Metal cored electrode for open root pass welding

A method of forming a root bead in a gap between spaced ends of at least one workpiece, said gap including an open root, said method comprising:

• a) selecting a metal cored electrode, said metal cored electrode including a metal sheath and core materials, said core material including at least about 0.5 weight percent metal alloying agent and less than about 0.5 weight percent slag forming agent content by total weight of said electrode, said metal cored electrode having a diameter and said gap having a width and a size ratio of said diameter of said metal cored electrode to said width of said gap of said open root is about 0.1-2:1;
• b) advancing said metal cored electrode at a given wire feed rate toward said open root to weld said ends together by substantially filling said open root in a first weld pass, said open root having a gap size of about 1-6 mm, said spaced ends off set by less than about ±3 mm;
• c) creating a welding current that includes an STT waveform;
• d) moving said metal cored electrode along said open root as said welding current is passed through said metal cored electrode to melt the metal cored electrode and transfer the melted metal cored electrode to said ends in said open root to form a root bead, said root bead having an upper surface that includes little or no slag;
• and,
• e) applying a shielding gas to at least partially protect molten metal in said open root from the atmosphere, said shielding gas including argon, carbon dioxide, helium, oxygen, or combinations thereof.

An apparatus for forming a root bead in a gap between spaced ends of at least one workpiece, said gap including an open root, said apparatus comprising:

• a) a metal cored electrode that includes a metal sheath and core materials, said core material including at least about 0.5 weight percent metal alloying agent and less than about 0.5 weight percent slag forming agent content by total weight of said electrode, said metal cored electrode having a diameter and said gap having a width and a size ratio of said diameter of said metal cored electrode to said width of said gap of said open root is about 0.1-2:1;
• b) a wire feeder to advance said metal cored electrode at a given wire feed rate toward said open root to weld said ends together by substantially filling said open root in a first weld pass, said open root having a gap size of about 1-6 mm, said spaced ends off set by less than about ±3 mm;
• c) a power supply and welding circuit to create a welding current that includes an STT waveform;
• d) a mechanized travel system to move a welding torch and said metal cored electrode along said open root as said welding current is passed through said metal cored electrode to melt the metal cored electrode and transfer the melted metal cored electrode to said ends in said open root to form a root bead, said root bead having an upper surface that includes little or no slag;
• and,
• e) a shielding gas that is directed to said open root to at least partially protect molten metal in said open root from the atmosphere, said shielding gas including argon, carbon dioxide, helium, oxygen. or combinations thereof.