Metallurgy and heat treating are a vital part of metal fusing. It is not simply a good bead or welding technique that assures a safe, quality weld. Filler material must match the base metal. Heat treatment is often involved after the machining and finish of alloy metals. Chemistry is a critical part of metal selection and the choice of welding filler materials used with specific alloys.
Metallurgy and heat treatment are not abstract processes for manufacturing only. I have repaired obsolete gears with chipped teeth, where the 8620 base metal has been case hardened to 0.035" or so depth at 56 or higher Rockwell C hardness. To repair such a gear requires "normalizing" first to nullify the heat treatment. I have the heat treating shop "normalize" the piece, then the weld repair is made with a specific filler that will fuse with 8620 completely and also heat treat with the same characteristics as 8620 going through heat treatment.
After welding, still in a normalized state, the gear is machinable without destroying the tooling. Once machined correctly, the gear can be returned to the heat treater for re-heat treatment. This will be a carburizing process in this case, again with case depth to 0.030" to 0.040" depth, preferably 0.035", with a finished Rockwell C hardness around 60.
Does this sound intriguing? It's simply a part of the process when you repair a heat treated, damaged part. TIG, MIG, stick and oxy-acetylene filler materials from a source like Weld Mold Company assure the chemistry that will not only fuse and match the base metal, but also allow the finished product to be heat treated successfully, with uniform results. For insights and sharing of metallurgy strategies and filler rod choices, join this forum and other welders striving for professional results!—Moses Ludel