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ORIGINAL ARTICLE

Investigation on Aging-Induced Degradation of Impact Toughness and Corrosion Performance of Duplex Stainless Steel Weldment Sumeet Singh1 • Jastej Singh1

•

A. S. Shahi1

Received: 13 December 2019 / Accepted: 10 August 2020 Ó The Indian Institute of Metals - IIM 2020

Abstract Duplex stainless steels (DSSs) are prone to formation of various secondary phases in their microstructure upon exposure to high temperatures which can lead to degradation in their engineering performance. The present work was aimed to study the effect of a wide range of isothermal treatments (475°–1050 °C) on the impact toughness and corrosion resistance besides microstructure, ferrite content and microhardness of gas tungsten arc (GTA) welded 2205 DSS. It was observed that the isothermal exposure at 850 °C for 2 h led to maximum ferrite content reduction, imparted maximum hardening, caused maximum embrittlement of the weld metal (203 J ? 2 J) and HAZ (204 J ? 3 J) regions of the weldment besides causing maximum degradation in the pitting corrosion resistance. Corresponding to the aging condition of 475 °C/20 h, reduction in the ferrite content was not much, however, a significant increase in the microhardness along with severe loss in the toughness of the weld metal (203 J ? 6 J) occurred, but the HAZ region was relatively tolerant (204 J ? 54 J) against loss of toughness. In general, impact and corrosion properties were highly sensitive to degradation at 850 °C. Hence it can be inferred that the amount of ferrite content reduction cannot be directly correlated with the extent of hardening,

& Jastej Singh [email protected] Sumeet Singh [email protected] A. S. Shahi [email protected] 1

Department of Mechanical Engineering, Sant Longowal Institute of Engineering & Technology, (Deemed-to-beUniversity), Longowal, Sangrur, Punjab 148106, India

decrease in the toughness and corrosion resistance; as such, changes will be primarily governed by the type of secondary precipitation which is temperature and exposure duration-dependent in the case of DSS welds. Keywords Gas tungsten arc welding  Duplex stainless steel  Ferrite  Austenite  Microhardness  Thermal aging  Impact toughness  Corrosion

1 Introduction Duplex stainless steels (DSSs) are characterized by a twophase microstructure comprising of austenite (c) and ferrite (a) in comparable proportions. The two-phase microstructure imparts combined attributes of ferritic and austenitic stainless steels in these alloys. The ferrite phase provides high strength and resistance against stress corrosion cracking, while austenite favors their toughness and ductility [1]. The alloying elements play a key role in the metallurgy of DSSs. The elements such as Ni, C, N, Mn, Cu and Co are austenite stabilizers, while Cr, Mo, Si, Nb, Ti, W and V are ferrite stabilizers. DSSs can contain Cr up to 30 wt% which is the main ferrite stabilizer and has a BCC structure below its melting point. Further, DSSs contain 5–9 wt% Ni which has FCC structure below its melting point and