Effect of weld metal chemistry and heat input on the structure and properties of duplex stainless steel welds
15 Oct 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing (Elsevier)-Vol. 358, Iss: 1, pp 9-16
TL;DR: In this article, a low heat input process viz., EBW and another commonly employed process, gas tungsten-arc welding have been employed for welding of duplex stainless steels with and without nickel enhancement.
Abstract: The excellent combination of strength and corrosion resistance in duplex stainless steels (DSS) is due to their strict composition control and microstructural balance. The ferrite–austenite ratio is often upset in DSS weld metals owing to the rapid cooling rates associated with welding. To achieve the desired ferrite–austenite balance and hence properties, either the weld metal composition and/or the heat input is controlled. In the current work, a low heat input process viz., EBW and another commonly employed process, gas tungsten-arc welding have been employed for welding of DSS with and without nickel enhancement. Results show that (i) chemical composition has got a greater influence on the ferrite–austenite ratio than the cooling rate, (ii) and even EBW which is considered an immature process in welding of DSS, can be employed provided means of filler addition could be devised.
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TL;DR: In this article, a comparison between the as-welded and solution-treated joints is carried out, and the main factors that affect pitting corrosion of the welded joints (microstructure, secondary phases, chemical composition of single phases) with the experimental data obtained from corrosion tests are presented.
Abstract: Welding of austenitic-ferritic stainless steels is a crucial operation and all the materials and parameters used in this process must be optimized in order to obtain the suitable corrosion and mechanical properties. Since a great part of super duplex stainless steels is used in very aggressive environment, their corrosion resistance, referred in particular to pitting and crevice corrosion, is an all-important facet in production and processing of this type of steels. Pitting corrosion resistance of super duplex stainless steels welded joints depends on several aspects: microstructure of the bead, elemental partitioning between ferrite and austenite, and the possible presence of secondary phases. For these reasons, a post-weld annealing is generally performed to homogenize the microstructure. The annealing temperature is the most important parameter to be optimized in this heat treatment. In the present work, a comparison between the as-welded and solution-treated joints is carried out. An effort has been made to correlate the main factors that affect pitting corrosion of the welded joints (microstructure, secondary phases, chemical composition of single phases) with the experimental data obtained from corrosion tests. In this first part of the work the results regarding microstructure and partitioning of elements are presented. The phase balance and the austenite morphology are locally upset during submerged-arc welding of UNS S32750. In the fusion zone, the two phases (ferrite and austenite) result to have approximately the same composition regarding Cr, Mo, and Ni content, while nitrogen is heavily concentrated in austenite. After annealing treatment, the austenite volume fraction increases and the partitioning ratios of elements reach the equilibrium values. The base material results to be less sensitive to annealing treatment than the fusion zone, and the partitioning of elements in the base material is in agreement with previous works reported in the literature.
33 citations
TL;DR: In this paper, the effect of post-weld annealing temperature on the pitting corrosion resistance of UNS S32750 submerged-arc welded joints was analyzed.
Abstract: This study deals with the effect of the annealing temperature on the pitting corrosion resistance of UNS S32750 submerged-arc welded joints. In a companion article (Part I), the influence of post-weld annealing temperature on microstructure evolution and chemical composition of austenite and ferrite was analyzed; this study can thus be considered directly connected with the previous one. The pitting corrosion resistance of the heat-treated welded joints was evaluated by using both electrochemical measurements and ASTM G48 standard gravimetric tests; examinations of initiation sites of pitting attack were carried out in order to correlate the experimental data obtained in this study with the predicted pitting corrosion behavior obtained by using the results described in Part I. Generally, the post-weld annealing treatment enhances the pitting corrosion resistance of UNS S32750 welded joints. By using PREN analysis of single phases, a correlation between the chemical composition evolution of ferrite and austenite and the experimental pitting behavior of the welded joints was found, in relation to welding and post-welding heat treatment temperature. In particular, an exponential relationship between PREN of weaker phase and pitting potential in 3.5% NaCl solution at 80 °C for the weld metal was obtained. The most favorable annealing temperature for the analyzed welded joints was found to be 1100 °C.
33 citations
TL;DR: In this article, the microstructures, secondary phase precipitation and susceptibility to localized corrosion of UNS S32101 duplex stainless-steel welded joints that were welded using underwater dry and wet flux-cored arc welding (FCAW-136).
33 citations
TL;DR: In this paper, the microstructural changes that occur when Duplex Stainless Steels (DSS) are welded could be evaluated when bead-on-plate welding was carried out on a 2205 DSS by the GMAW process.
Abstract: Key microstructural changes that occur when Duplex Stainless Steels (DSS) are welded could be evaluated when bead-on-plate welding was carried out on a 2205 DSS by the GMAW process. By using numerical simulations, it was possible to calculate locally the heating and cooling rates taking place during the 2205 DSS welding and discuss its correlation to the microstructural changes experimented by the parent metal. Results showed that increasing heat input has promoted the ferritic grain growth with a slight reduction in the austenite content present at the high temperature heat affected zone (HTHAZ), whereas the cooling rates remained above from those reported as critical for sigma phase precipitation in 2205 DSS. Furthermore, nitrogen has proved to be an effective austenite former at the fusion zone (FZ), which can contributes to get a balanced microstructure in DSS welds in contrast to the effects from the elevated cooling rates.
32 citations
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TL;DR: In this paper, a review of the use of non-destructive techniques (NDT) for the detection of σ-phase and their application in engineering failure analysis and field study cases is presented.
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References
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Book•
01 Jan 1997
TL;DR: In this paper, the authors present a non-destructive testing of welds for service experience, based on the application of service experience in metallurgy and metallurgical applications.
Abstract: 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.
449 citations