Drill bit materials are very important in metalworking. Because we should always use harder material than the workpiece. Material hardness is measured by the HRC (Rockwell hardness values). Higher HRC values are easy to use on most metals. The most used drill bit materials are HSS, cobalt, and titanium.
More than that, Tungston and aluminum are also used for mixing other metals. As well as some coats are also applied on the drill bits in order to improve the hardness, durability, and thermal resistance. Black oxide, TiN, TiCN, and TiAlN are the most used coatings on metal drill bits.
1. High Carbon Steel
When drill bit material mix with a higher percentage of carbon, these drill bits can be produced. Those are used to drill mild steel which is mixed with a lower percentage of carbon. We can see higher carbon steel and low carbon steel drill bits here that is according to the carbon percentage.
A lower carbon percentage can’t be used for drilling steel. It will tamper due to heat. But higher carbon steel can be used to drill steel without any problem. These bits are extremely good for the woods. These are really cheap, but I highly recommend you move one of the below drill bits if you need a durable drill bit.
2. High Speed Steel (HSS)
HSS is an abbreviation of High-Speed Steel. This drill bit is made from a combination of carbon steel and other elements. Vanadium and chrome to form an alloy can be used as other elements.
These are elements in the high-speed steel.
- Tungsten – 18%
- Chromium – 4%
- Vanadium -1% of
- Carbon – 0.5–0.8%
Due to these materials, HSS drill bits can withstand high temperatures produced during metal drilling. These drill bits can be used even at temperatures below 600oC
HSS drill bits can be used to drill iron, steel, and other metals such as brass, copper, and aluminum alloy because it has a 63-65 HRC value. A drill bit has two cutting surfaces on either side of the center axis and is cut at an angle of approximately 60 degrees. This cutting angle is selected according to the nature of the material required to drill.
3. Black Oxide
Black oxide coating, also known as blackening, is a type of surface conversion coating for ferrous materials, stainless steel, copper, and copper-based alloys, zinc, powdered metals, and silver solder. It is used to add mild corrosion resistance and for appearance.
The black oxide coating process involves immersing the drill bit in a bath of sodium hydroxide, nitrates, and nitrites. It is then heated to a temperature of around 141 degrees Celsius for steel and 121 degrees Celsius for stainless steel. The solution causes a reaction that incorporates the elements into the top layer of the metal, forming a dark black layer of magnetite (Fe3O4) on the surface.
Black oxide coating provides a number of benefits to the drill bits such as reduced light glare, improved lubricity, corrosion resistance, and improved appearance. and increase the durability of the drill bit.
Cobalt is used for cobalt drill bits. Cobalt is a harder drill bit material. It has a higher HRC value of 68 – 70 HRC. Cobalt drill bits are made by mixing HSS with mixing cobalt 5% to 8%. The 5% cobalt mixture is named M35, and 8% cobalt mixture is named as M42. They are highly resistant to heat and hard to abrasive.
Compared to the HSS drill bit, the cobalt drill bit can be used faster and longer without cooling. Therefore, the durability of these is high. Cobalt drill bits can be used to drill harder metals such as bronze, cast iron, stainless steel, titanium, etc.
5. Titanium Nitride (TiN)
Titanium nitride is a coating that is coated on the HSS drill bits in order to increase the abrasion resistance, reduce the friction and increase thermal condensation. This will increase the durability of the drill bit. When it comes to physical properties, titanium nitride has a high hardness level (HV 2400-2800) and a high melting point (2950°C). Because of its high thermal resistance, it can be used to make devices that are used in high temperatures. Further, it does not react with acids and bases.
Usually, titanium nitride drill bits are made from steel and apply titanium nitride coating. A titanium nitride drill bits can be sharpened but with sharpening, the coating will remove from the cutting edges. 135 Degrees can be identified as the suitable cutting angle for titanium nitride drill bits. The titanium drill bit has six times more durability than steel.
Titanium nitride drill bits can be used for drilling on several types of metals, such as mild steel, iron, copper, magnesium, wood, and plastic. (Not recommended for aluminium)
6. Aluminium Titanium Nitride (TiAlN)
Aluminium titanium nitride has a higher hardness level (2600 to 3300 HV) and a high melting point (2,947 °C). It has a higher aluminium content of 50%. The physical vapor deposition method is usually used industrially to make aluminium titanium nitride drill bits.
Aluminium Titanium Nitride drill bits are the same as AlTiN coated on the HSS drill bits. A thin Al203 film will be formed on the drill bit surface. This will increase the hardness, durability, and thermal resistance and reduce the friction of the drill bit. 118.0 degrees is the suitable cutting angle for this drill bit
Brass, Bronze, Fiberglass, Hardened Steel, Iron, Nickel, Plastic, Stainless Steel and Steel can be drilled using aluminium titanium nitride drill bits. Aluminium titanium nitride drill bits can be sharpened. But with the sharpening, the coating will be removed from the cutting edges.
7. Titanium-Carbonitride (TiCN)
Aluminum, Brass, Bronze, Fiberglass, Hardened Steel, Iron, Nickel, Plastic, Stainless Steel, Steel, Titanium, Tool Steel
Titanium-carbonitride (TiCN) drill bits are superior to the TiN drill bits. These drill bits have a hard, smooth finish that resists chipping and wear. It can prevent material accumulation at the edge. Hence these are very good for aluminum drilling.