Hardened steel is one of the hardest metals known to man, whilst it is very hard it is also brittle and is not ductile like regular mild steel. Whilst it is possible to cut hardened steel easily using an abrasive disk in a angle grinder it is much more difficult to drill. Drilling hardened steel with a normal drill but will not work as the material you are drilling is tougher than the drill bit itself.
These are profi-line drill bits made by Artu. These drill bits will drill virtually anything including hardened steel, tough porcelain, masonry and glass.
The drill bits look like masonry drill bits but they are much tougher. Here is a kit containing 8 drill bits, the cost of which is about £40 Some cobalt drills can also drill through hardened steel.
You can also drill hardened steel with solid carbide bits but they are very expensive and brittle
To be able to drill hardened steel with these drill bits you really need a pillar drill set to it's fastest speed. Here we are drilling through a bearing race, which is a very tough form of hardened steel.
Ensure that the work piece is securely clamped.
Safety glasses or goggles should be worn when drilling.
With the drill on it's fastest settling carefully touch the drill bit to the work piece and apply pressure to the drills handle.
Do not use any coolant or any lubricant with these drills. The drill actually seems to burn it's way through the hardened steel.
The swarf that is produced is hot, so be aware of it.
Here is the hole which has been successfully drilled in this hardened steel bearing race.