Numerical Simulation of Microstructural Evolution during Welding of Duplex Stainless Steels

Author(s)

Garzon, C. M. ; Gomes, J. ; Brandi, S. D. ; Ramirez, A. J. ; David, SA ; DebRoy, T ; Lippold, JC ; Smartt, HB ; Vitek, JM

• Document type: Journal article
• Source: TRENDS IN WELDING RESEARCH, PROCEEDINGS; v. N/A, p. 2-pg., 2006-01-01.

Abstract

During welding of duplex stainless steels (DSSs), in the high temperature heat-affected zone, a microstructure with high fractions of ferrite is formed. When this microstructure is reheated during multipass welding or during post-weld heat treatment, new austenite, called secondary austenite (gamma(2)), will form and nitride precipitation and/or dissolution will occur. In this work the thermodynamics and kinetics assessment of secondary austenite (gamma(2)) precipitation phenomenon during short-term reheat treatments, between 900 and 1200 degrees C, of welded UNS S32304 and UNS S32750 DSSs was made by using the Calphad method. The implemented model is able to compute both the gamma(2) growth kinetics and chemical composition profiles in the microstructure, as a function of reheating time and temperature. The relationship between the fraction of gamma(2) and temperature was non-monotonic: the maximum gamma(2) fraction is attained at similar to 1050 degrees C. During reheat treatments it was observed that significant growth of gamma(2) occurred during both the isothermal stage and the cooling stage; the lower the temperature the higher the relative fraction of gamma(2) that was formed during the isothermal stage when compared with the cooling stage. Numerical analysis predicts a variable alloying content on gamma(2) when compared with primary austenite (gamma(1)), depending on the precipitation temperature. (AU)