AISI 5140 is a medium-carbon chromium-molybdenum (Cr–Mo) alloy steel from the 51xx series, engineered to deliver a balanced combination of strength, toughness, wear resistance, and fatigue performance. It is primarily a through-hardening steel, capable of achieving uniform properties after quenching and tempering.
Because of its predictable heat-treatment response, moderate cost, and reliable mechanical performance, AISI 5140 is widely used in automotive, machinery, mining, and general engineering applications.
Chemical Composition
| Element | % | Role |
|---|---|---|
| Carbon (C) | 0.38 – 0.43 | Strength & hardness |
| Chromium (Cr) | 0.80 – 1.05 | Hardenability & wear resistance |
| Molybdenum (Mo) | 0.15 – 0.25 | Strength & fatigue resistance |
| Manganese (Mn) | 0.75 – 1.00 | Strength & hardenability |
| Silicon (Si) | 0.15 – 0.35 | Improves strength |
| Phosphorus (P) | ≤ 0.035 | Controlled impurity |
| Sulfur (S) | ≤ 0.040 | Machinability |
| Iron (Fe) | Balance | Base metal |
Key Characteristics
Good Hardenability
• Chromium and molybdenum enable deep, uniform hardening
• Suitable for medium-thickness sections
High Strength with Reliable Toughness
• Medium carbon content ensures strong load-bearing capability
• Maintains toughness under shock and vibration
Excellent Wear & Abrasion Resistance
• Performs well in sliding and rolling contact
• Can be enhanced by induction or flame hardening
Strong Fatigue Resistance
• Resists crack initiation under cyclic loading
• Ideal for shafts, axles, and rotating components
Dimensional Stability
• Predictable heat-treatment response
• Lower distortion risk than higher-carbon steels
Heat Treatment & Processing
Annealing: 820–860°C, furnace cooled – Improves machinability
Normalizing: 870–900°C, air cooled – Grain refinement
Quenching: Austenitize at 840–870°C, oil quench
Tempering: 400–650°C – Balances hardness and toughness
Surface Hardening: Induction or flame hardening (carburizing less common)
Machinability, Weldability & Fabrication
• Good machinability in annealed condition
• Weldability is fair; preheating (200–300°C) and post-weld stress relief required
• Suitable for hot forging and hot working
Available Forms
✔ Round, square & flat bars
✔ Forged shafts & blocks
✔ Plates & structural sections
✔ Tubes & hollow bars
✔ Precision-machined components
Standards & Equivalents
| Standard | Equivalent |
|---|---|
| AISI / SAE | 5140 |
| ASTM | A29 / A322 |
| EN | 1.7035 |
| DIN | 41Cr4 |
| JIS | SCr440 |
| BS | 530A40 |
Applications
Automotive: Axles, drive shafts, suspension components
Industrial Machinery: Shafts, spindles, gears, couplings
Mining & Construction: Heavy-duty pins, rollers, wear parts
General Engineering: Bolts, studs, power-transmission components
Comparison with Similar Grades
| Property | 5140 | 4140 | 4340 |
|---|---|---|---|
| Carbon Content | Medium | Medium | Medium |
| Alloy Content | Cr-Mo | Cr-Mo | Ni-Cr-Mo |
| Hardenability | Good | Very good | Excellent |
| Toughness | Good | Very good | Excellent |
| Cost | Moderate | Moderate | High |
Limitations
⚠ Lower toughness than 4140 and 4340
⚠ Limited corrosion resistance
⚠ Weldability requires careful control
Why Choose AISI 5140
AISI 5140 offers consistent mechanical performance, good hardenability, and durability at a reasonable cost. It is an excellent choice for shafts, axles, gears, and general engineering components where strength, fatigue resistance, and wear performance are required without the added expense of nickel-alloy steels.