M2 vs M35 vs ASP2030:
Which HSS Grade Do You Need?

What Is High-Speed Steel?

High-speed steel is a family of tool steels alloyed with tungsten, molybdenum, chromium, vanadium, and — in some grades — cobalt. The key property that makes HSS suitable for cutting tools is hot hardness: the ability to retain hardness at elevated temperatures generated during cutting.

Conventional carbon steel softens above ~200°C. HSS retains its hardness up to 600°C or more, depending on grade. This is why HSS broaches can cut at production speeds without losing their edge.

For broaching specifically, toughness matters as much as hardness. A broach tooth takes a full chip load with each stroke — the tool cannot flex or vibrate away. It must be hard enough to resist wear and tough enough not to chip.

The Three Grades: A Quick Overview

M2: The Standard Grade

M2 is the most widely used HSS grade in the world for cutting tools including drills, taps, end mills, and broaches. Its composition — roughly 6% tungsten, 5% molybdenum, 4% chromium, 2% vanadium — gives a well-balanced combination of hardness, toughness, and grindability.

When M2 is the right choice

• Broaching mild steel, low-alloy steel, and free-machining steels up to approximately 30 HRC
• Broaching cast iron, aluminium, brass, and bronze — all materials where heat generation is low
• Low to medium production volumes where tool cost per part is less critical
• Applications where the workpiece material is well within standard machinability ratings

Limitations of M2

• Hot hardness drops faster than cobalt grades — not ideal for high cutting speeds
• Wears faster on stainless steel (work-hardening), titanium, and high-alloy steels
• Carbide distribution in conventionally cast M2 is less uniform than PM grades, limiting grindability at high hardness

M35: Cobalt Grade for Harder Materials

M35 is essentially M2 with 5% cobalt (Co) added to the composition. Cobalt raises the solidus temperature of the matrix, allowing the steel to retain hardness at significantly higher cutting temperatures. The result is noticeably better wear resistance on hard or abrasive workpiece materials.

What cobalt actually does

Cobalt does not form carbides — it dissolves in the iron matrix and raises its hot hardness. This means M35 does not become significantly harder at room temperature than M2 (only 1–2 HRC more), but it holds its hardness much better as temperature rises during cutting. In stainless steel broaching, for example, the work-hardening effect generates considerable heat: M35 handles this far better than M2.

When M35 is the right choice

• Broaching stainless steel (austenitic grades like 304, 316) — the most common reason to upgrade from M2
• Broaching alloy steels above 35 HRC, including 4140, 4340, EN24
• Higher cutting speeds where more heat is generated at the tool tip
• Production environments where longer tool life directly reduces changeover cost
• Nickel-base superalloys in lighter cutting conditions

Limitations of M35

• Cobalt slightly reduces toughness — M35 is marginally more brittle than M2, though this rarely matters in broaching (which is a controlled-force operation)
• Higher cost — typically 1.5–2× the price of equivalent M2 tools
• Not sufficient for titanium alloys, Inconel, or hardened steels above ~42 HRC — PM grades are needed here

ASP2030: Powder Metallurgy HSS

ASP2030 (manufactured by Erasteel) is a powder metallurgy high-speed steel (PM-HSS). The "PM" process — atomising molten steel into fine powder and sintering it under pressure — produces a microstructure with extremely fine, uniformly distributed carbides. This is fundamentally different from conventionally cast HSS, where larger carbides can cluster unevenly.

Why PM microstructure matters for broaches

In a conventional HSS broach, carbide clusters act as stress risers. Under the intermittent high loads of broaching, micro-chipping initiates at these clusters. In ASP2030, the uniform fine carbide distribution means the tool edge stays sharp and resists chipping far longer. This is why PM-HSS tools can be ground to sharper edges without edge collapse.

ASP2030's composition — higher vanadium and cobalt content than M35 — also delivers both high wear resistance (from vanadium carbides) and high hot hardness (from cobalt), a combination not achievable in conventional HSS.

When ASP2030 is the right choice

• Broaching hardened steels above 40–45 HRC
• Broaching titanium alloys (Ti-6Al-4V and similar) — extremely abrasive, poor thermal conductivity
• Broaching Inconel, Hastelloy, and other nickel superalloys used in aerospace
• High-volume production where tool change frequency must be minimised — the higher cost is offset by dramatically longer tool life
• Applications requiring tight, consistent tolerances over a very long run — PM-HSS holds its geometry longer

Limitations of ASP2030

• Cost — typically 4–6× more than M2 equivalent. Only justified when workpiece material or production demands it
• Requires premium grinding wheels and careful heat treatment to realise the performance advantage
• For soft materials (mild steel, aluminium), the advantage over M2 is minimal — an expensive solution to a non-existent problem

Side-by-Side Comparison

A Note on TiN and TiAlN Coatings

Many broaches — particularly M2 and M35 — are available with physical vapour deposition (PVD) coatings such as TiN (Titanium Nitride) or TiAlN (Titanium Aluminium Nitride). These coatings add a thin hard layer (typically 2–4 microns) that reduces friction, resists oxidation, and extends tool life.

A TiN-coated M2 broach can perform comparably to an uncoated M35 in many stainless steel applications, at a lower cost. TiAlN coating pushes performance further, particularly at higher cutting temperatures.

Coatings should be considered before jumping to a more expensive grade. The right decision tree is: correct grade first, then consider coating. Coating does not fix a grade that is fundamentally wrong for the material.

Frequently Asked Questions

Conclusion

Selecting the right HSS grade for your broach is not complicated once you know the material you are cutting and your production volume. Start with M2 for standard materials — it covers the majority of broaching applications and is the most cost-effective choice. Move to M35 when stainless steel, higher-alloy steels, or faster production speeds are involved. Specify ASP2030 when you are dealing with hardened steels, titanium, or aerospace superalloys where conventional HSS simply cannot keep up.

If you are unsure which grade is right for your specific application, SK Broach's technical team can advise based on workpiece material, tolerance requirements, and production volume. We manufacture keyway broaches, spline broaches, serration broaches, and surface broaches in M2, M35, and ASP2030 grades to order.