Duplex stainless steels microstructure properties and applications pdf
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- Duplex stainless steel
- Duplex stainless steel—Microstructure and properties
- Duplex Stainless Steels Microstructure Properties and Applications
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When duplex stainless steel is melted it solidifies from the liquid phase to a completely ferritic structure. The duplex structure gives this family of stainless steels a combination of attractive properties:.
Microstructure characterization of a duplex stainless steel weld by electron backscattering diffraction and orientation imaging microscopy techniques. Paulo J. Modenesi 1. This paper describes the electron backscatter diffraction EBSD technique used to characterize the microstructure especially the morphology and constitution of the base metal BM , the heat-affected zone HAZ and the fusion zone FZ on a lean duplex stainless steel LDX. This technique provides advantages due to its simplicity of use and greater depth of information, thereby increasing the amount of information obtained by traditional characterization techniques such as optical microscopy OM , scanning electron microscopy SEM , and transmission electron microscopy TEM.
Duplex stainless steel
This study aims to improve the corrosion resistance of the low carbon steel by cladding it with super duplex stainless steel using laser powder bed fusion process. Critical process parameters such as laser power, laser scan speed, hatch spacing, and powder layer thickness were optimized to achieve the best possible metallurgical bonding between the clad and the substrate. The evaporative losses experienced during the laser melting process resulted in clad layers with lower chromium content 12—25 wt.
A clad thickness of Increasing scan speed had a negative impact on the thickness, corrosion resistance, and the pitting potential of the clads exposed to 3. Clads produced at the lowest scan speeds showed comparable corrosion resistance to rolled and annealed super duplex stainless steel.
This dual-phase structure imparts these steels a high strength, toughness, and increased corrosion resistance in environments containing acids, acid chlorides, seawater, and caustic chemicals. Although low carbon steel LCS remains to be the most widely used ferrous alloy, its applications are limited because it is highly vulnerable to corrosion in neutral, acidic, or saline environments 2.
Corrosion-resistant SDSS alloys possess superior corrosion resistance than the LCS for the aforementioned applications, albeit with a significantly higher material cost. One of the viable means to reduce the component cost without compromising on service life is to manufacture a composite with a low-cost tough and ductile substrate cladded with a wear and corrosion resistant surface, as in the case of SDSS clads on an LCS substrate.
These dissimilar metal composites cladded systems have been produced in the past using conventional manufacturing techniques such as welding 3 , 4 , 5 , diffusion bonding 6 , powder roll bonding 7 , hot rolling 8 , and reduction bonding 9.
However, conventionally manufactured composites are often unfit for field use due to substandard clad-substrate bonding, often leading to clad delamination when subjected to operational stresses in the field.
This substandard bond typically is a consequence of distinct and abrupt metallurgical transition at the clad-substrate interface. Furthermore, these conventional manufacturing techniques often result in a clad layer with imperfections such as porosity, undercuts, crevices, pinholes, and keyholes leading to reduced service life 2 , Recent developments in additive manufacturing AM technologies make them a good candidate to produce cladded systems with required properties 11 , 12 , 13 , Traditionally, the AM techniques have employed to produce three-dimensional 3D components, for which the physical and mechanical properties of the components are dictated by the cohesion between the layers of similar metal.
However, the key criteria for a successful and effective cladding operation is a superior clad-substrate bond, which involves adhesion of two or more dissimilar metals. Consequently, the production of 3D components and cladding operations are fundamentally different in regard to the bonding dynamics of materials. The laser powder bed fusion LPBF 15 is a promising method for cladding operations because of its higher resolution and dimensional accuracy than the other powder bed-based AM technologies such as directed energy deposition DED , electron beam melting EBM , and binder jetting 16 , 17 , 18 , Specifically, these methods result in lower-dimensional accuracy, higher material consumption per unit volume of print, and higher surface roughness of the components produced.
Therefore, surface preparation steps are often required after components are printed. On the other hand, LPBF operates at ambient pressures, room temperatures, and has a precise melting mechanism owing to its well-controlled laser and optics systems enabling the user to define the laser spot size for melting. The static powder bed ensures the minimum use of materials for the print without the need for support structures.
It was observed that the corrosion resistance and other electrochemical properties of the clads produced at lower scan speeds e. Since SDSS shows significantly higher stress corrosion cracking and pitting corrosion resistance than L-SS in chloride environments, e. It is fairly established that powder feed AM processes with travelling heating and feedstock source e. Among these benefits, those related to corrosion performance are important to highlight. It is widely recognized that surface imperfections are detrimental to corrosion properties, particularly for localized corrosion issues such as pitting and crevice corrosion These corrosion-resistant SDSS clads are intended to provide superior service life than their LCS counterparts and higher pitting and stresses corrosion cracking resistance than traditional stainless steels in chloride-containing aggressive environments.
We further characterize the physical, metallurgical, and electrochemical properties of SDSS clads in regards to changing laser scan speeds and energy density. Finally, a comparison of expected service lives of LCS and cladded systems is made based on general corrosion rates showing a significant increase in corrosion performance. Amongst all LPBF process parameters, the scan speed v s has a profound impact on the surface roughness and the dimensional accuracy of the 3D component For cladding operation in this study, similar observations were made in regard to the clad surface quality.
The minor balling around the perimeter is attributed to the changes in melt orientation causing excessive melt splashing and discontinuity in powder spreading at the edge of the clads. Furthermore, it was observed that the clad surface roughness and balling phenomenon at clad perimeter, increased with increasing scan speed. The balling phenomenon occurs due to a combination of factors including capillary instability, high scan speeds resulting in melt splashing, little liquid content in melt pools resulting from low or inadequate laser volumetric energy density VED , and Plateau-Rayleigh instability A detailed discussion on the balling phenomenon and its adverse effects of the component properties are discussed elsewhere 16 , 21 , 36 , 37 , 38 , 39 , 40 , 41 , The clads show increased surface roughness with increasing laser scan speeds, c Variation of SDSS clad roughness with increasing scan speed.
As Illustrated in figure, the average clad surface roughness increased with increasing laser scan speeds. This behavior is consistent with the previous studies dealing with surface characteristics of the AM parts 11 , 26 , 36 , Furthermore, the standard error associated with the measurements increased with the scan speeds.
This increasing roughness trend could be attributed to decreasing melt pool width and decreasing overlap between two adjoining melt tracks, resulting in creating of valley like features between two centers of melt tracks 25 , Furthermore, the intense melt pool splashing at higher scan speed results in spatter generation 44 , thereby causing increased surface roughness. As presented in Fig. However, it should be noted that the clads were produced using only 10 layers of printing. These optical micrographs were used to measure the clad thickness, and the measurements were validated using the elemental chromium contrast observed in the backscattered electron BSE imaging mode of SEM.
The Cr contrast was observed due to the difference in chromium content between Cr-rich clads and Cr-poor substrate. Clad thicknesses were measured at various locations along the width of the cladded sample, and Fig. It was observed that increasing scan speed had an adverse impact on the clad thicknesses. The maximum average clad thickness of In general, the average clad thickness decreased with increasing scan speeds.
This decreasing clad thickness trend with increasing scan speed can be elucidated on the basis of VED Eq. Bidare et al. This intensified interaction causes melt pool instability, which results in increasingly higher amounts of powder molten and unmelted being blown away from the melt pool.
Furthermore, high melt pool temperatures during laser melting of powder cause the evaporation of metal, resulting in a net upward flux of vapors from the melt pool. This upward flux creates a low-pressure zone at the base of the laser-plasma plume, which due to the pressure differential, results in the flow of the ambient inert gas present study: N 2 gas towards the melt track, and this phenomenon is commonly known as Bernoulli Effect 43 , This inward flux of the inert ambient gas is adequate to entrain powder particles from the vicinity of the melt pool, which can then either be ejected with the metal vapor or be incorporated into the melt pool.
As the Bernoulli effect intensifies with increasing scan speed, the width of the denudation zone increases. The denudation zone is the area adjoining the solidified melt track with depleted powder particles 43 , 45 , Consequently, the formation of wider denudation zones due to the increased Bernoulli effect results in the unavailability of feedstock powder for the subsequent melting to form the clad layer at higher scan speeds.
The results presented in Fig. In the context of the present study, the heat affected zone HAZ Fig. The HAZ at all scan speeds are presented in Fig. As illustrated in Fig. As a result, the microstructural changes in HAZ were observed at greater depths for slow scan speeds, and vice versa. The HAZ formed during laser welding has been shown to have lower corrosion resistance as compared to the base alloy or the cladding 13 , 47 , 48 , 49 , This higher corrosion susceptibility of the HAZ, amongst numerous other factors, is primarily due to microstructural effects, decarburization and sensitization.
Consequently, higher clad thickness would effectively delay the exposure of HAZ to the corrosives. Furthermore, higher scan speeds result in higher corrosion rates of the SDSS clads as presented in subsequent section. Therefore, low thickness with high corrosion rates of the clads would prematurely expose the HAZ at high scan speeds, thereby resulting in myriad of corrosion issues.
Some major issues such as galvanic coupling, crevice corrosion and HAZ corrosion would significantly deteriorate the service life of component, possibly resulting in catastrophic failure. Therefore, to eliminate the deleterious effect of HAZ, the cladded components would be heat treated before being employed in service. The investigation on the effects of heat treatment on HAZ and clads properties is beyond the scope of the work presented in this manuscript; the heat treatment study is presently underway.
The characteristic microstructure of the SDSS clads produced at different scan speeds are presented in Fig. The build direction black arrow and the melt pool boundaries white dashed lines within the clads are marked in Fig. It was observed that clads produced at low scan speed e. The rapid unidirectional cooling typically associated with the LPBF process results in a high aspect ratio columnar grain structure with grains transcending across multiple melt pool boundaries.
In the present context, unidirectional cooling was a consequence of heat dissipation from the clad layer to the underlying LCS substrate, which served as a heat sink. Furthermore, with increasing v s , the grain size decreased due to increasing cooling rates and decreasing VED. SDSS clads are expected to show lower corrosion performance as compared to base SDSS owing to higher grain boundary area, columnar grain morphology and higher residual stresses.
Typically, high cooling rates of LPBF result in high ferrite content ca. Similarly, Saeidi et al. At higher VED and clad thicknesses, when the top powder layer is laser melted, the previously fused layers underneath are subjected to reheating due to heat dissipation towards the substrate. The elemental loss from the clad region is discussed in further detail in subsequent sections.
Zones B, C, and D represent the HAZ of the substrate with varying microstructures depending on the heating cycles the zones were subjected to during laser melting. Therefore, zone D shows patches of pearlite formed in the ferrite matrix. Typically, the melt pool cooling rate varies linearly with the laser scan speeds which follows the Rosenthal formulation 57 , 58 , Numerous experimental and simulation studies have shown that low laser scan speeds result in deeper and wider melt pools 36 , 39 , 60 , Increasing melt pool volumes causes slower cooling rates due to low surface-to-volume ratio of the cooling liquid metal, resulting in low radiative cooling.
In contrast, at faster scan speeds, shallower and narrower melt pool results in rapid cooling of the liquid melt. Therefore, increasing laser scan speeds lead to increasing melt pool cooling rate resulting in the microstructural and metallurgical features discussed in subsequent sections. These microstructural changes are found at a higher depth of LCS substrate with increasing laser energy density or decreasing scan speeds due to deeper heat penetration.
As shown in Fig. Similarly, the SDSS clad produced at the lowest scan speed e. All the clad showed a mixture of austenite and ferrite peaks; however, the austenite peak intensity was significantly low as compared to the feedstock powder.
Duplex stainless steel—Microstructure and properties
Duplex stainless steels      are a family of stainless steels. These are called duplex or austenitic-ferritic grades because their metallurgical structure consists of two phases, austenite face-centered cubic lattice and ferrite body centered cubic lattice in roughly equal proportions. They are designed to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion, and higher strength than standard austenitic stainless steels such as Type or Both the low nickel content and the high strength enabling thinner sections to be used give significant cost benefits. They are therefore used extensively in the offshore oil and gas industry for pipework systems, manifolds, risers, etc and in the petrochemical industry in the form of pipelines and pressure vessels. In addition to the improved corrosion resistance compared with the series stainless steels duplex steels also have higher strength.
The purpose of this paper is to present an introduction to Duplex stainless steels by reviewing their main properties in terms of chemical composition, microstructure, mechanical characteristics and corrosion resistance. Toughness results obtained on base materials and welded specimens at various temperatures will be provided. Duplex stainless steels were born and have been actively developed by European companies since Their features made them very attractive compared to equivalent austenitic grades: higher resistance to Stress Corrosion Cracking, higher mechanical properties and lower alloy cost Charles and Chemelle, The production units that carry out these manufacturing processes, use reactors and piping systems that must often resist corrosive environments and high pressures see Tystad, The demands placed on materials increase steadily in terms of both quality and operating constraints. Duplex grades are commonly used in numerous industries, due to their intrinsic properties.
This paper aims to establish the microstructures and the process-structure relationships in duplex stainless steel powders consolidated by selective laser melting SLM. A priori data on energy density levels most appropriate to consolidation of duplex stainless steel powders through SLM served as the basis to converge on the laser settings. Experimental designs with varying laser power and scan speeds and test pieces generated allowed metallographic evaluations based on optical and scanning electron microscopy and electro backscatter diffraction analyses. Duplex stainless steel powders are established for processing by SLM. However, the dynamic point heat source and associated transient thermal fields affect the microstructures to be predominantly ferritic, with grains elongated in the build direction. Considerable CrN precipitation is also evidenced. Duplex stainless steels are relatively new candidates to be brought into the additive manufacturing realm.
Duplex Stainless Steels Microstructure Properties and Applications In summary, nickel does have some direct effect on corrosion properties, for instance.
Duplex Stainless Steels Microstructure Properties and Applications
Developments, grades and specifications; Alloy design; Microstructure; Forming and machining; Physical and mechanical properties; Corrosion; Stress corrosion cracking; Welding metallurgy; Welding processes; Weld properties; Non-destructive testing of welds; Applications; Service experience. Two very successful conferences - in Glasgow and Beaune - were held on duplex stainless steels during the first half of the '90s. This book takes keynote papers from each, and develops and expands them to bring the topics right up to date. There is new material to cover grades, specifications and standards, and the book is fully cross-references and indexed.
Pranut Potiyaraj, PhD. This journal is published under the terms of the Creative Commons Attribution 4. The duplex steel grades exhibit high strength property and excellent corrosion resistance. However, after welding and heat treatment their toughness and corrosion resistance could be significantly decreased due to the occurrences of various detrimental intermetallic phases like sigma phase. In this work, effect of heat treatment on microstructure and mechanical behavior of super duplex stainless steel grade SAF were investigated.
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Stainless steel is not a single material but the name for a family of corrosion resistant steels. Like many scientific discoveries the origins of stainless steel lies in a serendipitous accident. In Sheffield, England, Harry Brearley was investigating the development of new steel alloys for use in gun barrels. The first application of these steels was in cutlery for which Sheffield subsequently became world famous. Simultaneous work in France led to the development of the first austenitic stainless steels.
ГЛАВА 102 Стратмор спустился на нижний этаж ТРАНСТЕКСТА и ступил с лесов в дюймовый слой воды на полу. Гигантский компьютер содрогался мелкой дрожью, из густого клубящегося тумана падали капли воды. Сигналы тревоги гремели подобно грому. Коммандер посмотрел на вышедший из строя главный генератор, на котором лежал Фил Чатрукьян. Его обгоревшие останки все еще виднелись на ребрах охлаждения. Вся сцена напоминала некий извращенный вариант представления, посвященного празднику Хэллоуин. Хотя Стратмор и сожалел о смерти своего молодого сотрудника, он был уверен, что ее можно отнести к числу оправданных потерь.
Хиросима, 6 августа 1945 года, 8. 15 утра. Акт безжалостного уничтожения. Бесчувственная демонстрация силы страной, уже добившейся победы. С этим Танкадо сумел примириться.
Сверху хлестала вода, прямо как во время полночного шторма. Стратмор откинул голову назад, словно давая каплям возможность смыть с него вину. Я из тех, кто добивается своей цели. Стратмор наклонился и, зачерпнув воды, смыл со своих рук частицы плоти Чатрукьяна. Его мечта о Цифровой крепости рухнула, и он полностью отдавал себе в этом отчет. Теперь у него осталась только Сьюзан. Впервые за много лет он вынужден был признать, что жизнь - это не только служение своей стране и профессиональная честь.