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Breda M.,University of Padua | Basoni J.,De Pretto Industrie S.r.l. | Toldo F.,Laboratorio Prove Materiali San Marco | Bastianello C.,Laboratorio Prove Materiali San Marco | And 2 more authors.
Metallurgia Italiana | Year: 2015

Duplex Stainless Steels (DSS) are biphasic steels of increasing interest, employment as structural materials in aggressive environments. In these steels, the austenite-to-ferrite phase ratio is maintained at about one-even if a slightly wider range between 40/60 and 60/40 is in any case accepted-giving the best combination of mechanical and corrosion-resistance properties. However, DSS must be handled with extreme care, especially if thermal cycles are involved, owing to the possible formation of dangerous secondary compounds that can highly worsen their excellent features. In industry, the production of big pipes requires manufacturing welding operations on steel plates or sheets and the end products must satisfy specific requirements. Therefore, since DSS properties depend on phase ratio, ferrite quantification at an industrial scale represents a topic of great interest, which must be as reliable as possible and, at the same time, of fast execution. In the present paper, different methods currently employed for ferrite estimation in DSS weldments are compared, in order to understand the limits deriving from each technique.

Basoni J.,De Pretto Industrie | Calliari I.,University of Padua | Breda M.,University of Padua | Toldo F.,Laboratorio Prove Materiali San Marco | Meneghini R.,Laboratorio Prove Materiali San Marco
Rivista Italiana della Saldatura | Year: 2014

In this paper the development of a welding procedure for the joining of steel type UNS S32760 (Super duplex F55) for use in the off-shore application is described. The joint was realized by means of the TIG (GTAW) manual process for the first passes and by a manual filling process with stick electrode (SMAW), in order to obtain the combination of mechanical and microstructural characteristics desired by the customer. The results obtained from the tests on the joints must provide proof of successful completion of all the tests to be part of the joint in accordance with the contractual requirements and stabilized the base for actual use in the production. The particularity of the case, in addition obviously to the inherent difficulties posed by the type of steel chosen, consisted in the request by the customer of a combination of mechanical and microstructural characteristics to the limit of the possibilities of a welding procedure suitable for use in production mode and times compatible with the internal market and production requirements. It was therefore necessary to design the welding procedure and choose the most suitable process parameters to achieve the required results. The evaluation of the joints to achieve in production and the characteristics to be obtained, has led to decide to perform welding with welding processes previously mentioned and in the welding position-frontal plane (PB/2G). The main problems to be considered in the design phase of the welding procedure, are to be found in the value of the maximum heat input, interval of interpass temperatures to be observed and the type of shielding gas to use with which material can be welded to avoid the formation of intermetallic microstructure phases of the joint and sappers of corrosion resistance.

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