Introduction

20MnCr5 is a low-carbon case-hardening alloy steel grade, renowned for its excellent wear resistance, toughness, and core strength after heat treatment. It is particularly suited for producing components requiring a tough core and a hard, wear-resistant surface. The alloy is commonly used in the automotive and mechanical engineering industries where high surface hardness combined with good toughness is essential.

Properties of the Grade:

  • Excellent case hardening properties
  • High core toughness
  • Good fatigue strength
  • Excellent wear resistance after carburizing
  • Good machinability in annealed condition
  • High strength-to-weight ratio
  • Good dimensional stability after heat treatment

Uses/Applications of the Grade:

20MnCr5 is extensively used for:

  • Gears and pinions
  • Shafts
  • Crankshafts
  • Bushings
  • Camshafts
  • Axles
  • Transmission components
  • Gear wheels
  • Sleeves and hubs
  • Automotive and industrial machinery parts

Chemical Composition:

Element Content (%)
Carbon (C) 0.17 – 0.22
Silicon (Si) 0.40 max
Manganese (Mn) 1.10 – 1.40
Chromium (Cr) 0.80 – 1.10
Sulfur (S) 0.035 max
Phosphorus (P) 0.035 max

Mechanical Properties:

(After Carburizing and Hardening)

Property Typical Value
Tensile Strength 1000 – 1300 MPa
Yield Strength 600 – 800 MPa
Elongation ≥ 10%
Impact Value (ISO V-notch) ≥ 40 J
Surface Hardness (after Case Hardening) 58 – 62 HRC
Core Hardness 30 – 45 HRC

Physical Properties:

Property Typical Value
Density 7.85 g/cm³
Modulus of Elasticity 210 GPa
Thermal Conductivity ~ 46 W/m·K
Specific Heat Capacity ~ 460 J/kg·K
Coefficient of Thermal Expansion ~ 11.7 × 10⁻⁶ /°C

Forging:

Forging Temperature Range: 850°C – 1150°C

Forging Procedure:

  • Heat uniformly to 1150°C and forge down to 850°C.
  • Cooling should be done slowly in sand or dry ash to avoid internal stresses.

Heat Treatment:

  1. Annealing:
    • Heat to 630°C – 680°C.
    • Hold and cool slowly in the furnace.
  2. Carburizing:
    • Carburize at 880°C – 950°C to achieve a case depth of 0.8mm to 1.2mm.
  3. Hardening:
    • After carburizing, reheat to 780°C – 820°C.
    • Quench in oil for maximum hardness.
  4. Tempering:
    • Temper immediately after hardening at 150°C – 200°C to relieve internal stresses.
    • Air cooling is recommended.

Dimensional Tolerances:

  • Hot Rolled Bars: As per EN 10060 standard tolerances.
  • Bright Drawn Bars: Tolerances according to ISO h9/h11 standards.
  • Ground Bars: Tight tolerances available up to ISO h6 standard.

Machinability:

  • Good machinability when in the annealed condition.
  • Carbide or high-speed steel tools are recommended for effective machining.
  • Using proper coolant enhances tool life and surface finish.

Corrosion Resistance:

  • 20MnCr5 offers moderate corrosion resistance.
  • For environments prone to corrosion, protective coatings or surface treatments are necessary.
  • Not intended for direct use in highly corrosive environments without treatment.

Weldability:

  • Weldable with proper preheating at 200°C – 300°C.
  • Post-weld heat treatment is recommended to restore mechanical properties.
  • Low hydrogen welding processes (e.g., TIG or MIG) preferred.

Available Form:

20MnCr5 is commonly available in:

  • Hot Rolled Round Bars
  • Peeled and Ground Bars
  • Forged Bars
  • Bright Bars
  • Customized cut-to-size pieces
  • Supplied in annealed or hardened and tempered conditions

Conclusion:

20MnCr5 Alloy Steel Bar is a versatile, low-carbon alloy steel that delivers outstanding performance in case-hardened applications. It provides a strong, tough core and a hard, wear-resistant outer surface ideal for automotive and mechanical components. Its balanced composition, excellent hardenability, and good machinability make it one of the preferred materials for critical, high-performance parts across industries.

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