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3 pages, 187 KiB

Open AccessEditorial

Advances in Duplex Stainless Steels

by Luca Pezzato and Irene Calliari

Materials 2022, 15(20), 7132; https://doi.org/10.3390/ma15207132 - 13 Oct 2022

Cited by 4 | Viewed by 1213

Abstract

Duplex stainless steels (DSSs) are a group of stainless steels characterized by a biphasic microstructure consisting of ferrite and austenite [...] Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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18 pages, 6738 KiB

Open AccessArticle

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

by Claudio Gennari, Luca Pezzato, Gianmarco Tarabotti, Andrea Zambon, Andrea Di Schino and Irene Calliari

Materials 2020, 13(7), 1613; https://doi.org/10.3390/ma13071613 - 01 Apr 2020

Cited by 20 | Viewed by 2302

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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14 pages, 12735 KiB

Open AccessArticle

Maintenance of the Austenite/Ferrite Ratio Balance in GTAW DSS Joints Through Process Parameters Optimization

by Bryan R. Rodriguez, Argelia Miranda, David Gonzalez, Rolando Praga and Eduardo Hurtado

Materials 2020, 13(3), 780; https://doi.org/10.3390/ma13030780 - 08 Feb 2020

Cited by 14 | Viewed by 2880

Abstract

The present work describes the influence of the parameters employed in the gas tungsten arc welding process (GTAW) when nickel powder is used as a filler metal in 2304/2507 duplex stainless-steel dissimilar joints. Multi-objective optimization was applied in order to maintain the austenite/ferrite [...] Read more.

The present work describes the influence of the parameters employed in the gas tungsten arc welding process (GTAW) when nickel powder is used as a filler metal in 2304/2507 duplex stainless-steel dissimilar joints. Multi-objective optimization was applied in order to maintain the austenite/ferrite percentage in the welded zone. A microstructural and phase quantification analysis was performed in each sample through optical and scanning electron microscopes. It was found that a nickel powder addition combined with low heat input increased the biphasic ratio across the different zones of the dissimilar welded samples. Although the austenite volume fraction increased in the 2304 heat-affected zone (HAZ) near to 25%, it was not sufficient according to international standards. The obtained results led to the maintenance of the 50/50 phase percentage in the 2507 HAZ welded joint side, as well as to the increment of the austenite percentage in the 2304 HAZ. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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14 pages, 8322 KiB

Open AccessArticle

Study of the Thermochemical Surface Treatment Effect on the Phase Precipitation and Degradation Behaviour of DSS and SDSS

by Alisiya Biserova-Tahchieva, Jose Maria Cabrera and Nuria Llorca-Isern

Materials 2020, 13(1), 165; https://doi.org/10.3390/ma13010165 - 01 Jan 2020

Cited by 11 | Viewed by 2550

Abstract

In this study, the effect of a plasma ion carburizing process to duplex and superduplex stainless steels (DSS and SDSS), at 925 °C for a long time, as thermochemical process influencing the microstructural evolution is presented. The objective is to analyse the diffusion [...] Read more.

In this study, the effect of a plasma ion carburizing process to duplex and superduplex stainless steels (DSS and SDSS), at 925 °C for a long time, as thermochemical process influencing the microstructural evolution is presented. The objective is to analyse the diffusion elements’ influence on the precipitation of secondary phases after additional short thermal treatment. A comparison among the different treatments was performed after the resulting microstructures were analysed by Field Emission—Scanning Electron Microscope. Precipitation of secondary phases—sigma (σ), chi (χ), nitrides and carbides—seemed to occur during the treatments in a similar way for both steels (DSS and SDSS), although they showed a different morphology and precipitation mode. General corrosion behaviour of untreated and treated samples was investigated by potentiodynamic tests in order to prove their corrosion resistance. It was found that an improvement of the surface protection after the plasma carburizing process occurred. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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11 pages, 3958 KiB

Open AccessArticle

Nd: YAG Pulsed Laser Dissimilar Welding of UNS S32750 Duplex with 316L Austenitic Stainless Steel

by Carla Gabriela Silva Leite, Eli Jorge da Cruz Junior, Mattia Lago, Andrea Zambon, Irene Calliari and Vicente Afonso Ventrella

Materials 2019, 12(18), 2906; https://doi.org/10.3390/ma12182906 - 09 Sep 2019

Cited by 11 | Viewed by 3319

Abstract

Duplex stainless steels (DSSs), a particular category of stainless steels, are employed in all kinds of industrial applications where excellent corrosion resistance and high strength are necessary. These good properties are provided by their biphasic microstructure, consisting of ferrite and austenite in almost [...] Read more.

Duplex stainless steels (DSSs), a particular category of stainless steels, are employed in all kinds of industrial applications where excellent corrosion resistance and high strength are necessary. These good properties are provided by their biphasic microstructure, consisting of ferrite and austenite in almost equal volume fractions of phases. In the present work, Nd: YAG pulsed laser dissimilar welding of UNS S32750 super duplex stainless steel (SDSS) with 316L austenitic stainless steel (ASS), with different heat inputs, was investigated. The results showed that the fusion zone microstructure observed consisted of a ferrite matrix with grain boundary austenite (GBA), Widmanstätten austenite (WA) and intragranular austenite (IA), with the same proportion of ferrite and austenite phases. Changes in the heat input (between 45, 90 and 120 J/mm) did not significantly affect the ferrite/austenite phase balance and the microhardness in the fusion zone. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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23 pages, 11022 KiB

Open AccessArticle

Corrosion and Oxidation Behavior of a Fe-Al-Mn-C Duplex Alloy

by Silvia Barella, Andrea Francesco Ciuffini, Andrea Gruttadauria, Carlo Mapelli, Davide Mombelli and Eugenio Longaretti

Materials 2019, 12(16), 2572; https://doi.org/10.3390/ma12162572 - 12 Aug 2019

Cited by 7 | Viewed by 2796

Abstract

The low-density steels represent a topic of great interest within the scientific world because of the great demand from the steel market of increasingly lighter materials, also featured by an optimal mix of the mechanical properties. In this work, the corrosion and hot [...] Read more.

The low-density steels represent a topic of great interest within the scientific world because of the great demand from the steel market of increasingly lighter materials, also featured by an optimal mix of the mechanical properties. In this work, the corrosion and hot oxidation resistance of a Fe-15%Mn-9.5%Al-6.5%Ni-1%Cr-0.43%C were analyzed and related to the microstructural features. The material behavior was analyzed both in the as-cast and in the heat-treated state. For the corrosion test, the experimental plan was fulfilled using four different concentrations of HCl and four temperatures. In the case of hot oxidation resistance, the exposure time and the temperature effects were evaluated. The corrosion resistance in HCl was comparable to the stainless steel, and the iso-corrosion curves showed excellent resistance of the 1300 °C solution-treated material, especially at low temperatures, but it is also good at high temperatures due to the hot oxidation. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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19 pages, 6823 KiB

Open AccessFeature PaperArticle

Complex Study of Eutectoidal Phase Transformation of 2507-Type Super-Duplex Stainless Steel

by István Mészáros and Bálint Bögre

Materials 2019, 12(13), 2205; https://doi.org/10.3390/ma12132205 - 09 Jul 2019

Cited by 14 | Viewed by 3261

Abstract

The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat [...] Read more.

The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat treatment for the eutectoidal phase transformation. Samples were cold rolled at seven different rolling reductions which was followed by heat treatment at five different temperatures. The second sample set was prepared to determine the activation energy of the eutectoidal decomposition process using the Arrhenius equation. Samples were cold rolled at seven different rolling reductions and were heat treated at the same temperature during eight different terms. A third sample set was made to study how another plastic-forming technology, beside the cold rolling, can influence the eutectoidal decomposition. Samples were elongated by single axis tensile stress and were heat treated at the same temperature. The results of the first and the third sample sets were compared. The rest δ-ferrite contents were calculated using the results of AC and DC magnetometer measurements. DC magnetometer was used as a feritscope device in this work. Light microscope and electron back scattering diffraction (EBSD) images demonstrated the process of the eutectoidal decomposition. The thermoelectric power and the hardness of the samples were measured. The results of the thermoelectric power measurement were compared with the results of the δ-ferrite content measurement. The accurate value of the coercive field was determined by a Foerster-type DC coercimeter device. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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18 pages, 6799 KiB

Open AccessArticle

Investigation of Electroplastic Effect on Four Grades of Duplex Stainless Steels

by Claudio Gennari, Luca Pezzato, Enrico Simonetto, Renato Gobbo, Michele Forzan and Irene Calliari

Materials 2019, 12(12), 1911; https://doi.org/10.3390/ma12121911 - 13 Jun 2019

Cited by 33 | Viewed by 3528

Abstract

Since the late 1950s, an effect of electrical current in addition to joule heating on the deformation of metals called the Electroplastic Effect (EPE) has been known. It is used nowadays in the so-called Electrically Assisted Forming (EAF) processes, but the understanding of [...] Read more.

Since the late 1950s, an effect of electrical current in addition to joule heating on the deformation of metals called the Electroplastic Effect (EPE) has been known. It is used nowadays in the so-called Electrically Assisted Forming (EAF) processes, but the understanding of the phenomenon is not very clear yet. It has been found that EPE increases the formability of high stacking fault energy (SFE) materials, while low SFE materials reach fracture prematurely. Since Duplex Stainless Steels (DSSs) possess a microstructure consisting of two phases with very different SFE (low SFE austenite and high SFE ferrite) and they are widely used in industry, we investigated EPE on those alloys. Tensile tests at 5 A/mm², 10 A/mm² and 15 A/mm² current densities along with thermal counterparts were conducted on UNS S32101, UNS S32205, UNS S32304 and UNS S32750. The DSS grades were characterized by means of optical microscopy, X-ray diffraction and their mechanical properties (ultimate tensile strength, total elongation, uniform elongation and yield stress). An increase in uniform elongation for the electrical tests compared to the thermal counterparts as well as an increase in total elongation was found. No differences were observed on the yield stress and on the ultimate tensile strength. Un uneven distribution of the current because of the different resistivity and work hardening of the two phases has been hypothesized as the explanation for the positive effect of EPE. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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