Study on GMA Welding for 9% Ni Steel with Similary Composed Nickel Alloy Wire

Arc Stability and Behavior of Cathode Spots

Abstract

The development of GMA welding (D.C.R.P.) for 9%Ni-Steel with similarly composed nickel alloy wire through the study on the instability of welding arc based on the aspects of cathode spots movement is described. Under the condition of open arc in Ar atmosphere with constant current characteristic power supply, cathode spots move erratically and irregularly on the plate surface in front of weld pool, and it results in unstable welding arc.
The addition of oxygen to Ar shielding gas causes the concentration of cathode spots in the narrow region right under arc column, and the increase in melting efficiency of base metal and in oxygen content in weld metal.
On the other hand, under the condition of buried arc in He atmosphere with constant potential characteristic power supply, the arc root is confined within the well of weld pool and fairly good weld metal for 9%Ni-Steel with similarly composed nickel alloy wire is obtained. Very small blow holes are apt to appear at the root of fuzed zone in this case, but they are effectively decreased by applying a fast transverse weaving method to buried arc.