42crmo4 steel​

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42CrMo4 steel is a widely used medium-carbon low-alloy steel, often considered a standard against which other ultrahigh-strength steels are compared. It is known for its deep hardenability, high strength, and good toughness.

1. 42CrMo4 Steel Composition

CSiMnPSCrMoNiV
0.38-0.450.17-0.370.50-0.800.035 max0.035 max0.90-1.200.15-0.250.30 max0.06 max

Reference: ASM International. (1991). ASM Handbook, Volume 4: Heat Treating (p. 700). ASM International.

2. 42CrMo4 Steel Equivalent Standards

42CrMo4 is recognized internationally under various designations. Understanding these equivalents is crucial for sourcing and specification:

  • EN: 42CrMo4 (Material No.: 1.7225)
  • ISO: 42CrMo4
  • ASTM/AISI (USA): 4140 (G41400) and 4142 (G41420)
  • JIS (Japan): SCM440 / SCM445
  • GOST (Russia): 38XM
  • DIN (Germany): 42CrMo4
  • BS (UK):  42CrMo4 / 708M40
  • NF (France): 42CrMo4
  • GB/T (China): 42CrMo (A30422) / 42CrMoH (A30425)

3. Heat Treatment of 42CrMo4 Steel

42CrMo4 steel is a heat-treatable material, and its properties are highly dependent on the specific heat treatment process. It can be supplied in a pre-hardened state.

  • 42CrMo4 QT (Quenching & Tempering). The standard quenching and tempering process includes heating to 850-870°C, oil quenching, and then tempering at 500-600°C for 2 hours to obtain a hardness of 28-35 HRC.
  • Annealing. Hold at 830-850°C for 3-4 hours, then cool in the furnace to 500°C, followed by air cooling, resulting in a final hardness of ≤217 HBW. For softening annealing, heating to 740-800°C, cooling in the furnace at 15°C/h to 550°C, then air cooling.
  • Normalizing. Hold at 870-880°C for 1-2 hours, then cool naturally, resulting in a final hardness of ≤255 HBW.
  • High-temperature tempering. Temper at 680-700°C for 2-3 hours, then cool in the furnace to 500°C, followed by air cooling, resulting in a final hardness of ≤217 HBW.
  • Stress Relief Treatment. After rough machining, it is recommended to heat to 530°C, hold for 2 hours, and then cool in air.
42CrMo4 Steel

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4. 42CrMo4 Steel Mechanical Properties (Quenched and Tempered Condition)

In the quenched and tempered (Q+T) state, 42CrMo4 delivers excellent mechanical performance. Typical values after oil quenching (850°C) and tempering (580°C) can include:

  • Tensile Strength (Rm): ≥ 1100 MPa
  • Yield Strength (ReL): ≥ 950 MPa
  • Elongation (A): ≥ 12%
  • Impact Toughness (KV/KU or aK): Values depend on test method, but good toughness is characteristic (e.g., ≥ 80 J/cm²).

Remember, final properties depend directly on the specific heat treatment parameters used.

5. Common Applications

The combination of strength, toughness, and wear resistance makes 42CrMo4 suitable for a wide range of demanding components:

  • Machine Building: Highly stressed parts like gears, shafts, axles, connecting rods, crankshafts, and high-strength bolts.
  • Tooling: Large and medium-sized plastic molds, mold frames, forging dies (depending on application demands), cold heading dies.
  • Other: Large volume gas cylinders and components requiring high fatigue strength.
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