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1
Kaněra, Miloš. „Výroba odlitků z austeniticko-feritických hyperduplexních korozivzdorných ocelích“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-445174.
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The thesis deals with hyper duplex stainless austenitic-ferritic steels and their mechanical and castability properties. The evaluation of resistance to pitting corrosion is divided by PRE values. Steels with a PRE value higher than 48 belong to the group of hyper duplex steels. The theoretical part contains an introduction to the chemical composition, structure and properties of these steels. The practical part is focused on the conditions of tendency to crack castings during solidification and cooling. Furthermore, there is evaluated influence of intermetallic phases on mechanical properties.
2
Hutchings, D. „Hydrogen embrittlement of duplex stainless steel“. Thesis, University of Manchester, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.631722.
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Duplex stainless steels (DSS's) are frequently used in oil and gas production and are subsequently subjected to cathodic protection. There is now growing concern about the cathodic evolution of hydrogen produced from this protection system, which may diffuse into the alloy and cause an embrittled condition. DSS's have a microstructure that is a mixture of austenite and ferrite and combines the advantages of these grades, whilst minimising their deficiences. In this research, Zeron 100 DSS was studied in six conditions to investigate the effects of hydrogen embrittlement (HE) on the various strengths and microstructures. The six conditions wer~ as follows: as-received, cold worked, age-hardened (475°C embrittlement), high temperature heat treated, rod and powder. To simulate service environments, 3.5% wt NaCI solution at ambient temperature with an applied potential of -1.1 V (SCE) was used. The effect of pre-charging for up to 550 hours at 80°C was also investigated. Test methods included slow strain rate testing (SSRT), monitoring of transient crack propagation (TCP) using circumferentially notched tensile specimens using a DC potential drop method, acoustic emission CAE) and some conventional bolt loaded fracture mechanics specimens. Test results were correlated with the varying microstructures and environmental conditions and consisted of mechanical properties, threshold crack growth including transient effects and AE data. In this work transgranular cleavage cracks were obtained in the susceptible ferrite phase as a direct result of HE; the depth of these cracks implied a high hydrogen concentration throughout the specimen. The austenite failed by ductile tearing and acted as a physical barrier to the propagation of cleavage cracks. As a result of SSR testing the best material was found to be the powder material; the fine equally dispersed austenite phase caused a lowering of the effective K value. The worst material was the high temperature heat treated type because it contained more ferrite (11:1 72%). The age-hardened material was also susceptible because of the hard and brittle ex' phase. However, regardless of the environment the UTS remained virtua]]y unchanged for each individual material, indicating that most cracking occurred in the post-UTS stage of the test. With the TCP test a lowering of the fracture load was found when an HE environment was used; daldt vs Kq curves were produced, however the DC potential drop equipment could not accurately measure crack growth because of the bridging effect of the austenite phase. The most susceptible microstructures were again the age-hardened and heat treated types. The hydrogen evolution reaction (HER) was also investigated by creating a fresh surface on the as-received DSS and studying the changes in the HER. This work showed that the effect of scratching is irreversible. Also the oxide film can not be totaHy reduced electrochemica]]y and only mechanical methods can remove the oxide films entirely. Fina]]y a means of detecting "475°C embrittlement" of DSS's was investigated using an electrochemical technique in 5M HCI. i-E curves were produced which showed the reactivation of the ferrite and austenite phases in the as-received material. By age-hardening at 475°C the two reactivation peaks merged.
3
Sture, Henrik. „Integrity Evaluation of Duplex Stainless Steel Flanges“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19055.
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Duplex stainless steel flanges are normally forged to form, as required by the ASTM A182/A182M standard, but may also potentially be machined directly from forged stainless steel bar. In order to evaluate the integrity of such flanges, axisymmetric elastic-plastic finite element models have been developed, considering static effects such as bolt load and internal pressure. Additionally, tensile testing of a sample forged bar (UNS S31803) has been conducted. The stress distribution in a flange during gasket seating and operating conditions has been determined, as well as the degree of plastic strain caused by the bolt loads. The maximum stresses have been found to be around the same values as the minimum yield strength requirement of the studied material (UNS S31803), and the location of the maximum stress concentrations have been identified as the gasket groove. The tensile tests of the forged bar (UNS S31803) have shown that the yield and tensile strength properties are considerably higher than the standardized minimum requirements. The elastic modulus of the forged bar has also been determined, and was found to be lower than anticipated in the axisymmetric models. Some specimens have also been found to exhibit highly non-linear elastic properties.
4
Dalton, John Christian. „Surface Hardening of Duplex Stainless Steel 2205“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1480696856644048.
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5
Rieder, Ester Schmidt. „The passivity of a super duplex stainless steel“. Thesis, University of Birmingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272490.
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6
Marrow, Thomas James. „Fatigue mechanisms in an embrittled duplex stainless steel“. Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386998.
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7
Farrell, J. „Hyperbaric welding of duplex stainless steel pipelines offshore“. Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/4513.
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Three duplex stainless steels (Avesta 2205, Sandvik SAF2507 and Zeron 100) were successfully welded automatically at a range of pressures from 1 to 32bar. The gas tungsten arc (GTA) welding process was chosen as it allows a high degree of control to be exercised during welding. Initial autogenous bead on plate welds established the effects of pressure on the welding process and allowed the process parameters to be determined for subsequent experiments. Analysis of the effects of pressure on the weld thermal cycle showed that at higher pressures the precipitation of phases deleterious to the weld quality was less likely than at ambient pressure. It was also found that the arc melting efficiency increased as the pressure increased, which was taken into account when the process parameters for the joints were selected. A V-butt design with a 'land' on each side was chosen for the joints to counteract any tendency for the welding arc to wander at higher welding pressures. The root welds were performed using pulsed current welding techniques to overcome the difficulties in achieving consistent penetration that were encountered when welding at lower pressures. It was found that by employing standard welding consumables commonly used for welding duplex steels at ambient pressure satisfactory austenite-ferrite phase balances could be achieved in the weld metal at all pressures. Metallographic examination of the welds showed that the joints did not have any microstructural complications that were related to pressure and mechanical testing revealed that, in terms of impact toughness, the weld metal and heat affected zone (HAZ) performed as well as, if not better than, the parent plate material. This work shows that welding of duplex stainless steels using the hyperbaric welding method is a viable option for subsea operations up to a depth of at least 320m, automated hyperbaric welding being advantageous at depths greater than 40m.
8
Fang, Peijun. „Weldability and hydrogen relationships in super duplex stainless steel“. Thesis, Robert Gordon University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260057.
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9
Wang, Huei-Sen. „Thermal modelling of zeron 100 super duplex stainless steel“. Thesis, Robert Gordon University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287771.
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10
Renton, N. C. „Time-variant reliability of super-duplex stainless steel tubulars“. Thesis, University of Aberdeen, 2007. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU239879.
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The development of high pressure-high temperature oil wells in the U.K.'s north sea province has led to the application of high-strength, corrosion resistant alloys for production tubulars. One such alloy is super-duplex stainless steel (SDSS). The cold-worked material combines high strength with excellent corrosion resistance properties as a result of its chromium, molybdenum, tungsten and nitrogen content. The material's macro properties are a function of its two-phase microstructure made up of roughly equal parts austenite and ferrite. Recent in-service failures of SDSS tubulars have identified gaps in the understanding of the material's properties. The study investigated the link between the microstructure of the material and its mechanical and corrosion behaviours. The results revealed that the microstructure of the material was highly anisotropic and varied through the pipe-wall as a result of manufacturing techniques. A method of measuring the crack resistance of the material was developed, with the results showing that the spatial arrangement of the microstrucure determined the crack resistance of the fracture plane. The properties of ferrite were identified as the limiting factor on the crack resistance of the material. The investigation also revealed that a small difference in chemical composition between the two phases led to the preferential dissolution of ferrite in aqueous oxygen bearing chloride environments.
11
Haddad, Naseem Issa Abdallah. „The development of microstructure in duplex stainless steel welds“. Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/221890.
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12
Shendye, Sanjay B. „Effect of long term elevated temperature exposure on the mechanical properties and weldability of cast duplex stainless steels /“. Full text open access at:, 1985. http://content.ohsu.edu/u?/etd,115.
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13
Iversen, Torunn Hjulstad. „Intragranular Chromium Nitride Precipitates in Duplex and Superduplex Stainless Steel“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18904.
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Intragranular chromium nitrides is a phenomenon with detrimental effects on material properties in superduplex stainless steels which have not received much attention. Precipitation of nitrides occurs when the ferritic phase becomes supersaturated with nitrogen and there is insufficient time during cooling for diffusion of nitrogen into austenite. Heat treatment was carried out at between 1060◦C and 1160◦C to study the materials susceptibility to nitride precipitation with varying heat treatment temperature, nitrogen content and microstructure. Microhardness tests and Charpy v-notch tests were also carried out to investigate the nitrides effect on material properties. No standard method of quantification of nitrides exist. A method of quantifying the precipitation based on area fraction of nitrides was therefore introduced. The results show an increased amount of nitride precipitation with increased heat treatment temperature. A coarse microstructure with a large austenite spacing was found to promote higher fractions of nitride precipitation while nitrogen content was found to affect the amount of precipitation in less extent. The intragranular nitrides cause precipitation hardening in the ferrite and the precipitation was found to be at its most severe in the center of the ferritic regions, with precipitation free zones close to the phase boundaries. The microhardness of the phase was affected accordingly, with increasing hardness towards the center. Charpy v-notch test results show that nitride precipitation causes an embrittlement of the steel while intragranular secondary austenite improves the impact toughness of the material as it shortens the dif- fusion distance of nitrogen, decreasing the materials susceptibility to intragranular nitride precipitation.
14
McKenzie, S. G. „The effect of platinum group metals on duplex stainless steel“. Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37782.
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15
Ávila, Braz Thaís. „Shrinkage Calculation in the Continuous Casting of Duplex Stainless Steel“. Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76516.
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16
Saliba, Najib. „Structural behaviour of lean duplex stainless steel welded I-sections“. Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/39853.
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Despite growing interest in the use of stainless steel in the construction industry and the development of a number of national and regional design codes, stainless steel is often regarded as only suitable for specialised applications. This is attributed largely to the high initial material cost associated with the most commonly adopted austenitic grades of stainless steel, as well as some conservatism embedded in current stainless steel guidance. A recently developed grade, known as lean duplex stainless steel (EN 1.4162), possesses higher strength than the common austenitic grades and has a lower cost, along with good corrosion resistance and adequate weldability and fracture toughness. The structural performance of lean duplex stainless steel remains relatively unexplored to date with only a few studies having been performed. The main aim of this study is to examine the structural behaviour of lean duplex stainless steel welded I-sections, and to assess the applicability of the current European stainless steel design guidance. As part of this research, a total of fifty two material tests, four stub column tests, eight 3-point and 4-point bending tests, eight continuous beam tests and nine shear buckling tests were carried out. The experimental programme was complemented by a parallel numerical investigation, in which finite element models were initially validated against the test results and subsequently used for parametric studies. These test and numerical results were used in conjunction with existing test data on stainless steel welded I-sections to characterise the basic material properties, assess the codified slenderness limits for cross-section classification, investigate the applicability of plastic design to indeterminate stainless steel structures, and establish new shear resistance design equations for stainless steel plate girders. Based on the findings, it was concluded that the present European design provisions can be safely applied to lean duplex but are rather conservative in some areas. To rectify this, modifications have been proposed for cross-section classification, plastic design and shear resistance calculations. These proposals, together with additional developments to the strain based continuous strength method of design, are suitable for incorporation into future revisions of Eurocode 3.
17
Bhattacharya, Ananya. „Stress corrosion cracking of duplex stainless steels in caustic solutions“. Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26491.
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Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2009.Committee Chair: Singh, Preet M.; Committee Member: Carter, W. Brent; Committee Member: Gokhale, Arun, M.; Committee Member: Neu, Richard; Committee Member: Sanders, Thomas H., Jr.. Part of the SMARTech Electronic Thesis and Dissertation Collection.
18
Sieurin, Henrik. „Fracture toughness properties of duplex stainless steels“. Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3964.
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19
Elsherief, Ahmed Fathy Abd Elshafi. „The structure, mechanical and corrosion properties of duplex stainless weldments“. Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303482.
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20
Olden, Vigdis. „FE modelling of hydrogeninduced stress crackingin 25% Cr duplex stainless steel“. Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for produktutvikling og materialer, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-5026.
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21
Payares, Rios de Asprino M. C. „Numerical modelling of optimum microstructure behaviour in duplex stainless steel weldments“. Thesis, Swansea University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638433.
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A comprehensive study of DSS SAF 2205 weldments and nature of weld metal and heat-affected zones has been undertaken. Several DSSs SAF 2205 welds were fabricated using GMAW welding process at different welding conditions. The investigation focuses on the effect of the welding parameters are current, arc voltage, welding speed and heat input on the weld geometry, microstructure and mechanical properties. Also, the technique of the determination of “Response Surface” for the welding parameters was focused to optimise the effects on them each dependent. Variable. All weldments had the UTS, the yield strength and elongation in the range of weld mechanical according to ASTM A240. The welding parameters appeared to have much effect on the tensile properties of DSS weldments tested along transverse direction than the weldment tested along rolling direction. The hardness values vary with welding parameters employed. The trends show that HAZ hardness is slightly lower than base metal when 0.53 to 1.19 kJ/mm is used. However, the hardness in WM is higher than base metal for welding conditions with HI lower than 1.30 kJ/mm. DSS weldments showed no ductile to brittle transition. The fracture location for weld TST with head-off varied between HAZ and base metal. On the contrary, the fracture location along LT was generally at the base metal. SEM photographs shows that the mode of fracture of DSS welds is because microvoids coalescence (simples). Hence the fracture is ductile in DSS specimens. AS the heat input increases the simple size also increases.
22
張榮祥 und Wing-cheung Cheung. „Short-term isothermal annealing of a cold rolled duplex stainless steel“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31215129.
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23
石燦鴻 und Chan-hung Shek. „Ferrite decomposition in duplex stainless steel and its application intemperature measurement“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1994. http://hub.hku.hk/bib/B31233880.
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24
Huang, Yun'er, und 黃韵兒. „Behaviour and design of cold-formed lean duplex stainless steel members“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/195980.
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Cold-formed stainless steel sections have been increasingly used in architectural and structural applications. Yet the high price of stainless steel limits the application to construction projects. The lean duplex stainless steel (EN 1.4162) offers an opportunity for stainless steels to be used more widely due to its competitive in price, good mechanical properties and corrosion resistance. The lean duplex stainless steel is a relatively new material, and research on this material is limited. Currently, the lean duplex stainless steel is not covered in any design specification, and no design rules are available for such material. Therefore, the behaviour and design of cold-formed lean duplex stainless steel members are investigated in this study. The investigation focused on columns, beams and beam-columns of square and rectangular hollow sections. Both experimental and numerical investigations were performed and reported. Design rules for cold-form lean duplex stainless steel members are proposed.
The experimental investigation included material tests, column tests, beam tests and beam-column tests at room and elevated temperatures ranged from 24 – 900 °C. The test specimens were cold-rolled from flat strips. The test program consists of two square hollow sections and four rectangular hollow sections. Coupon specimens were extracted from each hollow section, and their material properties were obtained from tensile coupon tests at room temperature and elevated temperatures. In this study, a modified design rule was proposed to predict the cold-formed lean duplex stainless steel material properties at elevated temperatures. The local and overall geometric imperfections were measured. A total of 38 column tests were conducted. The effective column length ranged from 75 to 1660 mm in order to obtain a column curve for each test series. The test program for beams included 10 pure bending tests, and the bending capacities of the specimens were determined. A total of 37 beam-column specimens were compressed between pinned ends at different eccentricities in order to obtain an interactive curve for each series of test.
Numerical investigation on columns, beams and beam-columns at room temperature as well as elevated temperatures are also presented. Accurate finite element models were developed and verified against the experimental results for columns, beams and beam-columns at room temperature. The structural members at elevated temperatures were simulated by replacing the material properties with those obtained at elevated temperatures. Extensive parametric studies were carried out, including 150 columns, 126 beams and 150 beam-columns at room temperature, as well as 180 columns, 125 beams and 195 beam-columns at elevated temperatures.
Column, beam and beam-column strengths obtained from the experimental and numerical investigations as well as available data were compared with the design strengths calculated using American, Australian/New Zealand, European specifications for stainless steel structures of duplex material, since lean duplex material is not covered by these specifications. In addition, direct strength method for carbon steel and stainless steel as well as continuous strength method for stainless steel were assessed for cold-formed lean duplex stainless steel. Modified design rules were proposed. The reliability of the current and modified design rules was evaluated using reliability analysis.published_or_final_version
Civil Engineering
Doctoral
Doctor of Philosophy
25
Cheung, Wing-cheung. „Short-term isothermal annealing of a cold rolled duplex stainless steel /“. Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19131926.
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26
Silva, Eloy de Macedo. „Fractal analysis of fracture surface of Duplex Stainless steel UNS S31803“. Universidade Federal do CearÃ, 2002. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7306.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorIn the last years, the fractal geometry has become widely studied. Its application in several areas increased substantially, particularly in materials engineering and science, aiming the analysis of failures and the study of the mechanical properties of materials. Some studies have shown the relationship between the fracture surfaces and their mechanical properties using the fractal geometry and its properties of fractal dimension and selfsimilarity. In this research, the fracture surface of duplex stainless steel, which was obtained by the Charpy impact test, was studied applying the fractal geometry. Considering the 475ÂC embrittlement, the steel was submitted to thermal aging to obtain the fracture surfaces, whose images were captured by the scanning electron microscope (SEM). In the fractal analysis, a study was made applying the island method and profile analysis through the digitalization of the images and the application of image analyzing software. Emphasis was given on the calculation of the fractal dimension (FD) of the surface, on the energy absorbed during the impact test, on the involved fracture mechanisms and as well on the relationship between FD and thermal aging. In order to better understanding the subject, it was done the review about fracture mechanics, of duplex stainless steel and of fractal geometry. Finishing the research, the obtained fracture surface, the absorbed energy and the obtained values of FD were analyzed. The obtained results demonstrated a relationship between the fractal dimension, the size of the dimples in fracture surfaces and the impact energy to obtain them.
A geometria dos fractais nos Ãltimos anos tem se tornado bastante difundida no meio cientÃfico. O seu emprego em diversas Ãreas aumentou substancialmente, em particular na engenharia e ciÃncia dos materiais, com o objetivo de analisar falhas e estudar as propriedades mecÃnicas dos materiais. Alguns estudos tÃm mostrado a relaÃÃo entre as propriedades mecÃnicas de superfÃcies de fratura com a geometria dos fractais e suas propriedades de dimensÃo fractal e auto-similaridade. Nesta pesquisa, foi estudada, com base na geometria dos fractais, a superfÃcie de fratura do aÃo inoxidÃvel duplex obtida atravÃs do ensaio de impacto Charpy. Considerando a fragilizaÃÃo a 475C, o aÃo foi submetido ao tratamento tÃrmico de envelhecimento para a obtenÃÃo das superfÃcies de fraturas cujas imagens foram captadas no microscÃpio eletrÃnico de varredura (MEV). Na anÃlise fractal foi feito um estudo aplicando os mÃtodos das ilhas e anÃlise de perfil atravÃs da digitalizaÃÃo das imagens e aplicaÃÃo de softwares de anÃlise de imagem. Foi dada Ãnfase na anÃlise do cÃlculo da dimensÃo fractal (Df) da superfÃcie, na energia absorvida no ensaio de impacto, nos mecanismos de fratura envolvidos, bem como na relaÃÃo entre Df e o tratamento tÃrmico de envelhecimento. Para o melhor entendimento do trabalho foi feita uma revisÃo bibliogrÃfica sobre a mecÃnica da fratura, o aÃo inoxidÃvel duplex e a geometria dos fractais. Para finalizar a pesquisa, foi feita a anÃlise da superfÃcie da fratura obtida, da energia absorvia e de valores de Df alcanÃados. Os resultados obtidos demonstraram uma relaÃÃo entre a dimensÃo fractal, o tamanho dos dimples em superfÃcies de fratura e a energia de impacto para a obtenÃÃo das mesmas.
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Al-Rabie, Mohammed. „Observations of stress corrosion cracking behaviour in super duplex stainless steel“. Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/observations-of-stress-corrosion-cracking-behaviour-in-super-duplex-stainless-steel(51f53ed4-7bdc-469a-8ff7-7dfd9ff56339).html.
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The new generation of highly alloyed super duplex stainless steels such as Zeron 100 are preferable materials for industrial applications demanding high strength, toughness and superior corrosion resistance, especially against stress corrosion cracking (SCC). SCC is an environmentally assisted failure mechanism that occurs due to exposure to an aggressive environment while under a tensile stress. The mechanism by which SCC of duplex stainless steel is expected to suffer depends on the combination of electrochemical and the mechanical interaction between austenite and ferrite in the duplex alloys. The main aims of this work are to study the suitability of digital image correlation (DIC) to monitor the initiation and propagation of SCC and to understand how the microstructure of duplex stainless steel influences the kinetics of crack initiation and growth. The combined analysis of DIC, SEM and EBSD was used to study the relative crack propagation and the effect of interphase boundaries on crack growth as well. Cracking was initiated beneath saturated MgCl2 droplets in an atmospheric environment at 80°C and relative humidity of 30-33%. As-received and 10% cold rolled samples (with two orientations transverse and longitudinal to the loading direction) were subjected to an applied strain of 0.03 under displacement controlled tests. Regular optical observations were recorded of the droplets and their surrounding area. DIC analyses used the differentiation of the displacement fields to obtain the apparent surface strains used to detect crack initiation and propagation, and to measure crack opening displacements. It was found that DIC was efficiently observed the strain developments and the displacements in observed surfaces outside of the droplets but it could not identify or quantify the initiation of the cracks inside the droplets because of the mobility of the salt film and the high amount of the corrosion products formed which obscure the vision under the droplets. In addition, results showed that early stage microcracks were initiated in α phase and α/γ interfaces and propagated preferentially in the ferrite phase. Also, SCC initiation and propagation was accelerated by cold rolling and the grains orientations were of major effects on the retardation of crack propagation which was more severe in the transverse rolling direction. Also, there was no relation established between the strain level and the density of pitting in either phase.
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Ornek, Cem. „Performance characterisation of duplex stainless steel in nuclear waste storage environment“. Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/performance-characterisation-of-duplex-stainless-steel-in-nuclear-waste-storage-environment(4db73e9b-c87c-40a6-9778-0b823b1c499f).html.
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The majority of UK’s intermediate level radioactive waste is currently stored in 316L and 304L austenitic stainless steel containers in interim storage facilities for permanent disposal until a geological disposal facility has become available. The structural integrity of stainless steel canisters is required to persevere against environmental degradation for up to 500 years to assure a safe storage and disposal scheme. Hitherto existing severe localised corrosion observances on real waste storage containers after 10 years of exposure to an ambient atmosphere in an in-land warehouse in Culham at Oxfordshire, however, questioned the likelihood occurrence of stress corrosion cracking that may harm the canister’s functionality during long-term storage. The more corrosion resistant duplex stainless steel grade 2205, therefore, has been started to be manufactured as a replacement for the austenitic grades. Over decades, the threshold stress corrosion cracking temperature of austenitic stainless steels has been believed to be 50-60°C, but lab- and field-based research has shown that 304L and 316L may suffer from atmospheric stress corrosion cracking at ambient temperatures. Such an issue has not been reported to occur for the 2205 duplex steel, and its atmospheric stress corrosion cracking behaviour at low temperatures (40-50°C) has been sparsely studied which requires detailed investigations in this respect. Low temperature atmospheric stress corrosion cracking investigations on 2205 duplex stainless steel formed the framework of this PhD thesis with respect to the waste storage context. Long-term surface magnesium chloride deposition exposures at 50°C and 30% relative humidity for up to 15 months exhibited the occurrence of stress corrosion cracks, showing stress corrosion susceptibility of 2205 duplex stainless steel at 50°C.The amount of cold work increased the cracking susceptibility, with bending deformation being the most critical type of deformation mode among tensile and rolling type of cold work. The orientation of the microstructure deformation direction, i.e. whether the deformation occurred in transverse or rolling direction, played vital role in corrosion and cracking behaviour, as such that bending in transverse direction showed almost 3-times larger corrosion and stress corrosion cracking propensity. Welding simulation treatments by ageing processes at 750°C and 475°C exhibited substantial influences on the corrosion properties. It was shown that sensitisation ageing at 750°C can render the material enhanced susceptible to stress corrosion cracking at even low chloride deposition densities of ≤145 µm/cm². However, it could be shown that short-term heat treatments at 475°C can decrease corrosion and stress corrosion cracking susceptibility which may be used to improve the materials performance. Mechanistic understanding of stress corrosion cracking phenomena in light of a comprehensive microstructure characterisation was the main focus of this thesis.
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Alhoud, Abdulrezeg M. A. „Effect of process variables on the corrosion resistance of super duplex stainless steel“. Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=128219.
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The title of this research suggests the importance of manufacturing variables and their influence on the behavior of super duplex stainless steel (SDSS) alloy when exposed to corrosive aqueous environments. Studies show that SDSS alloys have many applications due to their good physical, mechanical and corrosion resistance properties. However, there are a number of cases of in-service failures of SDSS alloys, such as pitting corrosion, stress corrosion cracking and environmentally assisted cracking failures. The root cause of these failures was due to the impact of one or more manufacturing variables such as surface finish, microstructure defects or deficiencies after deformation. From this concept, a detailed study into the effect of manufacturing variables on the corrosion resistance of a UNS S39274 super duplex stainless steel has been carried out. The manufacturing variables studied are as follows: Effect of surface condition; The corrosion resistance of stainless steel components is very sensitive to the final surface condition. The effect of surface condition on the corrosion resistance was investigated by measuring the critical pitting temperature (CPT) and the pitting potential (Epit) of in-service UNS S39274 super duplex stainless steel tubular sections with three different surface roughness values of Ra =2.8, 3.2 and 3.5m. Experimental results confirmed that the surface roughness parameter Ra is a useful parameter as a general and basic guideline of surface texture but it’s not sufficient on its own to predict the likely effect of surface roughness on the in-service corrosion behaviour of SDSS materials. The manufacturer of super duplex stainless steel products should include the electrochemical corrosion evaluation such as the CPT or Epit values beside the surface roughness average value Ra and PRENs in SDSS alloy assessment. Effect of microstructure; The thermo-mechanical handling of super duplex stainless steels is an important factor in their performance. This is due to the complex nature of the material which is highly alloyed with Cr, Ni, Mo, and N. Exposure to certain temperature ranges leads to undesired secondary phases formation. The presence of intermetallic phases has been found to be harmful to super duplex stainless steel properties. A study was undertaken to evaluate the effect of thermal exposure of a solution annealed UNS S39274 super duplex stainless steel to temperatures of 850C, 1000ºC and 1300ºC on its microstructure and its localised corrosion resistance. Heat treatment at 850ºC and 1000C caused formation of intermetallics such as sigma () and chi () while at 1300C caused precipitation of secondary austenite and enlarged grains and percentage of ferrite was observed. The formation of intermetallics of sigma () and chi () had a drastic effect on the corrosion resistance of the super duplex stainless steel. Electrochemical measurements confirmed that the intermetallics affected the corrosion resistance by reducing the pitting potential by around 80% in the active direction. Evaluation of the corrosion morphology using SEM revealed depletion at the ferrite/austenite interfaces created intergranular corrosion path with preferential attack of the ferrite phase. The present results confirmed that PRENs is not suitable for corrosion assessment of SDSS after exposure to intermetallic temperature ranges. Effect of cold work; Cold work introduces metallurgical changes like dislocations and deformation bands which affect the corrosion resistance of stainless steel components. Cold work is still a complicated phenomenon for ferritic/austenitic alloys such SDSS. The effect of cold work (0%, 4%, 8%, 12% and 16% plastic strain) on the pitting corrosion behaviour of UNS S39274 SDSS was evaluated. The Ferrite phase of the material exhibits greater degrees of plastic deformation under straining providing a greater number of initiation sites than the austenite phase. The hydrogen embrittelement of the cold worked specimens was investigated after 48 hours cathodic charging in 0.1M H2SO4. Experimental results indicated that the increase in cold work caused reduction in mechanical properties such as elongation and strain to failure. The depth of embrittlement increased as the degree of cold work increased and revealed brittle surfaces of cleavage fracture mode. Manufacturer and users should consider the degree of plastic strain when cold worked SDSS components going to work in corrosive environments or hydrogen containing environments. The main conclusion of the work is that the interactions between corrosive environments and SDSS components containing one or more of the manufacturing variables evaluated must be considered if reductions in in-service life are to be avoided.
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Obi, Udoka. „Effect of ageing on phase evolution, mechanical and corrosion properties of a high tungsten super-duplex stainless steel“. Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=225950.
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Super duplex stainless steels (SDSSs) with lower nickel content are cost effective substitutes for higher alloyed austenitics and nickel alloys in demanding environments such as oil and gas production tubulars and pipelines due to their excellent corrosion resistance and high strength. The overall properties of SDSS are derived from its dual microstructure of equal ferrite and austenite, higher alloying additions of chromium, molybdenum, nitrogen and tungsten and its thermomechanical history. Higher alloying renders SDSS prone to secondary phase precipitation such as sigma phase during improper welding operations or fabrication, affecting the materials properties. Reports suggest that tungsten additions in SDSS delays sigma phase precipitation, hence the development of tungsten based SDSS such as UNS S39274. However, secondary phases cannot be entirely avoided in SDSS. Secondary phase evolution in DSS and the mechanical properties/corrosion behaviour of SDSS has been studied extensively yet their interaction is still not clear. In-service failures of SDSS components have identified gaps in the understanding of the link between secondary phase evolution and material properties, thus limiting the safe and efficient use of SDSS. The work presented in this thesis explored and quantified experimentally the role of aging on secondary phase evolution and ensuing effects on the mechanical properties, corrosion behaviour and toughness of UNS S39274 SDSS. The results revealed that chi phase precipitation occurred preferentially before the sigma phase, although chi phase was metastable in the studied alloy. Numerical modelling established that the measured concentration of the precipitated sigma phase follows the prediction by the Johnson-Mehl-Avrami kinetic model. The time-temperature -transformation was computed using experimental data, the results were compared with theoretical predictions. Results established that increase in both sigma and chi phase led to significant drop in the uniform strain and enhancement of the modulus, hardness and yield and tensile strengths. We note that the sigma phase was attacked by corrosion in comparison to other grades of 25Cr SDSS where the sigma phase remains inert to corrosion attack. Pitting corrosion resistance was influenced more by sigma phase than the chi phase composition. Chi phase was more damaging on the toughness than sigma phase. Another key finding is that the corrosion behaviour and fracture behaviour is more sensitive to lower secondary phase volume fraction than the tensile properties.
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Alsarraf, Jalal. „Hydrogen embrittlement susceptibility of super duplex stainless steels“. Thesis, Cranfield University, 2010. http://dspace.lib.cranfield.ac.uk/handle/1826/4562.
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This thesis describes the metallurgical and environmental factors that influence hydrogen embrittlement of super duplex stainless steels and presents a model to predict the rate at which embrittlement occurs. Super duplex stainless steel has an austenite and ferrite microstructure with an average fraction of each phase of approximately 50%. An investigation was carried out on the metallurgical and environmental factors that influence hydrogen embrittlement of super duplex stainless steels. Tensile specimens of super duplex stainless steel were pre-charged with hydrogen for two weeks in 3.5% NaCl solution at 50º C at a range of applied potentials to simulate the conditions that exist when subsea oilfield components are cathodically protected in seawater. The pre-charged specimens were then tested in a slow strain rate tensile test and their susceptibility to hydrogen embrittlement was assessed by the failure time, reduction in cross-sectional area and examination of the fracture surface. The ferrite and austenite in the duplex microstructures were identified by analysing their Cr, Ni, Mo and N contents in an electron microscope, as these elements partition in different concentrations in the two phases. It was shown that hydrogen embrittlement occurred in the ferrite phase, whereas the austenite failed in a ductile manner. An embrittled region existed around the circumference of each fracture surface and the depth of this embrittlement depended on the hydrogen charging time and the potential at which the charging had been carried out. The depth of embrittlement was shown to correlate with the rate of hydrogen diffusion in the alloy, which was measured electrochemically using hydrogen permeation and galvanostatic methods. A two-dimensional diffusion model was used to calculate the hydrogen distribution profiles for each experimental condition and the model could be employed to provide predictions of expected failure times in stressed engineering components.
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Shek, Chan-hung. „Ferrite decomposition in duplex stainless steel and its application in temperature measurement /“. [Hong Kong : University of Hong Kong], 1994. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13867660.
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Shoja, Chaeikar Siamak. „Examination of inclusion size distributions in duplex stainless steel using electrolytic extraction“. Thesis, KTH, Materialvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-161750.
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Nowadays due to large demand for clean and defect-free steels, several techniques based on different characteristics of particles are applied to investigate the steel cleanness. Outokumpu Stainless AB in Avesta has performed extensive work in this field by applying several methods, which all of them have specific advantages and limitations. However, it is necessary to find an accurate technique to investigate real properties of inclusions in duplex stainless steels. For routine analytical methods, calibration and parameters adjustment can be followed by help of these investigation results. The aim of present work is to apply automated INCA-Feature method for controlling cleanness of LDX 6112 duplex stainless steels after electrolytic extractions (EE) as a reference method. Three methods of investigations, INCA-Feature on polished samples as two-dimensional and on film-filter as three-dimensional and EE as three-dimensional analyses, were compared. The results of comparison between running INCA-Feature on polished samples and film filters show an acceptable agreement which proves the possibility of performing EE on this steel grade and using INCA-Feature for investigating this as a fast method. These methods are compared statistically and quantitative results are reported in details.
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El-Yazgi, Abdullatif Abdallah. „The effect of hydrogen on the mechanical behaviour of duplex stainless steel“. Thesis, University of Newcastle Upon Tyne, 1995. http://hdl.handle.net/10443/719.
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Duplex stainless steels are commonly used in environments that are expected to produce hydrogen i. e. in sour environments and sea water applications, often under cathodic protection. Under these conditions there is a concern about their susceptibility to hydrogen embrittlement. The effect of hydrogen, both external and internal, on the mechanical properties and the fracture characteristics of duplex stainless steels Type 2205 and 2507 have been studied by slow strain rate techniques using smooth tensile specimens. Specimens were strained to failure in air after high pressure hydrogen thermal charging, in a hydrogen atmosphere, in a hydrogen sulphide environment under open circuit potential condition, and whilst cathodically polarized at different potentials in distilled water with 100 wppm potassium sulphate added, in 3.5% aqueous sodium chloride, or in NACE solution. All the environments produced a major reduction in ductility that increases linearly with decrease in strain rate. The severity of the embrittlement depended upon whether the supply of hydrogen was external or internal. Internal hydrogen, as in thermally charged specimens, produced a more profound loss in ductility than straining in a hydrogen atmosphere and prolonged room temperature aging of these specimens, for up to 3 years, resulted in insignificant recovery of ductility, emphasizing the role of the austenite as a hydrogen reservoir. Provision of hydrogen at very high fugacities (cathodic polarization) during straining indicated that the potential at which loss in ductility is first noted corresponds to the hydrogen evolution potential for the particular solution involved. The presence of chloride ion seems to have no significant effect on the loss in ductility- The presence of hydrogen sulphide in the environment, however, introduced the complication of extensive chemical attack during and after crack propagation. The loss in ductility increased as the pH of the solution decreased and, irrespective of pH, maximum embrittlement occurred at some particular temperature between 20 and 90'C. The latter is attributed to the two competing processes of hydrogen ABSTRACT embrittlement and corrosion. A minimum chloride ion concentration of 300 wppm seems necessary to maintain the maximum embrittlement. The ultimate tensile strength of the steel is not affected by hydrogen since cracking only occurs after it is exceeded. Cracks initiate and grow preferentially through the ferrite phase, with fracture surfaces exhibiting quasi-cleavage features; the austenite often failed in a ductile mode. The proportion and distribution of the two phases has a significant effect on the degree of embrittlement. The presence of greater amounts of austenite seems to inhibit crack propagation, but may act as a hydrogen source or reservoir for the embrittlement of the ferrite phase. Straining of the as received weldments, which had been annealed after welding, showed no evidence of hydrogen embrittlement, but an attempt was made to simulate via heattreatment the structures that could occur in the heat affected zone of the weld and these structures had inferior mechanical properties in the presence of hydrogen.
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Adams, FV, PA Olubambi, FH Potgieter und Der Merwe F. Van. „Corrosion resistance of duplex stainless steels in selected organic acids and organic acid/chloride environments“. Anti-Corrosion Methods and Materials, 2010. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001195.
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Abstract
Purpose – The purpose of this paper is to supplement the scant previous investigations on the corrosion behaviour of 2205 and 2507 duplex stainless
steels in selected organic acids containing chloride additions.
Design/methodology/approach – Microstructural examination of the alloys was first carried out, after which the corrosion behaviour of the alloys in
citric, oxalic, formic and acetic acids containing chloride additions at varying temperatures was studied using electrochemical techniques.
Findings – The alloy 2507 material had a larger grain size than did the alloy 2205 sample. The corrosion resistances of the alloys generally are highest
in acetic acids and lowest in citric acid. The addition of chloride had a pronounced effect on their corrosion resistance. Alloy 2507 generally exhibited
higher corrosion resistance in all of the acids than alloy 2205, with the exception of acetic acid at room temperature. The 50:50 ratio of ferrite to
austenite composition, as revealed by phase compositional analysis, indicated no significant possibility for galvanic corrosion between the phases.
This suggests that the corrosion behaviour of the alloys is controlled by their grain sizes and chemical compositions.
Originality/value – Although the corrosion behaviour of duplex stainless steels in some organic acid media has been reported, this investigation
covers the major organic acids not previously reported. Since in real industrial systems a mixture of both organic and minerals acids/salts may typically
exist, investigations of the combined effect of chloride ions with the organic acids reported in this paper typify real industrial operations. The paper thus
provides a basis for material selection for the application of 2205 and 2507 in industrial systems where organic acids are mostly used.
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Yang, Di. „Cyclic stress effect on stress corrosion cracking of duplex stainless steel in chloride and caustic solutions“. Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42811.
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Duplex stainless steel (DSS) is a dual-phase material with approximately equal volume amount of austenite and ferrite. It has both great mechanical properties (good ductility and high tensile/fatigue strength) and excellent corrosion resistance due to the mixture of the two phases.
Cyclic loadings with high stress level and low frequency are experienced by many structures. However, the existing study on corrosion fatigue (CF) study of various metallic materials has mainly concentrated on relatively high frequency range. No systematic study has been done to understand the ultra-low frequency (10-5 Hz) cyclic loading effect on stress corrosion cracking (SCC) of DSSs.
In this study, the ultra-low frequency cyclic loading effect on SCC of DSS 2205 was studied in acidified sodium chloride and caustic white liquor (WL) solutions. The research work focused on the environmental effect on SCC of DSS 2205, the cyclic stress effect on strain accumulation behavior of DSS 2205, and the combined environmental and cyclic stress effect on the stress corrosion crack initiation of DSS 2205 in the above environments.
Potentiodynamic polarization tests were performed to investigate the electrochemical behavior of DSS 2205 in acidic NaCl solution. Series of slow strain rate tests (SSRTs) at different applied potential values were conducted to reveal the optimum applied potential value for SCC to happen. Room temperature static and cyclic creep tests were performed in air to illustrate the strain accumulation effect of cyclic stresses. Test results showed that cyclic loading could enhance strain accumulation in DSS 2205 compared to static loading. Moreover, the strain accumulation behavior of DSS 2205 was found to be controlled by the two phases of DSS 2205 with different crystal structures. The B.C.C. ferrite phase enhanced strain accumulation due to extensive cross-slips of the dislocations, whereas the F.C.C. austenite phase resisted strain accumulation due to cyclic strain hardening. Cyclic SSRTs were performed under the conditions that SCC occurs in sodium chloride and WL solutions. Test results show that cyclic stress facilitated crack initiations in DSS 2205. Stress corrosion cracks initiated from the intermetallic precipitates in acidic chloride environment, and the cracks initiated from austenite phase in WL environment. Cold-working has been found to retard the crack initiations induced by cyclic stresses.
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Ruiner, Thomas H. „Characterization of thermal damage in 2205 duplex stainless steel with nonlinear ultrasonics (nlu)“. Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37156.
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Duplex stainless steels have a microstructure that consists of almost equal shares of austenite and ferrite, which leads to excellent material properties. During production and processing, the steel can be exposed to high temperatures which leads to the development of a third (sigma) phase, and thus to a change in material properties. The objective of this research is to assess the material damage in thermally degraded 2205 duplex stainless steel using nonlinear ultrasonics (NLU). Seven 2205 duplex stainless steel specimens are thermally degraded at 700 C for a series of different time durations. Nonlinear Ultrasonic measurements are conducted in a pitch-catch setup to avoid any adverse nonlinear influences of reflections and wave interference. The material nonlinearity parameter, beta, is then obtained by directly applying the fast Fourier Transform (FFT) to the measured time-domain signal. The results show that the nonlinearity parameter beta increases to a peak at 30 minutes aging time, then droppes to a low at 360 minutes and then increases again for increasing thermal damage. This demonstrates that the nonlinearity parameter has the potential to be used as a quantitative tool to estimate thermal damage in a specimen.
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Kuan, Hong Cheng. „Influences of phase transformations on the pitting corrosion behavior of wrought duplex stainless steel in different environments“. Thesis, University of Macau, 2018. http://umaclib3.umac.mo/record=b3948877.
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Westin, Elin M. „Microstructure and properties of welds in the lean duplex stainless steel LDX 2101“. Doctoral thesis, KTH, Metallografi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-27387.
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Duplex stainless steels can be very attractive alternatives to austenitic grades due to their almost double strength at equal pitting corrosion resistance. When welding, the duplex alloys normally require addition of filler metal, while the commodity austenitic grades can often be welded autogenously. Over-alloyed consumables are used to counteract segregation of important alloying elements and to balance the two phases, ferrite and austenite, in the duplex weld metal. This work focuses on the weldability of the recently-developed lean duplex stainless steel LDX 2101® (EN 1.4162, UNS S32101). The pitting corrosion resistance of this grade is better than that of austenitic AISI 304 (EN 1.4307) and can reach the level of AISI 316L (EN 1.4404). The austenite formation is rapid in LDX 2101 compared to older duplex grades. Pitting resistance tests performed show that 1-2.5 mm thick laser and gas tungsten arc (GTA) welded LDX 2101 can have good corrosion properties even when welding autogenously. Additions of filler metal, nitrogen in the shielding gas, nitrogen-based backing gas and use of laser hybrid welding methods, however, increase the austenite formation. The pitting resistance may also be increased by suppressing formation of chromium nitrides in the weld metal and heat affected zone (HAZ). After thorough post-weld cleaning (pickling), pitting primarily occurred 1-3 mm from the fusion line, in the parent metal rather than in the HAZ. Neither the chromium nitride precipitates found in the HAZ, nor the element depletion along the fusion line that was revealed by electron probe microanalysis (EPMA) were found to locally decrease the pitting resistance. The preferential pitting location is suggested to be controlled by the residual weld oxide composition that varies over the surface. The composition and thickness of weld oxide formed on LDX 2101 and 2304 (EN 1.4362, UNS S32304) were determined using X-ray photoelectron spectroscopy (XPS). The heat tint on these lean duplex grades proved to contain significantly more manganese than what has been reported for standard austenitic stainless steels in the AISI 300 series. A new approach to heat tint formation is presented; whereby evaporation of material from the weld metal and subsequent deposition on the already-formed weld oxide are suggested to contribute to weld oxide formation. This is consistent with manganese loss from the weld metal, and nitrogen additions to the GTA shielding gas enhance the evaporation. The segregation of all elements apart from nitrogen is low in autogenously welded LDX 2101. This means that filler wire additions may not be required as for other duplex grades assuming that there is no large nitrogen loss that could cause excessive ferrite contents. As the nitrogen appears to be controlling the austenite formation, it becomes essential to avoid losing nitrogen during welding by choosing nitrogen-containing shielding and backing gas.QC 20101213
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Kabir, Md Jahidul. „Transient liquid phase bonding of a duplex stainless steel and assessment using ECT“. Thesis, Brunel University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408905.
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Humphreys, Alan Owen. „The low temperature fracture behaviour of the super duplex stainless steel Zeron 100“. Thesis, University of Birmingham, 1998. http://etheses.bham.ac.uk//id/eprint/1427/.
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The micromechanisms of fracture in an austenitic/ferritic super-duplex stainless steel (Zeron 100) have been studied for a range of product forms, including cross-rolled plate, conventional (ingot) route and powder route extruded pipe, hot isostatically pressed (HIP'd) powder, and weldments produced using both tungsten inert gas (TIG) and manual metal arc (MMA) techniques. The rolled plate material was also investigated after heat treatments at temperatures of 425 and 850°C, which were known to embrittle the material.
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Dana, Seresht Mahmoudreza. „Material Selection for Deepwater Gate Valves“. Thesis, KTH, Materialvetenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-170023.
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Material selection is an important step during the design process of an object. The goal is to produce an object to meet the requirement with minimum cost. During the recent years with discovery of oil and gas in deep water, oil and gas industry facing new challenges of handling corrosive material in seabed that gives more importance and criticality to material selection of equipment for this kind of application. Hydrogen sulfide (H2S), chloride and carbon dioxide (CO2) have made the big challenges for material that handle corrosive fluids in the seabed.This report presents a brief review of material selection for two parts of deepwater gate valve, Body and Gate. It is mostly focused on mechanical properties and required corrosion resistance. Ferritic alloys with low PRE numbers and low mechanical properties and also austenitic alloys with low yield strength are not a proper option for this case. Alloy 2205 is the most common stainless steel which is used in deep water gate valve production. There are other alloys in duplex group that show better mechanical and chemical properties than alloy 2205 but because of their high expense are not used by industries.
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Smuk, Olena. „Microstructure and properties of modern P/M super duplex stainless steels“. Doctoral thesis, KTH, Materials Science and Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3758.
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Mostafaee, Saman. „A Study of EAF Austenitic and Duplex Stainless Steelmaking Slags Characteristics“. Licentiate thesis, KTH, Materials Science and Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12064.
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The high temperature microstructure of the solid phases within the electric arc furnace (EAF) slag has a large effect on the process features such as foamability of the slag, chromium recovery, consumption of the ferroalloys and the wear rate of the refractory. The knowledge of the microstructural and compositional evolution of the slag phases during the EAF process stages is necessary for a good slag praxis.
In supplement 1, an investigation of the typical characteristics of EAF slags in the production of the AISI 304L stainless steel was carried out. In addition, compositional and microstructural evolution of the slag during the different EAF process stages was also investigated. Computational thermodynamics was also used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. Furthermore, the influence of different parameters (MgO wt%, Cr2O3 wt%, temperature and the top slag basicity) on the amount of the spinel phase in the slag was studied. In supplement 2, a novel study to characterize the electric arc furnace (EAF) slags in the production of duplex stainless steel at the process temperatures was performed. The investigation was focused on determining the microstructural and compositional evolution of the EAF slag during and at the end of the refining period.
Slag samples were collected from 14 heats of AISI 304L steel (2 slag samples per heat) and 7 heats of duplex steel (3 slags sample per heat). Simultaneously with each slag sampling, the temperature of the slag was measured. The selected slag samples were studied both using SEM-EDS and LOM. In some cases (supplement 2), X-ray diffraction (XRD) analyses were also performed on fine-powdered samples to confirm the existence of the observed phases.
It was observed that at the process temperature and at all process stages, the stainless steel EAF slag consists mainly of liquid oxides, magnesiochromite spinel particles and metallic droplets. Under normal operation and at the final stages of the EAF, 304L steelmaking slag contains 2-6 wt% magnesiochromite spinel crystals. It was also found that, within the compositional range of the slag samples, the only critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content. Petrographical investigation of the EAF duplex stainless steelmaking showed that, before FeSi-addition, the slag samples contain large amounts of undissolved particles and the apparent viscosity of the slag is higher, relative to the subsequent stages. In this stage, the slag also includes solid stoichiometric calcium chromite. It was also found that, after FeSi-injection into the EAF and during the refining period, the composition and the basicity of the slag in the EAF duplex steelmaking and EAF stainless steelmaking are fairly similar. This indicates that, during the refining period, the basic condition for the utilization of an EAF foaming-slag praxis, in both austenitic and duplex stainless steel cases, is the same. Depending on the slag basicity, the slag may contain perovskite and/or dicalcium silicate too. More specifically, the duplex stainless steel slag samples with a higher basicity than 1.55 found to contain perovskite crystals.
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Martins, Alessandra Souza. „Estudo comparativo da resistÃncia à corrosÃo dos aÃos inoxidÃveis super duplex ASTM A890 / A890M grau 5A e 6A“. Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=12591.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorUma liga metÃlica que vem apresentando um desempenho satisfatÃrio em ambientes de maior agressividade à o aÃo inoxidÃvel super duplex. Esse tipo de aÃo possui boas propriedades de resistÃncia mecÃnica, resistÃncia à corrosÃo e tenacidade ao impacto. Mesmo apresentando desempenho satisfatÃrio, esses aÃos podem apresentar problemas de corrosÃo quando sofrem algum tratamento tÃrmico devido à precipitaÃÃo de uma fase deletÃria chamada de alfa linha (â), a qual precipita em temperaturas entre 300 ⁰C e 550 ⁰C e pode ocasionar uma diminuiÃÃo da resistÃncia à corrosÃo e tenacidade do material. Portanto, o objetivo deste trabalho à avaliar a resistÃncia à corrosÃo dos aÃos inoxidÃveis super duplex fundidos de grau 5A e 6A apÃs sofrerem tratamento tÃrmico a 475 ⁰C. O grau 6A se difere do 5A pela presenÃa de cobre e tungstÃnio na sua composiÃÃo quÃmica. A resistÃncia à corrosÃo dos corpos de prova foi avaliada por meio das seguintes tÃcnicas eletroquÃmicas: monitoramento do potencial de circuito aberto, polarizaÃÃo anÃdica, polarizaÃÃo cÃclica, espectroscopia de impedÃncia eletroquÃmica e temperatura crÃtica de pite. Foi realizada a caraterizaÃÃo microestrutural dos materiais, onde foi possÃvel observar sua estrutura bifÃsica composta por uma matriz ferrÃtica e ilhas de austenita em proporÃÃes coerentes. O ensaio de dureza Brinell mostrou que a dureza aumenta nas primeiras horas de tratamento tÃrmico e, depois, hà uma diminuiÃÃo nessa taxa de aumento da dureza. Os resultados eletroquÃmicos indicaram que, para os dois tipos de aÃo estudados, as amostras com 10 horas de tratamento tÃrmico apresentaram uma maior resistÃncia à corrosÃo.
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Pilhagen, Johan. „The fracture mechanisms in duplex stainless steels at sub-zero temperatures“. Doctoral thesis, KTH, Materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-133677.
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The aim of the thesis was to study the susceptibility for brittle failures and the fracture process of duplex stainless steels at sub-zero temperatures (°C). In the first part of the thesis plates of hot-rolled duplex stainless steel with various thicknesses were used to study the influence of delamination (also known as splits) on the fracture toughness. The methods used were impact and fracture toughness testing. Light optical microscopy and scanning electron microscopy were used to investigate the microstructure and fracture surfaces. It was concluded that the delaminations caused a loss of constraint along the crack front which resulted in a stable fracture process despite the presence of cleavage cracks. These delaminations occurred when cleavage cracks are constrained by the elongated austenite lamellae. The pop-in phenomenon which is frequently observed in duplex stainless steels during fracture toughness testing was shown to occur due to these delaminations. The susceptibility for pop-in behaviour during testing increased with decreasing plate thickness. The toughness anisotropy was also explained by the delamination phenomenon.In the second part of the thesis duplex stainless steel weld metals from lean duplex and super duplex were investigated. For the lean duplex weldments with different nickel contents, tensile, impact and fracture toughness testing were conducted from room temperature to sub-zero temperatures. The result showed that increased nickel content decreased the susceptibility for critical cleavage initiation at sub-zero temperatures. The super duplex stainless steel weldment was post weld heat treated. The fracture sequence at low temperature was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture. Energy-dispersive X-ray spectroscopy investigation of the weld metals showed that substitutional element partitioning is small in the weld metal. However, for the post weld heat treated weldments element partitioning occurred which resulted in decreased nickel content in the ferrite.QC 20131108
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Reynolds, Nicholas A. „Behavior and design of concentrically loaded duplex stainless steel single equal-leg angle struts“. Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49074.
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Stainless steel has garnered attention as an alternative structural material to conventional carbon steel due to its corrosion resistance properties and aesthetic appearance. Of interest are single angles, which are frequently used in trusses, transmission towers, and as bracing diaphragms. When subjected to compression, knowledge concerning the behavior, analysis, and design of stainless steel single angles is very limited.
This thesis addresses the behavior of duplex stainless steel single equal-leg angles subject to concentric compressive loading. Two complementary approaches are used in this study, the first of which was experimental and consisted of conducting 33 full-scale buckling tests on S32003 duplex stainless steel single equal-leg angle components. Angles specimens had slenderness ratios ranging from 35 to 350 and leg width-to-thickness ratios of 7.5 to 12.3. In the second approach, computational models that accounted for material nonlinearity, material anisotropy, and geometric out-of-straightness were developed and validated using the experimentally obtained test results. These models were subsequently used to perform numerical buckling experiments to shed light on the behavior of axially loaded compression duplex stainless steel single angles for a wide range of practical leg width-to-thickness ratios.
Results from the full-scale tests and from the numerical models are shown to correlate well with the classical mechanics-based formulae, which considers nonlinear stress-strain relationships, for predicting flexural and flexural-torsional buckling strengths of singly symmetric stainless steel members. Finally, design criteria in the form of load and resistance factor design (LRFD) with a reliability index of 3 for buckling limit states are proposed for possible adoption in future US national standards.
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Gideon, Abdullah Mohammed Abdul Fatah, und barrygideon@hotmail com. „Structural Characterisation, Residual Stress Determination and Degree of Sensitisation of Duplex Stainless Steel Welds“. RMIT University. Civil, Environmental and Chemical Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20091110.101453.
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Welding of duplex stainless steel pipeline material for the oil and gas industry is now common practice. To date, research has been conducted primarily on the parent material and heat affected zones in terms of its susceptibility to various forms of corrosion. However, there has been little research conducted on the degree of sensitisation of the various successive weld layers, namely the root, fill and cap layers. The focus of this research study was to: (i) provide an in-depth microstructural analysis of the various weld passes, (ii) study the mechanical properties of the weld regions; (iii) determine degree of sensitisation of the various weld passes; and (iv) investigate the residual stress levels within the various regions/ phases of the welds. Four test conditions were prepared using manual Gas Tungsten Arc Welding with 'V' and 'U' bevel configuration. Structural analysis consisted of (i) optical microscopy, scanning electron microscopy and magnetic force microscopy; (ii) ferrite determination using Magna-Gauge, Fischer Ferrite-scope and Point Count method. Mechanical testing consisted of Vickers hardness measurements, Charpy impact studies and transverse tensile testing. The degree of sensitisation was determined by three test methods: a modified ASTM A262, ASTM A923 and a modified Double Loop Electrochemical Potentiodynamic Reactivation (DL-EPR) test. Residual stress levels were determined using two neutron diffraction techniques: a reactor source and a time of flight spallation source. Microstructure observed by optical microscopy and magnetic force microscopy shows the formation of both fine and coarse structures within the weld metal. There was no evidence of secondary austenite, being present in any of the weld metal conditions examined. In addition, no detrimental intermetallic phases or carbides were present. The DL-EPR test results revealed that the fill layer regions for all four conditions and the base material showed the highest values for Ir/Ia and Qr/Qa. All four test conditions passed the ASTM A262 and A923 qualitative type tests, even under restricted and modified conditions. Residual stress measurements by neutron diffraction conducted at Lucas Heights Hi-Flux Reactor revealed that the ferrite phase stress was tensile in the heat affected zones and weld, and appeared to be balanced by a local compressive austenite phase stresses in the normal and transverse directions. Residual stress measurements by neutron diffraction conducted at Los Alamos Nuclear Science Centre revealed that in the hoop direction, ferrite (211) and austenite (311) exhibit tensile strains in the weld. In the axial and radial direction, the strains for both phases were more compressive. Correlations between the degree of sensitization and microstructural changes / ferrite content were observed. Higher degrees of sensitization (Ir/Ia and Qr/Qa) were associated with reduced ferrite (increased austenite) content. Correlations between the stresses generated, the evolved microstructures and degree of sensitization were evident. Stresses within the cap region were generally shown to be of a tensile nature in the transverse and longitudinal direction. In summary, the study has shown that correlations exist between the weld microstructure, susceptibility to sensitisation and levels / distribution of internal stresses within the weld regions.
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GUIMARAES, MARINA DI GIOLO BERNARDES. „MICROSTRUCTURAL AND MECHANIC EVALUATION OF DUPLEX STAINLESS STEEL UNS S31803 UNDER DIFFERENT COOLING RATES“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2016. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=29729@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Aços inoxidáveis duplex são constituídos de matriz austeno-ferrítica e denominados AID s. A presença simultânea das fases austenita e ferrita em proporções similares faz com que esse aço apresente excelente combinação de propriedades como, elevada resistência à corrosão e altos valores de resistência mecânica. As melhores propriedades são atingidas quando é obtido um balanço apropriado de austenita e ferrita, sem a presença de fases deletérias. No entanto, devido ao alto teor de elementos de liga presente na composição química, os aços duplex apresentam um comportamento complexo de transformação e precipitação de fases. Durante a soldagem destes aços estas transformações de fase são influenciadas pela taxa de resfria mento imposta pelos ciclos térmicos associados ao aporte de calor. O objetivo deste trabalho foi avaliar as transformações microestruturais e como estas influenciam as propriedades mecânicas, em função de diferentes taxas de resfriamento a partir de diferentes temperaturas de solubilização, para o aço inoxidável duplex da classe UNS S31803. Foi realizada solubilização em quatro diferentes temperaturas (1000, 1100, 1200 e 1300 graus Celsius) seguido de resfriamento em diferentes meios tais como água gelada, água na temperatura ambiente e óleo, os quais forneceram taxas de resfriamento partindo de 228, 98 e 62 graus Celsius/s, respectivamente. Foi observado que o aço UNS S31803 em estudo apresentou limite de escoamento, dureza e limite de resistência em acordo com na norma ASTM A240-2015 para todas as condições estudadas. Verificou-se ainda, que a variação da fração volumétrica de fases foi mais significativa para as temperaturas de solubilização a 1200 e 1300 graus celsius, independente da taxa de resfriamento aplicada, a qual se refletiu nas propriedades mecânicas do aço.
Stainless steels constituted of austenitic-ferritic matrix are called duplex stainless steels (DSS). The presence of ferrite and austenite phases simultaneously in similar proportion causes to DSS an excellent arrangement of properties such as high corrosion resistance and high mechanical strength values. The best properties are reached by obtaining an appropriate balance of austenite and ferrite without deleterious phases. However, due to the high presence of alloying elements in its chemical composition, the DSS has a complex behavior of transformation and precipitation phases. During the welding process the phase transformation are influenced by the cooling rate imposed by the thermal cycles associated with the heat input. The purpose of the present work is to evaluate the UNS S31803 (DSS) microstructural transformation behavior and its mechanical properties variations based on different cooling rates from different solubilization temperatures. Four different temperatures were used (1000, 1100, 1200 and 1300 Celsius degrees) followed by cooling in ice water, water at room temperature and oil, which provided cooling rates starting respectively from 228, 98 and 62 Celsius/s degrees. In the test results, the studied DSS proved to have satisfactory response regarding the mechanical limits specified in ASTM A240-2015 for all conditions applied. Furthermore, the variation in the fractions of phases were more significant for solubilization temperatures at 1200 and 1300 Celsius degrees, regardless of the cooling rate applied, which was reflected in the mechanical properties of the steel.
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Garcia, Erick Renato Vargas. „Efeito da corrente de soldagem do processo TIG pulsado autógeno na microestrutura da zona fundida dos aços inoxidáveis duplex UNS S32304 e UNS S32101“. Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-12032012-121409/.
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A microestrutura e a composição química dos aços inoxidáveis duplex são responsáveis pela sua resistência mecânica e sua resistência à corrosão que, geralmente, é superior aos aços inoxidáveis ferríticos e austeníticos convencionais. A soldagem destes materiais causa tanto alteração de microestrutura como de composição química, que podem ser alteradas dependendo dos processos de soldagem, dos parâmetros de soldagem, da utilização ou não de metal de adição e da composição química do gás de proteção, nos processos que utilizam proteção gasosa. No caso dos aços inoxidáveis duplex baixa liga, a solidificação é completamente ferrítica, podendo produzir tamanho de grão exagerado no metal de solda e na ZAC. O objetivo deste trabalho é de avaliar o efeito da freqüência de pulsação do processo TIG autógeno na soldagem de aços inoxidáveis duplex baixa liga. Foram soldadas chapas de aços inoxidáveis duplex baixa liga UNS S32304 e UNS S32101 (lean duplex), sem metal de adição e empregando-se argônio como gás de proteção. A soldagem foi executada com o processo TIG, mantendo-se a energia de soldagem constante, de 340 J/mm, e variando-se a freqüência de pulsação entre 1, 5, 10 e 20 Hz. As microestruturas resultantes tanto no metal de solda, região central e região sem mistura, bem como na zona afetada pelo calor foram caracterizadas através de microscopia ótica. Os resultados mostraram que, na soldagem autógena, independente de ter ou não a pulsação da corrente, ocorre um aumento no tamanho do grão da zona fundida devido a solidificação ferrítica deste aço. Comparando-se os resultados do tamanho do grão e da fração volumétrica de ferrita no metal de solda, notouse um aumento no tamanho de grão e na fração volumétrica da ferrita com o aumento da freqüência de pulsação.The microstructure and chemical composition of duplex stainless steel are responsible for their mechanical strength and corrosion resistance. The welding of these materials produces a change in the microstructure and chemical composition. These changes depend on: welding processes, welding parameters, the use or absence of filler metal and composition of shielding gas in processes that use shielding gas. In the case of lean duplex stainless steel the solidification is fully ferritic, which may produce an excessive grain size in the weld metal and in the heat affected zone (HAZ). The main goal of this paper is to evaluate the effect of pulse frequency in autogenous TIG welding process of lean duplex stainless steel. In this sense, plates of UNS S32304 and UNS S32101 lean duplex were welded without filler metal and using argon as shielding gas. The welds were made using the GTAW process, keeping the heat input constant at 340 J/mm and varying the pulse frequency between 1,5,10 and 20 Hz. The results showed that, independent of pulse frequency, grain growth in the fusion zone took place since this duplex stainless steel type has a ferritic solidification mode. Comparing the grain size and ferrite volumetric fraction in the weld bead, an increase in the mean value of grain size in the central region and unmixed region of weld beads was related to an increase of pulse frequency.