What Are Cobalt Drill Bits Made Of? | The Alloy Truth

Cobalt drill bits are high-speed steel alloyed with 5% to 8% cobalt, which lets them cut hard metals without overheating.

If you’ve ever watched a cheap bit glow red while drilling stainless steel, you know the frustration. The reason cobalt bits handle that abuse is hiding inside the metal itself, not on the surface. What Are Cobalt Drill Bits Made Of comes down to one thing: a steel alloy with cobalt mixed through it, giving the cutting edge a heat resistance ordinary HSS simply lacks.

What Exactly Is A Cobalt Drill Bit?

A cobalt drill bit is not pure cobalt. It’s a high-speed steel (HSS) bit with cobalt blended into the alloy during manufacturing. This matters because some cheap “cobalt” bits are actually titanium-coated — a surface treatment that wears off. True cobalt bits have the element throughout the metal, so the heat resistance lasts as long as the bit does.

The two most common grades are M35, which contains about 5% cobalt, and M42, which contains about 8%. The higher the cobalt content, the better the bit holds up to friction heat, a property machinists call red hardness.

Why Cobalt Makes The Difference In Hard Metals

When you drill stainless steel or cast iron, friction generates intense heat at the cutting edge. Standard HSS bits soften once they get hot, which is why they dull fast on tough jobs. Cobalt raises the temperature at which the steel loses its hardness, so the edge stays sharp longer under load.

This is the core reason shop pros reach for them. As HowStuffWorks explains, the cobalt content is what separates these bits from standard HSS, letting them chew through materials that would wreck a cheaper tool. Kennametal’s engineering team similarly notes that the alloy’s heat resistance is the defining trait when comparing drill types.

How To Spot A Real Cobalt Bit

Before you buy, check the labeling. Reputable brands mark true cobalt bits clearly. Look for one of these codes on the shank or the package:

• M35 — about 5% cobalt, a solid all-rounder for stainless and hardened steel.
• M42 — about 8% cobalt, the premium choice for the toughest jobs.
• HSS-Co or HSS CO8 — explicit labels meaning cobalt is in the alloy, not just painted on.

If the label just says “cobalt” with no grade, treat it with suspicion. Titanium nitride bits are often sold with cobalt branding, but that coating is only a few microns thick and will not give you the same longevity.

Are Cobalt Drill Bits Safe To Handle?

Yes. While the raw powdered metals used in manufacturing can contain toxic components, OSHA’s interpretation treats the finished drill bit as an article — a solid, stable form considered nontoxic to the end user. The same safety logic applies to any hardened steel tool you’d hold in your hand. Use common sense, keep them away from heat that could release fumes, and they’re as safe as any other drill bit.

If you’re ready to upgrade your kit, our tested roundup of the best cobalt drill bits compares the top M35 and M42 models side by side.

The takeaway is simple. A cobalt drill bit is a high-speed steel tool with 5% to 8% cobalt fused into the alloy, built to survive the heat of hard-metal drilling. Check for the M35 or M42 grade on the label, and you’ll know you’re getting the real thing, not a coated imitation.