattice boundary influence the IGC resistance of the welded joints.

Microstructure, texture and mechanical properties of a nickel-free high nitrogen duplex stainless steel processed through friction stir spot welding

A nickel-free high nitrogen duplex stainless steel holding high Mn-content was friction stir spot welded under the various rotational speeds. The microstructure/texture evolutions of the joints and the correlated mechanical properties were investigated in detail. The ferrite and austenite constituent massive phases were refined down to the mean grain size of 0.9 μm and 1.1 μm, respectively. The microstructure evolutions revealed the activation of continuous dynamic recrystallization as the main restoration mechanism. This was further verified through the formation of Β- and Α-fiber shear texture in the specimens processed under the various processing condition. Besides the activation of different restoration micro-mechanisms in both ferrite and austenite, dynamic phase transformation of ferrite to austenite was also contributed in grain refinement. The transformation was facilitated by providing more diffusional paths through substructure development and grain refinement. The local and bulk mechanical properties of the joints were also assessed. The outstanding tensile-shear peak load of 12.8 KN obtained for the sample welded at 400 rpm was discussed relying on the developed ultrafine-grained microstructure and the maximum peak extension of 1.7 mm achieved at 600 rpm was attributed to the role of ferrite phase in strain accommodation.