The preferred methods for applying bare hardfacing rod to base metal are the oxyacetylene and the TIG (Gas Tungsten Arc) processes. The oxyacetylene process has a controlled, low dilution rate (0-5%) of the hardfacing alloy by the base metal. The TIG method is an alternative to oxyacetylene when large parts or difficult base metals are involved. It produces clean deposits and allows a high degree of control over heat input, the positioning of the arc and weld deposit.
Base Metal Characteristics
Some base metals can be hardfaced easier than others. Certain base metals require special techniques.
Base Metals Easily Hardfaced
- Low & medium carbon steels (carbon; 0.4% max)- Higher carbon steels (carbon greater than 0.4%) (oxyacetylene only)
- Low alloy steels
- Nickel-copper alloys
- Chromium-nickel stainless steels (excluding free machining or titanium bearing grades)
- Niobium stabilized stainless steel
- Manganese steel (11-14%)
Base Metals Hardfaced with Difficulty
- Cast iron
- Titanium stabilized stainless steel
- Straight chromium stainless steels
- Tool & die steels
- Water hardening grades
- Oil hardening grades
- Air hardening grades
- Hot work grades
Base Metal Surface Preparation
The workpiece must be clean and free of rust, dirt, scale, grease and other contaminants which could cause cracking, porosity, boiling and inclusions in the deposit. Wire brushing, grit blasting, grinding, machining, steam cleaning or chemical cleaning are effective methods used to clean the base metal. Defective areas in the base metal—high ridges, fatigued areas, cracks, laps, spongy areas—should be cut out or repaired prior to hardfacing. When building up edges of cutting tools and dies, a recess is required to provide adequate support for the hardfacing material. Thin sections should be backed up to avoid burn through. Areas to be hardfaced can be marked with chalk or soapstone to indicate bead orientation and sequence.