Cobalt Drill Bit
Cobalt drill bits are specialized drill bits and cobalt steel alloys variations on high speed with more cobalt in them. So a cobalt drill bit is not coated with cobalt but they are cobalt steel through and through. At the end of the manufacturing process a cobalt bit is baked in an oven to turn the surface color of the steel a dull gold color. This is done primarily for easy identification by color. If the gold wears off or is ground off in sharpening on a cobalt bit, it is still solid cobalt steel.
The cobalt drill bits are another variation on the metal drilling theme. Cobalt drill-bits are the next step up the hardness scale from HSS drill-bits. They are designed to drill very hard materials, and will cope better with metals like stainless steel and are mainly used for the same purpose.
The main advantage of a cobalt drill bit is that they hold their hardness even at very high temperatures and that is why they are peculiarly used to bore stainless steel. The main advantage of the cobalt drill bit is that they are more brittle than standard HSS.
