Understanding HSS Drill Grades: W1, M1, M2, M7, M42

High-Speed Steel is not a single material — it is a family of alloy steels with a wide range of compositions and performance characteristics. The letter-number designations (M2, M42, etc.) follow AISI classification and indicate specific alloying element percentages. Understanding what separates the grades lets you choose appropriately for your application and understand why one grade fails where another succeeds.

What Makes Steel "High Speed"

High-speed steels retain their hardness at elevated temperatures — a property called red hardness or hot hardness. Carbon steel cutting tools soften and lose their edge when they reach temperatures above roughly 400°F. HSS maintains cutting hardness up to 900-1000°F, which is why it can run at the surface speeds that earn the "high speed" name compared to carbon steel predecessors.

This temperature resistance comes from alloying elements — primarily tungsten, molybdenum, chromium, vanadium, and cobalt — that form hard carbides within the steel matrix. These carbides resist dissolution at cutting temperatures and prevent the underlying steel from softening. The specific balance of these elements determines the grade designation and the performance profile.

W1 — Water-Hardening Tool Steel

W1 is technically not a high-speed steel by modern classification — it is a plain carbon tool steel. Listed here because it appears in older tool catalogs and represents the starting point the HSS grades improved upon. W1 is approximately 1.0% carbon with minimal alloying. It hardens well but has almost no red hardness — above 300°F it rapidly loses edge retention. W1 is appropriate only for low-speed hand tool applications (files, chisels, some hand-turned lathe tools) and should never be used in powered drilling applications at production speeds.

M1 — Molybdenum HSS

M1 was developed as a lower-cost alternative to tungsten-based T-series HSS, using molybdenum as the primary alloying element. Composition is approximately 8% Mo, 1.5% W, 4% Cr, 1% V, with 0.80% carbon. M1 provides good toughness and decent red hardness, making it suitable for general-purpose drilling in carbon steels and aluminum at moderate speeds. It is not commonly sold as a premium grade today — M2 displaced it in most catalogs — but M1-grade drills remain in use and perform adequately in non-demanding applications.

M2 — The Industry Standard

M2 is the most widely used HSS grade in the world and the grade meant when a drill is sold without further specification. Composition: approximately 6% W, 5% Mo, 4% Cr, 2% V, 0.85% carbon. This balanced composition provides a good combination of hardness (63-65 HRC), toughness (resistance to chipping and breakage), and red hardness. M2 drills perform well in carbon steels, alloy steels, cast iron, aluminum, and most non-ferrous metals at standard production speeds.

M2 is the right choice for the vast majority of machining applications. Upgrading to a higher grade is justified only when M2 is demonstrably failing — either losing its edge too quickly in the target material or chipping due to hardness requirements beyond M2 range.

M7 — High-Vanadium for Abrasive Materials

M7 increases the vanadium content to approximately 2% compared to M2, with a composition of roughly 1.75% W, 8.75% Mo, 4% Cr, 2% V, 1% carbon. The higher vanadium content creates more vanadium carbides, which are extremely hard and resist abrasive wear. M7 excels in abrasive materials — fiberglass, plastics with abrasive fillers, certain cast irons — where the wear mechanism is primarily abrasion rather than thermal softening. It is slightly less tough than M2, so it is not the best choice for interrupted cuts or hard-spot impacts.

M42 — Cobalt for Heat Resistance

M42 adds 8% cobalt to a base similar to M2, along with higher overall alloying content. The composition is approximately 1.5% W, 9.5% Mo, 3.75% Cr, 1.15% V, 8% Co, 1.08% carbon. Cobalt significantly increases red hardness — M42 maintains cutting hardness at temperatures 100-150°F higher than M2. This translates to longer tool life in difficult materials: stainless steel, titanium, Inconel, hardened steel above 35 HRC.

M42 drills cost significantly more than M2 and are more brittle — they chip more easily under shock loading or interrupted cuts in hard materials. The correct application for M42 is continuous cutting in heat-generating materials where thermal softening is the primary failure mode. Using M42 in a situation where M2 chipping was the problem will not help — and may make breakage worse due to the increased brittleness.

When a machinist says "cobalt drill," they almost always mean M42 or a similar high-cobalt grade. This is the appropriate upgrade when M2 is losing its edge too quickly in stainless or high-temperature alloys — not a universal upgrade for all applications.

Choosing the Right Grade

Start with M2 for all standard work. Move to M42 when M2 is failing due to heat in stainless, titanium, or hardened steel. Consider M7 for abrasive non-metallic materials. Avoid W1 in powered applications. The grade of the drill matters, but sharpness matters more at any grade — a sharp M2 outperforms a dull M42 in every meaningful metric.