Hyundai SM-400/ST-400 description:
SM-400(ST-400) is a MIG(TIG) wire with about 65%Ni+30%Cu+2%Ti+1%Fe and used for welding similar alloys and for mixed welds between them or Cupronickels and carbon steels.
No preheat required, maximum interpass temperature 150C(302F) and no PWHT required.