Multicomponent Phase Diagram of Lean Duplex Stainless Steel UNS S82441 and Its Application to Evaluate the Microstructure in the Heat Affected Zone Evandro Armini de Pauli 1 • Claudio Geraldo Scho ¨n 1 • Se ´rgio Duarte Brandi 1 Submitted: 1 December 2016 / in revised form: 3 April 2017 Ó ASM International 2017 Abstract Duplex stainless steels are Fe-Cr-Ni-Mo-N alloys with nitrogen replacing some nickel to improve its properties. These steels have a balanced microstructure, which means that ferrite (a) and austenite (c) are in equal proportions of approximately 50% by volume. These alloys have a tendency to form intermetallic precipitates such as chromium nitrides and sigma phase (r), depending on their chemical composition and welding thermal history. Pre- cipitation of these intermetallic phases can impair mechanical and corrosion properties. In addition, material processes such as welding and heat treatment can change the balanced microstructure. The objective of this work was to compare phases formed during heat treatment and welding of duplex stainless steel UNS S82441 with the equilibrium phases predicted by Thermo-calc Ò software. In general, the results showed good agreement between pre- dicted and measured phases, as well as, agreement between the measured volume fraction of austenite in the heat-af- fected zone and austenite predicted by Thermo-calc Ò software. Keywords intermetallic phases  lean duplex stainless steel  Thermo-calc Ò  UNS S82441  welding 1 Introduction Duplex stainless steels are typically Fe-Cr-Ni-Mo-N alloys, with mostly N acting as an alloying element, partially substituting for nickel. This replacement of nickel by nitrogen improves the mechanical properties, [1,2] as well as the corrosion resistance. [2–8] Duplex stainless steels are used for a variety of industrial applications due to its excellent combination of strength, corrosion resistance and weldability. [9] These steels generally have a mixed microstructure of ferrite (a) and austenite (c) in the proportion of approxi- mately 50% by volume of each phase. [5,10–13] Any subse- quent changes in this volume fraction caused by hot processing the material can greatly reduce the properties of these stainless steel grades. [13] The microstructure is obtained by chemical composition, primarily by balancing the austenite stabilizing alloying elements (C, Ni, N, Cu and Mn) and the ferrite stabilizing alloying elements (Cr, Mo, W, Nb, and Si), [14] and also by thermomechanical treatment during its manufacture to help balance its microstructure. Duplex stainless steels have a tendency to form phases that impair their properties during welding, for example, sigma phase (r), secondary austenite (c 2 ), carbides (M 23 C 6 ) and chromium nitrides (Cr 2 N and CrN) among others. Depending on the chemical composition, the grades of duplex stainless steels solidifies in a different mode. [15–17] Duplex and lean duplex stainless steels have a primary ferritic solidification mode. On the other hand, superduplex and hyperduplex stainless steels present a ferritic-austenitic This article is an invited paper selected from presentations at TOFA 2016, the Discussion Meeting on Thermodynamics of Alloys, held September 4–9, 2016, in Santos, Brazil, and has been expanded from the original presentation. & Se ´rgio Duarte Brandi sebrandi@usp.br Evandro Armini de Pauli evandropauli@usp.br Claudio Geraldo Scho ¨n schoen@usp.br 1 Department of Metallurgical and Materials Engineering, Escola Politecnica da USP, Sa ˜o Paulo, Sa ˜o Paulo, Brazil 123 J. Phase Equilib. Diffus. DOI 10.1007/s11669-017-0551-x