Cobalt drill bits are made from steel that has particularity high cobalt content, typically five to eight percent. These unique products are used for aircraft drill bits because they can cut cleanly through hard material and keep their cutting edge for a considerable time before it is necessary to sharpen them. Although the addition of cobalt to the steel makes the material more brittle the hardness and the abrasive surface makes them ideal for continuous service. Drill bits made from this material puts them above the traditional high strength steel drill bits and those made from Titanium.
Many steels have a hard surface finish which is produced through various methods of heat treatment; this is not the case with steel containing a high percentage of cobalt. These drill bits are hard throughout the material, not just on the surface. This feature means that the drill bit can be sharpened repeatedly giving them a significant advantage over drill bits made from titanium. Although a titanium drill bit can go though harder material, the bit cannot be sharpened and still keep a cutting edge. High speed steel drill bits can be sharpened but more frequently than cobalt.
There are a host of names used in industry for cobalt drill bits but basically these names are representative of the cobalt content, either five percent or eight percent. The higher the cobalt content the harder the metal becomes but as it gets harder, it also gets more brittle. These drill bits can withstand a higher temperature than high strength steel before they deform.
These bits are commonly used as aircraft drill bits as many components on an aircraft are made from titanium and high strength steel, they are also often found in the arms industry where they are used to produce components for rifles and other weapons.
When the alloy is produced it often includes additional elements such as carbon and titanium, or if the material to be drilled is soft, the alloy is black oxide. The bit surface is heat treated which gives the finished bit a golden brown hue which makes it very easy to distinguish a cobalt drill bit from common bits. Although cobalt bits are superior to other bits and they can withstand elevated temperatures, drilling in a coolant bath is still recommended.
