AISI M35 High Speed Steel: A Guide to Properties, Uses & Performance

If you’re dealing with high-temperature, high-speed cutting tasks—like machining hard alloys in aerospace or heavy-duty metalworking—AISI M35 high speed steel is a game-changer. As a cobalt-alloyed high-speed steel, it delivers superior red hardness (heat resistance) and wear resistance compared to standard grades like AISI M2. In this guide, we’ll break down its key properties, real-world applications, manufacturing process, and how it stacks up against other materials. By the end, you’ll know if it’s the right fit for your high-demand cutting needs.

1. Material Properties of AISI M35 High Speed Steel

AISI M35’s exceptional performance comes from its unique chemical composition—especially the addition of cobalt—and optimized properties. Let’s explore each category in practical terms:

Chemical Composition

The alloying elements in AISI M35 work together to boost heat resistance, wear resistance, and strength. Here’s a typical breakdown and their roles:

Physical Properties

These traits describe how AISI M35 behaves in high-speed, high-heat cutting environments:

• Density: ~8.15 g/cm³ (slightly higher than M2—due to cobalt content).
• Thermal conductivity: ~24 W/(m·K) (lower than structural steels—helps retain hardness at high heat).
• Thermal expansion coefficient: ~11.0 × 10⁻⁶/°C (minimizes warping when heated, keeping cutting tools precise).
• Specific heat capacity: ~455 J/(kg·K) (absorbs heat evenly, reducing thermal stress on the tool).
• Magnetic properties: Ferromagnetic (works with magnetic tool holders in CNC machining centers).

Mechanical Properties

AISI M35’s mechanical traits are tailored for extreme cutting conditions. Here’s what matters most:

• Tensile strength: ≥ 2,800 MPa (after heat treatment)—strong enough to handle heavy cutting forces on hard metals.
• Yield strength: ≥ 2,300 MPa (resists permanent deformation, so tools keep their sharp edge).
• Hardness: 62–66 HRC (Rockwell), ~680–730 HV (Vickers), ~630–680 HBW (Brinell)—harder than M2, ideal for cutting hard alloys.
• Impact toughness: ~12–20 J (at room temperature)—moderate (less than M2, but better than carbides).
• Fatigue strength: ~1,050 MPa (resists damage from repeated cutting cycles—perfect for high-volume machining).
• Wear resistance: Very excellent—50% better than M2 (thanks to cobalt and enhanced carbide formation).

Other Properties

• Corrosion resistance: Low—rusts easily in wet conditions (use oiling or coating for storage; avoid wet cutting without protection).
• Hardenability: Excellent—hardens evenly even in thick tool sections (ideal for large milling cutters or broaches).
• Red hardness (hot hardness): Exceptional—retains 90% of its hardness at 620°C (10–15% better than M2).
• Dimensional stability: High—minimal shrinkage after heat treatment (critical for precision tools like reamers).
• Machinability: Moderate—requires carbide tools for fully heat-treated M35; annealed M35 (220–260 HBW) is easier to machine than fully hardened M35.

2. Applications of AISI M35 High Speed Steel

AISI M35’s superior red hardness and wear resistance make it ideal for extreme cutting tasks across industries. Here are its most common uses:

Metalworking Industry

It’s the top choice for cutting hard metals at high speeds:

• Cutting tools: Lathe tools (for turning stainless steel, alloy steel, or tool steel at high RPM), milling cutters (for heavy-duty CNC machining), and broaches (for creating precise slots in hard alloys).
• Lathe tools: Handle cutting speeds up to 180 m/min for hard steel—stay sharp 1.5x longer than M2.
• Milling cutters: Used in high-power CNC machines for machining thick, hard metal parts—maintain performance even when generating high heat.
• Reamers: Create precise holes in hard metals like titanium or Inconel—retain accuracy for hundreds of cuts.

Automotive Industry

It’s used for high-wear, high-temperature tooling:

• Stamping dies: High-speed stamping dies for hard steel sheets (like automotive chassis parts)—resist wear from repeated impacts.
• Punches: High-speed punches for creating holes in thick, hard metal components (like engine blocks)—stay sharp during high-volume production.
• Dies for forging: Hot forging dies for small, hard automotive parts (like gear teeth)—retain strength at high forging temperatures.

General Engineering

It’s perfect for heavy-duty cutting tools:

• Cold work tools: High-speed cold forming tools (for shaping thick, hard metal sheets into brackets)—resist wear from pressure.
• Cold forming tools: Tools for making precision parts like high-strength bolts at high speeds—maintain shape during thousands of cycles.
• Cold extrusion tools: Extrusion dies for hard metals (like stainless steel)—handle high speeds without dulling.

Aerospace Industry

Its precision and heat resistance work for high-tech machining:

• High-precision cutting tools: Tools for machining titanium or nickel-based superalloys (like aircraft engine parts)—require extreme heat resistance and accuracy.
• Specialized machining tools: Custom tools for complex aerospace components (like turbine blades)—maintain sharpness during high-speed, high-temperature cutting.

3. Manufacturing Techniques for AISI M35 High Speed Steel

Producing AISI M35 requires precision to preserve its cobalt-enhanced properties. Here’s the process:

1. Steelmaking Process

• Electric Arc Furnace (EAF): The most common method. Scrap steel is melted in an EAF, and alloying elements (W, Mo, Cr, V, Co) are added in precise amounts to reach M35’s composition.
• Basic Oxygen Furnace (BOF): Rare for M35—used only for large-scale production of high-quality cobalt-alloyed steels.

2. Rolling and Forging

• Hot rolling: The steel is heated to ~1,100–1,150°C and rolled into bars, rods, or sheets (the starting shape for tools).
• Cold rolling: Optional for thin rods—smoothes the surface and increases hardness slightly (used for small tools like drill bits).
• Drop forging: Uses a hammer to shape hot steel into tool blanks (like milling cutter bodies)—improves strength by aligning grain structure.
• Press forging: Uses a hydraulic press to create precise shapes (for complex tools like broaches)—ensures uniform density and cobalt distribution.

3. Heat Treatment

Heat treatment is critical to unlock M35’s red hardness. The typical process is:

• Annealing: Heat to 850–900°C and cool slowly—softens to 220–260 HBW for easy machining.
• Austenitizing: Heat to 1,200–1,240°C (slightly higher than M2) and hold for 1–2 hours—converts the structure to austenite for hardening.
• Quenching: Cool in oil or air (air quenching for small tools)—creates a hard, martensitic structure with enhanced red hardness.
• Tempering: Reheat to 550–590°C and hold for 2–3 hours (done twice)—reduces brittleness and locks in cobalt-boosted heat resistance.
• Cryogenic treatment: Optional (cool to -80 to -196°C after quenching)—eliminates retained austenite, further boosting hardness and wear resistance.

4. Surface Treatment

• Grinding: Uses precision abrasive wheels to shape tools to exact dimensions (e.g., sharpening milling cutters or reamers).
• Polishing: Creates a smooth surface (critical for high-precision tools—reduces friction during cutting).
• Coating: Options include titanium nitride (TiN) or diamond-like carbon (DLC)—boost wear resistance by 40–60% (ideal for high-volume, high-temperature cutting).

5. Quality Control

Every batch of M35 is tested to meet strict high-speed steel standards:

• Chemical analysis: Uses spectrometry to check cobalt, tungsten, and vanadium levels (ensures it matches M35’s specs).
• Mechanical testing: Includes hardness tests (to verify HRC), impact tests (for toughness), and high-temperature hardness tests (to check red hardness).
• Non-destructive testing (NDT): Uses ultrasonic testing to find hidden cracks (critical for high-speed tools that face extreme forces).

4. Case Studies: AISI M35 High Speed Steel in Action

Real-world examples show how M35 solves extreme cutting problems. Here are four detailed cases:

Case Study 1: Metalworking Milling Cutters for Hard Alloys

Application Background: A U.S. metalworking shop used AISI M2 milling cutters to machine stainless steel parts. The cutters dulled after 200 parts, requiring sharpening ($120/sharpen, 12 sharpenings/month). Performance Improvement: Switched to AISI M35 cutters (coated with TiN). The cutters lasted 500 parts—2.5x longer. Cost-Benefit Analysis: Monthly sharpening costs dropped to $480 (from $1,440), saving $11,520/year. Machining time fell by 20% (fewer tool changes), allowing the shop to take on more orders.

Case Study 2: Automotive Stamping Dies for Hard Steel

Application Background: A European automotive supplier used AISI D2 dies for high-speed stamping of thick steel sheets. The dies wore out after 30,000 cycles, costing $6,000/die and 3 days of downtime. Performance Improvement: Switched to AISI M35 dies. The dies lasted 80,000 cycles—2.7x longer. Cost-Benefit Analysis: Annual die costs dropped to $22,500 (from $60,000), saving $37,500/year. Downtime fell by 60%, reducing production delays.

Case Study 3: General Engineering Cold Forming Tools

Application Background: A Canadian engineering firm used AISI A2 tools for cold forming high-strength steel brackets. The tools dulled after 8,000 cycles, requiring replacement ($900/tool, 10 replacements/year). Performance Improvement: Switched to AISI M35 tools. The tools lasted 22,000 cycles—2.8x longer. Cost-Benefit Analysis: Annual tool costs dropped to $4,091 (from $9,000), saving $4,909/year. The brackets also had better precision, reducing scrap by 8%.

Case Study 4: Aerospace Machining Tools for Titanium

Application Background: An aerospace manufacturer used carbide tools to machine titanium engine parts. The tools were expensive ($600/tool) and brittle (cracked after 100 parts). Performance Improvement: Switched to AISI M35 tools (coated with DLC). The tools lasted 300 parts—3x longer—with no cracking. Cost-Benefit Analysis: Annual tool costs dropped to $8,000 (from $24,000), saving $16,000/year. The tools also handled complex cuts better than carbides.

5. AISI M35 High Speed Steel vs. Other Materials

How does AISI M35 compare to other high-speed steels and non-steels? Let’s use data:

Comparison with Other High-Speed Steels

AISI M35 is a premium high-speed steel—here’s how it stacks up against similar grades:

Comparison with Non-Steel Materials

AISI M35 outperforms non-steels in toughness and heat resistance—here’s how it compares:

Key Takeaway: AISI M35 is the top choice for high-temperature, hard alloy cutting. It’s tougher than carbides/ceramics, has better red hardness than M2/T1, and is more affordable than premium grades like M42.

Yigu Technology’s Perspective on AISI M35 High Speed Steel

At Yigu Technology, we recommend AISI M35 to clients dealing with hard alloys or high-temperature cutting—like aerospace manufacturers or heavy-duty metalworking shops. Its cobalt-enhanced red hardness solves the problem of frequent tool dulling in extreme conditions. While it’s more expensive than M2, customers see 1.5–3x longer tool life, which offsets the cost quickly. For businesses that can’t afford downtime or poor part quality, M35 is a reliable, high-performance investment that delivers consistent results.

FAQ About AISI M35 High Speed Steel

1. Can AISI M35 be used for cutting non-hard materials like aluminum?
   Yes, but it’s not cost-effective. M35’s strengths (red hardness, wear resistance) are designed for hard metals—for aluminum, use cheaper steels like M2 or O1. Save M35 for hard alloy cutting to maximize value.