Guides/Comparisons
1045 vs 4140 steel
1045-vs-4140-steelCarbon steel 1045 and Alloy steel AISI 4140 at a glance
This page compares Carbon steel 1045 and Alloy steel AISI 4140 using only values that carry a source, a test condition and an evidence level. Ranges run across temper, heat treatment and product form, measured at room temperature where the source says so.
- Composition: Carbon (1045 0.43 to 0.5%; 4140 0.38 to 0.43%), Manganese (1045 0.6 to 0.9%; 4140 0.75 to 1%), Phosphorus (1045 up to 0.040%; 4140 up to 0.035%), Sulfur (1045 up to 0.050%; 4140 up to 0.04%).
- Yield strength: 4140 is higher (1045 300 to 540 MPa; 4140 570 to 1,235 MPa), about 2.1 times the midpoint of 1045.
- Tensile strength: 4140 is higher (1045 552 to 700 MPa; 4140 745 to 1,283 MPa), about 1.6 times the midpoint of 1045.
- Young's modulus: the ranges overlap (1045 190 to 210 GPa; 4140 205 GPa).
"Higher" means the whole range is higher, not just one value. Where a value is a specified minimum, the table says "at least".
Side by side
| Property | Carbon steel 1045 | Alloy steel AISI 4140 |
|---|---|---|
| Yield strength | 300 to 540 MPa | 570 to 1,235 MPa |
| Tensile strength | 552 to 700 MPa | 745 to 1,283 MPa |
| Density | no data | 7.85 g/cm³ |
| Young's modulus | 190 to 210 GPa | 205 GPa |
| Thermal conductivity | no data | 42.6 W/(m·K) |
| Thermal expansion | no data | 12.2 to 14.6 ppm/K |
Composition
| Element | Carbon steel 1045 | Alloy steel AISI 4140 |
|---|---|---|
| Iron | balance | balance |
| Carbon | 0.43 to 0.5% | 0.38 to 0.43% |
| Manganese | 0.6 to 0.9% | 0.75 to 1% |
| Phosphorus | up to 0.040% | up to 0.035% |
| Sulfur | up to 0.050% | up to 0.04% |
| Silicon | up to 0.100% | 0.15 to 0.35% |
| Chromium | not listed | 0.8 to 1.1% |
| Molybdenum | not listed | 0.15 to 0.25% |
Shares are as printed in the sources, by weight.
When to use which
| Material | Best for | Weakest at |
|---|---|---|
| Carbon steel 1045 | Forged or machined axles, shafts, gears and machine parts that need more strength than low-carbon steel, and that are coated against rust | Rust in moist air and salt unless it is coated, and strength that depends on whether the bar was cold drawn, hot rolled, normalised or annealed |
| Alloy steel AISI 4140 | Machine parts and structures in medium and large sections that need high strength and toughness after quenching and tempering | Hydrogen gas, which cut notched strength by about 60 percent in one room-temperature study, and dilute sulfuric acid, which corroded it at 176.87 mpy |
Where each is used
| Material | Use |
|---|---|
| Carbon steel 1045 | Axles, clutch members and shafts |
| Carbon steel 1045 | Gears, pinions and stud bolts |
| Carbon steel 1045 | Heavy machinery parts |
| Alloy steel AISI 4140 | Axles, gears, shafts, spindles, pinions, sprockets and studs |
| Alloy steel AISI 4140 | Rams, crowbars and oil-patch and logging parts |
| Alloy steel AISI 4140 | Aerospace bar to AMS 6349 and AMS 6382 |