AISI 4130 is a chromium–molybdenum (Cr–Mo) low-alloy steel from the 41xx series, engineered to deliver high strength, excellent toughness, good weldability, and reliable hardenability. With a relatively low carbon content (~0.28–0.33%), it offers an outstanding strength-to-weight ratio.
AISI 4130 is widely used in automotive, aerospace, oil & gas, defense, and heavy engineering industries where fatigue resistance, structural reliability, and consistent mechanical performance are critical.
Chemical Composition
| Element | Range (%) | Function |
|---|---|---|
| Carbon (C) | 0.28 – 0.33 | Strength, hardenability |
| Manganese (Mn) | 0.40 – 0.60 | Toughness, hardenability |
| Chromium (Cr) | 0.80 – 1.10 | Wear & corrosion resistance |
| Molybdenum (Mo) | 0.15 – 0.25 | High-temperature strength |
| Silicon (Si) | 0.15 – 0.30 | Deoxidation, strength |
| Phosphorus (P) | ≤ 0.035 | Impurity control |
| Sulfur (S) | ≤ 0.040 | Machinability control |
| Iron (Fe) | Balance | Base metal |
Metallurgical Characteristics
• Fine-grained ferrite–pearlite structure in normalized condition
• Martensitic or tempered martensitic structure after quenching & tempering
• Chromium and molybdenum delay pearlite formation for uniform hardening
• Maintains toughness even at high strength levels
Mechanical Properties
| Condition | Tensile Strength | Yield Strength | Elongation | Hardness |
|---|---|---|---|---|
| Annealed | 560 MPa | 460 MPa | ~25% | 150–170 HB |
| Normalized | 670–760 MPa | 500–560 MPa | ~22% | ~200 HB |
| Quenched & Tempered | 850–1000 MPa | 700–850 MPa | 18–22% | 28–35 HRC |
Key Characteristics
High Strength & Toughness
• Excellent load-bearing capability
• Performs well under impact and dynamic stress
Good Hardenability
• Uniform hardness through medium-thickness sections
• Excellent response to quenching and tempering
Excellent Weldability
• Low carbon minimizes cracking risk
• Widely used in welded frames and tubing
Good Machinability
• Machines well in annealed or normalized condition
• Suitable for precision components
Good Fatigue Resistance
• Performs reliably under cyclic and torsional loads
Heat Treatment & Processing
Annealing: 840–870°C – Improves machinability
Normalizing: 870–900°C (air cooled) – Refines grain structure
Quenching: Oil or polymer – Increases strength and hardness
Tempering: 200–650°C – Balances strength and toughness
Stress Relieving: Improves dimensional stability
Available Forms
✔ Hot rolled bars & rods
✔ Cold drawn bars
✔ Seamless & welded tubes
✔ Plates & sheets
✔ Forgings & machined components
Common Standards & Equivalents
| Standard | Equivalent Grade |
|---|---|
| AISI / SAE | 4130 |
| ASTM | A29 / A322 |
| EN | 25CrMo4 |
| DIN | 1.7218 |
| JIS | SCM420 (closest) |
| BS | EN19 (similar class) |
Applications
Automotive & Aerospace: Chassis, roll cages, aircraft tubing
Oil & Gas: Pressure vessels, drill collars, valve bodies
Industrial: Shafts, gears, couplings, fasteners
Defense & Heavy Engineering: Structural frames and assemblies
Advantages
✔ Excellent strength-to-weight ratio
✔ Superior weldability compared to higher-carbon alloys
✔ Reliable hardenability and fatigue resistance
✔ Cost-effective high-performance alloy steel
Limitations
⚠ Lower maximum hardness than 4140 / 4340
⚠ Requires corrosion protection
⚠ Heat treatment control is critical