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AISI 4140 Alloy Steel CNC Machining Material
AISI 4140 is a low-alloy steel containing Chromium, Molybdenum, and Manganese. It is widely known as "Chromoly" steel and is renowned for its toughness, high fatigue strength, and abrasion and impact resistance. Unlike standard carbon steels, 4140 offers superior depth of hardening and ductility. At JUCHENG, we process 4140 extensively for heavy-duty industrial applications. We machine it in both the Annealed condition (for complex geometries) and the Pre-Hardened (HT) condition (for immediate use), delivering robust components like axles, crankshafts, and gears that withstand extreme stress.
4140 Alloy Steel

JUCHENG's 4140 Machining Capabilities

Handling tough alloy steels requires rigid equipment and smart strategies. We offer:
  • Hard Turning & Milling: We are equipped to machine 4140HT (Pre-hardened to 28-32 HRC) directly, eliminating the need for post-machining heat treatment and grinding for many parts.
  • Heat Treatment Services: For parts machined in the annealed state, we provide oil-quenching and tempering to achieve hardness levels up to 54 HRC.
  • Deep Hole Drilling: 4140 is a standard material for oil & gas components. We have specialized gun-drilling setups for long, straight bores.
  • Surface Finishing: To prevent corrosion, we offer Black Oxide, Zinc Plating, and Nitriding (for increased surface hardness) in-house or through certified partners.
4140 alloy steel

Advantages of CNC Machining 4140

Advantage Detailed Description Key Benefit
High Strength & Toughness Excellent balance of ductility and strength (Tensile > 1000 MPa in HT). Resists failure under high shock loads and twisting forces.
Good Hardenability Deep hardening capability due to Molybdenum content. Ensures uniform strength throughout the part cross-section, not just the surface.
Abrasion Resistance Harder surface resists wear better than mild steels. Ideal for gears, cams, and sliding surfaces.
Machinability Good machinability in the annealed state; fair in the pre-hardened state. Allows for the production of complex shapes before final hardening.
Fatigue Resistance High fatigue limit makes it durable under cyclic loading. Critical for rotating shafts and connecting rods.

Technical Parameters & Material Standards

We machine 4140 to meet international standards and specific conditions:
Grade Category Specification Characteristics & Ideal Uses
AISI 4140 (Annealed) Soft State Characteristics: Delivered soft (~200 HB). Easiest to machine. Must be heat treated after machining to achieve full strength.
Uses: Complex parts requiring extensive material removal.
AISI 4140 HT (Pre-Hard) Quenched & Tempered Characteristics: Hardened to 28-32 HRC (approx. 950-1000 MPa). Can be machined and used immediately without further heat treatment risks (distortion).
Uses: Axles, bolts, sprockets, hydraulic rams.
Equivalent Grades 42CrMo4 (EN) / SCM440 (JIS) Characteristics: Global equivalents with very similar chemical compositions. We can source these based on your regional requirements.
Uses: Automotive and heavy machinery components.

CNC Machining Guidelines 4140

  • Tooling: For 4140HT, we use carbide tools with TiAlN coatings to withstand the heat and abrasion. High-speed steel (HSS) is not recommended.
  • Welding: Difficult. 4140 is susceptible to cracking during welding. It requires pre-heating and post-weld heat treatment. We recommend bolting assemblies instead of welding.
  • Coolant: High-pressure emulsion coolant is required to break chips (which can be stringy) and maintain thermal stability.
  • Nitriding: 4140 responds very well to nitriding, which creates a super-hard case (60 HRC+) for extreme wear applications without distorting the core.

Application Scenarios

  • Oil & Gas: Drill collars, coupling bolts, valves, downhole tools.
  • Automotive: Crankshafts, steering knuckles, connecting rods, axles.
  • Industrial Machinery: Conveyor rolls, heavy-duty gears, pump shafts, hydraulic machinery parts.
  • Aerospace: Structural tubing, motor mounts, high-strength fasteners.

Physical Properties Table

Comparison: Annealed vs. Pre-Hardened (HT):
Property 4140 Annealed 4140 HT (Pre-Hard) Unit
Density 7.85 7.85 g/cm³
Tensile Strength 655 950 - 1100 MPa
Yield Strength 415 850 - 950 MPa
Hardness ~ 197 HB 28 - 32 HRC -
Elongation 25 15 - 20 %
Machinability 65% 50% (Ref: 1212=100%)
 
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