SCM420
Data verifiedSCM420 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.
Chemical composition
| Element | Content (%) |
|---|---|
| C | 0.18–0.23 |
| Si | 0.15–0.35 |
| Mn | 0.60–0.90 |
| P | ≤0.030 |
| S | ≤0.030 |
| Cr | 0.90–1.20 |
| Mo | 0.15–0.25 |
Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.
Properties
| Case hardness (carburized) | 58–63 HRC |
| Density | 7.85 g/cm³ |
Heat treatment
Carburize 900–930 °C; quench 850–880 °C oil; temper 150–200 °C.
Equivalent grades
| Standard | Designation |
|---|---|
| din | 20CrMo4 type (near) |
| aisi | 4120 (near) |
| jis | SCM420 (JIS G4053) |
| gb | 20CrMo (near) |
Compare side by side: SCM420 vs SCM415 · SCM420 vs SCM435
Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.
Applications & Processing
Applications: Medium gears, transmission shafts, pinions, motorcycle and automotive drivetrain parts.
Processing: Good machinability in the annealed/normalized state; carburize, harden and finish-grind as for 8620-class steels.
FAQ
- Is SCM420 a case steel or a Q&T steel?
- Primarily a carburizing (case-hardening) steel. It can be through-hardened in small sections, but its design point is a 58–63 HRC case on a tough 0.20% C core.
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Ask for a quotationVisit NasteelSource: JIS G4053 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.