Overview
SAE/AISI 4140 Steel is one of the most widely used chromium-molybdenum alloy steels in the world. It offers an outstanding combination of high strength, toughness, wear resistance, fatigue resistance, machinability, and heat treatment capability.
Compared with SAE 4130, SAE 4140 contains higher carbon content, providing significantly improved hardness and strength after heat treatment. It is widely used in demanding mechanical and structural applications where reliability under heavy loads is critical.
SAE 4140 is commonly used in:
- Heavy-Duty Shafts
- Gears & Sprockets
- Axles
- Hydraulic Components
- Oil & Gas Equipment
- Construction Machinery
- Automotive Components
- Aerospace Components
Because of its versatility and excellent mechanical properties, SAE 4140 is considered one of the benchmark engineering alloy steels worldwide.
Material Specification
| Property | Value |
|---|---|
| Material Designation | SAE/AISI 4140 |
| Standard | ASTM A29 / SAE J404 |
| UNS Number | G41400 |
| Material Family | Chromium-Molybdenum Alloy Steel |
| Density | 7.85 g/cm³ |
| Magnetic Property | Magnetic |
| Standard Forms | Bar, Plate, Forgings, Tube, Pipe, Shafting |
Chemical Composition
| Element | Content (%) |
|---|---|
| Iron (Fe) | Balance |
| 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 |
| Phosphorus (P) | ≤0.035 |
| Sulfur (S) | ≤0.040 |
The combination of chromium and molybdenum provides excellent hardenability, strength, and fatigue resistance.
Mechanical Properties
Annealed Condition
| Property | Value |
|---|---|
| Tensile Strength | 620–760 MPa |
| Yield Strength | 415–550 MPa |
| Elongation | 20–25% |
| Hardness | 170–220 HB |
| Elastic Modulus | 205 GPa |
Quenched & Tempered Condition
| Property | Value |
|---|---|
| Tensile Strength | 850–1200 MPa |
| Yield Strength | 655–1100 MPa |
| Elongation | 12–18% |
| Hardness | 28–38 HRC |
High Strength Condition
| Property | Value |
|---|---|
| Tensile Strength | Up to 1400 MPa |
| Yield Strength | Up to 1200 MPa |
| Hardness | Up to 55–58 HRC |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.85 g/cm³ |
| Melting Point | 1415–1540°C |
| Thermal Conductivity | 42.6 W/m·K |
| Electrical Resistivity | 0.22 μΩ·m |
| Thermal Expansion Coefficient | 12.3 × 10⁻⁶/K |
| Specific Heat Capacity | 475 J/kg·K |
Corrosion Resistance
| Environment | Performance |
|---|---|
| Indoor Environment | Good |
| Dry Atmosphere | Good |
| Outdoor Environment | Moderate |
| Marine Environment | Poor |
| Chemical Environment | Poor |
| Humid Environment | Moderate |
4140 provides slightly better corrosion resistance than plain carbon steels but is not considered a corrosion-resistant alloy.
Recommended surface treatments:
- Black Oxide
- Zinc Plating
- Hard Chrome Plating
- Electroless Nickel Plating
- Phosphate Coating
- Powder Coating
- QPQ / Salt Bath Nitriding
Weldability
| Welding Process | Rating |
|---|---|
| TIG Welding | Good |
| MIG Welding | Good |
| Arc Welding | Good |
| Resistance Welding | Moderate |
| Spot Welding | Moderate |
4140 can be welded successfully, but preheating and post-weld stress relief are generally recommended.
For critical components:
- Preheat: 200–315°C
- Post-Weld Tempering Recommended
Machinability
| Process | Rating |
|---|---|
| CNC Turning | Good |
| CNC Milling | Good |
| Drilling | Good |
| Grinding | Excellent |
| Threading | Good |
| Broaching | Good |
Machinability Comparison
| Material | Machinability |
|---|---|
| 1018 | Excellent |
| 1045 | Good–Excellent |
| 4130 | Good |
| 4140 | Good |
| 4340 | Moderate |
| D2 Tool Steel | Fair |
Pre-hardened 4140 (28–32 HRC) is one of the most popular materials for CNC machining.
Heat Treatment
Annealing
| Parameter | Value |
|---|---|
| Temperature | 815–870°C |
| Cooling Method | Furnace Cool |
Normalizing
| Parameter | Value |
|---|---|
| Temperature | 870–925°C |
| Cooling Method | Air Cool |
Quenching
| Parameter | Value |
|---|---|
| Temperature | 845–870°C |
| Cooling Medium | Oil |
Tempering
| Parameter | Value |
|---|---|
| Temperature | 200–700°C |
| Purpose | Strength & Toughness Adjustment |
Nitriding
| Property | Value |
|---|---|
| Surface Hardness | 60–70 HRC |
| Distortion | Very Low |
Induction Hardening
| Property | Value |
|---|---|
| Surface Hardness | 52–58 HRC |
| Hardened Depth | 1–8 mm |
International Equivalent Grades
| Standard | Equivalent Grade |
|---|---|
| SAE/AISI (USA) | 4140 |
| ASTM (USA) | ASTM A29 Grade 4140 |
| UNS | G41400 |
| GB/T (China) | 42CrMo |
| EN (Europe) | 42CrMo4 |
| DIN (Germany) | 1.7225 / 42CrMo4 |
| JIS (Japan) | SCM440 |
| ISO | 42CrMo4 |
Available Forms
| Product Type | Availability |
|---|---|
| Round Bar | Yes |
| Flat Bar | Yes |
| Alloy Plate | Yes |
| Forgings | Yes |
| Mechanical Tube | Yes |
| Seamless Pipe | Yes |
| Ground Shafting | Yes |
| Pre-Hardened Bar | Yes |
Typical Applications
Power Transmission Industry
- Drive Shafts
- Transmission Shafts
- Splined Shafts
- Couplings
Gear Manufacturing
- Spur Gears
- Helical Gears
- Worm Gears
- Gear Blanks
Hydraulic Industry
- Hydraulic Rods
- Cylinder Components
- Valve Bodies
- Pump Shafts
Oil & Gas Industry
- Drill Collars
- Wellhead Components
- Pressure Equipment
- Structural Components
Automotive Industry
- Axles
- Crankshafts
- Suspension Components
- Steering Parts
Construction Machinery
- Excavator Pins
- Loader Shafts
- Heavy Equipment Components
Manufacturing Characteristics
| Manufacturing Process | Rating |
|---|---|
| CNC Turning | Excellent |
| CNC Milling | Excellent |
| Grinding | Outstanding |
| Heat Treatment | Outstanding |
| Nitriding | Outstanding |
| Induction Hardening | Outstanding |
| Forging | Excellent |
| Hard Chrome Plating | Excellent |
| QPQ Treatment | Excellent |
Advantages
High Strength
Excellent load-bearing capability.
Outstanding Toughness
Performs well under shock and impact loads.
Excellent Fatigue Resistance
Suitable for cyclic loading applications.
Superior Heat Treatment Response
Can achieve a wide range of hardness and strength levels.
Excellent Wear Resistance
Especially after nitriding or induction hardening.
Widely Available
One of the most common alloy steels globally.
Limitations
Lower Corrosion Resistance Than Stainless Steel
Requires protective coatings.
More Expensive Than Carbon Steel
Higher material and processing costs.
Welding Requires Precautions
Preheating is recommended.
Heavier Than Aluminum Alloys
Not suitable for lightweight applications.
Comparison with Other Alloy Steels
| Property | 4140 | 4130 | 4340 | 1045 | 42CrMo |
|---|---|---|---|---|---|
| Carbon Content | 0.40% | 0.30% | 0.40% | 0.45% | 0.40% |
| Strength | Very High | High | Exceptional | Medium | |
| Wear Resistance | Excellent | Good | Outstanding | Good | |
| Weldability | Good | Excellent | Moderate | Good | |
| Hardenability | Excellent | Good | Outstanding | Moderate |
Comparison with Engineering Materials
| Material | Yield Strength | Hardness Potential | Fatigue Resistance |
|---|---|---|---|
| SAE 4140 | 655–1200 MPa | 58 HRC | Excellent |
| SAE 4130 | 650–900 MPa | 45 HRC | Excellent |
| SAE 4340 | 740–1400 MPa | 60 HRC | Outstanding |
| 1045 Steel | 550–700 MPa | 58 HRC | Good |
| 17-4PH Stainless | 860–1170 MPa | 44 HRC | Excellent |
| Aluminum 7075-T6 | 503 MPa | Low | Good |
Available Surface Finishes
Raw Finishes
- Annealed Finish
- Normalized Finish
- Quenched & Tempered Finish
- Pre-Hardened Finish
Protective Finishes
- Black Oxide
- Zinc Plating
- Electroless Nickel Plating
- Hard Chrome Plating
- QPQ Treatment
- Gas Nitriding
Decorative Finishes
- Powder Coating
- Spray Painting
- Electrophoretic Coating (E-Coating)
Frequently Asked Questions (FAQ)
What is SAE 4140 steel?
SAE 4140 is a chromium-molybdenum alloy steel known for its high strength, toughness, wear resistance, and heat treatment capability.
What is SAE 4140 used for?
Typical applications include:
- Shafts
- Gears
- Axles
- Hydraulic Components
- Oil & Gas Equipment
- Heavy Machinery
What is the difference between SAE 4140 and SAE 4130?
| Property | SAE 4140 | SAE 4130 |
|---|---|---|
| Carbon Content | Higher | Lower |
| Strength | Higher | Lower |
| Hardenability | Better | Lower |
| Weldability | Lower | Better |
What is the difference between SAE 4140 and 42CrMo?
SAE 4140 and 42CrMo are generally considered equivalent materials and are interchangeable in most engineering applications.
Can SAE 4140 be nitrided?
Yes. SAE 4140 is one of the most commonly nitrided steels and can achieve surface hardness of 60–70 HRC.
Is SAE 4140 suitable for shafts?
Yes. It is one of the most widely used shaft materials worldwide.
Can SAE 4140 be welded?
Yes, but preheating and post-weld heat treatment are recommended.
What hardness can SAE 4140 achieve?
- Quenched & Tempered: 28–38 HRC
- Induction Hardened: 52–58 HRC
- Nitrided Surface: 60–70 HRC
Why is SAE 4140 widely used in mechanical engineering?
Because it combines:
- High Strength
- Excellent Toughness
- Outstanding Fatigue Resistance
- Heat Treatability
- Wear Resistance
making it one of the most versatile engineering steels available.
Does GCNOV provide custom manufacturing services for SAE 4140?
Yes. GCNOV provides:
- CNC Turning
- CNC Milling
- Gear Manufacturing
- Shaft Machining
- Nitriding
- QPQ Treatment
- Induction Hardening
- Precision Grinding
- Hard Chrome Plating
- Prototype Development
- Low-Volume Production
- Mass Production