Consideration must also be given to the dilution that will occur with the base metal. A weld deposit is a mixture of the filler metal and the base metal, and the deposit chemistry will depend on how much of each is present. Wear resistance is reduced by high base metal dilution. The following suggestions will help minimize dilution, resulting in greater wear resistance.
1. Do not use excessive welding currents.
2. Direct the arc on the molten weld metal rather than on the base metal.
3. Use close overlap (50 to 75%) when placing weld beads side by side.
4. Use DC straight polarity if possible (electrode negative).
5. Do not use excessive preheat. Preheat with recommended ranges.
6. Regardless of stringer or wide weave beads, the travel speed should be adjusted to direct the arc on the weld puddle.
7. When using wire processes, a longer stick-out will reduce penetration.
8. In order of decreasing penetration and dilution - vertical up (highest), horizontal, up hill, flat and down hill (lowest).
Do not preheat manganese. The tough properties of manganese can be lost if the base metal is continually heated above 500°F (260°C). Weld beads should be distributed so as to avoid concentrated and prolonged heat input into one area.
Cast iron requires high preheat temperatures for hardfacing applications. A good rule of thumb is dull red.
Carbon and Low Alloys Steels.
Preheating of some carbon and low alloy steels may be necessary to minimize distortion, spalling, under bead cracking and cracking in the base metal. Preheat temperature is influenced by carbon and alloy content, part size and rigidity. The higher the carbon and alloy content, the higher the required preheat temperature. Consult the preheat chart or call Postle Industries for recommendations. The preheat should be uniform throughout the part and the part should be slow cooled.
Look for Part 4 in the October Newsletter – Cushion and Buffer Layers