Introduction

SCM420 is a chromium-molybdenum alloy steel that is widely used for parts that require higher toughness and strength. This steel is known for its good balance of hardness, wear resistance, and machinability. Its chromium and molybdenum content enhance its performance in heavy-duty applications such as gears, shafts, and industrial machinery. SCM420 is a commonly used material in industries that require high strength and durability under tough working conditions.

Properties of the Grade:

  • High strength and toughness: Offers excellent strength under tough working conditions.
  • Good hardenability: Ensures effective heat treatment response for improved mechanical properties.
  • Good machinability: In its annealed condition, SCM420 has good machinability.
  • Good fatigue strength: Suitable for parts that undergo cyclic loading.
  • Wear resistance: Excellent wear resistance when properly heat treated.
  • Good weldability: Suitable for welding with proper preheating and post-weld heat treatment.

Uses/Applications of the Grade:

SCM420 alloy steel is commonly used in the following applications:

  • Automotive parts such as gears, shafts, and connecting rods.
  • Machine components including spindles and bearings.
  • Heavy-duty industrial components like crankshafts and camshafts.
  • Transmission parts such as axles and gears.
  • Tooling components including dies and molds.
  • High-strength structural parts used in aerospace and industrial machinery.
  • Forged components used for high-impact applications.

Chemical Composition:

Element Content (%)
Carbon (C) 0.18 – 0.23
Manganese (Mn) 0.60 – 0.90
Chromium (Cr) 0.90 – 1.20
Molybdenum (Mo) 0.15 – 0.25
Silicon (Si) 0.20 – 0.35
Phosphorus (P) ≤ 0.035
Sulfur (S) ≤ 0.035

Mechanical Properties:

Property Value
Tensile Strength 850 – 1000 MPa
Yield Strength ≥ 600 MPa
Elongation (%) ≥ 10%
Reduction of Area ≥ 30%
Hardness (Annealed) 197 – 241 HB
Hardness (Hardened) 50 – 60 HRC

Physical Properties:

Property Value
Density 7.85 g/cm³
Modulus of Elasticity 210 GPa
Thermal Conductivity 46.6 W/m·K
Specific Heat Capacity 460 J/kg·K
Coefficient of Thermal Expansion 11.1 × 10⁻⁶ /°C

Forging:

Forging Temperature Range: 850°C – 1150°C.

Forging Process Recommendations:

  • Preheat the material uniformly before starting the forging process.
  • Ensure the temperature is maintained above 850°C to prevent cracking.
  • Proper cooling is necessary to avoid internal stresses.

Heat Treatment:

  1. Annealing:

    • Heat to 800°C – 850°C.
    • Cool slowly in the furnace to relieve internal stresses and achieve a soft microstructure.

  2. Hardening:

    • Heat to 850°C – 900°C.
    • Quench in oil to achieve the desired hardness.

  3. Tempering:

    • Temper at 150°C – 200°C for 30 minutes.
    • Adjust the tempering temperature to achieve the desired mechanical properties (hardness vs. toughness).

Dimensional Tolerances:

  • Standard Tolerances: The material typically follows ISO h9 and h11 standards for round bars.
  • Custom tolerances can be provided as per customer requirements.

Machinability:

Machinability in Annealed State: Good machinability.

Recommendations:

  • Carbide tooling is recommended for better efficiency in machining.
  • Ensure appropriate cutting speeds and feeds to optimize tool life and machining quality.
  • Proper lubrication or cooling is recommended to prevent overheating.

Weldability:

Weldability: Good, but requires preheating and post-weld heat treatment to minimize the risk of cracking.

Welding Recommendations:

  • Preheat the material to 150°C – 200°C before welding.
  • After welding, stress relief is essential to ensure mechanical properties are restored.

Corrosion Resistance:

  • Moderate corrosion resistance: SCM420 has good resistance to atmospheric corrosion and mild chemicals.
  • Surface treatments such as coatings, plating, or nitriding are recommended for harsh environments or highly corrosive conditions.

Available Form:

  • Hot Rolled Bars
  • Cold Drawn Bars
  • Peeled and Ground Bars
  • Bright Bars
  • Turned and Polished Bars
  • Forged Bars
  • Cut-to-Length Bars

Conclusion:

SCM420 alloy steel is a versatile material suitable for applications requiring a balance of strength, toughness, and wear resistance. Its excellent hardenability and machinability make it a popular choice in industries such as automotive, aerospace, and manufacturing. With appropriate heat treatment, SCM420 provides high performance under extreme working conditions, making it ideal for gears, shafts, and high-stress machine components. The steel’s moderate weldability and corrosion resistance add to its versatility, offering durable solutions across various applications.

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