Computer prediction of α/γ phase fraction in multi-pass weld of duplex stainless steel and microstructural improvement welding process

Abstract

A computer simulation of the α/γ phase transformation in a multi-pass weld of duplex stainless steel (DSS) was made to predict the distribution of the γ phase fraction in the heat-affected zone (HAZ). The kinetic equations including rate constants of the dissolution behavior as well as the precipitation behavior of the γ phase were determined by an isothermal heat treatment test. Based on the kinetic equations determined, the distribution of the γ phase fraction in a multi-pass weld of lean DSS was calculated by applying the incremental method combined with a heat conduction analysis of the welding process. The γ phase fraction was reduced in the higher temperature HAZ; however, that in the reheated HAZ was increased and recovered to the base metal level. Microstructural analysis revealed that the calculated results of the γ phase fraction in the multi-pass weld were consistent with experimental ones. Based on the computer prediction, the microstructural improvement welding (“reheat bead welding”) process, an analogous concept to the temper bead welding technique, is newly proposed for recovering the γ phase fraction in the weld just as in the as-welded situation.