Carbide Drill Bits for Hardened Steel

How to Choose the Best Drill Bit for Hardened Steel

Hardened steels generally range from 42-62 on the Rockwell C hardness scale.  The best drill bit for this hardness of steel will definitely be made from solid tungsten carbide material.  High speed steel drill bits will fail almost immediately, and cobalt drill bits won't last very long.  The flute twist or helix is also very important.  The higher the helix angle, the lower the strength of the cutting edge.  It is not recommended to have a helix angle higher than 15 degrees in these hardened materials.  The strongest edge is a straight flute drill bit where the helix angle is zero.  Whether to use coolant or not is also important.  Because of the high hardness the cutting temperatures at the edge can be very high.  With solid carbide drill bits it is best not to cool the edge, but make sure it is lubricated for the best results.  This reduces the cutting temperature and allows the metal to cut more freely.  Higher concentrations of water soluable coolant are recommended in the 8-12% range for harder steels.

All carbide drill bits are capable of drilling hardened steels, but for production machining the longest lasting drill bits will be straight fluted AlTiN carbide drill bits.

Solid Carbide Drills for Hard Metal and CNC Machining

Solid carbide construction supports higher cutting speeds, improved hole accuracy, and longer tool life in hardened steel and other difficult-to-machine metals. Carbide is also more brittle than high-speed steel or cobalt, so these tools perform best in rigid CNC machines, machining centers, drill presses, and other stable setups. They are generally not the best choice for flexible handheld drilling conditions.

Straight-flute carbide drills can be effective where controlled cutting action, hole accuracy, or specific chip behavior is important. Spiral-flute designs may provide better chip evacuation in other applications. The correct choice depends on the material, hole depth, drill diameter, coolant delivery, and manufacturer’s recommended cutting data.

For the most consistent results, minimize tool overhang, control spindle runout, secure the workpiece, and follow the recommended speeds and feeds. Excessive speed can accelerate wear, while insufficient feed can cause rubbing instead of cutting. Always confirm that the drill is rated for the hardness of the material being machined.