Best Drill Bits for Hardened Steel: 2026 Industrial Guide
Date：2026-01-24Number：285If you need drill bits that can actually cut through hardened metal, this guide will help you find the best options, from aerospace-grade cobalt drills to micro-grain carbide ones.
With 20 years of experience in precision CNC machining and fastener production, I've put together a database of drill bit life for different materials, covering tough situations from 4140 alloy steel to D2 tool steel.
You'll get a list of great tools and learn the exact RPM speeds to prevent burning out your bits, plus how to tell if your feed pressure is right by looking at the chips.
For working with hardened steel, solid carbide and M42 cobalt tools are the top choices. If you're dealing with extremely hard stuff, like HRC 45-65, then solid carbide is really the only way to go. But if you're working with more bendable metals and stainless steel that are less hard (below HRC 38), then M42 cobalt drills with 8% cobalt are the best value for the price.
| Material Type | Hardness Range (HRC) | Best Application |
| M35 Cobalt (5%) | Below HRC 30 | Stainless steel, Mild steel |
| M42 Cobalt (8%) | HRC 30 - HRC 40 | Grade 8 bolts, 4140 Alloy |
| Solid Carbide | HRC 45 - HRC 65 | Heat-treated Die Steel |
| Tungsten Carbide | HRC 65+ | Specialized hard facing |
M42 material has 8% cobalt, which gives it amazing red hardness. When drilling 316 stainless steel or Grade 8 bolts, it stays sharp even when the cutting edge heats up to 600°C.
When working with 304 stainless steel, keep the cutting speed between 10-15 m/min. For a common 6mm drill bit, set the speed between 400 and 500 RPM, and make sure you apply enough pressure for the drill bit to create continuous, curled shavings.
When you're dealing with steel harder than HRC 45, normal high-speed steel tools just can't cut it. That's when you need to switch to solid carbide drill bits. Their extreme stiffness lets them break through the hardened structure of the steel.
For D2 tool steel that's been heat-treated, try drilling without a pilot hole, using a 140-degree drill tip to start. Keep the feed rate very low, between 0.03 and 0.05 mm per revolution, so you get small chips.
Don't even think about using these bits in a handheld drill! Carbide is very hard, which also means it's brittle. Even a tiny bit of wobble can shatter the drill bit. These are for CNC machines or strong, stiff magnetic drills only.
TiAlN coatings react with oxygen in the air during cutting, which forms a super thin layer of aluminum oxide. This layer gets harder when it gets hot, and it can handle extreme heat up to 800°C, making it great for dry cutting.
When you're working with 4140 steel, this coating can make your cutting speeds way faster, like 30% faster. Plus, if you use a drill with a strong design, it'll stay steady and accurate even deep down in the hole.
Just a heads up, don't use TiAlN on pure aluminum or soft stuff. The aluminum in the coating can stick to the material you're cutting. This causes chips to build up fast and jam things up, which can break your drill in no time.
This cross-edge design effectively shortens the cross-cutting edge, achieving “self-centering.” It prevents the drill bit from walking laterally on hardened surfaces, ensuring hole positioning accuracy.
Check Material Hardness: Test the edge with a file. If the file skips without leaving marks, the hardness exceeds HRC 45, requiring Solid Carbide.
Lock in Tool Matching: For HRC 30-40, use M42 cobalt drill bits; for HRC 45+, select carbide tools with TiAlN coating.
Set Ultra-Low RPM: Follow the “large diameter, slow speed” principle. A 10mm drill bit on hardened steel should typically not exceed 300 RPM.
Inject Heavy Lubricant: Replace WD-40 with high-sulfur heavy-duty cutting oil or paste to ensure the oil film remains intact at elevated temperatures.
Maintain Constant Feed: Apply steady pressure without interrupting feed. Intermittent feeding causes severe work hardening and burns the drill point.
To drill hardened steel, you need special drill bits that can handle high heat and pressure. Let's look at the key materials, coatings, and design features that make these drill bits cut through this tough stuff well.
The best drill bits for working with hardened steel are made from tough, heat-resistant stuff. High-speed steel (HSS) bits are okay, but they can wear out fast when drilling really hard steel. Cobalt drill bits, especially those made with M42 cobalt steel, are better at resisting heat and wear, so they stay sharper longer when drilling hard metals.
For the toughest jobs, go with carbide drill bits. They're made of tungsten carbide, which is super hard and can easily cut through hardened steel. They cost more, but they last way longer than other types of drill bits.
Coatings can make drill bits last longer too. Titanium-coated bits handle heat better and cut through metal more smoothly. This is a good option for HSS bits, as it can really their performance.
The shape and material of a drill bit matter just as much. Split-point drill bits are great when working with hardened steel. This shape helps the bit start cutting faster and keeps it from wandering on tough surfaces. It also helps get rid of shavings faster, which means less heat.
The point angle of the drill bit is also important. A 135-degree point angle works really well for hardened steel. It cuts better than a standard 118-degree bit, which helps it get through hard surfaces.
How the flutes are designed impacts how well the drill bit gets rid of waste. U-shaped flutes are good for hardened steel. They move the shavings away quickly, keep the drill bit cool, and make sure you get a smooth cut.
The kind of shank you use is another thing to think about. Straight shanks work for most drills, but a short shank can keep the bit from slipping when drilling hard stuff with a keyless chuck.
Why do general purpose high-speed steel drill bits fail so quickly when drilling hardened steel? It all comes down to the tempering temperature.
Typical HSS drill bits are tempered around 200°C to 300°C. The heat generated when drilling hardened steel can easily exceed that, causing the drill bit tip to soften.
Once the tip softens, the cutting edge dulls and just rubs against the surface. This creates even more heat, which ruins the bit and makes the workpiece surface too hard to machine again.
1. Always keep the feed going. This is super important to stop re-hardening. Make sure each turn is cutting metal, not just rubbing on the surface, to get rid of most of the heat (about 80%).
2. Get your RPMs just right. Here's why: If you're working with 4140 steel at HRC 40, and you raise the speed by 60%, your tool life can drop by 70% because of heat buildup.
3. Use a step-by-step feed pressure thing. For holes bigger than 10mm, use 50% pressure to get started. Once you’re cutting steadily, go up to 100%. Right when you're about to break through, lower the pressure to keep the edge from chipping.
Material: Clearly marked as M42 (containing 8% cobalt) or ultra-fine grain cemented carbide.
Geometry: Features a 135° split-point structure.
Coating: Cemented carbide should be paired with TiAlN or AlTiN nano-coating.
Don't let a hardened workpiece stall your production line. At Jimmytool, we don’t just sell drill bits; we provide the exact M42 Cobalt and Solid Carbide solutions mentioned in this guide—engineered for maximum durability in extreme HRC environments.
Contact our technical team today. Let's solve your drilling bottlenecks together.
Can I drill a Grade 8 bolt?
Yes, but you must use an M42 cobalt bit. A standard HSS bit will burn out before it makes a 1mm dent.
Is cooling necessary?
Absolutely. For hardened steel, constant "flood cooling" or heavy cutting paste is the only way to protect good metal drill bits.
What if the bit gets stuck?
Stop immediately. Reverse the drill slowly. Check for chip buildup in the U-shaped flutes, clean them, re-lubricate, and restart.
person: Mr. Gong
Tel: +86 0769-82380083
Mobile phone:+86 15362883951
Email: info@jimmytool.com
Website: www.jimmytool.com
