4140 Alloy Steel CNC Machining —
Chrome-Moly · High Strength · All Conditions
AISI 4140 is the engineering world's most versatile alloy steel — outstanding strength, fatigue resistance, and through-hardenability. We machine all conditions: annealed, pre-hardened, and fully hardened.
Why Choose AISI 4140?
4140 chrome-moly steel is the go-to engineering steel for parts that demand strength, toughness, and fatigue resistance simultaneously. It is available in multiple conditions to match your application.
Outstanding Fatigue Resistance
4140's chromium and molybdenum content gives exceptional resistance to cyclic loading — ideal for shafts, gears, and structural parts under dynamic stress.
High Tensile Strength
Pre-hardened 4140 delivers 655–1,000 MPa tensile strength depending on temper. Heat-treated conditions can exceed 1,500 MPa.
Good Through-Hardening
4140 through-hardens reliably up to ~100 mm diameter. Suitable for heat treatment to HRC 20–54 to match your strength and wear requirements.
Good Machinability
In annealed or pre-hardened (P20 equivalent) condition, 4140 machines well with carbide tooling. Hardened grades require slower feeds and rigid fixturing.
4140 Supply Conditions
4140 is available in several heat treatment conditions. Choose the right condition before requesting a quote — it determines machining strategy, cost, and final properties.
| Condition | Hardness | Tensile Strength | Machinability | Best For | Typical Uses |
|---|---|---|---|---|---|
| Annealed | ≤ 197 HB | 655 MPa | Good | Heavy roughing, welding | Structural parts, weldments |
| Pre-Hardened (P/H) | 28–34 HRC | 930–1,080 MPa | Moderate | General engineering | Shafts, tooling, mould bases |
| Hardened & Tempered | 36–54 HRC | 1,170–1,800 MPa | Difficult | High-wear, high-load | Gears, dies, couplings |
| Normalised | 179–235 HB | 740–900 MPa | Good | Uniform grain structure | Precision machined parts |
Machining Specifications
Standard capabilities for 4140 steel CNC milling and turning at Ginwate.
| Property | Value |
|---|---|
| Standard Tolerance | ±0.01 mm |
| High-Precision Tolerance | ±0.005 mm |
| Max Part Size (Milling) | 600 × 400 × 300 mm |
| Max Part Size (Turning) | Ø300 × 1000 mm |
| Surface Finish (as-machined) | Ra 1.6 μm |
| Surface Finish (fine) | Ra 0.4 μm |
| Max Hardness Achievable | 54 HRC (heat treated) |
| Material Standard | AISI 4140 / DIN 42CrMo4 |
Surface Finishes for 4140 Steel
Post-machining treatments applied in-house or through our qualified partners. Specify finish and condition together on your drawing.
As-Machined
Ra 1.6–3.2 μm direct from machine. Accurate dimensions with visible tool marks. Most cost-effective option.
Black Oxide
Mild corrosion protection with flat black appearance. Minimal dimensional change (< 2 μm). Common for tooling and fixtures.
Electroless Nickel
Uniform 10–50 μm deposit. Excellent corrosion and wear resistance without sacrificing dimensional accuracy.
Hard Chrome
60–72 HRC surface hardness, excellent wear and corrosion resistance. Common for hydraulic rods and shaft journals.
Case Hardening / Nitriding
Surface hardness 55–65 HRC with a tough core. Gas nitriding produces 0.1–0.6 mm hard layer without distortion.
Induction Hardening
Selective surface hardening for gear teeth, journals, and bearing seats while keeping core tough.
Zinc Plating
Economical corrosion protection for non-critical environments. Clear or yellow chromate passivation.
Phosphating
Manganese or zinc phosphate for improved corrosion protection and paint adhesion. Common on tooling and automotive parts.
Design Tips for 4140 Steel Machining
4140 behaves very differently depending on its heat treatment condition. These tips prevent costly mistakes before machining begins.
Specify the required condition (annealed, pre-hardened, or hardened & tempered) on your drawing before quoting — it fundamentally changes machining strategy and cost.
For parts that will be heat-treated after machining, leave 0.1–0.3 mm stock on critical surfaces to accommodate distortion and allow finish grinding.
Thread roots and keyway corners are stress concentrators. Specify generous fillet radii (≥ 1.5 mm) in high-fatigue zones wherever possible.
4140 is weldable in the annealed condition with preheat (150–260°C) and post-weld stress relief. Welding pre-hardened stock is not recommended.
Inside corner radii in pockets should be ≥ 1.5 mm for annealed, and ≥ 2.0 mm for pre-hardened 4140 to avoid tool breakage.
For shafts requiring a combination of high fatigue life and wear resistance, consider induction hardening the bearing seats while keeping the body normalised.
4140 Steel CNC Applications
4140 steel parts from Ginwate are used across heavy industry, oil & gas, tooling, automotive, and defence sectors.
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