Hardened steel is called medium or high carbon, including steel. The hardness of the steel depends on the amount of carbon included, and according to the carbon percentage, its hardness is varied. Normally 0.5 – 1.5% carbon content in added to the hardened steel. The melting point of the hardened steel is 1,205-1,370 Celsius (°C). Due to the high hardness and melting point, regular drill bits are not able to use for drilling the hardened steel.
Cobalt drill bits are good for hardened steel drilling because cobalt drill bits have a higher hardness value of 70 HRC and a higher melting point of 1500 °C, which are greater than hardness steel. 700-1000 RPM and a lower feeding rate is highly recommended for hardened steel when using cobalt drill bits.
Due to the high hardness, the drilling process generates lots of heat. In order to prevent overheating drill bit, you should use suitable cutting oil. As well as always use a lower feeding rate and thrust. There are many things you should know when you use cobalt drill bits on hardened steel.
What is Hardened Steel?
A medium- or high-carbon steel that has undergone heat treatment, quenching, and tempering is frequently referred to as hardened steel.
Any steel with a carbon content higher than 0.75% can be solidified by heating it over its basic temperature and putting it out immediately in water or oil. In contrast to “Mild steel,” hardened steel has been exposed to this solidifying cycle. Steel is gradually heated to a high temperature with the aim of turning it red.
Hardened steel has an improved resistance to wear and abrasion, which is one of its main benefits. This substance can survive repeated misuse and huge loads without breaking down. Additionally, it can withstand rust and corrosion better than typical steel items.
Hardened steel may not be suitable for all applications, despite its many benefits. Even after being subjected to the tempering process, this material is still relatively fragile compared to ordinary carbon steel.
Additionally, quenching and tempering reduce steel’s melting point, which may cause issues with fire safety. This may also prevent the use of hardened steel in certain applications where it will be exposed to high temperatures, such as near engines or other large machines.
Can Cobalt Drill Bits Use for Hardened Steel?
Normally the cobalt drill bit contains steel or other alloys with 5-8% percent or cobalt. The cobalt is the reason for the higher hardness of the drill bit. And it has sharpened edges to do easy drilling, and it can also be re-sharpened as needed.
Mainly there have two types of cobalt drill bits.
- M35 cobalt drill bit – Contains 5% cobalt in addition to steel (or another alloy)
- M42 cobalt drill bit – Contains 8% cobalt in addition to steel (or another alloy)
According to the cobalt percentage of containing the ability to drill hardened steel depends. The higher the percentage of cobalt, the higher the hardness. Hardness is present by a value of HRC (Rockwell Hardness Scale).
- M35 – 65-67 HRC
- M42 – 68-70 HRC
So you can identify the M42 cobalt drill bit as a hardened cobalt drill bit type.
The melting point is also an important point to identify when studying this. Because the drilling of hardened steel may take a long duration of drilling purpose, high heat will produce. So the melting point of the cobalt drill bit must be high. Both M35 and M42 cobalt drill bits have higher melting points.
- M35 – 2723 oF
- M42 – 2853 oF
If you would like to know in-depth about M35 and M42 cobalt drill bits, this guide will help you.
Why You Should Use Cobalt Drill Bits on Hardened Steel?
You can use cobalt drill bits on metals.
Both soft metals such as aluminum and hard metals such as bronze, copper, titanium, cast iron, stainless steel, and many more can be drilled using cobalt drill bits.
- The hardness of normal steel is in the range of 64-68 HRC. So the hardness of the hardened steel has more hardness than normal steel.
- Steel or iron alloys melt at greater temperatures, between 2,200 and 2,500 degrees Fahrenheit (1,205 and 1,370 degrees Celsius). Cobalt drill bits have a higher melting point than hardened steel. Therefore, it can use for drilling purposes.
What are the RPM and SFM for Hardened Steel With Cobalt Drill Bits?
The drilling speed is present as an RPM (Revolution Per Minute). Normally, a higher RPM generates more heat during the drilling. Generally, steel allows drilling up to 700-1000 RPM. As a result, drilling hardened steel requires low feed rates and RPMs.
Speed guidelines are often specified in surface feet per minute (SFM), which is the fastest a cutter can be moved in a straight line. On drill bits, the circumference has the quickest cutting rate.
- SFM = RPM X 0.262 X Tool Diameter
If you do not maintain proper RPM and thrust and suitable cutting oil, drill bit will blunt easily. As a result of this, you need to sharpen the cobalt drill bit.
How to Drill Hardened Steel?
1. Mark the hole with a Dimple Measure, then make a small indentation with a center punch and a hammer. When drilling first begins, drill bits frequently stray. Consequently, the dimple aids in improving the stability of the drill bit. The dimple can be used as a guide when drilling your hole.
2. Make sure the metal object is placed in a flat, secure spot. It is not a good idea to hold the metal with one hand while operating the drill in the other. It is preferable to clamp the metal in place.
3. Both the drilling surface and the drill bit should be lubricated. Repeat this action in between drillings to lower the temperature.
3. Make sure to get appropriate intervals during the drilling to avoid the heat generated.
Conclusion
Cobalt drill bits are highly recommended for drilling hardened steel. Because regular drill bits will melt due to high friction and hardness of the metal. But cobalt drill bits will withstand the hardened steel successfully. When you use cobalt drill bits for hardened steel, use lower 700-1000 RPM and SFM.
It is better to start lower RPM and increase it slowly. In order to protect the tool and metal from overheating, use a suitable cutting oil always.
