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.
Structural versus high-strength. A36 is the cheap, weldable structural standard. 4140 is an alloy you heat-treat for much higher strength, at higher cost and trickier welding.
Compare data sheets: A36 Steel and 4140 Steel.