The Duplex stainless steels are materials that possess excellent mechanical characteristics with good corrosion resistance, even more, compared to conventional stainless steels. In the oil and gas industry, this fact benefits since the components design, with smaller thicknesses (and therefore lighter), did not compromised the corrosion resistance and avoids expensive anti-corrosion coatings. For welding, Super Duplex steels must be managed on a par with austenitic but with precautions, to limit the joints sensitization to corrosion caused by welding with too mild thermal cycles i (range 1000 to 600 °C). This paper describes the setting up and verification of welded joints in a steel type UNS S32760 (Super Duplex F55) for use in an offshore environment. The joint was created using the two manual welding processes TIG (GTAW) and coated electrode (SMAW), to obtain the mechanical and micro-examination characteristics desired for the project.

Duplex and Super Duplex Stainless Steels are very prone to secondary phases formation related to ferrite decomposition at high temperatures. In the present paper the results on secondary phase precipitation in a 2510 Duplex Stainless Steel, heat-treated in the temperature range 850–1050 °C for 3–30 min are presented. The precipitation starts at grain boundaries with a consistent ferrite transformation for very short times. The noses of the Time–Temperature–Precipitation (TTP) curves are at 1000 °C for σ-phase and at 900 °C for χ-phase, respectively. The precipitation sequence involves a partial transformation of χ into σ, as previously evidenced in 2205 and 2507 grades. Furthermore, the experimental data were compared to the results of Thermo-Calc calculations. Understanding and ability to predict phase stability in 2510 duplex stainless steel is a key factor to design optimal welding processes that avoid any secondary phase precipitation in the weld bead as well as in the heat-affected zone.

Duplex stainless steels (DSS) are biphasic austenitic-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for an almost equal volume fraction of the phases. In this work, the effect of secondary phases precipitation on the corrosion resistance of four DSS grades (2101, 2304, 2205 and 2507), after isothermal aging in the critical temperature range 750-900 °C, was studied. The corrosion resistance was investigated by potentiodynamic polarization tests in both 0.6 M NaCl solution (pH 7) and in an acid chlorinated solution (pH 3) at room temperature. Moreover, the critical pitting temperature was determined according to ASTM G150. The results showed that secondary phases precipitation mainly influenced the resistance to corrosion of the lean duplex grades.

Duplex stainless steels (DSS) are biphasic austeno-ferritic steels, whose favorable combination of mechanical strength and corrosion-resistance properties makes them highly suitable for structural applications in chemical, petrochemical, and nuclear industries. DSS are high-alloyed steels and their interesting features derive from the presence of an almost equal volume fraction of ferrite and austenite, obtained from a suitable balance of the alloying elements and after a proper post-forming heat treatment (solubilization). However, DSS suffer from ferrite instability when heating the material within certain temperature ranges that can cause the precipitation of harmful secondary phases, which consequently limits their utility to below 250 degrees C. Moreover, owing to austenite metastability at room temperature, a diffusionless martensitic transformation can occur after cold deformation, which leads to the formation of the so-called strain-induced martensite (SIM), especially when the phase is not adequately stabilized by a suitable amount of gamma-stabilizing elements. In the present work, cold rolling was adopted as a cold deformation process, and four different DSS grades (SAF 2101, 2304, 2205, and 2507) were subjected to thickness reductions from 15 to 85 %. The developed microstructural features were analyzed by means of various characterization techniques (optical and electron metallography, hardness tests, X-ray and neutron time-of-flight diffraction, magnetic measurements, and critical pitting temperature determination), in order to detect and evaluate the amount of transformed austenite and to observe associated changes in properties induced by the occurrence of SIM. The experimental results revealed that the low-alloyed Lean DSS (2101 and 2304) seem to be more prone to SIM formation, whereas 2205 and 2507 grades were found to be more stable, even after large deformations. Nevertheless, the performed analyses pointed out that SIM detection in DSS is not a straightforward process as in austenitic grades, owing to similar crystallographic and magnetic properties of SIM and ferrite.

Electrically assisted manufacturing is based on the electro-plastic effect induced by electricity on the material flow during deformation and represents an alternative method for forming materials. Several studies have pointed out the real effectiveness of this technique, but no relations among microstructure, electrical resistivity, crystal structure and deformation-mode have been revealed. In the present work, the stacking fault energy (SFE) was taken into account and three FCC materials possessing different SFEs were strained in electrically assisted uniaxial tension under continuous current application. The results showed an advantageous electric contribution only in the highest SFE material, whereas no enhancements in formability were revealed in the investigated low- and intermediate-SFE metals.

Studies of mechanical properties and residual stresses in cold-drawn eutectoid steel bars with a diameter of 10.0 mm after patenting and drawing, with further short tempering under tension, are presented in this article. The changes in ultimate tensile strength, the relations between ultimate tensile strength and yield strength and the percentage elongation, in a range of treatment temperatures of 320-400 degrees C and of tension force of 34300-58800 N were studied. Moreover, the residual stresses in steel bars after thermo mechanical treatments were evaluated.

Duplex Stainless steels (DSS) are biphasic austeno-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for almost equal volume fraction of the phases. These steels are classified according to their pitting corrosion resistance, assessed by the PREN index (Pitting Resistance Equivalent Number) which, although qualitatively, is widely employed as comparison. The present work is aimed to study the pitting resistance of four DSS grades (SAF 2101, 2304, 2205 and 2507) in the as-received condition and after isothermal aging in the critical range 750°C-900°C, to highlight the effect of secondary phases precipitation on the corrosion behavior. The materials were potentiodynamically tested in artificial seawater (pH7) at room temperature and the corresponding Critical Pitting Temperatures (CPT) were determined according to ASTM G150. Secondary phase precipitation mainly affected the lean duplex grades whereas the high-alloyed DSS were more stable even if large precipitation occurred.

In precious metals industry, heat treatments play a key role in the production process, since the type and the sequence of these treatments produce the right combination of hardness and workability. The production sequence usually involves rolling, plastic deformation, heat treating, and surface finishing. In this work, different heat treatments were performed on samples of 18Kt 5N gold–copper–silver alloy, and the evolution of the microstructure and the microindentation hardness was analyzed. The heat treatments were performed after the first and the second rolling process (a softening heat treatment) and before the final surface brushing and polishing (a hardening heat treatment). Two different softening heat treatments were tested: a continuous annealing treatment performed in a belt furnace and a solution heat treatment in static furnace. Two different hardening treatments were studied: an aging heat treatment and a treatment of solubilization followed by an aging treatment. The microstructural observation and mechanical analysis showed that the solution treatment in static furnace produced smaller and more homogeneous grain size than a continuous annealing treatment, whereas the hardness was not reduced. This could be very important because the reduction in the grain size results in a marked decrease in the orange peel defects on the final products. It was also found that between the two hardening treatments, solubilization and aging produced an increase of about 90 HV in the hardness with a significant reduction in the number of superficial defects during the final surface finishing steps. The optimization of the heat treatments, studied in this work, produces a significant decrease in the total number of defects at the end of the production cycle.

5 INTRODUCTION High-strength eutectoid steel is widely used in manufacturing bars for critical pre-stressed reinforced concrete structures (building floor structures, bays, bridge footings, reinforced concrete piles, power transmission line supports, reinforced concrete sleepers, light towers, TV towers, etc.). Bars are characterized by high strength and definite level of plastic properties, and strict requirements for special properties. Global trends focus on the research of an efficient combination of various treatments to optimize the steel microstructure [1-3]. The high-strength bars are usually produced by cold drawing of patented eutectoid steel, with high levels of deformation [4]. As a result of such treatment, cold-drawn steel has a ferrite-cementite structure with an interlamellar spacing of 0.1 0.2 μm, and a cementite lamella thickness of 200 400 Å, and this microstructure gives the high strength properties. To ensure high values of relaxation resistance, bars are additionally thermo-mechanical treated (TMT). The most advanced option of such treatment is represented by short tempering of cold-drawn steel bars, using induction heating at 250-420°C with applied stretching force. In this case, tensile stresses rised up to 30-70% of ultimate tensile strength of cold-drawn steel bars. The mechanical properties and relaxation resistance of finished bars are correlated to the steel microstructure and level of residual stresses after thermomechanical treatment [5]. M. Elices studied the effect of residual stresses in cold-drawn eutectoid steel wire on the mechanical properties [6]. Atienza et al. studied the distribution of residual stresses in cold-drawn eutectoid steel wire, after thermo-mechanical treatment with various tension forces, in both longitudinal and transverse direction [7]. X-ray and neutron diffraction analysis were performed to study the relaxation features of an eutectoid steel after drawing and different types of final treatment [8-9]. L. Caballero et al. carried out experiments to determine the effect of temperature and stretching level of the commercial stressrelieving treatments on pre-stressed eutectoid steel wire with the aim of reducing stress relaxation [10]. The studies about the thermo-mechanical treatment of pearlitic steels showed that this treatment is very successful in reducing the residual stresses produced by drawing, especially in the surface area of the wire [11-12]. Although recent scientific papers focus on the thermo-mechanical treatment of cold-drawn eutectoid steel long products, including short induction tempering, there are only few studies on the effect of process parameters on changes in mechanical properties and residual stresses, especially when the diameter of eutectoid steel products increases. Acciaio

Coins are widely studied in archaeometry because they provide a lot of information on social, economic and technological history of people and territories which they are related to. A lot of chemical analyses have been performed by different methods, but only a few of metallographic data are known. The combination of chemical analysis with metallurgical investigation results in a complete description of the coin and its production steps. This paper reports a summary of the results on the Cu base coinage in Italy (Roman and Byzantine Empires) with the aim to develop a protocol of investigation based on microstructural and chemical analysis in order to reinforce the numismatic classification.

Electrically Assisted Manufacturing (EAM) is a recently developed method for materials forming based on the Electro-Plastic Effect (EPE) induced by electric current on the flow properties of the material and enhancing their workability. In this technique, the concept of dislocations/electrons interaction and the localized resistive heating provided by electric current were found to be the main responsible for the observed increase in materials formability. However, the joule heating may hinder the induced EPE, since heat and electricity are contemporarily both present, and separation between these two contributions is mandatory to better understand the solely effect of electricity on plastic flow. The present experimental work on an AISI 316L austenitic stainless steel is aimed to study EPE by separating the effects of current from those of heating during EAM uniaxial tensile test, in order to ascribe the relative contributions.

The precipitation kinetics of secondary phases in two austeno-ferritic lean duplex stainless steels (lean DSS) were examined after aging the materials at 800 °C. Owing to the instability of ferrite, all DSS are known to be sensitive to solid-state phase transformations in the critical temperature range 600–1,000 °C and different secondary phases may form, depending on composition and microstructure. The performed thermodynamic simulations revealed the proneness to the precipitation of such phases also have been done in lean DSS, but only information on the equilibrium microstructures were achieved. Therefore, the materials were aged at various times, in order to verify the simulations and determine the precipitation kinetics. The occurred structural modifications were observed and quantified by scanning electron microscope and X-ray diffraction measurements, determining phase type, composition and volumetric fraction. At 800 °C, grade 2101 was found to be only affected by Cr2N nitrides precipitation, whereas a significant amount of σ-phase was found to form in LDX 2404 for treatment longer than 1 h, almost totally replacing ferrite after 50 h. Up to now, the intermetallic σ-phase has been observed only in the high alloyed DSS, and the unexpected precipitation in grade 2404 highlighted that the increased content of molybdenum in this steel might be considered as determinant for the formation.

Duplex Stainless Steels (DSS) are biphasic steels of increasing interest, employment as structural materials in aggressive environments. In these steels, the austenite-to-ferrite phase ratio is maintained at about one - even if a slightly wider range between 40/60 and 60/40 is in any case accepted - giving the best combination of mechanical and corrosion-resistance properties. However, DSS must be handled with extreme care, especially if thermal cycles are involved, owing to the possible formation of dangerous secondary compounds that can highly worsen their excellent features. In industry, the production of big pipes requires manufacturing welding operations on steel plates or sheets and the end products must satisfy specific requirements. Therefore, since DSS properties depend on phase ratio, ferrite quantification at an industrial scale represents a topic of great interest, which must be as reliable as possible and, at the same time, of fast execution. In the present paper, different methods currently employed for ferrite estimation in DSS weldments are compared, in order to understand the limits deriving from each technique.

Dipartimento di Ingegneria Industriale, Padova University, Via Marzolo 9, Padua, Italy Stainless steels (SS) in automobile sector were previously incorporated mainly due to their decorative applications. Nowadays, their functional and specific characteristics make them more required and employed in this sector. Especially attention from automotive manufacturers has been paid in order to improve the engine efficiency and reduce weight of the vehicle, stainless steels result to be enabled due to their high strength mechanical characteristics, energy absorption capability, fatigue and corrosion resistance; besides their ductility which is traduced to an easy manufacturability. When welding is applied some of their characteristics may be affected and could decrease their mechanical properties. In attempt to avoid these circumstances, welding experimental practices must be carried out. In this study plates of 308 austenitic and 409 ferritic stainless steels were welded by Gas Tungsten Arc Welding process with different current values in order to get their mechanical properties behavior. Tensile tests were performed, it results that for austenitic stainless steels welds all failed in the fusion zone presenting ductile behavior; however, for ferritic stainless steels brittle fracture was observed. The maximum value of hardness for 308 austenitic SS was founded in the base metal, instead for 409 ferritic SS was reached at the heat affected zone. This study can be a practical guide in the selection of adequate joining methods in order to determine the more efficient to use in structural automotive industry.

Duplex stainless steels (DSS) have good mechanical and corrosion resistance properties which allow their application in very aggressive environments. However, their aging at 600–1000 °C causes the precipitation of dangerous intermetallic phases, resulting in serious detrimental effects on their interesting properties. These secondary phases are structural discontinuities which act as preferential cracks initiation sites and their negative effect is especially highlighted on toughness. For these reasons, many standards related to the manufacturing of DSS require the microstructure of these steels "free from intermetallics". In this paper, the effect of isothermal heat treatments on the impact toughness in two Duplex steels (SAF 2205 and Zeron®100) has been investigated, in order to study the influence of different amount of secondary phases on the toughness response.

Duplex stainless steels (DSSs) are biphasic steels having a ferritic-austenitic microstructure that allows them to combine good mechanical and corrosion-resistance properties. However, these steels are sensitive to microstructural modifications, such as ferrite decomposition at high temperatures and the possibility of strain-induced martensite (SIM) formation from cold-worked austenite, which can significantly alter their interesting features. In the present work, the effects of cold rolling on the developed microstructural features in a cold-rolled SAF 2205 DSS and the onset of martensitic transformation are discussed. The material was deformed at room temperature from 3 to 85 pct thickness reduction, and several characterization techniques (scanning and transmission electron microscopy, X-ray diffraction, hardness measurements, and time-of-flight-neutron diffraction) were employed in order to fully describe the microstructural behavior of the steel. Despite the low stacking fault energy of DSS austenite, which contributed to SIM formation, the steel was found to be more stable than other stainless steel grades, such as AISI 304L. Rolling textures were similar to those pertaining to single-phase materials, but the presence of the biphasic (Duplex) microstructure imposed deformation constraints that affected the developed microstructural features, owing to phases interactions. Moreover, even if an intensification of the strain field in austenite was revealed, retarded SIM transformation kinetics and lower martensite amounts with respect to AISI 304L were observed.

Duplex Stainless Steels (DSS) are biphasic austeno-ferritic steels in which the best combination of mechanical and corrosion-resistance properties is achieved for almost equal volume fractions of the phases. These steels are classified according to their pitting corrosion resistance, assessed by the PREN index (Pitting Resistance Equivalent Number) which, although qualitatively, is widely employed as comparison. The present work is aimed to study the pitting resistance of four DSS grades (SAF 2101, 2304, 2205 and 2507) in the as-received conditions and after cold rolling. at various thickness reductions (from 15% to 85%), to highlight the effects of cold working on the corrosion behaviour. The materials were potentiodynamically tested in artificial seawater (pH 7) and the corresponding Critical Pitting Temperatures (CPT) were determined. Cold deformation mainly affected the Lean DSS grades, whereas the high-alloyed DSS were stable, even after heavy deformations. These differences can be attributed not only to composition but also to the onset of diffusionless phase transformations induced by cold working, which make the materials more prone to corrosive attacks.

Stainless steels (SS) in automobile sector were previously incorporated mainly due to their decorative applications. Nowadays, their functional and specific characteristics make them more required and employed in this sector. Especially attention from automotive manufacturers has been paid in order to improve the engine efficiency and reduce weight of the vehicle, stainless steels result to be enabled due to their high strength mechanical characteristics, energy absorption capability, fatigue and corrosion resistance; besides their ductility which is traduced to an easy manufacturability. When welding is applied some of their characteristics may be affected and could decrease their mechanical properties. In attempt to avoid these circumstances, welding experimental practices must be carried out. In this study plates of 308 austenitic and 409 ferritic stainless steels were welded by Gas Tungsten Arc Welding process with different current values in order to get their mechanical properties behavior. Tensile tests were performed, it results that for austenitic stainless steels welds all failed in the fusion zone presenting ductile behavior; however, for ferritic stainless steels brittle fracture was observed. The maximum value of hardness for 308 austenitic SS was founded in the base metal, instead for 409 ferritic SS was reached at the heat affected zone.This study can be a practical guide in the selection of adequate joining methods in order to determine the more efficient to use in structural automotive industry.