The evolution of microstructure and texture during cross-rolling and annealing was investigated by electron backscatter diffraction in a ferritic–austenitic duplex stainless steel. For this purpose ...an alloy with nearly equal volume fraction of the two phases was deformed by multi-pass cross-rolling process up to 90% reduction in thickness. The rolling and transverse directions were mutually interchanged in each pass by rotating the sample by 90° around the normal direction. In order to avoid deformation induced phase transformation and dynamic strain aging, the rolling was carried out at an optimized temperature of 898K (625°C) at the warm-deformation range. The microstructure after cross warm-rolling revealed a lamellar structure with alternate arrangement of the bands of two phases. Strong brass and rotated brass components were observed in austenite in the steel after processing by cross warm-rolling. The ferrite in the cross warm-rolling processed steel showed remarkably strong RD-fiber (RD// ) component {001} . The development of texture in the two phases after processing by cross warm-rolling could be explained by the stability of the texture components. During isothermal annealing of the 90% cross warm-rolling processed material the lamellar morphology was retained before collapse of the lamellar structure to the mutual interpenetration of the phase bands. Ferrite showed recovery resulting in annealing texture similar to the deformation texture. In contrast, the austenite showed primary recrystallization without preferential orientation selection leading to the retention of deformation texture. The evolution of deformation and annealing texture in the two phases of the steel was independent of one another.
•Effect of cross warm-rolling on texture formation is studied in duplex steel.•Brass texture in austenite and {001} in ferrite are developed.•Ferrite shows recovery during annealing retaining the {001} component.•Austenite shows recrystallization during annealing retaining the deformation texture.•The deformation of recrystallization of two phases is independent of one other.
Duplex stainless steels have been extensively used in parts that are subject to corrosive environments and that have high mechanical strength requirements. Welding usually distorts the well-balanced ...austenite-ferrite ratio, and can produce brittle intermetallic phases; therefore, post-welding heat treatments are usually required. For applications where post-welding treatments are not possible, low heat input methods, such as micro-tungsten inert gas welding (TIG) and laser beam welding (LBW), can be used. The present investigation analyzed the microstructure, mechanical, and corrosion properties of 2507-classduplex steel tubes after welding. The microstructures of the heat-affected zones and the fusion zones contained variable amounts of ferrite and austenite. In the heat-affected and fusion zones in the TIG samples, the microstructures were primarily composed of ferrite grains with allotriomorphic austenite at the grain boundaries, intragranular Widmanstatten needles and plate-like precipitates. The LBW samples showed much finer microstructures, which contained austenite in the grain boundaries and fine austenite precipitates in the ferrite grains. Deleterious intermetallic phases, such as sigma-phases, were not observed using X-ray diffraction. The tensile strength properties were very similar for the TIG and LBWsamples, reaching tensile strengths of approximately 840 MPa and total elongations between 61 and 87%. The heat-affected zone of the TIG welds were particularly susceptible to corrosion (0.05 mm/year) compared to the base metal (0.007 mm/year) and the laser welds (0.01 mm/year). Therefore, laser welding is a promising technique for the welding of 2507-class duplex tubes.
The electrochemical behaviour of ferritic and austenitic phases in duplex stainless steel (UNS S32304) and the modifications induced by straining during sliding were studied by potentiodynamic ...polarisation curves determined at the microscale in a 1
M NaCl (pH 3) solution, using an electrochemical microcell. The mechanical properties and stress state of each phase were determined by microhardness and X-ray microdiffraction measurements, before and after straining. The results show that sliding generates elastic straining of the ferrite and plastic deformation of the austenite. The electrochemical behaviour of these phases is dramatically altered, inducing a reduction of the corrosion resistance and of the passivation properties.
Atom-probe tomography was used to investigate phase separation and copper (Cu) clustering in the ferrite phase of a 25Cr-7Ni super duplex stainless steel. The steel was subjected to a tensile load ...during aging at 325°C for 5800 h. The degree of phase separation into α (Fe-rich) and α′ (Cr-rich) was small, but still, it was the highest in the steel subjected to the highest load. Cu was found to cluster, and the number density of clusters increased with increasing load. In the material subjected to the highest load, Cu was enriched in regions that were neither Fe-rich nor Cr-rich. These regions also had the highest number density of Cu clusters.
Summary
Up to 90% of the fatigue life of engineering alloys results from the initiation and propagation of microstructurally short cracks. Owing to their strong interactions with microstructural ...features, e.g. grain and phase boundaries, they exhibit substantially non‐uniform propagation kinetics as compared with the growth rate of long cracks, which can be well described using a power‐law function of the range of the stress‐intensity factor ΔK. In the present paper interactions between the crystallographic misorientation of grain and phase boundaries and microcracks in an austenitic/ferritic stainless steel are discussed and quantified by means of fatigue experiments in combination with the electron backscattered diffraction technique. In the second part a numerical model for the simulation of microcracks is introduced, which is capable of taking real microstructural arrangements into consideration.
This work concerns the development of a time–temperature-transformation (TTT) diagram for cast CD3MN, a duplex stainless steel. Samples were solution heat treated and quenched to temperatures ranging ...from 700 to 900 °C and held for times from 1 to 1000 min. Initial sigma phase precipitation was noted as low as 700 °C, with the nose of the transformation curve at approximately 800 °C and 100 min.
In a general manner, the austenitic stainless steels are used in the final phases of orthodontic treatments because of the remarkable stiffness and ultimate strength, in addition to its good ...corrosion resistance. Nowadays, a new class of materials, the austenic–ferritic stainless steels, is substituting the austenitic stainless steels in several industrial applications, where these properties are necessary. This work supports the hypothesis that orthodontic wires can be made with austenic–ferritic stainless steels. The advantages are the cost reduction of the raw material and the nickel hypersensitivity effect in patients undergoing orthodontic treatments. The proposal of this study was to manufacture wires from the austenitic–ferritic stainless steel SEW 410 Nr. 14517 (Cr26Ni6Mo3Cu3) and to evaluate the microstructure, mechanical properties and fracture morphology. The wires were obtained through swaging and drawing process and presented ultimate strength as required in the standard for medical devices. One other advantage is that the ordinary process to manufacture austenitic stainless steels wires can be used for the austenitic–ferritic steel due to its high ductility as seen in the tensile testing and fracture morphology analysis.
This paper presents the results of a study which has been carried out to investigate the crevice corrosion behavior of high-alloy stainless steel in a SWRO pilot plant. The study evaluated the ...corrosion performance of some austenitic and duplex steels in a crevice-forming environment created in a RO plant, especially in high-pressure feed and brine lines. The study of the effect of chemical dosing on crevice corrosion in the RO plant and electrochemical testing of crevice corrosion in the laboratory were the main objectives of this test program. High-alloy stainless steels, namely AL 6XNregisteredsign and 254 SMO (superaustenitic), 2205, 2507 and DP3W (Duplex) were used in the test program. The tests were carried out in natural seawater and RO concentrate (conductivity: 75, 000 to 80, 000 mu S/cm) at ambient temperature by operating the test plant at normal SWRO operating feed pressure of 54 bar. FeCl sub(3) was added as coagulant to maintain a silt density index of not, vert, similar3, and H sub(2)SO sub(4) was added to feed in order to maintain the feed pH of not, vert, similar 6.5. Chlorination and subsequent dechlorination agents were not added to the feed. For crevice corrosion tests in RO unit, the exposure periods were 6 and 12 months, respectively. The results of the tests showed that alloy DP3W has the best pitting resistance in crevice forming environment of seawater. In RO concentrate, alloys 2507 and 254 SMO showed lowest "maximum pit depth". The results of potentiodynamic cyclic polarization (PCP) indicate that all the alloys have high pitting potential and small hysteresis loop. The results of critical crevice solution pH (CCSpH) indicated excellent resistance of alloys 254 SMO and DP3W against crevice corrosion attack and 2205 had least resistance in most aggressive sodium chloride solution. Presented at the IDA World Congress on Desalination and Water Reuse, September 28-October 3, 2003, Paradise Island, Bahamas.
Le développement d’une troisième génération d’aciers Fe-Mn-Al-C à structure duplex, pour des teneurs en Mn et Al inférieures à 8 %mass, pourrait être une réponse prometteuse aux objectifs ...d’allègement de 20% des véhicules automobiles, tout en garantissant des propriétés de haute résistance mécanique et haute formabilité.Le choix des nuances et l’optimisation des conditions d’élaboration nécessitent de prévoir en particulier les compositions et proportions des phases existantes en fonction de la route métallurgique. Une base de données thermodynamiques fiable et précise est donc requise. Cependant les données de la littérature sur le système quaternaire Fe-Mn-Al-C, dans les domaines de composition envisagés, sont limitées.Ce mémoire est consacré à l’établissement des équilibres de phases ferrite-α, austénite-γ et carbure-κ (Fe,Mn)3AlC entre 700 et 1000°C par une approche couplée d’expériences ciblées et de modélisation thermodynamique. Pour appuyer l’évolution expérimentale des fractions de phases et des compositions, une modélisation cinétique (DICTRA) est proposée. La cinétique de formation de l’austénite en fonction de la composition de l’alliage et de la température de maintien dans le domaine intercritique a été caractérisée. Les phases en équilibre, caractérisées par DRX, MEB, microsonde, sont représentées sous forme de conodes α/γ, γ/κ, α/γ/κ, ce qui permet de définir les domaines de stabilité de l’austénite et du carbure κ. Ces données expérimentales sont utilisées pour affiner la description thermodynamique du système quaternaire mais il est nécessaire de réviser la modélisation du carbure κ.
A third generation of Fe-Mn-Al-C steels with a duplex structure, for Mn and Al contents less than 8%mass, could be a promising response to the 20% weight lightening of automotive vehicles, by keeping a high strength and a high formability.The knowledge of the corresponding quaternary phase diagram serves as a roadmap for the choice of compositions and the optimization of elaboration conditions. A reliable and precise thermodynamic database is therefore required. However, the literature data on the Fe-Mn-Al-C quaternary system in the targeted domains are limited.This study is devoted to the establishment of phase equilibria involving ferrite-α, austenite-γ and carbide-κ (Fe,Mn)3AlC between 700 and 1000°C by a coupled approach of experiments and thermodynamic modeling. A kinetic model (DICTRA) is proposed to support the experimental evolution of phase fraction and composition. The kinetics of austenite formation as a function of the alloy composition and of the maintaining temperature in the intercritical domain have been calculated. The phases in equilibrium, characterized by XRD, SEM, EPMA, are represented as α/γ, γ/κ, α/γ/κ tie-lines in order to specify the stability fields of γ and κ. These data are used to refine the thermodynamic description of the quaternary system but it is necessary to revise the modeling of κ carbide.
Forged duplex steels possess a highly anisotropic two-phase microstructure. Due to the mismatch of the coefficients of thermal expansion thermal stresses evolve during cyclic thermal loading which ...can lead to plastification of one or both phases. While the macroscopic deformation of specimens is well understood, open questions related to the effect of traction free surfaces still remain. Experimental evidence is found for a characteristic evolution of the surface roughness depending on the microstructure of the material. In this work micromechanical models based on a continuum mechanical description of the phase domains are evaluated with respect to surface roughness. Parameters for the description of the amplitude and the anisotropy of surface deformations are proposed and the model predictions are compared with experimental results.
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