The microstructure of Tungsten Inert Gas (TIG) and electron beam copper/stainless-steel welds were investigated using scanning electron microscopy. The relatively high cooling rates entailed in the welding result in high bulk supercooling, causing two microstructural effects : (i) melt separation into two liquids, iron-rich L1, and copper-poor L2, while each solidifies by a path dictated by the stable phase boundary; (ii) enhanced solute trapping of Cu in the alpha-Fe phase, and Fe in the epsilon-Cu phase.