Welding design methodology for optimization of phase balance in duplex stainless steels during autogenous arc welding under Ar–N2 atmosphere

Physical and Theoretical Modeling of the Nitrogen Content of Duplex Stainless Steel Weld Metal: Shielding Gas Composition and Heat Input Effects

“…Our improved model of N kinetics during autogenous TIG welding of DSS is based on Du Toit's model [35] for austenitic stainless-steel welding and Rokanopoulou's model [36] for plasma arc welding of DSS.…”

“…where A is the molten pool surface in m 2 , K a is the reaction rate constant for Equation (1) in kg·m −2 ·s −1 ·atm −1 , ρ is the density of the molten pool at the welding temperature in kg·m −3 , V is the molten pool volume in m 3 , N(g) is the monatomic nitrogen content in the arc plasma in atmospheres, N steel is the final nitrogen concentration in the solidified WM in wt %, and K is the apparent equilibrium constant for reaction Equation (1). The molten pool volume during welding (V) in m 3 is calculated according to [35,36]:…”

“…where T is the estimated molten pool temperature in Kelvin [36]: About the K a reaction rate constant, very limited data are available in the professional literature. As shown by [35,36], K a has a weak dependency on the chemical composition, and its average value for DSS is taken as:…”

“…At this point, the previous models of [35,36] are modified. For the calculation of N eq , Du Toit [35] and Wada et al [45] calculated with f N,1873 , which is the activity coefficient described for 1873 Kelvin not for the molten pool temperature T. Rokanopoulou et al [36] changed the activity coefficient to the molten pool temperature, based on two different calculations of the equilibrium nitrogen content of the molten metal, N eq . According to the conclusions of Rokanopoulou et al [36], the f N,T increased to 0.161 from f N,1873 = 0.134.…”

“…In the case of DSSs, an improved model is needed for the solubility prediction, as DSSs have higher nitrogen content as an alloying element (>0.15 wt %), which is needed to be taken into account. Rokanopoulou et al [36] recently modified this model for the case of DSS plasma arc welding (PAW). Their model is adequate for DSS molten pool N content prediction for lower nitrogen containing shielding gases, but sometimes, exaggerated results are given (such as N = 0.78%), which is over the equilibrium solubility limit of nitrogen in molten DSS grades.…”