Guides/Comparisons
1018 vs 4140 steel
1018-vs-4140-steelCarbon steel 1018 and Alloy steel AISI 4140 at a glance
This page compares Carbon steel 1018 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 (1018 0.14 to 0.2%; 4140 0.38 to 0.43%), Manganese (1018 0.6 to 0.9%; 4140 0.75 to 1%), Phosphorus (1018 up to 0.040%; 4140 up to 0.035%), Sulfur (1018 up to 0.050%; 4140 up to 0.04%).
- Yield strength: 4140 is higher (1018 240 to 370 MPa; 4140 570 to 1,235 MPa), about 3.0 times the midpoint of 1018.
- Tensile strength: 4140 is higher (1018 430 to 440 MPa; 4140 745 to 1,283 MPa), about 2.3 times the midpoint of 1018.
- Density: the ranges overlap (1018 7.67 to 7.9 g/cm³; 4140 7.85 g/cm³).
- Young's modulus: the ranges overlap (1018 190 to 210 GPa; 4140 205 GPa).
- Thermal conductivity: the ranges overlap (1018 25 to 93 W/(m·K); 4140 42.6 W/(m·K)).
- Yield strength for each unit of density (calculated from each grade's midpoint values): Carbon steel 1018 39.2 MPa per g/cm³; Alloy steel AISI 4140 115 MPa per g/cm³.
"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 1018 | Alloy steel AISI 4140 |
|---|---|---|
| Yield strength | 240 to 370 MPa | 570 to 1,235 MPa |
| Tensile strength | 430 to 440 MPa | 745 to 1,283 MPa |
| Density | 7.67 to 7.9 g/cm³ | 7.85 g/cm³ |
| Young's modulus | 190 to 210 GPa | 205 GPa |
| Thermal conductivity | 25 to 93 W/(m·K) | 42.6 W/(m·K) |
| Melting point | 1,480 to 1,526 °C | no data |
| Thermal expansion | no data | 12.2 to 14.6 ppm/K |
| Yield strength per densitycalculated | 39.2 MPa per g/cm³ | 115 MPa per g/cm³ |
Composition
| Element | Carbon steel 1018 | Alloy steel AISI 4140 |
|---|---|---|
| Iron | balance | balance |
| Carbon | 0.14 to 0.2% | 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 | not listed | 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 1018 | Machined shafts, pins and gears, and cost-sensitive structural parts 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 or hot rolled |
| 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 1018 | Shafts, pins and gears |
| Carbon steel 1018 | Low-stress structural components |
| Carbon steel 1018 | Car parts, pipes and construction steel |
| 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 |