Properties Of Duplex Stainless Steel Research Articles

Evolution of microstructure and mechanical properties in 2205 duplex stainless steels during additive manufacturing and heat treatment

Metal additive manufacturing (AM) offers exceptional design freedom, but its high thermal gradients often generate non-equilibrium microstructures with chemical and interfacial instabilities. Steels that solidify as δ-ferrite often experience a further solid-state phase transformation to austenite during AM. The detailed nature of this phase transformation during AM is yet to be fully understood. Duplex stainless steel, which is known for its unique combination of high corrosion resistance and mechanical properties, is a suitable alloy to further study this phase transformation.The current study aims to gain novel insights into solid-state phase transformations and mechanical properties of duplex stainless steels during laser powder-bed fusion (LPBF). As-printed microstructures exhibit significant deviations when compared to conventionally manufactured counterparts in terms of phase balance and morphology, elemental partitioning, and interface character distribution. During LPBF, only a small fraction of austenite forms, mostly at the ferrite-ferrite grain boundaries, via a phase transformation accompanied by diffusion of interstitials. Austenite/ferrite boundaries are shown to terminate on {100}F//{111}A planes. This is due to the character of parent ferrite-ferrite boundaries which is dictated by the sharp <100> texture and geometry of austenite grains induced by directional solidification and epitaxial growth of ferrite. Benchmarking mechanical properties against a wrought counterpart demonstrates that AM offers high strength but relatively low ductility and impact toughness. A short heat treatment reverts the microstructure back to its equilibrium state resulting in balanced tensile and toughness properties, comparable to or even better than those of wrought counterparts.

Study on fracture properties of duplex stainless steel and its weld based on micromechanical models

The application of stainless steel in structures is increasing recently, but few related seismic studies have been conducted. The purpose of this paper is to study the ductile fracture behavior, especially under Ultra-low-cycle fatigue (ULCF) of duplex stainless steel and its weld based on micromechanical fracture models. A total of 148 specimens covering multiple geometries were manufactured from duplex stainless steel base metal, heat-affected zone, and weld metal. To investigate the mechanical properties of these materials and calibrate the parameters of constitutive models, monotonic and cyclic tests of smooth round bars were conducted. Moreover, monotonic and cyclic tests of notched round bars were performed, followed by the finite element method analyses to calibrate the fracture models including void growth model (VGM), the stress modified critical strain (SMCS) model, and the cyclic void growth model (CVGM). VGM and SMCS were verified to be effective for these materials to predict ductile fracture under monotonic loading, but CVGM cannot calculate the accurate damage under different cyclic test conditions. Then the CVGM was modified by a novel damage variable. Desirable fitting results were obtained by adopting this damage variable. While duplex stainless steel base metal exhibits excellent ductility, that of the welds is much lower with large dispersion. The reason for the low toughness of welds was found to be related to the unbalanced microstructure formed in welding. The study contributes to developing fracture prediction models of duplex stainless steel, and benefits the research on the seismic behavior of duplex stainless steel structures.

Influence of Homogenization and Annealing Temperatures on the Microstructure, Mechanical Properties, and Passive Properties of Cold Rolled 2205 Duplex Stainless Steel

The effects of homogenization, cold working, and subsequent annealing treatment were studied on the microstructural evolution, mechanical properties, and passive properties of duplex stainless steel (DSS). A hot-rolled 2205 DSS was subjected to two processing routes. In one, the DSS goes through an extra homogenization step at 1100 °C for 1800 s before cold rolling. After cold deformation (~75%) the specimens were isothermally annealed at 900, 1000, and 1100 °C for 180 s. The microstructure evolution was studied by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XDR). Mechanical properties were evaluated by microhardness and tensile tests. The electrochemical behaviors were investigated by potentiodynamic measurements, electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis (MS). Chemical composition of the lowest corrosion resistant passive film was assessed by X-ray photoelectron spectroscopy (XPS). Homogenization before cold rolling lowered strain hardening, slowing the microstructural transformation process. The thermomechanical process did not change the semiconductor type of the passive films. However, grain refinement after annealing improved the corrosion resistance in borate buffer solution. Cold rolling significantly decreased the corrosion resistance. The passive film of the specimen homogenized before cold rolling had the lowest corrosion resistance and high amounts of Cr(OH)3 and FeO.

Influence of process parameters on microstructural and mechanical properties of duplex stainless steel 2205 (1.4462) processed by DED-LB\\M

Duplex stainless steels (DSS) combine excellent corrosion resistance with outstanding mechanical properties. Typical applications can be found in chemical, gas and offshore industries, where corresponding components usually feature a high degree of customization. This makes additive manufacturing an economically interesting production approach. However, a major challenge in additive manufacturing of DSS is a precise process control to achieve the required material properties. In this work, DED-LB\\M was used to process DSS 2205. A multistage experimental procedure was developed to generate nearly fully dense cuboidal specimens (relative density > 99.9 %). In addition, the complex interaction mechanisms between process parameters and resulting material properties such as microstructure and hardness were investigated. For specific process conditions, the desired ferrite-austenite balance of DSS could be obtained. Furthermore, the hardness was found to decrease with increasing build height and correlates with grain size as well as the slightly decreasing ferrite content.

Preparation and corrosion resistance properties of duplex stainless steel (00Cr22Ni6MnMoCu)

In the present paper, a new kind of duplex stainless steel (DSS, 00Cr22Ni6MnMoCu) was prepared. Cr30 was chosen as a comparison of microstructures and mechanical properties with 00Cr22Ni6MnMoCu. Corrosion tests with 3.5% NaCl solution and electrolytic solution for 00Cr22Ni6MnMoCu were carried out to analyze the corrosion pattern of test materials. It can be concluded that: (1) Austenitic and ferrite duplex stainless steel has an optimized phase distribution, high toughness and strength when the ratio of two-phase content is 1:1. (2) Corrosion tests show that the corrosion resistance of 00Cr22Ni6MnMoCu is 12 times compared to ferrite stainless steel Cr30. (3) Electrolytic corrosion tests show that for 00Cr22Ni6MnMoCu, the corrosion is caused by intergranular corrosion. For Cr30, it is mainly caused by pinholes. However, Cr30 has a poor corrosion resistance because of the presence of a large amount of carbides and their phase boundaries caused by the electric potential difference between the carbide and the matrix.

Enhanced corrosion resistance and wear resistance of duplex stainless steel processed by shot-peening combined with electrochemical nitriding

ABSTRACT To improve the wear resistance and anticorrosion property of duplex stainless steel (DSS), surface treatment combining high-energy shot-peening (HESP) and electrochemical nitriding was applied to DSS. The strong nitride peak detected through X-ray photoelectron spectroscopy indicated that HESP pretreatment accelerated the electrochemical nitriding process. The treatments improved the microhardness of DSS from 242 HV(100g) to 450 HV(100g) and the wear resistance of DSS was considerably enhanced. Electrochemical tests revealed that HESP pretreatment improved the passivation ability of the nitriding layer of DSS in the borate buffer and 3.5 wt-% NaCl solutions. The greater corrosion resistance of the nitriding layer was attributed to the passive film with lower a number of structural defects. The nitriding layer on the HESP-pretreated DSS showed good corrosion resistance in the 3.5 wt-% NaCl solution.

Quantitative Description of Duplex Stainless Steels Microstructure Using Selective Etching

The properties of duplex stainless steels (DSSs) depend on the ferrite–austenite ratio, on the content of secondary phases and on the contamination with non-metallic inclusions. To assess the quality of DSSs, it is necessary to use an integrated approach which includes controlling for the volume fraction, the morphology and the distribution of all phases and non-metallic inclusions. Samples of several grades of DSSs were obtained using various heat treatments, such as solution annealing and quenching from 1050 to 1250 °C to obtain different amounts of ferrite and to provoke annealing at 850 °C to precipitate σ-phase. As a result, a metallographic technique of phase analysis in DSSs based on selective etching and subsequent structure parameters estimation according to ASTM E1245 was developed. We demonstrated that the developed method of quantitative analysis based on selective etching and metallographic analysis according to ASTM E1245 allows us to obtaining much more accurate results, compared to the point count method described in ASTM E562 and to the XRD method.

Technology and Challenges in Additive Manufacturing of Duplex Stainless Steels

Duplex stainless steels (DSS) comprise equivalent proportions of ferrite (α) and austenite (γ) and exhibit excellent integration of mechanical and corrosion properties. The ferrite matrix provides better strength and stress corrosion resistance, whereas the austenite matrix accounts for good pitting corrosion resistance and toughness. Duplex stainless steels are widely utilized in the chemical industry, oil refineries, and machine industries. Direct energy deposition (DED) and powder bed fusion (PBF) are the two additive manufacturing techniques widely used for metals. This article covers the technologies like processing DSS by selective laser melting (SLM), variation in mechanical and microstructural properties of duplex stainless steels manufactured by additive manufacturing technique, and challenges of additive manufacturing processes.

The Effect of Microstructural Changes on Mechanical and Electrochemical Corrosion Properties of Duplex Stainless Steel Aged for Short Periods.

This work reports the effects of Microstructural changes due to the secondary phases, in particular sigma (σ), on the mechanical properties and electrochemical behavior of thermally aged duplex stainless steel (DSS). Structural, morphological, mechanical, and electrochemical characterizations were performed. Sigma phase content increased with increasing aging treatment time. It had a net-like shape, as observed by electron backscatter diffractometry (EBSD). Its presence directly damaged mechanical properties. The corrosion assessment included electrochemical impedance spectroscopy (EIS) in 1 M NaCl solution at temperatures of 25, 40, and 65 °C. EIS results demonstrate that an increase in the σ phase content decreased the corrosion resistance (21.1–0.8, 3.5–0.3, and 3.1–0.2 kΩ cm2 at 25, 40, and 60 °C, respectively).

Effect of Welding Processes on the Microstructure and Mechanical Properties of Duplex Stainless Steel Weld Joints

Abstract The objective of the present investigation involves studying the microstructure and mechanical properties of duplex stainless steel (DSS) alloy 2205 and super DSS (SDSS) alloy 2507 weld joints fabricated by tungsten inert gas (TIG) welding and its variant, activated TIG (A-TIG) welding. Square butt weld joints were fabricated from 10-mm-thick plates of DSS and SDSS using single pass A-TIG and multi-pass TIG welding processes. The filler wire ER2209 was used for multi-pass TIG welding of DSS 2205, and ER2594 filler wire was used for multi-pass TIG welding of SDSS 2507. The microstructure in the A-TIG weld metals was found to be coarser, which was caused by high peak temperatures during A-TIG welding. The microstructures exhibited different forms of austenite, including grain boundary allotriomorphs, Widmanstätten side plates, and intragranular precipitates in the weld metal. In the A-TIG weld metals, the microstructure exhibited a balanced ferrite-to-austenite ratio. The hardness values of multi-pass TIG weld joints were higher compared to A-TIG weld joints. The tensile and yield strengths of multi-pass TIG weld joints were higher compared to A-TIG weld joints, which was mainly due to higher delta ferrite content and finer microstructure. The toughness values obtained by Charpy impact testing were higher in A-TIG weld joints compared with multi-pass TIG weld joints at room temperature, which was mainly due to the balanced ferrite-to-austenite ratio in the weld microstructure. However, at subzero temperatures, the A-TIG weld joints exhibit lower impact toughness because of their coarser weld metal structure.

Microstructure-based multiscale approach to obtain mechanical property of duplex stainless steel according to ICME concept

We have proposed a microstructure-based multiscale simulation framework based on Integrated Computational Material Engineering (ICME) concept and applied it to the simulation of hot rolling process of a duplex stainless steel. In the study, the finite element simulation of the hot rolling process is performed. The mechanical property of a slab is calculated on the basis of its underlying solidified microstructures, which are simulated by the multi-phase field method coupled with CALPHAD thermodynamic database. The properties of constituent phases in the solidified microstructure is obtained by the first-principles calculation, the molecular dynamics simulation and nano-indentation tests. The mathematical homogenization method is used to calculate the property of slab based on the microstructure. This paper reviews the application of the multiscale simulation framework to a SUS304 duplex stainless steel.

Metallurgical behavior of duplex stainless steel 2205 joints welded using GTAW and FCAW process

Objectives: The aim of the present work was to investigate the influence of welding process variation as well as post weld thermal aging treatment on the metallurgical properties of Duplex Stainless Steel (DSS) 2205 welds. Method: Butt welded joints were fabricated using 10 mm thick plates of DSS 2205 by two different welding processes namely, Gas Tungsten Arc Welding (GTAW) process and Flux Cored Arc Welding (FCAW) process. These welded specimens were further subjected to thermal aging treatment at 800°C for 40 minutes to study the precipitation tendencies in the welds. Findings: Ferrite content was found to increase more in case of thermally aged FCAW joints as compared to the thermally aged GTAW joints. Also, GTAW weld metal showed a softening effect while FCAW weld metal underwent hardening after thermal aging treatment. Aging resulted into variation of ferrite content indicating that the process change can affect the important metallurgical ratio of austenite to ferrite in these welds. Ferrite phase was the predominating phase that showed dissolution which led to different inter-metallic phase formations like carbides, oxides as well as sigma phase formation. Application/Improvements: The present study is beneficial from the industrial view point, as the data generated through this piece of research can be directly used for DSS fabrications. Keywords: DSS, FCAW Process, GTAW Process, Metallurgical Properties, Welded Point

Post-fire mechanical and corrosion properties of duplex stainless steel: Comparison with ordinary reinforcing-bar steel

This paper is a preliminary study on the merits of using duplex stainless steel (DSS) as concrete reinforcements. It looks into the post-fire mechanical and corrosion properties of the wrought DSS 2205 after annealing at 500 °C, and compare them with those of an ordinary rebar steel. Spinodal decomposition of the ferrite phase strengthens and embrittles the 2205 DSS. For the rebar steel, however, softening occurs. Even after the 2205 DSS is exposed to 500 °C for 1 week, its ductility as indicated by fracture strain is still comparable to that of the unannealed rebar steel. The present data show that after short-term exposure to temperatures under 500 °C, the ductility and retention of strength of the 2205 DSS are better than those of the the rebar steel. The corrosion performance of the 2205 DSS, both in 3.5% NaCl and in 3.5% NaCl + Ca(OH)2, is also better than that of the unannealed rebar steel even if the former is exposed to 500 °C for 1 week.

Influence of heat input in electron beam process on microstructure and properties of duplex stainless steel welded interface

The influence of heat input in electron beam (EB) process on microstructure, mechanical properties, and pitting corrosion resistance of duplex stainless steel (DSS) welded interface was investigated. The rapid cooling in EB welding resulted in insufficient austenite formation. The austenite mainly consisted of grain boundary austenite and intragranular austenite, and there was abundant Cr2N precipitation in the ferrite. The Ni, Mo, and Si segregation indicated that the dendritic solidification was primarily ferrite in the weld. The weld exhibited higher hardness, lower toughness, and poorer pitting corrosion resistance than the base metal. The impact fractures of the welds were dominated by the transgranular cleavage failure of the ferrite. The ferrite was selectively attacked because of its lower pitting resistance equivalent number than that of austenite. The Cr2N precipitation accelerated the pitting corrosion. In summary, the optimised heat input slightly increased the austenite content, reduced the segregation degree and ferrite texture intensity, decreased the hardness, and improved the toughness and pitting corrosion resistance. However, the effects were limited. Furthermore, optimising the heat input could not suppress the Cr2N precipitation. Taking into full consideration the microstructure and properties, a heat input of 0.46 kJ/mm is recommended for the EB welding of DSS.

Structural and Magnetic Properties of Duplex Stainless steel (UNS S31803) Powders Obtained by high Energy Milling of Chips with Additions of NbC

In this study, the high energy mechanical milling was utilized to the production of duplex stainless steel powders from the recycling chips with and without the addition niobium carbide. The effect of milling time and addition carbide on the morphology, particle size and magnetic properties of the powders was investigated. The utilization of the powder metallurgy constitute an important alternative for the reuse of waste in the industrial sector. The milling was realized using a planetary ball mill for 20 hours at a milling speed of 350 rpm and ball-to-powder weight ratio of 15:1were used, and the (0% and 3 wt. %) niobium carbide (NbC) addition. Scanning electron microscopy and particle distribution analysis were used for characterization of morphology and measure of particle size. Also, to analyze the transformations of phases were investigated using the magnetic characterization and x-ray diffraction. The results indicated that the addition of niobium carbide results in the reduction of the particle size of steel of the order of 20%, besides the reduces the transformation of austenite into strain induced martensitic phase.

Effect of solution treatment on microstructure and properties of duplex stainless steel

The influence of solution treatment on microstructure and properties of 2205 duplex stainless steel (DSS) was studied. The microstructure, precipitates and corrosion resisting property were observed and analyzed by means of optical microscopy (OM), scanning electron microscopy (SEM) and electrochemical methods. The results showed that a large number of brittle σ-phase precipitates, which deteriorate the plasticity and corrosion resistance of the material, were easy to produce in the duplex stainless steel under the low temperature. The precipitation of σ-phase can be decreased and the plasticity and corrosion resistance can be improved by increasing solution temperature. In addition, the ferrite content increases with the increase of solution temperature, while less affected by cooling rate.

Effect of Sintering Atmosphere and Solution Treatment on Density, Microstructure and Tensile Properties of Duplex Stainless Steels Developed from Pre-alloyed Powders

In this research, Powder Metallurgy (P/M) of Duplex Stainless Steels (DSS) of different compositions were prepared through pre-alloyed powders and elemental powders with and without addition of copper. The powder mix was developed by pot mill for 12 h to obtain the homogeneous mixture of pre-alloyed powder with elemental compositions. Cylindrical green compacts with the dimensions of 30 mm diameter and 12 mm height were compacted through universal testing machine at a pressure level of 560 ± 10 MPa. These green compacts were sintered at 1350 °C for 2 h in hydrogen and argon atmospheres. Some of the sintered stainless steel preforms were solution treated at 1050 °C followed by water quenching. The sintered as well as solution treated samples were analysed by metallography examination, Scanning Electron Microscopy and evaluation of mechanical properties. Ferrite content of sintered and solution treated DSS were measured by Fischer Ferritoscope. It is inferred that the hydrogen sintered DSS depicted better density (94% theoretical density) and tensile strength (695 MPa) than the argon sintered steels. Similarly the microstructure of solution treated DSS revealed existence of more volume of ferrite grains than its sintered condition. Solution treated hydrogen sintered DSS A (50 wt% 316L + 50 wt% 430L) exhibited higher tensile strength of 716 MPa and elongation of 17%, which are 10–13% increment than the sintered stainless steels.

Influence of Ferrite Phase Content on the Electrochemical Properties of Duplex Stainless Steels

Duplex stainless steels have a large number of industrial applications and may replace high cost materials, especially in chloride-containing environments like seawater in off-shore platforms due to their high mechanical properties and good corrosion resistance. The influence of the ferrite content on the performance of duplex stainless steels in these corrosive environments is not well known. For the present paper, new superduplex stainless steels with ferrite between 30 and 60% were developed and their microstructure and corrosion resistance were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in NaCl 3.5% (wt %) at 26°C and 78°C. The results obtained at 26°C showed that the pitting potential (Epitt) is little affected by the ferrite content, but for the materials with higher ferrite it was possible to observe an increase in the repassivation potential with a decrease in the corrosion potential and passive currents due to the presence of more resistive passive films. Tests performed at 78°C indicated a high decrease in the Epitt for all the samples, independently of the ferrite percentage, although maintaining superiority in higher ferrite content. Alloys with a 55% ferrite phase content, i.e. less dependent of Ni element, present a superior performance of corrosion resistance.

Heat Treatment of Duplex Stainless Steel 2205 by Inserting Nano Nd2FeB14 in HIP Manifolds Under the Scope of Category Theory

In this paper, improving mechanical properties of duplex stainless steel by spinodal reaction inhibitors has been discussed. Spinodal gaps can be minimized when the host particles are minimized to the nanoscale. The Cahn-Hilliard Equation and the Allen-Cahn Equation on Manifolds with Conical Singularities can be related to manifolds produced by hot isostatic pressing (PM HIP) are used to improve mechanical strength. Spinodal reactions will be Inhibited by magnetic treatment and Nd-Fe-B Magnets. Grain refiners will be used to retard spinodal reactions. Mathematically, category theory is used to establish links between these different concepts.

Influences of hydrogen and textural anisotropy on the microstructure and mechanical properties of duplex stainless steel at high strain rate (~105 s−1)

Duplex stainless steels (DSS) have exceptional mechanical properties, such as high strength and ductility, and are commonly used for pressure vessels and underwater pipelines. One of the main problems experienced in maximizing DSS service life is their interaction with hydrogen. Hydrogen, which is common to most manufacturing processes and services, can lead to the deleterious effect known as hydrogen embrittlement. The susceptibility of steels to hydrogen failure is directly related to hydrogen’s interaction with steel’s defects (traps), and therefore grain texture can have a major influence on the trapping phenomenon. The purpose of this study is to analyze the influences of hydrogen and textural anisotropy on DSS mechanical properties at high strain rate (~105 s−1). This includes the influence of hydrogen on crystallographically isotropic (equiaxed grains) and in crystallographically anisotropic (elongated grains) DSS on dynamic properties. The simulation of DSS exposed to explosions during extreme conditions of failure was performed by planar shock wave experiments at a very high pressure (~19 GPa). The great importance of these experiments is their ability to change the plasticity and deformation mechanism of the metal, and therefore, provide new insights into hydrogen behavior at high deformation levels. The effect of grain texture on dynamic properties was shown to play an important role in the elastic–plastic response at high strain rate. This phenomenon repeats itself when hydrogen is involved in the process. It was shown that the susceptibility to hydrogen embrittlement decreases at very high pressures ≤8 GPa for elongated grains and ≤19 GPa for equiaxed grains.