C25 -- unalloyed machine steel between C20 and C35. Rm 470-620 MPa normalized. For lightly-loaded shafts, bolts and machine parts requiring more strength than C20 without alloy steel cost.
Standards
| Standard Body |
Designation |
Country |
| EN 10083-2 |
C25 / 1.0406 |
EU |
| DIN W.Nr |
1.0406 |
Germany |
| AISI/SAE |
1025 |
USA |
| JIS |
S25C |
Japan |
| GOST |
25 (25 steel) |
Russia |
| UNS |
G10250 |
USA |
| JUS |
C.1330 |
Yugoslavia/BiH |
Composition (wt.%)
| Element |
Symbol |
Min % |
Max % |
Typical % |
| Carbon |
C |
0.220 |
0.290 |
0.255 |
| Silicon |
Si |
0.150 |
0.400 |
0.250 |
| Manganese |
Mn |
0.400 |
0.700 |
0.550 |
Physical
Melting Range
1465 – 1500
°C
Thermal Conductivity
50
W/mK
Thermal Expansion
11.6
×10⁻⁶/K
Machinability
| Rating |
70.0% (B1112=100%) |
| Turning HSS |
42.0 m/min |
| Turning Carbide |
180.0 m/min |
| Surface Finish |
Ra 0.8-3.2 um |
| Coolant |
Soluble oil 5-8% |
Mechanical
| Condition |
Rm (MPa) | Re (MPa) | A (%) |
HB | HRC | KV (J) | E (GPa) |
| Normalized (+N) |
470 – 620 |
≥295 |
≥21 |
135 – 190 |
— |
— |
210 |
| Q+T (light hardening) (+QT) |
550 – 700 |
≥370 |
≥17 |
160 – 210 |
— |
— |
210 |
Heat Treatment
| Process |
Temperature |
Medium |
Duration |
Hardness After |
| Normalizing |
860 – 900°C |
Still Air |
- |
Standard delivery |
| Austenitizing (light Q+T) |
840 – 870°C |
Water or oil quench |
15-20 min |
HRC 40-48 |
| Tempering |
500 – 650°C |
Oven |
1-2 h |
HRC 22-38 |
| NOT case-hardening focused |
— |
Intermediate C content -- us |
N/A |
N/A |
Applications
Machine Shafts: Lightly loaded machine shafts and spindles.
Bolts: General machine bolts and fasteners.
General Components: Machine parts requiring moderate strength without alloy steel cost.
Notes
C25 position: C25 fills the narrow gap between C20 (case-hardening) and C35 (through-hardening focus). In practice many designers simply specify C20 or C35 directly, making C25 a less commonly stocked intermediate grade -- useful where a specific normalized-strength target between the two is genuinely required.