M35 high-speed steel is a widely used cobalt-containing high-speed steel, classified under the American AISI standard. It is valued for its balanced combination of hardness, wear resistance, and toughness, making it a preferred material in various industrial cutting and tooling applications.
The chemical composition of M35 high-speed steel is carefully formulated to enhance its performance, with key elements and their ranges as follows:
Carbon (C): 0.85~0.95% (improves hardness and wear resistance by forming carbides).
Silicon (Si): ≤0.40% (aids in deoxidation during smelting and enhances strength).
Manganese (Mn): ≤0.40% (improves hardenability and reduces brittleness).
Phosphorus (P): ≤0.030% (strictly controlled to avoid brittleness).
Sulfur (S): ≤0.030% (minimized to prevent reduced toughness).
Chromium (Cr): 3.75~4.50% (enhances corrosion resistance and forms wear-resistant carbides).
Vanadium (V): 1.75~2.25% (forms hard vanadium carbides to boost wear resistance).
Tungsten (W): 5.00~6.00% (improves red hardness and high-temperature strength).
Molybdenum (Mo): 4.50~5.50% (works with tungsten to enhance heat resistance and toughness).
Cobalt (Co): 4.50~5.50% (a critical alloying element that significantly improves red hardness and high-temperature performance).
2. Core Performance Characteristics
M35 high-speed steel stands out due to its well-rounded properties, making it suitable for demanding industrial environments:
High Hardness: After proper heat treatment, its hardness reaches 64~66 HRC, ensuring excellent cutting and wear resistance for long-term use.
Superior Red Hardness: It maintains a hardness of over HRC 58 at 600°C, allowing it to retain cutting performance even under prolonged high-temperature conditions (e.g., continuous heavy cutting).
Balanced Toughness: Compared to higher cobalt grades (e.g., M42), M35 offers better impact toughness, reducing the risk of chipping or breaking during intermittent cutting or heavy loads.
Good Wear Resistance: The uniform distribution of fine carbides (tungsten, vanadium, and chromium carbides) ensures resistance to abrasive wear, extending tool lifespan.
Machinability: It can be machined via grinding, milling, and turning in the annealed state, facilitating the production of complex tool shapes.
3. Heat Treatment Process
Proper heat treatment is crucial to unlock M35’s optimal performance. The standard process includes:
Annealing: Heat to 820~860°C, hold for 2~4 hours, then furnace cool to 500°C at a rate of 10~20°C/h, followed by air cooling. Annealed hardness is ≤255 HBW, ensuring ease of machining.
Preheating: Two-stage preheating is recommended: first to 600~650°C, then to 800~850°C, to reduce thermal stress and ensure uniform heating.
Quenching: Heat to 1180~1200°C, hold for 10~15 minutes (depending on workpiece size), then quench in oil or air. This step forms a martensitic structure for high hardness.
Tempering: Temper at 540~560°C for 2~3 hours, repeating the process 2~3 times to eliminate residual stress and stabilize the structure. Final hardness is adjusted to 64~66 HRC.
4. Typical Applications
M35 high-speed steel is widely used in manufacturing cutting tools and wear-resistant components across industries:
Cutting Tools: Ideal for producing high-performance tools such as drills, milling cutters, taps, reamers, and gear hobs. It excels in machining alloy steels, high-strength steels, and cast irons.
Heavy-Duty Machining: Suitable for continuous or interrupted cutting operations, including high-speed milling and turning of tough materials.
Tooling for Medium-Difficulty Materials: Performs well with materials that require a balance of hardness and toughness, such as stainless steels and heat-resistant alloys (though not as effective as M42 for extreme high-temperature applications).
Industrial Wear Parts: Used in manufacturing precision wear-resistant components like die-casting molds and high-stress bearings.
5. Advantages and Limitations
Advantages: Offers a cost-effective balance of red hardness, toughness, and wear resistance compared to higher cobalt steels; widely available and easy to process.
Limitations: Red hardness is lower than M42 (high-cobalt grade), making it less suitable for continuous cutting of ultra-high-temperature alloys or at extremely high speeds.
M35 high-speed steel remains a reliable choice in metalworking and manufacturing, valued for its versatility and performance in medium to heavy-duty applications. Its balanced properties make it a staple in tooling industries worldwide.