Phase transformation of δ→σ in multipass heat-affected and fusion zones of dissimilar stainless steels

The purpose of this report is to discuss the phase transformation from δ-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 δ-ferrite was attributed to the recrystallization. The order of morphological development of δ-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 σ 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→+σγ 2 .