Phase Transformation of δ - > σ in Multipass Heat-Affected and Fusion Zones of Dissimilar Stainless Steels

摘要

The purpose of this report is to discuss the phase transformation from 8-ferrite to σ phase in various welding regions of dissimilar stainless steel welds. Experimental results indicated the grain refinement was very obvious in the second and the third pass fusion zones (304-1 and 304-2) when the welding pass increased from 1 to 3. This refining phenomenon of 8-ferrite was attributed to the recrystallization. The order of morphological development of 8-ferrite in the multipass fusion zones was as follows: massive->columnar->equiaxed. The σ phase precipitated in the third pass fusion zone (304-2) and its solidification order is L- >δ +L - > δ - > δ + γ- > δ +σ+γ with a composition of c phase (60 wt.%Fe-35.7 wt.%Cr-4.2 wt.%Ni) of the third pass fusion zone. The precipitation mechanism of the σ phase was as a eutectoid decomposition of δ - > σ+γ_2.