Characterizations of dissimilar S32205/316L welds using austenitic, super-austenitic and super-duplex filler metals
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Characterizations of dissimilar S32205/316L welds using austenitic, super-austenitic and super-duplex filler metals A. Taheri1), B. Beidokhti2), B. Shayegh Boroujeny3), and A. Valizadeh4) 1) Department of Materials Engineering, Najafabad Branch, Islamic Azad University, Isfahan 8514143131, Iran 2) Materials and Metallurgical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad 9177948944, Iran 3) Department of Engineering, Shahrekord University, Shahrekord 88186-34141, Iran, 4) Brunel Centre for Advanced Solidification Technology (BCAST), Brunel University, Uxbridge UB8 3PH, UK (Received: 2 July 2019; revised: 27 September 2019; accepted: 16 October 2019)
Abstract: UNS S32205 duplex stainless steel plates were welded to AISI 316L stainless steel using the pulsed gas tungsten arc welding process with three different filler metals: ER2594, ER312, and ER385. The microstructures of the welds were characterized using optical and scanning electron microscopy, and all of the specimens were evaluated by ferrite measurements. The mechanical properties were studied through hardness, tensile, and impact tests. In addition, the pitting resistance equivalent number was calculated and cyclic polarization tests were performed to evaluate the corrosion resistance of the weld metal. The results showed that chromium nitride was formed in the heat-affected zone of the duplex side, whereas no sigma phase was detected in any of the specimens. The ferrite number increased from the root pass to the final pass. The absorbed energies of the impact test decreased with increasing ferrite number, whereas the tensile strength was enhanced. The fully austenitic microstructure of the specimen welded with ER385 exhibited the highest resistance to pitting corrosion at 25°C, and the super-duplex weld metal presented superior corrosion resistance at 50°C. Keywords: stainless steel; mechanical properties; microstructure; welding
1. Introduction Austenitic stainless steels have a wide range of applications in high-temperature environments and highly corrosive atmospheres [1]. Moreover, using a low-carbon type steel (AISI 316L stainless steel) reduces the susceptibility to cracking [2–3]. The high chromium and nickel contents in these steels lead to improved resistance to corrosion at elevated temperatures. Despite the austenitic stainless steels’ high resistance to corrosion, they are susceptible to pitting corrosion and stress corrosion cracking in highly corrosive atmospheres. Austenitic stainless steels have the lowest resistance to corrosion cracking when they contain 8wt%–12wt% Ni; however, their corrosion resistance increases with increasing Ni content [4]. Diagrams such as Schaeffler and DeLong diagrams have been very useful in predicting the amount of delta-ferrite in
the weld metal of stainless steels on the basis of calculated Cr and Ni equivalents. Eqs. (1) and (2) for Cr and Ni equivalents can be used to predict the ferrite number [5]: Creq = w (Cr) + 2.5w (Si) + 1.8w(Mo) + 2w (Nb) (1) Nieq = w (Ni)
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