A36 and 4140 sit at opposite ends of the steel spectrum. A36 is an inexpensive structural mild steel; 4140 is a heat-treatable chromoly alloy for high-stress parts.
| Property | undefined | undefined |
|---|---|---|
| Type | Structural mild steel | Chromoly alloy steel |
| Yield strength | 250 MPa (36 ksi) | 415 MPa min, 655+ heat-treated |
| Tensile strength | 400 to 550 MPa | 655 to 980+ MPa |
| Heat treatable | No | Yes |
| Weldability | Excellent | Fair, needs pre and post heat |
| Cost | Low | Higher |
| Typical use | Beams, plates, weldments | Shafts, gears, high-stress parts |
Which should you choose
Choose A36 for structural steelwork and weldments where its low cost and easy welding shine and extreme strength is not required.
Choose 4140 when you need a strong, tough, heat-treatable part such as a shaft or gear that will see high loads or fatigue.
FAQ
Can A36 be heat-treated to match 4140’s strength? No. A36 isn’t formulated for hardening response the way 4140 is, so it can’t reach comparable strength through heat treatment. If higher strength is needed, 4140 or another alloy steel is the appropriate substitute rather than heat-treating A36.
Compare data sheets: A36 Steel and 4140 Steel.