4140 - Chromium-Molybdenum Alloy Steel

Hardness & Properties

Hardness (heat treated): Up to 50-55 HRC (Rockwell C)

Tensile Strength: 655-1000 MPa (depending on heat treatment)

Yield Strength: 415-930 MPa (depending on heat treatment)

Material Type: Low-Alloy Chromium-Molybdenum Steel

Typical Thickness Range: 6mm - 200mm

Chemical Composition

Carbon (C): 0.38-0.43%

Chromium (Cr): 0.80-1.10%

Molybdenum (Mo): 0.15-0.25%

Manganese (Mn): 0.75-1.00%

Silicon (Si): 0.15-0.35%

Key Characteristics

• High toughness and fatigue resistance - Excellent impact properties
• Better wear resistance than 1045 - Superior performance in wear applications
• Excellent hardenability - Can be through-hardened in thick sections
• Good strength-to-weight ratio - Allows optimized designs
• Moderate formability - Can be formed in annealed condition

Applications

• Wear bars and tool components
• High-load sliding parts
• Construction machinery components
• Heavy-duty shafts and gears
• Hydraulic cylinder rods
• Axles and spindles
• Wear-resistant machine parts
• Mining equipment components

Heat Treatment

Annealing: Heat to 815-845°C, furnace cool. Produces soft, machinable structure.

Normalizing: Heat to 870-900°C, air cool. Refines grain structure.

Hardening: Austenitize at 830-870°C, quench in oil. Achieves maximum hardness.

Tempering: Reheat to 205-650°C depending on desired hardness/toughness balance. Lower tempering temperatures give higher hardness.

Typical Heat Treatment: Quench from 845°C in oil, temper at 540-650°C for 28-32 HRC, or at 205-315°C for 50-55 HRC.

Advantages

• Superior toughness - Excellent impact resistance even when hardened
• High wear resistance - Better than carbon steels
• Excellent hardenability - Through-hardens in thick sections
• Good fatigue resistance - Suitable for cyclic loading
• Versatile - Can be used in various heat-treated conditions

Processing Characteristics

Cutting: Can be cut in annealed condition using standard methods. More difficult when hardened.

Forming: Moderate formability in annealed condition. Should be heat treated after forming.

Welding: Weldable but requires preheat (200-400°C depending on thickness) and post-weld heat treatment for critical applications.

Machining: Good machinability in annealed condition. Difficult to machine when hardened - grinding preferred.

Comparison with Other Grades

vs. 1045: 4140 offers better hardenability, toughness, and wear resistance but at higher cost.

vs. AR400: AR400 offers higher surface hardness, but 4140 provides better through-hardening and toughness.

vs. 4340: 4340 offers higher toughness due to nickel content, but 4140 is more cost-effective.

Best for: Heavy-duty wear components requiring excellent toughness, fatigue resistance, and moderate to high wear resistance.