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A S Shahi - One of the best experts on this subject based on the ideXlab platform.
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effect of heat input on the microstructure and mechanical properties of gas tungsten Arc welded aisi 304 stainless steel joints
Materials & Design, 2011Co-Authors: Subodh Kumar, A S ShahiAbstract:Abstract Influence of heat input on the microstructure and mechanical properties of gas tungsten Arc welded 304 stainless steel (SS) joints was studied. Three heat input combinations designated as low heat (2.563 kJ/mm), medium heat (2.784 kJ/mm) and high heat (3.017 kJ/mm) were selected from the operating window of the gas tungsten Arc welding process (GTAW) and weld joints made using these combinations were subjected to microstructural evaluations and tensile testing so as to analyze the effect of thermal Arc Energy on the microstructure and mechanical properties of these joints. The results of this investigation indicate that the joints made using low heat input exhibited higher ultimate tensile strength (UTS) than those welded with medium and high heat input. Significant grain coarsening was observed in the heat affected zone (HAZ) of all the joints and it was found that the extent of grain coarsening in the heat affected zone increased with increase in the heat input. For the joints investigated in this study it was also found that average dendrite length and inter-dendritic spacing in the weld zone increases with increase in the heat input which is the main reason for the observable changes in the tensile properties of the weld joints welded with different Arc Energy inputs.
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modelling of the effects of welding conditions on dilution of stainless steel claddings produced by gas metal Arc welding procedures
Journal of Materials Processing Technology, 2008Co-Authors: A S Shahi, Sunil PandeyAbstract:Abstract This paper highlights an experimental study carried out to analyse the effects of various gas metal Arc welding (GMAW) and universal gas metal Arc welding (UGMAW) process parameters on dilution in single layer stainless steel cladding of low carbon structural steel plates. Four factors five levels central composite rotatable design was used to develop relationship for predicting dilution, which enables to quantify the direct and interactive effects of four numeric factors i.e. wire feed rate, open circuit voltage, welding speed and nozzle-to-plate distance and one categorical factor preheat current. This comparative study reveals that dilution obtained in UGMAW process is significantly lower than that with GMAW process due to external preheating of the filler wire in UGMAW process which results in greater contribution of Arc Energy by resistive heating and as a consequence, significant drop in the main welding current values in case of UGMAW process is observed. Mathematical models developed show that dilution increases with increase in wire feed rate, open circuit voltage and welding speed, whereas it decreases with increase in nozzle-to-plate distance and preheat current. Furthermore the optimization capabilities in design-expert software were used to numerically optimize the input parameters and the optimal solutions generated indicate that for same levels of dilution, higher deposition rates were achieved in UGMAW process thus establishing that UGMAW process can prove to be a good choice for low cost surfacing applications.
Leif Karlsson - One of the best experts on this subject based on the ideXlab platform.
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Wire-Arc additive manufacturing of a duplex stainless steel: thermal cycle analysis and microstructure characterization
Welding in the World, 2019Co-Authors: Vahid Hosseini, Mats Högström, Lars-erik Stridh, Maria Asuncion Valiente Bermejo, Kjell Hurtig, Leif KarlssonAbstract:The evolution of microstructures with thermal cycles was studied for wire-Arc additive manufacturing of duplex stainless steel blocks. To produce samples, Arc Energy of 0.5 kJ/mm and interlayer temperature of 150 °C were used as low heat input–low interlayer temperature (LHLT) and Arc Energy of 0.8 kJ/mm and interlayer temperature of 250 °C as high heat input–high interlayer temperature (HHHT). Thermal cycles were recorded with different thermocouples attached to the substrate as well as the built layers. The microstructure was analyzed using optical and scanning electron microscopy. The results showed that a similar geometry was produced with 14 layers—4 beads in each layer—for LHLT and 15 layers—3 beads in each layer—for HHHT. Although the number of reheating cycles was higher for LHLT, each layer was reheated for a shorter time at temperatures above 600 °C, compared with HHHT. A higher austenite fraction (+ 8%) was achieved for as-deposited LHLT beads, which experienced faster cooling between 1200 and 800 °C. The austenite fraction of the bulk of additively manufactured samples, reheated several times, was quite similar for LHLT and HHHT samples. A higher fraction of secondary phases was found in the HHHT sample due to longer reheating at a high temperature. In conclusion, an acceptable austenite fraction with a low fraction of secondary phases was obtained in the bulk of wire-Arc additively manufactured duplex stainless steel samples (35–60%), where higher austenite fractions formed with a larger number of reheating cycles as well as longer reheating at high peak temperatures (800–1200 °C).
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nitrogen loss and effects on microstructure in multipass tig welding of a super duplex stainless steel
Materials & Design, 2016Co-Authors: Vahid A Hosseini, Kjell Hurtig, Sten Wessman, Leif KarlssonAbstract:Nitrogen loss is an important phenomenon in welding of super duplex stainless steels. In this study, a super duplex stainless steel was autogenously TIG-welded with one to four bead-on-plate passes with low or high heat inputs using pure argon shielding gas. The goal was to monitor nitrogen content and microstructure for each weld pass. Nitrogen content, measured by wavelength dispersive X-ray spectrometry, was after four passes reduced from 0.28 wt% in the base metal to 0.17 wt% and 0.10 wt% in low and high heat input samples, respectively. Nitrogen loss resulted in a more ferritic structure with larger grains and nitride precipitates. The ferrite grain width markedly increased with increasing number of passes and heat input. Ferrite content increased from 55% in base metal to 75% at low and 79% at high heat inputs after four passes. An increasing amount of nitrides were seen with increasing number of weld passes. An equation was suggested for calculation of the final nitrogen content of the weld metal as functions of initial nitrogen content and Arc Energy. Acceptable ferrite contents were seen for one or two passes. The recommendation is to use nitrogen in shielding gas and proper filler metals.
S Barnikoloettler - One of the best experts on this subject based on the ideXlab platform.
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wire Arc additive manufacturing of hot work tool steel with cmt process
Journal of Materials Processing Technology, 2019Co-Authors: Yarop Ali, Philipp Henckell, Jorg Hildebrand, Jan Reimann, Jean Pierre Bergmann, S BarnikoloettlerAbstract:Abstract This study presents investigations on the additive manufacturing of hot work steel with the Energy-reduced gas metal Arc welding (GMAW) process, which is a cold metal transfer (CMT) process. The paper analyses the influence of Arc Energy and the thermal field on the resulting mechanical properties and microstructure of the material. The investigations were carried out with hot work tool steel X37CrMoV 5-1, which is used for the manufacturing of plastic moulds, hot extrusion dies, and forging dies. The results show that this steel can be used to generate 3D metal components or structures with high reproducibility, near-net-shaped geometry, absence of cracks, and a deposition rate of up to 3.6 kg/h. The variation of the wire feed speed and the welding speed enables the production of weld beads of width up to 9.4 mm. The mechanical properties of the generated structures can be adapted by the dominant thermal field, which in turn is influenced by the bypass temperature and the electric Arc Energy. A determining factor to describe the main variables of the welding process is represented by Energy per unit length EL. If the bypass temperature is above the martensite start temperature (Ms), there is a homogeneous hardness level along the height of the additively manufactured structure height as long as the Energy produced by the welding Arc is enough to keep the temperature of all layers above Ms.
Jianhua Wang - One of the best experts on this subject based on the ideXlab platform.
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a relationship between minimum Arcing interrupting capability and opening velocity of vacuum interrupters in short circuit current interruption
IEEE Transactions on Power Delivery, 2018Co-Authors: Bojian Zhang, Yingsan Geng, Jianhua Wang, Li Ren, Jiangang Ding, Satoru YanabuAbstract:Controlled switching technology operates circuit breakers at the minimum Arcing time for short-circuit current interruption. However, there is no report to reveal a relationship between the short-circuit current interrupting capability with the minimum Arcing time and the opening velocities of vacuum interrupters. The objective of this paper is to reveal a relationship between the short-circuit current interrupting capability with the minimum Arcing time and the opening velocities of vacuum interrupters. A 40.5-kV fast vacuum circuit breaker prototype was built up which was equipped with a commercial 40.5 kV–31.5 kA vacuum interrupter and it was driven by an electromagnetic repulsion mechanism. It provided an average velocities ranging from 2.5 to 5.5 m/s. A total of 50 times of 40-kA short-circuit current interrupting tests were carried out in a synthetic circuit. Test results showed that the minimum Arcing time of successful interruption decreased with the increasing of the average opening velocity. The minimum Arcing gap was determined as 1.8 mm and it kept as a constant as the average opening velocity increased. The experimental results also showed a relationship between the Arc Energy density and the Arc extinguishing gap, which acted a linear boundary between the successful and failure short-current interruptions.
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An Approach for Minimum Percussion Welding in Closing Operation of a 126-kV Vacuum Circuit Breaker
IEEE Transactions on Components Packaging and Manufacturing Technology, 2014Co-Authors: Li Yu, Yingsan Geng, Qian Li, Jianhua WangAbstract:SF6 circuit breakers are widely used, to safely and reliably protect the high-voltage (72.5-1000 kV) power system. However, SF6 is a greenhouse gas. It is necessary to develop high-voltage vacuum circuit breakers (VCBs) instead of SF6 circuit breakers above 110-kV power systems. To obtain the optimum performance from a high-voltage VCB design, the mechanism design must be perfectly matched to it. For a closing operation of a 126-kV VCB, most of the Arc Energy for performing percussion welding is from the prestrike Arc and the bounce Arcs if contacts close in vacuum when a high current passes through the contacts. An approach for minimum percussion welding in the closing operation of a 126-kV VCB is investigated by reducing both the prestrike Arc duration and the bounce open duration. The breakdown phenomena in 126-kV vacuum interrupters are investigated to obtain a prestrike gap of 4 mm. The bouncing-open time of a prototype of a 126-kV VCB is measured in the prestrike closing velocity range of 0.7 to 2.0 m/s. The results show that the total Arcing duration (including the prestrike Arc and bouncing Arc duration) is a function of the prestrike closing velocity (an average closing velocity in the prestrike gap (d) before the contacts touched each other). According to the function, the optimized prestrike closing velocity is 1.15 m/s, which can minimize the total Arcing duration to 4.91 ms in the 126-kV VCB. The prototype of the 126-kV VCB passes the full-voltage synthetic making test successfully by applying the closing characteristic.
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high current vacuum Arc phenomena of nanocrystalline cucr25 contact material
IEEE Transactions on Plasma Science, 2011Co-Authors: Jianhua Wang, Yingsan Geng, Guowei Kong, Zhiyuan LiuAbstract:Copper-chromium contact material is widely used in vacuum interrupters. In recent years, the nanocrystalline CuCr contact material has presented some excellent performances in high withstand voltage, low chopping current, and so on. There fore, it has a big potential for high-current interruption with vacuum interrupters. The objective of this paper is to investigate the high-current vacuum Arc phenomena of a nanocrystalline CuCr25 (Cr 25 wt%) contact material. Vacuum interrupters with 12- and 25-mm-diameter butt-type contacts were used in the tests. The vacuum interrupters were designed in a glass envelope without main shield for vacuum Arc observation by a high-speed charge coupled device camera. The test vacuum interrupters were operated by a permanent-magnet mechanism. The opening velocities were 1.1 and 2.0 m/s, respectively. The Arc current frequency was 50 Hz, and the Arcing time was nearly 10 ms. For comparison, vacuum interrupters with microcrystalline CuCr25 contact material were also prepared. The experimental results showed that both the Arc Energy and the mean value of the Arc voltage of the nanocrystalline CuCr25 contact material were lower than those of the microcrystalline one under the same experimental conditions. The carrying current per cathode spot of the nanocrystalline contact material (about 34 ± 10A)is about one-third of that of the micro crystalline one (about 107 ± 30 A). However, the diameters of the anode spots of the nanocrystalline CuCr25 contact material were significantly larger than those of the microcrystalline CuCr25 contact material under the same conditions. Moreover, the durations of the anode spots of the nanocrystalline CuCr25 contact material were longer than those of the microcrystalline one.
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high current vacuum Arc phenomena of nanocrystalline cucr25 contact material
International Symposium on Discharges and Electrical Insulation in Vacuum, 2010Co-Authors: Jianhua Wang, Yingsan Geng, Guowei Kong, Zhiyuan LiuAbstract:ReseArch on the vacuum Arc phenomena of the nanocrystalline CuCr25 contact material is interested for its potential application on high current interruption. In order to investigate the vacuum Arc phenomena of the nanocrystalline CuCr25 contact material, a traditional CuCr25 material was also prepared for comparison. 12mm and 25mm diameter contacts were assembled in vacuum interrupters, which have a glass envelope and no shield. A high-speed CCD camera was used to observe the anode phenomena and the cathode phenomena through the glass envelope. The test vacuum interrupters were operated by a permanent magnet mechanism. The average opening velocity can be adjusted to two velocities: 1.3m/s to 1.8 m/s. The Arc current frequency was 50Hz and Arc duration was 9ms∼10ms. The experimental results showed that at same current and average opening velocity, the Arc Energy and the mean value of Arc voltage of nanocrystalline CuCr25 was lower than the traditional CuCr25 contact material. The distribution of cathode spots on the nanocrystalline CuCr25 contact was more uniformly than of the traditional CuCr25 contact. And the carrying current per cathode spot of the nanocrystalline contact material was about ⅓ of that of the traditional contact material. However, the anode phenomena of the nanocrystalline CuCr25 contact were more active than the traditional CuCr25 contact material when passing the same high currents. At a threshold current at the first high-current anode mode appeared, it was found that the threshold current of nanocrystalline CuCr25 contact material was lower than that of traditional CuCr25 contact material, which means the nanocrystalline CuCr25 contact material was more prone to appear the high-current anode mode than the traditional CuCr25 contact material.
Gerhard J Pietsch - One of the best experts on this subject based on the ideXlab platform.
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cfd calculation of pressure rise due to internal ac and dc Arcing in a closed container
IEEE Transactions on Power Delivery, 2011Co-Authors: Mikimasa Iwata, Shinichi Tanaka, Toshiya Ohtaka, Tadashi Amakawa, Kittipong Anantavanich, Gerhard J PietschAbstract:Computational fluid dynamics calculation results of pressure rise and propagation due to high-current Arcs in a closed container are described. The pressure developments at different locations within the container are calculated by changing the current frequency (ac of 50 and 60 Hz, and dc) and the electric Arc Energy input (up to approximately 1000 kJ). The local pressure oscillation amplitude for AC/50 Hz within the container exceeds that for dc. From the pressure oscillation period and the sound speed distribution in the container, the following conclusions are made. With growing electric Arc Energy, the pressure amplitude increases because of the resonance effect between the Arc power oscillation and pressure waves reflected on the walls. When the electric Arc Energy reaches a value of around 500 kJ, the pressure amplitude rises significantly. This is considered attributable to superimposition of pressure waves near the container wall caused by low propagation velocity of the pressure waves near the wall. It is necessary to consider this phenomenon for public safety when designing electric power equipment.
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influence of current and electrode material on fraction k_ p of electric Arc Energy leading to pressure rise in a closed container during internal Arcing
IEEE Transactions on Power Delivery, 2010Co-Authors: Mikimasa Iwata, Kittipong Anantavanich, Gerhard J PietschAbstract:The fraction k_p of electric Arc Energy leading to pressure rise in its surroundings is determined in dependence on Arc current and electrode material for an Arc occurring in a closed container. It is shown that the kp values for closed containers depend apart from the electrode material on the level of Arc current, which, in turn, affects the Energy balance.
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calculation of pressure rise in electrical installations due to internal Arcs considering sf 6 air mixtures and Arc Energy absorbers
2010Co-Authors: Kittipong Anantavanich, Gerhard J PietschAbstract:Internal Arcs cause sudden temperature and thus pressure increase in electrical installations, which may endanger personnel, installation rooms or buildings as well as the security of power supply. Overpressure can be controlled by e.g. relief openings. The proof of internal Arc withstand is usually performed by tests in high power laboratories or by pressure calculations especially in cases, where tests are impractical. Nowadays, there exist reliable pressure calculation methods, which are able to determine pressure rise due to internal Arcing. For practical applications, two methods are of importance, the CFD calculation method, which provides spatially resolved results, and the standard calculation method providing spatially averaged results. However, the application range of these methods is limited. This is especially true if SF6-air mixtures have to be considered (SF6-insulated switchgear) or if Arc Energy absorbers are installed. In this thesis, both effects, which are important for pressure rise in the case of internal Arcing, are treated. The key point of modelling SF6-air mixture flows of changing composition is the generation and treatment of reliable gas data. A further main focus is the modelling of Arc Energy absorbers. For this purpose, heat absorption and flow resistance are considered first of all separately. In order to describe both effects simultaneously, existing and improved model approaches are evaluated and appropriate model combinations are proposed. SF6-air mixtures and the effect of Arc absorbers are implemented in both calculation methods for the first time with reliable gas data. Special care is taken on data handling and modification of the equation systems. The inclusion of the effect of absorbers is achieved by considering heat sinks and friction forces. Based on the standard calculation method, a versatile improved software tool (Improved Standard Calculation Method) for the determination of pressure developments is developed, which is fast, easy to handle, able to treat SF6-air mixtures and absorbers based on reliable gas data, platform independent and including any number of rooms and openings. Both calculation methods are validated by comparing measurements in different arrangements with calculation results. Berechnung des Druckanstieges in elektrischen Anlagen im Storlichtbogenfall unter Berucksichtigung von SF6-Luft-Gemischen und Lichtbogenenergieabsorbern Kurzfassung Storlichtbogen in elektrischen Anlagen verursachen einen schnellen Temperaturund damit Druckanstieg im betroffenen Anlagenraum, der das Bedienpersonal, die Anlage und sogar das Schaltanlagengebaude sowie die Versorgungssicherheit gefahrden kann. Der entstehende Uberdruck wird ublicherweise durch Druckentlastungsoffnungen begrenzt. Der Nachweis der Storlichtbogensicherheit erfolgt durch Versuche in Hochleistungspruffeldern oder – wo dieses nicht moglich oder praktikabel ist – uber Druckberechnungen. Heutzutage existieren bereits bewahrte Druckberechnungsverfahren, die den Druckanstieg aufgrund von Fehlerlichtbogen bestimmen konnen. Fur praktische Anwendungen haben sich zwei Arten von Druckberechnungsverfahren als bedeutsam erwiesen, das „CFD-Verfahren“, das ortsaufgeloste Ergebnisse mit einer Computational Fluid Dynamics-Software liefert und das sogenannte „Standardverfahren“, mit dem man raumlich gemittelte Druckverlaufe erhalt. Der Anwendungsbereich dieser Verfahren ist jedoch eingeschrankt. Zum Beispiel ist es bislang mit allen bekannten Verfahren nicht moglich, das Ausstromverhalten bei SF6-isolierten Anlagen zuverlassig in die Druckberechnung einzubeziehen. Dasselbe gilt fur Lichtbogenenergieabsorber, deren Wirkung bislang wenig theoretisch untersucht worden ist. In der vorliegenden Arbeit werden diese fur die Druckberechnung wichtigen Phanomene betrachtet. Schwerpunkt bei der Modellierung von ausstromenden SF6Luft-Gemischen mit sich verandernder Gaszusammensetzung ist die Erzeugung und Behandlung von zuverlassigen realen Gasdaten. Damit werden Effekte wie z.B. Dissoziation, Ionisation und Wechselwirkungen zwischen Gaspartikeln einschlieslich chemischer Reaktionen mitberucksichtigt. Ein weiterer Schwerpunkt der Arbeit ist die Modellierung von Absorbern. Hierzu werden zunachst die Warmeaufnahme und der Stromungswiderstand getrennt behandelt. Um beide Wirkungen gleichzeitig zu beschreiben, werden bestehende sowie verbesserte Modellansatze evaluiert und geeignete Kombinationen von Modellansatzen vorgeschlagen. Die Stromung von SF6-Luft-Gemischen und die Wirkung von Lichtbogenenergieabsorbern werden erstmalig in ein Standardverfahren und mit realistischen Gasdaten in ein CFD-Verfahren eingebunden. Dabei spielt die Behandlung der Gasdaten und die Modifizierung der Gleichungssysteme eine besondere Rolle. – Die Wirkung von Absorbern erfolgt durch die Berucksichtigung von Warmesenken und Reibungskraften. Weiterhin wird ein auf dem Standardverfahren beruhendes Rechenprogramm entwickelt, das schnell Resultate liefert, einfach zu handhaben ist und die beiden Phanomene Gasgemischstromung und die Wirkung von Energieabsorbern mitberucksichtigen kann (Improved Standard Calculation (ISC)-Methode). Dabei werden realistische Gasdaten verwendet. Das Programm ist in Java programmiert und damit plattformunabhangig, vielseitig einsetzbar und z.B. in der Lage, eine beliebige Anzahl von miteinander verbundenen Raumen und Druckentlastungsoffnungen zu berucksichtigen. Durch Vergleich von Messungen in verschiedenen Anordnungen mit Rechenergebnissen, durchgefuhrt mit dem CFDals auch dem ISC-Verfahren, wird die Einbindung von Gasgemischstromungen und Energieabsorbern in die beiden Druckberechnungsverfahren validiert.
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influence of Arc current on fraction kp of electric Arc Energy leading to pressure rise in a closed container
International Conference on Gas Discharges and Their Applications, 2008Co-Authors: M Iwata, Kittipong Anantavanich, Gerhard J PietschAbstract:When determining overpressure in electrical installations due to internal Arcing, it is crucial to know the values of Arc voltage and the portion of Arc Energy leading to pressure rise. In this contribution the fraction Kp of electric Arc Energy leading to pressure rise in its air surroundings is determined in dependence on Arc current, Arc Energy and electrode material for an Arc occurring in a closed container. When the Arc current and electric Arc Energy increases, Kp decreases some-what in the case of copper electrodes and increases in the case of iron and aluminium electrodes. These results are considered to be due to the change in Energy balance in the closed container in cases where the Arc current and electric Arc Energy increase.