Carbide Drills for Hardened Steel

In mold machining—such as press and injection molds—post-hardening processes like fitting adjustments or adding vent and cooling holes often involve materials exceeding HRC 50 in hardness, making conventional drilling extremely difficult.

This article features carbide drill options for hardened steel and outlines key challenges and solutions in hard material drilling.

AQUA REVO
OIL HOLE DRILL

This drill features a newly developed REVO Power Cooler oil-hole design, allowing for increased coolant flow. The high-volume internal coolant provides forced cooling at the cutting edge, preventing temper softening and wear progression—ensuring stability even in high-temperature hardened steel machining.

It also uses the heat- and wear-resistant REVO-D coating, which minimizes coating degradation under high-load, high-temperature conditions. This design offers excellent durability and efficiency when drilling hardened steel.

Product Lineup	Available in 3×D, 5×D, and 8×D depth options
Coolant Compatibility	“REVO Power Cooler” oil-hole system
Coating Types	“REVO-D” multilayer nano-coating (AlCr / AlTi-based)
Manufacturer Name	Nachi America

SDPX
（SumiDrill Power Series）

This carbide drill is built for stable drilling under high-load conditions such as hardened steel.

Its enhanced coating strength and fracture resistance help prevent edge chipping and cracking during interrupted cutting or under impact.

The coating also offers excellent oxidation resistance, with a degradation threshold of 1,100°C, protecting against thermal wear and delamination in high-temperature zones. According to the catalog's recommended cutting parameters, the tool is rated for high-hardness materials such as 45 HRC, 55 HRC, and 60 HRC—making it a highly reliable choice for post-heat-treatment components and hardened steels.

Product Lineup	Diameter range: Ø3.0 mm – Ø16.0 mm
Coolant Compatibility	Through-coolant capable
Coating Types	PVD “Sumi-Power Coating”
Manufacturer	Sumitomo Electric Hardmetal

Challenges in
Drilling Hardened Steel

Hardened steel refers to steel that has undergone heat treatment, such as quenching, to increase its hardness. It is widely used in automotive parts, molds, and machine components. However, due to its extreme hardness, drilling hardened steel is a technically demanding task.

Here are three of the most common challenges.

Severe Tool Wear
and Chipping

As the hardness of steel increases, so does the cutting resistance. This places significant pressure and heat on the drill tip.

Compared to standard steel machining, hardened steel accelerates tool wear and makes the cutting edge more prone to chipping.

Chipping leads to poor cutting performance, rough surface finishes, and in some cases, total tool failure.

When machining materials above HRC 50, conventional HSS drills are generally insufficient. Carbide drills specifically designed for hardened steel are essential, and optimizing cutting conditions, edge geometry, and coating selection is critical.

Increased Cutting Heat
and Poor Heat Dissipation

Hardened steel generates intense heat during cutting due to its high resistance.
Unlike standard steel, where heat is mostly carried away by the chips, hardened steel tends to produce short, fine chips, which are less effective at removing heat.

As a result, heat builds up in the tool and on the workpiece surface. This can cause coating degradation, tool softening, and accelerated wear.
In some cases, the surface of the workpiece may even experience tempering, reducing its hardness.

To address this, efficient cooling is essential.
Through-coolant drills that deliver cutting fluid directly to the cutting edge provide both localized cooling and improved chip evacuation, making them highly effective for hardened steel applications.

Maintaining Hole Accuracy
and Process Stability

Because hardened steel is extremely rigid, the material itself doesn’t deform during drilling.
However, even slight deflection or vibration from the tool or machine can significantly impact hole quality.

Any minor tool runout or uneven feed can compromise roundness, positional accuracy, and dimensional tolerances.
Thermal expansion or cutting-induced vibration can also lead to burrs at the hole entrance or exit, requiring additional finishing steps.

To prevent these issues, it's essential to maximize the rigidity of both the tool and holder, and to minimize runout during operation.