4118 vs 5120
These two grades are listed as equivalents of each other: their chemistry windows overlap and they serve the same applications. They are not always identical — check the differences below before substituting, especially in certified designs.
4118
Alloy & Engineering Steel
4118 is a low carbon Cr-Mo carburizing steel, the economy case-hardening grade of the 41xx family. Its small molybdenum addition gives a stronger, tougher core than plain chromium case steels such as 5120.
Standards: DIN 20CrMo4 type (near) · AISI 4118 · JIS SCM418 · GB 20CrMo
5120
Alloy & Engineering Steel
5120 is a chromium case-hardening steel for small gears and wear parts. With about 0.8% chromium it forms a hard carburized case over a tougher core than plain carbon carburizing grades give.
Standards: DIN 1.7027 (20Cr4, near) · AISI 5120 · JIS SCr420 · GB 20Cr
Chemical composition compared (%)
| Element | 4118 | 5120 |
|---|---|---|
| C | 0.18–0.23 | 0.17–0.22 |
| Si | 0.15–0.35 | 0.15–0.35 |
| Mn | 0.70–0.90 | 0.70–0.90 |
| P | ≤0.035 | ≤0.035 |
| S | ≤0.040 | ≤0.040 |
| Cr | 0.40–0.60 | 0.70–0.90 |
| Mo | 0.08–0.15 | — |
Properties compared
| Property | 4118 | 5120 |
|---|---|---|
| Case hardness (carburized) | 58–62 HRC | 58–62 HRC |
| Core tensile strength | 650–900 MPa (typ.) | 600–850 MPa (typ.) |
| Density | 7.85 g/cm³ | 7.85 g/cm³ |
Sourcing either grade?
Nasteel stocks both families from Shenzhen with EN 10204 3.1 mill certificates by heat number.
Ask for a quotationSee full data sheets: 4118 · 5120. Substitution decisions for certified parts stay with the design authority.