Weld Mold 4000-A description: 4000AC is used for welding various combinations of inconel, monel, stainless, nickel alloys and mild steels. It is a great maintenance alloy for welding equipment in severe service conditions. Some examples where 4000AC is used are; for welding 505, 330, 310, 304, 347, 410 and 316 stainless steel, Inconel alloys 625, 718, 825, 600, 601 and 800.