Steels
Source:
http://en.wikipedia.org/wiki/Drill_bit
https://www.americanmadedrillbits.com
- Soft low carbon steel bits are used only in wood, as they do not hold an edge well and require frequent sharpening. Working with hardwoods can noticeably shorten their lifespan. They are cheaper than longer-lived bits.
- Bits made from high carbon steel are an improvement on low-carbon steel due to the hardening and tempering capabilities of the material. These bits can be used on wood or metal, but lose their temper, resulting in a soft cutting edge, if overheated.
- High speed steel (HSS) is a form of tool steel; HSS bits are much more resistant to heat. They can be used to drill metal, hardwood, and most other materials at greater cutting speeds than carbon steel bits, and have largely replaced carbon steels in commercial applications.
- Cobalt steel alloys are variations on high speed steel which contain more cobalt. Their main advantage is that they hold their hardness at much higher temperatures, so they are used to drill stainless steel and other hard materials. The main disadvantage of cobalt steels is that they are more brittle than standard HSS.
- Hi-Moly Tool Steel is heat treated at 2185 degrees and then nitro-carburize finished at 950 degrees to be measurably harder than high-speed steel. Space age nitro-carburized steel withstands substantially higher drilling temperatures while maintaining sharpness.
- Tungsten carbide and other carbides are extremely hard materials that can drill in virtually all materials while holding an edge longer than other bits. Due to their brittleness and high cost they are mainly used for drill bit tips, small pieces of hard material fixed or brazed onto the tip of a bit made of less hard metal. However, it is becoming common in job shops to use solid carbide bits, and in certain industries, most notably PCB manufacturing, it has been commonplace for some time.
- Polycrystalline diamond (PCD) is among the hardest of all tool materials and is therefore extremely wear-resistant. It consists of a layer of diamond particles, typically about 0.5 mm (0.019") thick, bonded as a sintered mass to a tungsten carbide support. Bits are fabricated using this material by either brazing small segments to the tip of the tool to form the cutting edges, or by sintering PCD into a vein in the tungsten carbide "nib". The nib can later be brazed to a carbide shaft and ground to complex geometries that cause braze failure in the smaller "segments". PCD bits are typically used in the automotive, aerospace, and other industries to drill abrasive aluminum alloys, carbon fiber reinforced plastics and other abrasive materials, and in applications where machine downtime to replace or sharpen worn bits is exceptionally costly.
- Black oxide is an inexpensive black coating. A black oxide coating provides heat resistance and lubricity, as well as corrosion resistance. These result in a longer bit life than possible for the typical uncoated high-speed steel bits.
- Black & Gold is used for ultimate lubricity
- Titanium nitride (TiN) is a very hard ceramic material, and when used to coat a high-speed steel bit (usually twist bits), can extend the cutting life by three or more times. A titanium nitride bit cannot be properly sharpened, as the new edge will not have the coating, and will not have any of the benefits the coating provided.
- Titanium aluminum nitride (TiAlN) is another coating frequently used. It is considered superior to TiN and can extend tool life five or more times.
- Titanium carbon nitride (TiCN) is another coating and is also superior to TiN.
- Diamond powder is used as an abrasive, most often for cutting tile, stone, and other very hard materials. Large amounts of heat are generated, and diamond coated bits often have to be water cooled to prevent damage to the bit or the workpiece.
- Zirconium nitride has also been used as a drill bit coating for some Craftsman tools.
Source:
http://en.wikipedia.org/wiki/Drill_bit
https://www.americanmadedrillbits.com