20CrMo vs SCM420
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.
20CrMo
Alloy & Engineering Steel
20CrMo is the GB/T 3077 chromium-molybdenum carburizing steel — the molybdenum-bearing counterpart of 20Cr and the Chinese designation closest to JIS SCM420. The Mo addition lifts core hardenability and temper resistance over plain Cr carburizing grades, making it a staple for automotive and motorcycle gears.
Standards: DIN 18CrMo4 / 1.7243 (near) · AISI 4118 (near) · JIS SCM420 · GB 20CrMo (GB/T 3077)
SCM420
Alloy & Engineering Steel
SCM420 is the 0.20% carbon Cr-Mo carburizing steel of JIS G4053 (AISI 4120 class) — the standard Japanese grade for medium gears and transmission shafts that need a wear-resistant case over a stronger core than SCM415 gives.
Standards: DIN 20CrMo4 type (near) · AISI 4120 (near) · JIS SCM420 (JIS G4053) · GB 20CrMo (near)
Chemical composition compared (%)
| Element | 20CrMo | SCM420 |
|---|---|---|
| C | 0.17–0.24 | 0.18–0.23 |
| Si | 0.17–0.37 | 0.15–0.35 |
| Mn | 0.40–0.70 | 0.60–0.90 |
| P | ≤0.035 | ≤0.030 |
| S | ≤0.035 | ≤0.030 |
| Cr | 0.80–1.10 | 0.90–1.20 |
| Mo | 0.15–0.25 | 0.15–0.25 |
Properties compared
| Property | 20CrMo | SCM420 |
|---|---|---|
| Case hardness (carburized) | 58–63 HRC | 58–63 HRC |
| Tensile strength | ≥885 MPa (GB/T 3077 reference, carburized test piece) | — |
| 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: 20CrMo · SCM420. Substitution decisions for certified parts stay with the design authority.