When it comes to choosing the right alloy steel bar for mechanical, aerospace, or industrial applications, three names often come to the forefront — 4140, 4130, and 4340. These low-alloy chromium-molybdenum steels are renowned for their strength, toughness, and machinability. But how do you know which one is the right fit for your project?
In this comprehensive guide, we compare 4140 vs 4130 vs 4340 steel bars across key metrics such as chemical composition, mechanical properties, hardness, weldability, heat treatment, and application suitability — helping engineers, fabricators, and buyers make informed material decisions.
Low-alloy steels are carbon steels that include small amounts of alloying elements like chromium (Cr), molybdenum (Mo), and nickel (Ni) to improve specific properties.
4140 Steel: A versatile steel offering excellent strength and hardness, widely used in tool making, automotive parts, and general engineering.
4130 Steel: Known for its high toughness and weldability, often used in aviation and motorsports.
4340 Steel: A nickel-chromium-molybdenum alloy with ultra-high strength and fatigue resistance, favored for aerospace and heavy-duty applications.
| Element | 4130 (%) | 4140 (%) | 4340 (%) |
|---|---|---|---|
| Carbon (C) | 0.28 – 0.33 | 0.38 – 0.43 | 0.38 – 0.43 |
| Manganese (Mn) | 0.40 – 0.60 | 0.75 – 1.00 | 0.60 – 0.80 |
| Chromium (Cr) | 0.80 – 1.10 | 0.80 – 1.10 | 0.70 – 0.90 |
| Molybdenum (Mo) | 0.15 – 0.25 | 0.15 – 0.25 | 0.20 – 0.30 |
| Nickel (Ni) | – | – | 1.65 – 2.00 |
| Silicon (Si) | 0.15 – 0.35 | 0.15 – 0.30 | 0.15 – 0.30 |
4340 has added nickel, giving it higher toughness and fatigue resistance.
4130 has lower carbon content, improving weldability.
4140 has higher carbon and manganese, boosting hardness and strength.
| Property | 4130 Steel | 4140 Steel | 4340 Steel |
|---|---|---|---|
| Tensile Strength (MPa) | 670 – 850 | 850 – 1000 | 930 – 1080 |
| Yield Strength (MPa) | 460 – 560 | 655 – 785 | 745 – 860 |
| Elongation (%) | 20 – 25 | 20 – 25 | 16 – 20 |
| Hardness (HRC) | 18 – 25 | 28 – 32 | 28 – 45 |
| Impact Toughness (J) | High | Moderate | Very High |
Normalizing: 870–900°C
Hardening: Oil quench from 870°C
Tempering: 480–650°C
Best for: Applications needing weldability and toughness
Hardening: Oil quench from 840–875°C
Tempering: 540–680°C
Hardenability: Excellent — deeper case hardening achievable
Best for: High-strength shafts, gears, crankshafts
Hardening: Oil or polymer quench from 830–870°C
Tempering: 400–600°C
Notable: Retains strength even after deep hardening
Best for: Aircraft landing gear, heavy-duty drive components
| Property | 4130 | 4140 | 4340 |
|---|---|---|---|
| Weldability | Excellent | Fair to Good | Fair |
| Machinability | Good | Good | Moderate |
| Preheating | Recommended for thick sections (>12mm) | ||
| Post-Weld Heat Treatment | Recommended for 4140 and 4340 to reduce stress and cracking |
4130 stands out for being easily weldable using TIG/MIG without excessive cracking, ideal for tubing structures like roll cages or aircraft frames.
Aerospace tubing
Racing frames and roll cages
Motorcycle frames
Firearms receivers
Tool holders
Crankshafts
Gears
Axles and shafts
Aircraft landing gear
High-strength bolts and fasteners
Heavy machinery components
Oil and gas industry shafts
| Grade | Relative Cost | Availability |
|---|---|---|
| 4130 | Low | High |
| 4140 | Medium | High |
| 4340 | High | Moderate |
Due to its nickel content, 4340 is the most expensive. However, its performance in demanding applications often justifies the cost.
| Steel Grade | ASTM | SAE | EN/DIN | JIS |
|---|---|---|---|---|
| 4130 | A29/A519 | 4130 | 25CrMo4 | SCM430 |
| 4140 | A29/A322 | 4140 | 42CrMo4 | SCM440 |
| 4340 | A29/A322 | 4340 | 34CrNiMo6 | SNCM439 |
Ensure your steel supplier provides mill test certificates that comply with relevant standards like ASTM A29, EN 10250, or JIS G4053.
| Requirement | Recommended Grade |
|---|---|
| Best weldability | 4130 |
| Best balance of strength and cost | 4140 |
| Ultimate toughness and fatigue strength | 4340 |
| High wear resistance | 4340 or hardened 4140 |
| Aerospace or automotive | 4340 |
| General engineering | 4140 |
In the competition of Steel Bar 4140 vs 4130 vs 4340, there’s no one-size-fits-all winner — the right choice depends on your performance, strength, cost, and welding requirements.
Choose 4130 if you need excellent weldability and moderate strength.
Go with 4140 for a high-strength, cost-effective option suitable for shafts and gears.
Select 4340 when extreme toughness, fatigue strength, and shock resistance are critical.