Preparation of the Surface
A. Remove rust, dirt, grease, oil, and other contaminants from the surfaces to be welded.
B. A sound base is required, and this may necessitate removing fatigued or rolled over metal, high ridges or other major surface irregularities. This may be done by gouging (Postalloy®250), grinding or machining.
C. Cracks in the base metal should be arc gouged or ground out and repaired using compatible electrodes. If cracks are through the base metal make sure the end of the crack is removed by drilling or cutting at the end before gouging out the cracks.
D. Previous hardface should be removed if: • The type used is unknown • The type used is incompatible with the new deposit • Deposits are porous or contain voids • Deposits are badly cracked and deformed
E. If the surface is severely work-hardened, about 1/8” (3mm) of work hardened surface should be removed before hardfacing or build-up of a worn area. Failure to do so might result in weld bead spalling.
F. Edges should be rounded, no sharp edges. This causes excessive mixing of the base metal and hardfacing alloy.
G. if a build-up is needed prior to hardfacing, select a build-up that is compatible with the base metal composition. Never use 7018 as a build-up. Weld Polarity Weld polarity strongly effects the amount of dilution. Reverse polarity results in a first layer deposit that is up to 50% base metal and 50% weld metal. Straight polarity, on the other hand, results in less penetration and more favorable deposit chemistry. A second layer, in either case will produce a chemistry suitable for wear resistance.