1,721,049 research outputs found
Electroplastic effect in specimens of duplex stainless steel under tension
No full textDuplex stainless steels (DSSs) possess a typical biphasic microstructure consisting of equal amount of ferrite and austenite, which provides better combination of the mechanical and corrosion properties compared to the austenitic grade. Despite their good processability, they suffer from embrittlement of secondary phases in a very specific temperature range 450 – 1000°C depending on the composition. Solubilizing treatment after processing is required to obtain a perfect balance between austenite and ferrite and moreover, to dissolve any secondary phases that could have been formed during processing. This implies very high energy consumption of forming processes due to a high temperature (above 1000°C) or high power needed for the forming machines. The electroplastic effect could be used to reduce the force needed to form the material and extend the forming limits. The effect consists in direct interaction between the electrons of the electrical current and the ions of the material. The current mode (e.g., continuous current, pulsed current, pulse duration and duty cycle) plays an important role in the occurrence and the extent of the electroplastic effect. The electroplastic effect is investigated under tension in two-phase duplex stainless steel UNS S32205. Tensile tests under different current conditions (current density and frequency) are compared to room temperature tests. The best effect in terms of reduction of the ultimate tensile strength and increase in the fracture strain is achieved by introducing a multi-pulse current with the maximum density and pulse duration
Microstructural characterization of official and imitative nummi of Vth century A.D
No full textMetallography is an important tool that provides useful data on the fabrication technology, thermo-mechanical history of the object and on the nature of alloy employed. This research is part of a project aimed at reinforcing numismatic classification and description with chemical and microstrustural investigations. In this paper the attention has been focused on three bronze coins: Two Roman nummi struck under Arcadius/Honorius/Theodosius II in Rome (RIC, X, nn. 1271-1283, sample C9) and under Majorian in Ravenna (RIC, X, n. 2621,sample C26); the results of analyses on an italic imitation issued during the second half of V century AD are also presented, in order to evaluate possible connections between official and unofficial coins. The composition has been determined by XRF (Kevex 770) equipped whit a secondary target of Gd. The spectrometer operated at the following conditions: 55 kV, 1.00 mA. The microstructure of coins were investigated on metallographic cross-sections by light microscopy (Leica DM 100) and by SEM (Leica Cambridge Stereoscan 440) and analysed using the X-ray micro-analysis EDS (EDAX Philips) coupled to SEM. The EDS compositional profile is also obtained on the same coins to determine the element distribution and the concentration profile from the surface to the bulk. For EDS compositional profile the SEM operated at 25 kV. The semi-quantitative determination of element concentration was carried out standarless with the ZAF correction. In Tab.1 the bulk (b) and the surface (s) compositions (Wt%), determined whit EDS and XRF, are reported. The disagreement between XRF and SEM results are due to the different surface and bulk composition [2]. The high amount of Pb on the surface layer can be attributed to its preferential migration on the surface. The thickness and morphology of corrosion depend on chemical and physical properties of environment where coin was buried ; then the values obtained by SEM on the bulk (reported in tab 1) are reliable and show that specimens consist of a bronze alloy Cu-Sn with high rates of Pb. The content of Sn, shown in fig. 3, higher of 5%, identifies a western production [1, 10, 11], in contrast with what happens in the eastern mints. The micrographs show large grains flattened, evidence of the original cast microstructure with dendritic segregation; some slip lines were detected, confirming the plastic deformation (Fig 4, Fig 6, Fig 8). In Fig 5, 7, 9 BSE images show the directional preference of Pb. These characteristics can be attributed to identical production technologies for all the samples: The hypothesis is that the flans were obtained for solidification in the mold and then hammered to the desired thickness. Next, the plastic deformation could not be too strong because the Cu-Sn alloy whit an high amount of Pb is too brittle for further deformation. After being reduced in thickness, the flan was heated and coined. The process of hammering is evidenced by the shape of the grains that are not defined and polygonal but reflect a previous dendritic phase, which shows a fusion process. The presence of microsegregation zones shows the low working on metal surface after the melting process. XRF technique, instead, has not delivered the expected results in this work; in fact, the obtained data do not reflect the true composition of the sample but only the surface's layer composition of material
Mechanical and micro-examination characterization of welded joints in UNS S32760 for offshore applications
No full textThe 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 benefts 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 verifcation of welded joints in a steel type UNS S32760 (Super Duplex F55) for use in
an ofshore 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
Effects of the heat input on the phase balance of the duplex UNS S32205 joined by GTAW
No full textThe use of duplex stainless steels in industry is increasing due to their characteristics that combine good mechanical and corrosion resistance properties. These steels are comprised of a biphasic structure (50% ferrite and 50% austenite). Therefore, the development of techniques to improve the welding of duplex steels it is necessary, in order to ensure that the phase balance and the material properties are not severely harmed in the process. This paper aims to characterize welded joints with the GTAW process in UNS S32205 duplex stainless steel. Autogenous welds were performed with heat input ranging from 261.00 J/mm and 652.50 J/mm. The next step was the analysis of base metal and weld beads by Vickers hardness testing, EDS, electronic and optical microscopy. The results showed the weld metal region with volume fraction of austenite ranging between 22% and 34%. This variation is due to the lower cooling rates of high heat input values, which allow a greater formation of austenite. About the geometry, it was observed that higher values of heat input, led to wider and deeper welded joints, ranging between 3.9 and 5.9mm width and 0.65 and 1.29mm depth. In the nearest heat affected zone of the weld metal, Vickers hardness showed higher values than the base metal due to the presence of higher percentage of ferrite
APPROACH TO OBTAINING MEDIUM CARBON STEEL WIRE WITH A SPECIFIED SET OF MECHANICAL PROPERTIES AFTER COMBINED DEFORMATIONAL PROCESSING
No full textElectrically enhanced plastic deformation of duplex stainless steel UNS S32750
No full textIt is well known that increasing the temperature softens the materials and increases formability. This could be done in many ways, one of which is by joule heating. In the late fifties it has been observed an enhancement of formability for certain alloys when heated by electrical current, compared to traditional heating method. This led the researcher to investigate the effect of electrical current on the plastic flow of metallic materials discovering a new effect called Electroplastic Effect (EPE). EPE is used in the so called Electrically Assisted Manufacturing processes (EAM). The stacking fault energy (SFE) describes the dislocation dynamics of metallic materials and it has been hypothesized an a-Thermal effect which is caused by direct interaction between dislocations and electrical current. High SFE materials show an increase of formability while low SFE materials reach the fracture prematurely. In this work, duplex stainless steel (DSS) UNS S32750 has undergone uniaxially tested with the aid of continuous and pulsed electrical current in order to study the EPE of a metallic material that presents two different phases, high SFE (ferrite) and low SFE (austenite). Different current densities (continuous and pulsed) were tested while to separate the EPE from the effect of temperature some thermal tensile counterpart tests has been conducted. The DSS was then characterized through optical microscopy, scanning electron microscopy and x-ray diffraction. The DSS tested shows an increase in the elongation at rupture, either for the continuous current set-up and much more evident in the case of the pulsed current compared to the thermal tests, while the ultimate tensile strength and the yield strength were barely affected
Influence of small amount of secondary phases on impact toughness of UNS S32205 and Zeron® 100 Duplex Stainless Steel
No full textDuplex Stainless Steels (DSS) possess improved mechanical and corrosion properties, if compared to other stainless steels grades. Moreover, DSS retain good impact fracture toughness even at low temperatures, and, if compared with ferritic stainless steels, the ductile-to-brittle transitions is more gradual. However, DSS are sensitive to secondary phase's precipitation during isothermal heat treatments, even for very short time, mainly in the temperature range 550-950°C, or during quenching treatments at insufficient cooling rates in the same temperature range. The aim of this work is to investigate, using a regression analysis of experimental data, the effect of the precipitation of a slight amount of secondary phases (more or less 1%) on the impact toughness behaviour in the ductile-to-brittle transition region in two DSS: the UNS S32205 and the Zeron-100 grades. In aged materials, small amounts (more or less 1%) were present: mainly chi-phase in Zeron-100 and sigma in UNS S32205. Materials were tested in wrought ("as received" and "sigma-free") and aged (isothermally heat-treated) states by means of Charpy-V impact tests, in a temperature range between 20 and-196°C. The results show that in the UNS S32205 grade the small amounts of secondary phases reduce the impact toughness at room temperature to over 70%. This difference increase with lowering the temperature also because the wrought material maintain a good impact toughness response to about-40°C, with a successive decrease to 100 KJ at-90°C. Instead the Zeron-100 retain a good impact toughness even at-100°C, but a slight amount of secondary phases affects the toughness behaviour by lowering the absorbed energy by about 80 J at room temperature, and this difference in toughness can be considered almost constant for all the experimental temperature range. The lateral expansion was evaluated in order to achieve a further parameter to characterize the plastic deformation in the transition region
Effect of natural inhibitors on the corrosion properties of titanium and magnesium alloys|Effetto degli inibitori naturali sulla resistenza alla corrosione delle leghe di titanio e magnesio
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