HSS vs. Cobalt vs. Carbide Drill Bits — Which One Does Your Shop Actually Need

The drill bit aisle at any industrial supplier has dozens of options labeled with material grades, coatings, and geometry specs. Most shops settle into a default — usually whatever is cheapest or whatever has always been in the cabinet — and stick with it unless something goes wrong. That approach mostly works, but it leaves real performance and cost efficiency on the table.

The decision between HSS, cobalt HSS, and solid carbide is not complicated. Each material has a clear application range. Here's how to match them.

M2 HSS — The General-Purpose Baseline

M2 high-speed steel is the correct choice for a wide majority of drilling work. Mild steel (1018, 1020, A36), aluminum, soft cast iron, brass, bronze, wood, plastic, and copper all drill fine with quality M2 HSS. The key qualifier is quality — name-brand American or German HSS (Precision Twist, Norseman, Cleveland, Chicago-Latrobe) is a fundamentally different product from the mystery-steel imports in budget kits, even though both say HSS on the label.

M2 HSS is also the most resharpenable drill material. It grinds cleanly, holds geometry well through multiple cycles, and doesn't require special grinding wheels. If you're running a resharpening program, HSS is the material that makes it most economical.

M42 Cobalt HSS — The Upgrade for Heat and Hard Materials

M42 cobalt adds 8% cobalt to the HSS alloy. This raises the "red hardness" — the temperature at which the steel starts to lose hardness significantly — from around 600°F to around 900°F. That 300-degree buffer is the difference between a cutting edge that survives and one that softens at the cutting zone in demanding materials.

Upgrade to cobalt when drilling:

• Stainless steel (especially 300 series) — 304 and 316 work-harden rapidly at the cutting zone. The heat generated at typical drilling speeds is enough to soften M2 HSS quickly. Cobalt handles it comfortably at reasonable speeds with good cutting fluid.
• Tool steel, 4140 at hardened tempers — anything in the 35–45 HRC range. Above 45 HRC, you're looking at carbide.
• Nickel alloys, Inconel, Hastelloy — high-temperature alloys that generate extreme heat at the cutting zone.
• Any situation where you're burning through M2 bits faster than expected — if HSS drills are dying too quickly in a specific material or operation, cobalt is the first upgrade to try before jumping to carbide.

Cobalt HSS resharpens exactly like M2 HSS — same process, same equipment. The higher cost per bit is recovered quickly in extended tool life in the applications listed above. In mild steel and aluminum, you won't see a meaningful difference from the cobalt content — don't spend the premium there.

Solid Carbide — For Production, Hard Materials, and CNC

Solid carbide drills are not an upgrade to HSS — they're a different tool for different applications. Carbide is extremely hard and has excellent heat resistance, but it's brittle. It does not flex. Under shock loading, lateral deflection, or chip packing in a deep hole, carbide snaps where HSS would bend. A solid carbide drill in the wrong application fails suddenly and expensively.

Carbide is the right choice when:

• Drilling hardened materials above 45 HRC where HSS and cobalt can't maintain their edge
• High-production CNC drilling where the cycle count per bit needs to be very high and the setup is rigid and well-supported
• Abrasive materials — carbon fiber composite (CFRP), fiberglass (G10/FR4), and ceramics that would rapidly erode steel
• Micro-drilling (very small diameters where the rigidity of carbide helps maintain straightness)

For job shop variety work — different materials, different setups, manual machines or older CNCs — carbide is frequently the wrong answer even when a machinist reaches for it instinctively. The brittleness risk is real. A drill press with any runout, a vise that shifts at entry, or a deep hole with chip packing can all snap a carbide bit that HSS would have survived.

Solid carbide also costs 8 to 15 times what HSS costs. Resharpening carbide is possible but requires diamond grinding wheels and specialized equipment — typically not something a shop does in-house or sends to a general resharpening service.

The Practical Default for Most Job Shops

Keep quality M2 HSS in the standard sizes you use most. Keep M42 cobalt in the sizes you regularly use in stainless or tool steel. Reserve solid carbide for specific high-production or hard-material applications where you've confirmed it's needed.

The most common mistake is buying cheap HSS, having poor results, and attributing the problem to HSS as a material rather than to the specific import steel being used. Buy name-brand HSS first. Run it correctly at appropriate speeds with good cutting fluid. That fixes most problems before any material upgrade is needed.