Bar Forgings are used in many applications, from ship shafts to gears in machines we use daily; and bar forgings found in high-value applications, such as applications that undergo extreme conditions, need metal grades of the highest quality. To reach these qualities, engineers can choose “exotic” metals, which inherently hold choice qualities. But, with these high-end materials come high-end prices. Another, more cost-effective, way to reach high-quality material properties is through remelting processes like Vacuum Arc Remelting or Electro-Slag Remelting.
Both VAR and ESR help to produce clean material, reducing segregation and inclusions in steel or other alloys, refining them and improving grade properties – VAR is prevalent in the United States and ESR is more commonly seen in Europe, although U.S. ESR furnace capacity has been increasing over the past few years. The benefit of Vacuum Arc Remelting is cleaner materials with: reduced gas and oxide contents, improved homogeneity of the ingots obtained; improved ductility; greater uniformity of properties in the transverse, and longitudinal directions; improved fatigue properties; and uniformity of chemical composition.
To produce these ultra-clean metals, VAR materials go through a secondary melting process conducted in a vacuum-sealed, highly controlled environment. The steels and alloys gain tight chemical tolerances through the removal of dissolved gases, such as hydrogen and nitrogen (if desired); the reduction of undesired trace elements; directional solidification of the ingot from bottom to top, which alleviates macro-segregation and reduces micro-segregation. As mentioned above, VAR also provides oxide removal that is achieved through chemical and physical processes. The chemical process happens because less stable oxides or nitrides are thermally reduced by the carbon present in the alloy, allowing them to then be removed through the vacuum of the VAR process. However, in special alloys and high-alloyed steels, the non-metallic inclusions (e.g. alumina) are very stable, so they remain in the chemical makeup of the material. Other inclusions in the ingot will be removed physically by flotation that takes place during remelting (impurities float to the top where they get cut off). Any remaining inclusions are broken up and evenly distributed in the cross-section of the solidified ingot.
VAR grade materials are found in aerospace applications, including the “superalloys” needed for extreme applications of temperature and pressure. VAR steels are used in rocket-booster rings, landing gear and high-pressure tubes. Oil and gas, as well as the nuclear industry, are utilizing the remelt of reactive metals and their alloys.
Typical VAR grades:
4340 VAR
9310 VAR
PH Stainless
300M
3NiCrMoV
300 & 400 Series Stainless