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Austenitic - Ferritic stainless steels: A state-of-the-art review

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Austenitic - Ferritic stainless steels: A state-of-the-art review

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Abstract

Austenitic-ferritic stainless steels, more commonly known as duplex stainless steels, or DSS for short, consist of two basic phases. One is austenite, A, and the other is ferrite, F, present in about equal amounts (but not less than 30% each). The two phases owe their corrosion resistance to the high chromium content. Compared to austenitic stainless steels, ASS, they are stronger (without sacrificing ductility), resist corrosion better, and cost less due to their relatively low nickel content. DSS can be used in an environment where standard ASS are not durable enough, such as chloride solutions (ships, petrochemical plant, etc.). Due to their low nickel content and the presence of nickel, DSS have good weldability. However, they have a limited service temperature range (from −40 to 300°) because heating may cause them to give up objectionable excess phases and lower the threshold of cold brittleness in the heat-affected zone of welded joints. State-of-the art DSS are alloyed with nitrogen to stabilize their austenite, and in this respect the nitrogen does the job of nickel. Also, nitrogen enhances the strength and resistance to pitting and improves the structure of welds.

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... Duplex stainless steels (DSS) have become more attractive than austenitic and ferritic stainless steels in many applications because of their favourable mechanical properties and corrosion resistance. [1][2][3][4] These are due to balanced ferritic-austenitic fine grain microstructure and high proportion of alloying elements. 5 Generally, a balanced microstructure of austenite and ferrite would be the ideal structure. ...
... 5 Generally, a balanced microstructure of austenite and ferrite would be the ideal structure. [1][2][3][4][5] However, the DSS have a limited service temperature range, lower than 300uC, because a great number of detrimental secondary phases can be formed as a consequence of the thermodynamic instability of the ferrite. 3 Owing to their low nickel content, DSS have good weldability. ...
... [1][2][3][4][5] However, the DSS have a limited service temperature range, lower than 300uC, because a great number of detrimental secondary phases can be formed as a consequence of the thermodynamic instability of the ferrite. 3 Owing to their low nickel content, DSS have good weldability. Nevertheless, the melting and solidification associated with fusion welding processes can destroy the favourable duplex microstructure of these stainless steels, 6 although it is important to remark the better productivity using fusion welding 7 . ...
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Consolidated UNS S32205 duplex stainless steel joints welds were performed using a friction stir welding (FSW) process. An experimental set-up was used to record the thermal history of duplex stainless steel FSW joint. For points at equal distance from the weld centreline, temperature measured near the beginning of the weld was lower than that measured in the middle of the welded joint. This was attributed to a non-stationary transfer condition. FSW thermal cycle showed shorter time spent at elevated temperature compared that presented by fusion welding, indicating less propensity to detrimental second phase precipitation. To support temperature measurements with thermocouples, a three-dimensional finite element thermal model of FSW was implemented, which provided a good agreement with experimental data.
... The construction of equipment and engineering structures with duplex alloys frequently requires welding junction of parts. Although the fusion welding is a controlled and standardized process, DSS undergoes severe microstructure transformations due to the thermal cycles, affecting the phase distribution and balance in the high temperature heat affected zone (HTHAZ) and in the weld metal (WM) [4,5]. The phase transformations and precipitation of detrimental phases affect the mechanical properties and the resistance to localized corrosion of these alloys [4][5][6][7]. ...
... Although the fusion welding is a controlled and standardized process, DSS undergoes severe microstructure transformations due to the thermal cycles, affecting the phase distribution and balance in the high temperature heat affected zone (HTHAZ) and in the weld metal (WM) [4,5]. The phase transformations and precipitation of detrimental phases affect the mechanical properties and the resistance to localized corrosion of these alloys [4][5][6][7]. The thermal cycles during fusion welding stimulate the grain growth of the ferrite phase (δ) due to the total or partial dissolution of the austenite phase (γ) in the HTHAZ [4,5]. ...
... The phase transformations and precipitation of detrimental phases affect the mechanical properties and the resistance to localized corrosion of these alloys [4][5][6][7]. The thermal cycles during fusion welding stimulate the grain growth of the ferrite phase (δ) due to the total or partial dissolution of the austenite phase (γ) in the HTHAZ [4,5]. Detrimental phases like σ phase, nucleate along the δ/γ interfaces and grow into the δ phase in the HTHAZ decreasing the toughness and the resistance to localised corrosion [6][7][8]. ...
Article
The effect of the application of a 3 mT electromagnetic field (EMF) during the welding of a 2205 duplex stainless steel on the resistance to fatigue damage was investigated on samples subjected to high cycle fatigue (HCF) and very high cycle fatigue (VHCF) conditions. Ferrite grain refinement, high volume fraction of regenerated austenite in the heat affected zone and smaller columnar grains in the weld metal were induced by (EMF) application during gas metal arc welding. The improved microstructure evolution during the thermal cycle increased the number of microstructural barriers, hindering the nucleation and growth of microstructurally short fatigue cracks.
... Both alloy compositions are shown in Table 1. Since DSS's solidify completely within the ferrite phase field from the melting temperature back to room temperature, the ferrite is referred to as d-ferrite [16][17][18]. DSS's are known for offering superior corrosion resistance and mechanical properties compared to a fully austenitic or ferritic steel [17][18][19]. An ideal DSS matrix contains between 40-60% ferrite with the remainder consisting of austenite [17]. ...
... Since DSS's solidify completely within the ferrite phase field from the melting temperature back to room temperature, the ferrite is referred to as d-ferrite [16][17][18]. DSS's are known for offering superior corrosion resistance and mechanical properties compared to a fully austenitic or ferritic steel [17][18][19]. An ideal DSS matrix contains between 40-60% ferrite with the remainder consisting of austenite [17]. ...
... Between austenite and ferrite within a DSS, it has been shown in previous studies [20][21][22] that ferrite is the stronger of the two phases. In addition to the strengthening offered by ferrite formation, a grain size refinement also occurs during the peritectoid d → g + d transformation as a DSS cools from the d-ferrite phase field [18], leading to increased strength as described by the Hall-Petch relationship [23,24]. However, the RR2450 alloy has also been found to contain a recently identified silicide phase, named p-ferrosilicide [25] and was observed initially by Burdett [1]. ...
Article
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New powder-processed hardfacing Fe-based alloys are being developed to provide high wear and corrosion resistance in demanding pressurised water reactor environments. The triplex stainless steel alloy RR2450, developed from the parent austenitic alloy Tristelle 5183, has been created for this purpose. A detailed study into the stoichiometric sensitivity and phase balance within these alloys has been carried out, in order to better predict the microstructural evolution within this chemically complex class of alloys. After undergoing a hot isostatic pressing cycle, the RR2450 alloy is shown to evolve a triplex matrix of austenite, ferrite and a novel π-ferrosilicide phase, alongside numerous niobium, titanium and chromium precipitates. Investigation into large austenite and π-ferrosilicide phase variations between different batches of the RR2450 and Tristelle 5183 alloys has indicated that small stoichiometric adjustments allow these hardfacing alloys to be tailored to produce different microstructures for specific applications.
... Super duplex stainless steel (SDSS) are biphasic ferrite-austenite alloys based on the Fe-Cr-Ni system (1). The two-phase structure of ferrite and austenite combines the beneficial effects of the phases and allows a global high strength (ferrite) and toughness (austenite) even at low temperatures (1,2). SDSS exhibit higher resistance to stress corrosion cracking and strength than austenitic stainless steels, widely used in many applications as structural materials in various industrial sectors including chemical, petrochemical, power generation, pulp and paper, and pollution control industries (1). ...
... Using equation (2), the volume flux can be calculated analytically using Eq (2) = (2) where is the tool pin volume and is the percentage of heat generation from the pin side relative to the total heat generation. For this work, a value of 20% for was used based on the work of Colegrove et al (2000). ...
... Life-determining factors are size, shape and distribution of non-metallic inclusions and the ability of grain and phase boundaries to block cyclic slip or microcracks. Duplex stainless steels exhibit a good combination of high strength, ductility and corrosion resistance [4]. Many applications imply cyclic loading, for instance the power transmission in off-shore boats. ...
... The behavior of microstructurally short fatigue cracks were investigated in the VHCF regime on the austenitic ferritic duplex stainless steel DIN 1.4462. Duplex steel exhibit good strength and ductility values paired with excellent corrosion resistance [4]. The chemical composition of the material and the heat treatment pa-rameters for the homogenizing and grain coarsening (required for 3D synchrotron tomography) is given in Table 1. ...
Conference Paper
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The present paper reviews experimental results on the fatigue damage of grade 1.4462 austenitic- ferritic duplex steel in the very high cycle fatigue (VHCF) regime. Electrolytically polished miniature and bulk specimens have been fatigued in an ultrasonic fatigue testing machine while the surface is observed in-situ by an optical microscope. The pre-fatigued miniature specimens are investigated by synchrotron diffraction contrast tomography (DCT) to reveal three-dimensional crystallographic orientation data. These data are used for finite element modeling in combination with a material model accounting for elastic anisotropy and crystal plasticity to predict crack initiation sites. The bulk specimens are carefully analyzed by means of scanning electron microscopy (SEM) in combination with electron back-scatter diffraction (EBSD). Under VHCF loading conditions, slip band formation is limited to the softer austenite grains - in particular at twin boundaries. Once being formed, the bands generate high stress concentrations where they impinge the austenite- ferrite phase boundaries, eventually, leading to crack initiation. The results are discussed by means of a numerical modeling approach that is based on (i) the finite element method (FEM) mentioned above and (ii) a crack initiation model proposed by Tanaka and Mura [1] and Chan [2].
... The duplex stainless steels have been developed to provide a combination of strength and resistance to pitting and stress corrosion cracking in comparison with the 300-series austenitic stainless steels [1][2][3]. These unique properties of the duplex stainless steels have resulted in their use in a variety of industrial applications, including chemical process plant piping, oil and gas transmission lines, and structures for use in marine environments [4,5]. ...
Article
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The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, influence of different laser welding parameters was clarified. Both bead-on-plate and autogenously butt welded joints were made using carbon dioxide laser with a maximum output of 9 kW in the continuous wave mode. Welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests. Accelerated corrosion test was carried out based on tafel plot technique. The results achieved in this investigation disclosed that welding parameters play an important role in obtaining satisfactory properties of welded joint. High laser power and/or high welding speed together with adjusting laser focused spot at specimen surface have produced welded joints with a remarkable decrease in fusion zone size and an acceptable weld profile with higher weld depth/width ratio. Besides, acceptable mechanical and corrosion properties were obtained. Using nitrogen as a shielding gas has resulted in improving mechanical and corrosion properties of welded joints in comparison with argon shielding. This is related to maintaining proper fer-rite/austenite balance in both weld metal and HAZ in case of nitrogen shielding. As a conclusion, laser power, welding speed, defocusing distance and type of shielding gas combination have to be optimized for obtaining welded joints with acceptable profile as well as mechanical and corrosion properties.
... The strength and properties of the stainless steels are closely associated with its microstructure. Super duplex stainless steels contain approximately equal proportions of ferrite and austenite grains, which improve strength, resistance against pitting and stress corrosion cracking than their austenitic counterpart [1]. These materials are highly sensitive to the heat and their operating range of temperature is limited between À100°C and 300°C to avoid loss of ductility and formation of brittle phases [2]. ...
Article
Flux Cored Arc (FCA) welding process parameters are the most important factors which affecting the properties of the weld bead. This paper models the influence of welding parameters like welding voltage, welding speed, wire feed rate, standoff distance on bead geometry. The filler material used in this work was super duplex stainless steel of grade 2507. Set of experiments based on Taguchi technique has been used to acquire the data. An Orthogonal array and Taguchi signal to noise ratio (S-N Ratio) was employed to investigate the welding characteristics of super duplex stainless steel material and optimize the welding parameters. The success of FCA welding process in terms of providing weld ability good quality and high strength depends on the process conditions used in the setup. This research aims to identifying the main factors that have significant effect on weld bead geometry.
... Besides γ 2 and σ, the chi phase (χ) may also be formed in Mo containing steels heated in the 700 -900 °C range 9,10 . ...
Article
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This work investigates the influence of deleterious phases precipitation on the corrosion resistance of two wrought superduplex stainless steels UNS S32750 with similar composition, but different grain sizes. Isothermal treatments were carried out to introduce different amounts of deleterious phases, such as chi (Χ), sigma (σ) and secondary austenite (γ2). The specimens were tested by double loop electrochemical potentiodynamic reactivation test (DL-EPR). The kinetics of precipitation in the two steels was different due to the difference of the grain sizes. The results show a correlation between the sensitization degrees, measured by DL-EPR, with the amount of deleterious phases precipitated.
... Duplex stainless steels (DSS) that contain approximatelyequal amounts of ferrite and austenite offer an attractive combinationof mechanical properties and corrosion resistance [1]. ...
Article
The examined material comprised two grades of corrosion-resistant cast steel, namely GX2CrNiMoN25-6-3 and GX2CrNiMoCuN25-6-3- 3, used for example in elements of systems of wet flue gas desulphurisation in power industry. The operating conditions in media heated up to 70°C and containing Cl- And SO4 ions and solid particles produce high erosive and corrosive wear.The work proposes an application of the σ phase as a component of precipitation strengthening mechanism in order to increase the functional properties of the material. The paper presents the results of examination of the kinetics of σ phase precipitation at a temperature of 800°C and at times ranging from 30 to 180 minutes. Changes in the morphology of precipitates of the σ phase were determined using the value of shape factor R. Resistance to erosion-corrosion wear of duplex cast steel was correlated with the kinetics of sigma phase precipitating.
... This is due to well balanced austenite and ferrite content that provides a strong resistance to localized corrosion and mechanical properties 1) . It is also known as a nickel (Ni) saver and can save 70 to 210 kg Ni in per metric ton of steels 4) which attracted the worldwide attention. But, the major downside (DSSs) is, the less production comparable to the massive demand globally 5) , while, besides the Ni issue, market is still captured by austenitic stainless steel (ASS) grades and above mentioned industries also utilizes the ASS grade (commonly 316L, 316LN, 317LN ASS) 5,6) as a most important candidate material. ...
Article
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In the present study, the weldability, microstructures and mechanical properties of dissimilar welds (2205 austeno-ferritic and 316L austenitic stainless steel) was investigated by using shielded metal arc welding (SMAW) with the help of two different electrodes namely duplex (E2209) and austenitic (E309L). After welding, the microstructure of the different zones of joints was evaluated by using optical microscopy and scanning electron microscopy (SEM), while, the localized chemical information was obtained by energy dispersive spectrometer (EDS) attached to the SEM. In E2209 weld metal, the solidification was observed as the primary ferrite mode. While, 309L weld metal was observed as the primary ferrite with austenitic matrix. Optimum ferrite content was observed in both the electrode. Finally, it was concluded that for the joints between the 2205 austeno-ferritic and 316L austenitic stainless steel, the E2209 electrode was dominant property wise.
... The tube is an AISI 304L (UNS S30403) austenitic stainless steel and the base is a duplex UNS S31803. Accordingly to the owner the material specified in the project should be the duplex UNS S31803, which has higher mechanical and corrosion resistance than AISI 304L [1], but is considerably more expensive. Fig. 4 was produced by scanning the original radiography of the tube, which means that the light region is thinner than the dark ones. ...
Article
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A high pressure oil tube with nominal diameter 50.8 mm and nominal thickness 4 mm has prematurely failed with a longitudinal crack, as shown in Fig. 1. The failure was detected after 11 months of operation. The tube is part of the hydraulic power unit of an off shore oil and gas platform. The maximum designed internal pressure was 20 MPa and the service temperature was 25 °C with no significant variation. In practice, the internal pressure varies from 16 to 20 MPa under operation, and shutdowns rarely occur. Fig. 2 shows the tube failed in the line, before it has been took off for analysis. The arrow indicates a clamp missing in the line.
... The duplex alloys are more difficult to machine than the austenitic grades though these have better mechanical properties. The common basis for its poor machining behaviour stem primarily from the resulting high strength of the alloy but being exacerbated by lack of non-metallic inclusions and the low carbon content [4,17]. However, there is still a deficient understanding in machining of duplex stainless steel. ...
Article
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Machinability tests were conducted on duplex alloys SAF 2205 and SAF 2507, while employing austenite stainless steel 316L as a benchmark during drilling. Tool wear, cutting forces and machined surface finish were compared and analysed under similar machining conditions. Both duplex alloys displayed poorer machinability responses, with 2507 being worst. Abrasion and adhesion are the most common wears appeared on the flank and rake faces. Adhesion wear being the most severe on the flank face, was seen to be triggered by built-up edge formation. Duplex alloys 2507 and 2205 both show a higher response to built-up edge formation. Flute damage was found on the drill tool, while drilling both duplex alloys. It was found this damage can lead to catastrophic tool failure. Higher cutting force and poorer surface finish were found for second generation duplex (2507).
... The precipitation of the sigma and chi phases occurs in the temperature ranges 600-1000 °C and 700-950 °C, respectively 1,[4][5][6] , and the precipitation sites are at the α/γ (ferrite/austenite) interfaces. Chi phase can precipitate at the α/α interface, and both sigma and chi phases also precipitate at triple α/α/γ points. ...
Article
Full-text available
One of the most studied deleterious phases in stainless steels is the sigma phase, due to its high potential to decrease the toughness and corrosion resistance of these steels. Eight samples of as-received cold rolled UNS S32205 duplex stainless steel were submitted to isothermal heat treatments at 850 °C during 10, 15, 30, 60, 120, 180, 240, and 300 minutes in order to study the precipitation kinetics of the sigma and chi deleterious phases. Several complementary microstructural analysis techniques were used to determine the volume fraction of the intermetallic phases, including optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Evaluation was made of the kinetics of isothermal formation of sigma and chi phases in commercial duplex stainless steels (UNS S32205). The results indicated two different mechanisms for sigma phase precipitation: sigma phase formed from the chi phase for shorter isothermal heat treatment times, and sigma phase precipitated at the ferrite-austenite interface for longer isothermal heat treatment times, using a temperature of 850 °C. The phase transformation kinetics determined using the JMA equation indicated that chi phase precipitation caused faster sigma phase formation.
... Thanks to high strength and plastic properties [10][11][12][13][14], they can be used on mining platforms and in deep wells, even at a depth of 8000 meters, where the pressure can reaches 1600 bar and the temperature is 300°C. Geological data of Poland indicate [15] that our country has a large geothermal energy potential and is a site for industrial wells. ...
Article
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High-alloy corrosion-resistant ferritic-austenitic steels and cast steels are a group of high potential construction materials. This is evidenced by the development of new alloys both low alloys grades such as the ASTM 2101 series or high alloy like super or hyper duplex series 2507 or 2707 [ The analyzed AISI A3 type cast steel is widely used in both wet exhaust gas desulphurisation systems in coal fired power plants as well as in aggressive working environments. Technological problems such as hot cracking presented in works [ The presented in this work phenomena which occur during the crystallization and cooling of ferritic-austenitic cast steel were investigated using numerical methods with use of the ThermoCalc and FactSage® software, as well with use of experimental thermal-derivative analysis.
... If ASSs cannot be fully replaced, a combination of ASSs and DSSs can be used. It has been reported that the use of DSSs can result in saving approximately 70-210 kg of Ni for per metric ton of steel [14]. DSSs also give higher strength (at least 1.5 times more than ASSs) [15] and superior localized corrosion resistance such as pitting and stress corrosion cracking (SCC) [16]. ...
Article
There are many industrial situations particularly in petro-chemical, marine, power plant and other such industries where the use of dissimilar metal weldments is necessary, mainly due to economic benefits and also sometimes to improve the performance of the component. Both austenitic stainless steels and duplex stainless steels have received much attention in recent days due to their superior anti-corrosive and mechanical properties. Further, the use of shielded metal arc welding (SMAW) process is inevitable in engineering industries. In the present work, microstructure, mechanical and intergranular corrosion behavior of dissimilar 2205 duplex stainless steel and 316L austenitic stainless steel fabricated by SMAW process using E2209 electrode by taking two different heat input (0.45–0.60 kJ/mm) was investigated. The microstructures were characterized by using optical microscopy and scanning electron microscopy (SEM), while the localized chemical information was obtained by an energy dispersive spectrometer attached to the SEM. Double loop electrochemical potentiokinetic reactivation test was performed to quantitatively assessing the intergranular corrosion based on degree of sensitization. The effect of weld dilution on mechanical properties (i.e. tensile/hardness properties) was also studied. The ferrite content was experimentally measured by using ferritoscope and it was observed that the weld joint achieved the required ferrite content for both the heat inputs. Higher ferrite content (results of faster cooling rate) increased the hardness and tensile strength of low heat input as compared to high heat input. While, high heat input improved the corrosion resistance due to formation of higher austenitic phases. Higher impact energy was observed in E2209 weld metal than that of the base metals. No welding defects were observed and recommended for industrial use.
... Super duplex stainless steel (SDSS) are biphasic ferriteaustenite alloys based on the Fe-Cr-Ni system [1]. The two-phase structure of ferrite and austenite combines the beneficial effects of the phases and allows a global high strength (ferrite) and toughness (austenite) even at low temperatures [1][2][3][4]. SDSS exhibit higher resistance to stress corrosion cracking and strength than austenitic stainless steels, widely used in many applications as structural materials in various industrial sectors including chemical, petrochemical, power generation, pulp and paper, and pollution control industries [1,3] SDSS family alloys have good weldability, however, special care is required to assure mechanical properties are unchanged after the process. The interference on properties depends on the welding process used. ...
Article
Full-text available
The microstructure and mechanical properties of 8-mm-thick friction stir welded SAF 2507 super duplex stainless steel pipe was examined. High-quality welds were successfully produced using polycrystalline cubic boron nitride (PCBN) tool, force control mode of 38. kN, travel speed of 50. mm/min, rotational speed of 200. rpm. Hardness and tensile tests were performed, showing hardness increase in the stir zone and failure on the base metal. Thermal simulation showed maximum global temperatures around 1176. °C, and different thermal cycles along the joint thickness, providing microstructural and mechanical differences along the welded joint. © 2018 Brazilian Metallurgical, Materials and Mining Association.
... [3,4] The poor machinability is also worsened by the deficiency of nonmetallic additions and a lower proportion of carbon. [5,6] More plastic austenite at higher strain causes ferrite build-up [7] which may imbalance the phase proportion during conventional machining. Therefore, nonconventional machining such as wire electrical discharge machining (WEDM) process can be applied to process these materials. ...
Article
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This study investigates the manufacturing process of 2205 duplex stainless steel by wire electrical discharge machining where the effects of pulse-on time (PONT), wire tension and pulse-off time (POFT) on surface finish, kerf width, and material removal rate (MRR). It was found that the kerf width was unchanged with the change of PONT at long pulse-of time and higher wire tension. However, it decreased initially and then increased due to the rise of PONT at low values of wire tension and POFT. Low wire tension and PONT, POFT and contributed towards widest kerf. Longer PONT increased MRR due to higher machining/processing speed. Lower wire tension and shorter POFT increased MRR more than that of higher wire tension and POFT. Craters and recast layer were on the machined surfaces at all machining conditions. Increased PONT raised surface roughness at the lower POFT and tension in the wire. The surface finish at high wire tension and longer PONT is always better than that at smaller PONT and lower tension in the wire. The microstructure underneath the recast layer remains unchanged and the failure of wire electrode occurred at higher wire tension, longer PONT and shorter POFT.
... Thus family of stainless steel materials are considered as difficult to machine materials. On top of the above, duplex stainless steel makes the machining scenarios more challenging due to its high strength and to make it worse, duplex stainless steel usually have low carbon content without non-metallic inclusions [11,31]. In addition, duplex stainless steel has a tendency for built-up edge (BUE) formation which reduces machining efficiency due to material adherence to cutting tool and eventually reduce cutting speeds. ...
Article
The present paper studies different types of errors generated on the feature (cylindrical holes) which was fabricated by the wire EDM of 2205 duplex stainless steel. Different experimental parameters such as, pulse on time, pulse off time and wire tension on the feature as well as the contribution of these parameters on cylindricity error, circularity error and diameter error were explored. Moreover, interactions among the input parameters were also considered. It was found that the total contributions of interactions between different parameters are reasonably high for all the cases which make the modelling process very complex for cylindricity, circularity and diameter errors in term of the range of parameter considered in this investigation. Wire tension has highest contribution on cylindricity error which is lowest at high value wire tension. Pulse on time has minor contribution on the cylindricity error and it increases with the increase of pulse on time. Pulse of time does not have any influence on the cylindricity error. The circularity error was lowest at medium pulse off time and medium wire tension; and those two parameters have almost similar and highest contributions. The pulse on time has around 14% contribution on circularity error and the medium value of it minimizes the circularity error. The input parameters such has pulse on time, pulse off time and wire tension have around 13%, 16% and 7% contributions respectively on diameter error which is minimized at medium pulse on time, and low pulse off time and low wire tension.
... In the present case, the γ-precipitation within the α-matrix in both its forms leads to a grain refinement. Moreover, SDSSs additionally harden due to the increased percentage of alloying elements, such as chromium and molybdenum in solid solution [33,34]. ...
Article
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: Due to their unique combination of properties, Super Duplex Stainless Steels (SDSSs) are materials of choice in many industries. Their applications and markets are growing continuously, and without any doubt, there is a great potential for further volume increase. In recent years, intensive research has been performed on lean SDSSs improving mechanical properties exploiting the lack of nickel to generate metastable γ-austenite, resulting in transformation-induced plasticity (TRIP) effect. In the present work, a commercial F55-UNS S32760 SDSS have been studied coupling its microstructural features, especially secondary austenitic precipitates, and tensile properties, after different thermal treatments. First, the investigated specimens have been undergone to a thermal treatment solution, and then, to an annealing treatment with different holding times, in order to simulate the common hot-forming industrial practice. The results of microstructural investigations and mechanical testing highlight the occurrence of TRIP processes. This feature has been related to the Magee effect, concerning the secondary austenitic precipitates nucleated via martensitic-shear transformation.
... When heated for small periods and/or low temperatures in this temperature range the steel becomes sensitized and susceptible to intergranular corrosion attack, due to chromium depletion near the grain boundaries [5]. High chromium and/or Mo-alloyed austenitic and duplex stainless steels are also susceptible to sigma phase precipitation during prolonged aging at high temperatures [6,7]. AISI 316, 317 and 310 are the austenitic grades most susceptible to sigma phase precipitation, due to the Mo additions in AISI 316 and 317, and the high chromium content of AISI 310 (24-25%). ...
Article
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The microstructural changes in an AISI 310S stainless steel exposed to temperatures in the 600–800 °C range up to 210 h were investigated. Intense carbide precipitation occurs in all conditions. Sigma phase precipitation nucleates at the grain boundaries and becomes more intense with the increase of time and temperature. Intergranular corrosion resistance was evaluated by double loop electrochemical potentiodynamic reactivation tests. Sigma phase and chromium carbides cause severe sensitization, but healing is observed in specimens aged at 650 °C, 700 °C, 750 °C and 800 °C. Time to healing decreases with the increase of aging temperature. Anodic polarization tests were conducted in specimens aged for 210 h. Pitting potentials are found to decrease in all temperature tested.
... This causes the decrement in the mechanical properties and corrosion resistence in heat affected zone as compared to base metal. Therefore, the solid state joining especially FSW is suitable for DSS 2205 [64,81,82,90,91]. ...
... It was reported that after 60 min ageing of DSS2205 at 800°C sigma phases are formed in boundaries of ferrite and austenite and the volume fraction of chi phase is negligible in compression with sigma phase [36]. It was also reported that in this temperature Cr 2 N precipitates could be found in boundaries of ferrite and austenite and also ferrite/ferrite boundaries by increase in time [37]. The precipitates in 300 min sensitised specimens at both ageing temperatures were completely clear. ...
Article
In this study effect of different ageing conditions on intergranular corrosion, pitting corrosion and relation between critical pitting temperature (CPT) and degree of sensitisation (DOS) was investigated by potentiostatic polarisation and double loop-EPR methods. The results showed by increasing sensitisation time, DOS increased and measured CPT value decreased. In addition the values of DOS and CPT of specimens aged at 650 °C showed almost liner relation while this correlation was diminished for the specimens aged at 800 °C. The results may be attributed to the further formation of precipitates on specimens aged at temperature of 800 °C.Research highlights► Correlation between DOS and CPT on DSS2205 has been investigated. ► By increase in ageing time DOS increases and CPT decreases. ► Effect of ageing in 800 °C was higher on microstructural changes than 650 °C. ► DOS and CPT show liner relation in specimens aged at 650 °C. ► There was no relation between DOS and CPT in 800 °C aged specimens.
... In literature, there are a number of publications, which deal with the turning process of stainless steel. For example Voronesko [20], Tekiner and Yesilyurt [21] examines the machining of austenitic stainless steels and the appropriate cutting parameters. Furthermore Paro et. ...
Article
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This paper is dealing with the development of a surface roughness model for turning of femoral heads from AISI 316L stainless steel. The model is developed in terms of cutting speed, feed rate and depth of cut, using response surface methodology. Machining tests were carried out with TiN–Al2O3–TiC-coated carbide cutting tools under various conditions. First-order and second-order models predicting equations for surface roughness have been established by using the experimental results. The established equation shows that the depth of cut was the main influencing factor on the surface roughness. It increased with increasing the depth of cut and feed rate, respectively, but it decreased with increasing the cutting speed. In addition, analysis of variance for the second-order model shows that the interaction terms and the square terms are statistically insignificant. The predicted surface roughness of the samples was found close to the experimentally obtained results within a 95% confident interval. KeywordsFemoral head-High-speed machining-Surface roughness-Taguchi method
... Life-determining factors are size, shape and distribution of non-metallic inclusions and the ability of grain and phase boundaries to block cyclic slip or microcracks. Duplex stainless steels exhibit a good combination of high strength, ductility and corrosion resistance [2]. The martensitic steel SAE 4150 is used for high strength power transmission parts where a high ductility is needed. ...
Article
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The present paper deals with experimental results on the fatigue damage of grade SAE 318 LN austenitic-ferritic duplex steel and a modified SAE 4150 tempering steel in the very high cycle fatigue (VHCF) regime. Particular attention was paid to the relation- ship between the crystallographic orientation of individual grains and grain patches that exhibit slip band formation, fatigue crack initiation and growth. Therefore, electrolytically polished bulk specimens have been fatigued under fully reversed loading in an ultrasonic fatigue testing machine while the surface has been observed in-situ by an optical microscope. The specimens were carefully analyzed by means of scanning electron microscopy (SEM) in combination with automated electron back-scatter dif- fraction (EBSD). In case of the austenitic-ferritic duplex steel under VHCF loading conditions, slip band formation is limited to the softer austenite grains. Once being formed, the bands generate high stress concentrations where they impinge the austenite- ferrite (γ−α) phase boundaries, eventually, leading to the crack initiation. In case of the tempering steel crack initiation is caused by slip band formation within the martensitic laths structure. It was found that in both materials microcracks are sensitive to changing crystallographic orientations when crossing a grain or phase boundary.
Article
The purpose of the research was to explore the possibility of enhancing the tribological properties of the ferritic-austenitic cast steel which is widely used in combustion gas desulphurization systems in the power industry. The subject of the research is the GX2CrNiMoN25-6-3 cast steel, a material for making pump rotors and other parts intended for operation at a temperature of up to 70°C in a water suspension containing Cl -and SO 4 -2 ions and sand / gypsum particles. It seems that in some applications, at low dynamics of parts' operation and a predominance of erosive phenomena over corrosive ones, there is a potential for using the σ phase as a structural constitu-ent that enhances the tribological properties. However, due to the increased brittleness of the material, a need arises for optimizing the quantity of this phase and carrying out detailed research into the morphology of precipitates. To describe the tribological properties, the testing of the erosive and corrosive wear mechanism was used, which was carried out on a test stand of the authors' own construction. Metallographic and stereological examinations and hardness tests were performed, which enabled the understanding of the successive stages of tribological wear of the cast steel under investigation. The increasing volumetric share of the σ phase advantageously influenced the erosive wear resistance of the material.
Article
The welding heat input plays a significant role in determining the microstructure and composition of the super duplex stainless steel cladding. The welding process is represented in the form of mathematical models developed using response surface methodology. The models were then used to predict the weld bead characteristics with reasonable accuracy. In this work, the models were developed to relate the identified important process parameters like welding voltage, wire feed rate, welding speed, nozzle to plate distance and welding gun angle with bead geometry. The models found to satisfy the adequacy requirements. It was found that reinforcement form factor was influenced by the factors arc length, torch travel speed, melting rate and resistance heating of the electrode. In the same way penetration form factor is influenced by the arc length, torch travel speed and arc force at the weld puddle. Contact angle influenced by the melting rate and resistance heating of the electrode.
Article
Duplex stainless steels are high strength and corrosion resistant steels extensively used in the chemical and petrochemical industry. The best mechanical properties and corrosion resistance are obtained with a microstructure composed by equal parts of ferrite and austenite and free from tertiary phases. Sigma phase is one of these deleterious tertiary phases. In the present work different amounts of sigma phase were precipitated by heat treatments in a UNS S31803 stainless steel. Some specimens were cold rolled before sigma phase precipitation in order to evaluate the effect of deformation on the magnetic measurements. The amount of sigma phase was precisely determined by microscopy and image analysis for each heat treatment condition. The effects of sigma phase on the steel properties were investigated, confirming the detrimental effects of very small percentages on corrosion resistance and toughness. Two magnetic methods were used to detect sigma phase: magnetization saturation measurements in a Vibrating Sample Magnetometer and ferritoscope testing. Both methods were found to be sensitive to small percentages of sigma phase in the microstructure.
Article
Duplex stainless steels (DSS) are high strength corrosion resistant materials used in the chemical and petrochemical industries. When compared to conventional austenitic grades (AISI 304L, 316L, 317L), DSS are more expensive, but present higher strength levels and are more resistant to Cl− environments. In the present work it was investigated how microstructural variations can affect the corrosion resistance of a DSS UNS S31803 in artificial sea water media. Pitting corrosion resistance in 3.5%NaCl solution was evaluated by cyclic polarization tests at room temperature and 60 °C. The double loop electrochemical potentiodynamic reactivation test (DL-EPR) was also used to evaluate the degree of sensitization due to tertiary phases, such as σ and Cr2N. Structures containing sigma phase were found to be the most susceptible to pitting and localized corrosion. Cr2N, present in the as-melted sample, decreases the pitting potential but does not cause sensitization.
Article
DSS are more suitable alternatives for the applications requiring vehement resistance to corrosion in severe conditions and to stress corrosion cracking. Work hardening tendency, high toughness, design strength and built-up layer (BUL) formation contribute to machining difficulty of duplex stainless steel (DSS2205). The present investigations are aimed to detail machining performance in terms of tool wear, tool life and cutting temperatures. Comparison of performance of AlTiN coating using two advanced PVD coating deposition techniques, viz. HiPIMS and S3p, with multilayer TiN/TiAlN coating is studied. The coating deposition processes using S3p technique were carried out in a vacuum chamber at a pressure of 1.33 × 10–2 Pa to 1.33 × 10–8 Pa. AlTiN-coated tool deposited using S3p technique proved better, exhibiting the highest tool life of 7105 mm, three times more than uncoated tools, and ahead of AlTiN-coated tool deposited by HiPIMS technique (5390 mm). Among the coated tools, TiN/AlTiN-coated tools showed the highest rate of rise in cutting temperatures as 14 and 21%, for rise in cutting speeds from 100 to 140 m/min and from 140 to 180 m/min, respectively. Experimental results of cutting temperatures are found in close agreement with results of Boothroyd model within an error of ± 10%.
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This research work is focused on laser beam and GTA welding processes and their effect on the size and microstructure of the fusion zone then, on the mechanical and corrosion properties of 3 mm thick JIS SUS329J4L duplex stainless steel plates. In contrary to GTA welding, laser beam welding with its lower heat input has resulted in a pronounced decrease in distortion level as well as a remarkable decrease in fusion zone size with much better weld profile. On the other hand and in comparison with laser beam welding, GTA welding with its higher heat input has resulted in better ferrite/austenite balance in fusion zone due to slower cooling rate. However, laser beam welded joint with its improper ferrite/austenite balance has demonstrated better tensile, impact and corrosion properties due to the remarkable decrease in its fusion zone size. This means that properties of the welded joints are influenced not only by the ferrite/austenite balance but also by the fusion zone size as a function of the welding process. The remarkable reduction of fusion zone size in case of laser welding is more effective for maintaining tensile, impact and corrosion properties, compared to the effect of ferrite/austenite balance that could be pronounced for fusion zones having similar sizes.
Article
AISI type 316L stainless steel (SS) is used in the manufacturing of components that works in severe aggressive environments. These environments include petrochemical equipments, heat exchangers, power plants, waste water treatments, etc. After prolonged exposure in these environments, corrosion will initiate in these components. The aim of this study is to strengthen the anti-corrosion property of AISI type 316L SS by coating the Stellite 6 alloy via laser cladding. The cladded microstructure was analysed by the optical and FE-SEM micrographs along with the EDS spectra. The nanoindentation was made in the substrate and cladded region to compare the hardness property. In a three-electrode setup, the anti-corrosion behaviour of both AISI type 316L SS and Stellite 6 clad samples was evaluated at 0, 42 and 70 h, followed by the investigation of the corroded morphology and surface roughness (Ra). The results showed that the cladded region contains the Co-rich dendritic structure along with Cr-rich carbides decorated in the dendritic boundaries. These Cr-rich carbides were responsible for enhancing the hardness in the cladded layer. The corrosion test proved the existence of better passive (oxide) film on the cladded samples that provided significant resistance towards corrosion than the AISI type 316L SS samples. Further, the EIS analysis confirmed that the laser cladding of Stellite 6 seems to provide greater Rp values than the AISI type 316L SS. Notably, 70 h clad sample exhibited maximum corrosion resistance in terms of EIS, Tafel and surface roughness.
Article
Duplex stainless steels are successfully used in a wide variety of applications in areas such as the food industry, petrochemical installations, and sea water desalination plants, where high corrosion resistance and high mechanical strength are required. However, during fusion welding operations, there can be changes to the favorable microstructure of these materials that compromise their performance. Friction stir welding with a non-consumable pin enables welded joints to be obtained in the solid state, which avoids typical problems associated with solidification of the molten pool, such as segregation of alloying elements and the formation of solidification and liquefaction cracks. In the case of superduplex stainless steels, use of the technique can avoid unbalanced proportions of ferrite and austenite, formation of deleterious second phases, or growth of ferritic grains in the heat-affected zone. Consolidated joints with full penetration were obtained for 6-mm-thick plates of UNS S32101 and S32205 duplex stainless steels, and S32750 and S32760 superduplex steels. The welding heat cycles employed avoided the conditions required for formation of deleterious phases, except in the case of the welded joint of the S32760 steel, where SEM images indicated the formation of secondary phases, as corroborated by decreased mechanical performance. Analysis using EBSD and transmission electron microscopy revealed continuous dynamic recrystallization by the formation of cellular arrays of dislocations in the ferrite and discontinuous dynamic recrystallization in the austenite. Microtexture evaluation indicated the presence of fibers typical of shear in the thermomechanically affected zone. These fibers were not obviously present in the stir zone, probably due to the intensity of microstructural reformulation to which this region was subjected.
Article
Super duplex stainless steel is very harder and very difficult to machining than the other materials. To find the parameters of super duplex stainless steel alloy during drilling process. There are different types of tools are used for drilling the super duplex alloys but the most widely used tool is solid carbide drill bit. Solid carbide drill bits are used in two ways by either coating or without coating for increasing their performance during drilling. In our project super duplex alloy is machined in dry drilling method to predict which tool is efficient to drill holes in the super duplex alloy plates. Three types of solid carbide drill bits are used in our experiment they without coated solid carbide drill bit, single coated solid carbide drill bit, multi coated solid carbide drill bit. We have to calculate the cutting force and torque required to drill holes in the super duplex alloy plates by using Dynamometer. Whenever the values are noted from the dynamometer then we have to analyze which drill bit has desirable values of force and torque to drill holes in the super duplex alloy plates.This analysis has been successfully done with the help of MINITAB software. At last the most efficient drill bit which is used to drill the super duplex alloy plate during dry drilling process is determined.
Article
Dual phase duplex stainless steel comprised with ferrite and austenite shows its strength and corrosion resistance in many aggressive environments based on outstanding performance over the last 20 years establishment is a great attention for researchers, manufacturers and end users. The current worldwide rapid growth, demand, and consumption of duplex- stainless steels, particularly in petrochemical, marine, power plant and other engineering applications, where the multiphase steels are being utilized that require welding for fabrication of components. On the other hand, largest production and applications sectors are captured by austenitic stainless steels globally, but the Ni price volatility breaching the backbone of producers and end users. In such conditions for the cost flexibility, joining of dissimilar metals also reflects the overall industrial need. Joining of duplex alloys is a challenging, due to number of embrittling precipitates and metallurgical changes. On the other hand inappropriate welding conditions, imbalance phase ratio of austenite/ferrite leads to solidification cracking, corrosion susceptibility, and lower ductility. As the demand for higher productivity is increasing worldwide in many domains like oil pipeline, shipbuilding sectors etc., where the thick sections are used, which endorses the requirement of higher heat input, optimization of interpass temperature, cooling rate, proper selection of consumables, defect free joints for fast and rapid productivity. However, many advanced techniques like plasma, laser, PCGTAW, A-TIG and hybrid welding processes are developing to fulfill the requirements for higher productivity without distortion. But high ferritization is another issue with those processes. Moreover, suitability and standardization of duplex alloys for high current and large heat input are still in doubt. Even, no comprehensive accounts of the dissimilar welding operation on the effect of processes and welding conditions are found in the literature. This review paper systematically highlights the effect of welding processes and conditions on microstructure, mechanical properties and corrosion resistance of duplex stainless steels and its various combinations on the basis of structure–property co-relationship.
Article
Fusion zones of electron beam welded (EBW)2205 duplex stainless steel (DSS)joints pertaining to two different levels of heat input, exhibited variable microstructural morphology as well as ferrite-to-austenite (α/γ)ratio. Both the weld zones showed phase imbalance with ferrite being the dominating phase over austenite. However, as governed by the associated thermal cycles experienced by these welds, low heat input weld metal exhibited a relatively higher proportion of austenite as compared to the high heat input weld. Thermal aging at 850 °C/0.5 h promoted the formation of Cr and Mo-rich intermetallic σ-phase and carbides in the welds, whereas welding resulted into Cr 2 N precipitation, which consequentially influenced their impact toughness and fatigue crack growth behavior. The aged joints showed a severe degradation in their impact toughness, the extent of which was more in the base metal than in the weld metal. The role played by the prevalence of secondary phases, unlike impact toughness degradation, was not detrimental but rather beneficial, as aged weld metals exhibited significantly superior fatigue crack growth resistance as compared to their unaged counterparts, which probably could be attributed to dispersion strengthening that occurred due to intermetallic precipitation.
Article
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Duplex stainless steels are largely applied in petrochemical industries due to their high corrosion resistance and mechanical performance. Their applicability also requires a great wear resistance, which can be enhanced by friction stir processing (FSP), a surface hardening technique. In this work, FSP is utilized to process surfaces of UNS S32101 and UNS S32750. The materials were analyzed by EBSD in order to determine grain size and phase fraction. Microhardness tests were used to verify and compare the shifting of hardness values from 296 ± 8 to 314 ± 11 HV0.2/15 and from 323 ± 8 to 350 ± 8 HV0.2/15 for UNS S32101 and S32750, respectively. Abrasion tests were executed to study the wear behavior of both processed and unprocessed alloys. Abrasion tests indicated that the hardening by FSP promoted decrement of abrasive wear resistance. Volumetric loss increased after FSP, from 52.1 ± 0.5 to 53 ± 2 mm3, for UNS S32101, and from 50 ± 2 to 56.3 ± 0.3 mm3 for UNS S32750. Tensile tests results were fitted to Hollomon’s equation in order to identify mechanical properties and tendencies of strain hardening. SEM images were used to classify the wear micromechanisms acting on the samples. The results suggest that FSP can promote modifications of wear mechanisms and these changes can be correlated to the alloys’ microstructure.
Article
The AWJM process is highly used for the machining of very difficult to cut tough materials. In this study a novel attempt was made to find the influence of various process parameters of AWJM process over the machining of duplex 2205 stainless steel alloy. The process parameters considered in this study are transverse speed, abrasive flow rate and stand- off distance. The work is mainly concentrated to obtain reduced angle of kerf taper and minimum surface roughness. The taguchi L9 orthogonal array matrix was used to optimize the responses recorded after the machining. ANOVA table is used to verify the influence of each parameter on the machining of duplex 2205 alloy. The results showed that the stand –off distance is the major influencing parameter which is followed by transverse speed and abrasive flow rate.
Article
Stainless steel hardfacing alloys are being developed for wear and corrosion resistant applications in pressurised water reactor environments. Two examples of this, the austenitic Tristelle 5183 and triplex RR2450 were produced by gas-atomisation before undergoing consolidation using hot isostatic pressing. The phase evolution of these alloys during simulated hot isostatic pressing cycles was observed in-situ, using synchrotron x-ray diffraction. During these cycles, the metastability of the gas-atomised powders is revealed, which influences the rate of high-temperature γ→δ transformation within the RR2450 alloy. Additionally, a high-strength silicide phase, named π-ferrosilicide, forms within these alloys. It decomposes by a eutectoid π→δ+M7C3 transformation, demonstrating a high carbon solubility within this phase. The observations of this study demonstrate the need to carefully consider the process parameters during hot isostatic pressing for such complex alloys, since alloy phase transformation rates are heavily influenced by the starting condition of the gas-atomised powder.
Article
El presente proyecto forma parte de una investigación más extensa sobre laspropiedades del superdúplex UR52N+ usado en las plataformas petrolíferas por suselevadas propiedades mecánicas y resistencia a la corrosión. Este dúplex se puede utilizarbajo la forma de placas soldadas por FCAW y la presencia de un cordón de soldadurapuede afectar su resistencia a la fatiga.El objectivo de este proyecto es, primero, caracterizar la propagación por fatiga deuna grieta iniciada en el metal base y otra en el cordón de soldadura y, segundo, observarcomo se comporta un fisura frente a la interfase metal base/cordón de soldadura.Con el citado propósito, se hicieron dos tipos de ensayos de propagación de fisuraspor fatiga. El primer tipo de ensayos se hizo para determinar los parámetros de la zona deParis y el umbral tanto para el metal base como para el cordón. Para el segundo tipo, losensayos fueron a DK constante y permitieron determinar la variación de las velocidades depropagación cuando la grieta se acerca a la interfase. Se hicieron observaciones pormicroscopía óptica y al MEB, para poner de relieve las diferencias de microestructuras y loscaminos de las grietas.Se pudo observar valores mayores de la pendiente de Paris en el cordóncomparada con la del metal base, debida en particular a la gran diferencia demicroestructura entre las dos zonas. Se observó una disminución de la velocidad depropagación de la fisura al acercarse a la interfase que puede explicarse por las tensionesresiduales que aumentan la dureza cerca del cordón. Al encontrar la interfase, la grieta sedesvía hacia el cordón a causa de la microestructura.
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This paper presents an overview of duplex stainless steels (DSS) with particular emphasis on super DSS, i.e. steels containing sufficient amounts of chromium, molybdenum, and nitrogen to produce a pitting resistance equivalent greater than 40. Duplex stainless steels have an attractive combination of mechanical and corrosion properties and are thus suitable for many marine and petrochemical applications, particularly where chlorides are present. The paper covers the following aspects of DSS: physical metallurgy, mechanical properties, corrosion properties, metallurgy of welding, machinability, and applications. A large number of references to the literature are given to aid the reader who is interested in acquiring a deeper understanding of the behaviour of this family of steels.MST/1685
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Resistance to sulfide corrosion cracking (SCC) of some low-alloying steels and stainless steels were investigated. Low-alloying steels were sensitive to SCC. Duplex stainless steels was not practically sensitive to SCC during 720 hours. However for other steels the usage of coating was necessary to prevent SCC. The exception was steel 14Kh17N2 which had lower SCC resistance after diffusion chrome-plating. It was associated with damaged structure (considerable grain growth) and confirmed by pronounced deterioration of its plasticity after chemical and thermal treatments. Lower temperatures are advisable for this storage of the saturation process.
Article
A survey is given of properties, structures, melting, crystallization, weldability, heat treatment, corrosion resistance of low-nickel austenite-ferrite (duplex) stainless steels. Steel grades produced in the C1S and foreign countries are listed. Approximate composition is given for steels 10Kh18N3G3D2L, 10Kh20N6MD2T, 08Kh18G8N2T, 10Kh28N6M3L, 06Kh20N8M3D2L and 03Kh22N6M2. Steels under consideration can substitute not only high-nickel austenite stainless steels but a series of non-ferrous metals as well. They have a high corrosion resistance in various high corrosive media and resist well against erosion corrosion. They are very efficient for technology and economics. Steels have the drawback of limited temperature utility from -50°C to +300°C.
Article
The microstructure, mechanical properties, and oxidation behavior of Cr-Ni-Mn ferritic-austenitic steels at elevated temperatures were studied. Quenching from 1250 degree C (100% alpha -ferrite) and cold or hot rolling (80%) followed by tempering at 800 degree C/1 h provide superplasticity at 800 to 950 degree C for the steels studied. In these conditions and for a constant ratio alpha -ferrite/ gamma -phase during tensile tests, a decrease of the true stress with increasing deformation was observed. The alpha yields gamma transformation during superplastic flow causes strengthening of the steel, but it has practically no influence on the elongation of specimens. The influence of time and temperature on the oxidation behavior of the steels studied was determined as a function of phase composition (Mn, Ni and Cr content). Positive Ni influence on the oxidation is explained as a result of increasing Cr solubility in the gamma -phase. Fracture toughness is reciprocally dependent on ferrite microhardness.
Article
It is established that the coast 03Kh23N7M4 ferritic-austenitic steel is a promising material for use in hot concentrated caustic environments (both the stress corrosion threshold and crack resistance is equal to σs obtained in air and the parameter Kscc is equal Kc. This steel is resistant to stress corrosion cracking in low concentrated environments (sea water). It is shown that the steel possesses low resistance to stress corrosion cracking in hydrogen sulphide environments. The same is true for low pH corrosive media containing chloride ions. This is attributed to the tendency of steel to corrosion cracking and a high rate of general corrosion.
Article
In oil and gas production, the corrosion problems increase as the depth of the reservoirs increases. The oil and gas products contain chloride-rich waters and mixtures of H2S and CO2 at high pressures and temperatures. Materials that can be used under these conditions are only high strength high alloy steels and nickel base alloys. These materials must be assessed for corrosion resistance under these conditions. The environments contain chloride ions and hydrogen sulphide, which are known to be critical components for SCC. With the aid of autoclave experiments, the fields of corrosion resistance for the materials no. 1.4462, 1.4563 and 2.4618 were determined as a function of temperature and hydrogen sulphide pressure. The base environment was a 5 Molar sodium chloride solution at 20 bar carbon dioxide. While the corrosion resistance of the duplex steel, material no. 1.4462, decreases markedly as the strength of the material and the hydrogen sulphide pressure increase, the two austenitic materials are completely resistant up to 300°C and hydrogen sulphide pressure of 15 bar. Only at 300°C and high partial pressures of hydrogen sulphide the material no. 1.4563 did fail, when stressed to stress levels higher than the YS. The crack path was predominantly transgranular with minute fractions of intergranular cracking. The microstructure appears to have no effect. All results indicate that a mixed mechanism of hydrogen- and chloride induced SCC is operating, while a corrosion enhancement due to interaction of both critical components takes place.
Article
Tendency of cast two-phase corrosion-strength steels to corrosion cracking is investigated in different environments: hot and cold water, sea water, boiling chloride and alkali solutions and hydrogen sulfide containing solutions. It is stated that in all environments, except hydrogen sulfide, 04Kh25N7AM3 steel is resistant to corrosion cracking and general corrosion and can be used in perspective as structural material for case pieces. In the context of its sensitivity to hydrogen embrittlement, the steel is not usable in hydrogenating media such as H2S-containing oils and gases, acid solutions and with cathodic protection.
Article
Stainless steels have been immersed in continuous and intermittent chlorinated seawater, and the effect on electrode potential and bacterial activity has been observed. Effective bacterial kill is obtained by continuous chlorination with 0.1 ppm residual chlorine. Intermittent chlorination is also effective with 1 ppm chlorination 30 minutes per day. No corrosion of 254 SMO or SAF 2507 was observed for chlorine concentrations up to 0.2 ppm. Time dependent changes in the open-circuit potential and in the cathodic polarization curves, with and without chlorination, seems to indicate changes in the electronic properties of the oxide film during immersion in seawater.
Article
Slow tensile straining, over a range of strain rates, of specimens machined from two commercial duplex stainless steel pipes has identified the important factors influencing their degree of embrittlement by hydrogen. Despite their very different microstructures, both materials suffered a significant loss in ductility after thermally charging with hydrogen. However, a difference in behavior between the two steels becomes apparent when uncharged specimens are tested in hydrogen below two bar pressure. The steel having a strongly banded distribution of austenite exhibited behavior that was very dependent on orientation and this is ascribed to the barrier-to-crack propagation presented by the austenite stringers. Behavior generally seems to be dominated by the ferrite matrix, but the possible role of ε-martensite, where the ferrite is not so highly embrittled, is also discussed.
Article
A new intermetallic compound labelled the τ-phase with an orthorhombic structure (a = 0.4044 nm, b = 0.3436 nm and c = 0.2867 nm) is formed throughout the ¯ matrix during isothermal heat treatment in the temperature range below 650°C. The face-centred orthorhombic Bravais lattice and Fmmm space group are established by electron microdiffraction in conjunction with group theory analysis. The τ-phase crystal lattice is oriented with respect to the surrounding δ matrix according to the Bain orientation relationship. The defects inside τ particles were analysed as sequence faults.
Article
An verschiedenen rostfreien, austenitischen Stählen und einem Stahl mit ferritisch/austenitischem Gefüge wurde das Beizverhalten in Beizlösungen auf Basis Flußsäure unterschiedlicher Zusammensetzung geprüft. In einer weiteren Versuchsserie ist die Brauchbarkeit von wäßrigen Citronensäurelösungen bezüglich ihres Einsatzes als Beizchemikalien für die Werkstoffe W.-Nr. 1.4541 und W.-Nr. 1.4571 untersucht worden. Schließlich wurden die Beizverfahren auf Basis Salpetersäure/Flußsäure mit mechanischen Reinigungsverfahren einerseits und mit Beizverfahren auf Basis Citronensäurelösungen andererseits hinsichtlich ihres Einflusses auf die Korrosionsbeständigkeit der behandelten Werkstoffe verglichen. Die Bewertung erfolgte anhand eines Lochkorrosionstests in Natriumchloridlösungen verschiedener Konzentrationen nach Herbsleb und Schwenk. Bei korrosiver Belastung ist das Beizen mit Lösungen auf Basis Flußsäure den anderen Reinigungsverfahren überlegen. Die umweltfreundlichen Citronensäurelösungen vermögen lediglich die Anlauffarben an den Werkstoffen 1.4541 und 1.4571 zu entfernen.
Article
Very low tolerable partial pressures of H{sub 2}S(p{sub H{sub 2}s}) have been reported for duplex stainless steels in sour environments. However, such steels resist stress corrosion cracking (SCC) in sour environments even at substantial P{sub HS} values. This paper reports that, to assess the limits of applicability, SCC tests should include an environmental of reasonably accelerated severity. It is also important to take practical experience into account. Slow strain rate testing (SSRT) is considered to put unrealistic mechanical demands on the material, since the stress can reach the ultimate tensile strength (UTS) and the strain rate is controlled to give maximum SCC sensitivity. Constant-strain and constant-stress tests are more relevant to practical conditions. The actual environment is always more complex that the plain H{sub 2}S/Cr or H{sub 2}S/CO{sub 2}/Cl environments used in the majority of laboratory tests. Bicarbonate ions are most often present, and by increasing the pH value, they reduce the aggressiveness of the environment. Duplex stainless steels have been used for many years in applications with significantly higher P{sub H{sub 2}S} than many laboratory tests have indicated to be possible.
Conference Paper
Nonstabilized 300 series stainless steels stressed over yield are susceptible to intergranular stress corrosion cracking (SCC) when exposed in the heavily sensitized condition to 288 C (550 F), high purity water containing dissolved oxygen. The effects of stress, oxygen levels, and significant metallurgical parameters on intergranular SCC of AISI Type 304 are being evaluated. Several promising intergranular SCC resistant alternate alloys have been identified through preliminary investigations, e.g., austeno-ferritic duplex and stabilized austenitic stainless steels.
Article
This paper reports the effect of nickel and nitrogen contents on stress corrosion cracking (SCC) of 22%Cr {minus} 3%Mo-base duplex stainless steel investigated in simulated sour environments with respect to both the base metal and the heat-affected zone (HAZ) of welding. The threshold stress and the critical chloride concentration for SCC were evaluated as a function of the ferrite content ({alpha}-content) in the alloy. The threshold stress is highest at the {alpha}-content of 40 to 45%, and is lowered with decreasing and increasing the {alpha}-content from its value. The alloy whose {alpha}-content exceeds 80% at the HAZ has also high susceptibilities to pitting corrosion and intergranular corrosion (ICG). The critical chloride concentration for cracking increases with the decrease in the {alpha}-content. Moreover, the contents of chromium, nickel and molybdenum in the {alpha}-phase are considered to be an important factor for determining the critical chloride concentration.
Article
The decomposition of ?-ferrite to austenite has been studied in a 26%Cr-5%Ni stainless steel. The decomposition takes place via two mechanisms: by nucleation and growth in the high temperature range (650–1200°C) and by an athermal martensitic process in the low temperature range (300–650°C). The high temperature reaction exhibits growth kinetics which are intermediate between volume diffusion control and growth by a ledge mechanism. The morpho-logical variants of the austenite mirror those described in the Dubé morphological classification for low-alloy steels, and the steel was used as a ‘model system‘ for the study of bcc fcc transformations. In the low temperature range (400–600°C) the formation of ??, which gives rise to 475°C embrittlement, is shown to occur by a nucleation and growth process, and the subsequent dissolution of the ?? is explained by the precipitation of austenite. Finally, it is shown by STEM microanalysis that Ni partitions to the austenite and Cr partitions to the ferrite during the high temperature reaction and that there is no composition difference between the parent and product phases in the low-temperature martensitic formation of austenite.The decomposition of ?5-ferriteto austenite has been studied in a 26%Cr–5%Ni stainless steel. The decomposition takes place via two mechanisms: by nucleation and growth in the high temperature range (650–1200°C) and by an athermal martensitic process in the low temperature range (300–650°C). The high temperature reaction exhibits growth kinetics which are intermediate between volume diffusion control and growth by a ledge mechanism. The morphological variants of the austenite mirror those described in the Dube morphological classification for low-alloy steels, and the steel was used as a 'model system' for the study of bcc ? fcc transformations. In the low temperature range (400–600°C) the formation of ?', which gives rise to 475°C embrittlement, is shown to occur by a nucleation and growth process, and the subsequent dissolution of the ?' is explained by the precipitation of austenite. Finally, it is shown by STEM microanalysis that Ni partitions to the austenite and Cr partitions to the ferrite during the high temperature reaction and that there is no composition difference between the parent and product phases in the low-temperature martensitic formation of austenite.
Article
A description is given of Thermo-Calc, a databank for thermochemistry and metallurgy developed at the division of Physical Metallurgy of the Royal Institute of Technology (KTH) in Stockholm. Using the facilities of Thermo-Calc one can tabulate thermodynamic data, calculate the heat change of chemical reactions and their driving force, evaluate equilibria for chemical systems and phase transformations and calculate various types of multicomponent phase diagrams by an automatic mapping procedure. The databank is quite general and can be applied to all systems where data assessed by a model implemented in the databank are available. The assessment procedure necessary to develop and extend the the databank is discussed. A brief description of the modules of Thermo-Calc is given and two examples are included which demonstrate how flexibly the calculations can be made. These examples will also show that the system is quite easy to use and that there are extensive on-line help facilities.
Filler Materials for Manual and Automatic Welding
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Theory of Corrosion and Stainless Alloys
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An Atlas of Structure and Corrosion of Metals and Alloys
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A Handbook on Corrosion Resistance of Austenitic-Ferritic Steels
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Ul'yanin,Stainless Steels and Alloys
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Alliages anti-corrosion pour millieux chlorures, Cedex 33-F-9270
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