Numerical method applied to duplex stainless steel welding C. R. Xavier* 1 , M. F. Campos 2 and J. A. Castro 2 Microstructure plays an essential role in the attractive properties of the duplex stainless steels (DSSs) such as toughness and corrosion resistance. These properties are obtained by an adequate balance between the fractions of the ferrite and austenite phases, which can be modified when DSSs are welded. Besides the unbalanced fractions of ferrite and austenite, the precipitation of deleterious compounds at high temperatures such as sigma phase can also occur during DSS welding. In this work, a model based on transport equations was numerically implemented by the finite volume method in a computational code in order to simulate the 2205 DSS welding. It was able to evaluate qualitatively the sigma phase precipitation and the formation of the ferrite and austenite phases by calculating the cooling rates reached during 2205 DSS welding. The results are discussed in light of the previous work, and good agreement between numerical and experimental results was obtained. Keywords: Duplex stainless steel, Numerical simulation, Welding, HAZ microstructure List of symbols A (i) area vectors generated by two covariant vectors, m 2 A i k Cartesian components of the area vectors, m 2 a i covariant basis vector, m a i contravariant basis vector, m a k coefficients in discretised equation (k: W,E,S,N,B,T,P) b independent part of the linearised source term b NO non-orthogonal part of the linearised source term C i convective normal flux, kg s 21 F flux tensor g ij Cartesian components of covariant metric tensor, m 2 g ij Cartesian components of contravariant metric tensor, m 22 G ij Cartesian components of geometric diffusion coefficient I k Cartesian unit vectors J Jacobian determinant of coordinate trans- formation (volume in physical space), m 3 Pe Peclet number S w source term t time, s ~ U i velocity vector of moving grid, m s 21 x i Cartesian coordinate system, m j i covariant coordinate system, m r density, kg m 23 Introduction Duplex stainless steels (DSSs) present excellent properties due to their strict composition and balanced proportions between the austenitic and the ferritic phases. They combine the mechanical properties and corrosion resis- tance advantages of both austenitic and ferritic phases: the austenite imparts toughness and general corrosion resistance and the ferrite provides strength and resistance to chloride stress corrosion. It is generally accepted that the two phases must not be ,30% each. 1 Some examples of DSS application are in equipment destined for petro- chemical, petroleum and chemical industries, whose fabrication generally employs welding operations; thus, it is extremely important to provide a better under- standing of the influence of the thermal cycles and cooling rates involved in DSS welding in order to assure the adequate balance between the austenite and the ferrite phases and also to avoid the precipitation of brittle intermetallic phases as sigma (s) and chi (x). 2–9 Because of its harmful influence on mechanical proper- ties and corrosion resistance and high volume fraction observed, sigma phase is the most important intermetallic phase formed. 10–16 During continuous cooling, sigma phase appears as the first phase formed at more elevated cooling rates when compared with the chi phase that forms only in lower cooling rates. 16 Sigma phase is a hard, brittle and non-magnetic intermetallic phase with a tetragonal crystalline structure being formed basically by elements Fe, Cr and Mo 2,10,14 and usually forms after long holding times at temperatures between 650 and 950uC and after cooling from high temperatures as in the 1 UniFOA/PETROBRAS, Departamento de Engenharia Meca ˆ nica, Av. Paulo E. A. Abrantes, 1325, Tre ˆs Poc ¸os, Volta Redonda 27240-560, Rio de Janeiro, Brazil 2 Universidade Federal Fluminense, Programa de Po ´ s Graduac ¸a ˜o em Engenharia Metalu ´ rgica, PPGEM, Av. dos Trabalhadores, 420, Vila Santa Cecı ´lia, Volta Redonda 27255-125, Rio de Janeiro, Brazil *Corresponding author, email xavier@metal.eeimvr.uff.br 420 ß 2013 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 26 April 2012; accepted 18 July 2012 DOI 10.1179/1743281212Y.0000000065 Ironmaking and Steelmaking 2013 VOL 40 NO 6