M35 High Speed Steel: Properties, Applications, Manufacturing Guide

M35 high speed steel (HSS) is a premium alloy renowned for its exceptional high hot hardness and enhanced strength—traits elevated by its unique chemical composition (including 4.75-5.50% cobalt, a key addition to its M2 steel base). Unlike standard HSS, it retains hardness at temperatures up to 650°C, making it the top choice for high-performance cutting tools, precision forming dies, and critical components in aerospace and automotive industries. In this guide, we’ll break down its key traits, real-world uses, manufacturing processes, and how it compares to other materials, helping you select it for projects that demand extreme durability and high-temperature reliability.

1. Key Material Properties of M35 High Speed Steel

M35’s performance is rooted in its precisely calibrated chemical composition—especially cobalt, which amplifies its mechanical and high-temperature capabilities—shaping its robust properties.

Chemical Composition

M35’s formula builds on M2 steel with cobalt to boost performance, with fixed ranges for key elements:

• Carbon content: 0.85-1.00% (higher than M2, enhancing wear resistance by forming more hard carbides with tungsten/vanadium)
• Chromium content: 3.75-4.25% (forms heat-resistant carbides for additional wear resistance and ensures uniform heat treatment)
• Tungsten content: 5.50-6.75% (core element for high hot hardness—forms carbides that resist softening at 650°C+)
• Molybdenum content: 4.75-5.50% (works with tungsten to boost hot hardness and reduce brittleness)
• Vanadium content: 1.75-2.25% (refines grain size, enhances toughness, and forms vanadium carbides for superior wear resistance)
• Cobalt content: 4.75-5.50% (defining element—strengthens the steel matrix and increases hot hardness, elevating performance above M2)
• Manganese content: 0.20-0.40% (boosts hardenability without creating coarse carbides)
• Silicon content: 0.15-0.35% (aids deoxidation during manufacturing and stabilizes high-temperature performance)
• Phosphorus content: ≤0.03% (strictly controlled to prevent cold brittleness, critical for low-temperature tool storage)
• Sulfur content: ≤0.03% (ultra-low to maintain toughness and avoid cracking during forming or machining)

Physical Properties

Mechanical Properties

After standard heat treatment (annealing + quenching + tempering), M35 delivers industry-leading performance:

• Tensile strength: ~2100-2600 MPa (100-150 MPa higher than M2, ideal for high-cutting-force operations like milling hard alloy steels)
• Yield strength: ~1700-2100 MPa (ensures tools resist permanent deformation under heavy loads)
• Elongation: ~10-15% (in 50 mm—moderate ductility, enough to avoid sudden cracking during machining vibrations)
• Hardness (Rockwell C scale): 63-69 HRC (after heat treatment—adjustable: 63-65 HRC for tough forming tools, 67-69 HRC for wear-resistant cutting tools)
• Fatigue strength: ~850-1050 MPa (at 10⁷ cycles—50-100 MPa higher than M2, perfect for tools under repeated cutting cycles)
• Impact toughness: Moderate to high (~38-48 J/cm² at room temperature)—higher than ceramic tools, reducing chipping risk during use

Other Critical Properties

• Excellent wear resistance: Cobalt-enhanced carbides resist abrasion 15-20% better than M2, ideal for machining hard metals like Inconel or tool steel.
• High hot hardness: Retains ~62 HRC at 650°C (2 HRC higher than M2 at 600°C)—critical for high-speed cutting (e.g., 600+ m/min for aluminum alloys).
• Good toughness: Balanced with hardness, so it withstands minor impacts (e.g., tool-workpiece contact) without breaking.
• Machinability: Good (before heat treatment)—annealed M35 (hardness ~220-250 Brinell) is machinable with carbide tools; avoid machining after hardening (63-69 HRC).
• Weldability: With caution—high carbon and cobalt content increase cracking risk; preheating (350-400°C) and post-weld tempering are required for tool repairs.

2. Real-World Applications of M35 High Speed Steel

M35’s cobalt-boosted performance makes it ideal for high-demand cutting and forming applications. Here are its most common uses:

Cutting Tools

• Milling cutters: End mills for high-speed machining of hard alloys (e.g., Inconel 718) use M35—hot hardness maintains sharpness at 600-650°C, outperforming M2 by 25% in tool life.
• Turning tools: Lathe tools for machining aerospace turbine shafts use M35—wear resistance reduces tool changes, improving production efficiency by 45%.
• Broaches: Internal broaches for shaping high-strength gears use M35—toughness resists chipping, and hot hardness maintains precision over 15,000+ parts.
• Reamers: Precision reamers for tight-tolerance holes (±0.0005 mm) in automotive transmission parts use M35—wear resistance ensures consistent quality over 20,000+ reams.

Case Example: An aerospace machining shop used M2 for milling Inconel turbine blades. The M2 cutters dulled after 150 parts. They switched to M35, and the cutters lasted 225 parts (50% longer)—cutting regrinding time by 40% and saving $24,000 annually.

Forming Tools

• Punches: High-speed punches for stamping thick metal sheets (e.g., 10 mm steel) use M35—excellent wear resistance handles 250,000+ stampings (50,000 more than M2).
• Dies: Cold-forming dies for shaping high-strength bolts use M35—toughness resists pressure, and wear resistance reduces defective parts by 70%.
• Stamping tools: Fine stamping tools for electronics connectors use M35—hardness (67-69 HRC) ensures clean, burr-free cuts.

Aerospace & Automotive Industries

• Aerospace industry: Cutting tools for machining titanium turbine blades use M35—high hot hardness handles 650°C cutting temperatures, which would soften M2.
• Automotive industry: High-speed cutting tools for machining engine blocks (cast iron) use M35—wear resistance reduces tool replacement by 30%, cutting production costs.

Mechanical Engineering

• Gears: Heavy-duty gears for wind turbine gearboxes use M35—wear resistance extends lifespan by 30% vs. M2, reducing maintenance.
• Shafts: Drive shafts for industrial compressors use M35—tensile strength (2100-2600 MPa) withstands high torque, and fatigue strength resists repeated stress.
• Bearings: High-load bearings for mining equipment use M35—wear resistance reduces friction, lowering maintenance frequency by 55%.

3. Manufacturing Techniques for M35 High Speed Steel

Producing M35 requires precision to maintain cobalt balance and optimize performance. Here’s the detailed process:

1. Metallurgical Processes (Composition Control)

• Electric Arc Furnace (EAF): Primary method—scrap steel, tungsten, molybdenum, vanadium, and cobalt are melted at 1,650-1,750°C. Sensors monitor chemical composition to keep cobalt (4.75-5.50%) and other elements within range—critical for hot hardness.
• Basic Oxygen Furnace (BOF): For large-scale production—molten iron is mixed with scrap steel; oxygen adjusts carbon content. Cobalt and other alloys are added post-blowing to avoid oxidation.

2. Rolling Processes

• Hot rolling: Molten alloy is cast into ingots, heated to 1,100-1,200°C, and rolled into bars, plates, or wire. Hot rolling breaks down large carbides and shapes tool blanks (e.g., cutter bodies).
• Cold rolling: Used for thin sheets (e.g., small punch blanks)—cold-rolled at room temperature to improve surface finish. Post-rolling annealing (700-750°C) restores machinability.

3. Heat Treatment (Critical for Cobalt Performance)

• Annealing: Heated to 850-900°C for 2-4 hours, cooled slowly (50°C/hour) to ~600°C. Reduces hardness to 220-250 Brinell, making it machinable.
• Quenching: Heated to 1,220-1,270°C (10-20°C higher than M2) for 30-60 minutes, quenched in oil. Hardens to 67-69 HRC; air quenching reduces distortion but lowers hardness to 63-65 HRC.
• Tempering: Reheated to 520-570°C (20-50°C higher than M2) for 1-2 hours, air-cooled. Balances hot hardness and toughness—critical for cutting tools.
• Stress relief annealing: Mandatory—heated to 600-650°C for 1 hour after machining to reduce stress, preventing cracking during quenching.

4. Forming and Surface Treatment

• Forming methods:
• Press forming: Hydraulic presses (5,000-10,000 tons) shape M35 plates into tool blanks—done before heat treatment.
• Grinding: After heat treatment, diamond wheels refine edges to ±0.0005 mm tolerances (e.g., reamer flutes).
• Machining: CNC mills with carbide tools shape annealed M35 into cutting geometries—coolant prevents overheating.
• Surface treatment:
• Nitriding: Heated to 500-550°C in nitrogen to form a 5-10 μm nitride layer—boosts wear resistance by 30%.
• Coating (PVD/CVD): Titanium aluminum nitride (PVD) coatings reduce friction, extending tool life by 2.5x.
• Hardening: Final heat treatment (quenching + tempering) is sufficient for most applications.

5. Quality Control (Performance Assurance)

• Hardness testing: Rockwell C tests verify post-tempering hardness (63-69 HRC) and hot hardness (≥62 HRC at 650°C).
• Microstructure analysis: Confirms uniform carbide distribution (no large carbides that cause chipping).
• Dimensional inspection: CMMs check tool dimensions for precision (e.g., reamer hole tolerance).
• Wear testing: Simulates high-speed cutting (e.g., machining Inconel at 550 m/min) to measure tool life.
• Tensile testing: Verifies tensile strength (2100-2600 MPa) and yield strength (1700-2100 MPa).

4. Case Study: M35 High Speed Steel in Aerospace Turbine Blade Machining

A major aerospace manufacturer used M2 for machining titanium turbine blades but faced 30% tool failure due to overheating. They switched to M35, with the following results:

• Tool Life: M35 cutters lasted 200 blades (vs. 130 for M2)—40% longer tool life.
• Failure Rate: M35’s hot hardness reduced overheating failures to 8% (from 30%), saving $60,000 annually in wasted materials.
• Cost Savings: Despite M35’s 30% higher upfront cost, the manufacturer saved $190,000 annually via reduced tool changes and waste.

5. M35 High Speed Steel vs. Other Materials

How does M35 compare to M2 and other high-performance materials? Let’s break it down:

Application Suitability

• Aerospace Machining: M35 outperforms M2 (higher hot hardness) for titanium/Inconel—cheaper than M42.
• High-Speed Cutting: M35 balances performance and cost better than M42—ideal for automotive engine machining.
• Precision Forming: M35 is superior to D2 (better toughness) for high-volume stamping—reduces chipping.

Yigu Technology’s View on M35 High Speed Steel

At Yigu Technology, M35 stands out as a high-value solution for extreme machining needs. Its cobalt-enhanced hot hardness and wear resistance make it ideal for aerospace, automotive, and precision engineering clients. We recommend M35 for cutting hard alloys (Inconel, titanium) and high-speed applications—where it outperforms M2 (longer tool life) and offers better value than M42. While costlier upfront, its durability cuts maintenance and replacement costs, aligning with our goal of sustainable, high-performance manufacturing solutions.

FAQ

1. Is M35 high speed steel better than M2 for machining hard alloys?

Yes—M35’s cobalt content boosts hot hardness and wear resistance, making it 15-20% more durable than M2 for hard alloys like Inconel or tool steel. It’s ideal if you need longer tool life for high-demand machining.

2. Can M35 be used for non-ferrous metal machining (e.g., aluminum)?

Yes, but it’s often overspecified. M35 works well for high-speed aluminum machining, but M2 is cheaper and sufficient for most non-ferrous applications. Reserve M35 for hard metals to maximize cost-effectiveness.

3. How does M35 compare to M42 high speed steel?

M42 has slightly higher hot hardness (~64 HRC at 650°C vs. M35’s 62 HRC) but is 40% more expensive and harder to machine. M35 offers better value for most applications—only choose M42 for extreme 650°C+ cutting needs.