What's the difference between white, black, and yellow twist drills?
The yellowish brown drill, called cobalt cobalt drill in the industry, is the unspoken rule of the drill. Cobalt containing drills were originally white, produced by grinding, and when they were atomized at the later stage, they were made of yellow brown (commonly called amber), which is the best in circulation. M35 (Co 5%)
There are 3 processes for producing drills, black for rolling and worst for rolling. White for clean edges and ground. Because, unlike rolling, no high temperature oxidation, the steel grain structure is not damaged, used to drill a slightly higher hardness workpiece.
Black becomes nitrided and can be used to drill aluminum products, i.e., soft materials, after improved properties
