42crmo4 Steel | 1.7225

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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 Composition¹

2. 42CrMo4 Steel Equivalent Grades

• 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.

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4. Mechanical Properties

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. Applications

• 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), and cold heading dies.
• Other: Large volume gas cylinders and components requiring high fatigue strength.

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

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