Hard Steel Drill Bits: Why Your Standard Set is Failing and What to Buy Instead

You’re staring at a piece of stainless steel or perhaps a slab of cast iron, and your standard high-speed steel (HSS) bit is literally smoking. It happens fast. One second you're making progress, the next, the tip of your bit is glowing a dull orange and the "bite" is gone. You’ve just successfully annealed your tool, turning a sharp edge into a useless, rounded nub. It’s frustrating. It’s expensive. And honestly, it’s usually because we’re asking a tool designed for wood or soft mild steel to do a job it was never born for. To get through the tough stuff, you need hard steel drill bits that can handle the sheer thermal abuse of friction without losing their molecular integrity.

The reality of drilling into hardened materials isn't about muscle; it's about metallurgy. When you step up to materials like Grade 8 bolts, hardened spring steel, or T-304 stainless, the game changes. You aren't just cutting anymore. You're managing heat. If that heat stays in the bit, the bit dies. If the bit can't handle the heat, it softens. This is where most DIYers and even some pros get tripped up. They think a "titanium" coating is a magic bullet. It isn’t.

The Cobalt Secret (and Why Coatings are Often a Lie)

Most people head to the big-box store and grab the gold-colored bits. They see "Titanium" and think they’re buying something indestructible. Here’s the truth: Titanium Nitride (TiN) is just a coating. It’s a few microns thick. It’s great for lubrication and it helps with heat a bit, but once that thin layer wears off at the tip—which happens quickly in hard steel—you’re back to basic HSS.

If you want a bit that actually lasts, you look for Cobalt. Specifically, M35 or M42 grade.

M35 bits contain about 5% cobalt, while M42 contains 8%. Unlike a coating, the cobalt is alloyed throughout the entire metal. You can sharpen a cobalt bit on a bench grinder and it’s still a cobalt bit. It doesn’t "wear off." The cobalt doesn’t actually make the bit much harder in terms of Rockwell C scale points; instead, it raises the temperature at which the bit loses its hardness. This is known as "red hardness." You can get a cobalt bit hot enough to burn your fingers, and it will still keep its edge.

Why M42 Matters for the Really Tough Stuff

If you’re dealing with something like a broken Easy-Out or a leaf spring, M35 might still struggle. That extra 3% of cobalt in the M42 bits provides a significant jump in heat resistance. However, there’s a trade-off. Cobalt makes the steel more brittle. If you’re using a handheld drill and you tilt it slightly while drilling with an M42 bit, snap. It’s gone. These are precision tools. They want a drill press. They want stability.

Carbide: The Nuclear Option

Then there’s tungsten carbide. This is a different beast entirely. It’s not steel. It’s a ceramic-metal composite. If cobalt is a step up, carbide is a leap into another dimension.

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1. Solid Carbide: These are incredibly hard. They can drill through hardened tool steel that would laugh at a cobalt bit. But they are brittle as glass. Dropping one on a concrete floor can shatter it. Using one in a hand drill is almost a guaranteed way to waste $40 in three seconds.
2. Carbide-Tipped: These are more common in masonry, but specialized versions exist for metal. They give you a bit of the toughness of a steel body with the cutting power of a carbide edge.

Most folks don't need solid carbide unless they are working in a machine shop environment with a rigid CNC or a very heavy-duty manual mill. For the guy in the garage trying to fix a tractor frame, cobalt remains the sweet spot of "actually works" and "won't break if I sneeze."

The Physics of "Slow and Heavy"

I've seen so many people burn out hard steel drill bits because they treat them like they're drilling a 2x4. They crank the drill to its highest RPM and lean on it. That is a recipe for immediate failure.

With hard metals, you need to think about Surface Feet Per Minute (SFM).

Imagine the outer edge of your drill bit traveling in a circle. In stainless steel, that edge should be moving much slower than in aluminum. If you spin a 1/2-inch bit at 2,000 RPM in hard steel, the friction heat builds up faster than the metal can dissipate it. The tip hits the "critical temperature," and it’s over.

You need two things: Low speed and high feed pressure. You want to see "chips," not "dust." If you see fine powder coming out of the hole, you aren't cutting; you're grinding. Grinding creates heat. Heat kills bits. You want to see those long, curly spirals of metal. That means the bit is actually biting into the material. The chip itself actually carries away a huge percentage of the heat. If you aren't making chips, the heat is staying in the workpiece and the tool.

A Note on Cutting Fluid

Don't use WD-40. Just don't. It's a solvent, not a dedicated cutting lubricant. It’s better than nothing, sure, but it evaporates too fast. You want a high-sulfur cutting oil or a dedicated product like Oatey’s Dark Threading Oil or Tap Magic. These fluids do more than just cool the bit; they provide extreme pressure lubrication that prevents the metal you're cutting from "welding" itself to the tip of your drill bit—a phenomenon called "Built-Up Edge" (BUE).

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Anatomy of a Professional Bit: Split Points

Look at the tip of a cheap bit. It likely has a 118-degree angle and a flat "chisel" point in the middle. That chisel point doesn't cut; it just rubs. That’s why you usually have to drill a pilot hole.

High-quality hard steel drill bits usually feature a 135-degree split point.

• 135-degree angle: This flatter profile puts more of the cutting edge in contact with the hard material sooner and reduces the "walking" effect.
• Split Point: The "chisel" is ground away to create two additional cutting edges. This allows the bit to start cutting on contact. It bites immediately.

If you are trying to drill out a Grade 8 bolt, a 135-degree split-point cobalt bit is your best friend. It won't skitter across the surface, and it will start the hole without needing a tiny pilot bit that’s prone to snapping.

Common Myths That Ruin Your Tools

"Just get it glowing and it'll melt through." No. If you get it glowing, you've ruined the temper of the steel. Even if you manage to punch through, that bit is now soft.

"More pressure is always better." Sorta. You need enough pressure to keep the bit cutting. If you let it "dwell"—meaning the bit is spinning but not progressing—you are work-hardening the metal. Some metals, like 300-series stainless steel, will actually get harder the more you rub them. If you let a bit spin in one spot for ten seconds without cutting, you’ve just created a spot that is now harder than the bit itself. You've essentially "case-hardened" your workpiece. Now you’re really in trouble.

Real-World Application: The "Broken Bolt" Scenario

Let's say you're working on an exhaust manifold. A bolt snaps off flush. This is the ultimate test for hard steel drill bits.

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First, center punch it. Deeply. If your bit isn't centered, you're going to destroy the threads in the head, and then you're looking at a Helicoil or a much bigger headache.

Start with a small cobalt bit. Use a drop of real cutting oil. Set your drill to its lowest gear. Pulse the trigger. You want to feel the bit "grab." If the bit starts to whistle or squeak, stop. More oil. Less speed. Once you have a pilot hole, step up in size gradually. Don't jump from a 1/8" to a 3/8" bit. The 3/8" bit will catch on the edges of the small hole and likely snap or "hog in" too aggressively.

Where to Buy and What to Avoid

Avoid the "unbranded" sets on discount sites that claim to be M42 Cobalt for $15. It’s physically impossible. The raw material cost of cobalt alloy is too high for that. You’ll end up with "Cobalt Colored" HSS.

Instead, look for reputable brands that have been in the tool game for decades.

• Precision Twist Drill: These are industrial-grade. Not pretty, but they work.
• Viking / Drill Hog: Known for their "Super Mo-Max" or high-cobalt blends. They often have a lifetime warranty, even against breakage.
• Cleveland: A staple in machine shops.
• Nachi: Excellent Japanese metallurgy, specifically their Aqua Drills for hard materials.

Actionable Steps for Success

If you're ready to stop melting your tools and actually get through that workpiece, follow this protocol:

1. Identify the Material: If it's stainless or hardened steel, put the HSS bits away. Reach for Cobalt (M35 or M42).
2. Check the Tip: Ensure you’re using a 135-degree split point bit. If it’s a standard 118-degree, you must use a center punch or a pilot hole.
3. Speed Control: Check a speed chart. For a 1/4" cobalt bit in stainless, you should be around 600-800 RPM. Most cordless drills at full tilt are doing 1,500-2,000. Slow down.
4. Lubricate Constantly: Do not wait for smoke. If the oil is smoking, it’s already too hot. Add oil every 10-15 seconds of drilling.
5. Steady Pressure: Lean into it. Use your body weight if it’s a hand drill. You want those thick, beautiful chips.
6. Cooling Down: If the workpiece gets hot to the touch, stop. Let it air cool. Quenching a hot bit in cold water can cause micro-cracks in the metal (thermal shock), especially with cobalt.

Drilling hard steel isn't a race. It's a game of thermal management. Buy the right alloy, slow your drill down, and use the right oil. You'll find that what used to take twenty minutes and three ruined bits now takes two minutes and one bit that stays sharp for the next ten jobs.